import type { PiiData } from "../types";

const BASE64_ALPHABET =
  "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

const decodeBase64 = (value: string): Uint8Array => {
  const sanitized = value.replace(/=+$/, "");
  let buffer = 0;
  let bitsCollected = 0;
  const output: number[] = [];

  for (const character of sanitized) {
    const index = BASE64_ALPHABET.indexOf(character);
    if (index < 0) {
      continue;
    }

    buffer = (buffer << 6) | index;
    bitsCollected += 6;

    if (bitsCollected >= 8) {
      bitsCollected -= 8;
      output.push((buffer >> bitsCollected) & 0xff);
    }
  }

  return new Uint8Array(output);
};

const pemToArrayBuffer = (pem: string): ArrayBuffer => {
  const normalized = pem
    .replace(/-----BEGIN PUBLIC KEY-----/g, "")
    .replace(/-----END PUBLIC KEY-----/g, "")
    .replace(/\s+/g, "");
  const bytes = decodeBase64(normalized);
  const arrayBuffer = new ArrayBuffer(bytes.byteLength);
  new Uint8Array(arrayBuffer).set(bytes);
  return arrayBuffer;
};

const arrayBufferToBase64 = (buffer: ArrayBuffer): string => {
  const bytes = new Uint8Array(buffer);
  let output = "";

  for (let index = 0; index < bytes.length; index += 3) {
    const byte1 = bytes[index];
    const byte2 = bytes[index + 1];
    const byte3 = bytes[index + 2];

    const chunk = (byte1 << 16) | ((byte2 ?? 0) << 8) | (byte3 ?? 0);

    output += BASE64_ALPHABET[(chunk >> 18) & 63];
    output += BASE64_ALPHABET[(chunk >> 12) & 63];
    output +=
      typeof byte2 === "number" ? BASE64_ALPHABET[(chunk >> 6) & 63] : "=";
    output += typeof byte3 === "number" ? BASE64_ALPHABET[chunk & 63] : "=";
  }

  return output;
};

export const encryptPii = async (
  publicKeyPem: string,
  payload: PiiData
): Promise<string> => {
  const subtle = globalThis.crypto?.subtle;
  if (!subtle) {
    throw new Error(
      "No WebCrypto implementation found. Pass a custom piiEncryptor in SDK config for React Native."
    );
  }

  if (typeof TextEncoder === "undefined") {
    throw new Error(
      "TextEncoder is not available. Pass a custom piiEncryptor in SDK config for React Native."
    );
  }

  const key = await subtle.importKey(
    "spki",
    pemToArrayBuffer(publicKeyPem),
    {
      name: "RSA-OAEP",
      hash: "SHA-256",
    },
    false,
    ["encrypt"]
  );

  const encoded = new TextEncoder().encode(JSON.stringify(payload));
  const encrypted = await subtle.encrypt({ name: "RSA-OAEP" }, key, encoded);
  return arrayBufferToBase64(encrypted);
};