/**
 * @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 IMF_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"],
}

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 = "List<File>";
        this.presentType = "html";
        this.args = [
            {
                "name": "Decode Quoted Words",
                "type": "boolean",
                "value": false
            }
        ];
    }

    /**
     * Basic Email Parser that displays the header and mime sections as files.
     * Args 0 boolean decode quoted words
     *
     * @param {string} input
     * @param {Object[]} args
     * @returns {File[]}
     */
    run(input, args) {
        if (!input) {
            return [];
        }
        let headerBody = ParseIMF.splitHeaderFromBody(input);
        let header = headerBody[0];
        let headerArray = ParseIMF.parseHeader(header);
        if (args[0] && headerBody.length > 0) {
            headerBody[0] = ParseIMF.replaceDecodeWord(headerBody[0]);
        }
        let retfiles = ParseIMF.walkMime(headerBody[1], headerArray, input.indexOf("\r") >= 0);
        let retval = [];
        let i = 0;
        retfiles.forEach(function(file){
            file = new File([file.data], "test"+String(i), {type: "text/plain"});
            retval.push(file);
            i++;
        });
        return retval;
    }

    /**
     * Displays the files in HTML for web apps.
     *
     * @param {File[]} files
     * @returns {html}
     */
    async present(files) {
        return await Utils.displayFilesAsHTML(files);
    }

    /**
     * Walks a MIME document and returns an array of Mime data and header objects.
     *
     * @param {string} input
     * @param {object} header
     * @returns {object[]}
     */
    static walkMime(input, header, rn) {
        let new_line_length = rn ? 2 : 1;
        const content_type_reg = /([^;]+);\s+boundary\=(['"])(.+?)\2/g;
        const inner_content_type_reg = /^([^;]+);\s+type\=(['"])(.+?)\2;\s+boundary\=(['"])(.+?)\4/g;
        let output_sections = [];
        if (header.hasOwnProperty("mime-version") || (header.hasOwnProperty("content-type") && header["content-type"][0].startsWith("multipart/"))) {
            let content_boundary = null;
            let idx = 3;
            if (header["content-type"][0].indexOf("type=") > 0) {
                content_boundary = inner_content_type_reg.exec(header["content-type"][0]);
                idx = 5;
            } else {
                content_boundary = content_type_reg.exec(header["content-type"][0]);
            }
            const boundary_str = "--".concat(content_boundary[idx]);
            let start = input.indexOf(boundary_str) + boundary_str.length + new_line_length;
            let end = input.indexOf(boundary_str.concat("--")) - new_line_length;
            let output = input.substring(start, end);
            let headerBody = ParseIMF.splitHeaderFromBody(output);
            let headerArray = ParseIMF.parseHeader(headerBody[0]);
            let parts = ParseIMF.walkMime(headerBody[1], headerArray, rn);
            parts.forEach(function(part){
                output_sections.push(part);
            });
        } else if (header.hasOwnProperty("content-type") && header.hasOwnProperty("content-transfer-encoding")) {
            const cont_type_data_reg = /^([^;]+);\s+charset\=(['"])(.+?)\2/g;
            let cont_type = cont_type_data_reg.exec(header["content-type"][0]);
            let val = ParseIMF.decodeMimeData(input, cont_type[3], header["content-transfer-encoding"][0]);
            return [{type:cont_type[1], data: val}];
        } else {
            throw new OperationError("Invalid Mime section");
        }
        return output_sections;
     }

    /**
     * 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(/_/g, " ");
            }
            return ParseIMF.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) {
        switch (contEnc) {
            case "base64":
                input = fromBase64(input);
                break;
            case "quoted-printable":
                input = Utils.byteArrayToUtf8(decodeQuotedPrintable(input));
                break;
            case "7bit":
            case "8bit":
            default:
                break;
        }
        if (charEnc && MIME_FORMAT.hasOwnProperty(charEnc.toLowerCase())) {
            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