package domain

import (
	"fmt"
	"slices"
	"sort"
)

type SlotSourceKind string

const (
	SlotTeam   SlotSourceKind = "Team"
	SlotWinner SlotSourceKind = "Winner"
	SlotLoser  SlotSourceKind = "Loser"
)

type SlotSource struct {
	Kind    SlotSourceKind `json:"kind"`
	TeamID  string         `json:"teamId,omitempty"`
	MatchID string         `json:"matchId,omitempty"`
}

type BracketMatch struct {
	ID           string     `json:"id"`
	Round        int        `json:"round"`
	Order        int        `json:"order"`
	SlotA        SlotSource `json:"slotA"`
	SlotB        SlotSource `json:"slotB"`
	SeriesID     string     `json:"seriesId,omitempty"`
	TeamAID      string     `json:"teamAId,omitempty"`
	TeamBID      string     `json:"teamBId,omitempty"`
	WinnerTeamID string     `json:"winnerTeamId,omitempty"`
	Series       *Series    `json:"series,omitempty"`
}

type BracketDraft struct {
	EventID   string         `json:"eventId"`
	TeamIDs   []string       `json:"teamIds"`
	Matches   []BracketMatch `json:"matches"`
	Version   int            `json:"version"`
	Confirmed bool           `json:"confirmed"`
}

func NewBracketDraft(eventID string, teamIDs []string) (*BracketDraft, error) {
	if eventID == "" || len(teamIDs) < 2 {
		return nil, fmt.Errorf("%w: bracket needs at least two teams", ErrInvalid)
	}
	draft := &BracketDraft{EventID: eventID, TeamIDs: slices.Clone(teamIDs)}
	add := func(round, order int, a, b SlotSource) string {
		id := fmt.Sprintf("%s-match-%d", eventID, len(draft.Matches)+1)
		draft.Matches = append(draft.Matches, BracketMatch{ID: id, Round: round, Order: order, SlotA: a, SlotB: b})
		return id
	}
	team := func(id string) SlotSource { return SlotSource{Kind: SlotTeam, TeamID: id} }
	winner := func(id string) SlotSource { return SlotSource{Kind: SlotWinner, MatchID: id} }
	loser := func(id string) SlotSource { return SlotSource{Kind: SlotLoser, MatchID: id} }
	if len(teamIDs) == 2 {
		add(0, 0, team(teamIDs[0]), team(teamIDs[1]))
	} else if len(teamIDs) == 3 {
		first := add(0, 0, team(teamIDs[0]), team(teamIDs[1]))
		second := add(1, 0, loser(first), team(teamIDs[2]))
		add(2, 0, winner(first), winner(second))
	} else if len(teamIDs)&(len(teamIDs)-1) == 0 {
		previous := make([]string, 0, len(teamIDs)/2)
		for i := 0; i < len(teamIDs); i += 2 {
			previous = append(previous, add(0, i/2, team(teamIDs[i]), team(teamIDs[i+1])))
		}
		for round := 1; len(previous) > 1; round++ {
			next := make([]string, 0, len(previous)/2)
			for i := 0; i < len(previous); i += 2 {
				next = append(next, add(round, i/2, winner(previous[i]), winner(previous[i+1])))
			}
			previous = next
		}
	} else {
		previous := add(0, 0, team(teamIDs[0]), team(teamIDs[1]))
		for i := 2; i < len(teamIDs); i++ {
			previous = add(i-1, 0, winner(previous), team(teamIDs[i]))
		}
	}
	return draft, draft.Validate()
}

func (d BracketDraft) ValidateDraft() error {
	return d.validate(false)
}

func (d BracketDraft) Validate() error {
	return d.validate(true)
}

func (d BracketDraft) validate(requireComplete bool) error {
	if d.EventID == "" || len(d.TeamIDs) < 2 || len(d.Matches) == 0 {
		return fmt.Errorf("%w: incomplete bracket", ErrInvalid)
	}
	teams := make(map[string]bool, len(d.TeamIDs))
	for _, id := range d.TeamIDs {
		if id == "" || teams[id] {
			return fmt.Errorf("%w: invalid bracket teams", ErrInvalid)
		}
		teams[id] = true
	}
	matches := make(map[string]BracketMatch, len(d.Matches))
	positions := make(map[string]bool, len(d.Matches))
	maxRound := -1
	for _, match := range d.Matches {
		position := fmt.Sprintf("%d:%d", match.Round, match.Order)
		if match.ID == "" || match.Round < 0 || match.Order < 0 || matches[match.ID].ID != "" || positions[position] {
			return fmt.Errorf("%w: invalid bracket match", ErrInvalid)
		}
		matches[match.ID] = match
		positions[position] = true
		if match.Round > maxRound {
			maxRound = match.Round
		}
	}
	finals := 0
	for _, match := range d.Matches {
		if match.Round == maxRound {
			finals++
		}
		for _, source := range []SlotSource{match.SlotA, match.SlotB} {
			switch source.Kind {
			case SlotTeam:
				if source.MatchID != "" || (source.TeamID != "" && !teams[source.TeamID]) {
					return fmt.Errorf("%w: unknown team source", ErrInvalid)
				}
				if requireComplete && source.TeamID == "" {
					return fmt.Errorf("%w: empty bracket slot", ErrInvalid)
				}
			case SlotWinner, SlotLoser:
				upstream, ok := matches[source.MatchID]
				if !ok || upstream.Round >= match.Round || source.TeamID != "" {
					return fmt.Errorf("%w: match source must reference an earlier round", ErrInvalid)
				}
			default:
				if requireComplete || source.Kind != "" || source.TeamID != "" || source.MatchID != "" {
					return fmt.Errorf("%w: empty bracket slot", ErrInvalid)
				}
			}
		}
		if requireComplete && match.SlotA.Kind == SlotTeam && match.SlotB.Kind == SlotTeam && match.SlotA.TeamID == match.SlotB.TeamID {
			return fmt.Errorf("%w: a team cannot play itself", ErrInvalid)
		}
	}
	if requireComplete && finals != 1 {
		return fmt.Errorf("%w: the last round must contain exactly one match", ErrInvalid)
	}
	return nil
}

func NewGraphTournament(id, eventID, name string, draft BracketDraft) (*Tournament, error) {
	if err := draft.Validate(); err != nil {
		return nil, err
	}
	t := &Tournament{ID: id, EventID: eventID, Name: name, TeamIDs: slices.Clone(draft.TeamIDs), Matches: slices.Clone(draft.Matches), Version: 0}
	for i := range t.Matches {
		t.Matches[i].SeriesID, t.Matches[i].TeamAID, t.Matches[i].TeamBID, t.Matches[i].WinnerTeamID, t.Matches[i].Series = "", "", "", "", nil
	}
	if err := t.Resolve(); err != nil {
		return nil, err
	}
	t.BuildRounds()
	return t, nil
}

func (t *Tournament) Resolve() error {
	byID := make(map[string]*BracketMatch, len(t.Matches))
	for i := range t.Matches {
		byID[t.Matches[i].ID] = &t.Matches[i]
	}
	resolve := func(source SlotSource) string {
		if source.Kind == SlotTeam {
			return source.TeamID
		}
		match := byID[source.MatchID]
		if match == nil || match.WinnerTeamID == "" {
			return ""
		}
		if source.Kind == SlotWinner {
			return match.WinnerTeamID
		}
		if match.WinnerTeamID == match.TeamAID {
			return match.TeamBID
		}
		return match.TeamAID
	}
	for i := range t.Matches {
		match := &t.Matches[i]
		match.TeamAID, match.TeamBID = resolve(match.SlotA), resolve(match.SlotB)
		if match.TeamAID != "" && match.TeamAID == match.TeamBID {
			return fmt.Errorf("%w: bracket match resolved to the same team", ErrConflict)
		}
	}
	t.BuildRounds()
	return nil
}

func (t *Tournament) ApplySeries(series Series) error {
	found := false
	for i := range t.Matches {
		if t.Matches[i].ID == series.ID || t.Matches[i].SeriesID == series.ID {
			t.Matches[i].SeriesID = series.ID
			t.Matches[i].TeamAID, t.Matches[i].TeamBID = series.TeamAID, series.TeamBID
			t.Matches[i].WinnerTeamID = series.WinnerTeamID
			copy := series
			t.Matches[i].Series = &copy
			found = true
			break
		}
	}
	if !found {
		return ErrNotFound
	}
	if err := t.Resolve(); err != nil {
		return err
	}
	t.Version++
	if t.Complete() {
		last := slices.MaxFunc(t.Matches, func(a, b BracketMatch) int {
			if a.Round != b.Round {
				return a.Round - b.Round
			}
			return a.Order - b.Order
		})
		t.WinnerTeamID = last.WinnerTeamID
	}
	return nil
}

func (t *Tournament) ReadyMatches() []BracketMatch {
	out := make([]BracketMatch, 0)
	for _, match := range t.Matches {
		if match.TeamAID != "" && match.TeamBID != "" && match.SeriesID == "" {
			out = append(out, match)
		}
	}
	return out
}

func (t *Tournament) Complete() bool {
	if len(t.Matches) == 0 {
		return false
	}
	for _, match := range t.Matches {
		if match.WinnerTeamID == "" {
			return false
		}
	}
	return true
}

func (t *Tournament) BuildRounds() {
	if len(t.Matches) == 0 {
		return
	}
	maxRound := 0
	for _, match := range t.Matches {
		if match.Round > maxRound {
			maxRound = match.Round
		}
	}
	t.Rounds = make([][]Series, maxRound+1)
	matches := slices.Clone(t.Matches)
	sort.Slice(matches, func(i, j int) bool {
		return matches[i].Round < matches[j].Round || matches[i].Round == matches[j].Round && matches[i].Order < matches[j].Order
	})
	for _, match := range matches {
		if match.Series != nil {
			t.Rounds[match.Round] = append(t.Rounds[match.Round], *match.Series)
		} else {
			t.Rounds[match.Round] = append(t.Rounds[match.Round], Series{ID: match.ID, EventID: t.EventID, TournamentID: t.ID, TeamAID: match.TeamAID, TeamBID: match.TeamBID, WinnerTeamID: match.WinnerTeamID, BestOf: 3})
		}
	}
}