package main

import (
	"encoding/json"
	"os"
	"sort"
	"strings"
	"sync"
	"time"
)

// history.go - 每日电费记录存储（JSON 文件）与耗电统计

type record struct {
	Date      string  `json:"date"`   // YYYY-MM-DD
	Surplus   float64 `json:"surplus"`
	Amount    float64 `json:"amount"`
	Source    string  `json:"source"` // auto / manual
	CreatedAt int64   `json:"created_at"`
}

type dailyStat struct {
	Date     string   `json:"date"`
	Surplus  float64  `json:"surplus"`
	Amount   float64  `json:"amount"`
	Usage    *float64 `json:"usage"`     // nil 表示无前一天基线
	Recharge *float64 `json:"recharge"`  // 当天充值电量(度), nil=无充值
	Money    *float64 `json:"money"`     // 当天充值金额(元), nil=无充值
}

// monthSummary 月度汇总
type monthSummary struct {
	Month        string   `json:"month"`          // YYYY-MM
	RecordCount  int      `json:"record_count"`   // 记录天数
	StartSurplus *float64 `json:"start_surplus"`  // 月初首次电量
	EndSurplus   *float64 `json:"end_surplus"`    // 月末末次电量
	TotalUsage   *float64 `json:"total_usage"`    // 月总耗电
	AvgUsage     *float64 `json:"avg_usage"`      // 日均耗电
	RechargeDays int      `json:"recharge_days"`  // 充值天数
	RechargeKwh  *float64 `json:"recharge_kwh"`   // 月充值电量(度)
	RechargeMoney *float64 `json:"recharge_money"` // 月充值金额(元)
	MaxUsage     *float64 `json:"max_usage"`      // 单日最大耗电
}

var (
	historyPath   = envOr("HISTORY_FILE", "data/electric_history.json")
	historyLock   sync.Mutex
	historyLoaded bool
	historyCache  []record
)

// loadHistory 读取历史记录
func loadHistory() []record {
	historyLock.Lock()
	defer historyLock.Unlock()
	if historyLoaded {
		return historyCache
	}
	b, err := os.ReadFile(historyPath)
	if err != nil {
		historyLoaded = true
		return nil
	}
	_ = json.Unmarshal(b, &historyCache)
	historyLoaded = true
	return historyCache
}

// saveHistory 持久化历史记录
func saveHistory(records []record) error {
	historyLock.Lock()
	defer historyLock.Unlock()
	if err := os.MkdirAll(dirName(historyPath), 0o755); err != nil {
		return err
	}
	b, _ := json.MarshalIndent(records, "", "  ")
	if err := os.WriteFile(historyPath, b, 0o644); err != nil {
		return err
	}
	historyCache = records
	return nil
}

// hasRecord 判断指定日期是否已有记录
func hasRecord(dateStr string) bool {
	for _, r := range loadHistory() {
		if r.Date == dateStr {
			return true
		}
	}
	return false
}

// addRecord 写入（或覆盖）一条记录
func addRecord(dateStr string, surplus, amount float64, source string) error {
	records := loadHistory()
	updated := false
	for i, r := range records {
		if r.Date == dateStr {
			records[i] = record{Date: dateStr, Surplus: surplus, Amount: amount, Source: source, CreatedAt: time.Now().Unix()}
			updated = true
			break
		}
	}
	if !updated {
		records = append(records, record{Date: dateStr, Surplus: surplus, Amount: amount, Source: source, CreatedAt: time.Now().Unix()})
	}
	return saveHistory(records)
}

// getRecords 返回降序（新→旧）记录列表
func getRecords() []record {
	records := loadHistory()
	sort.Slice(records, func(i, j int) bool {
		return records[i].Date > records[j].Date
	})
	return records
}

// buildDailyStats 按日期升序生成每日统计（含日耗电 = 前一天剩余 - 当天剩余 + 当天充值电量）
// 注意: 耗电计算跨月时使用上月末记录作为基线（若存在）
// rechargeMap: date -> 当天充值电量(度)；精确修正充值当天的耗电
func buildDailyStats(records []record, month string, rechargeMap map[string]float64) []dailyStat {
	all := loadHistory()
	// 若指定月份，额外包含上一月最后一条记录作为基线（不计入本月输出）
	var prevMonthLast *record
	if month != "" {
		prevPrefix := prevMonth(month) + "-"
		var last *record
		for i := range all {
			if strings.HasPrefix(all[i].Date, prevPrefix) {
				if last == nil || all[i].Date > last.Date {
					last = &all[i]
				}
			}
		}
		prevMonthLast = last
	}

	// 筛选目标记录
	var target []record
	if month != "" {
		target = filterByMonth(records, month)
	} else {
		target = records
	}
	sort.Slice(target, func(i, j int) bool {
		return target[i].Date < target[j].Date
	})

	var daily []dailyStat
	var prevSurplus *float64
	if prevMonthLast != nil {
		prevSurplus = &prevMonthLast.Surplus
	}
	for _, r := range target {
		var usage *float64
		if prevSurplus != nil {
			// 精确耗电 = 剩余变化 + 当天充值电量
			u := round2(*prevSurplus - r.Surplus + rechargeMap[r.Date])
			if u < 0 {
				u = 0 // 极端异常(数据缺口)归零
			}
			usage = &u
		}
		var recharge, money *float64
		if kwh, ok := rechargeMap[r.Date]; ok && kwh > 0 {
			recharge = &kwh
			m := round2(kwh * unitPrice())
			money = &m
		}
		daily = append(daily, dailyStat{
			Date: r.Date, Surplus: r.Surplus, Amount: r.Amount,
			Usage: usage, Recharge: recharge, Money: money,
		})
		s := r.Surplus
		prevSurplus = &s
	}
	return daily
}

// prevMonth 返回上个月的 YYYY-MM
func prevMonth(month string) string {
	t, err := time.Parse("2006-01", month)
	if err != nil {
		return ""
	}
	return t.AddDate(0, -1, 0).Format("2006-01")
}

// filterByMonth 按月份(YYYY-MM)筛选记录
func filterByMonth(records []record, month string) []record {
	if month == "" {
		return records
	}
	prefix := month + "-"
	var out []record
	for _, r := range records {
		if strings.HasPrefix(r.Date, prefix) {
			out = append(out, r)
		}
	}
	return out
}

// buildMonthSummary 生成某月的月度汇总
func buildMonthSummary(daily []dailyStat, month string) *monthSummary {
	if len(daily) == 0 {
		return &monthSummary{Month: month, RecordCount: 0}
	}
	// daily 已是升序
	m := month
	if m == "" {
		m = daily[0].Date[:7]
	}
	start := daily[0].Surplus
	end := daily[len(daily)-1].Surplus

	var total float64
	var max float64
	var totalRechargeKwh float64
	var totalRechargeMoney float64
	rechargeDays := 0
	countWithUsage := 0
	for _, d := range daily {
		if d.Usage != nil {
			total += *d.Usage
			if *d.Usage > max {
				max = *d.Usage
			}
			countWithUsage++
		}
		if d.Recharge != nil {
			totalRechargeKwh += *d.Recharge
			rechargeDays++
		}
		if d.Money != nil {
			totalRechargeMoney += *d.Money
		}
	}

	var totalP, avgP, maxP, startP, endP, rkwhP, rmoneyP *float64
	startP, endP = &start, &end
	totalP = &total
	if countWithUsage > 0 {
		avg := round2(total / float64(countWithUsage))
		avgP = &avg
	}
	maxP = &max
	if totalRechargeKwh > 0 {
		rkwhP = &totalRechargeKwh
	}
	if totalRechargeMoney > 0 {
		rmoneyP = &totalRechargeMoney
	}

	return &monthSummary{
		Month:         m,
		RecordCount:   len(daily),
		StartSurplus:  startP,
		EndSurplus:    endP,
		TotalUsage:    totalP,
		AvgUsage:      avgP,
		RechargeDays:  rechargeDays,
		RechargeKwh:   rkwhP,
		RechargeMoney: rmoneyP,
		MaxUsage:      maxP,
	}
}