/**
 * @fileoverview Net-related functions
 * @author <a href="mailto:Jeff@pcjs.org">Jeff Parsons</a> (@jeffpar)
 * @copyright © Jeff Parsons 2012-2017
 *
 * This file is part of PCjs, a computer emulation software project at <http://pcjs.org/>.
 *
 * PCjs is free software: you can redistribute it and/or modify it under the terms of the
 * GNU General Public License as published by the Free Software Foundation, either version 3
 * of the License, or (at your option) any later version.
 *
 * PCjs is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without
 * even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along with PCjs.  If not,
 * see <http://www.gnu.org/licenses/gpl.html>.
 *
 * You are required to include the above copyright notice in every modified copy of this work
 * and to display that copyright notice when the software starts running; see COPYRIGHT in
 * <http://pcjs.org/modules/shared/lib/defines.js>.
 *
 * Some PCjs files also attempt to load external resource files, such as character-image files,
 * ROM files, and disk image files. Those external resource files are not considered part of PCjs
 * for purposes of the GNU General Public License, and the author does not claim any copyright
 * as to their contents.
 */

"use strict";

if (NODE) {
    var fs = require("fs");
    var http = require("http");
    var path = require("path");
    var url = require("url");
}

class Net {
    /**
     * hasParm(sParm, sValue, req)
     *
     * @param {string} sParm
     * @param {string|null} sValue (pass null to check for the presence of ANY sParm)
     * @param {Object} [req] is the web server's (ie, Express) request object, if any
     * @return {boolean} true if the request Object contains the specified parameter/value, false if not
     *
     * TODO: Consider whether sParm === null should check for the presence of ANY parameter in Net.asPropagate.
     */
    static hasParm(sParm, sValue, req)
    {
        return (req && req.query && req.query[sParm] && (!sValue || req.query[sParm] == sValue));
    }

    /**
     * propagateParms(sURL, req)
     *
     * Propagates any "special" query parameters (as listed in Net.asPropagate) from the given
     * request object (req) to the given URL (sURL).
     *
     * We do not modify an sURL that already contains a '?' OR that begins with a protocol
     * (eg, http:, mailto:, etc), in order to keep this function simple, since it's only for
     * debugging purposes anyway.  I also considered blowing off any URLs with a '#' for the
     * same reason, since any hash string must follow any query parameters, but stripping
     * and re-appending the hash string is pretty trivial, so we do handle that.
     *
     * TODO: Make propagateParms() more general-purpose (eg, capable of detecting any URL
     * to the same site, and capable of merging any of our "special" query parameters with any
     * existing query parameters.
     *
     * @param {string|null} sURL
     * @param {Object} [req] is the web server's (ie, Express) request object, if any
     * @return {string} massaged sURL
     */
    static propagateParms(sURL, req)
    {
        if (sURL !== null && sURL.indexOf('?') < 0) {
            var i;
            var sHash = "";
            if ((i = sURL.indexOf('#')) >= 0) {
                sHash = sURL.substr(i);
                sURL = sURL.substr(0, i);
            }
            var match = sURL.match(/^([a-z])+:(.*)/);
            if (!match && req && req.query) {
                for (i = 0; i < Net.asPropagate.length; i++) {
                    var sQuery = Net.asPropagate[i];
                    var sValue;
                    if ((sValue = req.query[sQuery])) {
                        var sParm = (sURL.indexOf('?') < 0 ? '?' : '&');
                        sParm += sQuery + '=';
                        if (sURL.indexOf(sParm) < 0) sURL += sParm + encodeURIComponent(sValue);
                    }
                }
            }
            sURL += sHash;
        }
        return sURL;
    }

    /**
     * encodeURL(sURL, req, fDebug)
     *
     * Used to encodes any URLs presented on the current page, using this, um, simple 5-step process:
     *
     *  1) Replace any backslashes with slashes, in case the URL was derived from a file system path
     *  2) Remap links that begin with "archive/" to the corresponding URL at "http://archive.pcjs.org/"
     *  3) Use decodeURI() to eliminate escape sequences (like "%20") so that encodeURI() won't re-encode the "%"
     *  4) Use encodeURI() to transform all "htmlspecialchars" and reserved characters into the appropriate sequences
     *  5) Massage the result with Net.propagateParms(), so that any special parameters are passed along
     *
     * @param {string} sURL
     * @param {Object} req is the web server's (ie, Express) request object, if any
     * @param {boolean} [fDebug]
     * @return {string} encoded URL
     */
    static encodeURL(sURL, req, fDebug)
    {
        if (sURL) {
            sURL = sURL.replace(/\\/g, '/');
            if (!fDebug) {
                if (sURL.match(/^[^:?]*archive\//)) {
                    if (sURL.charAt(0) != '/') sURL = path.join(req.path, sURL);
                    /*
                     * NOTE: "http://archive.pcjs.org" is now "https://s3-us-west-2.amazonaws.com/archive.pcjs.org"
                     */
                    sURL = "https://s3-us-west-2.amazonaws.com/archive.pcjs.org" + sURL.replace("/archive/", "/");
                }
            }
            /*
             * If the incoming URL already contains URI-style escape sequences (eg, "%20" instead of spaces),
             * calling decodeURI() first will eliminate them, preventing encodeURI() from converting leading
             * "%" into "%25" and corrupting sequences like "%20" by turning them into "%2520".
             */
            return Net.propagateParms(encodeURI(decodeURI(sURL)), req);
        }
        return sURL;
    }

    /**
     * isRemote(sPath)
     *
     * TODO: Add support for FTP? HTTPS? Anything else?
     *
     * @param {string} sPath
     * @return {boolean} true if sPath is a (supported) remote path, false if not
     */
    static isRemote(sPath)
    {
        return (sPath.indexOf("http:") === 0);
    }

    /**
     * getStat(sURL, done)
     *
     * @param {string} sURL
     * @param {function(Error,Object)} done
     */
    static getStat(sURL, done)
    {
        var options = url.parse(sURL);
        options.method = "HEAD";
        options.path = options.pathname;    // TODO: Determine the necessity of aliasing this
        var req = http.request(options, function(res)
        {
            var err = null;
            var stat = null;
            // console.log(JSON.stringify(res.headers));
            if (res.statusCode == 200) {
                /*
                 * Apparently Node lower-cases response headers (at least incoming headers, despite
                 * lots of amusing whining by certain people in the Node community), which seems like
                 * a good thing, because that means I can do two simple key look-ups.
                 */
                var sLength = res.headers['content-length'];
                var sModified = res.headers['last-modified'];
                stat = {
                    size: sLength ? parseInt(sLength, 10) : -1,
                    mtime: sModified ? new Date(sModified) : null,
                    remote: true            // an additional property we provide to indicate this is not your normal stats object
                };
            } else {
                err = new Error("unexpected response code: " + res.statusCode);
            }
            done(err, stat);
        });
        req.on('error', function(err)
        {
            done(err, null);
        });
        req.end();
    }

    /**
     * getFile(sURL, sEncoding, done)
     *
     * TODO: Add support for FTP? HTTPS? Anything else?
     *
     * @param {string} sURL is the source file
     * @param {string|null} sEncoding is the encoding to assume, if any
     * @param {function(Error,number,(string|Buffer))} done receives an Error, an HTTP status code, and a Buffer (if any)
     */
    static getFile(sURL, sEncoding, done)
    {
        /*
         * Buffer objects are a fixed size, so my choices are: 1) call getStat() first, hope it returns
         * the true size, and then preallocate a buffer; or 2) create a new, larger buffer every time a new
         * chunk arrives.  The latter seems best.
         *
         * However, if an encoding is given, we'll simply concatenate all the data into a String and return
         * that instead.  Note that the incoming data is always a Buffer, but concatenation with a String
         * performs an implied "toString()" on the Buffer.
         *
         * WARNING: Even when an encoding is provided, we don't make any attempt to verify that the incoming
         * data matches that encoding.
         */
        var sFile = "";
        var bufFile = null;
        http.get(sURL, function(res)
        {
            res.on('data', function(data)
            {
                if (sEncoding) {
                    sFile += data;
                    return;
                }
                if (!bufFile) {
                    bufFile = data;
                    return;
                }
                /*
                 * We need to grow bufFile.  I used to do this myself, using the "copy" method:
                 *
                 *      buf.copy(targetBuffer, [targetStart], [sourceStart], [sourceEnd])
                 *
                 * which defaults to 0 for [targetStart] and [sourceStart], but the docs don't clearly
                 * define the default value for [sourceEnd].  They say "buffer.length", but there is no
                 * parameter here named "buffer".  Let's hope that in the case of "bufFile.copy(buf)"
                 * they meant "bufFile.length".
                 *
                 * However, it turns out this is moot, because there's a new kid in town: Buffer.concat().
                 *
                 *      buf = new Buffer(bufFile.length + data.length);
                 *      bufFile.copy(buf);
                 *      data.copy(buf, bufFile.length);
                 *      bufFile = buf;
                 */
                bufFile = Buffer.concat([bufFile, data], bufFile.length + data.length);
            }).on('end', function()
            {
                /*
                 * TODO: Decide what to do when res.statusCode is actually an error code (eg, 404), because
                 * in such cases, the file content will likely just be an HTML error page.
                 */
                if (res.statusCode < 400) {
                    done(null, res.statusCode, sEncoding? sFile : bufFile);
                } else {
                    done(new Error(sEncoding? sFile : bufFile), res.statusCode, null);
                }
            }).on('error', function(err)
            {
                done(err, res.statusCode, null);
            });
        });
    }

    /**
     * downloadFile(sURL, sFile, done)
     *
     * @param {string} sURL is the source file
     * @param {string} sFile is a fully-qualified target file
     * @param {function(Error,number)} done is a callback that receives an Error and a HTTP status code
     */
    static downloadFile(sURL, sFile, done)
    {
        var file = fs.createWriteStream(sFile);

        /*
         * http.get() accepts a "url" string in lieu of an "options" object; it automatically builds
         * the latter from the former using url.parse(). This is good, because it relieves me from
         * building my own "options" object, and also from wondering why http functions expect "options"
         * to contain a "path" property, whereas url.parse() returns a "pathname" property.
         *
         * Either the documentation isn't quite right for url.parse() or http.request() (the big brother
         * of http.get), or one of those "options" properties is aliased to the other, or...?
         */
        http.get(sURL, function(res)
        {
            res.on('data', function(data)
            {
                file.write(data);
            }).on('end', function()
            {
                file.end();
                /*
                 * TODO: We should try to update the file's modification time to match the 'last-modified'
                 * response header value, if any.
                 *
                 * TODO: Decide what to do when res.statusCode is actually an error code (eg, 404), because
                 * in such cases, the file content will likely just be an HTML error page.
                 */
                done(null, res.statusCode);
            }).on('error', function(err)
            {
                done(err, res.statusCode);
            });
        });
    }

    /**
     * getResource(sURL, dataPost, fAsync, done)
     *
     * Request the specified resource (sURL), and once the request is complete, notify done().
     *
     * @param {string} sURL
     * @param {Object|null} [dataPost] for a POST request (default is a GET request)
     * @param {boolean} [fAsync] is true for an asynchronous request
     * @param {function(string,string|null,number)} [done]
     * @return {Array|null} Array containing [sResource, nErrorCode], or null if no response yet
     */
    static getResource(sURL, dataPost, fAsync, done)
    {
        var nErrorCode = -1, sResource = null, response = null;

        if (Net.isRemote(sURL)) {
            /*
             * TODO: This code is nothing more than a band-aid.  It assumes the URL uses "http:"
             * (hence the call to getFile(), which only supports HTTP GET operations), it assumes
             * the requested data is UTF-8 string data (which is normally the case, because nearly
             * all our requests are for JSON files), it doesn't deal with dataPost, it assumes
             * that fAsync is true, and it performs very simplistic error code mapping.
             *
             * But, it gets the job done for what little we actually ask of it, when our machines
             * are running in the Node environment.
             */
            Net.getFile(sURL, "utf8", function(err, status, data) {
                if (done) done(sURL, data, err? status : 0);
            });
        } else {
            if (!Net.sServerRoot) {
                Net.sServerRoot = path.join(path.dirname(fs.realpathSync(__filename)), "../../../");
            }
            var sFile = path.join(Net.sServerRoot, sURL);
            if (fAsync) {
                fs.readFile(sFile, {encoding: "utf8"}, function(err, s)
                {
                    /*
                     * TODO: If err is set, is there an error code we should return (instead of -1)?
                     */
                    if (!err) {
                        sResource = s;
                        nErrorCode = 0;
                    }
                    if (done) done(sURL, sResource, nErrorCode);
                });
            } else {
                try {
                    sResource = fs.readFileSync(sFile, {encoding: "utf8"});
                    nErrorCode = 0;
                } catch (err) {
                    /*
                     * TODO: If err is set, is there an error code we should return (instead of -1)?
                     */
                    console.log(err.message);
                }
                if (done) done(sURL, sResource, nErrorCode);
                response = [sResource, nErrorCode];
            }
        }
        return response;
    }
}

/*
 * The following are (super-secret) commands that can be added to the URL to enable special features.
 *
 * Our super-secret command processor is affectionately call Gort, and while Gort doesn't understand commands
 * like "Klaatu barada nikto", it does understand commands like "debug" and "rebuild"; eg:
 *
 *      http://www.pcjs.org/?gort=debug
 *
 * hasParm() detects the presence of the specified command, and propagateParms() is a URL filter that ensures
 * any commands listed in Net.asPropagate are passed through to all other URLs on the same page; using any of these
 * commands also forces the page to be rebuilt and not cached (since we would never want a cached "index.html" to
 * contain/expose any of these commands).
 */
Net.GORT_COMMAND    = "gort";
Net.GORT_DEBUG      = "debug";          // use this to force uncompiled JavaScript even on a Release server
Net.GORT_NODEBUG    = "nodebug";        // use this to force uncompiled JavaScript but with DEBUG code disabled
Net.GORT_RELEASE    = "release";        // use this to force the use of compiled JavaScript even on a Debug server
Net.GORT_REBUILD    = "rebuild";        // use this to force the "index.html" in the current directory to be rebuilt

Net.REVEAL_COMMAND  = "reveal";
Net.REVEAL_PDFS     = "pdfs";

/*
 * This is a list of the URL parameters that propagateParms() will propagate from the requester's URL to
 * other URLs provided by the requester.
 */
Net.asPropagate     = [Net.GORT_COMMAND, "autostart"];
Net.sServerRoot     = null;

if (NODE) module.exports = Net;