package seating

import (
	"context"
	"crypto/rand"
	"database/sql"
	"encoding/json"
	"fmt"
	"math/big"
	"sort"

	"github.com/felt-app/felt/internal/audit"
	"github.com/felt-app/felt/internal/server/ws"
)

// ---------- Types ----------

// BreakTableResult shows all moves from breaking a table.
type BreakTableResult struct {
	BrokenTableID   int              `json:"broken_table_id"`
	BrokenTableName string           `json:"broken_table_name"`
	Moves           []BreakTableMove `json:"moves"`
}

// BreakTableMove describes one player's reassignment when a table is broken.
type BreakTableMove struct {
	PlayerID   string `json:"player_id"`
	PlayerName string `json:"player_name"`
	ToTableID  int    `json:"to_table_id"`
	ToTableName string `json:"to_table_name"`
	ToSeat     int    `json:"to_seat"`
}

// ---------- Service ----------

// BreakTableService handles breaking a table and redistributing players.
type BreakTableService struct {
	db    *sql.DB
	audit *audit.Trail
	hub   *ws.Hub
}

// NewBreakTableService creates a new BreakTableService.
func NewBreakTableService(db *sql.DB, auditTrail *audit.Trail, hub *ws.Hub) *BreakTableService {
	return &BreakTableService{
		db:    db,
		audit: auditTrail,
		hub:   hub,
	}
}

// ---------- Break Table ----------

// BreakTable dissolves a table and distributes its players evenly across
// remaining active tables. This is fully automatic per CONTEXT.md -- the
// moves are applied immediately and the result is informational.
func (s *BreakTableService) BreakTable(ctx context.Context, tournamentID string, tableID int) (*BreakTableResult, error) {
	// Load the table being broken
	var tableName string
	var isActive int
	err := s.db.QueryRowContext(ctx,
		`SELECT name, is_active FROM tables WHERE id = ? AND tournament_id = ?`,
		tableID, tournamentID,
	).Scan(&tableName, &isActive)
	if err == sql.ErrNoRows {
		return nil, fmt.Errorf("table not found")
	}
	if err != nil {
		return nil, fmt.Errorf("load table: %w", err)
	}
	if isActive == 0 {
		return nil, fmt.Errorf("table is already inactive")
	}

	// Load all players at the table being broken
	type playerInfo struct {
		id   string
		name string
	}
	playerRows, err := s.db.QueryContext(ctx,
		`SELECT tp.player_id, p.name
		 FROM tournament_players tp
		 JOIN players p ON p.id = tp.player_id
		 WHERE tp.tournament_id = ? AND tp.seat_table_id = ?
		   AND tp.status IN ('registered', 'active')
		 ORDER BY tp.seat_position`,
		tournamentID, tableID,
	)
	if err != nil {
		return nil, fmt.Errorf("load players: %w", err)
	}
	defer playerRows.Close()

	var players []playerInfo
	for playerRows.Next() {
		var pi playerInfo
		if err := playerRows.Scan(&pi.id, &pi.name); err != nil {
			return nil, fmt.Errorf("scan player: %w", err)
		}
		players = append(players, pi)
	}
	if err := playerRows.Err(); err != nil {
		return nil, err
	}

	// Load remaining active tables (exclude the one being broken)
	type destTable struct {
		id        int
		name      string
		seatCount int
		players   int
	}
	destRows, err := s.db.QueryContext(ctx,
		`SELECT t.id, t.name, t.seat_count,
		        (SELECT COUNT(*) FROM tournament_players tp
		         WHERE tp.seat_table_id = t.id AND tp.tournament_id = t.tournament_id
		           AND tp.status IN ('registered', 'active')) AS player_count
		 FROM tables t
		 WHERE t.tournament_id = ? AND t.is_active = 1 AND t.id != ?
		 ORDER BY player_count ASC, t.name ASC`,
		tournamentID, tableID,
	)
	if err != nil {
		return nil, fmt.Errorf("load destination tables: %w", err)
	}
	defer destRows.Close()

	var dests []destTable
	for destRows.Next() {
		var dt destTable
		if err := destRows.Scan(&dt.id, &dt.name, &dt.seatCount, &dt.players); err != nil {
			return nil, fmt.Errorf("scan dest table: %w", err)
		}
		dests = append(dests, dt)
	}
	if err := destRows.Err(); err != nil {
		return nil, err
	}

	if len(dests) == 0 {
		return nil, fmt.Errorf("no remaining active tables to distribute players to")
	}

	// Build occupied seat sets for destination tables
	occupiedSeats := make(map[int]map[int]bool)
	for _, dt := range dests {
		occupiedSeats[dt.id] = make(map[int]bool)
		seatRows, err := s.db.QueryContext(ctx,
			`SELECT seat_position FROM tournament_players
			 WHERE tournament_id = ? AND seat_table_id = ? AND seat_position IS NOT NULL
			   AND status IN ('registered', 'active')`,
			tournamentID, dt.id,
		)
		if err != nil {
			return nil, fmt.Errorf("get occupied seats for table %d: %w", dt.id, err)
		}
		for seatRows.Next() {
			var pos int
			seatRows.Scan(&pos)
			occupiedSeats[dt.id][pos] = true
		}
		seatRows.Close()
	}

	// Distribute players evenly: for each player, assign to the table with fewest players
	var moves []BreakTableMove

	for _, pi := range players {
		// Sort destinations by current player count (ascending)
		sort.Slice(dests, func(i, j int) bool {
			if dests[i].players == dests[j].players {
				return dests[i].id < dests[j].id
			}
			return dests[i].players < dests[j].players
		})

		// Find a table with available seats
		assigned := false
		for idx := range dests {
			dt := &dests[idx]
			if dt.players >= dt.seatCount {
				continue // table is full
			}

			// Pick a random empty seat
			var emptySeats []int
			for pos := 1; pos <= dt.seatCount; pos++ {
				if !occupiedSeats[dt.id][pos] {
					emptySeats = append(emptySeats, pos)
				}
			}
			if len(emptySeats) == 0 {
				continue
			}

			seatIdx := 0
			if len(emptySeats) > 1 {
				n, _ := rand.Int(rand.Reader, big.NewInt(int64(len(emptySeats))))
				seatIdx = int(n.Int64())
			}
			seat := emptySeats[seatIdx]

			// Execute the move
			_, err := s.db.ExecContext(ctx,
				`UPDATE tournament_players SET seat_table_id = ?, seat_position = ?, updated_at = unixepoch()
				 WHERE tournament_id = ? AND player_id = ? AND status IN ('registered', 'active')`,
				dt.id, seat, tournamentID, pi.id,
			)
			if err != nil {
				return nil, fmt.Errorf("move player %s: %w", pi.id, err)
			}

			occupiedSeats[dt.id][seat] = true
			dt.players++

			moves = append(moves, BreakTableMove{
				PlayerID:    pi.id,
				PlayerName:  pi.name,
				ToTableID:   dt.id,
				ToTableName: dt.name,
				ToSeat:      seat,
			})

			assigned = true
			break
		}

		if !assigned {
			return nil, fmt.Errorf("no available seat for player %s (%s)", pi.id, pi.name)
		}
	}

	// Deactivate the broken table
	_, err = s.db.ExecContext(ctx,
		`UPDATE tables SET is_active = 0, updated_at = unixepoch()
		 WHERE id = ? AND tournament_id = ?`,
		tableID, tournamentID,
	)
	if err != nil {
		return nil, fmt.Errorf("deactivate table: %w", err)
	}

	result := &BreakTableResult{
		BrokenTableID:   tableID,
		BrokenTableName: tableName,
		Moves:           moves,
	}

	s.recordAudit(ctx, tournamentID, audit.ActionSeatBreakTable, "table", fmt.Sprintf("%d", tableID), nil, result)
	s.broadcast(tournamentID, "table.broken", result)

	return result, nil
}

// ---------- Helpers ----------

func (s *BreakTableService) recordAudit(ctx context.Context, tournamentID, action, targetType, targetID string, prevState, newState interface{}) {
	if s.audit == nil {
		return
	}
	var prev, next json.RawMessage
	if prevState != nil {
		prev, _ = json.Marshal(prevState)
	}
	if newState != nil {
		next, _ = json.Marshal(newState)
	}
	tid := tournamentID
	s.audit.Record(ctx, audit.AuditEntry{
		TournamentID:  &tid,
		Action:        action,
		TargetType:    targetType,
		TargetID:      targetID,
		PreviousState: prev,
		NewState:      next,
	})
}

func (s *BreakTableService) broadcast(tournamentID, msgType string, data interface{}) {
	if s.hub == nil {
		return
	}
	payload, err := json.Marshal(data)
	if err != nil {
		return
	}
	s.hub.Broadcast(tournamentID, msgType, payload)
}