1 files changed, 91 insertions, 0 deletions
diff --git a/cli/js/type_directives.ts b/cli/js/type_directives.ts
new file mode 100644
index 000000000..9b27887b5
--- /dev/null
+++ b/cli/js/type_directives.ts
@@ -0,0 +1,91 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+
+interface FileReference {
+  fileName: string;
+  pos: number;
+  end: number;
+}
+
+/** Remap the module name based on any supplied type directives passed. */
+export function getMappedModuleName(
+  source: FileReference,
+  typeDirectives: Map<FileReference, string>
+): string {
+  const { fileName: sourceFileName, pos: sourcePos } = source;
+  for (const [{ fileName, pos }, value] of typeDirectives.entries()) {
+    if (sourceFileName === fileName && sourcePos === pos) {
+      return value;
+    }
+  }
+  return source.fileName;
+}
+
+/** Matches directives that look something like this and parses out the value
+ * of the directive:
+ *
+ *      // @deno-types="./foo.d.ts"
+ *
+ * [See Diagram](http://bit.ly/31nZPCF)
+ */
+const typeDirectiveRegEx = /@deno-types\s*=\s*(["'])((?:(?=(\\?))\3.)*?)\1/gi;
+
+/** Matches `import`, `import from` or `export from` statements and parses out the value of the
+ * module specifier in the second capture group:
+ *
+ *      import "./foo.js"
+ *      import * as foo from "./foo.js"
+ *      export { a, b, c } from "./bar.js"
+ *
+ * [See Diagram](http://bit.ly/2lOsp0K)
+ */
+const importExportRegEx = /(?:import|export)(?:\s+|\s+[\s\S]*?from\s+)?(["'])((?:(?=(\\?))\3.)*?)\1/;
+
+/** Parses out any Deno type directives that are part of the source code, or
+ * returns `undefined` if there are not any.
+ */
+export function parseTypeDirectives(
+  sourceCode: string | undefined
+): Map<FileReference, string> | undefined {
+  if (!sourceCode) {
+    return;
+  }
+
+  // collect all the directives in the file and their start and end positions
+  const directives: FileReference[] = [];
+  let maybeMatch: RegExpExecArray | null = null;
+  while ((maybeMatch = typeDirectiveRegEx.exec(sourceCode))) {
+    const [matchString, , fileName] = maybeMatch;
+    const { index: pos } = maybeMatch;
+    directives.push({
+      fileName,
+      pos,
+      end: pos + matchString.length
+    });
+  }
+  if (!directives.length) {
+    return;
+  }
+
+  // work from the last directive backwards for the next `import`/`export`
+  // statement
+  directives.reverse();
+  const results = new Map<FileReference, string>();
+  for (const { end, fileName, pos } of directives) {
+    const searchString = sourceCode.substring(end);
+    const maybeMatch = importExportRegEx.exec(searchString);
+    if (maybeMatch) {
+      const [matchString, , targetFileName] = maybeMatch;
+      const targetPos =
+        end + maybeMatch.index + matchString.indexOf(targetFileName) - 1;
+      const target: FileReference = {
+        fileName: targetFileName,
+        pos: targetPos,
+        end: targetPos + targetFileName.length
+      };
+      results.set(target, fileName);
+    }
+    sourceCode = sourceCode.substring(0, pos);
+  }
+
+  return results;
+}