Merge pull request #107 from adobe/config-merging

allow merging of configs

src/HelixConfig.js

@@ -16,6 +16,9 @@ const YAML = require('yaml');
 const Strain = require('./Strain.js');
 const Strains = require('./Strains.js');
 const ConfigValidator = require('./ConfigValidator.js');
+const { concat, uniq, each } = require('./sequence.js');
+const { pipe } = require('./functional.js');
+
 
 const HELIX_CONFIG = 'helix-config.yaml';
 
@@ -64,6 +67,33 @@ class HelixConfig {
     return this;
   }
 
+  /**
+   * @name ResolveFn
+   * @function
+   * @param {Strain} left the current candidate strain (can be undefined)
+   * @param {Strain} right the alternative candidate strain (can be undefined)
+   */
+
+  /**
+   * Updates the current configuration with the strains of another configuration
+   * object and a user-defined resolver function.
+   * @param {HelixConfig} other another Helix Config to merge
+   * @param {ResolveFn} resolvefn a resolver function that returns either a strain or undefined
+   * @returns {HelixConfig} the merged Helix Config
+   */
+  merge(other, resolvefn) {
+    const filtered = new Strains();
+    pipe(concat(other.strains.keys(), this.strains.keys()), uniq, each((name) => {
+      const strain = resolvefn(this.strains.get(name), other.strains.get(name));
+      if (strain) {
+        filtered.add(strain);
+      }
+    }));
+
+    this._strains = filtered;
+    return this;
+  }
+
   get directory() {
     return this._cwd;
   }

test/config.test.js

@@ -142,6 +142,29 @@ describe('Helix Config Loading', () => {
   });
 });
 
+describe('Helix Config Merging', () => {
+  it('can merge two configs', async () => {
+    const oldconf = await new HelixConfig()
+      .withConfigPath(path.resolve(SPEC_ROOT, 'minimal.yaml'))
+      .init();
+
+    assert.deepEqual(Array.from(oldconf.strains.keys()), ['default']);
+
+    const newconf = await new HelixConfig()
+      .withConfigPath(path.resolve(SPEC_ROOT, 'minimal-foo.yaml'))
+      .init();
+
+    oldconf.merge(newconf, (left, right) => {
+      if (left && left.name === 'default') {
+        return left;
+      }
+      return right;
+    });
+
+    assert.deepEqual(Array.from(oldconf.strains.keys()), ['default', 'foo']);
+  });
+});
+
 describe('Helix Config Serializing', () => {
   it('can serialize strains as json', async () => {
     const cfg = await new HelixConfig()