package main

import (
	"bufio"
	"encoding/binary"
	"io"
	"log"

	"github.com/klauspost/compress/zstd"
)

func mustWrite(w io.Writer, buf []byte) {
	if _, err := w.Write(buf); err != nil {
		log.Fatalln(err)
	}
}

func writer(dst io.Writer, sink chan Ent) {
	comp, err := zstd.NewWriter(dst)
	if err != nil {
		log.Fatalln(err)
	}
	bw := bufio.NewWriterSize(comp, 1<<17)
	num := make([]byte, 8)
	var name string
	for ent := range sink {
		name = ent.name[len(ent.name)-1]
		if len(ent.name) >= 1<<16 {
			panic("too long")
		}
		binary.BigEndian.PutUint16(num[:2], uint16(len(name)))
		mustWrite(bw, num[:2])
		mustWrite(bw, []byte(name))
		if len(ent.name) >= 1<<8 {
			panic("too deep")
		}
		mustWrite(bw, []byte{byte(len(ent.name) - 1)})
		binary.BigEndian.PutUint64(num, uint64(ent.mtime))
		mustWrite(bw, num)
		binary.BigEndian.PutUint64(num, uint64(ent.size))
		mustWrite(bw, num)
	}
	if err = bw.Flush(); err != nil {
		log.Fatalln(err)
	}
	if err = comp.Close(); err != nil {
		log.Fatalln(err)
	}
}