Let the coordinator set a workspace's picture

update_workspace now takes an image media id (or null to remove the
picture). updateWorkspace writes image_media_id through
resolveWorkspacePicture, which only accepts the caller's own image and
deletes the picture it replaced, so a bot can never show someone else's
file or drop a picture it is still using.

src/utils/resolve-workspace-picture.test.ts

@@ -0,0 +1,66 @@
+import { describe, expect, test } from "bun:test";
+import AppError from "./app-error";
+import resolveWorkspacePicture from "./resolve-workspace-picture";
+
+const image = (id: number) => ({ id, media_type: "image" });
+
+describe("resolveWorkspacePicture", () => {
+    test("leaves the picture alone when nothing is asked for", () => {
+        expect(resolveWorkspacePicture({ current: 4 })).toBeUndefined();
+    });
+
+    test("sets a new image of the caller's", () => {
+        expect(
+            resolveWorkspacePicture({ requested: 9, current: 4, media: image(9) }),
+        ).toBe(9);
+    });
+
+    test("clears the picture with null", () => {
+        expect(
+            resolveWorkspacePicture({ requested: null, current: 4 }),
+        ).toBeNull();
+    });
+
+    test("naming the picture it already has changes nothing, so it is never deleted", () => {
+        expect(
+            resolveWorkspacePicture({ requested: 4, current: 4 }),
+        ).toBeUndefined();
+        expect(
+            resolveWorkspacePicture({ requested: "4", current: 4, media: image(4) }),
+        ).toBeUndefined();
+    });
+
+    test("refuses media that isn't the caller's", () => {
+        expect(() =>
+            resolveWorkspacePicture({ requested: 9, current: null, media: null }),
+        ).toThrow(AppError);
+    });
+
+    test("refuses anything that isn't an image", () => {
+        expect(() =>
+            resolveWorkspacePicture({
+                requested: 9,
+                current: null,
+                media: { id: 9, media_type: "document" },
+            }),
+        ).toThrow(`A workspace picture has to be an image.`);
+    });
+
+    test("refuses an id that names a different row than the one looked up", () => {
+        expect(() =>
+            resolveWorkspacePicture({
+                requested: 9,
+                current: null,
+                media: image(10),
+            }),
+        ).toThrow(AppError);
+    });
+
+    test("refuses an id that isn't a positive integer", () => {
+        for (const requested of [0, -3, 1.5, "abc"]) {
+            expect(() =>
+                resolveWorkspacePicture({ requested, current: null }),
+            ).toThrow(AppError);
+        }
+    });
+});

src/utils/resolve-workspace-picture.ts

@@ -0,0 +1,51 @@
+import AppError from "@/src/utils/app-error";
+
+type Params = {
+    /**
+     * The `workspace_media_id` the caller asked for: a new picture, or
+     * null to remove the one it has. Undefined leaves it alone.
+     */
+    requested?: number | string | null;
+    /**
+     * The picture the workspace has now.
+     */
+    current?: number | string | null;
+    /**
+     * The media row the requested id names, when it was found for the
+     * caller (`grabOwnPictureMedia`); required to set a new picture.
+     */
+    media?: { id?: number | string | null; media_type?: string | null } | null;
+};
+
+/**
+ * What `updateWorkspace` should write into `workspaces.image_media_id`:
+ * undefined to leave it as it is, null to clear it, or the new media id.
+ *
+ * A new picture has to be the caller's own image: the resolver refuses an
+ * id that isn't an image, and the media lookup refuses one that isn't
+ * theirs. Handing back the picture it already has changes nothing, so
+ * saying "use this picture" twice never deletes it.
+ */
+export default function resolveWorkspacePicture({ requested, current, media }: Params) {
+    if (requested === undefined) return undefined;
+
+    if (requested === null) return null;
+
+    const id = Number(requested);
+
+    if (!Number.isInteger(id) || id <= 0) {
+        throw new AppError(`Pick an image for the workspace.`);
+    }
+
+    if (current != null && Number(current) == id) return undefined;
+
+    if (!media || Number(media.id) != id) {
+        throw new AppError(`That picture isn't one of yours. Upload it again.`);
+    }
+
+    if (media.media_type != "image") {
+        throw new AppError(`A workspace picture has to be an image.`);
+    }
+
+    return id;
+}