1 files changed, 57 insertions, 0 deletions
diff --git a/llparse-builder/src/span.ts b/llparse-builder/src/span.ts
new file mode 100644
index 0000000..99cafb0
--- /dev/null
+++ b/llparse-builder/src/span.ts
@@ -0,0 +1,57 @@
+import * as assert from 'assert';
+
+import { Span as SpanCallback } from './code';
+import { Node, SpanEnd, SpanStart } from './node';
+
+/**
+ * Spans are used for notifying parser user about matched data. Each byte after
+ * span start will be sent to the span callback until span end is called.
+ */
+export class Span {
+  private readonly startCache: Map<Node, SpanStart> = new Map();
+  private readonly endCache: Map<Node, SpanEnd> = new Map();
+
+  /**
+   * @param callback  External callback, must be `code.span(...)` result.
+   */
+  constructor(public readonly callback: SpanCallback) {
+  }
+
+  /**
+   * Create `SpanStart` that indicates the start of the span.
+   *
+   * @param otherwise Optional convenience value. Same as calling
+   *                  `span.start().otherwise(...)`
+   */
+  public start(otherwise?: Node) {
+    if (otherwise !== undefined && this.startCache.has(otherwise)) {
+      return this.startCache.get(otherwise)!;
+    }
+
+    const res = new SpanStart(this);
+    if (otherwise !== undefined) {
+      res.otherwise(otherwise);
+      this.startCache.set(otherwise, res);
+    }
+    return res;
+  }
+
+  /**
+   * Create `SpanEnd` that indicates the end of the span.
+   *
+   * @param otherwise Optional convenience value. Same as calling
+   *                  `span.end().otherwise(...)`
+   */
+  public end(otherwise?: Node) {
+    if (otherwise !== undefined && this.endCache.has(otherwise)) {
+      return this.endCache.get(otherwise)!;
+    }
+
+    const res = new SpanEnd(this);
+    if (otherwise !== undefined) {
+      res.otherwise(otherwise);
+      this.endCache.set(otherwise, res);
+    }
+    return res;
+  }
+}