Coverage Summary for Class: TransactionPeriodWindowKt (com.georgeci.moneysurfer.domain.util)

 package com.georgeci.moneysurfer.domain.util
 
 import com.georgeci.moneysurfer.domain.preferences.TransactionPeriodMode
 import kotlinx.datetime.DateTimeUnit
 import kotlinx.datetime.LocalDate
 import kotlinx.datetime.minus
 import kotlinx.datetime.plus
 
 private const val DAYS_PER_WEEK = 7
 
 /** Epoch day 0 (1970-01-01) was a Thursday, so Monday is three days later. */
 private const val EPOCH_DAY_TO_MONDAY_OFFSET = 3
 
 /** ISO-8601 pins week 1 as the week containing January 4th. */
 private const val ISO_WEEK_ANCHOR_DAY = 4
 
 /**
  * A closed date window `[from, to]` the transactions list is scoped to, or an unbounded one
  * (both ends `null`) for [TransactionPeriodMode.AllTime].
  *
  * Closed rather than half-open because the bounds go straight into a SQL
  * `operationDate BETWEEN` comparison against ISO date text — see `TransactionDao`.
  */
 data class TransactionPeriodWindow(
     val from: LocalDate?,
     val to: LocalDate?,
 ) {
     val isUnbounded: Boolean get() = from == null && to == null
 
     operator fun contains(date: LocalDate): Boolean =
         (from == null || date >= from) && (to == null || date <= to)
 
     companion object {
         val Unbounded = TransactionPeriodWindow(from = null, to = null)
     }
 }
 
 /**
  * The window of [mode] containing [anchor]. Pure — the caller supplies the date, so there is no
  * `Clock` dependency and the maths stays trivially testable.
  */
 fun periodWindow(mode: TransactionPeriodMode, anchor: LocalDate): TransactionPeriodWindow =
     when (mode) {
         TransactionPeriodMode.Month -> {
             val start = LocalDate(anchor.year, anchor.month, 1)
             TransactionPeriodWindow(start, start.plus(1, DateTimeUnit.MONTH).minus(1, DateTimeUnit.DAY))
         }
         TransactionPeriodMode.Week -> {
             val start = anchor.startOfIsoWeek()
             TransactionPeriodWindow(start, start.plus(DAYS_PER_WEEK - 1, DateTimeUnit.DAY))
         }
         TransactionPeriodMode.AllTime -> TransactionPeriodWindow.Unbounded
     }
 
 /**
  * [anchor] shifted by [by] whole periods (negative goes back). A no-op for
  * [TransactionPeriodMode.AllTime], which has nothing to page through.
  *
  * Month steps are taken from the first of the month so a short-month clamp can never
  * accumulate: Jan 31 → Feb 28 → Mar 28 is avoided by anchoring on Jan 1 → Feb 1 → Mar 1.
  */
 fun shiftPeriod(mode: TransactionPeriodMode, anchor: LocalDate, by: Int): LocalDate = when (mode) {
     TransactionPeriodMode.Month -> LocalDate(anchor.year, anchor.month, 1).plus(by, DateTimeUnit.MONTH)
     TransactionPeriodMode.Week -> anchor.startOfIsoWeek().plus(by * DAYS_PER_WEEK, DateTimeUnit.DAY)
     TransactionPeriodMode.AllTime -> anchor
 }
 
 /** The Monday of the ISO week containing this date. */
 fun LocalDate.startOfIsoWeek(): LocalDate {
     val epochDay = toEpochDays()
     val daysSinceMonday = (epochDay + EPOCH_DAY_TO_MONDAY_OFFSET).mod(DAYS_PER_WEEK.toLong())
     return LocalDate.fromEpochDays(epochDay - daysSinceMonday)
 }
 
 /**
  * ISO-8601 week number (1..53) and the week-based year it belongs to. The two can disagree with
  * the calendar year around New Year: 2027-01-01 is week 53 of week-year 2026.
  */
 data class IsoWeek(val weekNumber: Int, val weekYear: Int)
 
 fun LocalDate.isoWeek(): IsoWeek {
     val weekStart = startOfIsoWeek()
     // The week-based year is the calendar year of the week's Thursday, by definition.
     val weekYear = weekStart.plus(EPOCH_DAY_TO_MONDAY_OFFSET, DateTimeUnit.DAY).year
     val firstWeekStart = LocalDate(weekYear, 1, ISO_WEEK_ANCHOR_DAY).startOfIsoWeek()
     val weeksBetween = (weekStart.toEpochDays() - firstWeekStart.toEpochDays()) / DAYS_PER_WEEK
     return IsoWeek(weekNumber = weeksBetween.toInt() + 1, weekYear = weekYear)
 }