/**
 * @author n1474335 [n1474335@gmail.com]
 * @copyright Crown Copyright 2016
 * @license Apache-2.0
 */

import Operation from "../Operation";
import Utils from "../Utils";
import forge from "node-forge/dist/forge.min.js";
import OperationError from "../errors/OperationError";

/**
 * AES Decrypt operation
 */
class AESDecrypt extends Operation {

    /**
     * AESDecrypt constructor
     */
    constructor() {
        super();

        this.name = "AES Decrypt";
        this.module = "Ciphers";
        this.description = "Advanced Encryption Standard (AES) is a U.S. Federal Information Processing Standard (FIPS). It was selected after a 5-year process where 15 competing designs were evaluated.<br><br><b>Key:</b> The following algorithms will be used based on the size of the key:<ul><li>16 bytes = AES-128</li><li>24 bytes = AES-192</li><li>32 bytes = AES-256</li></ul><br><br><b>IV:</b> The Initialization Vector should be 16 bytes long. If not entered, it will default to 16 null bytes.<br><br><b>Padding:</b> In CBC and ECB mode, PKCS#7 padding will be used.<br><br><b>GCM Tag:</b> This field is ignored unless 'GCM' mode is used.";
        this.infoURL = "https://wikipedia.org/wiki/Advanced_Encryption_Standard";
        this.inputType = "string";
        this.outputType = "string";
        this.args = [
            {
                "name": "Key",
                "type": "toggleString",
                "value": "",
                "toggleValues": ["Hex", "UTF8", "Latin1", "Base64"]
            },
            {
                "name": "IV",
                "type": "toggleString",
                "value": "",
                "toggleValues": ["Hex", "UTF8", "Latin1", "Base64"]
            },
            {
                "name": "Mode",
                "type": "option",
                "value": ["CBC", "CFB", "OFB", "CTR", "GCM", "ECB"]
            },
            {
                "name": "Padding",
                "type": "option",
                "value": ["PKCS#7", "Null byte", "No padding"]
            },
            {
                "name": "Input",
                "type": "option",
                "value": ["Hex", "Raw"]
            },
            {
                "name": "Output",
                "type": "option",
                "value": ["Raw", "Hex"]
            },
            {
                "name": "GCM Tag",
                "type": "toggleString",
                "value": "",
                "toggleValues": ["Hex", "UTF8", "Latin1", "Base64"]
            }
        ];
    }

    /**
     * @param {string} input
     * @param {Object[]} args
     * @returns {string}
     *
     * @throws {OperationError} if cannot decrypt input or invalid key length
     */
    run(input, args) {
        const key = Utils.convertToByteArray(args[0].string, args[0].option),
            iv = Utils.convertToByteArray(args[1].string, args[1].option),
            gcmTag = Utils.convertToByteString(args[6].string, args[6].option),
            [,, mode, padding, inputType, outputType,] = args;

        if ([16, 24, 32].indexOf(key.length) < 0) {
            throw new OperationError(`Invalid key length: ${key.length} bytes

The following algorithms will be used based on the size of the key:
  16 bytes = AES-128
  24 bytes = AES-192
  32 bytes = AES-256`);
        }

        input = Utils.convertToByteString(input, inputType);

        const decipher = forge.cipher.createDecipher("AES-" + mode, key);
        decipher.start({
            iv: iv,
            tag: gcmTag
        });
        decipher.update(forge.util.createBuffer(input));
        var result = null;
        if (padding === "PKCS#7") {
            result = decipher.finish();
        } else if (padding === "Null byte") {
            result = decipher.finish(function(blockSize, buffer, decrypt) {
                if (decrypt) {
                    var len = buffer.length(), count = 0;
                    for(var i = len - 1; i >= 8; --i) {
                        if (buffer.at(i) == "00") {
                            count += 1;
                        } else {
                            break;
                        }
                    }
                    return buffer.truncate(count);
                }
            });
        } else {
            result = decipher.finish(function(blockSize, buffer, decrypt) {
                return true;
            });
        };

        if (result) {
            return outputType === "Hex" ? decipher.output.toHex() : decipher.output.getBytes();
        } else {
            throw new OperationError("Unable to decrypt input with these parameters.");
        }
    }

}

export default AESDecrypt;