Keyboard navigation shortcuts for lemmy

Rewrote something I made for kbin to work with lemmy. Mimics some of RES’ keyboard navigation functionality.
Edit: updated so that expanded images scroll into view.
Edit 2: 2023/07/04
added ability to open links/comments (hold shift to open in new tab, might have to disable popup blocker)
traversing through entries while expand was toggled on will collapse previous entry and expand current entry preview
handle expanding of text posts
Edit 3: 2023/07/04
add ability to change to next/previous page
/*
==UserScript==
@name             lemmy navigation
@match            https://lemmy.world/*
@match            https://lemm.ee/*
@version          1.1
@run-at           document-start
==/UserScript==
*/

// Set selected entry colors
const backgroundColor = 'darkslategray';
const textColor = 'white';

// Set navigation keys with keycodes here: https://www.toptal.com/developers/keycode
const nextKey = 'KeyJ';
const prevKey = 'KeyK';
const expandKey = 'KeyX';
const openCommentsKey = 'KeyC';
const openLinkKey = 'Enter';
const nextPageKey = 'KeyN';
const prevPageKey = 'KeyP';


const css = [
".selected {",
"  background-color: " + backgroundColor + " !important;",
"  color: " + textColor + ";",
"}"
].join("\n");

if (typeof GM_addStyle !== "undefined") {
    GM_addStyle(css);
} else if (typeof PRO_addStyle !== "undefined") {
    PRO_addStyle(css);
} else if (typeof addStyle !== "undefined") {
    addStyle(css);
} else {
    let node = document.createElement("style");
    node.type = "text/css";
    node.appendChild(document.createTextNode(css));
    let heads = document.getElementsByTagName("head");
    if (heads.length > 0) {
        heads[0].appendChild(node);
    } else {
        // no head yet, stick it whereever
        document.documentElement.appendChild(node);
    }
}
const selectedClass = "selected";

let currentEntry;
let entries = [];
let previousUrl = "";
let expand = false;

const targetNode = document.documentElement;
const config = { childList: true, subtree: true };

const observer = new MutationObserver(() => {
    entries = document.querySelectorAll(".post-listing, .comment-node");

    if (entries.length > 0) {
        if (location.href !== previousUrl) {
            previousUrl = location.href;
            currentEntry = null;
        }
        init();
    }
});

observer.observe(targetNode, config);

function init() {
    // If jumping to comments
    if (window.location.search.includes("scrollToComments=true") &&
        entries.length > 1 &&
        (!currentEntry || Array.from(entries).indexOf(currentEntry) < 0)
    ) {
        selectEntry(entries[1], true);
    }
    // If jumping to comment from anchor link
    else if (window.location.pathname.includes("/comment/") &&
            (!currentEntry || Array.from(entries).indexOf(currentEntry) < 0)
    ) {
        const commentId = window.location.pathname.replace("/comment/", "");
        const anchoredEntry = document.getElementById("comment-" + commentId);

        if (anchoredEntry) {
            selectEntry(anchoredEntry, true);
        }
    }
    // If no entries yet selected, default to first
    else if (!currentEntry || Array.from(entries).indexOf(currentEntry) < 0) {
        selectEntry(entries[0]);
    }

    Array.from(entries).forEach(entry => {
        entry.removeEventListener("click", clickEntry, true);
        entry.addEventListener('click', clickEntry, true);
    });

    document.removeEventListener("keydown", handleKeyPress, true);
    document.addEventListener("keydown", handleKeyPress, true);
}

function handleKeyPress(event) {
    if (["TEXTAREA", "INPUT"].indexOf(event.target.tagName) > -1) {
        return;
    }

    switch (event.code) {
        case nextKey:
        case prevKey:
            let selectedEntry;

            // Next button
            if (event.code === nextKey) {
                // if shift key also pressed
                if (event.shiftKey) {
                    selectedEntry = getNextEntrySameLevel(currentEntry);
                } else {
                    selectedEntry = getNextEntry(currentEntry);
                }
            }

            // Previous button
            if (event.code === prevKey) {
                // if shift key also pressed
                if (event.shiftKey) {
                    selectedEntry = getPrevEntrySameLevel(currentEntry);
                } else {
                    selectedEntry = getPrevEntry(currentEntry);
                }
            }

            if (selectedEntry) {
                if (expand) collapseEntry();
                selectEntry(selectedEntry, true);
                if (expand) expandEntry();
            }
            break;
        case expandKey:
            toggleExpand();
            expand = isExpanded() ? true : false;
            break;
        case openCommentsKey:
            if (event.shiftKey) {
                window.open(
                    currentEntry.querySelector("a.btn[title$='Comments']").href,
                );
            } else {
                currentEntry.querySelector("a.btn[title$='Comments']").click();
            }
            break;
        case openLinkKey:
            const linkElement = currentEntry.querySelector(".col.flex-grow-0.px-0>div>a")
            if (linkElement) {
                if (event.shiftKey) {
                    window.open(linkElement.href);
                } else {
                    linkElement.click();
                }
            }
            break;
        case nextPageKey:
        case prevPageKey:
            const pageButtons = Array.from(document.querySelectorAll(".paginator>button"));

            if (pageButtons) {
                const buttonText = event.code === nextPageKey ? "Next" : "Prev";
                pageButtons.find(btn => btn.innerHTML === buttonText).click();
            }
            
    }
}

function getNextEntry(e) {
    const currentEntryIndex = Array.from(entries).indexOf(e);
    
    if (currentEntryIndex + 1 >= entries.length) {
        return e;
    }
    
    return entries[currentEntryIndex + 1];
}

function getPrevEntry(e) {
    const currentEntryIndex = Array.from(entries).indexOf(e);
    
    if (currentEntryIndex - 1 < 0) {
        return e;
    }
    
    return entries[currentEntryIndex - 1];
}

function getNextEntrySameLevel(e) {
    const nextSibling = e.parentElement.nextElementSibling;

    if (!nextSibling || nextSibling.getElementsByTagName("article").length < 1) {
        return getNextEntry(e);
    }
    
    return nextSibling.getElementsByTagName("article")[0];
}

function getPrevEntrySameLevel(e) {
    const prevSibling = e.parentElement.previousElementSibling;

    if (!prevSibling || prevSibling.getElementsByTagName("article").length < 1) {
        return getPrevEntry(e);
    }
    
    return prevSibling.getElementsByTagName("article")[0];
}

function clickEntry(event) {
    const e = event.currentTarget;
    const target = event.target;

    // Deselect if already selected, also ignore if clicking on any link/button
    if (e === currentEntry && e.classList.contains(selectedClass) &&
        !(
            target.tagName.toLowerCase() === "button" || target.tagName.toLowerCase() === "a" ||
            target.parentElement.tagName.toLowerCase() === "button" ||
            target.parentElement.tagName.toLowerCase() === "a" ||
            target.parentElement.parentElement.tagName.toLowerCase() === "button" ||
            target.parentElement.parentElement.tagName.toLowerCase() === "a"
        )
    ) {
        e.classList.remove(selectedClass);
    } else {
        selectEntry(e);
    }
}

function selectEntry(e, scrollIntoView=false) {
    if (currentEntry) {
        currentEntry.classList.remove(selectedClass);
    }
    currentEntry = e;
    currentEntry.classList.add(selectedClass);

    if (scrollIntoView) {
        scrollIntoViewWithOffset(e, 15)
    }
}

function isExpanded() {
    if (
        currentEntry.querySelector("a.d-inline-block:not(.thumbnail)") ||
        currentEntry.querySelector("#postContent") ||
        currentEntry.querySelector(".card-body")
    ) {
        return true;
    }

    return false;
}

function toggleExpand() {
    const expandButton = currentEntry.querySelector("button[aria-label='Expand here']");
    const textExpandButton = currentEntry.querySelector(".post-title>button");

    if (expandButton) {
        expandButton.click();

        // Scroll into view if picture/text preview cut off
        const imgContainer = currentEntry.querySelector("a.d-inline-block");

        if (imgContainer) {
            // Check container positions once image is loaded
            imgContainer.querySelector("img").addEventListener("load", function() {
                scrollIntoViewWithOffset(
                    imgContainer,
                    currentEntry.offsetHeight - imgContainer.offsetHeight + 10
                );
            }, true);
        }
    }

    if (textExpandButton) {
        textExpandButton.click();

        const textContainers =  [currentEntry.querySelector("#postContent"), currentEntry.querySelector(".card-body")];
        textContainers.forEach(container => {
            if (container) {
                scrollIntoViewWithOffset(
                    container,
                    currentEntry.offsetHeight - container.offsetHeight + 10
                );
            }
        });
    }
}

function expandEntry() {
    if (!isExpanded()) toggleExpand();
}

function collapseEntry() {
    if (isExpanded()) toggleExpand();
}

function scrollIntoViewWithOffset(e, offset) {
    if (e.getBoundingClientRect().top < 0 ||
        e.getBoundingClientRect().bottom > window.innerHeight
    ) {
        const y = e.getBoundingClientRect().top + window.pageYOffset - offset;
        window.scrollTo({
            top: y
        });
    }
}