package search

import (
	"fmt"
	"time"
)

// DateRange represents a time range [Start, End) in a specific year.
type DateRange struct {
	Start time.Time
	End   time.Time
	Year  int // the year this range belongs to (for scoring)
}

// BuildCELFilter creates a CEL filter string for a date range using created_ts.
func BuildCELFilter(dr DateRange) string {
	return fmt.Sprintf("created_ts >= %d && created_ts < %d",
		dr.Start.Unix(), dr.End.Unix())
}

func isLeapYear(year int) bool {
	return year%4 == 0 && (year%100 != 0 || year%400 == 0)
}

func daysInMonth(year int, month time.Month) int {
	return time.Date(year, month+1, 0, 0, 0, 0, 0, time.UTC).Day()
}

// tier1Ranges returns date ranges for the exact same day in previous years.
// Special handling for Feb 29 / Feb 28.
func tier1Ranges(today time.Time, maxYears int, loc *time.Location) []DateRange {
	month := today.Month()
	day := today.Day()
	currentYear := today.Year()

	var ranges []DateRange

	for y := currentYear - maxYears; y < currentYear; y++ {
		if month == time.February && day == 29 {
			// Today is Feb 29 — only include leap years
			if !isLeapYear(y) {
				continue
			}
		}

		// Check that this day exists in that year
		if day > daysInMonth(y, month) {
			continue
		}

		start := time.Date(y, month, day, 0, 0, 0, 0, loc)
		end := start.AddDate(0, 0, 1)
		ranges = append(ranges, DateRange{Start: start, End: end, Year: y})
	}

	// Special: if today is Feb 28 in a non-leap year, also check Feb 29 in past leap years
	if month == time.February && day == 28 && !isLeapYear(currentYear) {
		for y := currentYear - maxYears; y < currentYear; y++ {
			if isLeapYear(y) {
				start := time.Date(y, time.February, 29, 0, 0, 0, 0, loc)
				end := start.AddDate(0, 0, 1)
				ranges = append(ranges, DateRange{Start: start, End: end, Year: y})
			}
		}
	}

	return ranges
}

// tier2Ranges returns date ranges for the same day-of-month in previous months (last 24 months).
// Excludes the current month (covered by Tier 1).
func tier2Ranges(today time.Time, loc *time.Location) []DateRange {
	day := today.Day()
	currentYear := today.Year()
	currentMonth := today.Month()

	var ranges []DateRange

	for i := 1; i <= 24; i++ {
		t := time.Date(currentYear, currentMonth, 1, 0, 0, 0, 0, loc).AddDate(0, -i, 0)
		y := t.Year()
		m := t.Month()

		// Skip if this day doesn't exist in that month
		if day > daysInMonth(y, m) {
			continue
		}

		start := time.Date(y, m, day, 0, 0, 0, 0, loc)
		end := start.AddDate(0, 0, 1)
		ranges = append(ranges, DateRange{Start: start, End: end, Year: y})
	}

	return ranges
}

// tier3Ranges returns ±3 day ranges around the exact date in previous years,
// excluding the exact day itself (which is Tier 1).
func tier3Ranges(today time.Time, maxYears int, loc *time.Location) []DateRange {
	month := today.Month()
	day := today.Day()
	currentYear := today.Year()

	var ranges []DateRange

	for y := currentYear - maxYears; y < currentYear; y++ {
		// The center date in that year
		if day > daysInMonth(y, month) {
			continue
		}
		center := time.Date(y, month, day, 0, 0, 0, 0, loc)
		weekStart := center.AddDate(0, 0, -3)
		weekEnd := center.AddDate(0, 0, 4) // +3 days inclusive = +4 exclusive

		// We need to exclude the center day: split into [weekStart, center) and [center+1day, weekEnd)
		centerEnd := center.AddDate(0, 0, 1)

		ranges = append(ranges,
			DateRange{Start: weekStart, End: center, Year: y},
			DateRange{Start: centerEnd, End: weekEnd, Year: y},
		)
	}

	return ranges
}

// tier4Ranges returns the same month in previous years,
// excluding the ±3 day window around the exact date (covered by Tier 1+3).
func tier4Ranges(today time.Time, maxYears int, loc *time.Location) []DateRange {
	month := today.Month()
	day := today.Day()
	currentYear := today.Year()

	var ranges []DateRange

	for y := currentYear - maxYears; y < currentYear; y++ {
		monthStart := time.Date(y, month, 1, 0, 0, 0, 0, loc)
		monthEnd := time.Date(y, month+1, 1, 0, 0, 0, 0, loc)

		d := min(day, daysInMonth(y, month))
		center := time.Date(y, month, d, 0, 0, 0, 0, loc)
		excludeStart := center.AddDate(0, 0, -3)
		excludeEnd := center.AddDate(0, 0, 4)

		// Before the exclude window
		if excludeStart.After(monthStart) {
			ranges = append(ranges, DateRange{Start: monthStart, End: excludeStart, Year: y})
		}
		// After the exclude window
		if excludeEnd.Before(monthEnd) {
			ranges = append(ranges, DateRange{Start: excludeEnd, End: monthEnd, Year: y})
		}
	}

	return ranges
}

// tier5Ranges returns the same quarter in previous years, excluding the current month.
func tier5Ranges(today time.Time, maxYears int, loc *time.Location) []DateRange {
	month := today.Month()
	currentYear := today.Year()

	qStart := (month-1)/3*3 + 1 // first month of quarter (1, 4, 7, 10)
	var quarterMonths [3]time.Month
	for i := range 3 {
		quarterMonths[i] = time.Month(int(qStart) + i)
	}

	var ranges []DateRange

	for y := currentYear - maxYears; y < currentYear; y++ {
		for _, m := range quarterMonths {
			if m == month {
				continue // exclude current month (covered by Tier 4)
			}
			start := time.Date(y, m, 1, 0, 0, 0, 0, loc)
			end := time.Date(y, m+1, 1, 0, 0, 0, 0, loc)
			ranges = append(ranges, DateRange{Start: start, End: end, Year: y})
		}
	}

	return ranges
}

// tier6Ranges returns the same half-year in previous years, excluding the current quarter.
func tier6Ranges(today time.Time, maxYears int, loc *time.Location) []DateRange {
	month := today.Month()
	currentYear := today.Year()

	// Half-year: H1 = Jan-Jun, H2 = Jul-Dec
	var halfStart time.Month
	if month <= 6 {
		halfStart = 1
	} else {
		halfStart = 7
	}

	// Current quarter start
	qStart := (month-1)/3*3 + 1

	var ranges []DateRange

	for y := currentYear - maxYears; y < currentYear; y++ {
		for m := halfStart; m < halfStart+6; m++ {
			// Skip months in the current quarter
			if m >= qStart && m < qStart+3 {
				continue
			}
			start := time.Date(y, m, 1, 0, 0, 0, 0, loc)
			end := time.Date(y, m+1, 1, 0, 0, 0, 0, loc)
			ranges = append(ranges, DateRange{Start: start, End: end, Year: y})
		}
	}

	return ranges
}

// tier7Ranges returns 2 to 6 months ago (recent past).
func tier7Ranges(today time.Time, loc *time.Location) []DateRange {
	end := time.Date(today.Year(), today.Month(), 1, 0, 0, 0, 0, loc).AddDate(0, -2, 0)
	start := time.Date(today.Year(), today.Month(), 1, 0, 0, 0, 0, loc).AddDate(0, -6, 0)

	return []DateRange{
		{Start: start, End: end, Year: 0}, // Year=0 means "recent"
	}
}