package main

import (
	"context"
	"database/sql"
	"fmt"
	"log"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	"time"

	_ "github.com/go-sql-driver/mysql"
)

func main() {
	dsn := os.Getenv("TAPM_DATABASE_DSN")
	if dsn == "" {
		log.Fatal("TAPM_DATABASE_DSN is required")
	}
	directory := os.Getenv("TAPM_MIGRATIONS_DIR")
	if directory == "" {
		directory = "/app/migrations"
	}

	db, err := sql.Open("mysql", dsn)
	if err != nil {
		log.Fatal(err)
	}
	defer db.Close()

	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
	defer cancel()
	if err := db.PingContext(ctx); err != nil {
		log.Fatalf("database: %v", err)
	}

	var locked int
	if err := db.QueryRowContext(ctx, `SELECT GET_LOCK('tapm_schema_migrations', 30)`).Scan(&locked); err != nil {
		log.Fatal(err)
	}
	if locked != 1 {
		log.Fatal("could not acquire migration lock")
	}
	defer db.ExecContext(context.Background(), `SELECT RELEASE_LOCK('tapm_schema_migrations')`)

	if _, err := db.ExecContext(ctx, `CREATE TABLE IF NOT EXISTS schema_migrations (
		version BIGINT UNSIGNED NOT NULL PRIMARY KEY,
		applied_at TIMESTAMP(6) NOT NULL DEFAULT CURRENT_TIMESTAMP(6)
	) ENGINE=InnoDB`); err != nil {
		log.Fatal(err)
	}

	entries, err := os.ReadDir(directory)
	if err != nil {
		log.Fatal(err)
	}
	sort.Slice(entries, func(i, j int) bool { return entries[i].Name() < entries[j].Name() })
	for _, entry := range entries {
		if entry.IsDir() || !strings.HasSuffix(entry.Name(), ".sql") {
			continue
		}
		versionText, _, ok := strings.Cut(entry.Name(), "_")
		if !ok {
			log.Fatalf("migration %q must begin with a numeric version and underscore", entry.Name())
		}
		version, err := strconv.ParseUint(versionText, 10, 64)
		if err != nil {
			log.Fatalf("migration %q: %v", entry.Name(), err)
		}
		var applied int
		if err := db.QueryRowContext(
			ctx,
			`SELECT COUNT(*) FROM schema_migrations WHERE version = ?`,
			version,
		).Scan(&applied); err != nil {
			log.Fatal(err)
		}
		if applied != 0 {
			continue
		}

		body, err := os.ReadFile(filepath.Join(directory, entry.Name()))
		if err != nil {
			log.Fatal(err)
		}
		if _, err := db.ExecContext(ctx, string(body)); err != nil {
			log.Fatalf("apply %s: %v", entry.Name(), err)
		}
		fmt.Printf("applied migration %s\n", entry.Name())
	}
}