Extract custom classes into a separate block

This is done by checking the error repeatedly for custom classes and moving them to another array until no more error is presented.

Also: Refactor API code to simplify some constants and to remove unneeded parts like @tailwind directives and finding `.generated` text.

pages/api/generate-css.ts

@@ -1,4 +1,4 @@
-import postcss from "postcss";
+import postcss, { type CssSyntaxError } from "postcss";
 import tailwindcss from "tailwindcss";
 import autoprefixer from "autoprefixer";
 import { NextApiRequest, NextApiResponse } from "next";
@@ -8,52 +8,69 @@ interface RequestBody {
   classes: string;
 }
 
+const processor = postcss([
+  tailwindcss({
+    config: { content: ["./*.none"], corePlugins: { preflight: false } },
+  }),
+  autoprefixer,
+]);
+
+const beautifyOptions: Parameters<typeof cssbeautify>[1] = {
+  indent: "  ",
+  openbrace: "end-of-line",
+  autosemicolon: true,
+};
+
 export default async function handler(
   req: NextApiRequest,
   res: NextApiResponse
 ): Promise<void> {
-  const { classes }: RequestBody = req.body;
-
-  const css = `
-    @tailwind base;
-    @tailwind components;
-    @tailwind utilities;
-    .generated {
-      @apply ${classes};
-    }
-  `;
-
-  try {
-    const result = await postcss([
-      tailwindcss({
-        config: { content: ["./*.none"], corePlugins: { preflight: false } },
-      }),
-      autoprefixer,
-    ])
-      .process(css, { from: undefined })
-      .then((result) => {
-        let css = result.css;
-
-        // Find ".generated" text and extract everything after it.
-        const generatedIndex = css.indexOf(".generated");
-        if (generatedIndex !== -1) {
-          css = css.substring(generatedIndex);
-        } else {
-          css = "no: result;";
-        }
+  const body: RequestBody = req.body;
+  const classes: string[] = body.classes.split(" ");
+  const customClasses: string[] = [];
+  let doneProcessing = false;
+
+  do {
+    try {
+      const css = `.generated { @apply ${classes.join(" ")}; }`;
+
+      let result = await processor
+        .process(css, { from: undefined })
+        .then((result) => result.css);
 
-        // Format the CSS using cssbeautify
-        css = cssbeautify(css, {
-          indent: "  ",
-          openbrace: "end-of-line",
-          autosemicolon: true,
-        });
+      if (customClasses.length) {
+        const classes = customClasses.join(", .");
+        result = `.${classes} {\n  /* Custom classes not found in Tailwind CSS */} ${result}`;
+      }
 
-        return css.trim();
-      });
+      result = cssbeautify(result, beautifyOptions);
 
-    res.status(200).send(result);
-  } catch (error) {
-    res.status(500).send(error.toString());
-  }
+      res.status(200).send(result);
+      doneProcessing = true;
+
+      //
+    } catch (error) {
+      if (error?.name === "CssSyntaxError") {
+        const cssError = error as CssSyntaxError;
+        const customClass = cssError.reason.match(
+          /`([^`]+)` class does not exist/
+        )?.[1];
+
+        if (customClass) {
+          customClasses.push(customClass);
+          classes.splice(classes.indexOf(customClass), 1);
+
+          //
+        } else {
+          res.status(500).send(error.toString());
+          doneProcessing = true;
+        }
+
+        //
+      } else {
+        res.status(500).send(error.toString());
+        doneProcessing = true;
+      }
+    }
+  } while (!doneProcessing);
 }