package fileUtilities

import (
	"fmt"
	"io"
)

func parityStream(in1, in2 io.Reader, out io.Writer) error {
	var err error
	byteSize := 1024
	done1 := false
	done2 := false
	for !done1 && !done2 {
		// get bytes from in1 and in2 and write the parity to buf
		// if either in1 or in2 is done, write the remaining bytes from the other to buf
		in1Bytes := make([]byte, byteSize)
		in2Bytes := make([]byte, byteSize)
		read1 := 0
		read2 := 0
		if !done1 {
			read1, err = in1.Read(in1Bytes)
			if err != nil {
				if err == io.EOF {
					done1 = true
				} else {
					return err
				}
			}
		}
		if !done2 {
			read2, err = in2.Read(in2Bytes)
			if err != nil {
				if err == io.EOF {
					done2 = true
				} else {
					return err
				}
			}
		}
		maxRead := read1
		if read2 > maxRead {
			maxRead = read2
		}

		parityBytes := make([]byte, maxRead)
		for i := 0; i < maxRead; i++ {
			parityBytes[i] = in1Bytes[i] ^ in2Bytes[i]
		}
		_, err := out.Write(parityBytes)
		if err != nil {
			return fmt.Errorf("error writing to buffer: %w", err)
		}
	}
	return nil
}