function throttledDebounce(callback, maxDebounceTimes, debounceDelay) {
    let debounceTimeout;
    let timesDebounced = 0;

    return function () {
        if (timesDebounced == maxDebounceTimes) {
            clearTimeout(debounceTimeout);
            timesDebounced = 0;
            callback();
            return;
        }

        clearTimeout(debounceTimeout);
        timesDebounced++;

        debounceTimeout = setTimeout(() => {
            timesDebounced = 0;
            callback();
        }, debounceDelay);
    };
};


async function fetchPageContent(pageSlug) {
    // TODO: handle non 200 status codes/time outs
    // TODO: add retries
    const response = await fetch(`/api/pages/${pageSlug}/content/`);
    const content = await response.text();

    return content;
}

function setupCarousels() {
    const carouselElements = document.getElementsByClassName("carousel-container");

    if (carouselElements.length == 0) {
        return;
    }

    for (let i = 0; i < carouselElements.length; i++) {
        const carousel = carouselElements[i];
        carousel.classList.add("show-right-cutoff");
        const itemsContainer = carousel.getElementsByClassName("carousel-items-container")[0];

        const determineSideCutoffs = () => {
            if (itemsContainer.scrollLeft != 0) {
                carousel.classList.add("show-left-cutoff");
            } else {
                carousel.classList.remove("show-left-cutoff");
            }

            if (Math.ceil(itemsContainer.scrollLeft) + itemsContainer.clientWidth < itemsContainer.scrollWidth) {
                carousel.classList.add("show-right-cutoff");
            } else {
                carousel.classList.remove("show-right-cutoff");
            }
        }

        const determineSideCutoffsRateLimited = throttledDebounce(determineSideCutoffs, 20, 100);

        itemsContainer.addEventListener("scroll", determineSideCutoffsRateLimited);
        document.addEventListener("resize", determineSideCutoffsRateLimited);

        afterContentReady(determineSideCutoffs);
    }
}

const minuteInSeconds = 60;
const hourInSeconds = minuteInSeconds * 60;
const dayInSeconds = hourInSeconds * 24;
const monthInSeconds = dayInSeconds * 30;
const yearInSeconds = monthInSeconds * 12;

function relativeTimeSince(timestamp) {
    const delta = Math.round((Date.now() / 1000) - timestamp);

    if (delta < minuteInSeconds) {
        return "1m";
    }
    if (delta < hourInSeconds) {
        return Math.floor(delta / minuteInSeconds) + "m";
    }
    if (delta < dayInSeconds) {
        return Math.floor(delta / hourInSeconds) + "h";
    }
    if (delta < monthInSeconds) {
        return Math.floor(delta / dayInSeconds) + "d";
    }
    if (delta < yearInSeconds) {
        return Math.floor(delta / monthInSeconds) + "mo";
    }

    return Math.floor(delta / yearInSeconds) + "y";
}

function updateRelativeTimeForElements(elements)
{
    for (let i = 0; i < elements.length; i++)
    {
        const element = elements[i];
        const timestamp = element.dataset.dynamicRelativeTime;

        if (timestamp === undefined)
            continue

        element.textContent = relativeTimeSince(timestamp);
    }
}

function setupDynamicRelativeTime() {
    const elements = document.querySelectorAll("[data-dynamic-relative-time]");
    const updateInterval = 60 * 1000;
    let lastUpdateTime = Date.now();

    updateRelativeTimeForElements(elements);

    const updateElementsAndTimestamp = () => {
        updateRelativeTimeForElements(elements);
        lastUpdateTime = Date.now();
    };

    const scheduleRepeatingUpdate = () => setInterval(updateElementsAndTimestamp, updateInterval);

    if (document.hidden === undefined) {
        scheduleRepeatingUpdate();
        return;
    }

    let timeout = scheduleRepeatingUpdate();

    document.addEventListener("visibilitychange", () => {
        if (document.hidden) {
            clearTimeout(timeout);
            return;
        }

        const delta = Date.now() - lastUpdateTime;

        if (delta >= updateInterval) {
            updateElementsAndTimestamp();
            timeout = scheduleRepeatingUpdate();
            return;
        }

        timeout = setTimeout(() => {
            updateElementsAndTimestamp();
            timeout = scheduleRepeatingUpdate();
        }, updateInterval - delta);
    });
}

function setupLazyImages() {
    const images = document.querySelectorAll("img[loading=lazy]");

    if (images.length == 0) {
        return;
    }

    function imageFinishedTransition(image) {
        image.classList.add("finished-transition");
    }

    afterContentReady(() => {
        setTimeout(() => {
            for (let i = 0; i < images.length; i++) {
                const image = images[i];

                if (image.complete) {
                    image.classList.add("cached");
                    setTimeout(() => imageFinishedTransition(image), 1);
                } else {
                    // TODO: also handle error event
                    image.addEventListener("load", () => {
                        image.classList.add("loaded");
                        setTimeout(() => imageFinishedTransition(image), 400);
                    });
                }
            }
        }, 1);
    });
}

function attachExpandToggleButton(collapsibleContainer) {
    const showMoreText = "Show more";
    const showLessText = "Show less";

    let expanded = false;
    const button = document.createElement("button");
    const icon = document.createElement("span");
    icon.classList.add("expand-toggle-button-icon");
    const textNode = document.createTextNode(showMoreText);
    button.classList.add("expand-toggle-button");
    button.append(textNode, icon);
    button.addEventListener("click", () => {
        expanded = !expanded;

        if (expanded) {
            collapsibleContainer.classList.add("container-expanded");
            button.classList.add("container-expanded");
            textNode.nodeValue = showLessText;
            return;
        }

        const topBefore = button.getClientRects()[0].top;

        collapsibleContainer.classList.remove("container-expanded");
        button.classList.remove("container-expanded");
        textNode.nodeValue = showMoreText;

        const topAfter = button.getClientRects()[0].top;

        if (topAfter > 0)
            return;

        window.scrollBy({
            top: topAfter - topBefore,
            behavior: "instant"
        });
    });

    collapsibleContainer.after(button);

    return button;
};


function setupCollapsibleLists() {
    const collapsibleLists = document.querySelectorAll(".list.collapsible-container");

    if (collapsibleLists.length == 0) {
        return;
    }

    for (let i = 0; i < collapsibleLists.length; i++) {
        const list = collapsibleLists[i];

        if (list.dataset.collapseAfter === undefined) {
            continue;
        }

        const collapseAfter = parseInt(list.dataset.collapseAfter);

        if (collapseAfter == -1) {
            continue;
        }

        if (list.children.length <= collapseAfter) {
            continue;
        }

        attachExpandToggleButton(list);

        for (let c = collapseAfter; c < list.children.length; c++) {
            const child = list.children[c];
            child.classList.add("collapsible-item");
            child.style.animationDelay = ((c - collapseAfter) * 20).toString() + "ms";
        }

        list.classList.add("ready");
    }
}

function setupCollapsibleGrids() {
    const collapsibleGridElements = document.querySelectorAll(".cards-grid.collapsible-container");

    if (collapsibleGridElements.length == 0) {
        return;
    }

    for (let i = 0; i < collapsibleGridElements.length; i++) {
        const gridElement = collapsibleGridElements[i];

        if (gridElement.dataset.collapseAfterRows === undefined) {
            continue;
        }

        const collapseAfterRows = parseInt(gridElement.dataset.collapseAfterRows);

        if (collapseAfterRows == -1) {
            continue;
        }

        const getCardsPerRow = () => {
            return parseInt(getComputedStyle(gridElement).getPropertyValue('--cards-per-row'));
        };

        const button = attachExpandToggleButton(gridElement);

        let cardsPerRow = 2;

        const resolveCollapsibleItems = () => {
            const hideItemsAfterIndex = cardsPerRow * collapseAfterRows;

            if (hideItemsAfterIndex >= gridElement.children.length) {
                button.style.display = "none";
            } else {
                button.style.removeProperty("display");
            }

            let row = 0;

            for (let i = 0; i < gridElement.children.length; i++) {
                const child = gridElement.children[i];

                if (i >= hideItemsAfterIndex) {
                    child.classList.add("collapsible-item");
                    child.style.animationDelay = (row * 40).toString() + "ms";

                    if (i % cardsPerRow + 1 == cardsPerRow) {
                        row++;
                    }
                } else {
                    child.classList.remove("collapsible-item");
                    child.style.removeProperty("animation-delay");
                }
            }
        };

        afterContentReady(() => {
            cardsPerRow = getCardsPerRow();
            resolveCollapsibleItems();
            gridElement.classList.add("ready");
        });

        window.addEventListener("resize", () => {
            const newCardsPerRow = getCardsPerRow();

            if (cardsPerRow == newCardsPerRow) {
                return;
            }

            cardsPerRow = newCardsPerRow;
            resolveCollapsibleItems();
        });
    }
}

const contentReadyCallbacks = [];

function afterContentReady(callback) {
    contentReadyCallbacks.push(callback);
}

const weekDayNames = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];
const monthNames = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December'];

function makeSettableTimeElement(element, hourFormat) {
    const fragment = document.createDocumentFragment();
    const hour = document.createElement('span');
    const minute = document.createElement('span');
    const amPm = document.createElement('span');
    fragment.append(hour, document.createTextNode(':'), minute);

    if (hourFormat == '12h') {
        fragment.append(document.createTextNode(' '), amPm);
    }

    element.append(fragment);

    return (date) => {
        const hours = date.getHours();

        if (hourFormat == '12h') {
            amPm.textContent = hours < 12 ? 'AM' : 'PM';
            hour.textContent = hours % 12 || 12;
        } else {
            hour.textContent = hours < 10 ? '0' + hours : hours;
        }

        const minutes = date.getMinutes();
        minute.textContent = minutes < 10 ? '0' + minutes : minutes;
    };
};

function timeInZone(now, zone) {
    let timeInZone;

    try {
        timeInZone = new Date(now.toLocaleString('en-US', { timeZone: zone }));
    } catch (e) {
        // TODO: indicate to the user that this is an invalid timezone
        console.error(e);
        timeInZone = now
    }

    const diffInHours = Math.round((timeInZone.getTime() - now.getTime()) / 1000 / 60 / 60);

    return { time: timeInZone, diffInHours: diffInHours };
}

function setupClocks() {
    const clocks = document.getElementsByClassName('clock');

    if (clocks.length == 0) {
        return;
    }

    const updateCallbacks = [];

    for (var i = 0; i < clocks.length; i++) {
        const clock = clocks[i];
        const hourFormat = clock.dataset.hourFormat;
        const localTimeContainer = clock.querySelector('[data-local-time]');
        const localDateElement = localTimeContainer.querySelector('[data-date]');
        const localWeekdayElement = localTimeContainer.querySelector('[data-weekday]');
        const localYearElement = localTimeContainer.querySelector('[data-year]');
        const timeZoneContainers = clock.querySelectorAll('[data-time-in-zone]');

        const setLocalTime = makeSettableTimeElement(
            localTimeContainer.querySelector('[data-time]'),
            hourFormat
        );

        updateCallbacks.push((now) => {
            setLocalTime(now);
            localDateElement.textContent = now.getDate() + ' ' + monthNames[now.getMonth()];
            localWeekdayElement.textContent = weekDayNames[now.getDay()];
            localYearElement.textContent = now.getFullYear();
        });

        for (var z = 0; z < timeZoneContainers.length; z++) {
            const timeZoneContainer = timeZoneContainers[z];
            const diffElement = timeZoneContainer.querySelector('[data-time-diff]');

            const setZoneTime = makeSettableTimeElement(
                timeZoneContainer.querySelector('[data-time]'),
                hourFormat
            );

            updateCallbacks.push((now) => {
                const { time, diffInHours } = timeInZone(now, timeZoneContainer.dataset.timeInZone);
                setZoneTime(time);
                diffElement.textContent = (diffInHours <= 0 ? diffInHours : '+' + diffInHours) + 'h';
            });
        }
    }

    const updateClocks = () => {
        const now = new Date();

        for (var i = 0; i < updateCallbacks.length; i++)
            updateCallbacks[i](now);

        setTimeout(updateClocks, (60 - now.getSeconds()) * 1000);
    };

    updateClocks();
}

async function setupPage() {
    const pageElement = document.getElementById("page");
    const pageContentElement = document.getElementById("page-content");
    const pageContent = await fetchPageContent(pageData.slug);

    pageContentElement.innerHTML = pageContent;

    try {
        setupClocks()
        setupCarousels();
        setupCollapsibleLists();
        setupCollapsibleGrids();
        setupDynamicRelativeTime();
        setupLazyImages();
    } finally {
        pageElement.classList.add("content-ready");

        for (let i = 0; i < contentReadyCallbacks.length; i++) {
            contentReadyCallbacks[i]();
        }

        setTimeout(() => {
            document.body.classList.add("page-columns-transitioned");
        }, 300);
    }
}

if (document.readyState === "loading") {
    document.addEventListener("DOMContentLoaded", setupPage);
} else {
    setupPage();
}