package soy.iko.opencode.ui.components

import java.time.Instant
import java.time.LocalDate
import java.time.ZoneId
import java.util.concurrent.TimeUnit

/**
 * The time unit + count resolved from a delta, before locale-specific formatting. Kept as a
 * pure value so unit tests can verify the boundary logic without a [android.content.Context]
 * (string-resource resolution is Android-only and stubs to null under `isReturnDefaultValues`).
 */
sealed class RelativeTimeUnit {
    data class Now(val count: Int = 0) : RelativeTimeUnit()
    data class Minutes(val count: Long) : RelativeTimeUnit()
    data class Hours(val count: Long) : RelativeTimeUnit()
    data class Days(val count: Long) : RelativeTimeUnit()
    data class Weeks(val count: Long) : RelativeTimeUnit()
    data class Months(val count: Long) : RelativeTimeUnit()
    data class Years(val count: Long) : RelativeTimeUnit()
}

/**
 * Resolves the [RelativeTimeUnit] for a delta without any locale-specific formatting, so the
 * boundary logic is unit-testable on the JVM without a [android.content.Context].
 *
 * Months and years are computed via [java.time] calendar arithmetic (not `days / 30` or
 * `days / 365`), so the displayed "N months ago" / "N years ago" matches the calendar-month
 * difference a user expects rather than drifting at month/year boundaries of varying length.
 */
fun relativeTimeUnit(epochMillis: Long?): RelativeTimeUnit? {
    if (epochMillis == null || epochMillis <= 0) return null
    val now = System.currentTimeMillis()
    val diff = now - epochMillis
    if (diff < 0) return RelativeTimeUnit.Now()
    val minutes = TimeUnit.MILLISECONDS.toMinutes(diff)
    if (minutes < 1) return RelativeTimeUnit.Now()
    if (minutes < 60) return RelativeTimeUnit.Minutes(minutes)
    val hours = TimeUnit.MILLISECONDS.toHours(diff)
    if (hours < 24) return RelativeTimeUnit.Hours(hours)
    val days = TimeUnit.MILLISECONDS.toDays(diff)
    if (days < 7) return RelativeTimeUnit.Days(days)
    val weeks = days / 7
    if (weeks < 5) return RelativeTimeUnit.Weeks(weeks)
    // Beyond ~5 weeks, switch to calendar months/years so the label tracks the user's
    // mental model of "months ago" rather than a 30-day approximation that drifts at
    // month boundaries (28/29/30/31 days). java.time is available on minSdk 26+.
    val zone = ZoneId.systemDefault()
    val past = Instant.ofEpochMilli(epochMillis).atZone(zone).toLocalDate()
    val today = Instant.ofEpochMilli(now).atZone(zone).toLocalDate()
    val monthsBetween = java.time.Period.between(past, today).toTotalMonths()
    if (monthsBetween < 12) return RelativeTimeUnit.Months(monthsBetween)
    val years = monthsBetween / 12
    return RelativeTimeUnit.Years(years)
}