import CID from "cids";
import { getCodec, rmPrefix } from "multicodec";
import { decode, toB58String } from "multihashes";

export function hexToUint8Array(hex: string): Uint8Array {
  hex = hex.startsWith("0x") ? hex.substr(2) : hex;
  if (hex.length % 2 !== 0)
    throw new Error("hex must have length that is multiple of 2");
  const arr = new Uint8Array(hex.length / 2);
  for (let i = 0; i < arr.length; i++) {
    arr[i] = parseInt(hex.substr(i * 2, 2), 16);
  }
  return arr;
}

const UTF_8_DECODER = new TextDecoder("utf-8");

/**
 * Returns the URI representation of the content hash for supported codecs
 * @param contenthash to decode
 */
export default function contenthashToUri(contenthash: string): string {
  const buff = hexToUint8Array(contenthash);
  const codec = getCodec(buff as Buffer); // the typing is wrong for @types/multicodec
  switch (codec) {
    case "ipfs-ns": {
      const data = rmPrefix(buff as Buffer);
      const cid = new CID(data);
      return `ipfs://${toB58String(cid.multihash)}`;
    }
    case "ipns-ns": {
      const data = rmPrefix(buff as Buffer);
      const cid = new CID(data);
      const multihash = decode(cid.multihash);
      if (multihash.name === "identity") {
        return `ipns://${UTF_8_DECODER.decode(multihash.digest).trim()}`;
      } else {
        return `ipns://${toB58String(cid.multihash)}`;
      }
    }
    default:
      throw new Error(`Unrecognized codec: ${codec}`);
  }
}