package database

import (
	"database/sql"
	"fmt"
	"log"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"time"

	_ "github.com/lib/pq"
)

var DB *sql.DB

func InitDB() {
	var err error
	connStr, err := BuildConnectionString()
	if err != nil {
		log.Fatalf("Configuration error: %v", err)
	}

	DB, err = sql.Open("postgres", connStr)
	if err != nil {
		log.Fatalf("Error opening database: %v", err)
	}

	// Connection Pool Settings
	// Adjust these values based on your production load and database resources
	DB.SetMaxOpenConns(25)                 // Limit total connections
	DB.SetMaxIdleConns(25)                 // Keep connections open for reuse
	DB.SetConnMaxLifetime(5 * time.Minute) // Recycle connections every 5 min (avoids stale connections dropped by firewalls)
	DB.SetConnMaxIdleTime(5 * time.Minute) // Close idle connections after 5 min

	if err = DB.Ping(); err != nil {
		log.Fatalf("Error connecting to database: %v", err)
	}

	log.Println("✅ Successfully connected to the database")
}

func BuildConnectionString() (string, error) {
	if dbURL := os.Getenv("DATABASE_URL"); dbURL != "" {
		log.Println("Using DATABASE_URL for connection")
		return dbURL, nil
	}

	return "", fmt.Errorf("DATABASE_URL environment variable not set")
}

func RunMigrations() {
	migrationDir, err := resolveMigrationDir()
	if err != nil {
		log.Printf("⚠️  Warning: Could not list migrations directory: %v", err)
		return
	}

	if err := ensureMigrationsTable(); err != nil {
		log.Fatalf("❌ Error ensuring migrations table: %v", err)
	}

	entries, err := os.ReadDir(migrationDir)
	if err != nil {
		log.Fatalf("❌ Error reading migrations directory: %v", err)
	}

	var files []os.DirEntry
	for _, entry := range entries {
		if entry.IsDir() || !strings.HasSuffix(entry.Name(), ".sql") {
			continue
		}
		files = append(files, entry)
	}

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

	warnDuplicateMigrationPrefixes(files)

	for _, file := range files {
		name := file.Name()
		if isMigrationApplied(name) {
			log.Printf("⏭️  Migration %s skipped (already tracked)", name)
			continue
		}

		path := filepath.Join(migrationDir, name)
		content, err := os.ReadFile(path)
		if err != nil {
			log.Fatalf("❌ Error reading migration file %s: %v", name, err)
		}

		log.Printf("📦 Running migration: %s", name)
		if err := executeMigration(name, string(content)); err != nil {
			log.Fatalf("❌ Error running migration %s: %v", name, err)
		}
		log.Printf("✅ Migration %s executed successfully", name)
	}

	log.Println("All migrations processed")
}

func resolveMigrationDir() (string, error) {
	candidateDirs := []string{"migrations", "../../migrations"}

	for _, dir := range candidateDirs {
		if _, err := os.ReadDir(dir); err == nil {
			return dir, nil
		}
	}

	return "", fmt.Errorf("migrations directory not found in any known location")
}

func ensureMigrationsTable() error {
	_, err := DB.Exec(`
		CREATE TABLE IF NOT EXISTS schema_migrations (
			filename TEXT PRIMARY KEY,
			applied_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
		)
	`)
	return err
}

func isMigrationApplied(filename string) bool {
	var exists bool
	err := DB.QueryRow("SELECT EXISTS(SELECT 1 FROM schema_migrations WHERE filename = $1)", filename).Scan(&exists)
	if err != nil {
		log.Fatalf("❌ Error checking migration %s: %v", filename, err)
	}
	return exists
}

func executeMigration(filename, sqlContent string) error {
	tx, err := DB.Begin()
	if err != nil {
		return err
	}
	defer tx.Rollback()

	if _, err := tx.Exec(sqlContent); err != nil {
		errStr := strings.ToLower(err.Error())
		if !strings.Contains(errStr, "already exists") {
			return err
		}
		log.Printf("⏭️  Migration %s skipped due to existing resources", filename)
	}

	if _, err := tx.Exec("INSERT INTO schema_migrations (filename) VALUES ($1)", filename); err != nil {
		return err
	}

	return tx.Commit()
}

func warnDuplicateMigrationPrefixes(files []os.DirEntry) {
	prefixCount := make(map[string]int)
	for _, file := range files {
		parts := strings.SplitN(file.Name(), "_", 2)
		if len(parts) == 2 {
			prefixCount[parts[0]]++
		}
	}

	for prefix, count := range prefixCount {
		if count > 1 {
			log.Printf("⚠️  Duplicate migration prefix detected (%s appears %d times)", prefix, count)
		}
	}
}