/**
 * @author bwhitn [brian.m.whitney@outlook.com]
 * @copyright Crown Copyright 2016
 * @license Apache-2.0
 */

import Operation from "../Operation";
import OperationError from "../errors/OperationError";
import cptable from "../vendor/js-codepage/cptable.js";
import {fromBase64} from "../lib/Base64";
import {decodeQuotedPrintable} from "../lib/QuotedPrintable";
import {MIME_FORMAT} from "../lib/ChrEnc";
import Utils from "../Utils";


// TODO: fix function header
/**
 * Return the conetent encoding for a mime section from a header object.
 * CONTENT_TYPE returns the content type of a mime header from a header object.
 * Returns the filename from a mime header object.
 * Returns the boundary value for the mime section from a header object.
 * @constant
 * @default
 */
const FIELD_ITEM = {
    FILENAME: [/filename=".*?([^~#%&*\][\\:<>?/|]+)"/, "content-disposition"],
    CONTENT_TYPE: [/\s*([^;\s]+)/, "content-type"],
    BOUNDARY: [/boundary="(.+?)"/, "content-type"],
    CHARSET: [/charset=([a-z0-9-]+)/, "content-type"],
    TRANSER_ENCODING: [/\s*([A-Za-z0-9-]+)\s*/, "content-transfer-encoding"],
}

/**
 * @constant
 * @default
 */
// TODO: should 8 bit and 7 bit be treated the same?
const DECODER = {
    "base64": function (input) {
        return fromBase64(input);
    },
    "quoted-printable": function (input) {
        return Utils.byteArrayToUtf8(decodeQuotedPrintable(input));
    },
    "7bit": function (input) {
        return input;
    },
    "8bit": function (input) {
        return input;
    },
}


class ParseIMF extends Operation {

    /**
     * Internet MessageFormat constructor
     */
    constructor() {
        super();
        this.name = "Parse Internet Message Format";
        this.module = "Default";
        this.description = ["Parser an IMF formatted messages following RFC5322.",
            "<br><br>",
            "Parses an IMF formated message. These often have the file extention &quot;.eml&quote; and contain the email headers and body. The output will be a file list of the headers and mime parts.",
        ].join("\n");
        this.infoURL = "https://tools.ietf.org/html/rfc5322";
        this.inputType = "string";
        this.outputType = "string";
        this.args = [];
    }

    /**
     * Basic Email Parser that displays the header and mime sections as files.
     *
     * @param {string} input
     * @param {Object[]} args
     * @returns {string}
     */
    run(input, args) {
        if (!input) {
            return "";
        }
        let headerBody = splitHeaderFromBody(input);
        let header = headerBody[0];
        let headerArray = parseHeader(header);
        if (true) {
            header = replaceDecodeWord(header);
        }
        return header;
    }

    /**
     * Breaks the header from the body and returns [header, body]
     *
     * @param {string} input
     * @returns {string[]}
     */
    static splitHeaderFromBody(input) {
        const emlRegex = /^([\x20-\xff\n\r\t]+?)(?:\r?\n){2}([\x20-\xff\t\n\r]*)/;
        let splitEmail = emlRegex.exec(input);
        if (splitEmail) {
            //TODO: Array splice vs shift?
            splitEmail.shift();
            return splitEmail;
        }
    }

    /**
     * Takes a string and decodes quoted words inside them
     * These take the form of =?utf-8?Q?Hello?=
     *
     * @param {string} input
     * @returns {string}
     */
    static replaceDecodeWord(input) {
        return input.replace(/=\?([^?]+)\?(Q|B)\?([^?]+)\?=/g, function (a, charEnc, contEnc, input) {
            contEnc = (contEnc === "B") ? "base64" : "quoted-printable";
            if (contEnc === "quoted-printable") {
                input = input.replace("_", " ");
            }
            return decodeMimeData(input, charEnc, contEnc);
        });
    }

    /**
     * Breaks a header into a object to be used by other functions.
     * It removes any line feeds or carriage returns from the values and
     * replaces it with a space.
     *
     * @param {string} input
     * @returns {object}
     */
    static parseHeader(input) {
        const sectionRegex = /([A-Z-]+):\s+([\x20-\x7e\r\n\t]+?)(?=$|\r?\n\S)/gi;
        let header = {}, section;
        while ((section = sectionRegex.exec(input))) {
            let fieldName = section[1].toLowerCase();
            let fieldValue = section[2].replace(/\n|\r/g, " ");
            if (header[fieldName]) {
                header[fieldName].push(fieldValue);
            } else {
                header[fieldName] = [fieldValue];
            }
        }
        return header;
    }

    /**
     * Return decoded MIME data given the character encoding and content encoding.
     *
     * @param {string} input
     * @param {string} charEnc
     * @param {string} contEnc
     * @returns {string}
     */
    static decodeMimeData(input, charEnc, contEnc) {
      //TODO: make exceptions for unknown charEnc and contEnc?
      input = DECODER[contEnc](input);
      if (charEnc) {
          input = cptable.utils.decode(MIME_FORMAT[charEnc.toLowerCase()], input);
      }
      return input;
    }

    /**
     * Returns a header item given a header object, itemName, and index number.
     *
     * @param {object} header
     * @param {object} FIELD_ITEM
     * @param {integer} fieldNum
     * @returns {string}
     */
    static getHeaderItem(header, fieldItem, fieldNum = 0){
        if (fieldItem[1] in header && header[fieldItem[1]].length > fieldNum) {
            let field = header[fieldItem[1]][fieldNum], item;
            if ((item = fieldItem[0].exec(field))) {
                return item[1];
            }
        }
    }

}

export default ParseIMF