package timeagent

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

const ActivationPrompt = "提供当前日期、时间和常用时间范围。当用户问题包含今天、明天、昨天、本周、本月、本年、最近、日程安排等相对时间表达时，应先调用此工具；如果后续还需要查数据库，可继续调用 sql。"

type Range struct {
	Start time.Time
	End   time.Time
}

type Context struct {
	Now       time.Time
	Today     Range
	Tomorrow  Range
	Yesterday Range
	ThisWeek  Range
	ThisMonth Range
	ThisYear  Range
}

func Resolve(now time.Time) Context {
	loc := now.Location()
	today := Range{Start: startOfDay(now), End: startOfDay(now).AddDate(0, 0, 1)}
	tomorrowStart := today.End
	tomorrow := Range{Start: tomorrowStart, End: tomorrowStart.AddDate(0, 0, 1)}
	yesterdayEnd := today.Start
	yesterday := Range{Start: yesterdayEnd.AddDate(0, 0, -1), End: yesterdayEnd}
	weekdayOffset := (int(now.Weekday()) + 6) % 7
	weekStart := today.Start.AddDate(0, 0, -weekdayOffset)
	monthStart := time.Date(now.Year(), now.Month(), 1, 0, 0, 0, 0, loc)
	yearStart := time.Date(now.Year(), 1, 1, 0, 0, 0, 0, loc)
	return Context{
		Now:       now,
		Today:     today,
		Tomorrow:  tomorrow,
		Yesterday: yesterday,
		ThisWeek:  Range{Start: weekStart, End: weekStart.AddDate(0, 0, 7)},
		ThisMonth: Range{Start: monthStart, End: monthStart.AddDate(0, 1, 0)},
		ThisYear:  Range{Start: yearStart, End: yearStart.AddDate(1, 0, 0)},
	}
}

func BuildContext(ctx Context, routeReason string) string {
	var b strings.Builder
	b.WriteString("时间工具结果。后续工具必须优先使用这里的绝对日期解释用户问题中的相对时间，不要自行猜测当前日期。\n")
	fmt.Fprintf(&b, "当前本地日期时间：%s\n", ctx.Now.Format("2006-01-02 15:04:05 MST"))
	fmt.Fprintf(&b, "今天：%s\n", FormatSQLRange(ctx.Today))
	fmt.Fprintf(&b, "明天：%s\n", FormatSQLRange(ctx.Tomorrow))
	fmt.Fprintf(&b, "昨天：%s\n", FormatSQLRange(ctx.Yesterday))
	fmt.Fprintf(&b, "本周：%s\n", FormatSQLRange(ctx.ThisWeek))
	fmt.Fprintf(&b, "本月：%s\n", FormatSQLRange(ctx.ThisMonth))
	fmt.Fprintf(&b, "本年：%s\n", FormatSQLRange(ctx.ThisYear))
	b.WriteString("SQL 日期过滤建议：对日程/事件类表使用半开区间，例如 event_time >= start AND event_time < end；如果实际字段名不同，必须使用 schema 中存在的时间字段。\n")
	if strings.TrimSpace(routeReason) != "" {
		b.WriteString("激活原因：" + strings.TrimSpace(routeReason) + "\n")
	}
	return b.String()
}

func FormatDate(t time.Time) string {
	return t.Format("2006-01-02")
}

func FormatSQLRange(r Range) string {
	return fmt.Sprintf("start=%s, end_exclusive=%s", r.Start.Format("2006-01-02 15:04:05"), r.End.Format("2006-01-02 15:04:05"))
}

func startOfDay(t time.Time) time.Time {
	y, m, d := t.Date()
	return time.Date(y, m, d, 0, 0, 0, 0, t.Location())
}