package service

import (
	"fmt"
	"regexp"
	"strconv"
	"strings"
	"time"
)

var (
	reTimeHHMM  = regexp.MustCompile(`^(\d{1,2}):(\d{2})$`)
	reTimeHHJMM = regexp.MustCompile(`^(\d{1,2})時(\d{1,2})分$`)
	reTimeHHJ   = regexp.MustCompile(`^(\d{1,2})時$`)
	reDateMD    = regexp.MustCompile(`^(\d{1,2})/(\d{1,2})$`)
	reDateMJDJ  = regexp.MustCompile(`^(\d{1,2})月(\d{1,2})日$`)
)

var weekdayNames = map[string]time.Weekday{
	"月": time.Monday,
	"火": time.Tuesday,
	"水": time.Wednesday,
	"木": time.Thursday,
	"金": time.Friday,
	"土": time.Saturday,
	"日": time.Sunday,
}

// ParseAddCommand parses the arguments after /add.
// Format: <title> <date> [time] [#subject] [!priority]
// Returns title, dueDate, subject, priority (Go string: "high"/"medium"/"low"), error.
// On format error, err.Error() == "usage" means show usage hint.
func ParseAddCommand(text string) (title string, dueDate time.Time, subject string, priority string, err error) {
	priority = "medium"
	tokens := strings.Fields(text)
	if len(tokens) == 0 {
		err = fmt.Errorf("usage")
		return
	}

	// Extract #subject and !priority modifiers
	var core []string
	for _, tok := range tokens {
		switch {
		case strings.HasPrefix(tok, "#") && len(tok) > 1:
			subject = tok[1:]
		case strings.HasPrefix(tok, "!") && len(tok) > 1:
			priority = parsePriorityJP(tok[1:])
		default:
			core = append(core, tok)
		}
	}

	if len(core) < 2 {
		err = fmt.Errorf("usage")
		return
	}

	// Extract optional time token from end
	hour, minute := 23, 59
	if h, m, ok := parseTimeToken(core[len(core)-1]); ok {
		hour, minute = h, m
		core = core[:len(core)-1]
	}

	if len(core) < 2 {
		err = fmt.Errorf("usage")
		return
	}

	// Extract date token from end
	dateTok := core[len(core)-1]
	parsedDate, ok := parseDateToken(dateTok, hour, minute)
	if !ok {
		err = fmt.Errorf("日付が読み取れませんでした: %q\n使える形式: 今日/明日/明後日/月〜日/MM/DD/M月D日", dateTok)
		return
	}
	dueDate = parsedDate
	core = core[:len(core)-1]

	if len(core) == 0 {
		err = fmt.Errorf("usage")
		return
	}
	title = strings.Join(core, " ")
	return
}

func parsePriorityJP(s string) string {
	switch s {
	case "高":
		return "high"
	case "低":
		return "low"
	default:
		return "medium"
	}
}

func parseTimeToken(s string) (hour, minute int, ok bool) {
	if m := reTimeHHMM.FindStringSubmatch(s); m != nil {
		h, _ := strconv.Atoi(m[1])
		min, _ := strconv.Atoi(m[2])
		if h <= 23 && min <= 59 {
			return h, min, true
		}
	}
	if m := reTimeHHJMM.FindStringSubmatch(s); m != nil {
		h, _ := strconv.Atoi(m[1])
		min, _ := strconv.Atoi(m[2])
		if h <= 23 && min <= 59 {
			return h, min, true
		}
	}
	if m := reTimeHHJ.FindStringSubmatch(s); m != nil {
		h, _ := strconv.Atoi(m[1])
		if h <= 23 {
			return h, 0, true
		}
	}
	return 0, 0, false
}

func parseDateToken(s string, hour, minute int) (time.Time, bool) {
	now := time.Now()
	loc := now.Location()

	switch s {
	case "今日":
		return time.Date(now.Year(), now.Month(), now.Day(), hour, minute, 0, 0, loc), true
	case "明日":
		d := now.AddDate(0, 0, 1)
		return time.Date(d.Year(), d.Month(), d.Day(), hour, minute, 0, 0, loc), true
	case "明後日":
		d := now.AddDate(0, 0, 2)
		return time.Date(d.Year(), d.Month(), d.Day(), hour, minute, 0, 0, loc), true
	}

	if wd, ok := weekdayNames[s]; ok {
		d := nextWeekdayFrom(now, wd)
		return time.Date(d.Year(), d.Month(), d.Day(), hour, minute, 0, 0, loc), true
	}

	var month, day int
	if m := reDateMD.FindStringSubmatch(s); m != nil {
		month, _ = strconv.Atoi(m[1])
		day, _ = strconv.Atoi(m[2])
	} else if m := reDateMJDJ.FindStringSubmatch(s); m != nil {
		month, _ = strconv.Atoi(m[1])
		day, _ = strconv.Atoi(m[2])
	} else {
		return time.Time{}, false
	}

	if month < 1 || month > 12 || day < 1 || day > 31 {
		return time.Time{}, false
	}
	t := time.Date(now.Year(), time.Month(month), day, hour, minute, 0, 0, loc)
	if t.Before(now) {
		t = t.AddDate(1, 0, 0)
	}
	return t, true
}

// nextWeekdayFrom returns the date of the next occurrence of wd from 'from'.
func nextWeekdayFrom(from time.Time, wd time.Weekday) time.Time {
	days := (int(wd) - int(from.Weekday()) + 7) % 7
	return from.AddDate(0, 0, days)
}