package storage

import (
	"database/sql"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"runtime"
	"sort"
	"strings"
	"sync"

	_ "modernc.org/sqlite"

	"github.com/stig/goaichat/internal/config"
)

// Manager handles access to the SQLite database storing chat sessions and metadata.
type Manager struct {
	path string
	cfg  config.StorageConfig
	mu   sync.Mutex
	db   *sql.DB
}

// NewManager constructs a Manager and ensures the data directory exists.
func NewManager(cfg config.Config) (*Manager, error) {
	path, err := resolvePath(cfg.Storage)
	if err != nil {
		return nil, err
	}

	if err := ensureDir(filepath.Dir(path)); err != nil {
		return nil, err
	}

	return &Manager{path: path, cfg: cfg.Storage}, nil
}

// Open lazily opens the SQLite database connection.
func (m *Manager) Open() (*sql.DB, error) {
	m.mu.Lock()
	defer m.mu.Unlock()

	if m.db != nil {
		return m.db, nil
	}

	dsn := fmt.Sprintf("file:%s?_pragma=journal_mode(WAL)&_busy_timeout=5000", m.path)
	db, err := sql.Open("sqlite", dsn)
	if err != nil {
		return nil, fmt.Errorf("open sqlite: %w", err)
	}

	if err := db.Ping(); err != nil {
		_ = db.Close()
		return nil, fmt.Errorf("ping sqlite: %w", err)
	}

	if err := applyMigrations(db); err != nil {
		_ = db.Close()
		return nil, err
	}

	m.db = db
	return db, nil
}

// Close releases the underlying database connection.
func (m *Manager) Close() error {
	m.mu.Lock()
	defer m.mu.Unlock()

	if m.db == nil {
		return nil
	}

	err := m.db.Close()
	m.db = nil
	return err
}

func resolvePath(cfg config.StorageConfig) (string, error) {
	if strings.TrimSpace(cfg.Path) != "" {
		return cfg.Path, nil
	}

	username := cfg.Username
	if username == "" {
		username = os.Getenv("USER")
		if username == "" {
			username = "default"
		}
	}

	base := filepath.Join("/var/log/goaichat", username)
	if cfg.BaseDir != "" {
		base = cfg.BaseDir
	}

	return filepath.Join(base, "goaichat.db"), nil
}

func ensureDir(dir string) error {
	if dir == "" {
		return errors.New("directory path cannot be empty")
	}
	if err := os.MkdirAll(dir, 0o700); err != nil {
		return fmt.Errorf("create data directory: %w", err)
	}

	if runtime.GOOS != "windows" {
		if err := os.Chmod(dir, 0o700); err != nil {
			return fmt.Errorf("chmod data directory: %w", err)
		}
	}

	return nil
}

func applyMigrations(db *sql.DB) error {
	migrationsFS := os.DirFS("internal/storage/migrations")

	entries, err := fs.ReadDir(migrationsFS, ".")
	if err != nil {
		return fmt.Errorf("read migrations: %w", err)
	}

	var files []string
	for _, entry := range entries {
		if entry.IsDir() {
			continue
		}
		if filepath.Ext(entry.Name()) != ".sql" {
			continue
		}
		files = append(files, entry.Name())
	}

	sort.Strings(files)

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

	for _, name := range files {
		data, readErr := fs.ReadFile(migrationsFS, name)
		if readErr != nil {
			_ = tx.Rollback()
			return fmt.Errorf("read migration %s: %w", name, readErr)
		}

		if _, execErr := tx.Exec(string(data)); execErr != nil {
			_ = tx.Rollback()
			return fmt.Errorf("apply migration %s: %w", name, execErr)
		}
	}

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

	return nil
}