(function(){
    var jqScreen = $('#screen_problem_list'),
        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
        problemCache = {}, // problem data cache, 3-level, keyed by: language, problem group, and problem identifier
        langs, Nlangs, // constants, set on init

        // ================================================================================
        // Hint processing: extract hints from the translations and return them in the
        // processed form, hint key -> translation language -> value
        // ================================================================================

        defaultHintCondition = function (translation) {
            // must contain at least one translation
            var key;
            if (!translation || typeof translation !== 'object') return false;
            for (key in translation) {
                if (!translation.hasOwnProperty(key)) continue;
                return true;
            }
            return false;
        },
        processHints = function (rawTranslations) {
            var defaultHint = {}, // here we put all the hints with their default translations
                allHints = {}, // the result
                allHintKeys = [],
                tr, key, i, lang, hint, h, j;
            // find the default hint translations, they will form the basis of default hints
            tr = chooseDefaultTranslation(rawTranslations, 'hint', defaultHintCondition) || {};
            for (key in tr) { // copy the hints
                if (!tr.hasOwnProperty(key)) continue;
                defaultHint[key] = tr[key];
                allHintKeys.push(key);
            }
            // copy any hints not in the default hints to the default hints
            for (i = langs.length - 1; i >= 0; i--) {
                lang = langs[i];
                tr = rawTranslations[lang];
                if (!tr || !defaultHintCondition(tr.hint)) continue; // skip unavailable translations or translations with no hints
                hint = tr.hint;
                for (key in hint) {
                    if (!hint.hasOwnProperty(key) || !hint[key]) continue;
                    if (!(key in defaultHint)) {
                        defaultHint[key] = hint[key];
                        allHintKeys.push(key);
                    }
                }
            }
            // create all translations for hints
            for (i = allHintKeys.length - 1; i >= 0; i--) {
                allHints[allHintKeys[i]] = {}; // create keys with no translations, we'll fill them in the next loop
            }
            for (i = langs.length - 1; i >= 0; i--) {
                lang = langs[i];
                tr = rawTranslations[lang];
                // set up hints
                if (!tr || !defaultHintCondition(tr.hint)) {
                    // there's no hint in the current language, copy the default in its entirety
                    for (j = allHintKeys.length - 1; j >= 0; j--) {
                        key = allHintKeys[j];
                        allHints[key][lang] = defaultHint[key];
                    }
                }
                else {
                    // make a copy of all hints, using the default hint value where a hint value is missing
                    h = tr.hint;
                    for (j = allHintKeys.length - 1; j >= 0; j--) {
                        key = allHintKeys[j];
                        allHints[key][lang] = h[key] || defaultHint[key];
                    }
                }
            }
            return allHints;
        },

        // ================================================================================
        // Plan processing: extract plans from the translations and return them in the
        // processed form, hint key -> translation language -> value
        // ================================================================================

        defaultPlanCondition = function (translation) {
            // default plan must be non-empty
            if (!translation || !(translation instanceof Array)) return false;
            return translation.length > 0;
        },
        /**
         * Structurally converts the plan definition into something that the
         * hint module can work with.
         * The input is the translations object from problem.json in the form
         * {'sl': { ..., 'plan': [hint1_sl, hint2_sl, ...]}, 'en': { ..., 'plan': [hint1_en, hint2_en, ...]}, ...}
         * The output is a list of hints in the plan, translations are in each hint:
         * [{'sl': hint1_sl, 'en': hint1_en, ...}, {'sl': hint2_sl, 'en': hint2_en}, ...]
         */
        processPlans = function (rawTranslations) {
            // find the default plan translation
            var defaultPlan = chooseDefaultTranslation(rawTranslations, 'plan', defaultPlanCondition) || [],
                result = [],
                i, lang, tr, plan, j, fragment;
            if (defaultPlan.length == 0) return result; // no plan
            // copy all translations from plan
            for (i = langs.length - 1; i >= 0; i--) {
                lang = langs[i];
                tr = rawTranslations[lang];
                // set up plan
                if (tr && defaultPlanCondition(tr.plan)) {
                    plan = tr.plan;
                }
                else {
                    // there's no plan in the current language, copy the default plan
                    plan = defaultPlan;
                }
                if (!(plan instanceof Array)) plan = [plan];
                for (j = 0; j < plan.length; j++) {
                    if (j < result.length) fragment = result[j];
                    else {
                        fragment = {};
                        result.push(fragment);
                    }
                    fragment[lang] = plan[j];
                }
            }
            // ensure each plan element has all translations
            for (j = result.length - 1; j >= 0; j--) {
                fragment = result[j];
                for (i = langs.length - 1; i >= 0; i--) {
                    lang = langs[i];
                    if (!fragment[lang]) fragment[lang] = 'Missing plan for language ' + lang + ' at index ' + j;
                }
            }
            return result;
        },

        // ================================================================================
        // Group + problems directory processing
        // ================================================================================

        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 every 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
                rawTranslations = data.translations || {},
                groups = data.groups || [],
                Ngroups = groups.length,
                html = [],
                problemReferences = [],
                group, problems, Nproblems, problem, i, j;
            var langDict = convertTranslations(rawTranslations, '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" ', ta(langDict.name), '></h1><hr>');
            html.push('<p class="language-description" ', ta(langDict.description), '></p>');
            // content: problem directory
            for (i = 0; i < Ngroups; i++) {
                group = groups[i] || {};
                groupDict = convertTranslations(group.translations, 'name', 'description'); // the group-level translations, added will
                // group content
                html.push('<h2 class="group-title" ', ta(groupDict.name), '></h2>');
                html.push('<p class="group-description" ', ta(groupDict.description), '></p>');
                html.push('<ul class="group-problems">');
                // problem content
                problems = group.problems || [];
                Nproblems = problems.length;
                for (j = 0; j < Nproblems; j++) {
                    problem = problems[j] || {};
                    problemDict = convertTranslations(problem.translations, 'name');
                    html.push('<li><a class="problem-', '' + problemReferences.length, '" ', ta(problemDict.name), '></a></li>');
                    problemReferences.push({'g': group.identifier || 'nogroup', 'p': problem.identifier || 'noproblem', 'id': problem.id});
                }
                html.push('</ul>');
            }

            return {
                'language': languageIdentifier, // 'prolog', 'python', ...
                'html': html.join(''), // the DOM structure (without textual content), as HTML text
                'refs': problemReferences, // array of problem info {g: group, p: problem, id: problem_id}, referenced from DOM <a> elements
                'commonDef': {
                    'hint': processHints(rawTranslations), // hint translations: keyword -> lang -> value
                    'hint_type': data.hint_type || {}
                }
            };
        },

        // ================================================================================
        // DOM instantiation.
        // The transition to problem solving takes place here, after the user clicks on a
        // problem and all the required data is loaded.
        // ================================================================================
        /**
         * Instantiates the screen from the given processed data.
         */
        createDom = function (data) { // data is the (cached) result of createLanguageData()
            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;
                }
                codeq.wait(
                        Q.all([
                            codeq.comms.getCurrentSolution(ref.id), // the current user's solution to the selected problem
                            getProblemData(language, ref.g, ref.p) // the (cached) result of processProblemData()
                        ])
                        .spread(function (userProblemData, generalProblemData) {
                            if (userProblemData.code !== 0) throw new Error('Failed to obtain user problem data, code: ' + userProblemData.code + ', message: ' + userProblemData.message);
                            if (!generalProblemData) throw new Error('General problem data is not defined');
                            codeq.globalStateMachine.transition(language, generalProblemData, data.commonDef, userProblemData.data.solution);
                        })
                    )
                    .fail(function (reason) {
                        codeq.log.error('Failed to obtain the problem definition: ' + reason, reason);
                        alert('Failed to obtain the problem definition: ' + reason);
                    })
                    .done();
            });
        },

        // ================================================================================
        // Problem definition processing
        // ================================================================================

        chooseDefaultTranslation = function (rawTranslations, translationKey, condition) {
            var tr = rawTranslations.en, // try English as the default
                lang;
            if (typeof condition !== 'function') condition = function (x) { return !!x; };
            if (tr && condition(tr[translationKey])) return tr[translationKey];
            for (lang in rawTranslations) { // find a translation with content
                if (!rawTranslations.hasOwnProperty(lang)) continue;
                tr = rawTranslations[lang];
                if (tr && condition(tr[translationKey])) return tr[translationKey];
            }
            return null; // default must be chosen by the caller
        },

        processProblemData = function (rawData, language, group, problem) {
            var rawTranslations = rawData.translations || {};
            return {
                'language': language,
                'group': group,
                'problem': problem,
                'id': rawData.id,
                'translations': convertTranslations(rawTranslations, 'title', 'name', 'slug', 'description'), // GUI translations: keyword -> lang -> value
                'hint': processHints(rawTranslations), // hint translations: keyword -> lang -> value
                'plan': processPlans(rawTranslations), // plan translations: keyword -> lang -> value
                'hint_type': rawData.hint_type || {}
            };
        },

        getProblemData = function (language, group, problem) {
            var langCache = problemCache[language],
                groupCache, cachedProblem, promise;
            if (langCache) {
                groupCache = langCache[group];
                if (!groupCache) {
                    groupCache = {};
                    langCache[group] = groupCache;
                }
            }
            else {
                langCache = {};
                problemCache[language] = langCache;
                groupCache = {};
                langCache[group] = groupCache;
            }
            cachedProblem = groupCache[problem];
            if (cachedProblem) return Q(cachedProblem);
            return codeq.comms.getProblemDef(language, group, problem).then(function (rawData) {
                var data = processProblemData(rawData, language, group, problem);
                groupCache[problem] = data;
                return data;
            });
        },

        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_list', {
        'enter': function(language){
            var data = null; // language data

            $("#navigation-problem_list").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-problem_list').css('display', 'none').removeClass("active");
        }
    });
})();