package business

import (
	"context"
	"crypto/sha256"
	"fmt"
	"kra/pkg/task"
	"math"
	"math/big"
	"strconv"
	"time"

	"github.com/go-kratos/kratos/v3/errors"
)

var ErrEffectivenessConflict = errors.Conflict("SW_EFFECTIVENESS_CONFLICT", "有效端规则或数据已更新，请重试")
var ErrEffectivenessUnavailable = errors.BadRequest("SW_EFFECTIVENESS_UNAVAILABLE", "有效端计算所需渠道或充值数据尚未接入")

func EffectivenessRuleKey(rule OtherSettings) string {
	return fmt.Sprintf("%x", sha256.Sum256([]byte(strconv.FormatInt(rule.Amount, 10)+":"+strconv.FormatInt(rule.Days, 10))))
}

type EffectivenessUsecase struct {
	repo     EffectivenessRepo
	settings OtherSettingsRepo
	gate     chan struct{}
	now      func() time.Time
}

func NewEffectivenessUsecase(repo EffectivenessRepo, settings OtherSettingsRepo) *EffectivenessUsecase {
	gate := make(chan struct{}, 1)
	gate <- struct{}{}
	return &EffectivenessUsecase{repo: repo, settings: settings, gate: gate, now: time.Now}
}
func (uc *EffectivenessUsecase) Rule(ctx context.Context) (OtherSettings, error) {
	v, err := uc.settings.Find(ctx)
	if err != nil {
		return OtherSettings{}, err
	}
	if v == nil {
		return DefaultOtherSettings(), nil
	}
	return *v, nil
}
func (uc *EffectivenessUsecase) Ensure(ctx context.Context) error {
	rule, err := uc.Rule(ctx)
	if err != nil {
		return err
	}
	state, err := uc.repo.State(ctx)
	if err != nil {
		return err
	}
	if state.RuleKey == EffectivenessRuleKey(rule) && !state.BuiltAt.IsZero() {
		return nil
	}
	_, err = uc.rebuild(ctx, rule, false, false, true)
	return err
}
func (uc *EffectivenessUsecase) Refresh(ctx context.Context, full bool) error {
	rule, err := uc.Rule(ctx)
	if err != nil {
		return err
	}
	_, err = uc.rebuild(ctx, rule, false, full, false)
	return err
}
func (uc *EffectivenessUsecase) Reconfigure(ctx context.Context, rule OtherSettings) (*OtherSettings, error) {
	if err := requireSettingsAdmin(ctx); err != nil {
		return nil, err
	}
	if err := ValidateOtherSettings(rule); err != nil {
		return nil, err
	}
	return uc.rebuild(ctx, rule, true, true, false)
}
func (uc *EffectivenessUsecase) rebuild(ctx context.Context, rule OtherSettings, save, full, ensureOnly bool) (*OtherSettings, error) {
	select {
	case <-ctx.Done():
		return nil, ctx.Err()
	case <-uc.gate:
	}
	defer func() { uc.gate <- struct{}{} }()
	state, err := uc.repo.State(ctx)
	if err != nil {
		return nil, err
	}
	key := EffectivenessRuleKey(rule)
	if ensureOnly && state.RuleKey == key && !state.BuiltAt.IsZero() {
		return &rule, nil
	}
	full = full || state.RuleKey != key
	duration := int64(math.MaxInt64)
	if rule.Days <= math.MaxInt64/86400 {
		duration = rule.Days * 86400
	}
	now := uc.now().Unix()
	candidates, err := uc.repo.Candidates(ctx, key, duration, now, full)
	if err != nil {
		return nil, err
	}
	task.Logf(ctx, "有效端计算：全量=%t；注册后 %d 天内满 %d 元；待计算渠道=%d", full, rule.Days, rule.Amount, len(candidates))
	type accumulator struct {
		candidate *EffectivenessCandidate
		sum       *big.Rat
		at        *int64
		complete  bool
	}
	values := map[ChannelKey]*accumulator{}
	threshold := big.NewRat(rule.Amount, 1)
	for _, c := range candidates {
		a := &accumulator{candidate: c, sum: new(big.Rat), at: c.PreviousAt, complete: true}
		if c.CreatedAt != nil && *c.CreatedAt > now {
			a.complete = false
		}
		if c.CreatedAt != nil && *c.CreatedAt > 0 && *c.CreatedAt <= now {
			a.complete = duration <= now-*c.CreatedAt
			if rule.Amount == 0 {
				at := *c.CreatedAt
				a.at = &at
			}
		}
		values[c.ChannelKey] = a
	}
	charges := 0
	err = uc.repo.Charges(ctx, candidates, duration, now, full, func(charge EffectivenessCharge) error {
		charges++
		a := values[charge.ChannelKey]
		if a == nil {
			return nil
		}
		amount, err := portraitNumber(charge.Amount)
		if err != nil {
			return err
		}
		a.sum.Add(a.sum, amount)
		if a.sum.Cmp(threshold) >= 0 && (a.at == nil || charge.PaidAt < *a.at) {
			at := charge.PaidAt
			a.at = &at
		}
		return nil
	})
	if err != nil {
		return nil, err
	}
	results := make([]EffectivenessResult, 0, len(values))
	for _, c := range candidates {
		a := values[c.ChannelKey]
		results = append(results, EffectivenessResult{ChannelKey: c.ChannelKey, QualifiedAt: a.at, WindowPay: portraitDecimal(a.sum, 2), Complete: a.complete})
	}
	updated, err := uc.repo.Publish(ctx, state, rule, key, results, save)
	if err == nil {
		qualified := 0
		for _, result := range results {
			if result.QualifiedAt != nil {
				qualified++
			}
		}
		task.Logf(ctx, "有效端结果已提交；扫描流水=%d；更新渠道=%d；本批达标渠道=%d", charges, len(results), qualified)
	}
	return updated, err
}