import * as BigNumber from 'bignumber.js';
import * as ethUtil from 'ethereumjs-util';
import {assert} from './utils/assert';

/**
 * Elliptic Curve signature
 */
export interface ECSignature {
    v: number;
    r: string;
    s: string;
}

const MAX_DIGITS_IN_UNSIGNED_256_INT = 78;

export class ZeroEx {
    /**
     * Verifies that the elliptic curve signature `signature` was generated
     * by signing `data` with the private key corresponding to the `signer` address.
     */
    public static isValidSignature(data: string, signature: ECSignature, signer: ETHAddressHex): boolean {
        assert.isString('data', data);
        assert.isObject('signature', signature);
        assert.isETHAddressHex('signer', signer);

        const dataBuff = ethUtil.toBuffer(data);
        const msgHashBuff = ethUtil.hashPersonalMessage(dataBuff);
        try {
            const pubKey = ethUtil.ecrecover(msgHashBuff,
                signature.v,
                ethUtil.toBuffer(signature.r),
                ethUtil.toBuffer(signature.s));
            const retrievedAddress = ethUtil.bufferToHex(ethUtil.pubToAddress(pubKey));
            return retrievedAddress === signer;
        } catch (err) {
            return false;
        }
    }
    /** Generates pseudo-random 256 bits salt */
    public static generatePseudoRandomSalt(): BigNumber.BigNumber {
        // BigNumber.random returns a pseudo-random number between 0 & 1 with a passed in number of decimal places.
        // Source: https://mikemcl.github.io/bignumber.js/#random
        const randomNumber = BigNumber.random(MAX_DIGITS_IN_UNSIGNED_256_INT);
        const factor = new BigNumber(10).pow(MAX_DIGITS_IN_UNSIGNED_256_INT - 1);
        const salt = randomNumber.times(factor).round();
        return salt;
    }
}