Mermaid-Preview-Nova/Scripts/preview.js

//
// preview.js — where the generated HTML lives and how it gets in front of you.
//
// Nova has no API for contributing a previewer, so this extension does not try
// to be one. It writes an ordinary HTML file inside the workspace's preview root
// and opens it; from there Nova's own preview tab does the work, including
// reloading the page when the file underneath it changes.
//

const { conf, log, warn, exists, writeFile, copyFile, removeTree, shortHash } = require("./util.js");
const { buildDocument } = require("./render.js");

const MARKDOWN_EXTENSIONS = ["md", "markdown", "mdown", "mkd", "mdx"];
const MERMAID_EXTENSIONS = ["mmd", "mermaid"];

const VENDOR_FILES = ["markdown-it.min.js", "mermaid.min.js"];
const ASSET_FILES = ["preview.css", "preview.js"];

// Bumped whenever anything in Assets/ changes, so an installed copy from an
// older version of the extension gets replaced instead of quietly persisting.
const ASSET_VERSION = "1";

class PreviewError extends Error {}

/** The directory Nova serves previews from, or null when previewing is unavailable. */
function previewRoot() {
    return nova.workspace.previewRootPath || nova.workspace.path || null;
}

/** Absolute path of the directory generated files are written to. */
function outputDirectory() {
    const root = previewRoot();
    if (!root) {
        throw new PreviewError(
            "This workspace has no preview root, so there is nowhere to put the generated page. " +
                "Open a folder as a project, or set a preview root in Project Settings → Preview."
        );
    }

    const configured = String(conf("mermaidpreview.outputDirectory", ".nova/MermaidPreview")).trim();
    const directory = nova.path.isAbsolute(configured) ? configured : nova.path.join(root, configured);

    // A page outside the preview root is not reachable by the preview server,
    // which fails as a blank tab rather than an error worth reading.
    if (!nova.path.join(directory, "/").startsWith(nova.path.join(root, "/"))) {
        throw new PreviewError(
            `The generated files directory (${configured}) is outside the preview root, so Nova cannot serve it.`
        );
    }

    return directory;
}

/** Describes the file in `editor`, or null when it is not something we preview. */
function describeSource(editor) {
    if (!editor || !editor.document) return null;

    const document = editor.document;
    if (document.isUntitled || document.isRemote || !document.path) return null;

    const syntax = document.syntax;
    const extension = (nova.path.extname(document.path) || "").replace(/^\./, "").toLowerCase();

    let mode = null;
    if (syntax === "markdown" || MARKDOWN_EXTENSIONS.includes(extension)) {
        mode = "markdown";
    } else if (syntax === "mermaid" || MERMAID_EXTENSIONS.includes(extension)) {
        mode = "mermaid";
    }
    if (!mode) return null;

    return { path: document.path, mode, editor };
}

/** Reads the editor's current text, including edits that have not been saved. */
function currentText(editor) {
    const document = editor.document;
    return document.getTextInRange(new Range(0, document.length));
}

/** Absolute path of the HTML page generated for `sourcePath`. */
function outputPathFor(sourcePath) {
    const directory = outputDirectory();
    const base = nova.path.splitext(nova.path.basename(sourcePath))[0] || "preview";
    const slug = base.replace(/[^A-Za-z0-9._-]+/g, "-").replace(/^-+|-+$/g, "") || "preview";
    return nova.path.join(directory, `${slug}-${shortHash(sourcePath)}.html`);
}

/**
 * Copies the stylesheet, the page script and the two vendored bundles into the
 * output directory. They are served alongside the page rather than inlined, so
 * regenerating on every keystroke stays a few-kilobyte write.
 */
function installAssets(directory) {
    const assets = nova.path.join(directory, "assets");
    const stamp = nova.path.join(assets, ".version");

    let installed = null;
    if (exists(stamp)) {
        const file = nova.fs.open(stamp, "r");
        try {
            installed = (file.read() || "").trim();
        } finally {
            file.close();
        }
    }

    const complete =
        installed === ASSET_VERSION &&
        ASSET_FILES.every((name) => exists(nova.path.join(assets, name))) &&
        VENDOR_FILES.every((name) => exists(nova.path.join(assets, "vendor", name)));
    if (complete) return "assets";

    log(`Installing preview assets into ${assets}`);
    for (const name of ASSET_FILES) {
        copyFile(nova.path.join(nova.extension.path, "Assets", name), nova.path.join(assets, name));
    }
    for (const name of VENDOR_FILES) {
        copyFile(
            nova.path.join(nova.extension.path, "Assets", "vendor", name),
            nova.path.join(assets, "vendor", name)
        );
    }
    writeFile(stamp, ASSET_VERSION);

    return "assets";
}

/**
 * Regenerates the page for `source`. Returns the path of the generated file.
 */
function generate(source) {
    const directory = outputDirectory();
    const assetsRelDir = installAssets(directory);
    const outputPath = outputPathFor(source.path);

    const sourceRelDir = nova.path.relative(nova.path.dirname(outputPath), nova.path.dirname(source.path));

    const html = buildDocument({
        markdown: currentText(source.editor),
        title: nova.path.basename(source.path),
        sourcePath: source.path,
        sourceRelDir: sourceRelDir ? `${sourceRelDir}/` : "./",
        assetsRelDir,
        mode: source.mode,
        theme: String(conf("mermaidpreview.theme", "auto")),
        contentWidth: Number(conf("mermaidpreview.contentWidth", 860)),
    });

    writeFile(outputPath, html);
    return outputPath;
}

/**
 * Regenerates the page for `source` and opens it, ready to switch to Preview.
 * Resolves to the generated path and the editor Nova opened it in, which is
 * null when Nova opened the file straight into its preview state.
 */
async function open(source) {
    const outputPath = generate(source);
    const editor = await nova.workspace.openFile(outputPath);
    return { outputPath, editor: editor || null };
}

/** The editor `path` is open in, or null. */
function editorFor(path) {
    return nova.workspace.textEditors.find((editor) => editor.document && editor.document.path === path) || null;
}

/** True while `path` is still open somewhere in the workspace. */
function isOpen(path) {
    return editorFor(path) !== null;
}

/**
 * Deletes one generated page, and the assets with it once it was the last page
 * left — closing every preview should leave the project as it was found.
 */
function discard(outputPath) {
    if (exists(outputPath)) nova.fs.remove(outputPath);

    let directory;
    try {
        directory = outputDirectory();
    } catch (err) {
        return;
    }
    if (!exists(directory)) return;

    const pages = nova.fs.listdir(directory).filter((name) => name.endsWith(".html"));
    if (pages.length === 0) removeTree(directory);
}

/** Deletes every generated file, assets included. */
function clean() {
    const directory = outputDirectory();
    if (!exists(directory)) return false;
    removeTree(directory);
    return true;
}

module.exports = {
    PreviewError,
    describeSource,
    generate,
    open,
    editorFor,
    isOpen,
    discard,
    clean,
    outputDirectory,
    outputPathFor,
};