feat: add figma plugin

src/figma/figma-api.ts

@@ -0,0 +1,80 @@
+/**
+ * This is a magic file that allows us to run code in the Figma plugin context
+ * from the iframe. It does this by getting the code as a string, and sending it
+ * to the plugin via postMessage. The plugin then evals the code and sends the
+ * result back to the iframe. There are a few caveats:
+ * 1. The code cannot reference any variables outside of the function. This is
+ *   because the code is stringified and sent to the plugin, and the plugin
+ *   evals it. The plugin has no access to the variables in the iframe.
+ * 2. The return value of the function must be JSON serializable. This is
+ *    because the result is sent back to the iframe via postMessage, which only
+ *    supports JSON.
+ *
+ * You can get around these limitations by passing in the variables you need
+ * as parameters to the function.
+ *
+ * @example
+ * ```ts
+ * const result = await figmaAPI.run((figma, {nodeId}) => {
+ *   return figma.getNodeById(nodeId)?.name;
+ * }, {nodeId: "0:2"});
+ *
+ * console.log(result); // "Page 1"
+ * ```
+ */
+class FigmaAPI {
+  private id = 0
+
+  /**
+   * Run a function in the Figma plugin context. The function cannot reference
+   * any variables outside of itself, and the return value must be JSON
+   * serializable. If you need to pass in variables, you can do so by passing
+   * them as the second parameter.
+   */
+  run<T, U>(fn: (figma: PluginAPI, params: U) => Promise<T> | T, params?: U): Promise<T> {
+    return new Promise((resolve, reject) => {
+      const id = this.id++
+      const cb = (event: MessageEvent) => {
+        if (event.origin !== 'https://www.figma.com' && event.origin !== 'https://staging.figma.com') {
+          return
+        }
+
+        if (event.data.pluginMessage?.type === 'EVAL_RESULT') {
+          if (event.data.pluginMessage.id === id) {
+            window.removeEventListener('message', cb)
+            resolve(event.data.pluginMessage.result)
+          }
+        }
+
+        if (event.data.pluginMessage?.type === 'EVAL_REJECT') {
+          if (event.data.pluginMessage.id === id) {
+            window.removeEventListener('message', cb)
+            const message = event.data.pluginMessage.error
+            reject(new Error(typeof message === 'string' ? message : 'An error occurred in FigmaAPI.run()'))
+          }
+        }
+      }
+      window.addEventListener('message', cb)
+
+      const msg = {
+        pluginMessage: {
+          type: 'EVAL',
+          code: fn.toString(),
+          id,
+          params,
+        },
+        pluginId: '*',
+      }
+
+        ;['https://www.figma.com', 'https://staging.figma.com'].forEach((origin) => {
+          try {
+            parent.postMessage(msg, origin)
+          } catch (e) {
+            console.error(e)
+          }
+        })
+    })
+  }
+}
+
+export const figmaAPI = new FigmaAPI()