package incrt

import (
	"io"
	"time"

	logging "github.com/ipfs/go-log/v2"
)

var log = logging.Logger("incrt")

var now = time.Now

type ReaderDeadline interface {
	Read([]byte) (int, error)
	SetReadDeadline(time.Time) error
}

type incrt struct {
	rd ReaderDeadline

	waitPerByte time.Duration
	wait        time.Duration
	maxWait     time.Duration
}

// New creates an Incremental Reader Timeout, with minimum sustained speed of
// minSpeed bytes per second and with maximum wait of maxWait
func New(rd ReaderDeadline, minSpeed int64, maxWait time.Duration) io.Reader {
	return &incrt{
		rd:          rd,
		waitPerByte: time.Second / time.Duration(minSpeed),
		wait:        maxWait,
		maxWait:     maxWait,
	}
}

type errNoWait struct{}

func (err errNoWait) Error() string {
	return "wait time exceeded"
}
func (err errNoWait) Timeout() bool {
	return true
}

func (crt *incrt) Read(buf []byte) (int, error) {
	start := now()
	if crt.wait == 0 {
		return 0, errNoWait{}
	}

	err := crt.rd.SetReadDeadline(start.Add(crt.wait))
	if err != nil {
		log.Warnf("unable to set deadline: %+v", err)
	}

	n, err := crt.rd.Read(buf)

	crt.rd.SetReadDeadline(time.Time{})
	if err == nil {
		dur := now().Sub(start)
		crt.wait -= dur
		crt.wait += time.Duration(n) * crt.waitPerByte
		if crt.wait < 0 {
			crt.wait = 0
		}
		if crt.wait > crt.maxWait {
			crt.wait = crt.maxWait
		}
	}
	return n, err
}