import { getDB } from './db.js';

function getStore(storeName, mode = 'readonly') {

    const db = getDB();

    const tx = db.transaction(storeName, mode);

    return tx.objectStore(storeName);
}

export async function saveWords(lang, list, words) {

    const store = getStore('words', 'readwrite');

    for (const word of words) {

        store.put({
            key: `${lang}:${list}:${word.id}`,
            lang,
            list,
            ...word
        });
    }
}

export async function getWords(lang, list) {

    return new Promise((resolve) => {

        const store = getStore('words');

        const req = store.getAll();

        req.onsuccess = () => {

            const result = req.result.filter(
                w => w.lang === lang && w.list === list
            );

            resolve(result);
        };
    });
}

export async function getNextWord(lang, list) {

    const words = await getWords(lang, list);

    if (!words.length) {
        return null;
    }

    const today = new Date().toISOString().split('T')[0];

    let due = words.filter(word => {
        return !word.nextReview ||
            word.nextReview <= today;
    });

    if (!due.length) {
        due = words;
    }

    const random =
        Math.floor(Math.random() * due.length);

    return due[random];
}

export async function answerWord(word, answer) {

    const correct =
        word.answer.trim().toLowerCase() ===
        answer.trim().toLowerCase();

    const store =
        getStore('words', 'readwrite');

    const updated = { ...word };

    if (correct) {

        const days =
            updated.interval
                ? updated.interval * 2
                : 1;

        updated.interval = days;

        const d = new Date();
        d.setDate(d.getDate() + days);

        updated.nextReview =
            d.toISOString().split('T')[0];

    } else {

        updated.interval = 1;

        const d = new Date();
        d.setDate(d.getDate() + 1);

        updated.nextReview =
            d.toISOString().split('T')[0];
    }

    store.put(updated);

    await updateSessionStats(correct);

    await queueSync({
        wordId: word.id,
        lang: word.lang,
        list: word.list,
        correct,
        timestamp: Date.now()
    });

    return {
        correct
    };
}

async function queueSync(item) {

    const store =
        getStore('sync_queue', 'readwrite');

    store.add(item);
}

export async function updateSessionStats(correct) {

    const store =
        getStore('session', 'readwrite');

    const req =
        store.get('stats');

    req.onsuccess = () => {

        let stats = req.result;

        if (!stats) {
            stats = {
                key: 'stats',
                correct: 0,
                wrong: 0
            };
        }

        if (correct) {
            stats.correct++;
        } else {
            stats.wrong++;
        }

        store.put(stats);
    };
}

export async function getSessionStats() {

    return new Promise(resolve => {

        const store =
            getStore('session');

        const req =
            store.get('stats');

        req.onsuccess = () => {

            resolve(
                req.result || {
                    correct: 0,
                    wrong: 0
                }
            );
        };
    });
}

export async function resetSessionStats() {

    const store =
        getStore('session', 'readwrite');

    store.put({
        key: 'stats',
        correct: 0,
        wrong: 0
    });
}