package store

import (
	"context"
	"database/sql"
	"embed"
	"fmt"
	"sort"
	"strings"
)

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

// MigrationVersion returns the name of the highest applied migration
// (e.g. "0005_node_capacity.sql"). Returns ("", nil) if no migrations
// have been applied (fresh or empty database).
func MigrationVersion(ctx context.Context, db *sql.DB) (string, error) {
	var name string
	err := db.QueryRowContext(ctx, `SELECT name FROM schema_migrations ORDER BY name DESC LIMIT 1`).Scan(&name)
	if err == sql.ErrNoRows {
		return "", nil
	}
	if err != nil {
		return "", fmt.Errorf("query migration version: %w", err)
	}
	return name, nil
}

func migrate(db *sql.DB) error {
	entries, err := migrationsFS.ReadDir("migrations")
	if err != nil {
		return fmt.Errorf("read migrations dir: %w", err)
	}
	names := make([]string, 0, len(entries))
	for _, e := range entries {
		if !e.IsDir() && strings.HasSuffix(e.Name(), ".sql") {
			names = append(names, e.Name())
		}
	}
	sort.Strings(names)

	if _, err := db.ExecContext(context.Background(), `CREATE TABLE IF NOT EXISTS schema_migrations (name TEXT PRIMARY KEY, applied_at DATETIME NOT NULL)`); err != nil {
		return fmt.Errorf("create schema_migrations: %w", err)
	}

	for _, name := range names {
		var existing string
		err := db.QueryRowContext(context.Background(), `SELECT name FROM schema_migrations WHERE name = ?`, name).Scan(&existing)
		if err == nil {
			continue
		}
		if err != sql.ErrNoRows {
			return fmt.Errorf("check migration %s: %w", name, err)
		}
		sqlBytes, err := migrationsFS.ReadFile("migrations/" + name)
		if err != nil {
			return fmt.Errorf("read migration %s: %w", name, err)
		}
		if _, err := db.ExecContext(context.Background(), string(sqlBytes)); err != nil {
			return fmt.Errorf("apply migration %s: %w", name, err)
		}
		if _, err := db.ExecContext(context.Background(), `INSERT INTO schema_migrations (name, applied_at) VALUES (?, datetime('now'))`, name); err != nil {
			return fmt.Errorf("record migration %s: %w", name, err)
		}
	}
	return nil
}