/* CodeQ: an online programming tutor.
   Copyright (C) 2016 UL FRI

This program is free software: you can redistribute it and/or modify it under
the terms of the GNU Affero General Public License as published by the Free
Software Foundation, either version 3 of the License, or (at your option) any
later version.

This program 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 Affero General Public License for more
details.

You should have received a copy of the GNU Affero General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */

(function () {
    "use strict";
    // regular expressions for the templating function, etc.
    var regexpQuote = new RegExp('"', 'g'),
        regexpBackslash = new RegExp('\\\\', 'g'),
        regexpWhiteSpaceStart = new RegExp('^[ \r\n\t]+'),
        regexpWhiteSpaceEnd = new RegExp('[ \r\n\t]+$'),
        regexpWhiteSpaceTrim = new RegExp('^[ \\t\\r\\n]*(.*[^ \\t\\r\\n])[ \\t\\r\\n]*$', 'm'),
        regexpCR = new RegExp('\\r', 'g'),
        regexpLF = new RegExp('\\n', 'g'),
        regexpTab = new RegExp('\\t', 'g');

    // convert a string into its definition (javascript literal)
    var stringToDef = function (str) {
        return str.replace(regexpBackslash, '\\\\')
                  .replace(regexpQuote, '\\"')
                  .replace(regexpCR, '\\r')
                  .replace(regexpLF, '\\n')
                  .replace(regexpTab, '\\t');
    };

    var tokenize = function (line) {
        var result = [],
            N = line.length,
            i = 0, // character index into line
            storedAtom = null, // the previous atom, to decide whether to store a string or an object {key:'', value:''}
            atom = [], // currently parsed content
            isKeyValue = false,
            storeAtom = function () {
                if (atom.length == 0) return;
                if (storedAtom === null) storedAtom = atom.join('');
                else if (isKeyValue) {
                    result.push({'key': storedAtom, 'value': atom.join('')});
                    storedAtom = null;
                    isKeyValue = false;
                }
                else {
                    result.push(storedAtom);
                    storedAtom = atom.join('');
                }
                atom.length = 0;
            },
            c, q;

        while (i < N) {
            c = line[i++];
            switch (c) {
                // end-of-atom characters
                case ' ':
                case '\r':
                case '\n':
                case '\t':
                    storeAtom();
                    break;

                // escape character
                case '\\':
                    if (i < N) atom.push(line[i++]);
                    break;

                // key-value delimiter character
                case '=':
                    if (storedAtom) {
                        if (isKeyValue) atom.push(c);
                        else if (atom.length == 0) isKeyValue = true; // must have been a whitespace before "="
                        else {
                            storeAtom();
                            isKeyValue = true;
                        }
                    }
                    else atom.push(c); // "=" is delimiter only before the value, not before the key
                    break;

                // quoted string
                case '"':
                case "'":
                    stringConsume:
                    while (i < N) {
                        q = line[i++];
                        switch (q) {
                            case '\\':
                                if (i < N) atom.push(line[i++]);
                                break;
                            case c:
                                break stringConsume;
                            default:
                                atom.push(q);
                                break;
                        }
                    }
                    break;

                default:
                    atom.push(c);
                    break;
            }
        }
        // purge anything in cache
        storeAtom();
        if (storedAtom !== null) result.push(storedAtom);
        return result;
    };

    // resource tree, loaded from data/resources.json in the boot sequence
    var resources = {};

    var resolveResource = function (resourceName, resourceBranches) {
        var traversedPath = ['data'], // top-level directory
            branch = resources,
            candidate = null,
            i, fragment;
        if (!resourceName) {
            codeq.log.error('No resource name provided; path: "' + resourceBranches.join('/') + '"');
            return null;
        }
        if (branch[resourceName]) candidate = 'data/' + resourceName; // top-level match
        for (i = 0; i < resourceBranches.length; i++) {
            fragment = resourceBranches[i];
            branch = branch[fragment];
            if (!branch) {
                codeq.log.error('Resource sub-branch ' + fragment + ' does not exist; resource: "' + resourceName + '", path: "' + resourceBranches.join('/') + '"');
                break;
            }
            traversedPath.push(fragment);
            if (branch[resourceName]) candidate = traversedPath.join('/') + '/' + resourceName;
        }
        if (candidate) return codeq.ajaxPrefix + candidate;
        codeq.log.error('Resource ' + resourceName + ' was not found; path: "' + resourceBranches.join('/') + '"');
        return null;
    };

    var directiveHandlers = {
        'resource': function (code, tokens, templatePath) {
            code.push('_result.push("', resolveResource(tokens[1], templatePath) || 'data/broken.png', '");\n');
        },

        'img': function (code, tokens, templatePath) {
            var N = tokens.length,
                attrs = [],
                token, i;
            for (i = 1; i < N; i++) {
                token = tokens[i];
                if (!token || typeof token !== 'object') {
                    codeq.log.error('Invalid token at position ' + i + ' in @img');
                    continue;
                }
                switch (token.key) {
                    case 'src':
                        attrs.push('src="' + resolveResource(token.value, templatePath) + '"');
                        break;
                    case 'alt':
                        attrs.push('alt="' + codeq.escapeHtml(token.value) + '"');
                        break;
                    case 'class':
                        attrs.push('class="' + token.value + '"');
                        break;
                }
            }
            code.push('_result.push("<img ', attrs.join(' ').replace(regexpQuote, '\\"'), '>");\n');
        }
    };

    var templator = function (str, templatePath) {
        var templateName,
            f, parts, i, subparts, subpart,
            src = [ 'var _result = [], echo = function (s) { _result.push(s); };\n' ],
            atoms, j, atom, debugPrefix, s, r, tokens, handler;

        if (!templatePath) templatePath = [];
        templateName = templatePath.join('/');
        debugPrefix = '[' + templateName + ']';

        // remove comments
        parts = str.split('[%--'); // break on start-of-comment
        atoms = [ parts[0] ]; // first part is not a comment
        for (i = 1; i < parts.length; i++) { // iterate over start-of-comments
            atom = parts[i].split('--%]'); // break on end-of-comment
            if (atom.length > 1) { // if end-of-comment was encountered
                atoms.push(atom[1]); // add whatever is trailing it
                for (j = 2; j < atom.length; j++) { // re-add even dangling end-of-comments
                    atoms.push('--%]');
                    atoms.push(atom[j]);
                }
            }
        }

        // start processing
        parts = atoms.join('').split('[%');

        if (parts[0].length > 0) src.push('_result.push("', stringToDef(parts[0]), '");\n'); // the first part that doesn't begin with '[%'
        for (i = 1; i < parts.length; i++) { // for every part that begins with '[%'
            if (parts[i].slice(0, 2) === '--') { // a comment start
                subparts = parts[i].split('--%]'); // split at comment end
            }
            else { // a start of a statement or of a value reference
                subparts = parts[i].split('%]'); // there should be only one terminating '%]', find it
                subpart = subparts[0].replace(regexpWhiteSpaceStart, '').replace(regexpWhiteSpaceEnd, ''); // trim the white space
                if (subpart.length > 0) {
                    if (subpart[0] === '=') { // a value reference
                        s = subpart.slice(1);
                        r = regexpWhiteSpaceTrim.exec(s);
                        r = r && r[1] || s;
                        src.push('_result.push(typeof this.', r, ' === \'undefined\' ? \'', r, ' missing\' : this.', r, ');\n');
                    }
                    else if (subpart[0] === '@') { // a directive
                        tokens = tokenize(subpart.slice(1));
                        if (tokens.length === 0) {
                            codeq.log.error('An empty directive in ' + templateName);
                        }
                        else {
                            handler = directiveHandlers[tokens[0]];
                            if (!handler) {
                                codeq.log.error('An unknown directive in ' + templateName + ': ' + tokens[0]);
                            }
                            else {
                                handler(src, tokens, templatePath);
                            }
                        }
                    }
                    else { // javascript statement(s)
                        src.push(subpart, '\n');
                    }
                }
            }
            if ((subparts.length > 1) && (subparts[1].length > 0)) { // there's a trailing text
                src.push('_result.push("', stringToDef(subparts[1]), '");\n');
            }
        }
        src.push('return _result.join("");');
        try {
            f = new Function(src.join('')); // create a function based on the given template
        }
        catch (e) {
            codeq.log.error('createTemplate(): ' + debugPrefix + ' Failed to instantiate template function: ' + e + '\nfunction() {\n' + src.join('') + '\n}\n=== Created from template: ===\n' + str, e);
            throw e;
        }

        return function (args) {
            var esc = codeq.escapeHtml,
                escArgs = {},
                key;
            if ((typeof args === 'object') && (args !== null)) {
                for (key in args) {
                    if (!args.hasOwnProperty(key)) continue;
                    escArgs[key] = esc(args[key]);
                }
            }
            try {
                return f.apply(escArgs);
            }
            catch (e) {
                codeq.log.error('Error evaluating template ' + templateName + ' function: ' + e + '\nfunction() {\n' + src.join('') + '\nCreated from template:\n' + str, e);
                throw e;
            }
        };
    };

    codeq.template = {
        'setResources': function (newResources) {
            resources = newResources;
        },

        // instantiate a template
        'process': function (template, templatePath, args) {
            var fn = templator(template, templatePath);
            return fn(args);
        },

        // instantiate templates in a lang→template dictionary
        'processDictionary': function (dict, templatePath, args) {
            var lang;
            for (lang in dict) {
                if (!dict.hasOwnProperty(lang)) continue;
                dict[lang] = codeq.template.process(dict[lang], templatePath, args);
            }
        }
    };
})();