refactor(server): rename md -> markdown for consistency

src/services/export/markdown.ts

@@ -0,0 +1,104 @@
+"use strict";
+
+import TurndownService from "turndown";
+import turndownPluginGfm from "@joplin/turndown-plugin-gfm";
+
+let instance: TurndownService | null = null;
+
+const fencedCodeBlockFilter: TurndownService.Rule = {
+    filter: function (node, options) {
+        return options.codeBlockStyle === "fenced" && node.nodeName === "PRE" && node.firstChild !== null && node.firstChild.nodeName === "CODE";
+    },
+
+    replacement: function (content, node, options) {
+        if (!node.firstChild || !("getAttribute" in node.firstChild) || typeof node.firstChild.getAttribute !== "function") {
+            return content;
+        }
+
+        const className = node.firstChild.getAttribute("class") || "";
+        const language = rewriteLanguageTag((className.match(/language-(\S+)/) || [null, ""])[1]);
+
+        return "\n\n" + options.fence + language + "\n" + node.firstChild.textContent + "\n" + options.fence + "\n\n";
+    }
+};
+
+function toMarkdown(content: string) {
+    if (instance === null) {
+        instance = new TurndownService({
+            headingStyle: "atx",
+            codeBlockStyle: "fenced"
+        });
+        // Filter is heavily based on: https://github.com/mixmark-io/turndown/issues/274#issuecomment-458730974
+        instance.addRule("fencedCodeBlock", fencedCodeBlockFilter);
+        instance.addRule("img", buildImageFilter());
+        instance.use(turndownPluginGfm.gfm);
+    }
+
+    return instance.turndown(content);
+}
+
+function rewriteLanguageTag(source: string) {
+    if (!source) {
+        return source;
+    }
+
+    switch (source) {
+        case "text-x-trilium-auto":
+            return "";
+        case "application-javascript-env-frontend":
+        case "application-javascript-env-backend":
+            return "javascript";
+        case "text-x-nginx-conf":
+            return "nginx";
+        default:
+            return source.split("-").at(-1);
+    }
+}
+
+// TODO: Remove once upstream delivers a fix for https://github.com/mixmark-io/turndown/issues/467.
+function buildImageFilter() {
+    const ESCAPE_PATTERNS = {
+        before: /([\\*`[\]_]|(?:^[-+>])|(?:^~~~)|(?:^#{1-6}))/g,
+        after: /((?:^\d+(?=\.)))/
+    }
+
+    const escapePattern = new RegExp('(?:' + ESCAPE_PATTERNS.before.source + '|' + ESCAPE_PATTERNS.after.source + ')', 'g');
+
+    function escapeMarkdown (content: string) {
+        return content.replace(escapePattern, function (match, before, after) {
+            return before ? '\\' + before : after + '\\'
+        })
+    }
+
+    function escapeLinkDestination(destination: string) {
+        return destination
+            .replace(/([()])/g, '\\$1')
+            .replace(/ /g, "%20");
+    }
+
+    function escapeLinkTitle (title: string) {
+        return title.replace(/"/g, '\\"')
+    }
+
+    function cleanAttribute (attribute: string) {
+        return attribute ? attribute.replace(/(\n+\s*)+/g, '\n') : ''
+    }
+
+    const imageFilter: TurndownService.Rule = {
+        filter: "img",
+        replacement(content, node) {
+            const untypedNode = (node as any);
+            const alt = escapeMarkdown(cleanAttribute(untypedNode.getAttribute('alt')))
+            const src = escapeLinkDestination(untypedNode.getAttribute('src') || '')
+            const title = cleanAttribute(untypedNode.getAttribute('title'))
+            const titlePart = title ? ' "' + escapeLinkTitle(title) + '"' : ''
+
+            return src ? '![' + alt + ']' + '(' + src + titlePart + ')' : ''
+        }
+    };
+    return imageFilter;
+}
+
+export default {
+    toMarkdown
+};