package scha

import (
	"errors"
	"crypto/sha512"
	"git.xdrm.io/schastsp/internal/xor"
)

/* (0) Static
---------------------------------------------------------*/
/* (1) Constants */
const HSIZE    uint16 = sha512.Size;
const HBITSIZE uint32 = uint32(HSIZE) * 8;




/* (1) Basic hash function
*
* @input<[]byte>					Byte array input
*
* @return digest<[]byte]>			Byte array digest
*
---------------------------------------------------------*/
func hash(input []byte) []byte{

	/* (1) Create sha512 hasher */
	hasher := sha512.New();

	/* (2) Defer memory cleanup */
	defer hasher.Reset();

	/* (3) Set input to be hashed */
	hasher.Write(input);

	/* (4) Extract digest */
	return hasher.Sum(nil);

}


/* (2) Public hashing interface
*
* @input<[]byte>					Byte array input
* @depth<uint>						Number of time to hash recursively (must be > 1)
* @salt<[]byte>						[OPT] Optional salt
* @pepper<[]byte>					[OPT] Optional pepper
*
* @return digest<[]byte]>			Byte array digest
* @return err<error>				If consistence error
*
---------------------------------------------------------*/
func Hash(input []byte, depth uint16, options... []byte) ([]byte, error) {


	/* (1) Manage errors errors
	---------------------------------------------------------*/
	/* (1) Avoid no depth (no hash at all) */
	if( depth < 1 ){
		return nil, errors.New("Cannot use a 'depth' of zero. This is inconsistent and means that no hash will be processed");
	}

	/* (2) Avoir empty input */
	if( len(input) < 1 ){
		return nil, errors.New("Cannot use an empty 'input'. This is inconsistent");
	}


	/* (2) Extract optional arguments
	---------------------------------------------------------*/
	/* (1) Optional salt */
	salt := make([]byte, 0)
	if len(options) > 0 { salt = options[0] }

	/* (2) Optional pepper */
	pepper := make([]byte, 0)
	if len(options) > 0 { pepper = options[0] }


	/* (3) Process cyclic hash
	---------------------------------------------------------*/
	/* (1) Initialise digest */
	digest := make([]byte, 0, HSIZE)

	/* (2) Process first hash + salt */
	digest = hash( xor.ByteArray(input, salt) )

	/* (3) Iterate @depth times */
	for depth--; depth > 0; depth-- {

		// Add Pepper only for last time
		if( depth == 1 ){
			digest = hash( xor.ByteArray(digest, pepper) )
		} else {
			digest = hash(digest)
		}

	}

	return digest, nil
}