// Package db provides database connectivity and migrations.
package db

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

	_ "github.com/lib/pq"
)

//go:embed migrations/*.sql
var migrationsFS embed.FS

// Config holds database connection configuration.
type Config struct {
	Host     string
	Port     int
	User     string
	Password string
	Database string
	SSLMode  string
}

// DefaultConfig returns config from environment defaults.
func DefaultConfig() Config {
	return Config{
		Host:     "postgres.databases.svc",
		Port:     5432,
		User:     "appuser",
		Password: "",
		Database: "rdev",
		SSLMode:  "disable",
	}
}

// DSN returns the connection string.
func (c Config) DSN() string {
	return fmt.Sprintf(
		"host=%s port=%d user=%s password=%s dbname=%s sslmode=%s",
		c.Host, c.Port, c.User, c.Password, c.Database, c.SSLMode,
	)
}

// DB wraps the sql.DB with additional functionality.
type DB struct {
	*sql.DB
	logger *slog.Logger
}

// New creates a new database connection and runs migrations.
func New(cfg Config, logger *slog.Logger) (*DB, error) {
	db, err := sql.Open("postgres", cfg.DSN())
	if err != nil {
		return nil, fmt.Errorf("open db: %w", err)
	}

	// Configure connection pool
	// MaxOpenConns: limit concurrent connections to avoid overloading database
	db.SetMaxOpenConns(25)
	// MaxIdleConns: maintain some connections for reuse
	db.SetMaxIdleConns(10)
	// ConnMaxLifetime: recycle connections to pick up config changes
	db.SetConnMaxLifetime(5 * time.Minute)
	// ConnMaxIdleTime: close idle connections to free resources
	db.SetConnMaxIdleTime(1 * time.Minute)

	// Verify connection
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()

	if err := db.PingContext(ctx); err != nil {
		return nil, fmt.Errorf("ping db: %w", err)
	}

	wrapped := &DB{DB: db, logger: logger}

	// Run migrations
	if err := wrapped.migrate(); err != nil {
		return nil, fmt.Errorf("migrate: %w", err)
	}

	return wrapped, nil
}

// migrate runs all pending migrations.
func (db *DB) migrate() error {
	// Create migrations table if not exists
	_, err := db.Exec(`
		CREATE TABLE IF NOT EXISTS schema_migrations (
			version VARCHAR(255) PRIMARY KEY,
			applied_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
		)
	`)
	if err != nil {
		return fmt.Errorf("create migrations table: %w", err)
	}

	// Get applied migrations
	applied := make(map[string]bool)
	rows, err := db.Query("SELECT version FROM schema_migrations")
	if err != nil {
		return fmt.Errorf("query migrations: %w", err)
	}
	defer func() { _ = rows.Close() }()

	for rows.Next() {
		var version string
		if err := rows.Scan(&version); err != nil {
			return fmt.Errorf("scan version: %w", err)
		}
		applied[version] = true
	}

	// Read migration files
	entries, err := migrationsFS.ReadDir("migrations")
	if err != nil {
		return fmt.Errorf("read migrations dir: %w", err)
	}

	// Sort by filename (version order)
	var files []string
	for _, e := range entries {
		if !e.IsDir() && strings.HasSuffix(e.Name(), ".sql") {
			files = append(files, e.Name())
		}
	}
	sort.Strings(files)

	// Apply pending migrations
	for _, file := range files {
		version := strings.TrimSuffix(file, ".sql")
		if applied[version] {
			continue
		}

		content, err := migrationsFS.ReadFile("migrations/" + file)
		if err != nil {
			return fmt.Errorf("read migration %s: %w", file, err)
		}

		db.logger.Info("applying migration", "version", version)

		tx, err := db.Begin()
		if err != nil {
			return fmt.Errorf("begin tx: %w", err)
		}

		if _, err := tx.Exec(string(content)); err != nil {
			_ = tx.Rollback()
			return fmt.Errorf("exec migration %s: %w", version, err)
		}

		if _, err := tx.Exec("INSERT INTO schema_migrations (version) VALUES ($1)", version); err != nil {
			_ = tx.Rollback()
			return fmt.Errorf("record migration %s: %w", version, err)
		}

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

		db.logger.Info("applied migration", "version", version)
	}

	return nil
}

// Close closes the database connection.
func (db *DB) Close() error {
	return db.DB.Close()
}