Add framework for block execution

The runtime now stores a mapping of opcode to function.
The `wedo2` and `scratch3` packages are currently stubs.

src/blocks/scratch3.js

@@ -0,0 +1,14 @@
+
+function Scratch3Blocks() {
+}
+
+/**
+ * Retrieve the block primitives implemented by this package.
+ * @return {Object.<string, Function>} Mapping of opcode to Function.
+ */
+Scratch3Blocks.prototype.getPrimitives = function() {
+    return {
+    };
+};
+
+module.exports = Scratch3Blocks;

src/blocks/wedo2.js

@@ -0,0 +1,14 @@
+
+function WeDo2Blocks() {
+}
+
+/**
+ * Retrieve the block primitives implemented by this package.
+ * @return {Object.<string, Function>} Mapping of opcode to Function.
+ */
+WeDo2Blocks.prototype.getPrimitives = function() {
+    return {
+    };
+};
+
+module.exports = WeDo2Blocks;

src/engine/runtime.js

@@ -3,6 +3,11 @@ var Sequencer = require('./sequencer');
 var Thread = require('./thread');
 var util = require('util');
 
+var defaultBlockPackages = {
+    'scratch3': require('../blocks/scratch3'),
+    'wedo2': require('../blocks/wedo2')
+};
+
 /**
  * Manages blocks, stacks, and the sequencer.
  */
@@ -34,6 +39,14 @@ function Runtime () {
 
     /** @type {!Sequencer} */
     this.sequencer = new Sequencer(this);
+
+    /**
+     * Map to look up a block primitive's implementation function by its opcode.
+     * This is a two-step lookup: package name first, then primitive name.
+     * @type {Object.<string, Function>}
+     */
+    this._primitives = {};
+    this._registerBlockPackages();
 }
 
 /**
@@ -184,6 +197,37 @@ Runtime.prototype.deleteBlock = function (e) {
 // -----------------------------------------------------------------------------
 // -----------------------------------------------------------------------------
 
+/**
+ * Register default block packages with this runtime.
+ * @todo Prefix opcodes with package name.
+ * @private
+ */
+Runtime.prototype._registerBlockPackages = function () {
+    for (var packageName in defaultBlockPackages) {
+        if (defaultBlockPackages.hasOwnProperty(packageName)) {
+            var packageObject = new (defaultBlockPackages[packageName])();
+            var packageContents = packageObject.getPrimitives();
+            for (var op in packageContents) {
+                if (packageContents.hasOwnProperty(op)) {
+                    this._primitives[op] = packageContents[op];
+                }
+            }
+        }
+    }
+};
+
+/**
+ * Retrieve the function associated with the given opcode.
+ * @param {!string} opcode The opcode to look up.
+ * @return {Function} The function which implements the opcode.
+ */
+Runtime.prototype.getOpcodeFunction = function (opcode) {
+    return this._primitives[opcode];
+};
+
+// -----------------------------------------------------------------------------
+// -----------------------------------------------------------------------------
+
 /**
  * Create a thread and push it to the list of threads.
  * @param {!string} id ID of block that starts the stack
@@ -306,4 +350,14 @@ Runtime.prototype._getSubstack = function (id) {
     return this.blocks[id].fields['SUBSTACK'];
 };
 
+/**
+ * Helper to get the opcode for a particular block
+ * @param {?string} id ID of block to query
+ * @return {?string} the opcode corresponding to that block
+ */
+Runtime.prototype._getOpcode = function (id) {
+    if (typeof this.blocks[id] === 'undefined') return null;
+    return this.blocks[id].opcode;
+};
+
 module.exports = Runtime;

src/engine/sequencer.js

@@ -58,10 +58,22 @@ Sequencer.prototype.stepThreads = function (threads) {
  * @param {!Thread} thread Thread object to step
  */
 Sequencer.prototype.stepThread = function (thread) {
-    // @todo Actually run the blocks
-    // Currently goes to the next block in the sequence.
-    var nextBlock = this.runtime._getNextBlock(thread.nextBlock);
-    thread.nextBlock = nextBlock;
+    var opcode = this.runtime._getOpcode(thread.nextBlock);
+
+    if (!opcode) {
+        console.log('Could not get opcode for block: ' + thread.nextBlock);
+    }
+    else {
+        var blockFunction = this.runtime.getOpcodeFunction(opcode);
+        if (!blockFunction) {
+            console.log('Could not get implementation for opcode: ' + opcode);
+        }
+        else {
+            blockFunction();
+        }
+    }
+
+    thread.nextBlock = this.runtime._getNextBlock(thread.nextBlock);
 };
 
 module.exports = Sequencer;