package slow

import (
	"context"
	"io"

	"golang.org/x/time/rate"
)

type Reader struct {
	ctx     context.Context
	limiter *rate.Limiter
	r       io.Reader
}

var _ io.Reader = Reader{}

func NewReader(ctx context.Context, bps rate.Limit, r io.Reader) Reader {
	return Reader{
		ctx:     ctx,
		limiter: rate.NewLimiter(bps, 8192),
		r:       r,
	}
}

func (r Reader) Read(b []byte) (int, error) {
	n, err := r.r.Read(b)

	m := 0
	burst := r.limiter.Burst()
	for m < n {
		if err := r.limiter.WaitN(r.ctx, burst); err != nil {
			return n, err
		}
		m += burst
	}

	return n, err
}