Add support for exclusions

Paths can be negated to stop searching through the remaining patterns in
a the glob list. All changed files tested and at least one matching file
will result in a label being added.

Fixes #9

README.md

@@ -15,9 +15,16 @@ label2: example2/*
 label3:
 - example3/*
 - example3/**/*.yml
+
+label4:
+- !example4/foo/*
+- example4/**/*
 ```
 Where `"label1"` is the name of the label on your repository that you want to add (eg: "merge conflict", "needs-updating") and `"example1/**/*"` is the path of the changed files.
 
+Exclusions are supported by preceding the pattern with `"!"`.
+
+Patterns are evaluated in order and the first match will result in the label being assigned. If an exclusion rule matches, all remaining patterns are skipped for the path being evaluated.
 
 Then create a workflow (eg: `.github/workflows/label.yml` see [Creating a Workflow file](https://help.github.com/en/articles/configuring-a-workflow#creating-a-workflow-file)) utilizing the labeler action, granting access to the GITHUB_TOKEN so the action can make calls to GitHub's rest API:
 ```

src/main.ts

@@ -1,7 +1,7 @@
 import * as core from '@actions/core';
 import * as github from '@actions/github';
 import * as yaml from 'js-yaml';
-import {Minimatch} from 'minimatch';
+import {Minimatch, IMinimatch} from 'minimatch';
 
 async function run() {
   try {
@@ -116,15 +116,28 @@ function getLabelGlobMapFromObject(configObject: any): Map<string, string[]> {
   return labelGlobs;
 }
 
+function printPattern(matcher: IMinimatch): string {
+  return (matcher.negate ? "!" : "") + matcher.pattern;
+}
+
 function checkGlobs(changedFiles: string[], globs: string[]): boolean {
-  for (const glob of globs) {
-    core.debug(` checking pattern ${glob}`);
-    const matcher = new Minimatch(glob);
-    for (const changedFile of changedFiles) {
-      core.debug(` - ${changedFile}`);
+  const matchers = globs.map(g => new Minimatch(g));
+  for (const changedFile of changedFiles) {
+    core.debug(` testing patterns against ${changedFile}`);
+    for (const matcher of matchers) {
+      core.debug(` - ${printPattern(matcher)}`);
       if (matcher.match(changedFile)) {
-        core.debug(` ${changedFile} matches`);
-        return true;
+        // match and not an exclusion rule
+        if (!matcher.negate) {
+          core.debug(` ${printPattern(matcher)} matches`);
+          return true;
+        }
+      } else {
+        // non-match, but is an exclusion rule
+        if (matcher.negate) {
+          core.debug(` ${printPattern(matcher)} excluded`);
+          break;
+        }
       }
     }
   }