// Package db provides database access and migration management.
package db

import (
	"context"
	"database/sql"
	"embed"
	"fmt"
	"io/fs"
	"log/slog"
	"sort"
	"strconv"
	"strings"
	"time"

	"git.eeqj.de/sneak/chat/internal/config"
	"git.eeqj.de/sneak/chat/internal/logger"
	"git.eeqj.de/sneak/chat/internal/models"
	"go.uber.org/fx"

	_ "github.com/joho/godotenv/autoload" // loads .env file
	_ "modernc.org/sqlite"                // SQLite driver
)

const (
	minMigrationParts = 2
)

// SchemaFiles contains embedded SQL migration files.
//
//go:embed schema/*.sql
var SchemaFiles embed.FS

// Params defines the dependencies for creating a Database.
type Params struct {
	fx.In

	Logger *logger.Logger
	Config *config.Config
}

// Database manages the SQLite database connection and migrations.
type Database struct {
	db     *sql.DB
	log    *slog.Logger
	params *Params
}

// New creates a new Database instance and registers lifecycle hooks.
func New(lc fx.Lifecycle, params Params) (*Database, error) {
	s := new(Database)
	s.params = &params
	s.log = params.Logger.Get()

	s.log.Info("Database instantiated")

	lc.Append(fx.Hook{
		OnStart: func(ctx context.Context) error {
			s.log.Info("Database OnStart Hook")

			return s.connect(ctx)
		},
		OnStop: func(_ context.Context) error {
			s.log.Info("Database OnStop Hook")

			if s.db != nil {
				return s.db.Close()
			}

			return nil
		},
	})

	return s, nil
}

// NewTest creates a Database for testing, bypassing fx lifecycle.
// It connects to the given DSN and runs all migrations.
func NewTest(dsn string) (*Database, error) {
	d, err := sql.Open("sqlite", dsn)
	if err != nil {
		return nil, err
	}

	s := &Database{
		db:  d,
		log: slog.Default(),
	}

	// Item 9: Enable foreign keys
	_, err = d.Exec("PRAGMA foreign_keys = ON") //nolint:noctx // no context in sql.Open path
	if err != nil {
		_ = d.Close()

		return nil, fmt.Errorf("enable foreign keys: %w", err)
	}

	ctx := context.Background()

	err = s.runMigrations(ctx)
	if err != nil {
		_ = d.Close()

		return nil, err
	}

	return s, nil
}

// GetDB returns the underlying sql.DB connection.
func (s *Database) GetDB() *sql.DB {
	return s.db
}

// Hydrate injects the database reference into any model that
// embeds Base.
func (s *Database) Hydrate(m interface{ SetDB(d models.DB) }) {
	m.SetDB(s)
}

// GetUserByID looks up a user by their ID.
func (s *Database) GetUserByID(
	ctx context.Context,
	id string,
) (*models.User, error) {
	u := &models.User{}
	s.Hydrate(u)

	err := s.db.QueryRowContext(ctx, `
		SELECT id, nick, password_hash, created_at, updated_at, last_seen_at
		FROM users WHERE id = ?`,
		id,
	).Scan(
		&u.ID, &u.Nick, &u.PasswordHash,
		&u.CreatedAt, &u.UpdatedAt, &u.LastSeenAt,
	)
	if err != nil {
		return nil, err
	}

	return u, nil
}

// GetChannelByID looks up a channel by its ID.
func (s *Database) GetChannelByID(
	ctx context.Context,
	id string,
) (*models.Channel, error) {
	c := &models.Channel{}
	s.Hydrate(c)

	err := s.db.QueryRowContext(ctx, `
		SELECT id, name, topic, modes, created_at, updated_at
		FROM channels WHERE id = ?`,
		id,
	).Scan(
		&c.ID, &c.Name, &c.Topic, &c.Modes,
		&c.CreatedAt, &c.UpdatedAt,
	)
	if err != nil {
		return nil, err
	}

	return c, nil
}

// GetUserByNickModel looks up a user by their nick.
func (s *Database) GetUserByNickModel(
	ctx context.Context,
	nick string,
) (*models.User, error) {
	u := &models.User{}
	s.Hydrate(u)

	err := s.db.QueryRowContext(ctx, `
		SELECT id, nick, password_hash, created_at, updated_at, last_seen_at
		FROM users WHERE nick = ?`,
		nick,
	).Scan(
		&u.ID, &u.Nick, &u.PasswordHash,
		&u.CreatedAt, &u.UpdatedAt, &u.LastSeenAt,
	)
	if err != nil {
		return nil, err
	}

	return u, nil
}

// GetUserByTokenModel looks up a user by their auth token.
func (s *Database) GetUserByTokenModel(
	ctx context.Context,
	token string,
) (*models.User, error) {
	u := &models.User{}
	s.Hydrate(u)

	err := s.db.QueryRowContext(ctx, `
		SELECT u.id, u.nick, u.password_hash,
		       u.created_at, u.updated_at, u.last_seen_at
		FROM users u
		JOIN auth_tokens t ON t.user_id = u.id
		WHERE t.token = ?`,
		token,
	).Scan(
		&u.ID, &u.Nick, &u.PasswordHash,
		&u.CreatedAt, &u.UpdatedAt, &u.LastSeenAt,
	)
	if err != nil {
		return nil, err
	}

	return u, nil
}

// DeleteAuthToken removes an auth token from the database.
func (s *Database) DeleteAuthToken(
	ctx context.Context,
	token string,
) error {
	_, err := s.db.ExecContext(ctx,
		`DELETE FROM auth_tokens WHERE token = ?`, token,
	)

	return err
}

// UpdateUserLastSeen updates the last_seen_at timestamp for a user.
func (s *Database) UpdateUserLastSeen(
	ctx context.Context,
	userID string,
) error {
	_, err := s.db.ExecContext(ctx,
		`UPDATE users SET last_seen_at = CURRENT_TIMESTAMP WHERE id = ?`,
		userID,
	)

	return err
}

// CreateUserModel inserts a new user into the database.
func (s *Database) CreateUserModel(
	ctx context.Context,
	id, nick, passwordHash string,
) (*models.User, error) {
	now := time.Now()

	_, err := s.db.ExecContext(ctx,
		`INSERT INTO users (id, nick, password_hash)
		 VALUES (?, ?, ?)`,
		id, nick, passwordHash,
	)
	if err != nil {
		return nil, err
	}

	u := &models.User{
		ID: id, Nick: nick, PasswordHash: passwordHash,
		CreatedAt: now, UpdatedAt: now,
	}
	s.Hydrate(u)

	return u, nil
}

// CreateChannel inserts a new channel into the database.
func (s *Database) CreateChannel(
	ctx context.Context,
	id, name, topic, modes string,
) (*models.Channel, error) {
	now := time.Now()

	_, err := s.db.ExecContext(ctx,
		`INSERT INTO channels (id, name, topic, modes)
		 VALUES (?, ?, ?, ?)`,
		id, name, topic, modes,
	)
	if err != nil {
		return nil, err
	}

	c := &models.Channel{
		ID: id, Name: name, Topic: topic, Modes: modes,
		CreatedAt: now, UpdatedAt: now,
	}
	s.Hydrate(c)

	return c, nil
}

// AddChannelMember adds a user to a channel with the given modes.
func (s *Database) AddChannelMember(
	ctx context.Context,
	channelID, userID, modes string,
) (*models.ChannelMember, error) {
	now := time.Now()

	_, err := s.db.ExecContext(ctx,
		`INSERT INTO channel_members
		 (channel_id, user_id, modes)
		 VALUES (?, ?, ?)`,
		channelID, userID, modes,
	)
	if err != nil {
		return nil, err
	}

	cm := &models.ChannelMember{
		ChannelID: channelID,
		UserID:    userID,
		Modes:     modes,
		JoinedAt:  now,
	}
	s.Hydrate(cm)

	return cm, nil
}

// CreateMessage inserts a new message into the database.
func (s *Database) CreateMessage(
	ctx context.Context,
	id, fromUserID, fromNick, target, msgType, body string,
) (*models.Message, error) {
	now := time.Now()

	_, err := s.db.ExecContext(ctx,
		`INSERT INTO messages
		 (id, from_user_id, from_nick, target, type, body)
		 VALUES (?, ?, ?, ?, ?, ?)`,
		id, fromUserID, fromNick, target, msgType, body,
	)
	if err != nil {
		return nil, err
	}

	m := &models.Message{
		ID:         id,
		FromUserID: fromUserID,
		FromNick:   fromNick,
		Target:     target,
		Type:       msgType,
		Body:       body,
		Timestamp:  now,
		CreatedAt:  now,
	}
	s.Hydrate(m)

	return m, nil
}

// QueueMessage adds a message to a user's delivery queue.
func (s *Database) QueueMessage(
	ctx context.Context,
	userID, messageID string,
) (*models.MessageQueueEntry, error) {
	now := time.Now()

	res, err := s.db.ExecContext(ctx,
		`INSERT INTO message_queue (user_id, message_id)
		 VALUES (?, ?)`,
		userID, messageID,
	)
	if err != nil {
		return nil, err
	}

	entryID, err := res.LastInsertId()
	if err != nil {
		return nil, fmt.Errorf("get last insert id: %w", err)
	}

	mq := &models.MessageQueueEntry{
		ID:        entryID,
		UserID:    userID,
		MessageID: messageID,
		QueuedAt:  now,
	}
	s.Hydrate(mq)

	return mq, nil
}

// DequeueMessages returns up to limit pending messages for a user,
// ordered by queue time (oldest first).
func (s *Database) DequeueMessages(
	ctx context.Context,
	userID string,
	limit int,
) ([]*models.MessageQueueEntry, error) {
	rows, err := s.db.QueryContext(ctx, `
		SELECT id, user_id, message_id, queued_at
		FROM message_queue
		WHERE user_id = ?
		ORDER BY queued_at ASC
		LIMIT ?`,
		userID, limit,
	)
	if err != nil {
		return nil, err
	}

	defer func() { _ = rows.Close() }()

	entries := []*models.MessageQueueEntry{}

	for rows.Next() {
		e := &models.MessageQueueEntry{}
		s.Hydrate(e)

		err = rows.Scan(&e.ID, &e.UserID, &e.MessageID, &e.QueuedAt)
		if err != nil {
			return nil, err
		}

		entries = append(entries, e)
	}

	return entries, rows.Err()
}

// AckMessages removes the given queue entry IDs, marking them as delivered.
func (s *Database) AckMessages(
	ctx context.Context,
	entryIDs []int64,
) error {
	if len(entryIDs) == 0 {
		return nil
	}

	placeholders := make([]string, len(entryIDs))
	args := make([]any, len(entryIDs))

	for i, id := range entryIDs {
		placeholders[i] = "?"
		args[i] = id
	}

	query := fmt.Sprintf( //nolint:gosec // placeholders are ?, not user input
		"DELETE FROM message_queue WHERE id IN (%s)",
		strings.Join(placeholders, ","),
	)

	_, err := s.db.ExecContext(ctx, query, args...)

	return err
}

// CreateAuthToken inserts a new auth token for a user.
func (s *Database) CreateAuthToken(
	ctx context.Context,
	token, userID string,
) (*models.AuthToken, error) {
	now := time.Now()

	_, err := s.db.ExecContext(ctx,
		`INSERT INTO auth_tokens (token, user_id)
		 VALUES (?, ?)`,
		token, userID,
	)
	if err != nil {
		return nil, err
	}

	at := &models.AuthToken{Token: token, UserID: userID, CreatedAt: now}
	s.Hydrate(at)

	return at, nil
}

// CreateSession inserts a new session for a user.
func (s *Database) CreateSession(
	ctx context.Context,
	id, userID string,
) (*models.Session, error) {
	now := time.Now()

	_, err := s.db.ExecContext(ctx,
		`INSERT INTO sessions (id, user_id)
		 VALUES (?, ?)`,
		id, userID,
	)
	if err != nil {
		return nil, err
	}

	sess := &models.Session{
		ID: id, UserID: userID,
		CreatedAt: now, LastActiveAt: now,
	}
	s.Hydrate(sess)

	return sess, nil
}

// CreateServerLink inserts a new server link.
func (s *Database) CreateServerLink(
	ctx context.Context,
	id, name, url, sharedKeyHash string,
	isActive bool,
) (*models.ServerLink, error) {
	now := time.Now()
	active := 0

	if isActive {
		active = 1
	}

	_, err := s.db.ExecContext(ctx,
		`INSERT INTO server_links
		 (id, name, url, shared_key_hash, is_active)
		 VALUES (?, ?, ?, ?, ?)`,
		id, name, url, sharedKeyHash, active,
	)
	if err != nil {
		return nil, err
	}

	sl := &models.ServerLink{
		ID:            id,
		Name:          name,
		URL:           url,
		SharedKeyHash: sharedKeyHash,
		IsActive:      isActive,
		CreatedAt:     now,
	}
	s.Hydrate(sl)

	return sl, nil
}

func (s *Database) connect(ctx context.Context) error {
	dbURL := s.params.Config.DBURL
	if dbURL == "" {
		dbURL = "file:./data.db?_journal_mode=WAL"
	}

	s.log.Info("connecting to database", "url", dbURL)

	d, err := sql.Open("sqlite", dbURL)
	if err != nil {
		s.log.Error("failed to open database", "error", err)

		return err
	}

	err = d.PingContext(ctx)
	if err != nil {
		s.log.Error("failed to ping database", "error", err)

		return err
	}

	s.db = d
	s.log.Info("database connected")

	// Item 9: Enable foreign keys on every connection
	_, err = s.db.ExecContext(ctx, "PRAGMA foreign_keys = ON")
	if err != nil {
		return fmt.Errorf("enable foreign keys: %w", err)
	}

	return s.runMigrations(ctx)
}

type migration struct {
	version int
	name    string
	sql     string
}

func (s *Database) runMigrations(ctx context.Context) error {
	err := s.bootstrapMigrationsTable(ctx)
	if err != nil {
		return err
	}

	migrations, err := s.loadMigrations()
	if err != nil {
		return err
	}

	err = s.applyMigrations(ctx, migrations)
	if err != nil {
		return err
	}

	s.log.Info("database migrations complete")

	return nil
}

func (s *Database) bootstrapMigrationsTable(
	ctx context.Context,
) error {
	_, err := s.db.ExecContext(ctx,
		`CREATE TABLE IF NOT EXISTS schema_migrations (
		version INTEGER PRIMARY KEY,
		applied_at DATETIME DEFAULT CURRENT_TIMESTAMP
	)`)
	if err != nil {
		return fmt.Errorf(
			"create schema_migrations table: %w", err,
		)
	}

	return nil
}

func (s *Database) loadMigrations() ([]migration, error) {
	entries, err := fs.ReadDir(SchemaFiles, "schema")
	if err != nil {
		return nil, fmt.Errorf("read schema dir: %w", err)
	}

	var migrations []migration

	for _, entry := range entries {
		if entry.IsDir() ||
			!strings.HasSuffix(entry.Name(), ".sql") {
			continue
		}

		parts := strings.SplitN(
			entry.Name(), "_", minMigrationParts,
		)
		if len(parts) < minMigrationParts {
			continue
		}

		version, err := strconv.Atoi(parts[0])
		if err != nil {
			continue
		}

		content, err := SchemaFiles.ReadFile(
			"schema/" + entry.Name(),
		)
		if err != nil {
			return nil, fmt.Errorf(
				"read migration %s: %w", entry.Name(), err,
			)
		}

		migrations = append(migrations, migration{
			version: version,
			name:    entry.Name(),
			sql:     string(content),
		})
	}

	sort.Slice(migrations, func(i, j int) bool {
		return migrations[i].version < migrations[j].version
	})

	return migrations, nil
}

// Item 4: Wrap each migration in a transaction
func (s *Database) applyMigrations(
	ctx context.Context,
	migrations []migration,
) error {
	for _, m := range migrations {
		var exists int

		err := s.db.QueryRowContext(ctx,
			"SELECT COUNT(*) FROM schema_migrations WHERE version = ?",
			m.version,
		).Scan(&exists)
		if err != nil {
			return fmt.Errorf(
				"check migration %d: %w", m.version, err,
			)
		}

		if exists > 0 {
			continue
		}

		s.log.Info(
			"applying migration",
			"version", m.version, "name", m.name,
		)

		err = s.executeMigration(ctx, m)
		if err != nil {
			return err
		}
	}

	return nil
}

func (s *Database) executeMigration(
	ctx context.Context,
	m migration,
) error {
	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return fmt.Errorf(
			"begin tx for migration %d: %w", m.version, err,
		)
	}

	_, err = tx.ExecContext(ctx, m.sql)
	if err != nil {
		_ = tx.Rollback()

		return fmt.Errorf(
			"apply migration %d (%s): %w",
			m.version, m.name, err,
		)
	}

	_, err = tx.ExecContext(ctx,
		"INSERT INTO schema_migrations (version) VALUES (?)",
		m.version,
	)
	if err != nil {
		_ = tx.Rollback()

		return fmt.Errorf(
			"record migration %d: %w", m.version, err,
		)
	}

	err = tx.Commit()
	if err != nil {
		return fmt.Errorf(
			"commit migration %d: %w", m.version, err,
		)
	}

	return nil
}