(function(){
    var jqScreen = $('#screen_problem'),
        languageCache = {}, // keyed by language identifier: processed data about languages
        translationCache = [], // keys are autogenerated in ta(), a value is a dictionary of translations of a translation key for every language
        langs, Nlangs, // constants, set on init

        chooseTranslation = function (keyword, lang, currentDict, enDict, translations) {
            var tr = currentDict[keyword],
                otherLang;
            if (tr) return tr; // if there is a translation in the current dictionary: return it
            tr = enDict[keyword];
            if (tr) { // if there is a translation in the english dictionary: return it
                codeq.log.info('Translation for ' + keyword + ' not set for language ' + lang + ', using translation from en');
                return tr;
            }
            for (otherLang in translations) {
                if (!translations.hasOwnProperty(otherLang)) continue;
                tr = (translations[otherLang] || {})[keyword];
                if (tr) { // otherwise: return the first available translation in any language
                    codeq.log.info('Translation for ' + keyword + ' not set for language ' + lang + ', using translation from ' + otherLang);
                    return tr;
                }
            }
            return keyword + ' not set for language ' + lang;
        },

        /**
         * convert the input translations (arg0) for given keys (arg1..argN)
         * so each keys holds all its translations for ever language
         */
        convertTranslations = function () {
            var translations = arguments[0] || {},
                result = {},
                enDict = translations['en'] || {},
                lang, dict, i, keyword, l;
            // initialize result: one lang-dict per keyword
            for (i = arguments.length - 1; i > 0; i--) result[arguments[i]] = {};
            // convert translations: one keyword-dict per lang -> one lang-dict per keyword
            for (l = Nlangs - 1; l >= 0; l--) {
                lang = langs[l];
                dict = translations[lang] || {};
                for (i = arguments.length - 1; i > 0; i--) {
                    keyword = arguments[i];
//                    result[keyword][lang] = dict[keyword] || keyword + ' not set for language ' + lang;
                    result[keyword][lang] = chooseTranslation(keyword, lang, dict, enDict, translations);
                }
            }
            return result;
        },

        /**
         * Connect the given translations of a key with the DOM, returning
         * the string of arguments to use with a HTML tag which will contain
         * a translation chosen from the given dictionary.
         */
        ta = function (trObj) { // an object of the form: {'en': 'english content', 'sl': 'slovenska vsebina'}
            var result = ['data-dict="directory" data-tkey="', translationCache.length, '"'].join('');
            translationCache.push(trObj);
            return result;
        },

        /**
         * Assemble the display structure and translations from the server's
         * language.json for the given language identifier.
         */
        createLanguageData = function (data, languageIdentifier) { // data is the content of language.json
            var li = languageIdentifier, // a shorthand
                groups = data.groups || {},
                html = [],
                problemReferences = [],
                groupIdentifier, group, problems, problemIdentifier, problem;
            var langDict = convertTranslations(data.translations, 'name', 'description'), // this will be the resulting dictionary: multi-level keys that lead up to the lang-dict
                groupDict, problemDict;
            // title: HTML structure for "name" and "desc"
            html.push('<h1 class="language-title translatable" ', ta(langDict.name), '></h1><hr>');
            html.push('<div class="language-description translatable" ', ta(langDict.description), '></div>');
            // content: problem directory
            html.push('<ul class="language-problems">');
            for (groupIdentifier in groups) {
                if (!groups.hasOwnProperty(groupIdentifier)) continue;
                group = groups[groupIdentifier] || {};
                groupDict = convertTranslations(group.translations, 'name', 'description'); // the group-level translations, added will
                // group content
                html.push('<li><div class="group-title translatable" ', ta(groupDict.name), '></div>');
                html.push('<div class="group-description translatable" ', ta(groupDict.description), '></div>');
                html.push('<ul class="group-problems">');
                // problem content
                problems = group.problems || {};
                for (problemIdentifier in problems) {
                    if (!problems.hasOwnProperty(problemIdentifier)) continue;
                    problem = problems[problemIdentifier] || {};
                    problemDict = convertTranslations(problem.translations, 'name');
                    html.push('<li><a class="problem-', '' + problemReferences.length, ' translatable" ', ta(problemDict.name), '></a></li>');
                    problemReferences.push({'g': groupIdentifier, 'p': problemIdentifier});
                }
                html.push('</ul></li>');
            }
            html.push('</ul>');

            return {
                'language': languageIdentifier,
                'html': html.join(''),
                'refs': problemReferences,
                'hints': {}  // TODO: prepare common hints for the language
            };
        },

        /**
         * Instantiates the screen from the given processed data.
         */
        createDom = function (data) {
            var language = data.language;
            jqScreen.html(data.html);
            codeq.tr.translateDom(jqScreen);
            jqScreen.find('a').on('click', function () {
                var index = +$(this).attr('class').split(' ')[0].split('-')[1],
                    ref = data.refs[index];
                if (!ref) {
                    codeq.log.error('Clicked on a problem link having erroneous index: ' + index);
                    return;
                }
                // transition
                codeq.wait(
                    codeq.comms.getProblem(language, ref.g, ref.p)
                        .then(function (data) {
                            if (data.code !== 0) throw new Error('Failed to obtain problem data, code: ' + data.code + ', message: ' + data.message);
                            codeq.globalStateMachine.transition(language, data);
                        })
                    )
                    .fail(function (reason) {
                        codeq.log.error('Failed to obtain the problem definition: ' + reason, reason);
                        alert('Failed to obtain the problem definition: ' + reason);
                    })
                    .done();
            });
        },
        currentLanguage; // the currently active language

    // ================================================================================
    // Initialization, invoked from the boot sequence
    // ================================================================================

    codeq.on('init', function () {
        codeq.tr.registerDictionary('directory', translationCache);
        langs = codeq.availableLangs; // cache for easier access
        Nlangs = langs.length;
    });

    // ================================================================================
    // Register with the state machine
    // ================================================================================

    codeq.globalStateMachine.register('problem', {
        'enter': function(language){
            var data = null; // language data

            $('#navigation-login').css('display', '');
            $('#navigation-language').css('display', '');
            $("#navigation-problem").addClass("active").css('display', '');

            if (!language) language = currentLanguage; // This happens when we hit this with the back button

            if (currentLanguage !== language) {
                jqScreen.empty();
                currentLanguage = language;
                data = languageCache[language];
                if (data) {
                    createDom(data);
                }
                else {
                    codeq.wait(codeq.comms.getLanguageDef(language).then(function (rawData) {
                        var data = createLanguageData(rawData, language);
                        languageCache[language] = data;
                        createDom(data);
                    })).done();
                }
            }

            jqScreen.css('display', '');
        },
        'exit' : function(){
            jqScreen.css('display', 'none');
            $('#navigation-login').css('display', 'none');
            $('#navigation-language').css('display', 'none');
            $('#navigation-problem').css('display', 'none').removeClass("active");
        }
    });
})();