Add attendance calculator (#1597)

---------

Co-authored-by: Mikołaj Pich <m.pich@outlook.com>
Co-authored-by: Faierbel <RafalBO99@outlook.com>

app/src/main/java/io/github/wulkanowy/data/Resource.kt

@@ -1,11 +1,16 @@
 package io.github.wulkanowy.data
 
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.FlowPreview
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.catch
 import kotlinx.coroutines.flow.collect
+import kotlinx.coroutines.flow.combine
+import kotlinx.coroutines.flow.debounce
 import kotlinx.coroutines.flow.emitAll
 import kotlinx.coroutines.flow.filter
 import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.flow.flatMapLatest
 import kotlinx.coroutines.flow.flow
 import kotlinx.coroutines.flow.flowOf
 import kotlinx.coroutines.flow.map
@@ -14,8 +19,10 @@ import kotlinx.coroutines.flow.takeWhile
 import kotlinx.coroutines.sync.Mutex
 import kotlinx.coroutines.sync.withLock
 import timber.log.Timber
+import kotlin.time.Duration
+import kotlin.time.Duration.Companion.seconds
 
-sealed class Resource<T> {
+sealed class Resource<out T> {
 
     open class Loading<T> : Resource<T>()
 
@@ -64,6 +71,19 @@ fun <T, U> Resource<T>.mapData(block: (T) -> U) = when (this) {
     is Resource.Error -> Resource.Error(this.error)
 }
 
+inline fun <T1, T2, R> Flow<Resource<T1>>.combineWithResourceData(
+    flow: Flow<T2>,
+    crossinline block: suspend (T1, T2) -> R
+): Flow<Resource<R>> =
+    combine(flow) { resource, inject ->
+        when (resource) {
+            is Resource.Success -> Resource.Success(block(resource.data, inject))
+            is Resource.Intermediate -> Resource.Intermediate(block(resource.data, inject))
+            is Resource.Loading -> Resource.Loading()
+            is Resource.Error -> Resource.Error(resource.error)
+        }
+    }
+
 fun <T> Flow<Resource<T>>.logResourceStatus(name: String, showData: Boolean = false) = onEach {
     val description = when (it) {
         is Resource.Intermediate -> "intermediate data received" + if (showData) " (data: `${it.data}`)" else ""
@@ -74,8 +94,29 @@ fun <T> Flow<Resource<T>>.logResourceStatus(name: String, showData: Boolean = fa
     Timber.i("$name: $description")
 }
 
-fun <T, U> Flow<Resource<T>>.mapResourceData(block: (T) -> U) = map {
+fun <T, U> Flow<Resource<T>>.mapResourceData(block: suspend (T) -> U) = map {
-    it.mapData(block)
+    when (it) {
+        is Resource.Success -> Resource.Success(block(it.data))
+        is Resource.Intermediate -> Resource.Intermediate(block(it.data))
+        is Resource.Loading -> Resource.Loading()
+        is Resource.Error -> Resource.Error(it.error)
+    }
+}
+
+@OptIn(ExperimentalCoroutinesApi::class)
+fun <T, U> Flow<Resource<T>>.flatMapResourceData(
+    inheritIntermediate: Boolean = true, block: suspend (T) -> Flow<Resource<U>>
+) = flatMapLatest {
+    when (it) {
+        is Resource.Success -> block(it.data)
+        is Resource.Intermediate -> block(it.data).map { newRes ->
+            if (inheritIntermediate && newRes is Resource.Success) Resource.Intermediate(newRes.data)
+            else newRes
+        }
+
+        is Resource.Loading -> flowOf(Resource.Loading())
+        is Resource.Error -> flowOf(Resource.Error(it.error))
+    }
 }
 
 fun <T> Flow<Resource<T>>.onResourceData(block: suspend (T) -> Unit) = onEach {
@@ -105,13 +146,13 @@ fun <T> Flow<Resource<T>>.onResourceSuccess(block: suspend (T) -> Unit) = onEach
     }
 }
 
-fun <T> Flow<Resource<T>>.onResourceError(block: (Throwable) -> Unit) = onEach {
+fun <T> Flow<Resource<T>>.onResourceError(block: suspend (Throwable) -> Unit) = onEach {
     if (it is Resource.Error) {
         block(it.error)
     }
 }
 
-fun <T> Flow<Resource<T>>.onResourceNotLoading(block: () -> Unit) = onEach {
+fun <T> Flow<Resource<T>>.onResourceNotLoading(block: suspend () -> Unit) = onEach {
     if (it !is Resource.Loading) {
         block()
     }
@@ -121,6 +162,55 @@ suspend fun <T> Flow<Resource<T>>.toFirstResult() = filter { it !is Resource.Loa
 
 suspend fun <T> Flow<Resource<T>>.waitForResult() = takeWhile { it is Resource.Loading }.collect()
 
+// Can cause excessive amounts of `Resource.Intermediate` to be emitted. Unless that is desired,
+// use `debounceIntermediates` to alleviate this behavior.
+inline fun <reified T> combineResourceFlows(
+    flows: Iterable<Flow<Resource<T>>>,
+): Flow<Resource<List<T>>> = combine(flows) { items ->
+    var isIntermediate = false
+    val data = mutableListOf<T>()
+    for (item in items) {
+        when (item) {
+            is Resource.Success -> data.add(item.data)
+            is Resource.Intermediate -> {
+                isIntermediate = true
+                data.add(item.data)
+            }
+
+            is Resource.Loading -> return@combine Resource.Loading()
+            is Resource.Error -> continue
+        }
+    }
+    if (data.isEmpty()) {
+        // All items have to be errors for this to happen, so just return the first one.
+        // mapData is functionally useless and exists only to satisfy the type checker
+        items.first().mapData { listOf(it) }
+    } else if (isIntermediate) {
+        Resource.Intermediate(data)
+    } else {
+        Resource.Success(data)
+    }
+}
+
+@OptIn(FlowPreview::class)
+fun <T> Flow<Resource<T>>.debounceIntermediates(timeout: Duration = 5.seconds) = flow {
+    var wasIntermediate = false
+
+    emitAll(this@debounceIntermediates.debounce {
+        if (it is Resource.Intermediate) {
+            if (!wasIntermediate) {
+                wasIntermediate = true
+                Duration.ZERO
+            } else {
+                timeout
+            }
+        } else {
+            wasIntermediate = false
+            Duration.ZERO
+        }
+    })
+}
+
 inline fun <ResultType, RequestType> networkBoundResource(
     mutex: Mutex = Mutex(),
     showSavedOnLoading: Boolean = true,

app/src/main/java/io/github/wulkanowy/data/enums/AttendanceCalculatorSortingMode.kt

@@ -0,0 +1,13 @@
+package io.github.wulkanowy.data.enums
+
+enum class AttendanceCalculatorSortingMode(private val value: String) {
+    ALPHABETIC("alphabetic"),
+    ATTENDANCE("attendance_percentage"),
+    LESSON_BALANCE("lesson_balance");
+
+    companion object {
+        fun getByValue(value: String) =
+            AttendanceCalculatorSortingMode.values()
+                .find { it.value == value } ?: ALPHABETIC
+    }
+}

app/src/main/java/io/github/wulkanowy/data/pojos/AttendanceData.kt

@@ -0,0 +1,14 @@
+package io.github.wulkanowy.data.pojos
+
+data class AttendanceData(
+    val subjectName: String,
+    val lessonBalance: Int,
+    val presences: Int,
+    val absences: Int,
+) {
+    val total: Int
+        get() = presences + absences
+
+    val presencePercentage: Double
+        get() = if (total == 0) 0.0 else (presences.toDouble() / total) * 100
+}

app/src/main/java/io/github/wulkanowy/data/repositories/AttendanceSummaryRepository.kt

@@ -1,12 +1,12 @@
 package io.github.wulkanowy.data.repositories
 
 import androidx.room.withTransaction
+import io.github.wulkanowy.data.*
 import io.github.wulkanowy.data.db.AppDatabase
 import io.github.wulkanowy.data.db.dao.AttendanceSummaryDao
 import io.github.wulkanowy.data.db.entities.Semester
 import io.github.wulkanowy.data.db.entities.Student
 import io.github.wulkanowy.data.mappers.mapToEntities
-import io.github.wulkanowy.data.networkBoundResource
 import io.github.wulkanowy.sdk.Sdk
 import io.github.wulkanowy.utils.AutoRefreshHelper
 import io.github.wulkanowy.utils.getRefreshKey

app/src/main/java/io/github/wulkanowy/data/repositories/PreferencesRepository.kt

@@ -10,6 +10,7 @@ import com.fredporciuncula.flow.preferences.Serializer
 import dagger.hilt.android.qualifiers.ApplicationContext
 import io.github.wulkanowy.R
 import io.github.wulkanowy.data.enums.AppTheme
+import io.github.wulkanowy.data.enums.AttendanceCalculatorSortingMode
 import io.github.wulkanowy.data.enums.GradeColorTheme
 import io.github.wulkanowy.data.enums.GradeExpandMode
 import io.github.wulkanowy.data.enums.GradeSortingMode
@@ -41,6 +42,18 @@ class PreferencesRepository @Inject constructor(
             R.bool.pref_default_attendance_present
         )
 
+    val targetAttendanceFlow: Flow<Int>
+        get() = flowSharedPref.getInt(
+            context.getString(R.string.pref_key_attendance_target),
+            context.resources.getInteger(R.integer.pref_default_attendance_target)
+        ).asFlow()
+
+    val attendanceCalculatorSortingModeFlow: Flow<AttendanceCalculatorSortingMode>
+        get() = flowSharedPref.getString(
+            context.getString(R.string.pref_key_attendance_calculator_sorting_mode),
+            context.resources.getString(R.string.pref_default_attendance_calculator_sorting_mode)
+        ).asFlow().map(AttendanceCalculatorSortingMode::getByValue)
+
     private val gradeAverageModePref: Preference<GradeAverageMode>
         get() = getObjectFlow(
             R.string.pref_key_grade_average_mode,

app/src/main/java/io/github/wulkanowy/domain/attendance/GetAttendanceCalculatorDataUseCase.kt

@@ -0,0 +1,103 @@
+package io.github.wulkanowy.domain.attendance
+
+import io.github.wulkanowy.data.*
+import io.github.wulkanowy.data.db.entities.AttendanceSummary
+import io.github.wulkanowy.data.db.entities.Semester
+import io.github.wulkanowy.data.db.entities.Student
+import io.github.wulkanowy.data.db.entities.Subject
+import io.github.wulkanowy.data.enums.AttendanceCalculatorSortingMode
+import io.github.wulkanowy.data.enums.AttendanceCalculatorSortingMode.*
+import io.github.wulkanowy.data.pojos.AttendanceData
+import io.github.wulkanowy.data.repositories.AttendanceSummaryRepository
+import io.github.wulkanowy.data.repositories.PreferencesRepository
+import io.github.wulkanowy.data.repositories.SubjectRepository
+import io.github.wulkanowy.utils.allAbsences
+import io.github.wulkanowy.utils.allPresences
+import kotlinx.coroutines.flow.Flow
+import javax.inject.Inject
+import kotlin.math.ceil
+import kotlin.math.floor
+
+class GetAttendanceCalculatorDataUseCase @Inject constructor(
+    private val subjectRepository: SubjectRepository,
+    private val attendanceSummaryRepository: AttendanceSummaryRepository,
+    private val preferencesRepository: PreferencesRepository,
+) {
+
+    operator fun invoke(
+        student: Student,
+        semester: Semester,
+        forceRefresh: Boolean,
+    ): Flow<Resource<List<AttendanceData>>> =
+        subjectRepository.getSubjects(student, semester, forceRefresh)
+            .mapResourceData { subjects -> subjects.sortedBy(Subject::name) }
+            .combineWithResourceData(preferencesRepository.targetAttendanceFlow, ::Pair)
+            .flatMapResourceData { (subjects, targetFreq) ->
+                combineResourceFlows(subjects.map { subject ->
+                    attendanceSummaryRepository.getAttendanceSummary(
+                        student = student,
+                        semester = semester,
+                        subjectId = subject.realId,
+                        forceRefresh = forceRefresh
+                    ).mapResourceData { summaries ->
+                        summaries.toAttendanceData(subject.name, targetFreq)
+                    }
+                })
+                    // Every individual combined flow causes separate network requests to update data.
+                    // When there is N child flows, they can cause up to N-1 items to be emitted. Since all
+                    // requests are usually completed in less than 5s, there is no need to emit multiple
+                    // intermediates that will be visible for barely any time.
+                    .debounceIntermediates()
+            }
+            .combineWithResourceData(preferencesRepository.attendanceCalculatorSortingModeFlow, List<AttendanceData>::sortedBy)
+}
+
+private fun List<AttendanceSummary>.toAttendanceData(subjectName: String, targetFreq: Int): AttendanceData {
+    val presences = sumOf { it.allPresences }
+    val absences = sumOf { it.allAbsences }
+    return AttendanceData(
+        subjectName = subjectName,
+        lessonBalance = calcLessonBalance(
+            targetFreq.toDouble() / 100, presences, absences
+        ),
+        presences = presences,
+        absences = absences,
+    )
+}
+
+private fun calcLessonBalance(targetFreq: Double, presences: Int, absences: Int): Int {
+    val total = presences + absences
+    // The `+ 1` is to avoid false positives in close cases. Eg.:
+    // target frequency 99%, 1 presence. Without the `+ 1` this would be reported shown as
+    // a positive balance of +1, however that is not actually true as skipping one class
+    // would make it so that the balance would actually be negative (-98). The `+ 1`
+    // fixes this and makes sure that in situations like these, it's not reporting incorrect
+    // balances
+    return when {
+        presences / (total + 1f) >= targetFreq -> calcMissingAbsences(
+            targetFreq, absences, presences
+        )
+        presences / (total + 0f) < targetFreq -> -calcMissingPresences(
+            targetFreq, absences, presences
+        )
+        else -> 0
+    }
+}
+
+private fun calcMissingPresences(targetFreq: Double, absences: Int, presences: Int) =
+    calcMinRequiredPresencesFor(targetFreq, absences) - presences
+
+private fun calcMinRequiredPresencesFor(targetFreq: Double, absences: Int) =
+    ceil((targetFreq / (1 - targetFreq)) * absences).toInt()
+
+private fun calcMissingAbsences(targetFreq: Double, absences: Int, presences: Int) =
+    calcMinRequiredAbsencesFor(targetFreq, presences) - absences
+
+private fun calcMinRequiredAbsencesFor(targetFreq: Double, presences: Int) =
+    floor((presences * (1 - targetFreq)) / targetFreq).toInt()
+
+private fun List<AttendanceData>.sortedBy(mode: AttendanceCalculatorSortingMode) = when (mode) {
+    ALPHABETIC -> sortedBy(AttendanceData::subjectName)
+    ATTENDANCE -> sortedByDescending(AttendanceData::presencePercentage)
+    LESSON_BALANCE -> sortedBy(AttendanceData::lessonBalance)
+}

app/src/main/java/io/github/wulkanowy/ui/modules/attendance/AttendanceFragment.kt

@@ -14,6 +14,7 @@ import io.github.wulkanowy.data.db.entities.Attendance
 import io.github.wulkanowy.databinding.DialogExcuseBinding
 import io.github.wulkanowy.databinding.FragmentAttendanceBinding
 import io.github.wulkanowy.ui.base.BaseFragment
+import io.github.wulkanowy.ui.modules.attendance.calculator.AttendanceCalculatorFragment
 import io.github.wulkanowy.ui.modules.attendance.summary.AttendanceSummaryFragment
 import io.github.wulkanowy.ui.modules.main.MainActivity
 import io.github.wulkanowy.ui.modules.main.MainView
@@ -134,6 +135,7 @@ class AttendanceFragment : BaseFragment<FragmentAttendanceBinding>(R.layout.frag
 
     override fun onOptionsItemSelected(item: MenuItem): Boolean {
         return if (item.itemId == R.id.attendanceMenuSummary) presenter.onSummarySwitchSelected()
+        else if (item.itemId == R.id.attendanceMenuCalculator) presenter.onCalculatorSwitchSelected()
         else false
     }
 
@@ -253,6 +255,10 @@ class AttendanceFragment : BaseFragment<FragmentAttendanceBinding>(R.layout.frag
         (activity as? MainActivity)?.pushView(AttendanceSummaryFragment.newInstance())
     }
 
+    override fun openCalculatorView() {
+        (activity as? MainActivity)?.pushView(AttendanceCalculatorFragment.newInstance())
+    }
+
     override fun startActionMode() {
         actionMode = (activity as MainActivity?)?.startSupportActionMode(actionModeCallback)
     }

app/src/main/java/io/github/wulkanowy/ui/modules/attendance/AttendancePresenter.kt

@@ -1,16 +1,36 @@
 package io.github.wulkanowy.ui.modules.attendance
 
 import android.annotation.SuppressLint
-import io.github.wulkanowy.data.*
+import io.github.wulkanowy.data.Resource
 import io.github.wulkanowy.data.db.entities.Attendance
 import io.github.wulkanowy.data.db.entities.Semester
+import io.github.wulkanowy.data.flatResourceFlow
+import io.github.wulkanowy.data.logResourceStatus
+import io.github.wulkanowy.data.mapResourceData
+import io.github.wulkanowy.data.onResourceData
+import io.github.wulkanowy.data.onResourceError
+import io.github.wulkanowy.data.onResourceIntermediate
+import io.github.wulkanowy.data.onResourceLoading
+import io.github.wulkanowy.data.onResourceNotLoading
+import io.github.wulkanowy.data.onResourceSuccess
 import io.github.wulkanowy.data.repositories.AttendanceRepository
 import io.github.wulkanowy.data.repositories.PreferencesRepository
 import io.github.wulkanowy.data.repositories.SemesterRepository
 import io.github.wulkanowy.data.repositories.StudentRepository
+import io.github.wulkanowy.data.resourceFlow
 import io.github.wulkanowy.ui.base.BasePresenter
 import io.github.wulkanowy.ui.base.ErrorHandler
-import io.github.wulkanowy.utils.*
+import io.github.wulkanowy.utils.AnalyticsHelper
+import io.github.wulkanowy.utils.capitalise
+import io.github.wulkanowy.utils.getLastSchoolDayIfHoliday
+import io.github.wulkanowy.utils.isExcusableOrNotExcused
+import io.github.wulkanowy.utils.isHolidays
+import io.github.wulkanowy.utils.monday
+import io.github.wulkanowy.utils.nextSchoolDay
+import io.github.wulkanowy.utils.previousOrSameSchoolDay
+import io.github.wulkanowy.utils.previousSchoolDay
+import io.github.wulkanowy.utils.sunday
+import io.github.wulkanowy.utils.toFormattedString
 import kotlinx.coroutines.flow.firstOrNull
 import kotlinx.coroutines.flow.onEach
 import timber.log.Timber
@@ -195,6 +215,11 @@ class AttendancePresenter @Inject constructor(
         return true
     }
 
+    fun onCalculatorSwitchSelected(): Boolean {
+        view?.openCalculatorView()
+        return true
+    }
+
     private fun loadData(forceRefresh: Boolean = false) {
         Timber.i("Loading attendance data started")
 

app/src/main/java/io/github/wulkanowy/ui/modules/attendance/AttendanceView.kt

@@ -56,6 +56,8 @@ interface AttendanceView : BaseView {
 
     fun openSummaryView()
 
+    fun openCalculatorView()
+
     fun startSendMessageIntent(date: LocalDate, numbers: String, reason: String)
 
     fun startActionMode()

app/src/main/java/io/github/wulkanowy/ui/modules/attendance/calculator/AttendanceCalculatorAdapter.kt

@@ -0,0 +1,63 @@
+package io.github.wulkanowy.ui.modules.attendance.calculator
+
+import android.annotation.SuppressLint
+import android.view.LayoutInflater
+import android.view.ViewGroup
+import androidx.core.view.isVisible
+import androidx.recyclerview.widget.RecyclerView
+import io.github.wulkanowy.R
+import io.github.wulkanowy.data.pojos.AttendanceData
+import io.github.wulkanowy.databinding.ItemAttendanceCalculatorHeaderBinding
+import javax.inject.Inject
+import kotlin.math.abs
+import kotlin.math.roundToInt
+
+class AttendanceCalculatorAdapter @Inject constructor() :
+    RecyclerView.Adapter<AttendanceCalculatorAdapter.ViewHolder>() {
+
+    var items = emptyList<AttendanceData>()
+
+    override fun getItemCount() = items.size
+
+    override fun onCreateViewHolder(
+        parent: ViewGroup, viewType: Int
+    ) = ViewHolder(
+        ItemAttendanceCalculatorHeaderBinding.inflate(
+            LayoutInflater.from(parent.context), parent, false
+        )
+    )
+
+    @SuppressLint("SetTextI18n")
+    override fun onBindViewHolder(parent: ViewHolder, position: Int) {
+        with(parent.binding) {
+            val item = items[position]
+            attendanceCalculatorPercentage.text = "${item.presencePercentage.roundToInt()}"
+
+            if (item.lessonBalance > 0) {
+                attendanceCalculatorSummaryBalance.text = root.context.getString(
+                    R.string.attendance_calculator_summary_balance_positive,
+                    item.lessonBalance
+                )
+            } else if (item.lessonBalance < 0) {
+                attendanceCalculatorSummaryBalance.text = root.context.getString(
+                    R.string.attendance_calculator_summary_balance_negative,
+                    abs(item.lessonBalance)
+                )
+            } else {
+                attendanceCalculatorSummaryBalance.text = root.context.getString(
+                    R.string.attendance_calculator_summary_balance_neutral,
+                )
+            }
+            attendanceCalculatorWarning.isVisible = item.lessonBalance < 0
+            attendanceCalculatorTitle.text = item.subjectName
+            attendanceCalculatorSummaryValues.text = root.context.getString(
+                R.string.attendance_calculator_summary_values,
+                item.presences,
+                item.total
+            )
+        }
+    }
+
+    class ViewHolder(val binding: ItemAttendanceCalculatorHeaderBinding) :
+        RecyclerView.ViewHolder(binding.root)
+}

app/src/main/java/io/github/wulkanowy/ui/modules/attendance/calculator/AttendanceCalculatorFragment.kt

@@ -0,0 +1,105 @@
+package io.github.wulkanowy.ui.modules.attendance.calculator
+
+import android.os.Bundle
+import android.view.View
+import androidx.core.view.isVisible
+import androidx.recyclerview.widget.LinearLayoutManager
+import dagger.hilt.android.AndroidEntryPoint
+import io.github.wulkanowy.R
+import io.github.wulkanowy.data.pojos.AttendanceData
+import io.github.wulkanowy.databinding.FragmentAttendanceCalculatorBinding
+import io.github.wulkanowy.ui.base.BaseFragment
+import io.github.wulkanowy.ui.modules.main.MainView
+import io.github.wulkanowy.ui.widgets.DividerItemDecoration
+import io.github.wulkanowy.utils.getThemeAttrColor
+import javax.inject.Inject
+
+@AndroidEntryPoint
+class AttendanceCalculatorFragment :
+    BaseFragment<FragmentAttendanceCalculatorBinding>(R.layout.fragment_attendance_calculator),
+    AttendanceCalculatorView, MainView.TitledView {
+
+    @Inject
+    lateinit var presenter: AttendanceCalculatorPresenter
+
+    @Inject
+    lateinit var attendanceCalculatorAdapter: AttendanceCalculatorAdapter
+
+    override val titleStringId get() = R.string.attendance_title
+
+    companion object {
+        fun newInstance() = AttendanceCalculatorFragment()
+    }
+
+    override val isViewEmpty get() = attendanceCalculatorAdapter.items.isEmpty()
+
+    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
+        super.onViewCreated(view, savedInstanceState)
+        binding = FragmentAttendanceCalculatorBinding.bind(view)
+        messageContainer = binding.attendanceCalculatorRecycler
+        presenter.onAttachView(this)
+    }
+
+    override fun initView() {
+        with(binding.attendanceCalculatorRecycler) {
+            layoutManager = LinearLayoutManager(context)
+            adapter = attendanceCalculatorAdapter
+            addItemDecoration(DividerItemDecoration(context))
+        }
+
+        with(binding) {
+            attendanceCalculatorSwipe.setOnRefreshListener(presenter::onSwipeRefresh)
+            attendanceCalculatorSwipe.setColorSchemeColors(requireContext().getThemeAttrColor(R.attr.colorPrimary))
+            attendanceCalculatorSwipe.setProgressBackgroundColorSchemeColor(requireContext().getThemeAttrColor(R.attr.colorSwipeRefresh))
+            attendanceCalculatorErrorRetry.setOnClickListener { presenter.onRetry() }
+            attendanceCalculatorErrorDetails.setOnClickListener { presenter.onDetailsClick() }
+        }
+    }
+
+    override fun updateData(data: List<AttendanceData>) {
+        with(attendanceCalculatorAdapter) {
+            items = data
+            notifyDataSetChanged()
+        }
+    }
+
+    override fun clearView() {
+        with(attendanceCalculatorAdapter) {
+            items = emptyList()
+            notifyDataSetChanged()
+        }
+    }
+
+    override fun showEmpty(show: Boolean) {
+        binding.attendanceCalculatorEmpty.isVisible = show
+    }
+
+    override fun showErrorView(show: Boolean) {
+        binding.attendanceCalculatorError.isVisible = show
+    }
+
+    override fun setErrorDetails(message: String) {
+        binding.attendanceCalculatorErrorMessage.text = message
+    }
+
+    override fun showProgress(show: Boolean) {
+        binding.attendanceCalculatorProgress.isVisible = show
+    }
+
+    override fun enableSwipe(enable: Boolean) {
+        binding.attendanceCalculatorSwipe.isEnabled = enable
+    }
+
+    override fun showContent(show: Boolean) {
+        binding.attendanceCalculatorRecycler.isVisible = show
+    }
+
+    override fun showRefresh(show: Boolean) {
+        binding.attendanceCalculatorSwipe.isRefreshing = show
+    }
+
+    override fun onDestroyView() {
+        presenter.onDetachView()
+        super.onDestroyView()
+    }
+}

app/src/main/java/io/github/wulkanowy/ui/modules/attendance/calculator/AttendanceCalculatorPresenter.kt

@@ -0,0 +1,84 @@
+package io.github.wulkanowy.ui.modules.attendance.calculator
+
+import io.github.wulkanowy.data.*
+import io.github.wulkanowy.data.repositories.SemesterRepository
+import io.github.wulkanowy.data.repositories.StudentRepository
+import io.github.wulkanowy.domain.attendance.GetAttendanceCalculatorDataUseCase
+import io.github.wulkanowy.ui.base.BasePresenter
+import io.github.wulkanowy.ui.base.ErrorHandler
+import timber.log.Timber
+import javax.inject.Inject
+
+class AttendanceCalculatorPresenter @Inject constructor(
+    errorHandler: ErrorHandler,
+    studentRepository: StudentRepository,
+    private val semesterRepository: SemesterRepository,
+    private val getAttendanceCalculatorData: GetAttendanceCalculatorDataUseCase,
+) : BasePresenter<AttendanceCalculatorView>(errorHandler, studentRepository) {
+
+    private lateinit var lastError: Throwable
+
+    override fun onAttachView(view: AttendanceCalculatorView) {
+        super.onAttachView(view)
+        view.initView()
+        Timber.i("Attendance calculator view was initialized")
+        errorHandler.showErrorMessage = ::showErrorViewOnError
+        loadData()
+    }
+
+    fun onSwipeRefresh() {
+        Timber.i("Force refreshing the attendance calculator")
+        loadData(forceRefresh = true)
+    }
+
+    fun onRetry() {
+        view?.run {
+            showErrorView(false)
+            showProgress(true)
+        }
+        loadData()
+    }
+
+    fun onDetailsClick() {
+        view?.showErrorDetailsDialog(lastError)
+    }
+
+    private fun loadData(forceRefresh: Boolean = false) {
+        flatResourceFlow {
+            val student = studentRepository.getCurrentStudent()
+            val semester = semesterRepository.getCurrentSemester(student)
+            getAttendanceCalculatorData(student, semester, forceRefresh)
+        }
+            .logResourceStatus("load attendance calculator")
+            .onResourceData {
+                view?.run {
+                    showProgress(false)
+                    showErrorView(false)
+                    showContent(it.isNotEmpty())
+                    showEmpty(it.isEmpty())
+                    updateData(it)
+                }
+            }
+            .onResourceIntermediate { view?.showRefresh(true) }
+            .onResourceNotLoading {
+                view?.run {
+                    enableSwipe(true)
+                    showRefresh(false)
+                    showProgress(false)
+                }
+            }
+            .onResourceError(errorHandler::dispatch)
+            .launch()
+    }
+
+    private fun showErrorViewOnError(message: String, error: Throwable) {
+        view?.run {
+            if (isViewEmpty) {
+                lastError = error
+                setErrorDetails(message)
+                showErrorView(true)
+                showEmpty(false)
+            } else showError(message, error)
+        }
+    }
+}

app/src/main/java/io/github/wulkanowy/ui/modules/attendance/calculator/AttendanceCalculatorView.kt

@@ -0,0 +1,29 @@
+package io.github.wulkanowy.ui.modules.attendance.calculator
+
+import io.github.wulkanowy.data.pojos.AttendanceData
+import io.github.wulkanowy.ui.base.BaseView
+
+interface AttendanceCalculatorView : BaseView {
+
+    val isViewEmpty: Boolean
+
+    fun initView()
+
+    fun showRefresh(show: Boolean)
+
+    fun showContent(show: Boolean)
+
+    fun showProgress(show: Boolean)
+
+    fun enableSwipe(enable: Boolean)
+
+    fun showEmpty(show: Boolean)
+
+    fun showErrorView(show: Boolean)
+
+    fun setErrorDetails(message: String)
+
+    fun updateData(data: List<AttendanceData>)
+
+    fun clearView()
+}

app/src/main/java/io/github/wulkanowy/ui/modules/settings/appearance/AppearanceFragment.kt

@@ -4,6 +4,7 @@ import android.content.SharedPreferences
 import android.os.Bundle
 import android.view.View
 import androidx.preference.PreferenceFragmentCompat
+import androidx.preference.SeekBarPreference
 import com.yariksoffice.lingver.Lingver
 import dagger.hilt.android.AndroidEntryPoint
 import io.github.wulkanowy.R
@@ -36,6 +37,15 @@ class AppearanceFragment : PreferenceFragmentCompat(),
 
     override fun onCreatePreferences(savedInstanceState: Bundle?, rootKey: String?) {
         setPreferencesFromResource(R.xml.scheme_preferences_appearance, rootKey)
+        val attendanceTargetPref =
+            findPreference<SeekBarPreference>(requireContext().getString(R.string.pref_key_attendance_target))!!
+        attendanceTargetPref.setOnPreferenceChangeListener { _, newValueObj ->
+            val newValue = (((newValueObj as Int).toDouble() + 2.5) / 5).toInt() * 5
+            attendanceTargetPref.value =
+                newValue.coerceIn(attendanceTargetPref.min, attendanceTargetPref.max)
+
+            false
+        }
     }
 
     override fun onSharedPreferenceChanged(sharedPreferences: SharedPreferences?, key: String?) {

app/src/main/java/io/github/wulkanowy/utils/AttendanceExtension.kt

@@ -10,19 +10,19 @@ import io.github.wulkanowy.sdk.scrapper.attendance.AttendanceCategory
  * (https://www.vulcan.edu.pl/vulcang_files/user/AABW/AABW-PDF/uonetplus/uonetplus_Frekwencja-liczby-obecnych-nieobecnych.pdf)
  */
 
-private inline val AttendanceSummary.allPresences: Double
+inline val AttendanceSummary.allPresences: Int
-    get() = presence.toDouble() + absenceForSchoolReasons + lateness + latenessExcused
+    get() = presence + absenceForSchoolReasons + lateness + latenessExcused
 
-private inline val AttendanceSummary.allAbsences: Double
+inline val AttendanceSummary.allAbsences: Int
-    get() = absence.toDouble() + absenceExcused
+    get() = absence + absenceExcused
 
 inline val Attendance.isExcusableOrNotExcused: Boolean
     get() = (excusable || ((absence || lateness) && !excused)) && excuseStatus == null
 
-fun AttendanceSummary.calculatePercentage() = calculatePercentage(allPresences, allAbsences)
+fun AttendanceSummary.calculatePercentage() = calculatePercentage(allPresences.toDouble(), allAbsences.toDouble())
 
 fun List<AttendanceSummary>.calculatePercentage(): Double {
-    return calculatePercentage(sumOf { it.allPresences }, sumOf { it.allAbsences })
+    return calculatePercentage(sumOf { it.allPresences.toDouble() }, sumOf { it.allAbsences.toDouble() })
 }
 
 private fun calculatePercentage(presence: Double, absence: Double): Double {

app/src/main/res/drawable/ic_menu_attendance_calculator.xml

@@ -0,0 +1,5 @@
+<vector android:height="24dp" android:tint="#FFFFFF"
+    android:viewportHeight="24" android:viewportWidth="24"
+    android:width="24dp" xmlns:android="http://schemas.android.com/apk/res/android">
+    <path android:fillColor="@android:color/white" android:pathData="M19,7H9C7.9,7 7,7.9 7,9v10c0,1.1 0.9,2 2,2h10c1.1,0 2,-0.9 2,-2V9C21,7.9 20.1,7 19,7zM19,9v2H9V9H19zM13,15v-2h2v2H13zM15,17v2h-2v-2H15zM11,15H9v-2h2V15zM17,13h2v2h-2V13zM9,17h2v2H9V17zM17,19v-2h2v2H17zM6,17H5c-1.1,0 -2,-0.9 -2,-2V5c0,-1.1 0.9,-2 2,-2h10c1.1,0 2,0.9 2,2v1h-2V5H5v10h1V17z"/>
+</vector>

app/src/main/res/layout/fragment_attendance_calculator.xml

@@ -0,0 +1,103 @@
+<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    tools:context=".ui.modules.attendance.calculator.AttendanceCalculatorFragment">
+
+    <androidx.swiperefreshlayout.widget.SwipeRefreshLayout
+        android:id="@+id/attendanceCalculatorSwipe"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent">
+
+        <androidx.recyclerview.widget.RecyclerView
+            android:id="@+id/attendanceCalculatorRecycler"
+            android:layout_width="match_parent"
+            android:layout_height="match_parent"
+            tools:listitem="@layout/item_attendance_calculator_header" />
+    </androidx.swiperefreshlayout.widget.SwipeRefreshLayout>
+
+    <com.google.android.material.progressindicator.CircularProgressIndicator
+        android:id="@+id/attendanceCalculatorProgress"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_gravity="center"
+        android:indeterminate="true"
+        tools:visibility="gone" />
+
+    <LinearLayout
+        android:id="@+id/attendanceCalculatorEmpty"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        android:gravity="center"
+        android:orientation="vertical"
+        android:visibility="invisible"
+        tools:ignore="UseCompoundDrawables">
+
+        <ImageView
+            android:layout_width="100dp"
+            android:layout_height="100dp"
+            app:srcCompat="@drawable/ic_main_attendance"
+            app:tint="?colorOnBackground"
+            tools:ignore="contentDescription" />
+
+        <TextView
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="20dp"
+            android:gravity="center"
+            android:text="@string/attendance_no_items"
+            android:textSize="20sp" />
+    </LinearLayout>
+
+    <LinearLayout
+        android:id="@+id/attendanceCalculatorError"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        android:gravity="center"
+        android:orientation="vertical"
+        android:visibility="invisible"
+        tools:ignore="UseCompoundDrawables"
+        tools:visibility="invisible">
+
+        <ImageView
+            android:layout_width="100dp"
+            android:layout_height="100dp"
+            app:srcCompat="@drawable/ic_error"
+            app:tint="?colorOnBackground"
+            tools:ignore="contentDescription" />
+
+        <TextView
+            android:id="@+id/attendanceCalculatorErrorMessage"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="20dp"
+            android:gravity="center"
+            android:padding="8dp"
+            android:text="@string/error_unknown"
+            android:textSize="20sp" />
+
+        <LinearLayout
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="16dp"
+            android:gravity="center"
+            android:orientation="horizontal">
+
+            <com.google.android.material.button.MaterialButton
+                android:id="@+id/attendanceCalculatorErrorDetails"
+                style="@style/Widget.MaterialComponents.Button.OutlinedButton"
+                android:layout_width="wrap_content"
+                android:layout_height="wrap_content"
+                android:layout_marginEnd="8dp"
+                android:layout_marginRight="8dp"
+                android:text="@string/all_details" />
+
+            <com.google.android.material.button.MaterialButton
+                android:id="@+id/attendanceCalculatorErrorRetry"
+                android:layout_width="wrap_content"
+                android:layout_height="wrap_content"
+                android:text="@string/all_retry" />
+        </LinearLayout>
+    </LinearLayout>
+</FrameLayout>

app/src/main/res/layout/item_attendance_calculator_header.xml

@@ -0,0 +1,111 @@
+<?xml version="1.0" encoding="utf-8"?>
+<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:layout_width="match_parent"
+    android:layout_height="wrap_content"
+    android:paddingStart="8dp"
+    android:paddingTop="6dp"
+    android:paddingEnd="12dp"
+    android:paddingBottom="6dp">
+
+    <TextView
+        android:id="@+id/attendanceCalculatorPercentage"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:gravity="right|center_vertical"
+        android:minWidth="32dp"
+        android:minHeight="36dp"
+        android:textSize="22sp"
+        android:textStyle="bold"
+        app:layout_constraintBottom_toBottomOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toTopOf="parent"
+        tools:text="50" />
+
+    <TextView
+        android:id="@+id/attendanceCalculatorPercentagePercentSign"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="%"
+        android:textColor="?android:textColorSecondary"
+        app:layout_constraintBaseline_toBaselineOf="@+id/attendanceCalculatorPercentage"
+        app:layout_constraintStart_toEndOf="@+id/attendanceCalculatorPercentage" />
+
+    <TextView
+        android:id="@+id/attendanceCalculatorSummaryValues"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:gravity="left"
+        android:maxLines="1"
+        android:textColor="?android:textColorSecondary"
+        android:textSize="13sp"
+        app:layout_constraintEnd_toStartOf="@+id/attendanceCalculatorSummaryDot"
+        app:layout_constraintHorizontal_bias="0.0"
+        app:layout_constraintHorizontal_chainStyle="packed"
+        app:layout_constraintStart_toStartOf="@+id/attendanceCalculatorTitle"
+        app:layout_constraintTop_toBottomOf="@+id/attendanceCalculatorTitle"
+        tools:text="11/123 obecności" />
+
+    <TextView
+        android:id="@+id/attendanceCalculatorSummaryDot"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginHorizontal="4dp"
+        android:gravity="center"
+        android:text="·"
+        android:textColor="?android:textColorSecondary"
+        android:textSize="13sp"
+        app:layout_constraintEnd_toStartOf="@+id/attendanceCalculatorSummaryBalance"
+        app:layout_constraintHorizontal_bias="0.0"
+        app:layout_constraintStart_toEndOf="@+id/attendanceCalculatorSummaryValues"
+        app:layout_constraintTop_toBottomOf="@+id/attendanceCalculatorTitle" />
+
+    <TextView
+        android:id="@+id/attendanceCalculatorSummaryBalance"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:gravity="left"
+        android:maxLines="1"
+        android:minWidth="24dp"
+        android:textColor="?android:textColorSecondary"
+        android:textSize="13sp"
+        app:layout_constraintEnd_toStartOf="@+id/attendanceCalculatorWarning"
+        app:layout_constraintHorizontal_bias="0"
+        app:layout_constraintHorizontal_chainStyle="packed"
+        app:layout_constraintStart_toEndOf="@+id/attendanceCalculatorSummaryDot"
+        app:layout_constraintTop_toBottomOf="@+id/attendanceCalculatorTitle"
+        tools:text="12 powyżej celu" />
+
+    <TextView
+        android:id="@+id/attendanceCalculatorTitle"
+        android:layout_width="0dp"
+        android:layout_height="wrap_content"
+        android:layout_marginStart="10dp"
+        android:layout_marginEnd="8dp"
+        android:ellipsize="end"
+        android:maxLines="1"
+        android:textSize="16sp"
+        android:textStyle="bold"
+        app:layout_constraintEnd_toStartOf="@+id/attendanceCalculatorWarning"
+        app:layout_constraintStart_toEndOf="@+id/attendanceCalculatorPercentagePercentSign"
+        app:layout_constraintTop_toTopOf="parent"
+        tools:text="Informatyka" />
+
+    <ImageView
+        android:id="@+id/attendanceCalculatorWarning"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:contentDescription=""
+        android:layout_marginStart="12dp"
+        android:gravity="center_vertical|right"
+        android:minWidth="24dp"
+        android:visibility="gone"
+        app:layout_constraintBottom_toBottomOf="parent"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintTop_toTopOf="parent"
+        app:srcCompat="@drawable/ic_all_round_mark"
+        app:tint="?colorPrimary"
+        tools:visibility="visible" />
+
+</androidx.constraintlayout.widget.ConstraintLayout>

app/src/main/res/layout/pref_target_attendance.xml

@@ -0,0 +1,140 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+Taken from https://android.googlesource.com/platform/frameworks/support/+/refs/heads/androidx-camerax-release/preference/preference/res/layout/preference_widget_seekbar_material.xml.
+
+  ~ Copyright (C) 2018 The Android Open Source Project
+  ~
+  ~ Licensed under the Apache License, Version 2.0 (the "License");
+  ~ you may not use this file except in compliance with the License.
+  ~ You may obtain a copy of the License at
+  ~
+  ~      http://www.apache.org/licenses/LICENSE-2.0
+  ~
+  ~ Unless required by applicable law or agreed to in writing, software
+  ~ distributed under the License is distributed on an "AS IS" BASIS,
+  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  ~ See the License for the specific language governing permissions and
+  ~ limitations under the License.
+  -->
+<!-- Layout used by SeekBarPreference for the seekbar widget style. -->
+<LinearLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="wrap_content"
+    android:minHeight="?android:attr/listPreferredItemHeightSmall"
+    android:gravity="center_vertical"
+    android:paddingLeft="?android:attr/listPreferredItemPaddingLeft"
+    android:paddingStart="?android:attr/listPreferredItemPaddingStart"
+    android:paddingRight="?android:attr/listPreferredItemPaddingRight"
+    android:paddingEnd="?android:attr/listPreferredItemPaddingEnd"
+    android:background="?android:attr/selectableItemBackground"
+    android:clipChildren="false"
+    android:clipToPadding="false"
+    android:baselineAligned="false">
+    <include layout="@layout/image_frame"/>
+    <LinearLayout
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:orientation="vertical"
+        android:layout_marginTop="8dp"
+        android:layout_marginBottom="8dp"
+        android:clipChildren="false"
+        android:clipToPadding="false">
+        <RelativeLayout
+            android:layout_width="wrap_content"
+            android:layout_height="0dp"
+            android:layout_weight="1">
+            <TextView
+                android:id="@android:id/title"
+                android:layout_width="wrap_content"
+                android:layout_height="wrap_content"
+                android:singleLine="true"
+                android:textAppearance="?android:attr/textAppearanceListItem"
+                android:ellipsize="marquee"/>
+            <TextView
+                android:id="@android:id/summary"
+                android:layout_width="wrap_content"
+                android:layout_height="wrap_content"
+                android:layout_below="@android:id/title"
+                android:layout_alignLeft="@android:id/title"
+                android:layout_alignStart="@android:id/title"
+                android:layout_gravity="start"
+                android:textAlignment="viewStart"
+                android:textColor="?android:attr/textColorSecondary"
+                android:maxLines="4"
+                style="@style/PreferenceSummaryTextStyle"/>
+        </RelativeLayout>
+        <!-- Using UnPressableLinearLayout as a workaround to disable the pressed state propagation
+        to the children of this container layout. Otherwise, the animated pressed state will also
+        play for the thumb in the AbsSeekBar in addition to the preference's ripple background.
+        The background of the SeekBar is also set to null to disable the ripple background -->
+        <androidx.preference.UnPressableLinearLayout
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:gravity="center_vertical"
+            android:paddingLeft="0dp"
+            android:paddingStart="0dp"
+            android:paddingRight="16dp"
+            android:paddingEnd="16dp"
+            android:clipChildren="false"
+            android:clipToPadding="false">
+            <!-- The total height of the Seekbar widget's area should be 48dp - this allows for an
+            increased touch area so you do not need to exactly tap the thumb to move it. However,
+            setting the Seekbar height directly causes the thumb and seekbar to be misaligned on
+            API 22 and 23 - so instead we just set 15dp padding above and below, to account for the
+            18dp default height of the Seekbar thumb for a total of 48dp.
+            Note: we set 0dp padding at the start and end of this seekbar to allow it to properly
+            fit into the layout, but this means that there's no leeway on either side for touch
+            input - this might be something we should reconsider down the line. -->
+            <SeekBar
+                android:id="@+id/seekbar"
+                android:layout_width="0dp"
+                android:layout_weight="1"
+                android:layout_height="wrap_content"
+                android:paddingLeft="@dimen/preference_seekbar_padding_horizontal"
+                android:paddingStart="@dimen/preference_seekbar_padding_horizontal"
+                android:paddingRight="@dimen/preference_seekbar_padding_horizontal"
+                android:paddingEnd="@dimen/preference_seekbar_padding_horizontal"
+                android:paddingTop="@dimen/preference_seekbar_padding_vertical"
+                android:paddingBottom="@dimen/preference_seekbar_padding_vertical"
+
+                android:background="@null"/>
+            <!-- If the value is shown, we reserve a minimum width of 36dp to allow for consistent
+            seekbar width for smaller values. If the value is ~4 or more digits, it will expand
+            into the seekbar width. -->
+            <TextView
+                android:id="@+id/seekbar_value"
+                android:minWidth="@dimen/preference_seekbar_value_minWidth"
+                android:paddingLeft="8dp"
+                android:paddingStart="8dp"
+                android:paddingRight="0dp"
+                android:paddingEnd="0dp"
+                android:layout_width="wrap_content"
+                android:layout_height="wrap_content"
+                android:gravity="right"
+                android:singleLine="true"
+                android:textAppearance="?android:attr/textAppearanceListItem"
+                android:ellipsize="marquee"
+                android:fadingEdge="horizontal"
+                android:scrollbars="none"/>
+            <!-- Wulkanowy start -->
+            <TextView
+                android:minWidth="0dp"
+                android:paddingLeft="0dp"
+                android:paddingStart="0dp"
+                android:paddingRight="0dp"
+                android:paddingEnd="0dp"
+                android:layout_width="wrap_content"
+                android:layout_height="wrap_content"
+                android:gravity="left"
+                android:singleLine="true"
+                android:textAppearance="?android:attr/textAppearanceListItem"
+                android:ellipsize="marquee"
+                android:fadingEdge="horizontal"
+                android:scrollbars="none"
+                android:text="%"
+                />
+            <!-- Wulkanowy end -->
+        </androidx.preference.UnPressableLinearLayout>
+    </LinearLayout>
+</LinearLayout>

app/src/main/res/menu/action_menu_attendance.xml

@@ -1,6 +1,13 @@
 <?xml version="1.0" encoding="utf-8"?>
 <menu xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto">
+    <item
+        android:id="@+id/attendanceMenuCalculator"
+        android:icon="@drawable/ic_menu_attendance_calculator"
+        android:orderInCategory="0"
+        android:title="@string/attendance_calculator_button"
+        app:iconTint="@color/material_on_surface_emphasis_medium"
+        app:showAsAction="ifRoom" />
     <item
         android:id="@+id/attendanceMenuSummary"
         android:icon="@drawable/ic_menu_attendance_summary"

app/src/main/res/values-pl/strings.xml

@@ -876,4 +876,7 @@
     <string name="message_unmute">Wyłącz wyciszenie</string>
     <string name="message_mute_success">Wyciszyleś tego użytkownika</string>
     <string name="message_unmute_success">Wyłączyłeś wyciszenie tego użytkownika</string>
+    <!-- attendance calculator -->
+    <string name="pref_attendance_target">Docelowa frekwencja (w %)</string>
+    <string name="attendance_calculator_button">Kalkulator frekwencji</string>
 </resources>

app/src/main/res/values/preferences_defaults.xml

@@ -2,6 +2,8 @@
 <resources xmlns:tools="http://schemas.android.com/tools" tools:ignore="MissingTranslation">
     <string name="pref_default_startup">0</string>
     <bool name="pref_default_attendance_present">true</bool>
+    <integer name="pref_default_attendance_target">50</integer>
+    <string name="pref_default_attendance_calculator_sorting_mode">alphabetic</string>
     <string name="pref_default_grade_average_mode">only_one_semester</string>
     <bool name="pref_default_grade_average_force_calc">false</bool>
     <string name="pref_default_expand_grade_mode">one</string>

app/src/main/res/values/preferences_keys.xml

@@ -2,6 +2,8 @@
 <resources xmlns:tools="http://schemas.android.com/tools" tools:ignore="MissingTranslation">
     <string name="pref_key_start_menu">default_menu_index</string>
     <string name="pref_key_attendance_present">attendance_present</string>
+    <string name="pref_key_attendance_target">attendance_target</string>
+    <string name="pref_key_attendance_calculator_sorting_mode">attendance_calculator_sorting_mode</string>
     <string name="pref_key_app_theme">app_theme</string>
     <string name="pref_key_dashboard_tiles">dashboard_tiles</string>
     <string name="pref_key_grade_color_scheme">grade_color_scheme</string>

app/src/main/res/values/preferences_values.xml

@@ -79,6 +79,17 @@
         <item>0.75</item>
     </string-array>
 
+    <string-array name="attendance_calculator_sorting_mode_entries">
+        <item>Alphabetically</item>
+        <item>By attendance percentage</item>
+        <item>By lesson balance</item>
+    </string-array>
+    <string-array name="attendance_calculator_sorting_mode_values" translatable="false">
+        <item>alphabetic</item>
+        <item>attendance_percentage</item>
+        <item>lesson_balance</item>
+    </string-array>
+
     <string-array name="grade_sorting_mode_entries">
         <item>Alphabetically</item>
         <item>By date</item>

app/src/main/res/values/strings.xml

@@ -258,6 +258,11 @@
 
     <!--Attendance-->
     <string name="attendance_summary_button">Attendance summary</string>
+    <string name="attendance_calculator_button">Attendance calculator</string>
+    <string name="attendance_calculator_summary_balance_positive"><b>%1$d</b> over target</string>
+    <string name="attendance_calculator_summary_balance_neutral">right on target</string>
+    <string name="attendance_calculator_summary_balance_negative"><b>%1$d</b> under target</string>
+    <string name="attendance_calculator_summary_values">%1$d/%2$d presences</string>
     <string name="attendance_absence_school">Absent for school reasons</string>
     <string name="attendance_absence_excused">Excused absence</string>
     <string name="attendance_absence_unexcused">Unexcused absence</string>
@@ -715,6 +720,8 @@
     <string name="pref_view_grade_average_mode">Calculated average options</string>
     <string name="pref_view_grade_average_force_calc">Force average calculation by app</string>
     <string name="pref_view_present">Show presence</string>
+    <string name="pref_attendance_target">Attendance target</string>
+    <string name="pref_view_attendance_calculator_sorting_mode">Attendance calculator sorting</string>
     <string name="pref_view_app_theme">Theme</string>
     <string name="pref_view_expand_grade">Grades expanding</string>
     <string name="pref_view_timetable_show_groups">Show groups next to subjects</string>

app/src/main/res/xml/scheme_preferences_appearance.xml

@@ -85,6 +85,25 @@
             app:iconSpaceReserved="false"
             app:key="@string/pref_key_attendance_present"
             app:title="@string/pref_view_present" />
+        <SeekBarPreference
+            app:defaultValue="@integer/pref_default_attendance_target"
+            app:iconSpaceReserved="false"
+            android:layout="@layout/pref_target_attendance"
+            app:key="@string/pref_key_attendance_target"
+            app:title="@string/pref_attendance_target"
+            app:min="1"
+            app:updatesContinuously="true"
+            android:max="99"
+            app:showSeekBarValue="true"
+            />
+        <ListPreference
+            app:defaultValue="@string/pref_default_attendance_calculator_sorting_mode"
+            app:entries="@array/attendance_calculator_sorting_mode_entries"
+            app:entryValues="@array/attendance_calculator_sorting_mode_values"
+            app:iconSpaceReserved="false"
+            app:key="@string/pref_key_attendance_calculator_sorting_mode"
+            app:title="@string/pref_view_attendance_calculator_sorting_mode"
+            app:useSimpleSummaryProvider="true" />
     </PreferenceCategory>
     <PreferenceCategory
         android:layout_height="wrap_content"