package com.example.aiapp

import java.time.Duration
import java.time.OffsetDateTime

/**
 * How long is left in a usage window.
 *
 * Shared by the session bar and the usage screen: the arithmetic is the same in both and only the
 * sentence around it differs, so this returns the span on its own and leaves the wording to the
 * caller.
 */

/** "1d 4h", "3h 12m", "12m" -- the span alone, with no leading or trailing words. */
fun formatSpan(until: Duration): String =
    when {
        until.toHours() >= 24 -> "${until.toDays()}d ${until.toHours() % 24}h"
        until.toHours() > 0 -> "${until.toHours()}h ${until.toMinutes() % 60}m"
        else -> "${until.toMinutes()}m"
    }

/**
 * Time from [now] until [resetsAt], or null when that timestamp cannot be read.
 *
 * Null rather than a zero duration, because a string this app failed to parse is not a window that
 * has just run out: a caller given zero for both would tell the reader to refresh on the strength
 * of something nobody measured.
 *
 * [now] is a parameter rather than read here so a caller can drive it from state and have the
 * countdown recompute on its own schedule.
 */
fun remainingUntil(resetsAt: String, now: OffsetDateTime): Duration? =
    try {
        Duration.between(now, OffsetDateTime.parse(resetsAt))
    } catch (_: Exception) {
        null
    }