string-hashing/sha2

import {copy} from '@array-like/copy';
import {NotImplementedError} from '@failure-abstraction/error';

import {sha512InitialState, sha512Call, sha512Finalize} from './sha512.js';

export class SHA512Hasher {
    constructor() {
        this._state = sha512InitialState();
        this._totalBits = 0;
        this._buffer = new Uint8Array(128);
        this._bufferBits = 0;
    }

    update(bytes, offset = 0, length = bytes.length - offset) {
        if ((this._bufferBits & 0xf_ff) !== 0) {
            throw new NotImplementedError('Cannot add bytes to bits (for now).');
        }

        this._totalBits += length << 3;

        const bufferBytes = this._bufferBits >> 3;

        if (bufferBytes > 0) {
            const bufferComplement = 128 - bufferBytes;

            if (length < bufferComplement) {
                // Buffer is not full
                copy(bytes, offset, offset + length, this._buffer, bufferBytes);
                this._bufferBits += length << 3;
                return this;
            }

            // Pad buffer with head of bytes and process it
            copy(bytes, offset, offset + bufferComplement, this._buffer, bufferBytes);
            sha512Call(this._state, this._buffer, 0);
            this._bufferBits = 0;
            offset += bufferComplement;
            length -= bufferComplement;
        }

        const fullBlocks = length >> 7;

        for (let i = 0; i < fullBlocks; ++i) {
            sha512Call(this._state, bytes, offset);
            offset += 128;
            length -= 128;
        }

        copy(bytes, offset, offset + length, this._buffer, 0);
        this._bufferBits = length << 3;
        return this;
    }

    digest(digest) {
        return sha512Finalize(
            this._buffer,
            this._totalBits,
            digest,
            this._bufferBits >> 3,
            0,
            this._bufferBits,
            this._state,
        );
    }
}