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

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

	"git.eeqj.de/sneak/chat/internal/config"
	"git.eeqj.de/sneak/chat/internal/logger"
	"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
}

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

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")

	if _, err := s.db.ExecContext(ctx, "PRAGMA foreign_keys = ON"); 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.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)
	}

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

	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)

		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)
		}

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

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