import { chacha20Block } from "./chacha20_block/chacha20_block.ts";
import { chacha20InitState } from "./chacha20_init_state/chacha20_init_state.ts";
import { xor } from "./util/util.ts";

export const KEY_BYTES: number = 32;
export const NONCE_BYTES: number = 12;

export function chacha20(
  out: Uint8Array,
  key: Uint8Array,
  nonce: Uint8Array,
  counter: number,
  text: Uint8Array
): void {
  const keyChunk: Uint8Array = new Uint8Array(64);
  const state: Uint32Array = new Uint32Array(16);
  const initialState: Uint32Array = chacha20InitState(key, nonce, counter);

  const loopEnd: number = Math.floor(text.byteLength / 64);
  const rmd: number = text.byteLength % 64;

  let textOffset: number = 0;
  let outOffset: number = 0;
  let i: number;

  for (i = 0; i < loopEnd; ++i, textOffset = i * 64, outOffset += 64) {
    chacha20Block(keyChunk, null!, null!, counter + i, state, initialState);
    
    xor(
      text.subarray(textOffset, textOffset + 64),
      keyChunk,
      64,
      out,
      outOffset
    );
  }

  if (rmd) {
    chacha20Block(
      keyChunk,
      null!,
      null!,
      counter + loopEnd,
      state,
      initialState
    );
    
    xor(
      text.subarray(loopEnd * 64, text.byteLength),
      keyChunk,
      rmd,
      out,
      outOffset
    );
  }

  keyChunk.fill(0x00, 0, keyChunk.byteLength);
  state.fill(0, 0, state.byteLength);
  initialState.fill(0, 0, initialState.byteLength);
}