package database

import (
	"database/sql"
	"embed"
	"fmt"
	"io/fs"
	"sort"
	"strings"
)

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

func getAppliedMigrationsSet(db *sql.DB) (map[string]bool, error) {
	set := make(map[string]bool)

	rows, err := db.Query("SELECT id FROM migrations")

	if err != nil {
		return nil, err
	}

	defer rows.Close()

	for rows.Next() {
		var id string

		err := rows.Scan(&id)
		if err != nil {
			return nil, err
		}

		set[id] = true
	}

	err = rows.Err()
	if err != nil {
		return nil, err
	}

	return set, nil
}

func getMigrations() ([]string, error) {
	var items []string

	entries, err := migrationStorage.ReadDir("migrations")
	if err != nil {
		return nil, err
	}

	for _, entry := range entries {
		if !entry.IsDir() && strings.HasSuffix(entry.Name(), ".sql") {
			items = append(items, strings.TrimSuffix(entry.Name(), ".sql"))
		}
	}

	if err != nil {
		return nil, err
	}

	sort.Strings(items)

	return items, nil
}

func getMigrationContent(id string) (string, error) {
	content, err := fs.ReadFile(migrationStorage, "migrations/"+id+".sql")

	if err != nil {
		return "", err
	}

	return string(content), nil
}

func getPendingMigrations(db *sql.DB) ([]string, error) {
	var migrationsToRun []string

	migrationSet, err := getAppliedMigrationsSet(db)

	if err != nil {
		return nil, err
	}

	storedMigrations, err := getMigrations()

	if err != nil {
		return nil, fmt.Errorf("failed to load stored migrations: %w", err)
	}

	for _, storedMigration := range storedMigrations {
		if !migrationSet[storedMigration] {
			migrationsToRun = append(migrationsToRun, storedMigration)
		}
	}

	return migrationsToRun, nil
}