// Package db opens Postgres and runs SQL migrations.
package db

import (
	"context"
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strings"

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

// Connect opens a pgx pool using DATABASE_URL-style DSN.
func Connect(ctx context.Context, databaseURL string) (*pgxpool.Pool, error) {
	pool, err := pgxpool.New(ctx, databaseURL)
	if err != nil {
		return nil, fmt.Errorf("pgxpool: %w", err)
	}
	if err := pool.Ping(ctx); err != nil {
		pool.Close()
		return nil, fmt.Errorf("ping: %w", err)
	}
	return pool, nil
}

// Migrate applies *.up.sql files under dir that are not yet recorded.
func Migrate(ctx context.Context, pool *pgxpool.Pool, dir string) 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("schema_migrations: %w", err)
	}

	entries, err := os.ReadDir(dir)
	if err != nil {
		return fmt.Errorf("read migrations: %w", err)
	}
	var ups []string
	for _, e := range entries {
		name := e.Name()
		if strings.HasSuffix(name, ".up.sql") {
			ups = append(ups, name)
		}
	}
	sort.Strings(ups)

	for _, name := range ups {
		version := strings.TrimSuffix(name, ".up.sql")
		var exists bool
		if err := pool.QueryRow(ctx,
			`SELECT EXISTS(SELECT 1 FROM schema_migrations WHERE version=$1)`, version,
		).Scan(&exists); err != nil {
			return err
		}
		if exists {
			continue
		}
		body, err := os.ReadFile(filepath.Join(dir, name))
		if err != nil {
			return err
		}
		// DDL (incl. CREATE EXTENSION) may not run inside a transaction.
		if _, err := pool.Exec(ctx, string(body)); err != nil {
			return fmt.Errorf("migrate %s: %w", name, err)
		}
		if _, err := pool.Exec(ctx,
			`INSERT INTO schema_migrations(version) VALUES ($1)`, version,
		); err != nil {
			return err
		}
	}
	return nil
}