diff --git a/src/cache.ts b/src/cache.ts
index b34928e..e2b9030 100644
--- a/src/cache.ts
+++ b/src/cache.ts
@@ -2,6 +2,7 @@ import * as ts from "typescript";
 import * as graph from "graphlib";
 import * as hash from "object-hash";
 import * as fs from "fs";
+import * as _ from "lodash";
 
 interface ICode
 {
@@ -40,6 +41,7 @@ export class Cache
 
 	public setDependency(importee: string, importer: string): void
 	{
+		// importer -> importee
 		this.dependencyTree.setEdge(importer, importee);
 	}
 
@@ -48,61 +50,65 @@ export class Cache
 		this.treeComplete = true;
 	}
 
-	public markAsDirty(fileName: string, _snapshot: ts.IScriptSnapshot)
+	public markAsDirty(id: string, _snapshot: ts.IScriptSnapshot)
 	{
-		this.dependencyTree.setNode(fileName, { dirty: true });
+		this.dependencyTree.setNode(id, { dirty: true });
 	}
 
-	public isDirty(fileName: string, _snapshot: ts.IScriptSnapshot): boolean
+	// returns true if node or any of its imports changed
+	public isDirty(id: string, _snapshot: ts.IScriptSnapshot, checkImports: boolean): boolean
 	{
-		let label = this.dependencyTree.node(fileName) as INodeLabel;
+		let label = this.dependencyTree.node(id) as INodeLabel;
 
-		// TODO: also if any dependencies are dirty
+		if (checkImports || label.dirty)
+			return label.dirty;
 
-		return label.dirty;
+		let dependencies = graph.alg.dijkstra(this.dependencyTree, id);
+
+		return _.some(_.keys(dependencies), (dependencyId: string) => (this.dependencyTree.node(dependencyId) as INodeLabel).dirty);
 	}
 
-	public getCompiled(fileName: string, snapshot: ts.IScriptSnapshot, transform: () =>  ICode | undefined): ICode | undefined
+	public getCompiled(id: string, snapshot: ts.IScriptSnapshot, transform: () =>  ICode | undefined): ICode | undefined
 	{
-		let path = this.makePath(fileName, snapshot);
+		let path = this.makePath(id, snapshot);
 
-		if (!fs.existsSync(path) || this.isDirty(fileName, snapshot))
+		if (!fs.existsSync(path) || this.isDirty(id, snapshot, false))
 		{
 			let data = transform();
-			this.setCache(path, fileName, snapshot, data);
+			this.setCache(path, id, snapshot, data);
 			return data;
 		}
 
 		return JSON.parse(fs.readFileSync(path, "utf8")) as ICode;
 	}
 
-	public getDiagnostics(fileName: string, snapshot: ts.IScriptSnapshot, check: () => ts.Diagnostic[]): ts.Diagnostic[]
+	public getDiagnostics(id: string, snapshot: ts.IScriptSnapshot, check: () => ts.Diagnostic[]): ts.Diagnostic[]
 	{
-		let path = `${this.makePath(fileName, snapshot)}.diagnostics`;
+		let path = `${this.makePath(id, snapshot)}.diagnostics`;
 
-		if (!fs.existsSync(path) || this.isDirty(fileName, snapshot))
+		if (!fs.existsSync(path) || this.isDirty(id, snapshot, true))
 		{
 			let data = check();
-			this.setCache(path, fileName, snapshot, data);
+			this.setCache(path, id, snapshot, data);
 			return data;
 		}
 
 		return JSON.parse(fs.readFileSync(path, "utf8")) as ts.Diagnostic[];
 	}
 
-	private setCache(path: string, fileName: string, snapshot: ts.IScriptSnapshot, data: ts.Diagnostic[] | ICode | undefined): void
+	private setCache(path: string, id: string, snapshot: ts.IScriptSnapshot, data: ts.Diagnostic[] | ICode | undefined): void
 	{
 		if (data === undefined)
 			return;
 
 		fs.writeFileSync(path, JSON.stringify(data));
 
-		this.markAsDirty(fileName, snapshot);
+		this.markAsDirty(id, snapshot);
 	}
 
-	private makePath(fileName: string, snapshot: ts.IScriptSnapshot): string
+	private makePath(id: string, snapshot: ts.IScriptSnapshot): string
 	{
 		let data = snapshot.getText(0, snapshot.getLength());
-		return `${this.cacheRoot}/${hash.sha1({ data, fileName })}`;
+		return `${this.cacheRoot}/${hash.sha1({ data, id })}`;
 	}
 }