feat: add --check flag

Author: gajus

.README/README.md

@@ -44,6 +44,8 @@ Gitdown adds [additional functionality](#features) (generating table of contents
 
 {"gitdown": "include", "file": "./usage.md"}
 
+a
+
 ## Features
 
 {"gitdown": "include", "file": "./helpers/contents.md"}
@@ -61,23 +63,20 @@ Gitdown adds [additional functionality](#features) (generating table of contents
 
 ### Automating Gitdown
 
-Use [Husky](https://www.npmjs.com/package/husky) to automate generation of README.md and committing it to the version control.
+Use [Husky](https://www.npmjs.com/package/husky) to check if user generated README.md before committing his changes.
 
 ```json
 "husky": {
   "hooks": {
-    "post-commit": "npm run create-readme && git add README.md && git commit -m 'docs: generate docs' --no-verify",
-    "pre-commit": "npm run lint && npm run test && npm run build"
+    "pre-commit": "npm run lint && npm run test && npm run build",
+    "pre-push": "gitdown ./.README/README.md --output-file ./README.md --check",
   }
 }
 
 ```
 
-Where `create-readme` is your script to generate `README.md`, e.g.
+`--check` attributes makes Gitdown check if the target file differes from the source template. If the file differs then the program exits with an error code and message:
 
-```json
-"scripts": {
-  "create-readme": "gitdown ./.README/README.md --output-file ./README.md",
-}
+> Gitdown destination file does not represent the current state of the template.
 
-```
+Do not automate generating and committing documentation: automating commits will result in a noisy commit log.

.README/helpers/date.md

@@ -22,8 +22,8 @@ Prints a string formatted according to the given [moment format](http://momentjs
 Generates:
 
 ```markdown
-{"gitdown": "date"}
-{"gitdown": "date", "format": "YYYY"}
+1563038327
+2019
 
 ```
 

README.md

@@ -207,6 +207,8 @@ foo: bar
 ```
 
 
+a
+
 <a name="features"></a>
 ## Features
 
@@ -675,23 +677,20 @@ master
 <a name="recipes-automating-gitdown"></a>
 ### Automating Gitdown
 
-Use [Husky](https://www.npmjs.com/package/husky) to automate generation of README.md and committing it to the version control.
+Use [Husky](https://www.npmjs.com/package/husky) to check if user generated README.md before committing his changes.
 
 ```json
 "husky": {
   "hooks": {
-    "post-commit": "npm run create-readme && git add README.md && git commit -m 'docs: generate docs' --no-verify",
-    "pre-commit": "npm run lint && npm run test && npm run build"
+    "pre-commit": "npm run lint && npm run test && npm run build",
+    "pre-push": "gitdown ./.README/README.md --output-file ./README.md --check",
   }
 }
 
 ```
 
-Where `create-readme` is your script to generate `README.md`, e.g.
+`--check` attributes makes Gitdown check if the target file differes from the source template. If the file differs then the program exits with an error code and message:
 
-```json
-"scripts": {
-  "create-readme": "gitdown ./.README/README.md --output-file ./README.md",
-}
+> Gitdown destination file does not represent the current state of the template.
 
-```
+Do not automate generating and committing documentation: automating commits will result in a noisy commit log.

package.json

@@ -45,8 +45,8 @@
   },
   "husky": {
     "hooks": {
-      "post-commit": "if [[ -z \"$SKIP_CREATE_README\" ]]; then export SKIP_CREATE_README=1 && npm run create-readme && git commit -m 'docs: generate docs' --no-verify -- README.md; else unset SKIP_CREATE_README; fi",
-      "pre-commit": "npm run lint && npm run test && npm run build"
+      "pre-commit": "npm run lint && npm run test && npm run build",
+      "pro-push": "babel-node ./src/bin/index.js ./.README/README.md --output-file ./README.md --check"
     }
   },
   "keywords": [

src/bin/index.js

@@ -9,9 +9,13 @@ const argv = yargs
   .usage('Usage: $0 <README.md> [options]')
   .demand(1, 1, 'Gitdown program must be executed with exactly one non-option argument.')
   .options({
+    check: {
+      default: false,
+      description: 'Checks if the destination file represents the current state of the template. Terminates program with exit status 1 if generating a new document would result in changes of the target document. Terminates program with exit status 0 otherwise (without writng to the destination).',
+      type: 'boolean'
+    },
     force: {
       default: false,
-      demand: false,
       describe: 'Write to file with different extension than ".md".',
       type: 'boolean'
     },
@@ -61,17 +65,35 @@ const argv = yargs
   .strict()
   .argv;
 
-((inputFile, outputFile) => {
+const main = async () => {
+  const inputFile = argv._[0];
+  const outputFile = argv.outputFile;
+
   const resolvedInputFile = path.resolve(process.cwd(), inputFile);
   const resolvedOutputFile = path.resolve(process.cwd(), outputFile);
 
   // eslint-disable-next-line global-require
-  const Gitdown = require('./..');
+  const Gitdown = require('..');
 
   const gitdown = Gitdown.readFile(resolvedInputFile);
 
+  if (argv.check) {
+    const generatedMarkdown = await gitdown.get();
+
+    if (fs.readFileSync(resolvedOutputFile, 'utf-8') === generatedMarkdown) {
+      return;
+    } else {
+      // eslint-disable-next-line no-console
+      console.error('Gitdown destination file does not represent the current state of the template.');
+
+      // eslint-disable-next-line no-process-exit
+      process.exit(1);
+    }
+
+    return;
+  }
+
   gitdown.writeFile(resolvedOutputFile);
-})(
-  argv._[0],
-  argv.outputFile
-);
+};
+
+main();