package wego

import (
	"errors"
	"io"
	"net/http"
)

type maxBytesReader struct {
	w   http.ResponseWriter
	r   io.ReadCloser // underlying reader
	n   int64         // max bytes remaining
	err error         // sticky error
}

func (l *maxBytesReader) Read(p []byte) (n int, err error) {
	if l.err != nil {
		return 0, l.err
	}
	if len(p) == 0 {
		return 0, nil
	}
	if int64(len(p)) > l.n+1 {
		p = p[:l.n+1]
	}
	n, err = l.r.Read(p)

	if int64(n) <= l.n {
		l.n -= int64(n)
		l.err = err
		return n, err
	}

	n = int(l.n)
	l.n = 0

	type requestTooLarger interface {
		requestTooLarge()
	}
	if res, ok := l.w.(requestTooLarger); ok {
		res.requestTooLarge()
	}
	l.err = errors.New("http: request body too large")
	return n, l.err
}

func (l *maxBytesReader) Close() error {
	return l.r.Close()
}