Replace Hotpatch with save patching

Remove Hotpatch and implement a save patcher in its place.  The save
patcher takes a normal Factorio save and adds modules to it that's
loaded by a generated control.lua file.  This greatly reduces the
difficulty of adding an existing game to Clusterio and using scenario
code in plugins.

The mechanism for selecting what code to patch into the saves from
plugins is temorary and expected to change with #220.

test/integration/patch.js

@@ -0,0 +1,31 @@
+const assert = require("assert").strict;
+const fs = require("fs-extra");
+const jszip = require("jszip");
+const path = require("path");
+
+const factorio = require("lib/factorio");
+
+
+// The server integration test is required to run before this one
+require("./server")
+
+describe("Integration of lib/factorio/patch", function() {
+	describe("patch()", function() {
+		let savePath = path.join("test", "temp", "integration", "saves", "test.zip");
+		it("should patch a freeplay game", async function() {
+			await factorio.patch(savePath, [{
+				name: "test",
+				files: [{ path: "test.lua", content: "-- test" }]
+			}]);
+
+			let zip = await jszip.loadAsync(await fs.readFile(savePath));
+			let content = await zip.file("test/modules/test.lua").async("string");
+			assert.equal(content, "-- test");
+		});
+		it("should remove old modules in a save", async function() {
+			await factorio.patch(savePath, [{ name: "test", files: [] }]);
+			let zip = await jszip.loadAsync(await fs.readFile(savePath));
+			assert.equal(zip.file("test/modules/test.lua"), null);
+		});
+	});
+});

test/lib/factorio/patch.js

@@ -0,0 +1,94 @@
+const assert = require("assert").strict;
+const fs = require("fs-extra");
+const jszip = require("jszip");
+const path = require("path");
+
+const factorio = require("lib/factorio");
+
+
+describe("lib/factorio", function() {
+	describe("findRoot()", function() {
+		it("should find the root of a zip", function() {
+			let zip = new jszip();
+			zip.file("root/foo.txt", "");
+			zip.file("root/bar.txt", "");
+
+			assert.equal(factorio._findRoot(zip), "root");
+		});
+
+		it("should throw if files are at the root of the zip", function() {
+			let zip = new jszip();
+			zip.file("root/foo.txt", "");
+			zip.file("bar.txt", "");
+
+			assert.throws(
+				() => factorio._findRoot(zip),
+				new Error("Zip contains file 'bar.txt' in root dir")
+			);
+		});
+
+		it("should throw if there are multiple root dirs", function() {
+			let zip = new jszip();
+			zip.file("root-1/foo.txt", "");
+			zip.file("root-2/bar.txt", "");
+
+			assert.throws(
+				() => factorio._findRoot(zip),
+				new Error("Zip contains multiple root folders")
+			);
+		});
+
+		it("should throw if given an empty zip file", function() {
+			let zip = new jszip();
+
+			assert.throws(
+				() => factorio._findRoot(zip),
+				new Error("Empty zip file")
+			);
+		});
+	});
+
+	describe("generateLoader()", function() {
+		let reference = [
+			'-- Auto generated scenario module loader created by Clusterio',
+			'-- Modifications to this file will be lost when loaded in Clusterio',
+			'',
+			'local event_handler = require("event_handler")',
+			'',
+			'-- Scenario modules',
+			'event_handler.add_lib(require("foo"))',
+			'',
+			'-- Clusterio modules',
+			'event_handler.add_lib(require("modules/bar"))',
+			'',
+		].join('\n');
+		let patchInfo = {
+			"scenario": { "modules": ["foo"] },
+			"modules": [{
+				"name": "spam",
+				"files": [
+					{ "path": "bar.lua", "load": true },
+					{ "path": "excluded.lua", "load": false },
+				],
+			}],
+		};
+
+		it("should produce output matching the reference", function() {
+			assert.equal(factorio._generateLoader(patchInfo), reference);
+		});
+	});
+
+	describe("patch()", function() {
+		it("should throw on unknown scenario", async function() {
+			let zip = new jszip();
+			zip.file("world/control.lua", "-- unknown\n");
+			let zipPath = path.join("test", "temp", "patch.zip");
+			await fs.outputFile(zipPath, await zip.generateAsync({type: "nodebuffer"}))
+
+			await assert.rejects(
+				factorio.patch(zipPath, []),
+				new Error("Unable to patch save, unknown scenario (3acc3be3861144e55604f5ac2f2555071885ebc4)")
+			);
+		});
+	});
+});