package erasureencode

import (
	"fmt"
)

func merkleSha256(inputHashes [][]byte) []byte {
	CHILD_NUM := 2

	hashesLen := len(inputHashes)
	if hashesLen == 0 {
		panic(fmt.Errorf("input must be at least one hash"))
	}
	hashLen := len(inputHashes[0])
	hashes := make([][]byte, hashesLen)
	copy(hashes, inputHashes)

	for true {
		for i := 0; i < hashesLen; i += CHILD_NUM {
			hashData := make([]byte, hashLen*CHILD_NUM)
			for j := 0; j < CHILD_NUM && i+j < hashesLen; j++ {
				copy(hashData[j*hashLen:], hashes[i+j])
			}
			hashes[i/CHILD_NUM] = sha256sum(hashData)
		}
		newLen := hashesLen / CHILD_NUM
		if hashesLen%CHILD_NUM > 0 {
			newLen += 1
		}
		hashes = hashes[0:newLen]
		hashesLen = newLen

		if hashesLen == 1 {
			return hashes[0]
		}
	}
	panic(fmt.Errorf("unexpected code path"))
}