import { addMeltEventListener, makeElement, createElHelpers, executeCallbacks, } from '../../internal/helpers/index.js';
import { dequal } from 'dequal';
import { derived, writable } from 'svelte/store';
import { safeOnMount } from '../../internal/helpers/lifecycle.js';
import { withGet } from '../../internal/helpers/withGet.js';
const defaults = {
    exclude: ['h1'],
    scrollOffset: 0,
    scrollBehaviour: 'smooth',
    activeType: 'lowest',
};
export function createTableOfContents(args) {
    const argsWithDefaults = { ...defaults, ...args };
    const { selector, exclude, activeType, scrollBehaviour, scrollOffset, headingFilterFn, scrollFn, } = argsWithDefaults;
    const { name } = createElHelpers('table-of-contents');
    // Variables
    const possibleHeadings = ['h1', 'h2', 'h3', 'h4', 'h5', 'h6'];
    let headingsList = [];
    let elementsList = [];
    /** Lookup to see which heading an element belongs to. */
    let elementHeadingLU = {};
    /** Lookup to see which parent headings a heading has. */
    let headingParentsLU = {};
    /** List of the active parent indexes. */
    const activeParentIdxs = withGet.writable([]);
    /** List of the indexes of the visible elements. */
    const visibleElementIdxs = withGet.writable([]);
    let elementTarget = null;
    let mutationObserver = null;
    let observer = null;
    const observer_threshold = 0.01;
    // Stores
    const activeHeadingIdxs = withGet(writable([]));
    const headingsTree = withGet(writable([]));
    // Helpers
    function generateInitialLists(elementTarget) {
        let headingsList = [];
        let elementsList = [];
        const includedHeadings = possibleHeadings.filter((h) => !exclude.includes(h));
        const targetHeaders = elementTarget?.querySelectorAll(includedHeadings.join(', '));
        // Create a unique ID for each heading which doesn't have one.
        targetHeaders?.forEach((el) => {
            if (!el.id) {
                const uniqueID = el.innerText
                    .replaceAll(/[^a-zA-Z0-9 ]/g, '')
                    .replaceAll(' ', '-')
                    .toLowerCase();
                el.id = `${uniqueID}`;
            }
            headingsList.push(el);
        });
        headingsList = [...headingsList];
        if (headingFilterFn) {
            headingsList = headingsList.filter((heading) => headingFilterFn(heading));
        }
        // Get all elements in our elementTarget and convert it from an HTMLCollection to an array.
        elementsList = [].slice.call(elementTarget?.getElementsByTagName('*'));
        // Filter the array, so that only the allowed headings and elements with no children are in the list to avoid problems with elements that wrap around others.
        elementsList = elementsList.filter((el) => includedHeadings.includes(el.nodeName.toLowerCase()) || el.children.length === 0);
        // We don't care about elements before our first header element, so we can remove those as well.
        elementsList.splice(0, elementsList.indexOf(headingsList[0]));
        return {
            headingsList,
            elementsList,
        };
    }
    /**
     * Create a tree view of our headings so that the hierarchy is represented.
     * @param arr An array of heading elements.
     * @param startIndex The parent elements original index in the array.
     */
    function createTree(arr, startIndex = 0) {
        const tree = [];
        let i = 0;
        while (i < arr.length) {
            const node = {
                title: arr[i].innerText,
                index: startIndex + i,
                id: arr[i].id,
                node: arr[i],
                children: [],
            };
            let j = i + 1;
            while (j < arr.length &&
                parseInt(arr[j].tagName.charAt(1)) > parseInt(arr[i].tagName.charAt(1))) {
                j++;
            }
            // Recursive call.
            node.children = createTree(arr.slice(i + 1, j), startIndex + i + 1);
            tree.push(node);
            i = j;
        }
        return tree;
    }
    /**
     * Scrolls to the element specified by the selector.
     * The offset and scroll behaviour are determined by the
     * builder arguments.
     *
     * Source: https://stackoverflow.com/questions/49820013/javascript-scrollintoview-smooth-scroll-and-offset?answertab=scoredesc#tab-top
     *
     * @param selector The id of the element.
     */
    function scrollToTargetAdjusted(selector) {
        const element = document.getElementById(selector);
        if (element) {
            const elementPosition = element.getBoundingClientRect().top;
            const offsetPosition = elementPosition + window.scrollY - scrollOffset;
            window.scrollTo({
                top: offsetPosition,
                behavior: scrollBehaviour,
            });
        }
    }
    const shouldHighlightParents = activeType === 'highest-parents' ||
        activeType === 'lowest-parents' ||
        activeType === 'all-parents';
    function handleElementObservation(entries) {
        // Iterate through all elements that crossed the observer_threshold.
        for (let i = 0; i < entries.length; i++) {
            // Get the index of the observed element in our elementsList, as well as the ToC heading it belongs to.
            const el_idx = elementsList.indexOf(entries[i].target);
            const toc_idx = elementHeadingLU[el_idx];
            let tempVisibleElementIdxs = visibleElementIdxs.get();
            if (entries[i].intersectionRatio >= observer_threshold) {
                // Only add the observed element to the visibleElementIdxs list if it isn't added yet.
                if (tempVisibleElementIdxs.indexOf(el_idx) === -1) {
                    tempVisibleElementIdxs = [...tempVisibleElementIdxs, el_idx];
                    visibleElementIdxs.set(tempVisibleElementIdxs);
                    // Only add active parents if parent headings should be highlighted.
                    if (shouldHighlightParents && headingParentsLU[toc_idx]) {
                        activeParentIdxs.update((prev) => {
                            return [...prev, ...headingParentsLU[toc_idx]];
                        });
                    }
                }
            }
            else {
                // Remove the observed element from the visibleElementIdxs list if the intersection ratio is below the threshold.
                tempVisibleElementIdxs = tempVisibleElementIdxs.filter((item) => item !== el_idx);
                visibleElementIdxs.set(tempVisibleElementIdxs);
                // Remove all parents of obsIndex from the activeParentIdxs list.
                if (shouldHighlightParents && headingParentsLU[toc_idx]) {
                    activeParentIdxs.update((prev) => {
                        const newArr = [...prev];
                        headingParentsLU[toc_idx]?.forEach((parent) => {
                            const index = newArr.indexOf(parent);
                            newArr.splice(index, 1);
                        });
                        return newArr;
                    });
                }
            }
        }
        const allActiveHeaderIdxs = Array.from(new Set(visibleElementIdxs.get().map((idx) => elementHeadingLU[idx])));
        let activeHeaderIdxs;
        if (allActiveHeaderIdxs.length === 0) {
            activeHeaderIdxs = [];
        }
        else {
            switch (activeType) {
                case 'highest':
                    activeHeaderIdxs = [Math.min(...allActiveHeaderIdxs)];
                    break;
                case 'lowest':
                    activeHeaderIdxs = [Math.max(...allActiveHeaderIdxs)];
                    break;
                case 'all':
                    activeHeaderIdxs = allActiveHeaderIdxs;
                    break;
                case 'all-parents': {
                    const parentIdxs = allActiveHeaderIdxs.flatMap((idx) => headingParentsLU[idx] ?? []);
                    activeHeaderIdxs = [...allActiveHeaderIdxs, ...parentIdxs];
                    break;
                }
                default: {
                    const activeHeaderIdx = activeType === 'highest-parents'
                        ? Math.min(...allActiveHeaderIdxs)
                        : Math.max(...allActiveHeaderIdxs);
                    if (headingParentsLU[activeHeaderIdx]) {
                        activeHeaderIdxs = [...headingParentsLU[activeHeaderIdx], activeHeaderIdx];
                    }
                    else {
                        activeHeaderIdxs = [activeHeaderIdx];
                    }
                }
            }
        }
        // Set store to active indexes.
        activeHeadingIdxs.set(activeHeaderIdxs);
    }
    function initialization() {
        observer?.disconnect();
        /** Get all parents for each heading element, by checking
         *  which previous headings in the list have a lower H value,
         *  so H1 < H2 < H3 < ...
         */
        headingsList.forEach((h, i) => {
            headingParentsLU[i] = null;
            let current_heading = h.tagName;
            let parents = [];
            for (let j = i - 1; j >= 0; j--) {
                if (headingsList[j].tagName < current_heading) {
                    current_heading = headingsList[j].tagName;
                    parents = [...parents, j];
                }
            }
            headingParentsLU[i] = parents.length > 0 ? parents : null;
            // Find all elements between the current heading and the next one and assign them the current heading.
            const startIndex = elementsList.indexOf(headingsList[i]);
            const endIndex = i !== headingsList.length - 1
                ? elementsList.indexOf(headingsList[i + 1])
                : elementsList.length;
            for (let j = startIndex; j < endIndex; j++) {
                elementHeadingLU[j] = i;
            }
        });
        headingsTree.set(createTree(headingsList));
        if (activeType !== 'none') {
            // Create observer and observe all elements.
            observer = new IntersectionObserver(handleElementObservation, {
                root: null,
                threshold: observer_threshold,
            });
            elementsList.forEach((el) => observer?.observe(el));
        }
    }
    function mutationHandler() {
        const newElementTarget = document.querySelector(selector);
        if (!newElementTarget)
            return;
        const { headingsList: newHeadingsList, elementsList: newElementsList } = generateInitialLists(newElementTarget);
        if (dequal(headingsList, newHeadingsList))
            return;
        // Update lists and LUs and re-run initialization.
        headingsList = newHeadingsList;
        elementsList = newElementsList;
        headingParentsLU = {};
        elementHeadingLU = {};
        initialization();
    }
    safeOnMount(() => {
        elementTarget = document.querySelector(selector);
        if (!elementTarget)
            return;
        ({ headingsList, elementsList } = generateInitialLists(elementTarget));
        initialization();
        mutationObserver = new MutationObserver(mutationHandler);
        mutationObserver.observe(elementTarget, { childList: true, subtree: true });
        return () => {
            observer?.disconnect();
            mutationObserver?.disconnect();
        };
    });
    // Elements
    const item = makeElement(name('item'), {
        stores: activeHeadingIdxs,
        returned: ($activeHeadingIdxs) => {
            return (id) => {
                const idx = headingsList.findIndex((heading) => heading.id === id);
                const active = $activeHeadingIdxs.includes(idx);
                return {
                    'data-id': id,
                    'data-active': active ? '' : undefined,
                };
            };
        },
        action: (node) => {
            const id = node.getAttribute('data-id');
            const unsub = executeCallbacks(addMeltEventListener(node, 'click', (e) => {
                e.preventDefault();
                if (scrollFn) {
                    scrollFn(`${id}`);
                }
                else {
                    scrollToTargetAdjusted(`${id}`);
                }
                // Add items hash to URL
                if (id) {
                    history.pushState({}, '', `#${id}`);
                }
            }));
            return {
                destroy: unsub,
            };
        },
    });
    // Helpers
    const isActive = derived(activeHeadingIdxs, ($activeHeadingIdxs) => {
        return (headingId) => {
            const idx = headingsList.findIndex((heading) => heading.id === headingId);
            return $activeHeadingIdxs.includes(idx);
        };
    });
    return {
        elements: {
            item,
        },
        states: {
            activeHeadingIdxs,
            headingsTree,
        },
        helpers: {
            isActive,
        },
    };
}