package domain

import (
	"fmt"
	"math"
	"sort"
)

// rankEpsilon 用于判定「成绩相同」。计时/测距保留两位小数，1e-9 足够区分。
const rankEpsilon = 1e-9

// ScoreOptions 控制引擎的可选行为；零值即本次运动会的口径。
type ScoreOptions struct {
	// UnionAttribution 决定联队成绩的归属；空值等同 UnionWhole（整体记给主单位）。
	// 未实现：生产链路没有赋值入口，联队份额也无处加载（见 UnionAttribution 注释）。
	UnionAttribution UnionAttribution
	// IncludeDrafts 为 true 时草稿成绩也参与计分；默认只算已发布（草稿不上屏也不计分）。
	IncludeDrafts bool
}

// EventScoreInput 是一次小项（某组别）计分的全部输入，引擎只读不改。
type EventScoreInput struct {
	Event        Event
	Category     EventCategory
	Channels     []ScoreChannel
	Profiles     map[int64]ScoringProfile
	Entries      []Entry
	Results      []Result
	RecordBonus  *RecordBonusConfig
	RecordBreaks []RecordBreak
	Options      ScoreOptions
}

// EventScore 是一次小项计分的结果。
type EventScore struct {
	Ledger []LedgerEntry
	Ranked []RankedResult
}

// RankedResult 记录「某条报名项在某通道下拿到的名次与原始积分」。
// Points 尚未按联队份额拆分、也未乘个人→单位系数，因此可直接用于奖牌判定与分项成绩表。
type RankedResult struct {
	EntryID     int64
	ResultID    int64
	EventID     int64
	CategoryID  int64
	ChannelID   int64
	Scope       Scope
	Basis       Basis
	AthleteID   int64
	AthleteName string
	TeamID      int64
	Shares      []TeamShare
	Rank        int
	Points      float64
	ResultValue *float64
	Status      ResultStatus
}

// ScoreEvent 按项目的计分通道逐条计算名次与积分，输出流水与名次明细。
// 计分与排名解耦：项目 scored=false 或没有通道时照样产出名次（Points=0），只是不写流水。
// 没有通道时按小项自身的录入方式（result_mode）推导排名口径，见 rankOnlyChannel。
func ScoreEvent(in EventScoreInput) (EventScore, error) {
	var out EventScore
	rankOnly := len(in.Channels) == 0
	// 只排名不计分：scored=false 或没有计分通道时都不产出任何流水（含破纪录加分）。
	scoreEnabled := in.Event.Scored && !rankOnly

	channels := sortedChannels(in.Channels)
	if rankOnly {
		channels = []ScoreChannel{rankOnlyChannel(in)}
	}

	for _, ch := range channels {
		// 不计分时不需要积分表：既不查模板，也不可能算出非零分。
		profile := ScoringProfile{}
		if scoreEnabled {
			p, ok := in.Profiles[ch.ProfileID]
			if !ok {
				return EventScore{}, fmt.Errorf("%w: 通道 %d 引用模板 %d", ErrProfileNotFound, ch.ID, ch.ProfileID)
			}
			profile = p
		}
		ranked, err := scoreChannel(in, ch, profile)
		if err != nil {
			return EventScore{}, err
		}
		if !scoreEnabled {
			for i := range ranked {
				ranked[i].Points = 0
			}
		}
		out.Ranked = append(out.Ranked, ranked...)
		if scoreEnabled {
			out.Ledger = append(out.Ledger, ledgerFromRanked(in, ch, ranked)...)
		}
	}

	if !scoreEnabled {
		return out, nil
	}
	bonus, err := recordBonusLedger(in)
	if err != nil {
		return EventScore{}, err
	}
	out.Ledger = append(out.Ledger, bonus...)
	return out, nil
}

// rankOnlyChannel 在没有计分通道时，按小项自身的录入方式推导排名口径：
// manual 直接录名次，其余按成绩自动排名；名次记给个人，团体/对抗项目记给单位。
// 「个人+团体」的双计靠两条通道表达，这条退化路径只排个人榜，故不入单位分支。
func rankOnlyChannel(in EventScoreInput) ScoreChannel {
	basis := BasisResult
	if in.Event.ResultMode == ResultModeManual {
		basis = BasisManual
	}
	scope := ScopeAthlete
	if in.Event.EventType == EventTypeTeam || in.Event.EventType == EventTypeMatch {
		scope = ScopeTeam
	}
	return ScoreChannel{EventID: in.Event.ID, Scope: scope, Basis: basis}
}

// sortedChannels 固定通道处理顺序，保证同一份输入每次产出同样的流水顺序。
func sortedChannels(channels []ScoreChannel) []ScoreChannel {
	out := append([]ScoreChannel(nil), channels...)
	sort.SliceStable(out, func(i, j int) bool {
		if out[i].SortOrder != out[j].SortOrder {
			return out[i].SortOrder < out[j].SortOrder
		}
		return out[i].ID < out[j].ID
	})
	return out
}

func scoreChannel(in EventScoreInput, ch ScoreChannel, profile ScoringProfile) ([]RankedResult, error) {
	switch ch.Basis {
	case BasisResult:
		return scoreByResult(in, ch, profile)
	case BasisManual:
		return scoreByManual(in, ch, profile)
	case BasisAggregate:
		return scoreByAggregate(in, ch, profile)
	default:
		return nil, fmt.Errorf("%w: %q", ErrUnknownBasis, ch.Basis)
	}
}

// candidate 是排名过程的中间态：一条可参与排名的报名项 + 它的比较值。
type candidate struct {
	entry   Entry
	result  Result
	subject int64   // 聚合通道的排名主体（单位或运动员）
	value   float64 // 排序用比较值
	rankIn  int     // manual 通道录入的名次
}

// entryMatches 判断报名项是否属于本次计分的小项与组别。
func entryMatches(in EventScoreInput, e Entry) bool {
	if in.Event.ID != 0 && e.EventID != 0 && e.EventID != in.Event.ID {
		return false
	}
	if in.Category.ID != 0 && e.CategoryID != in.Category.ID {
		return false
	}
	return true
}

// collectCandidates 过滤出本通道真正参与排名的报名项：
// 只取已发布、状态正常、且带有本通道所需数据的成绩。聚合通道不用本函数，见 scoreByAggregate。
func collectCandidates(in EventScoreInput, ch ScoreChannel) ([]candidate, error) {
	if ch.Basis == BasisResult && in.Event.Compare == CompareNone {
		return nil, ErrCompareRequired
	}

	byEntry := make(map[int64]Result, len(in.Results))
	for _, r := range in.Results {
		byEntry[r.EntryID] = r
	}

	out := make([]candidate, 0, len(in.Entries))
	for _, e := range in.Entries {
		if !entryMatches(in, e) {
			continue
		}
		if !e.Status.rankable() {
			continue
		}
		r, ok := byEntry[e.ID]
		if !ok {
			continue
		}
		if r.State == ResultStateDraft && !in.Options.IncludeDrafts {
			continue
		}
		if !r.Status.rankable() {
			continue
		}

		c := candidate{entry: e, result: r}
		switch ch.Basis {
		case BasisManual:
			if r.Rank <= 0 {
				continue
			}
			c.rankIn = r.Rank
		default: // result 按成绩值排序
			if r.ResultValue == nil {
				continue
			}
			c.value = *r.ResultValue
		}
		out = append(out, c)
	}
	return out, nil
}

func scoreByResult(in EventScoreInput, ch ScoreChannel, profile ScoringProfile) ([]RankedResult, error) {
	cands, err := collectCandidates(in, ch)
	if err != nil {
		return nil, err
	}
	sortCandidatesByValue(cands, in.Event.Compare)
	return rankGroups(in, ch, profile, groupByValue(cands)), nil
}

func scoreByManual(in EventScoreInput, ch ScoreChannel, profile ScoringProfile) ([]RankedResult, error) {
	cands, err := collectCandidates(in, ch)
	if err != nil {
		return nil, err
	}
	sort.SliceStable(cands, func(i, j int) bool {
		if cands[i].rankIn != cands[j].rankIn {
			return cands[i].rankIn < cands[j].rankIn
		}
		return cands[i].entry.ID < cands[j].entry.ID
	})
	return rankGroups(in, ch, profile, groupByManualRank(cands)), nil
}

// tieGroup 是一组并列的参赛者；startRank 是它们共同展示的名次。
type tieGroup struct {
	startRank int
	members   []candidate
}

// groupByValue 按成绩值分组：值相同即并列，名次按「占位顺推」计算（skip 口径）。
func groupByValue(cands []candidate) []tieGroup {
	var groups []tieGroup
	pos := 1
	for i := 0; i < len(cands); {
		j := i + 1
		for j < len(cands) && nearlyEqual(cands[j].value, cands[i].value) {
			j++
		}
		groups = append(groups, tieGroup{startRank: pos, members: cands[i:j]})
		pos += j - i
		i = j
	}
	return groups
}

// groupByManualRank 按录入名次分组：录入名次就是展示名次，不做顺推改写。
func groupByManualRank(cands []candidate) []tieGroup {
	var groups []tieGroup
	for i := 0; i < len(cands); {
		j := i + 1
		for j < len(cands) && cands[j].rankIn == cands[i].rankIn {
			j++
		}
		groups = append(groups, tieGroup{startRank: cands[i].rankIn, members: cands[i:j]})
		i = j
	}
	return groups
}

// rankGroups 给每组分配积分并产出名次明细。
func rankGroups(in EventScoreInput, ch ScoreChannel, profile ScoringProfile, groups []tieGroup) []RankedResult {
	lastRank := 0
	for _, g := range groups {
		if r := g.startRank + len(g.members) - 1; r > lastRank {
			lastRank = r
		}
	}

	var out []RankedResult
	for _, g := range groups {
		pts := groupPoints(profile, g.startRank, len(g.members), lastRank, in.Event, in.Category)
		for _, c := range g.members {
			out = append(out, rankedResult(in, ch, c, g.startRank, pts))
		}
	}
	return out
}

// groupPoints 计算一组并列者拿到的分。
// 三种口径都先确定这组「占用了哪些名次」：startRank .. startRank+size-1。
func groupPoints(profile ScoringProfile, startRank, size, lastRank int, ev Event, cat EventCategory) float64 {
	if startRank <= 0 || size <= 0 {
		return 0
	}
	// lastPlaceZero 是对「最后一名」的覆盖；并列在末位的整组都按最后一名处理，
	// 否则同组出现 0 与 1 两种分数，违背「并列同分」的语义。
	if profile.LastPlaceZero && startRank <= lastRank && lastRank <= startRank+size-1 {
		return 0
	}

	switch profile.tieMode() {
	case TieAverage:
		var sum float64
		for r := startRank; r < startRank+size; r++ {
			p, _ := basePoints(profile, r, ev, cat)
			sum += p
		}
		return sum / float64(size)
	case TieHigher:
		best := 0.0
		for r := startRank; r < startRank+size; r++ {
			if p, ok := basePoints(profile, r, ev, cat); ok && p > best {
				best = p
			}
		}
		return best
	default: // TieSkip
		p, _ := basePoints(profile, startRank, ev, cat)
		return p
	}
}

// basePoints 查表得分并乘项目权重、组别权重；超出录取名次或表中无名次一律 0。
func basePoints(profile ScoringProfile, rank int, ev Event, cat EventCategory) (float64, bool) {
	if rank <= 0 {
		return 0, false
	}
	if profile.AwardRanks > 0 && rank > profile.AwardRanks {
		return 0, false
	}
	p, ok := profile.pointsAt(rank)
	if !ok {
		return 0, false
	}
	return p * ev.multiplier() * cat.multiplier(), true
}

func rankedResult(in EventScoreInput, ch ScoreChannel, c candidate, rank int, points float64) RankedResult {
	rr := RankedResult{
		EntryID:     c.entry.ID,
		ResultID:    c.result.ID,
		EventID:     in.Event.ID,
		CategoryID:  in.Category.ID,
		ChannelID:   ch.ID,
		Scope:       ch.Scope,
		Basis:       ch.Basis,
		AthleteID:   c.entry.AthleteID,
		AthleteName: c.entry.AthleteName,
		TeamID:      c.entry.primaryTeamID(),
		Shares:      c.entry.resolvedShares(in.Options.UnionAttribution),
		Rank:        rank,
		Points:      points,
		Status:      c.result.Status,
	}
	if c.result.ResultValue != nil {
		v := *c.result.ResultValue
		rr.ResultValue = &v
	}
	return rr
}

// scoreByAggregate 实现 basis=aggregate：把同一主体（单位/运动员）在本组别的成绩取平均，
// 得到团体成绩后按项目的 compare 方向排名（并列沿用模板的 tieMode，默认顺延）。
// 平均值分母由项目的 avg_mode 决定：
//   - valid：分子 = 有效成绩之和，分母 = 有有效成绩的人数；一个人都没成绩就不参与排名、不得分；
//   - all：分子 = 有效成绩之和（没成绩的按 0），分母 = 该主体的报名人数。
//     没有报名项的主体不会成桶，自然不参与。
//
// 弃权 / 失格（status 非 registered）的报名项既不算参与也不算进分母，与「不占名次」的既有口径一致。
func scoreByAggregate(in EventScoreInput, ch ScoreChannel, profile ScoringProfile) ([]RankedResult, error) {
	if in.Event.Compare == CompareNone {
		return nil, ErrCompareRequired
	}

	byEntry := make(map[int64]Result, len(in.Results))
	for _, r := range in.Results {
		byEntry[r.EntryID] = r
	}

	type bucket struct {
		subject int64
		entry   Entry
		sum     float64 // 有效成绩之和
		valid   int     // 有有效成绩的人数（valid 口径的分母）
		roster  int     // 报名人数（all 口径的分母）
	}
	order := make([]int64, 0)
	buckets := make(map[int64]*bucket)
	for _, e := range in.Entries {
		if !entryMatches(in, e) || !e.Status.rankable() {
			continue
		}
		subject := e.TeamID
		if ch.Scope == ScopeAthlete {
			subject = e.AthleteID
		}
		if subject == 0 {
			continue
		}
		b, ok := buckets[subject]
		if !ok {
			b = &bucket{subject: subject, entry: e}
			buckets[subject] = b
			order = append(order, subject)
		}
		b.roster++
		r, found := byEntry[e.ID]
		if v, ok := validResultValue(r, found, in.Options); ok {
			b.sum += v
			b.valid++
		}
	}
	agg := make([]candidate, 0, len(order))
	for _, id := range order {
		b := buckets[id]
		var value float64
		if in.Event.avgMode() == AvgModeAll {
			// 分母 = 报名人数：没成绩的人按 0 计入，也就是只累加有效成绩之和。
			value = b.sum / float64(b.roster)
		} else {
			if b.valid == 0 {
				// 一个人都没有效成绩的单位不参与团体排名，也不得分。
				continue
			}
			value = b.sum / float64(b.valid)
		}
		c := candidate{entry: b.entry, subject: b.subject, value: value}
		c.entry.ID = 0 // 聚合结果不对应单条报名项
		agg = append(agg, c)
	}
	sortCandidatesByValue(agg, in.Event.Compare)

	groups := groupByValue(agg)
	lastRank := 0
	for _, g := range groups {
		if r := g.startRank + len(g.members) - 1; r > lastRank {
			lastRank = r
		}
	}

	var out []RankedResult
	for _, g := range groups {
		pts := groupPoints(profile, g.startRank, len(g.members), lastRank, in.Event, in.Category)
		for _, c := range g.members {
			rr := RankedResult{
				EventID:    in.Event.ID,
				CategoryID: in.Category.ID,
				ChannelID:  ch.ID,
				Scope:      ch.Scope,
				Basis:      ch.Basis,
				TeamID:     c.entry.primaryTeamID(),
				Rank:       g.startRank,
				Points:     pts,
			}
			if ch.Scope == ScopeTeam {
				rr.TeamID = c.subject
				rr.Shares = []TeamShare{{TeamID: c.subject, Weight: 1}}
			} else {
				rr.AthleteID = c.subject
				rr.AthleteName = c.entry.AthleteName
				rr.Shares = c.entry.resolvedShares(in.Options.UnionAttribution)
			}
			v := c.value
			rr.ResultValue = &v
			out = append(out, rr)
		}
	}
	return out, nil
}

func sortCandidatesByValue(cands []candidate, compare CompareMode) {
	sort.SliceStable(cands, func(i, j int) bool {
		if nearlyEqual(cands[i].value, cands[j].value) {
			return cands[i].entry.ID < cands[j].entry.ID
		}
		if compare == CompareDesc {
			return cands[i].value > cands[j].value
		}
		return cands[i].value < cands[j].value
	})
}

func nearlyEqual(a, b float64) bool {
	return math.Abs(a-b) <= rankEpsilon
}

// validResultValue 判断一条成绩是否算「有效成绩」：成绩存在、已发布（或允许草稿）、
// 状态正常，且有可比较的数值。聚合通道按 avg_mode 决定没成绩的人算不算进分母。
func validResultValue(r Result, found bool, opts ScoreOptions) (float64, bool) {
	if !found {
		return 0, false
	}
	if r.State == ResultStateDraft && !opts.IncludeDrafts {
		return 0, false
	}
	if !r.Status.rankable() || r.ResultValue == nil {
		return 0, false
	}
	return *r.ResultValue, true
}

// ledgerFromRanked 把名次明细转成积分流水：按通道 scope 决定记给个人还是单位，
// 联队按份额拆分；0 分不产生流水，避免流水表被零分噪声撑大。
// 流水是否计入单位总分由通道的 countToTeam 决定（个人通道可以只记个人）。
func ledgerFromRanked(in EventScoreInput, ch ScoreChannel, ranked []RankedResult) []LedgerEntry {
	var out []LedgerEntry
	for _, rr := range ranked {
		if rr.Points == 0 {
			continue
		}
		athleteID := int64(0)
		if rr.Scope == ScopeAthlete {
			athleteID = rr.AthleteID
		}
		sourceID := rr.ResultID
		if sourceID == 0 {
			sourceID = rr.EntryID
		}
		if sourceID == 0 {
			sourceID = ch.ID
		}
		for _, s := range rr.Shares {
			pts := rr.Points * s.Weight
			if pts == 0 {
				continue
			}
			out = append(out, LedgerEntry{
				TeamID:      s.TeamID,
				AthleteID:   athleteID,
				EventID:     in.Event.ID,
				CategoryID:  in.Category.ID,
				EntryID:     rr.EntryID,
				ResultID:    rr.ResultID,
				ChannelID:   ch.ID,
				SourceType:  SourceResult,
				SourceID:    sourceID,
				Points:      pts,
				CountToTeam: ch.countToTeam(),
			})
		}
	}
	return out
}

// resolvedShares 解析报名项的归属：默认整体归主单位，联队模式才按份额拆分。
func (e Entry) resolvedShares(mode UnionAttribution) []TeamShare {
	shares := e.teamShares()
	if len(shares) == 0 {
		return nil
	}
	if mode != UnionSplit {
		return []TeamShare{{TeamID: e.primaryTeamID(), Weight: 1}}
	}
	return normalizeShares(shares)
}

// normalizeShares 把份额归一化到总和 1，避免配置里权重不标准导致总分被放大。
func normalizeShares(shares []TeamShare) []TeamShare {
	var sum float64
	for _, s := range shares {
		sum += s.Weight
	}
	out := make([]TeamShare, len(shares))
	if sum <= 0 {
		w := 1 / float64(len(shares))
		for i, s := range shares {
			out[i] = TeamShare{TeamID: s.TeamID, Weight: w}
		}
		return out
	}
	for i, s := range shares {
		out[i] = TeamShare{TeamID: s.TeamID, Weight: s.Weight / sum}
	}
	return out
}