package com.vgmlr.varnish

import java.time.Instant
import java.time.LocalDate
import java.time.LocalDateTime
import java.time.Month
import java.time.ZoneId
import java.time.format.DateTimeFormatter
import java.time.temporal.ChronoUnit
import java.util.Locale

object VarnishClock {
    private val YY = DateTimeFormatter.ofPattern("yy")
    private val HM = DateTimeFormatter.ofPattern("HH:mm")
    private val DM = DateTimeFormatter.ofPattern("dd MMM", Locale.ENGLISH)
    private val SPLIT = Regex("[\\s,]+")

    fun stamp(millis: Long): String =
        stamp(LocalDateTime.ofInstant(Instant.ofEpochMilli(millis), ZoneId.systemDefault()))

    fun stamp(dt: LocalDateTime): String {
        val start = yearStart(dt.toLocalDate())
        val day = ChronoUnit.DAYS.between(start, dt.toLocalDate()) + 1
        val year = "0" + start.format(YY)
        return "${dt.format(HM)} $day $year (${dt.format(DM)})"
    }

    private fun yearStart(d: LocalDate): LocalDate {
        val mark = LocalDate.of(d.year, 3, 20)
        return if (d.isBefore(mark)) mark.minusYears(1) else mark
    }

    fun matcher(q: String): ((Long) -> Boolean)? {
        val parts = q.lowercase(Locale.ROOT).split(SPLIT).filter(String::isNotEmpty)
        var year: Int? = null
        var month: Int? = null
        var day: Int? = null
        for (p in parts) {
            val n = p.toIntOrNull()
            when {
                n != null && p.length == 4 && year == null -> year = n
                n != null && p.length <= 2 && n in 1..31 && day == null -> day = n
                n == null && month == null -> month = monthOf(p) ?: return null
                else -> return null
            }
        }
        if (year == null && month == null) return null
        val y = year
        val m = month
        val d = day
        val zone = ZoneId.systemDefault()
        return { ms ->
            val at = Instant.ofEpochMilli(ms).atZone(zone).toLocalDate()
            (y == null || at.year == y) &&
                    (m == null || at.monthValue == m) &&
                    (d == null || at.dayOfMonth == d)
        }
    }

    private fun monthOf(p: String): Int? =
        if (p.length < 3) null
        else Month.entries.firstOrNull { it.name.lowercase(Locale.ROOT).startsWith(p) }?.value
}