package db

import (
	"context"
	"database/sql"
	_ "embed"
	"errors"
	"fmt"
	"log/slog"
	"os"
	"path/filepath"
	"time"

	"github.com/mattn/go-sqlite3"
)

//go:embed schema.sql
var ddl string

// DBConfig holds database configuration.
type DBConfig struct {
	DSN             string        // Data Source Name for SQLite
	MaxOpenConns    int           // Maximum number of open connections
	MaxIdleConns    int           // Maximum number of idle connections
	ConnMaxLifetime time.Duration // Maximum lifetime of connections
	ConnMaxIdleTime time.Duration // Maximum idle time for connections
	MaxRetries      int           // Maximum number of connection retry attempts
	RetryDelay      time.Duration // Delay between retry attempts
}

// DefaultDBConfig returns a DBConfig with sensible defaults for SQLite.
func DefaultDBConfig(dsn string) *DBConfig {
	return &DBConfig{
		DSN:             dsn,
		MaxOpenConns:    25,
		MaxIdleConns:    10,
		ConnMaxLifetime: 30 * time.Minute,
		ConnMaxIdleTime: 5 * time.Minute,
		MaxRetries:      3,
		RetryDelay:      time.Second,
	}
}

// isRetryableError checks if an error is worth retrying.
// This checks SQLite error codes for transient locking/busy conditions.
func isRetryableError(err error) bool {
	if err == nil {
		return false
	}

	// Check if it's a sqlite3.Error
	var sqliteErr sqlite3.Error
	if errors.As(err, &sqliteErr) {
		switch sqliteErr.Code {
		case sqlite3.ErrBusy,
			sqlite3.ErrLocked:
			return true
		}

		// Check extended error codes for more specific busy conditions
		switch sqliteErr.ExtendedCode {
		case sqlite3.ErrBusyRecovery,
			sqlite3.ErrBusySnapshot:
			return true
		}
	}

	return false
}

// retryOperation executes an operation with retry logic for transient SQLite errors.
func retryOperation(ctx context.Context, logger *slog.Logger, config *DBConfig, operationName string, operation func() error) error {
	for attempt := 0; attempt <= config.MaxRetries; attempt++ {
		if attempt > 0 {
			logger.Info("retrying operation",
				slog.String("operation", operationName),
				slog.Int("attempt", attempt),
				slog.Int("max_retries", config.MaxRetries))

			select {
			case <-ctx.Done():
				return fmt.Errorf("context canceled during %s retry: %w", operationName, ctx.Err())
			case <-time.After(config.RetryDelay):
			}
		}

		err := operation()
		if err != nil {
			if isRetryableError(err) && attempt < config.MaxRetries {
				logger.Warn("retryable error during operation",
					slog.String("operation", operationName),
					slog.Any("error", err),
					slog.Int("attempt", attempt))
				continue
			}
			return fmt.Errorf("failed to %s: %w", operationName, err)
		}

		return nil
	}

	// This should never be reached due to the loop condition, but for safety
	return fmt.Errorf("unexpected retry loop exit for %s", operationName)
}

// openAndConfigureDB opens the database connection and configures the connection pool.
func openAndConfigureDB(config *DBConfig) (*sql.DB, error) {
	// Ensure the directory for the SQLite file exists
	dbDir := filepath.Dir(config.DSN)
	if err := os.MkdirAll(dbDir, 0755); err != nil {
		return nil, fmt.Errorf("failed to create database directory %s: %w", dbDir, err)
	}

	// Open database connection
	db, err := sql.Open("sqlite3", config.DSN+"?_foreign_keys=on") // Enable foreign key constraints
	if err != nil {
		return nil, fmt.Errorf("failed to open database: %w", err)
	}

	// Configure connection pool
	db.SetMaxOpenConns(config.MaxOpenConns)
	db.SetMaxIdleConns(config.MaxIdleConns)
	db.SetConnMaxLifetime(config.ConnMaxLifetime)
	db.SetConnMaxIdleTime(config.ConnMaxIdleTime)

	return db, nil
}

// NewDB initializes and returns a new database connection pool and runs migrations.
func NewDB(ctx context.Context, logger *slog.Logger, config *DBConfig) (*sql.DB, error) {
	db, err := openAndConfigureDB(config)
	if err != nil {
		return nil, err
	}

	// Test the actual connection with retry logic
	err = retryOperation(ctx, logger, config, "database connection", func() error {
		return db.PingContext(ctx)
	})
	if err != nil {
		db.Close()
		return nil, err
	}

	logger.Info("database connection established",
		slog.String("dsn", config.DSN),
		slog.Int("max_open_conns", config.MaxOpenConns),
		slog.Int("max_idle_conns", config.MaxIdleConns))

	// Execute schema with retry logic
	err = retryOperation(ctx, logger, config, "schema execution", func() error {
		_, err := db.ExecContext(ctx, ddl)
		return err
	})
	if err != nil {
		db.Close()
		return nil, err
	}

	logger.Info("database schema applied")
	return db, nil
}