package main

// holidays.go 给 AI 任务拆解提供「本月 + 未来几个月」节假日公历对照。
// 农历节日每年换算不同，法定放假以国务院已公布年份为准；未公布年份只给节日当天。

import (
	"fmt"
	"sort"
	"strings"
	"time"
)

type holidayItem struct {
	day      time.Time
	offStart time.Time // 放假开始；零值表示仅节日当天
	offEnd   time.Time // 放假结束（含）
	work     []time.Time
	zh, en   string
	aka      string
}

// upcomingHolidays 从本月 1 日到未来 months 个月月末（默认 6）的节日，按日期排序。
func upcomingHolidays(now time.Time, months int) []holidayItem {
	if months <= 0 {
		months = 6
	}
	loc := now.Location()
	start := time.Date(now.Year(), now.Month(), 1, 0, 0, 0, 0, loc)
	end := start.AddDate(0, months+1, 0) // 不含：覆盖「未来几个月」整月
	var out []holidayItem
	for y := start.Year(); y <= end.Year(); y++ {
		for _, h := range yearHolidays(y, loc) {
			if !h.day.Before(start) && h.day.Before(end) {
				out = append(out, h)
			}
		}
	}
	sort.Slice(out, func(i, j int) bool { return out[i].day.Before(out[j].day) })
	return out
}

func formatHolidayBlock(now time.Time, en bool) string {
	list := upcomingHolidays(now, 6)
	if len(list) == 0 {
		return ""
	}
	var b strings.Builder
	if en {
		b.WriteString("Holidays this month and the next 6 months (use these exact dates; do not guess):\n")
	} else {
		b.WriteString("本月及未来 6 个月节假日对照（必须用表中公历，禁止自己换算农历）：\n")
	}
	for _, h := range list {
		name := h.zh
		if en {
			name = h.en
			if h.aka != "" {
				name += " / " + h.aka
			} else if h.zh != "" {
				name += " / " + h.zh
			}
		} else if h.aka != "" {
			name += " / " + h.aka
		}
		line := fmt.Sprintf("- %s：%s", name, h.day.Format("2006-01-02"))
		if !h.offStart.IsZero() && !h.offEnd.IsZero() {
			line += fmt.Sprintf("（放假 %s～%s", h.offStart.Format("2006-01-02"), h.offEnd.Format("2006-01-02"))
			if len(h.work) > 0 {
				ws := make([]string, len(h.work))
				for i, w := range h.work {
					ws[i] = w.Format("2006-01-02")
				}
				line += "；调休上班 " + strings.Join(ws, "、")
			}
			line += "）"
		}
		b.WriteString(line + "\n")
	}
	if en {
		b.WriteString("Phrases: “before X” → day before the festival; “during X” → official holiday span if listed, else the festival day; “after X” → day after the holiday ends.\n")
	} else {
		b.WriteString("说法对照：「X前 / X之前」= 节日前一天；「X期间 / X放假」= 表中放假区间（没有区间就用当天）；「X后 / X之后」= 假期结束后一天。国庆可说十一，春节可说过年，元旦可说新年（公历）。\n")
	}
	return b.String()
}

func yearHolidays(year int, loc *time.Location) []holidayItem {
	d := func(m, day int) time.Time {
		return time.Date(year, time.Month(m), day, 0, 0, 0, 0, loc)
	}
	items := []holidayItem{
		{day: d(1, 1), zh: "元旦", en: "New Year's Day", aka: "新年"},
		{day: d(2, 14), zh: "情人节", en: "Valentine's Day"},
		{day: d(3, 8), zh: "妇女节", en: "Women's Day"},
		{day: d(3, 12), zh: "植树节", en: "Arbor Day (CN)"},
		{day: d(4, 1), zh: "愚人节", en: "April Fools' Day"},
		{day: d(5, 1), zh: "劳动节", en: "Labor Day", aka: "五一"},
		{day: d(5, 4), zh: "青年节", en: "Youth Day"},
		{day: nthWeekday(year, time.May, time.Sunday, 2, loc), zh: "母亲节", en: "Mother's Day"},
		{day: d(6, 1), zh: "儿童节", en: "Children's Day"},
		{day: nthWeekday(year, time.June, time.Sunday, 3, loc), zh: "父亲节", en: "Father's Day"},
		{day: d(7, 1), zh: "建党节", en: "CPC Founding Day"},
		{day: d(8, 1), zh: "建军节", en: "PLA Day"},
		{day: d(9, 10), zh: "教师节", en: "Teachers' Day"},
		{day: d(10, 1), zh: "国庆节", en: "National Day", aka: "十一、国庆黄金周"},
		{day: d(10, 24), zh: "程序员节", en: "Programmer's Day"},
		{day: d(10, 31), zh: "万圣节", en: "Halloween"},
		{day: nthWeekday(year, time.November, time.Thursday, 4, loc), zh: "感恩节", en: "Thanksgiving"},
		{day: d(11, 11), zh: "双十一", en: "Singles' Day", aka: "光棍节"},
		{day: d(12, 12), zh: "双十二", en: "Double 12"},
		{day: d(12, 24), zh: "平安夜", en: "Christmas Eve"},
		{day: d(12, 25), zh: "圣诞节", en: "Christmas"},
	}
	// 黑色星期五 = 感恩节次日
	for i := range items {
		if items[i].zh == "感恩节" {
			bf := items[i].day.AddDate(0, 0, 1)
			items = append(items, holidayItem{day: bf, zh: "黑色星期五", en: "Black Friday"})
			break
		}
	}
	items = append(items, lunarHolidays(year, loc)...)
	items = append(items, solarTermHolidays(year, loc)...)
	applyOfficialOff(year, loc, items)
	return items
}

func nthWeekday(year int, month time.Month, wd time.Weekday, n int, loc *time.Location) time.Time {
	d := time.Date(year, month, 1, 0, 0, 0, 0, loc)
	delta := int(wd - d.Weekday())
	if delta < 0 {
		delta += 7
	}
	return d.AddDate(0, 0, delta+7*(n-1))
}

// lunarHolidays 农历节日的公历对照（2025–2029）。春节 day=正月初一。
func lunarHolidays(year int, loc *time.Location) []holidayItem {
	type row struct{ m, d int }
	// key → 公历月日
	table := map[int]map[string]row{
		2025: {
			"除夕": {1, 28}, "春节": {1, 29}, "元宵": {2, 12}, "端午": {5, 31},
			"七夕": {8, 29}, "中元": {9, 6}, "中秋": {10, 6}, "重阳": {10, 29},
		},
		2026: {
			"除夕": {2, 16}, "春节": {2, 17}, "元宵": {3, 3}, "端午": {6, 19},
			"七夕": {8, 19}, "中元": {8, 27}, "中秋": {9, 25}, "重阳": {10, 18},
		},
		2027: {
			"除夕": {2, 5}, "春节": {2, 6}, "元宵": {2, 20}, "端午": {6, 9},
			"七夕": {8, 8}, "中元": {8, 16}, "中秋": {9, 15}, "重阳": {10, 8},
		},
		2028: {
			"除夕": {1, 25}, "春节": {1, 26}, "元宵": {2, 9}, "端午": {5, 28},
			"七夕": {8, 26}, "中元": {9, 3}, "中秋": {10, 3}, "重阳": {10, 26},
		},
		2029: {
			"除夕": {2, 12}, "春节": {2, 13}, "元宵": {2, 27}, "端午": {6, 16},
			"七夕": {8, 16}, "中元": {8, 24}, "中秋": {9, 22}, "重阳": {10, 16},
		},
	}
	names := map[string][2]string{
		"除夕": {"除夕", "Lunar New Year's Eve"},
		"春节": {"春节", "Spring Festival"},
		"元宵": {"元宵节", "Lantern Festival"},
		"端午": {"端午节", "Dragon Boat Festival"},
		"七夕": {"七夕", "Qixi Festival"},
		"中元": {"中元节", "Ghost Festival"},
		"中秋": {"中秋节", "Mid-Autumn Festival"},
		"重阳": {"重阳节", "Double Ninth Festival"},
	}
	aka := map[string]string{
		"春节": "过年、农历新年、正月初一",
		"端午": "端阳",
		"中秋": "八月十五",
		"除夕": "年三十",
	}
	m, ok := table[year]
	if !ok {
		return nil
	}
	var out []holidayItem
	for k, r := range m {
		n := names[k]
		out = append(out, holidayItem{
			day: time.Date(year, time.Month(r.m), r.d, 0, 0, 0, 0, loc),
			zh:  n[0], en: n[1], aka: aka[k],
		})
	}
	return out
}

// solarTermHolidays 常用节气（用户会当日期说）。
func solarTermHolidays(year int, loc *time.Location) []holidayItem {
	type row struct {
		m, d   int
		zh, en string
	}
	table := map[int][]row{
		2025: {{2, 3, "立春", "Start of Spring"}, {4, 4, "清明", "Qingming"}, {6, 21, "夏至", "Summer Solstice"}, {12, 21, "冬至", "Winter Solstice"}},
		2026: {{2, 4, "立春", "Start of Spring"}, {4, 5, "清明", "Qingming"}, {6, 21, "夏至", "Summer Solstice"}, {12, 22, "冬至", "Winter Solstice"}},
		2027: {{2, 4, "立春", "Start of Spring"}, {4, 5, "清明", "Qingming"}, {6, 21, "夏至", "Summer Solstice"}, {12, 22, "冬至", "Winter Solstice"}},
		2028: {{2, 4, "立春", "Start of Spring"}, {4, 4, "清明", "Qingming"}, {6, 21, "夏至", "Summer Solstice"}, {12, 21, "冬至", "Winter Solstice"}},
		2029: {{2, 3, "立春", "Start of Spring"}, {4, 4, "清明", "Qingming"}, {6, 21, "夏至", "Summer Solstice"}, {12, 22, "冬至", "Winter Solstice"}},
	}
	var out []holidayItem
	for _, r := range table[year] {
		aka := ""
		if r.zh == "清明" {
			aka = "清明节"
		}
		out = append(out, holidayItem{
			day: time.Date(year, time.Month(r.m), r.d, 0, 0, 0, 0, loc),
			zh:  r.zh, en: r.en, aka: aka,
		})
	}
	return out
}

type offSpan struct {
	offStart [2]int // month, day（可能早于节日当天，如春节）
	offEnd   [2]int
	work     [][2]int
}

// applyOfficialOff 套上已公布的国务院放假调休（2026）。
func applyOfficialOff(year int, loc *time.Location, items []holidayItem) {
	spans, ok := officialOff[year]
	if !ok {
		return
	}
	md := func(p [2]int) time.Time {
		return time.Date(year, time.Month(p[0]), p[1], 0, 0, 0, 0, loc)
	}
	for i := range items {
		sp, hit := spans[items[i].zh]
		if !hit {
			continue
		}
		items[i].offStart = md(sp.offStart)
		items[i].offEnd = md(sp.offEnd)
		for _, w := range sp.work {
			items[i].work = append(items[i].work, md(w))
		}
	}
}

// officialOff 国务院已公布年份。2026：国办发〔2025〕通知。
var officialOff = map[int]map[string]offSpan{
	2026: {
		"元旦":  {offStart: [2]int{1, 1}, offEnd: [2]int{1, 3}, work: [][2]int{{1, 4}}},
		"春节":  {offStart: [2]int{2, 15}, offEnd: [2]int{2, 23}, work: [][2]int{{2, 14}, {2, 28}}},
		"清明":  {offStart: [2]int{4, 4}, offEnd: [2]int{4, 6}},
		"清明节": {offStart: [2]int{4, 4}, offEnd: [2]int{4, 6}},
		"劳动节": {offStart: [2]int{5, 1}, offEnd: [2]int{5, 5}, work: [][2]int{{5, 9}}},
		"端午节": {offStart: [2]int{6, 19}, offEnd: [2]int{6, 21}},
		"中秋节": {offStart: [2]int{9, 25}, offEnd: [2]int{9, 27}},
		"国庆节": {offStart: [2]int{10, 1}, offEnd: [2]int{10, 7}, work: [][2]int{{9, 20}, {10, 10}}},
	},
}