package db

import (
	"context"
	"errors"
	"fmt"
	"io/fs"
	"path"
	"sort"
	"strings"

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

// ApplyPostgresMigrations runs ordered *.up.sql from an embedded subtree (idempotent via schema_migrations).
func ApplyPostgresMigrations(ctx context.Context, pool *pgxpool.Pool, fsys fs.FS, subdir string) error {
	if _, err := pool.Exec(ctx, `CREATE TABLE IF NOT EXISTS schema_migrations (version TEXT NOT NULL PRIMARY KEY)`); err != nil {
		return fmt.Errorf("db: schema_migrations: %w", err)
	}
	entries, err := fs.ReadDir(fsys, subdir)
	if err != nil {
		return err
	}
	var ups []string
	for _, e := range entries {
		if e.IsDir() || !strings.HasSuffix(e.Name(), ".up.sql") {
			continue
		}
		ups = append(ups, e.Name())
	}
	sort.Strings(ups)
	for _, name := range ups {
		ver := strings.TrimSuffix(name, ".up.sql")
		var dummy int
		err := pool.QueryRow(ctx, `SELECT 1 FROM schema_migrations WHERE version = $1`, ver).Scan(&dummy)
		if err == nil {
			continue
		}
		if !errors.Is(err, pgx.ErrNoRows) {
			return err
		}
		body, err := fs.ReadFile(fsys, path.Join(subdir, name))
		if err != nil {
			return err
		}
		if _, err := pool.Exec(ctx, string(body)); err != nil {
			return fmt.Errorf("db: migrate %s: %w", name, err)
		}
		if _, err := pool.Exec(ctx, `INSERT INTO schema_migrations (version) VALUES ($1)`, ver); err != nil {
			return err
		}
	}
	return nil
}