package store

import (
	"context"
	"embed"
	"fmt"
	"io/fs"

	"github.com/jackc/pgx/v5/pgxpool"
)

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

// migrate applies every embedded migration not yet recorded in
// schema_migrations, in file-name order, each in its own transaction.
func migrate(ctx context.Context, pool *pgxpool.Pool) error {
	if _, err := pool.Exec(ctx, `CREATE TABLE IF NOT EXISTS schema_migrations (
		version    text PRIMARY KEY,
		applied_at timestamptz NOT NULL DEFAULT now()
	)`); err != nil {
		return fmt.Errorf("create schema_migrations: %w", err)
	}
	entries, err := fs.ReadDir(migrationsFS, "migrations")
	if err != nil {
		return fmt.Errorf("read migrations: %w", err)
	}
	for _, e := range entries {
		name := e.Name()
		var applied bool
		if err := pool.QueryRow(ctx,
			`SELECT EXISTS (SELECT 1 FROM schema_migrations WHERE version = $1)`, name,
		).Scan(&applied); err != nil {
			return fmt.Errorf("check migration %s: %w", name, err)
		}
		if applied {
			continue
		}
		sql, err := migrationsFS.ReadFile("migrations/" + name)
		if err != nil {
			return fmt.Errorf("read migration %s: %w", name, err)
		}
		if err := applyMigration(ctx, pool, name, string(sql)); err != nil {
			return err
		}
	}
	return nil
}

func applyMigration(ctx context.Context, pool *pgxpool.Pool, name, sql string) error {
	tx, err := pool.Begin(ctx)
	if err != nil {
		return fmt.Errorf("begin migration %s: %w", name, err)
	}
	defer func() { _ = tx.Rollback(ctx) }()
	// Exec without arguments uses the simple protocol, which allows the
	// several statements a migration file contains.
	if _, err := tx.Exec(ctx, sql); err != nil {
		return fmt.Errorf("migration %s: %w", name, err)
	}
	if _, err := tx.Exec(ctx, `INSERT INTO schema_migrations (version) VALUES ($1)`, name); err != nil {
		return fmt.Errorf("record migration %s: %w", name, err)
	}
	if err := tx.Commit(ctx); err != nil {
		return fmt.Errorf("commit migration %s: %w", name, err)
	}
	return nil
}