function showApplication(toggle) {
    if (toggle) {
        document.getElementById('real-body').classList.remove('d-none');
    } else {
        document.getElementById('real-body').classList.add('d-none');
    }
}

function showLoadingIndicator(toggle) {
    if (toggle) {
        document.getElementById('loading').classList.remove('d-none');
    } else {
        document.getElementById('loading').classList.add('d-none');
    }
}

function displayError(querySelector, category, ex) {
    console.error(ex);
    const errorDiv = document.querySelector(querySelector);
    const errorHeading = errorDiv.querySelector('.alert-heading');

    let message = ex.message;

    if (ex.hasOwnProperty('cause')) {
        if (ex.cause.hasOwnProperty('message')) {
            message += ': ' + ex.cause.message;
        } else {
            message += ex.cause;
        }
    }

    //clear all error text, but not heading
    const errorMessages = errorDiv.querySelectorAll('span');
    errorMessages.forEach(message => errorDiv.removeChild(message));

    //add new message and show the error alert
    const errorSpan = document.createElement('span');
    errorSpan.innerText = message;
    errorDiv.appendChild(errorSpan);

    errorHeading.innerText = category;
    errorDiv.classList.remove('d-none');
}

function displayFatalError(category, ex) {
    showApplication(false);
    showLoadingIndicator(false);
    displayError('#fatal-error', category, ex);
}

function displayNonFatalError(category, ex) {
    showApplication(true);
    showLoadingIndicator(false);
    displayError('#display-backup-error', category, ex);
}

function hideErrors() {
    document
        .querySelectorAll('#fatal-error, #display-backup-error')
        .forEach(el => el.classList.add('d-none'));
}

function importStylesheet(xsl) {
    //Firefox does not seem to report XML parsing errors into the
    //exception tree. So we catch here, log, and return some friendly
    //error.
    try {
        const xsltProcessor = new XSLTProcessor();
        xsltProcessor.importStylesheet(xsl);
        return xsltProcessor;
    } catch (cause) {
        console.error(cause);
        throw new Error('Stylesheet parsing failed', { cause });
    }
}

async function createXSLTProcessor() {
    return fetch("/MessageLog.xsl")
        .then(resp => {
            if (resp.ok)
                return resp.text();
            else
                throw new Error(resp.status + ' ' + resp.statusText);
        })
        .then(str => new DOMParser().parseFromString(str, "text/xml"))
        .then(importStylesheet)
        .catch(cause => {
            throw new Error('Could not load XSL stylesheet', { cause });
        });
}

function removeChildren(element) {
    while (element.hasChildNodes()) {
        element.removeChild(element.lastChild);
    }
}

function checkOverflow(elem) {
    const elemHeight = elem.scrollHeight;
    const parentHeight = elem.offsetHeight;
    return elemHeight > parentHeight;
}

function processFragment() {
    document
        .querySelectorAll('[data-bs-toggle="popover"]')
        .forEach(popover => new bootstrap.Popover(popover));

    document.querySelectorAll('.message-content div').forEach(div => {
        if (checkOverflow(div)) {
            div.parentElement.classList.add('overflow-icon');
        }
    });
}

function parseXML(xmlText) {
    const xmlDoc = parser.parseFromString(xmlText, "text/xml");
}

function displayBackup(xsltProcessor, file) {
    hideErrors();

    //document.getElementById('intro-card').classList.add('d-none');

    const chatDisplay = document.getElementById("chat-display");
    removeChildren(chatDisplay);

    file.text().then(xmlText => {
        document.getElementById('currently-viewing').innerText = file.name;
        const parser = new DOMParser();
        const xmlDoc = parser.parseFromString(xmlText, "text/xml");
        const errorNode = xmlDoc.querySelector('parsererror');

        if (!errorNode) {
            try {
                const fragment = xsltProcessor.transformToFragment(xmlDoc, document);
                chatDisplay.appendChild(fragment);
                processFragment();
            }
            catch (e) {
                displayNonFatalError('Could not load backup', e);
            }
        } else {
            const err = new Error(errorNode.firstChild.nodeValue);
            displayNonFatalError('Could not load backup', err);
        }

    });
}

function initEvents(xsltProcessor) {
    const selectFileButtons = document.querySelectorAll("#backup-file-button, #backup-file-button-card");
    const fileSelector = document.getElementById("backup-file");

    selectFileButtons.forEach(button => button.addEventListener("click", e => {
        fileSelector.click();
        e.preventDefault();
    }));

    fileSelector.addEventListener("change", async (e) => {
        const file = e.currentTarget.files[0];
        displayBackup(xsltProcessor, file);
    });
}

window.addEventListener('resize', () => {
    if (window.innerWidth <= 500) {
        document.querySelector('#chat-display table').classList.add('table-sm');
    } else {
        document.querySelector('#chat-display table').classList.remove('table-sm');
    }
});

window.addEventListener('DOMContentLoaded', async () => {
    createXSLTProcessor()
        .then(initEvents)
        .then(_ => {
            showLoadingIndicator(false);
            showApplication(true);
        })
        .catch(ex => displayFatalError('Initialiation Failed', ex));
});