// SPDX-License-Identifier: Unlicense

// Package test contains helpers for testing parsers.
package test

import (
	"io"

	"git.codemonkeysoftware.net/b/gigaparsec"
	"git.codemonkeysoftware.net/b/gigaparsec/cursor"
	"github.com/shoenig/test"
)

type errReaderAt struct {
	err error
}

func (r errReaderAt) ReadAt([]byte, int64) (int, error) {
	return 0, r.err
}

// ErrReaderAt returns an [io.ReaderAt] with a ReadAt method that always returns err.
func ErrReaderAt(err error) io.ReaderAt {
	return errReaderAt{err: err}
}

type errCursor[T any] struct {
	err error
	pos uint64
}

func (c errCursor[T]) Read([]T) (uint64, cursor.Cursor[T], error) {
	return 0, c, c.err
}

func (c errCursor[T]) At(pos uint64) cursor.Cursor[T] {
	c.pos = pos
	return c
}

func (c errCursor[T]) Pos() uint64 {
	return c.pos
}

// ErrCursor return a [cursor.Cursor] with a Read method that always returns err.
func ErrCursor[T any](err error) cursor.Cursor[T] {
	return errCursor[T]{err: err}
}

func StateIsAt[Input any](t test.T, s gigaparsec.State[Input], pos uint64) {
	test.EqOp(t, pos, s.Pos(), test.Sprintf("expected parser state to be at position %d, got %d", pos, s.Pos()))
}