// Package vwb provides utilities for working with variable-width byte slices,
// usually in the context of network requests.
package vwb

import (
	"fmt"
	"io"
)

func debugf(msg string, args ...any) {
	fmt.Printf("(encoding/vwb): "+msg, args...)
}

// Encode ...
func Encode(w io.Writer, input []byte) error {
	debugf("encoding %d bytes\n", len(input))
	buf := make([]byte, 0, len(input)+2)

	// Write the length of the input
	buf = append(buf, byte(len(input)>>8), byte(len(input)))
	// Write the input
	buf = append(buf, input...)

	debugf("writing %d bytes\n", len(buf))
	// Write the buffer to the writer
	if _, err := w.Write(buf); err != nil {
		return err
	}

	return nil
}

// Decode ...
func Decode(r io.Reader) ([]byte, error) {
	debugf("beginning decode\n")
	var lenbuf [2]byte
	// Read the length of the input
	if _, err := io.ReadFull(r, lenbuf[:]); err != nil {
		return nil, err
	}

	debugf("read %d bytes for length\n", lenbuf)
	// Calculate the length of the input
	length := int(lenbuf[0])<<8 | int(lenbuf[1])

	debugf("reading %d byte sized message\n", length)
	// Read the input
	data := make([]byte, length)
	if _, err := io.ReadFull(r, data); err != nil {
		return nil, err
	}

	debugf("done\n")
	return data, nil
}