package operationsreport

import (
	"context"
	"time"

	domainreport "github.com/break/junhong_cmp_fiber/internal/domain/operationsreport"
)

// trendPeriod 是趋势的一个期：期标识、期末快照日与（按月粒度时）期内全部快照日。
type trendPeriod struct {
	Key               string
	RepresentativeDay time.Time
	Days              []time.Time
}

// activationPeriods 返回激活情况趋势的期序列（升序）。
//
// 按日粒度的期是该区间内的每个快照日；按月粒度的期是每个自然月，期末取该月最后一个快照日。
// 无快照的期不出现在结果中。
func (q *Query) activationPeriods(ctx context.Context, granularity string, start, end *time.Time) ([]trendPeriod, error) {
	if granularity == domainreport.GranularityDay {
		days, err := q.matchedDays(ctx, lowerDay(start), upperDay(end))
		if err != nil {
			return nil, err
		}
		periods := make([]trendPeriod, 0, len(days))
		for _, day := range days {
			periods = append(periods, trendPeriod{
				Key:               domainreport.FormatPeriod(granularity, day),
				RepresentativeDay: day,
				Days:              []time.Time{day},
			})
		}
		return periods, nil
	}
	lower, upper := monthSpan(start, end)
	days, err := q.matchedDays(ctx, lower, upper)
	if err != nil {
		return nil, err
	}
	return groupMonthPeriods(granularity, days, lowerDay(start), upperDay(end)), nil
}

// previousPeriodRepresentatives 返回每个期的前一期期末快照日；前一期无快照的期不出现在结果中。
//
// 前一期指日历上的上一自然日或上一自然月，即使它早于请求区间起点也必须读取：
// 新增类指标按「期末 − 前一期期末」计算，任一侧无快照时为空。
func (q *Query) previousPeriodRepresentatives(ctx context.Context, granularity string,
	periods []trendPeriod) (map[string]time.Time, error) {
	result := make(map[string]time.Time, len(periods))
	if len(periods) == 0 {
		return result, nil
	}
	earliest := domainreport.PeriodOf(granularity, periods[0].RepresentativeDay)
	for _, period := range periods {
		start := domainreport.PeriodOf(granularity, period.RepresentativeDay)
		if start.Before(earliest) {
			earliest = start
		}
	}
	searchFrom := domainreport.PreviousPeriodStart(granularity, earliest)
	days, err := q.matchedDays(ctx, &searchFrom, nil)
	if err != nil {
		return nil, err
	}
	for _, period := range periods {
		periodStart := domainreport.PeriodOf(granularity, period.RepresentativeDay)
		previousStart := domainreport.PreviousPeriodStart(granularity, periodStart)
		previousEnd := previousStart
		if granularity == domainreport.GranularityMonth {
			previousEnd = endOfMonth(previousStart)
		}
		if representative, ok := lastDayWithin(days, previousStart, previousEnd); ok {
			result[period.Key] = representative
		}
	}
	return result, nil
}

// monthSpan 把区间换算为覆盖整月的日期范围，供按月趋势读取所需的快照日集合。
func monthSpan(start, end *time.Time) (*time.Time, *time.Time) {
	var lower, upper *time.Time
	if start != nil {
		day := domainreport.LowerBoundDay(*start)
		first := domainreport.PeriodOf(domainreport.GranularityMonth, day)
		lower = &first
	}
	if end != nil {
		day := domainreport.UpperBoundDay(*end)
		last := endOfMonth(domainreport.PeriodOf(domainreport.GranularityMonth, day))
		upper = &last
	}
	return lower, upper
}

// groupMonthPeriods 把快照日按月聚合为趋势期。
// 期末快照日落在请求区间之外的月份不作为期出现（其快照日仅用于推断前一期）。
func groupMonthPeriods(granularity string, days []time.Time, lower, upper *time.Time) []trendPeriod {
	order := make([]string, 0, len(days))
	buckets := make(map[string][]time.Time, len(days))
	for _, day := range days {
		key := domainreport.FormatPeriod(granularity, day)
		if _, exists := buckets[key]; !exists {
			order = append(order, key)
		}
		buckets[key] = append(buckets[key], day)
	}
	periods := make([]trendPeriod, 0, len(order))
	for _, key := range order {
		bucket := buckets[key]
		representative := bucket[len(bucket)-1]
		if lower != nil && representative.Before(*lower) {
			continue
		}
		if upper != nil && representative.After(*upper) {
			continue
		}
		periods = append(periods, trendPeriod{Key: key, RepresentativeDay: representative, Days: bucket})
	}
	return periods
}

// endOfMonth 返回该月最后一天（上海自然日）。
func endOfMonth(monthStart time.Time) time.Time {
	return time.Date(monthStart.Year(), monthStart.Month()+1, 0, 0, 0, 0, 0, domainreport.ShanghaiLocation())
}

// lastDayWithin 返回闭区间内最后一个存在的快照日。
func lastDayWithin(days []time.Time, from, to time.Time) (time.Time, bool) {
	var found time.Time
	ok := false
	for _, day := range days {
		if day.Before(from) || day.After(to) {
			continue
		}
		found = day
		ok = true
	}
	return found, ok
}