From c857dcb056429616c581059c4a2ba50ac0cab3e8 Mon Sep 17 00:00:00 2001
From: Mike Gerwitz <gerwitzm@lovullo.com>
Date: Fri, 25 Aug 2017 11:55:40 -0400
Subject: [PATCH] Add ConfLoader

* src/conf/ConfLoader.js: Add class.
* test/conf/ConfLoaderTest.js: Respective test case.
---
 src/conf/ConfLoader.js      | 123 ++++++++++++++++++++++++++++++++
 test/conf/ConfLoaderTest.js | 136 ++++++++++++++++++++++++++++++++++++
 2 files changed, 259 insertions(+)
 create mode 100644 src/conf/ConfLoader.js
 create mode 100644 test/conf/ConfLoaderTest.js

diff --git a/src/conf/ConfLoader.js b/src/conf/ConfLoader.js
new file mode 100644
index 0000000..fd06e4b
--- /dev/null
+++ b/src/conf/ConfLoader.js
@@ -0,0 +1,123 @@
+/**
+ * Configuration loader
+ *
+ *  Copyright (C) 2017 R-T Specialty, LLC.
+ *
+ *  This file is part of the Liza Data Collection Framework.
+ *
+ *  liza is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+'use strict';
+
+const { Class } = require( 'easejs' );
+
+
+/**
+ * Load system configuration from JSON
+ *
+ * @example
+ *   ConfLoader( require( 'fs' ), SomeStore )
+ *     .fromFile( 'conf/vanilla-server.json' )
+ *     .then( conf => conf.get( 'foo' ) );
+ *
+ * TODO: Merging multiple configuration files would be convenient for
+ * modular configuration.
+ */
+module.exports = Class( 'ConfLoader',
+{
+    /**
+     * Filesystem module
+     * @type {fs}
+     */
+    'private _fs': null,
+
+    /**
+     * Store object constructor
+     * @type {function():Store}
+     */
+    'private _storeCtor': null,
+
+
+    /**
+     * Initialize with provided filesystem module and Store constructor
+     *
+     * The module should implement `#readFile` compatible with
+     * Node.js'.  The Store constructor `store_ctor` is used to instantiate
+     * new stores to be populated with configuration data.
+     *
+     * @param {fs}               fs         filesystem module
+     * @param {function():Store} store_ctor Store object constructor
+     */
+    constructor( fs, store_ctor )
+    {
+        this._fs        = fs;
+        this._storeCtor = store_ctor;
+    },
+
+
+    /**
+     * Produce configuration from file
+     *
+     * A Store will be produced, populated with the configuration data.
+     *
+     * @param {string} filename path to configuration JSON
+     *
+     * @return {Promise.<Store>} a promise of a populated Store
+     */
+    'public fromFile'( filename )
+    {
+        return new Promise( ( resolve, reject ) =>
+        {
+            this._fs.readFile( filename, 'utf8', ( err, data ) =>
+            {
+                if ( err )
+                {
+                    reject( err );
+                    return;
+                }
+
+                try
+                {
+                    const store = this._storeCtor();
+
+                    resolve(
+                        this.parseConfData( data )
+                            .then( parsed => store.populate( parsed ) )
+                            .then( _ => store )
+                    );
+                }
+                catch ( e )
+                {
+                    reject( e );
+                }
+            } );
+        } );
+    },
+
+
+    /**
+     * Parse raw configuration string
+     *
+     * Parses configuration string as JSON.
+     *
+     * @param {string} data raw configuration data
+     *
+     * @return {Promise.<Object>} `data` parsed as JSON
+     */
+    'virtual protected parseConfData'( data )
+    {
+        return Promise.resolve( JSON.parse( data ) );
+    },
+} );
diff --git a/test/conf/ConfLoaderTest.js b/test/conf/ConfLoaderTest.js
new file mode 100644
index 0000000..b942216
--- /dev/null
+++ b/test/conf/ConfLoaderTest.js
@@ -0,0 +1,136 @@
+/**
+ * Tests ConfLoader
+ */
+
+'use strict';
+
+const chai                = require( 'chai' );
+const expect              = chai.expect;
+const {
+    conf: {
+        ConfLoader: Sut,
+    },
+    store: {
+        MemoryStore: Store,
+    },
+} = require( '../../' );
+
+chai.use( require( 'chai-as-promised' ) );
+
+
+describe( 'ConfLoader', () =>
+{
+    it( "loads Store'd configuration from file", () =>
+    {
+        const expected_path = "/foo/bar/baz.json";
+        const expected_data = '{ "foo": "bar" }';
+
+        const fs = {
+            readFile( path, encoding, callback )
+            {
+                expect( path ).to.equal( expected_path );
+                expect( encoding ).to.equal( 'utf8' );
+
+                callback( null, expected_data );
+            },
+        };
+
+        return expect(
+            Sut( fs, Store )
+                .fromFile( expected_path )
+                .then( conf => conf.get( 'foo' ) )
+        ).to.eventually.deep.equal( JSON.parse( expected_data ).foo );
+    } );
+
+
+    it( "fails on read error", () =>
+    {
+        const expected_err = Error( 'rejected' );
+
+        const fs = {
+            readFile( _, __, callback )
+            {
+                callback( expected_err, null );
+            },
+        };
+
+        return expect( Sut( fs ).fromFile( '' ) )
+            .to.eventually.be.rejectedWith( expected_err );
+    } );
+
+
+    it( "can override #parseConfData for custom parser", () =>
+    {
+        const result = { foo: {} };
+        const input  = "foo";
+
+        const fs = {
+            readFile( _, __, callback )
+            {
+                callback( null, input );
+            },
+        };
+
+        const sut = Sut.extend(
+        {
+            'override parseConfData'( given_input )
+            {
+                expect( given_input ).to.equal( input );
+                return Promise.resolve( result );
+            },
+        } )( fs, Store );
+
+        return expect(
+            sut.fromFile( '' )
+                .then( conf => conf.get( 'foo' ) )
+        ).to.eventually.equal( result.foo );
+    } );
+
+
+    it( 'rejects promise on parsing error', () =>
+    {
+        const expected_err = SyntaxError( 'test parsing error' );
+
+        const fs = {
+            readFile( _, __, callback )
+            {
+                // make async so that we clear the stack, and therefore
+                // try/catch
+                process.nextTick( () => callback( null, '' ) );
+            },
+        };
+
+        const sut = Sut.extend(
+        {
+            'override parseConfData'( given_input )
+            {
+                throw expected_err;
+            },
+        } )( fs, Store );
+
+        return expect( sut.fromFile( '' ) )
+            .to.eventually.be.rejectedWith( expected_err );
+    } );
+
+
+    it( "rejects promise on Store ctor error", () =>
+    {
+        const expected_err = Error( 'test Store ctor error' );
+
+        const fs = {
+            readFile: ( _, __, callback ) => callback( null, '' ),
+        };
+
+        const badstore = () => { throw expected_err };
+
+        return expect( Sut( fs, badstore ).fromFile( '' ) )
+            .to.eventually.be.rejectedWith( expected_err );
+    } );
+
+
+    it( "rejects promise on bad fs call", () =>
+    {
+        return expect( Sut( {}, Store ).fromFile( '' ) )
+            .to.eventually.be.rejected;
+    } );
+} );