feat: add a basic function to find out the output file extension

Author: learosema

README.md

@@ -6,9 +6,9 @@ Muh (say: Moo!) stands for "mustached hypertext" and is the template language th
 
 Muh comes in 2 flavors. Both of them live in the `@sissijs/muh` package.
 
-`@sissijs/muh` includes everything. A full-fledged `processTemplateFile` function that supports SmolYAML/JSON frontmatter, layout files, basic preprocessing such as (a minimal) markdown, handling css imports and resolving `<html-include src="">` directives. In roughly 9KB of JavaScript
+`@sissijs/muh` includes everything. A full-fledged `processTemplateFile` function that supports SmolYAML/JSON frontmatter, layout files, basic preprocessing such as (a minimal) markdown, handling css imports and resolving `<html-include src="">` directives. In roughly 10KB of JavaScript.
 
-`@sissijs/muh/template` is just the `template` function that implements the mustache syntax. It also provides the built-in filters for formatting dates/numbers, and built-in helper functions. The helper functions provided are small wrappers around fetch, namely `fetchText()` and `fetchJson()`. All that is contained in roughly 3KB of JavaScript.
+`@sissijs/muh/template` is just the `template` function that implements the mustache syntax. It also provides the built-in filters for formatting dates/numbers, and built-in helper functions. The helper functions provided are small wrappers around fetch, namely `fetchText()` and `fetchJson()`. All that is contained in roughly 4KB of JavaScript.
 
 Sizes are measured with minification and without compression.
 

src/get-output-file-extension.js

@@ -0,0 +1,30 @@
+///<reference path="typedefs.js"/>
+import { htmlPreprocessor } from "./preprocessors/html.js";
+import { cssPreprocessor } from "./preprocessors/css.js";
+import { markdownPreprocessor } from "./preprocessors/markdown.js";
+
+/**
+ * Get the output file extension for an input file.
+ * @param {string} inputFilePath 
+ * @param {ProcessTemplateFileConfig} [config] optional configuration object with preprocessors property
+ */
+export function getOutputFileExtension(inputFilePath, config) {
+  const extensionIdx = inputFilePath ? inputFilePath.lastIndexOf('.') : -1;
+  if (extensionIdx < 0) {
+    return '';
+  }
+  const preprocessors = config?.preprocessors ?? [htmlPreprocessor, cssPreprocessor, markdownPreprocessor];
+  const preprocessor = preprocessors.find(p => {
+    if (typeof p.extension === 'string' &&
+      inputFilePath.endsWith(p.extension)) {
+      return true;
+    }
+    if (p.extension instanceof RegExp && 
+      p.extension.test(inputFilePath)) {
+      return true;
+    }
+    return false;
+  });
+  return (preprocessor?.outputExtension) ?
+    preprocessor?.outputExtension : inputFilePath.slice(extensionIdx);
+}

src/muh.js

@@ -1,5 +1,6 @@
 ///<reference path="typedefs.js"/>
 import { processTemplateFile } from "./process-template-file.js";
+import { getOutputFileExtension } from "./get-output-file-extension.js";
 import { markdown, markdownPreprocessor } from "./preprocessors/markdown.js";
 import { cssPreprocessor } from "./preprocessors/css.js";
 import { htmlPreprocessor } from "./preprocessors/html.js";
@@ -14,4 +15,5 @@ export { smolYAML };
 export { frontmatter };
 
 export { processTemplateFile };
+export { getOutputFileExtension };
 export { template };

src/preprocessors/html.js

@@ -2,7 +2,8 @@ import { replaceAsync } from "../utils/replace-async.js";
 
 export const htmlPreprocessor = {
   name: 'html',
-  extension: /.html?$/,
+  extension: /(\.muh$)|(\.html?$)/,
+  outputExtension: '.html',
   /**
    * Process HTML. Resolves `<html-include>` directives via an `include` function provided in data.
    * 

tests/get-output-file-extension.test.js

@@ -0,0 +1,22 @@
+import { describe, it } from 'node:test';
+import assert from 'node:assert/strict';
+
+import { getOutputFileExtension } from '../src/get-output-file-extension.js';
+
+describe('getOutputFileExtension', () => {
+  it('should find out that markdown files transform to .html by default', () => {
+    assert.equal(getOutputFileExtension('readme.md'), '.html');
+  });
+
+  it('should find out that .muh files transform to .html by default', () => {
+    assert.equal(getOutputFileExtension('readme.muh'), '.html');
+  });
+
+  it('should find out that html files stay .html', () => {
+    assert.equal(getOutputFileExtension('readme.html'), '.html');
+  });
+
+  it('should find out that css files stay .css', () => {
+    assert.equal(getOutputFileExtension('styles.css'), '.css');
+  });
+})