import * as sha3 from 'js-sha3';

export function isValidAddress(address: string): boolean {
    if (!/^0x[0-9a-fA-F]{40}$/.test(address)) {
        // Check if it has the basic requirements of an address
        return false;
    }

    if (/^0x[0-9a-f]{40}$/.test(address) || /^0x?[0-9A-F]{40}$/.test(address)) {
        // If it's all small caps or all all caps, return true
        return true;
    }

    // Otherwise check each case
    return verifyChecksum(address);
}

function verifyChecksum(address: string): boolean {
    // Check each case
    address = address.replace('0x','');

    var addressHash = sha3.keccak256(address.toLowerCase());

    for (var i = 0; i < 40; i++ ) {
        // The nth letter should be uppercase if the nth digit of casemap is 1
        if ((parseInt(addressHash[i], 16) > 7 && address[i].toUpperCase() !== address[i]) ||
            (parseInt(addressHash[i], 16) <= 7 && address[i].toLowerCase() !== address[i])) {
            return false;
        }
    }

    return true;
}