package httpapi

import (
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"net/http"
	"sort"
	"strings"

	"git.yeij.top/AskaEth/Scoreboard/server/internal/domain"
)

// ---------- 变更历史（recorder/admin 可读） ----------

// 成绩变化的三种形态，与前端展示文案一一对应。
const (
	revisionChangeAdded   = "added"
	revisionChangeRemoved = "removed"
	revisionChangeChanged = "changed"
)

func (s *server) listRevisionsHandler(w http.ResponseWriter, r *http.Request) (any, error) {
	eventID, _ := int64Query(r, "eventId")
	limit := intQuery(r, "limit", 50)
	if limit < 1 {
		limit = 50
	}
	if limit > 200 {
		limit = 200
	}
	offset := intQuery(r, "offset", 0)
	if offset < 0 {
		offset = 0
	}
	return s.listRevisions(r.Context(), eventID, limit, offset)
}

func (s *server) getRevisionDetailHandler(w http.ResponseWriter, r *http.Request) (any, error) {
	id, err := pathID(r, "id")
	if err != nil {
		return nil, err
	}
	return s.getRevisionDetail(r.Context(), id)
}

// revisionRow 是 result_revisions 的一行，含解析后的快照。
type revisionRow struct {
	id        int64
	parentID  *int64
	eventID   int64
	eventName string
	action    string
	actorID   *int64
	message   *string
	createdAt string
	snapshot  []resultDTO
}

const revisionColumns = `r.id, r.parent_id, r.event_id, r.action, r.actor_id, r.message, r.created_at, r.snapshot_json`

func scanRevision(row interface{ Scan(...any) error }) (revisionRow, error) {
	var (
		out       revisionRow
		parentID  sql.NullInt64
		actorID   sql.NullInt64
		message   sql.NullString
		snapshot  string
		eventName sql.NullString
	)
	if err := row.Scan(&out.id, &parentID, &out.eventID, &out.action, &actorID, &message,
		&out.createdAt, &snapshot, &eventName); err != nil {
		return out, err
	}
	out.parentID = i64Ptr(parentID)
	out.actorID = i64Ptr(actorID)
	out.message = strPtr(message)
	out.eventName = eventName.String
	if err := json.Unmarshal([]byte(snapshot), &out.snapshot); err != nil {
		return out, internal(err)
	}
	return out, nil
}

func (s *server) listRevisions(ctx context.Context, eventID int64, limit, offset int) (revisionPageDTO, error) {
	where := []string{"1 = 1"}
	args := []any{}
	if eventID > 0 {
		where = append(where, "r.event_id = ?")
		args = append(args, eventID)
	}
	clause := " WHERE " + joinAnd(where)

	var total int
	if err := s.ev.QueryRowContext(ctx, `SELECT COUNT(*) FROM result_revisions r`+clause, args...).Scan(&total); err != nil {
		return revisionPageDTO{}, internal(err)
	}

	query := `SELECT ` + revisionColumns + `, COALESCE(e.name, '')
	            FROM result_revisions r
	            LEFT JOIN events e ON e.id = r.event_id` + clause + ` ORDER BY r.id DESC LIMIT ? OFFSET ?`
	args = append(args, limit, offset)
	rows, err := s.ev.QueryContext(ctx, query, args...)
	if err != nil {
		return revisionPageDTO{}, internal(err)
	}
	defer func() { _ = rows.Close() }()

	list := make([]revisionRow, 0)
	for rows.Next() {
		row, err := scanRevision(rows)
		if err != nil {
			return revisionPageDTO{}, internal(err)
		}
		list = append(list, row)
	}
	if err := rows.Err(); err != nil {
		return revisionPageDTO{}, internal(err)
	}

	items, err := s.revisionListItems(ctx, list)
	if err != nil {
		return revisionPageDTO{}, err
	}
	return revisionPageDTO{Items: items, Total: total, Limit: limit, Offset: offset}, nil
}

// revisionListItems 为每行补上操作人姓名与「与父节点相比的成绩变化条数」。
func (s *server) revisionListItems(ctx context.Context, list []revisionRow) ([]revisionListItemDTO, error) {
	actorIDs := make([]int64, 0, len(list))
	for _, row := range list {
		if row.actorID != nil {
			actorIDs = append(actorIDs, *row.actorID)
		}
	}
	names, err := s.userNames(ctx, actorIDs)
	if err != nil {
		return nil, err
	}

	items := make([]revisionListItemDTO, 0, len(list))
	for _, row := range list {
		parent, _, err := s.parentSnapshot(ctx, row)
		if err != nil {
			return nil, err
		}
		items = append(items, revisionListItem(row, names, len(diffSnapshots(parent, row.snapshot))))
	}
	return items, nil
}

func revisionListItem(row revisionRow, names map[int64]string, changedCount int) revisionListItemDTO {
	item := revisionListItemDTO{
		ID:           row.id,
		ParentID:     row.parentID,
		EventID:      row.eventID,
		EventName:    row.eventName,
		Action:       row.action,
		ActorID:      row.actorID,
		Message:      row.message,
		CreatedAt:    row.createdAt,
		ChangedCount: changedCount,
	}
	if row.actorID != nil {
		item.ActorName = names[*row.actorID]
	}
	return item
}

func (s *server) getRevision(ctx context.Context, id int64) (revisionRow, error) {
	row, err := scanRevision(s.ev.QueryRowContext(ctx,
		`SELECT `+revisionColumns+`, COALESCE(e.name, '')
		   FROM result_revisions r
		   LEFT JOIN events e ON e.id = r.event_id
		  WHERE r.id = ?`, id))
	if errors.Is(err, sql.ErrNoRows) {
		return row, notFound("变更记录不存在")
	}
	if err != nil {
		return row, internal(err)
	}
	return row, nil
}

func (s *server) getRevisionDetail(ctx context.Context, id int64) (revisionDetailDTO, error) {
	row, err := s.getRevision(ctx, id)
	if err != nil {
		return revisionDetailDTO{}, err
	}
	parent, _, err := s.parentSnapshot(ctx, row)
	if err != nil {
		return revisionDetailDTO{}, err
	}
	changes := diffSnapshots(parent, row.snapshot)

	entryTeams, err := s.entryTeams(ctx, changeEntryIDs(changes))
	if err != nil {
		return revisionDetailDTO{}, err
	}
	for i := range changes {
		if teamID := entryTeams[changes[i].EntryID]; teamID != 0 {
			changes[i].TeamID = &teamID
		}
	}

	// 分数增减依赖当前计分配置重算快照；配置被删改时降级为只返回成绩差异。
	teams, err := s.revisionTeamDeltas(ctx, row.eventID, parent, row.snapshot, changes, entryTeams)
	if err != nil {
		s.logger.Warn("变更历史分数差异计算失败", "revisionId", id, "eventId", row.eventID, "err", err)
		teams = []revisionTeamDeltaDTO{}
	}

	names, err := s.userNames(ctx, actorIDList(row.actorID))
	if err != nil {
		return revisionDetailDTO{}, err
	}
	return revisionDetailDTO{
		revisionListItemDTO: revisionListItem(row, names, len(changes)),
		Snapshot:            row.snapshot,
		Diff:                revisionDiffDTO{Results: changes, Teams: teams},
	}, nil
}

// parentSnapshot 返回父节点快照：优先用显式 parent_id；
// 现有写入逻辑不写 parent_id，因此退化为「同小项上一条记录」，与文档「每个小项一条主线」一致。
func (s *server) parentSnapshot(ctx context.Context, row revisionRow) ([]resultDTO, bool, error) {
	var (
		raw string
		err error
	)
	if row.parentID != nil {
		err = s.ev.QueryRowContext(ctx, `SELECT snapshot_json FROM result_revisions WHERE id = ?`, *row.parentID).Scan(&raw)
	} else {
		err = s.ev.QueryRowContext(ctx,
			`SELECT snapshot_json FROM result_revisions WHERE event_id = ? AND id < ? ORDER BY id DESC LIMIT 1`,
			row.eventID, row.id).Scan(&raw)
	}
	if errors.Is(err, sql.ErrNoRows) {
		return nil, false, nil
	}
	if err != nil {
		return nil, false, internal(err)
	}
	var snapshot []resultDTO
	if err := json.Unmarshal([]byte(raw), &snapshot); err != nil {
		return nil, false, internal(err)
	}
	return snapshot, true, nil
}

func actorIDList(id *int64) []int64 {
	if id == nil {
		return nil
	}
	return []int64{*id}
}

func changeEntryIDs(changes []revisionResultChangeDTO) []int64 {
	out := make([]int64, 0, len(changes))
	for _, c := range changes {
		out = append(out, c.EntryID)
	}
	return out
}

// diffSnapshots 按成绩 id 对比两份快照，输出新增/删除/修改。
func diffSnapshots(parent, current []resultDTO) []revisionResultChangeDTO {
	parentByID := make(map[int64]resultDTO, len(parent))
	for _, r := range parent {
		parentByID[r.ID] = r
	}
	currentByID := make(map[int64]resultDTO, len(current))
	for _, r := range current {
		currentByID[r.ID] = r
	}

	out := make([]revisionResultChangeDTO, 0)
	for _, r := range current {
		after := r
		old, ok := parentByID[r.ID]
		if !ok {
			out = append(out, revisionResultChangeDTO{
				ResultID: r.ID, EntryID: r.EntryID, Change: revisionChangeAdded, After: &after,
			})
			continue
		}
		before := old
		if fields := changedResultFields(before, after); len(fields) > 0 {
			out = append(out, revisionResultChangeDTO{
				ResultID: r.ID, EntryID: r.EntryID, Change: revisionChangeChanged,
				Fields: fields, Before: &before, After: &after,
			})
		}
	}
	for _, r := range parent {
		if _, ok := currentByID[r.ID]; ok {
			continue
		}
		before := r
		out = append(out, revisionResultChangeDTO{
			ResultID: r.ID, EntryID: r.EntryID, Change: revisionChangeRemoved, Before: &before,
		})
	}
	sort.SliceStable(out, func(i, j int) bool { return out[i].ResultID < out[j].ResultID })
	return out
}

func changedResultFields(a, b resultDTO) []string {
	fields := make([]string, 0, 4)
	if !intPtrEqual(a.Rank, b.Rank) {
		fields = append(fields, "rank")
	}
	if a.ResultText != b.ResultText {
		fields = append(fields, "resultText")
	}
	if !f64PtrEqual(a.ResultValue, b.ResultValue) {
		fields = append(fields, "resultValue")
	}
	if a.Unit != b.Unit {
		fields = append(fields, "unit")
	}
	if a.IsTie != b.IsTie {
		fields = append(fields, "isTie")
	}
	if !f64PtrEqual(a.PointsOverride, b.PointsOverride) {
		fields = append(fields, "pointsOverride")
	}
	if a.Status != b.Status {
		fields = append(fields, "status")
	}
	if a.State != b.State {
		fields = append(fields, "state")
	}
	if !strPtrEqual(a.Note, b.Note) {
		fields = append(fields, "note")
	}
	return fields
}

func intPtrEqual(a, b *int) bool {
	if a == nil || b == nil {
		return a == nil && b == nil
	}
	return *a == *b
}

func f64PtrEqual(a, b *float64) bool {
	if a == nil || b == nil {
		return a == nil && b == nil
	}
	return *a == *b
}

func strPtrEqual(a, b *string) bool {
	if a == nil || b == nil {
		return a == nil && b == nil
	}
	return *a == *b
}

// revisionTeamDeltas 用快照重算受影响单位的分数增减。
// 快照里没有单位与积分，只能借当前计分配置重算；仅用于展示，不参与任何计算。
func (s *server) revisionTeamDeltas(ctx context.Context, eventID int64, parent, current []resultDTO, changes []revisionResultChangeDTO, entryTeams map[int64]int64) ([]revisionTeamDeltaDTO, error) {
	before, err := s.snapshotTeamPoints(ctx, eventID, parent)
	if err != nil {
		return nil, err
	}
	after, err := s.snapshotTeamPoints(ctx, eventID, current)
	if err != nil {
		return nil, err
	}

	counts := make(map[int64]int)
	for _, c := range changes {
		if teamID := entryTeams[c.EntryID]; teamID != 0 {
			counts[teamID]++
		}
	}
	// 成绩本身没变、但积分因重算而变的单位也要列出来。
	for teamID, points := range after {
		if points != before[teamID] {
			if _, ok := counts[teamID]; !ok {
				counts[teamID] = 0
			}
		}
	}

	teams, err := s.teamMap(ctx)
	if err != nil {
		return nil, err
	}
	out := make([]revisionTeamDeltaDTO, 0, len(counts))
	for teamID, n := range counts {
		t := teams[teamID]
		out = append(out, revisionTeamDeltaDTO{
			TeamID:         teamID,
			TeamCode:       t.Code,
			TeamName:       t.Name,
			PointsBefore:   before[teamID],
			PointsAfter:    after[teamID],
			PointsDelta:    after[teamID] - before[teamID],
			ChangedResults: n,
		})
	}
	sort.SliceStable(out, func(i, j int) bool { return out[i].TeamID < out[j].TeamID })
	return out, nil
}

// snapshotTeamPoints 把一份成绩快照按当前通道/模板重算成「单位 → 总分」。
func (s *server) snapshotTeamPoints(ctx context.Context, eventID int64, snapshot []resultDTO) (map[int64]float64, error) {
	out := make(map[int64]float64)
	ev, err := loadEventQ(ctx, s.ev, eventID)
	if err != nil {
		return nil, err
	}
	categories, err := loadCategoriesQ(ctx, s.ev, eventID)
	if err != nil {
		return nil, err
	}
	channels, err := loadChannelsQ(ctx, s.ev, eventID)
	if err != nil {
		return nil, err
	}
	profileIDs := make(map[int64]bool, len(channels))
	for _, ch := range channels {
		profileIDs[ch.ProfileID] = true
	}
	profiles, err := loadProfilesQ(ctx, s.ev, profileIDs)
	if err != nil {
		return nil, err
	}
	entries, err := loadEntriesQ(ctx, s.ev, eventID, 0)
	if err != nil {
		return nil, err
	}
	bonus, err := loadRecordBonusQ(ctx, s.ev)
	if err != nil {
		return nil, err
	}
	breaks, err := loadRecordBreaksQ(ctx, s.ev, eventID)
	if err != nil {
		return nil, err
	}

	results := make([]domain.Result, 0, len(snapshot))
	for _, r := range snapshot {
		results = append(results, resultDTOToDomain(r))
	}

	for _, cat := range categories {
		score, err := domain.ScoreEvent(domain.EventScoreInput{
			Event:        ev,
			Category:     cat,
			Channels:     channels,
			Profiles:     profiles,
			Entries:      entries,
			Results:      results,
			RecordBonus:  &bonus,
			RecordBreaks: breaks,
		})
		if err != nil {
			return nil, mapDomainError(err)
		}
		for _, l := range score.Ledger {
			out[l.TeamID] += l.Points
		}
	}
	return out, nil
}

func resultDTOToDomain(r resultDTO) domain.Result {
	out := domain.Result{
		ID:             r.ID,
		EventID:        r.EventID,
		EntryID:        r.EntryID,
		ResultText:     r.ResultText,
		ResultValue:    r.ResultValue,
		Unit:           r.Unit,
		IsTie:          r.IsTie,
		PointsOverride: r.PointsOverride,
		Status:         domain.ResultStatus(r.Status),
		State:          domain.ResultState(r.State),
	}
	if r.Rank != nil {
		out.Rank = *r.Rank
	}
	if r.Note != nil {
		out.Note = *r.Note
	}
	return out
}

func (s *server) entryTeams(ctx context.Context, ids []int64) (map[int64]int64, error) {
	out := make(map[int64]int64)
	if len(ids) == 0 {
		return out, nil
	}
	args := make([]any, 0, len(ids))
	for _, id := range ids {
		args = append(args, id)
	}
	rows, err := s.ev.QueryContext(ctx,
		`SELECT id, team_id FROM entries WHERE id IN (`+placeholders(len(ids))+`)`, args...)
	if err != nil {
		return nil, internal(err)
	}
	defer func() { _ = rows.Close() }()
	for rows.Next() {
		var entryID, teamID int64
		if err := rows.Scan(&entryID, &teamID); err != nil {
			return nil, internal(err)
		}
		out[entryID] = teamID
	}
	if err := rows.Err(); err != nil {
		return nil, internal(err)
	}
	return out, nil
}

// userNames 从系统库取用户显示名（result_revisions.actor_id 跨库，不能 JOIN）。
func (s *server) userNames(ctx context.Context, ids []int64) (map[int64]string, error) {
	out := make(map[int64]string, len(ids))
	if len(ids) == 0 {
		return out, nil
	}
	args := make([]any, 0, len(ids))
	for _, id := range ids {
		args = append(args, id)
	}
	rows, err := s.sys.QueryContext(ctx,
		`SELECT id, display_name FROM users WHERE id IN (`+placeholders(len(ids))+`)`, args...)
	if err != nil {
		return nil, internal(err)
	}
	defer func() { _ = rows.Close() }()
	for rows.Next() {
		var id int64
		var name string
		if err := rows.Scan(&id, &name); err != nil {
			return nil, internal(err)
		}
		out[id] = name
	}
	if err := rows.Err(); err != nil {
		return nil, internal(err)
	}
	return out, nil
}

func placeholders(n int) string {
	return strings.TrimSuffix(strings.Repeat("?,", n), ",")
}