"""Double Elimination Tournament Engine for ServeSync"""
from sqlalchemy.orm import Session
from app.models.tournament import Tournament, TournamentEntry, TournamentMatch, TournamentStatus, BracketType, TournamentMatchStatus
from app.models.player import Player
from app.models.court import Court
from app.models.match import Match, MatchPlayer, MatchStage, MatchStatus, MatchType
from app.services.matchmaking import find_available_court
from datetime import datetime
from typing import Optional, List
import math


def create_tournament(db: Session, name: str, max_participants: int = 8) -> Tournament:
    """Create a new tournament"""
    t = Tournament(name=name, max_participants=max_participants)
    db.add(t)
    db.commit()
    db.refresh(t)
    return t


def register_player(db: Session, tournament_id: int, player_id: int) -> Optional[TournamentEntry]:
    """Register a player for the tournament"""
    t = db.query(Tournament).filter(Tournament.id == tournament_id).first()
    if not t or t.status != TournamentStatus.REGISTRATION:
        return None

    current_count = db.query(TournamentEntry).filter(TournamentEntry.tournament_id == tournament_id).count()
    if current_count >= t.max_participants:
        return None

    existing = db.query(TournamentEntry).filter(
        TournamentEntry.tournament_id == tournament_id,
        TournamentEntry.player_id == player_id
    ).first()
    if existing:
        return existing

    entry = TournamentEntry(tournament_id=tournament_id, player_id=player_id)
    db.add(entry)
    db.commit()
    db.refresh(entry)
    return entry


def start_tournament(db: Session, tournament_id: int) -> Optional[Tournament]:
    """Start tournament and generate initial bracket"""
    t = db.query(Tournament).filter(Tournament.id == tournament_id).first()
    if not t or t.status != TournamentStatus.REGISTRATION:
        return None

    entries = db.query(TournamentEntry).filter(
        TournamentEntry.tournament_id == tournament_id
    ).join(Player).order_by(Player.elo_rating.desc()).all()

    if len(entries) < 4:
        return None

    # Seed players by ELO
    for i, entry in enumerate(entries):
        entry.seed = i + 1

    # Generate bracket matches
    _generate_winners_bracket(db, t, entries)

    t.status = TournamentStatus.IN_PROGRESS
    t.started_at = datetime.utcnow()
    db.commit()
    db.refresh(t)
    return t


def _generate_winners_bracket(db: Session, tournament: Tournament, entries: List[TournamentEntry]):
    """Generate the initial winners bracket matches"""
    n = len(entries)
    # Pair up by seeding (1 vs n, 2 vs n-1, etc.)
    match_num = 1
    pairs = []
    for i in range(n // 2):
        p1 = entries[i]
        p2 = entries[n - 1 - i]
        pairs.append((p1, p2))

    for p1, p2 in pairs:
        tm = TournamentMatch(
            tournament_id=tournament.id,
            round_number=1,
            match_number=match_num,
            bracket_type=BracketType.WINNERS,
            status=TournamentMatchStatus.PENDING,
            player1_id=p1.player_id,
            player2_id=p2.player_id,
        )
        db.add(tm)
        match_num += 1

    db.flush()


def complete_tournament_match(
    db: Session,
    tournament_match_id: int,
    team1_score: int,
    team2_score: int
) -> Optional[TournamentMatch]:
    """Complete a tournament match and advance bracket"""
    tm = db.query(TournamentMatch).filter(TournamentMatch.id == tournament_match_id).first()
    if not tm:
        return None

    tm.team1_score = team1_score
    tm.team2_score = team2_score
    tm.winner_team = 1 if team1_score > team2_score else 2
    tm.status = TournamentMatchStatus.COMPLETED
    tm.completed_at = datetime.utcnow()

    winner_player_id = tm.player1_id if tm.winner_team == 1 else tm.player2_id
    loser_player_id = tm.player2_id if tm.winner_team == 1 else tm.player1_id

    # Update entry stats
    winner_entry = db.query(TournamentEntry).filter(
        TournamentEntry.tournament_id == tm.tournament_id,
        TournamentEntry.player_id == winner_player_id
    ).first()
    loser_entry = db.query(TournamentEntry).filter(
        TournamentEntry.tournament_id == tm.tournament_id,
        TournamentEntry.player_id == loser_player_id
    ).first()

    if winner_entry:
        winner_entry.wins += 1
    if loser_entry:
        loser_entry.losses += 1

    # Double elimination logic
    if loser_entry and loser_entry.losses < 2:
        # Move to losers bracket
        loser_entry.is_in_losers = True
        _create_losers_match(db, tm, loser_player_id)
    elif loser_entry:
        # Eliminated
        loser_entry.is_eliminated = True
        _assign_final_ranks(db, tm.tournament_id)

    db.commit()
    db.refresh(tm)
    return tm


def _create_losers_match(db: Session, completed_match: TournamentMatch, loser_id: int):
    """Route loser to losers bracket"""
    # Find existing pending losers match in next round
    next_round = completed_match.round_number + 1
    existing = db.query(TournamentMatch).filter(
        TournamentMatch.tournament_id == completed_match.tournament_id,
        TournamentMatch.bracket_type == BracketType.LOSERS,
        TournamentMatch.round_number == next_round,
        TournamentMatch.player2_id.is_(None),
    ).first()

    if existing:
        existing.player2_id = loser_id
    else:
        # Create a new losers match
        match_count = db.query(TournamentMatch).filter(
            TournamentMatch.tournament_id == completed_match.tournament_id,
            TournamentMatch.bracket_type == BracketType.LOSERS,
            TournamentMatch.round_number == next_round,
        ).count()

        tm = TournamentMatch(
            tournament_id=completed_match.tournament_id,
            round_number=next_round,
            match_number=match_count + 1,
            bracket_type=BracketType.LOSERS,
            status=TournamentMatchStatus.PENDING,
            player1_id=loser_id,
        )
        db.add(tm)


def _assign_final_ranks(db: Session, tournament_id: int):
    """Assign final ranks to eliminated players"""
    entries = db.query(TournamentEntry).filter(
        TournamentEntry.tournament_id == tournament_id,
        TournamentEntry.is_eliminated == True,
        TournamentEntry.final_rank.is_(None)
    ).order_by(TournamentEntry.losses.desc()).all()

    remaining = db.query(TournamentEntry).filter(
        TournamentEntry.tournament_id == tournament_id,
        TournamentEntry.is_eliminated == False
    ).count()

    base_rank = remaining + 1
    for i, entry in enumerate(entries):
        entry.final_rank = base_rank + i


def get_bracket_data(db: Session, tournament_id: int) -> dict:
    """Get structured bracket data for frontend visualization"""
    tournament = db.query(Tournament).filter(Tournament.id == tournament_id).first()
    if not tournament:
        return {}

    matches = db.query(TournamentMatch).filter(
        TournamentMatch.tournament_id == tournament_id
    ).order_by(TournamentMatch.round_number, TournamentMatch.match_number).all()

    entries = db.query(TournamentEntry).filter(
        TournamentEntry.tournament_id == tournament_id
    ).all()

    players_map = {}
    for entry in entries:
        player = db.query(Player).filter(Player.id == entry.player_id).first()
        if player:
            players_map[player.id] = {
                "id": player.id,
                "name": player.name,
                "elo": player.elo_rating,
                "seed": entry.seed,
                "wins": entry.wins,
                "losses": entry.losses,
                "is_eliminated": entry.is_eliminated,
                "is_in_losers": entry.is_in_losers,
                "final_rank": entry.final_rank,
            }

    winners_bracket = []
    losers_bracket = []
    grand_final = []

    for m in matches:
        match_data = {
            "id": m.id,
            "round": m.round_number,
            "match_number": m.match_number,
            "status": m.status.value,
            "player1": players_map.get(m.player1_id),
            "player2": players_map.get(m.player2_id),
            "team1_score": m.team1_score,
            "team2_score": m.team2_score,
            "winner_team": m.winner_team,
        }
        if m.bracket_type == BracketType.WINNERS:
            winners_bracket.append(match_data)
        elif m.bracket_type == BracketType.LOSERS:
            losers_bracket.append(match_data)
        else:
            grand_final.append(match_data)

    # Build leaderboard
    leaderboard = sorted(
        [
            {
                "player": players_map[e.player_id],
                "wins": e.wins,
                "losses": e.losses,
                "is_eliminated": e.is_eliminated,
                "is_in_losers": e.is_in_losers,
                "final_rank": e.final_rank,
            }
            for e in entries
            if e.player_id in players_map
        ],
        key=lambda x: (x["final_rank"] or 999, -x["wins"]),
    )

    return {
        "tournament": {
            "id": tournament.id,
            "name": tournament.name,
            "status": tournament.status.value,
            "current_round": tournament.current_round,
        },
        "winners_bracket": winners_bracket,
        "losers_bracket": losers_bracket,
        "grand_final": grand_final,
        "leaderboard": leaderboard,
    }