1 files changed, 54 insertions, 0 deletions
diff --git a/llparse-builder/src/edge.ts b/llparse-builder/src/edge.ts
new file mode 100644
index 0000000..f6b55cc
--- /dev/null
+++ b/llparse-builder/src/edge.ts
@@ -0,0 +1,54 @@
+import * as assert from 'assert';
+
+import { Buffer } from 'buffer';
+import { Invoke, Node } from './node';
+
+/**
+ * This class represents an edge in the parser graph.
+ */
+export class Edge {
+  /**
+   * Comparator for `.sort()` function.
+   */
+  public static compare(a: Edge, b: Edge): number {
+    if (typeof a.key === 'number') {
+      return a.key - (b.key as number);
+    }
+    return a.key!.compare(b.key as Buffer);
+  }
+
+  /**
+   * @param node       Edge target
+   * @param noAdvance  If `true` - the parent should not consume bytes before
+   *                   moving to the target `node`
+   * @param key        `Buffer` for `node.Match`, `number` for `node.Invoke`,
+   *                   `undefined` for edges created with `.otherwise()`
+   * @param value      `.select()` value associated with the edge
+   */
+  constructor(public readonly node: Node,
+              public readonly noAdvance: boolean,
+              public readonly key: Buffer | number | undefined,
+              public readonly value: number | undefined) {
+    if (node instanceof Invoke) {
+      if (value === undefined) {
+        assert.strictEqual(node.code.signature, 'match',
+          'Invalid Invoke\'s code signature');
+      } else {
+        assert.strictEqual(node.code.signature, 'value',
+          'Invalid Invoke\'s code signature');
+      }
+    } else {
+      assert.strictEqual(value, undefined,
+        'Attempting to pass value to non-Invoke node');
+    }
+
+    if (Buffer.isBuffer(key)) {
+      assert(key.length > 0, 'Invalid edge buffer length');
+
+      if (noAdvance) {
+        assert.strictEqual(key.length, 1,
+          'Only 1-char keys are allowed in `noAdvance` edges');
+      }
+    }
+  }
+}