# frozen_string_literal: true

# Business-hours decision: Mon-Fri 08:00-16:00 Europe/Prague, excluding Czech public holidays.
# This is the authoritative backend check (the device's util/BusinessHours.java is only a local
# reflex when the network is down). Pure functions over a supplied local Time — deterministic + testable.
# Note: prague_now uses a TZ-env trick for DST; a tz library would be sturdier if this grows.

require "date"

module Helpdesk
  module BusinessHours
    OPEN_HOUR  = 8
    CLOSE_HOUR = 16 # closed at 16:00 sharp

    module_function

    # `local` must be a Time already in Europe/Prague.
    def open?(local)
      return false if weekend?(local)
      return false if holiday?(local.to_date)
      local.hour >= OPEN_HOUR && local.hour < CLOSE_HOUR
    end

    def weekend?(local) = [0, 6].include?(local.wday) # Sun=0, Sat=6

    # Czech public holidays (fixed) + movable Good Friday & Easter Monday.
    def holiday?(date)
      y = date.year
      fixed = [[1, 1], [5, 1], [5, 8], [7, 5], [7, 6], [9, 28], [10, 28], [11, 17], [12, 24], [12, 25], [12, 26]]
      return true if fixed.include?([date.month, date.day])
      easter = easter_date(y)
      date == (easter - 2) || date == (easter + 1) # Good Friday, Easter Monday
    end

    # Anonymous Gregorian algorithm.
    def easter_date(y)
      a = y % 19; b = y / 100; c = y % 100; d = b / 4; e = b % 4
      f = (b + 8) / 25; g = (b - f + 1) / 3
      h = (19 * a + b - d - g + 15) % 30
      i = c / 4; k = c % 4
      l = (32 + 2 * e + 2 * i - h - k) % 7
      m = (a + 11 * h + 22 * l) / 451
      month = (h + l - 7 * m + 114) / 31
      day = ((h + l - 7 * m + 114) % 31) + 1
      Date.new(y, month, day)
    end

    # Prague "now" without a tz gem AND without mutating the process-global ENV["TZ"] (the old
    # `ENV["TZ"]=` trick raced across WEBrick request threads: concurrent /status polls could
    # permanently leak TZ, and libc setenv isn't thread-safe against getenv in other threads). Instead
    # apply the Europe/Prague UTC offset (CET/CEST) directly to a UTC clock — pure, thread-safe.
    def prague_now
      utc = Time.now.utc
      utc.getlocal(prague_offset(utc))
    end

    # "+02:00" during EU summer time (CEST), else "+01:00" (CET). EU DST runs from 01:00 UTC on the
    # last Sunday of March to 01:00 UTC on the last Sunday of October.
    def prague_offset(utc)
      y = utc.year
      dst_start = Time.utc(y, 3, last_sunday(y, 3).day, 1)
      dst_end   = Time.utc(y, 10, last_sunday(y, 10).day, 1)
      (utc >= dst_start && utc < dst_end) ? "+02:00" : "+01:00"
    end

    def last_sunday(y, month)
      d = Date.new(y, month, -1) # last day of the month
      d - d.wday                 # step back to Sunday (Date#wday: Sunday=0)
    end

    # Out-of-hours SMS text (Czech).
    OUT_OF_HOURS_SMS = "Mimo pracovní dobu (Po–Pá 8–16). Zavolejte prosím zítra v 8:00. Děkujeme."
  end
end