package quota

import (
	_ "time/tzdata" // embedded zone database: TZ-aware windows work in scratch containers

	"time"

	"ukrrs.com/mopac/harness/internal/config"
)

// Schedule is the TZ-aware peak window. z.ai peak hours are documented as
// Monday-Friday 14:00-18:00 Singapore (UTC+8), which is 01:00-05:00
// America/Chicago in winter (CST) / 00:00-04:00 during US DST — the default
// matches Charles's "0100 to 0500 CST" and is configurable to the minute.
// The window may wrap midnight (start > end): then it covers evenings of
// the start day plus early mornings of the following day.
type Schedule struct {
	Start, End   time.Duration // minutes-since-midnight in Loc
	Loc          *time.Location
	WeekdaysOnly bool
}

// NewSchedule parses the window out of the [quota] config fields.
func NewSchedule(peakStart, peakEnd, tzName string, weekdaysOnly bool) (Schedule, error) {
	start, err := config.ParseHHMM(peakStart)
	if err != nil {
		return Schedule{}, err
	}
	end, err := config.ParseHHMM(peakEnd)
	if err != nil {
		return Schedule{}, err
	}
	loc, err := time.LoadLocation(tzName)
	if err != nil {
		return Schedule{}, err
	}
	return Schedule{Start: start, End: end, Loc: loc, WeekdaysOnly: weekdaysOnly}, nil
}

// SameDay reports whether t is inside the window without crossing midnight
// (start <= t < end, single-day window).
func (s Schedule) inWindow(mins time.Duration) bool {
	if s.Start <= s.End {
		return mins >= s.Start && mins < s.End
	}
	// Wrapped window: [start, 24h) of the start day, [0, end) of the next.
	return mins >= s.Start || mins < s.End
}

// InPeak reports whether t falls inside the peak window, evaluated in the
// schedule's timezone. For wrapped windows the weekday check applies to the
// day the window STARTED on (a Sunday 22:00-02:00 window is off all week
// when weekdays-only, because it starts on Sunday).
func (s Schedule) InPeak(t time.Time) bool {
	local := t.In(s.Loc)
	mins := time.Duration(local.Hour())*time.Hour + time.Duration(local.Minute())*time.Minute
	if s.Start <= s.End {
		if !s.inWindow(mins) {
			return false
		}
		return !s.WeekdaysOnly || isWeekday(local)
	}
	// Evening half: today carries the window.
	if mins >= s.Start {
		return !s.WeekdaysOnly || isWeekday(local)
	}
	// Morning half: the window started yesterday.
	if mins < s.End {
		return !s.WeekdaysOnly || isWeekday(local.AddDate(0, 0, -1))
	}
	return false
}

func isWeekday(t time.Time) bool {
	wd := t.Weekday()
	return wd >= time.Monday && wd <= time.Friday
}