Support page header setting of changelog file (#42)

* Support page header setting of changelog file

It is the same as the conventional-changelog-config-spec setting of standard-version.

* Update tests to support header settings

* fix extra line break logic

* replace header newline symbol

index.js

@@ -90,8 +90,18 @@ class ConventionalChangelog extends Plugin {
     });
   }
 
-  async writeChangelog() {
+  getOldChangelog() {
     const { infile } = this.options;
+    return new Promise((resolve, reject) => {
+      const readStream = fs.createReadStream(infile);
+      const resolver = result => resolve(result.toString().trim());
+      readStream.pipe(concat(resolver));
+      readStream.on('error', reject);
+    });
+  }
+
+  async writeChangelog() {
+    const { infile, header } = this.options;
     let { changelog } = this.config.getContext();
 
     let hasInfile = false;
@@ -102,12 +112,20 @@ class ConventionalChangelog extends Plugin {
       this.debug(err);
     }
 
+    let oldChangelog = ""
+    try{
+      oldChangelog = await this.getOldChangelog();
+      oldChangelog = oldChangelog.replace(header.split(/\r\n|\r|\n/g).join(EOL), '');
+    }catch(err){
+      this.debug(err);
+    }
+
     if (!hasInfile) {
       changelog = await this.generateChangelog({ releaseCount: 0 });
       this.debug({ changelog });
     }
 
-    await prependFile(infile, changelog + EOL + EOL);
+    fs.writeFileSync(infile, header + EOL + EOL + changelog + oldChangelog);
 
     if (!hasInfile) {
       await this.exec(`git add ${infile}`);

test.js

@@ -130,15 +130,16 @@ test('should use provided version', async t => {
 });
 
 test(`should write and update infile (${infile})`, async t => {
-  const options = { [namespace]: { preset, infile }, git };
+  const header = "The header"
+  const options = { [namespace]: { preset, infile, header }, git };
   const plugin = factory(Plugin, { namespace, options });
   await runTasks(plugin);
   const changelog = fs.readFileSync(infile);
-  assert.strictEqual(changelog.toString().trim(), 'The changelog');
+  assert.strictEqual(changelog.toString().trim(), `${header}${EOL}${EOL}The changelog`);
   {
     await runTasks(plugin);
     const changelog = fs.readFileSync(infile);
-    assert.strictEqual(changelog.toString().trim(), `The changelog${EOL}${EOL}The changelog`);
+    assert.strictEqual(changelog.toString().trim(), `${header}${EOL}${EOL}The changelog${EOL}${EOL}The changelog`);
   }
   fs.unlinkSync(infile);
 });