const axios = require('axios');
const {DOMParser} = require('xmldom');
const UserError = require('vn-loopback/util/user-error');

module.exports = Self => {
    Self.remoteMethod('exchangeRateUpdate', {
        description: 'Updates the exchange rates from an XML feed',
        accessType: 'WRITE',
        accepts: [],
        http: {
            path: '/exchangeRateUpdate',
            verb: 'post'
        }
    });

    Self.exchangeRateUpdate = async(options = {}) => {
        const models = Self.app.models;
        const myOptions = {};
        Object.assign(myOptions, options);

        let createdTx = false;
        if (!myOptions.transaction) {
            myOptions.transaction = await Self.beginTransaction({});
            createdTx = true;
        }

        try {
            const response = await axios.get('http://www.ecb.europa.eu/stats/eurofxref/eurofxref-hist-90d.xml');
            const xmlData = response.data;

            const doc = new DOMParser({errorHandler: {warning: () => {}}})
                .parseFromString(xmlData, 'text/xml');
            const cubes = doc?.getElementsByTagName('Cube');
            if (!cubes || cubes.length === 0)
                throw new UserError('No cubes found. Exiting the method.');

            const maxDateRecord = await models.ReferenceRate.findOne({order: 'dated DESC'}, myOptions);
            const maxDate = maxDateRecord?.dated ? new Date(maxDateRecord.dated) : null;
            let lastProcessedDate = maxDate;

            for (const cube of Array.from(cubes)) {
                if (cube.nodeType === doc.ELEMENT_NODE && cube.attributes.getNamedItem('time')) {
                    const xmlDate = new Date(cube.getAttribute('time'));
                    const xmlDateWithoutTime = new Date(
                        xmlDate.getFullYear(),
                        xmlDate.getMonth(),
                        xmlDate.getDate()
                    );

                    if (!maxDate || xmlDateWithoutTime > maxDate) {
                        if (lastProcessedDate && xmlDateWithoutTime > lastProcessedDate) {
                            for (const code of ['USD', 'CNY', 'GBP']) {
                                const currency = await models.Currency.findOne(
                                    {where: {code}},
                                    myOptions
                                );
                                if (!currency)
                                    throw new UserError(`Currency not found for code: ${code}`);

                                await fillMissingDates(
                                    models, currency, lastProcessedDate, xmlDateWithoutTime, myOptions
                                );
                            }
                        }
                    }
                    for (const rateCube of Array.from(cube.childNodes)) {
                        if (rateCube.nodeType === doc.ELEMENT_NODE) {
                            const currencyCode = rateCube.getAttribute('currency');
                            const rate = rateCube.getAttribute('rate');
                            if (['USD', 'CNY', 'GBP'].includes(currencyCode)) {
                                const currency = await models.Currency.findOne(
                                    {where: {code: currencyCode}},
                                    myOptions
                                );
                                if (!currency)
                                    throw new UserError(`Currency not found for code: ${currencyCode}`);

                                const existingRate = await models.ReferenceRate.findOne({
                                    where: {currencyFk: currency.id, dated: xmlDateWithoutTime}
                                }, myOptions);

                                if (existingRate) {
                                    if (existingRate.value !== rate)
                                        await existingRate.updateAttributes({value: rate}, myOptions);
                                } else {
                                    await models.ReferenceRate.create({
                                        currencyFk: currency.id,
                                        dated: xmlDateWithoutTime,
                                        value: rate
                                    }, myOptions);
                                }
                            }
                        }
                    }

                    lastProcessedDate = xmlDateWithoutTime;
                }
            }

            if (createdTx)
                await myOptions.transaction.commit();
        } catch (error) {
            if (createdTx)
                await myOptions.transaction.rollback();

            throw error;
        }
    };

    async function getLastValidRate(models, currencyId, date, myOptions) {
        return models.ReferenceRate.findOne({
            where: {currencyFk: currencyId, dated: {lt: date}},
            order: 'dated DESC'
        }, myOptions);
    }

    async function fillMissingDates(models, currency, startDate, endDate, myOptions) {
        const cursor = new Date(startDate);
        cursor.setDate(cursor.getDate() + 1);
        while (cursor < endDate) {
            const existingRate = await models.ReferenceRate.findOne({
                where: {currencyFk: currency.id, dated: cursor}
            }, myOptions);

            if (!existingRate) {
                const lastValid = await getLastValidRate(models, currency.id, cursor, myOptions);
                if (lastValid) {
                    await models.ReferenceRate.create({
                        currencyFk: currency.id,
                        dated: new Date(cursor),
                        value: lastValid.value
                    }, myOptions);
                }
            }
            cursor.setDate(cursor.getDate() + 1);
        }
    }
};