module JosieHealth::Utils
  module Timezone
    # Common timezone abbreviation aliases -> IANA timezone names
    ALIASES = {
      # Europe
      "cet"  => "Europe/Berlin",
      "cest" => "Europe/Berlin",
      "wet"  => "Europe/London",
      "gmt"  => "Europe/London",
      "bst"  => "Europe/London",
      "eet"  => "Europe/Helsinki",
      "eest" => "Europe/Helsinki",
      # Americas
      "est" => "America/New_York",
      "edt" => "America/New_York",
      "cst" => "America/Chicago",
      "cdt" => "America/Chicago",
      "mst" => "America/Denver",
      "mdt" => "America/Denver",
      "pst" => "America/Los_Angeles",
      "pdt" => "America/Los_Angeles",
      # Asia/Pacific
      "jst"  => "Asia/Tokyo",
      "kst"  => "Asia/Seoul",
      "cst8" => "Asia/Shanghai",
      "hkt"  => "Asia/Hong_Kong",
      "ist"  => "Asia/Kolkata",
      "aest" => "Australia/Sydney",
      "aedt" => "Australia/Sydney",
      "awst" => "Australia/Perth",
      "nzst" => "Pacific/Auckland",
      "nzdt" => "Pacific/Auckland",
      # UTC
      "utc" => "UTC",
      "z"   => "UTC",
    }

    # Resolve timezone abbreviation to IANA name
    # Returns nil if not a known alias
    def self.resolve_alias(input : String) : String?
      ALIASES[input.downcase.strip]?
    end

    # Check if input is a known timezone alias
    def self.alias?(input : String) : Bool
      ALIASES.has_key?(input.downcase.strip)
    end

    # Parse UTC offset format (+02:00, -05:00, +2, -5)
    # Returns tuple of (sign, hours, minutes) or nil if invalid
    def self.parse_offset(input : String) : NamedTuple(sign: String, hours: Int32, minutes: Int32)?
      if match = input.match(/^([+-])(\d{1,2})(?::?(\d{2}))?$/)
        sign = match[1]
        hours = match[2].to_i
        minutes = match[3]?.try(&.to_i) || 0

        return nil if hours > 14 || minutes > 59

        {sign: sign, hours: hours, minutes: minutes}
      end
    end

    # Format offset as string (e.g., "+02:00")
    def self.format_offset(sign : String, hours : Int32, minutes : Int32) : String
      "#{sign}#{hours.to_s.rjust(2, '0')}:#{minutes.to_s.rjust(2, '0')}"
    end

    # Validate if input is a valid IANA timezone name
    def self.valid_iana?(input : String) : Bool
      begin
        Time::Location.load(input)
        true
      rescue Time::Location::InvalidLocationNameError
        false
      end
    end

    # Get current UTC offset string for a timezone
    def self.current_offset(tz : String) : String
      # Handle stored offset format (+02:00)
      if tz.match(/^[+-]\d{2}:\d{2}$/)
        return "UTC#{tz}"
      end

      begin
        location = Time::Location.load(tz)
        now = Time.local(location)
        offset_seconds = now.offset
        hours = offset_seconds // 3600
        minutes = (offset_seconds.abs % 3600) // 60
        sign = offset_seconds >= 0 ? "+" : "-"
        "UTC#{sign}#{hours.abs.to_s.rjust(2, '0')}:#{minutes.to_s.rjust(2, '0')}"
      rescue
        "UTC"
      end
    end

    # All known timezone aliases
    def self.all_aliases : Array(String)
      ALIASES.keys
    end
  end
end