package hmac

import "smesh.lol/web/common/jsbridge/schnorr"

const blockSize = 64

// Sum computes HMAC-SHA256(key, message).
func Sum(key, message []byte) [32]byte {
	// If key > blockSize, hash it.
	var k [blockSize]byte
	if len(key) > blockSize {
		h := schnorr.SHA256Sum(key)
		copy(k[:], h)
	} else {
		copy(k[:], key)
	}

	var ipad, opad [blockSize]byte
	for i := 0; i < blockSize; i++ {
		ipad[i] = k[i] ^ 0x36
		opad[i] = k[i] ^ 0x5c
	}

	// inner = SHA256(ipad || message)
	inner := []byte{:blockSize+len(message)}
	copy(inner, ipad[:])
	copy(inner[blockSize:], message)
	innerHash := schnorr.SHA256Sum(inner)

	// outer = SHA256(opad || inner_hash)
	outer := []byte{:blockSize+32}
	copy(outer[:blockSize], opad[:])
	copy(outer[blockSize:], innerHash)
	result := schnorr.SHA256Sum(outer)
	var out [32]byte
	copy(out[:], result)
	return out
}