import {
  ArrayPrototypeJoin as join,
  ArrayPrototypePush as push,
  String,
  StringPrototypeSlice as slice,
  uncurryThis,
} from "ext:core/primordials";
import { createException } from "./events.js";
import { array, required, string } from "./idl.js";

const alphabet =
  "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
const charCode = uncurryThis(String.prototype.charCodeAt);
const fromCharCode = String.fromCharCode;
function invalidCharacter(): Error {
  return createException({
    message: "The string contains characters outside the Latin1 range.",
    name: "InvalidCharacterError",
  }) as Error;
}
function sextet(code: number): number {
  if (code >= 65 && code <= 90) return code - 65;
  if (code >= 97 && code <= 122) return code - 71;
  if (code >= 48 && code <= 57) return code + 4;
  if (code === 43) return 62;
  if (code === 47) return 63;
  return -1;
}

const api = {
  btoa(data: unknown): string {
    required(arguments.length, 1);
    data = string(data);
    const output = array<string>();
    let chunk = "";
    for (let index = 0; index < (data as string).length; index += 3) {
      const a = charCode(data as string, index);
      const b = index + 1 < (data as string).length
        ? charCode(data as string, index + 1)
        : -1;
      const c = index + 2 < (data as string).length
        ? charCode(data as string, index + 2)
        : -1;
      if (a > 255 || b > 255 || c > 255) throw invalidCharacter();
      chunk += alphabet[a >> 2];
      chunk += alphabet[((a & 3) << 4) | (b < 0 ? 0 : b >> 4)];
      chunk += b < 0
        ? "=="
        : c < 0
        ? alphabet[(b & 15) << 2] + "="
        : alphabet[((b & 15) << 2) | (c >> 6)] + alphabet[c & 63];
      if (chunk.length >= 4096) {
        push(output, chunk);
        chunk = "";
      }
    }
    if (chunk) push(output, chunk);
    return join(output, "");
  },

  atob(data: unknown): string {
    required(arguments.length, 1);
    data = string(data);
    const inputParts = array<string>();
    for (let index = 0; index < (data as string).length; index++) {
      const code = charCode(data as string, index);
      if (
        code === 9 || code === 10 || code === 12 || code === 13 || code === 32
      ) {
        continue;
      }
      push(inputParts, (data as string)[index]);
    }
    let input = join(inputParts, "");
    const length = input.length;
    if (
      length % 4 === 0 && length >= 2 &&
      charCode(input, length - 1) === 61 &&
      charCode(input, length - 2) === 61
    ) {
      input = slice(input, 0, length - 2);
    } else if (length % 4 === 0 && charCode(input, length - 1) === 61) {
      input = slice(input, 0, length - 1);
    }
    const remainder = input.length % 4;
    if (remainder === 1) throw invalidCharacter();
    const values = array<number>();
    for (let index = 0; index < input.length; index++) {
      const value = sextet(charCode(input, index));
      if (value < 0) throw invalidCharacter();
      values[index] = value;
    }
    const output = array<string>();
    let chunk = "";
    let index = 0;
    for (; index + 3 < values.length; index += 4) {
      chunk += fromCharCode(
        (values[index] << 2) | (values[index + 1] >> 4),
        ((values[index + 1] & 15) << 4) | (values[index + 2] >> 2),
        ((values[index + 2] & 3) << 6) | values[index + 3],
      );
      if (chunk.length >= 4096) {
        push(output, chunk);
        chunk = "";
      }
    }
    if (remainder === 2) {
      chunk += fromCharCode((values[index] << 2) | (values[index + 1] >> 4));
    } else if (remainder === 3) {
      chunk += fromCharCode(
        (values[index] << 2) | (values[index + 1] >> 4),
        ((values[index + 1] & 15) << 4) | (values[index + 2] >> 2),
      );
    }
    if (chunk) push(output, chunk);
    return join(output, "");
  },
};
const { atob, btoa } = api;
export { atob, btoa };