// @flow

import BN from 'bn.js';
import bs58 from 'bs58';
import nacl from 'tweetnacl';
import {sha256} from 'crypto-hash';
import {Buffer} from 'buffer';

let naclLowLevel = nacl.lowlevel;

type PublicKeyNonce = [PublicKey, number]; // This type exists to workaround an esdoc parse error

/**
 * Maximum length of derived pubkey seed
 */
export const MAX_SEED_LENGTH = 32;

/**
 * A public key
 */
export class PublicKey {
  _bn: BN;

  /**
   * Create a new PublicKey object
   */
  constructor(value: number | string | Buffer | Uint8Array | Array<number>) {
    if (typeof value === 'string') {
      // assume base 58 encoding by default
      const decoded = bs58.decode(value);
      if (decoded.length != 32) {
        throw new Error(`Invalid public key input`);
      }
      this._bn = new BN(decoded);
    } else {
      this._bn = new BN(value);
    }

    if (this._bn.byteLength() > 32) {
      throw new Error(`Invalid public key input`);
    }
  }

  /**
   * Checks if two publicKeys are equal
   */
  equals(publicKey: PublicKey): boolean {
    return this._bn.eq(publicKey._bn);
  }

  /**
   * Return the base-58 representation of the public key
   */
  toBase58(): string {
    return bs58.encode(this.toBuffer());
  }

  /**
   * Return the Buffer representation of the public key
   */
  toBuffer(): Buffer {
    const b = this._bn.toArrayLike(Buffer);
    if (b.length === 32) {
      return b;
    }

    const zeroPad = Buffer.alloc(32);
    b.copy(zeroPad, 32 - b.length);
    return zeroPad;
  }

  /**
   * Returns a string representation of the public key
   */
  toString(): string {
    return this.toBase58();
  }

  /**
   * Derive a public key from another key, a seed, and a program ID.
   */
  static async createWithSeed(
    fromPublicKey: PublicKey,
    seed: string,
    programId: PublicKey,
  ): Promise<PublicKey> {
    const buffer = Buffer.concat([
      fromPublicKey.toBuffer(),
      Buffer.from(seed),
      programId.toBuffer(),
    ]);
    const hash = await sha256(new Uint8Array(buffer));
    return new PublicKey(Buffer.from(hash, 'hex'));
  }

  /**
   * Derive a program address from seeds and a program ID.
   */
  static async createProgramAddress(
    seeds: Array<Buffer | Uint8Array>,
    programId: PublicKey,
  ): Promise<PublicKey> {
    let buffer = Buffer.alloc(0);
    seeds.forEach(function (seed) {
      if (seed.length > MAX_SEED_LENGTH) {
        throw new Error(`Max seed length exceeded`);
      }
      buffer = Buffer.concat([buffer, Buffer.from(seed)]);
    });
    buffer = Buffer.concat([
      buffer,
      programId.toBuffer(),
      Buffer.from('ProgramDerivedAddress'),
    ]);
    let hash = await sha256(new Uint8Array(buffer));
    let publicKeyBytes = new BN(hash, 16).toArray(undefined, 32);
    if (is_on_curve(publicKeyBytes)) {
      throw new Error(`Invalid seeds, address must fall off the curve`);
    }
    return new PublicKey(publicKeyBytes);
  }

  /**
   * Find a valid program address
   *
   * Valid program addresses must fall off the ed25519 curve.  This function
   * iterates a nonce until it finds one that when combined with the seeds
   * results in a valid program address.
   */
  static async findProgramAddress(
    seeds: Array<Buffer | Uint8Array>,
    programId: PublicKey,
  ): Promise<PublicKeyNonce> {
    let nonce = 255;
    let address;
    while (nonce != 0) {
      try {
        const seedsWithNonce = seeds.concat(Buffer.from([nonce]));
        address = await this.createProgramAddress(seedsWithNonce, programId);
      } catch (err) {
        nonce--;
        continue;
      }
      return [address, nonce];
    }
    throw new Error(`Unable to find a viable program address nonce`);
  }
}

// Check that a pubkey is on the curve.
// This function and its dependents were sourced from:
// https://github.com/dchest/tweetnacl-js/blob/f1ec050ceae0861f34280e62498b1d3ed9c350c6/nacl.js#L792
function is_on_curve(p) {
  var r = [
    naclLowLevel.gf(),
    naclLowLevel.gf(),
    naclLowLevel.gf(),
    naclLowLevel.gf(),
  ];

  var t = naclLowLevel.gf(),
    chk = naclLowLevel.gf(),
    num = naclLowLevel.gf(),
    den = naclLowLevel.gf(),
    den2 = naclLowLevel.gf(),
    den4 = naclLowLevel.gf(),
    den6 = naclLowLevel.gf();

  naclLowLevel.set25519(r[2], gf1);
  naclLowLevel.unpack25519(r[1], p);
  naclLowLevel.S(num, r[1]);
  naclLowLevel.M(den, num, naclLowLevel.D);
  naclLowLevel.Z(num, num, r[2]);
  naclLowLevel.A(den, r[2], den);

  naclLowLevel.S(den2, den);
  naclLowLevel.S(den4, den2);
  naclLowLevel.M(den6, den4, den2);
  naclLowLevel.M(t, den6, num);
  naclLowLevel.M(t, t, den);

  naclLowLevel.pow2523(t, t);
  naclLowLevel.M(t, t, num);
  naclLowLevel.M(t, t, den);
  naclLowLevel.M(t, t, den);
  naclLowLevel.M(r[0], t, den);

  naclLowLevel.S(chk, r[0]);
  naclLowLevel.M(chk, chk, den);
  if (neq25519(chk, num)) naclLowLevel.M(r[0], r[0], I);

  naclLowLevel.S(chk, r[0]);
  naclLowLevel.M(chk, chk, den);
  if (neq25519(chk, num)) return 0;
  return 1;
}
let gf1 = naclLowLevel.gf([1]);
let I = naclLowLevel.gf([
  0xa0b0,
  0x4a0e,
  0x1b27,
  0xc4ee,
  0xe478,
  0xad2f,
  0x1806,
  0x2f43,
  0xd7a7,
  0x3dfb,
  0x0099,
  0x2b4d,
  0xdf0b,
  0x4fc1,
  0x2480,
  0x2b83,
]);
function neq25519(a, b) {
  var c = new Uint8Array(32),
    d = new Uint8Array(32);
  naclLowLevel.pack25519(c, a);
  naclLowLevel.pack25519(d, b);
  return naclLowLevel.crypto_verify_32(c, 0, d, 0);
}