introduce native promise support incl. documentation & types

package.json

@@ -3,7 +3,19 @@
     "version": "1.7.0",
     "description": "Comprehensive NodeJS API wrapper for the Robinhood API",
     "main": "src/robinhood.js",
-    "typings": "robinhood.d.ts",
+    "typings": "types/robinhood.d.ts",
+    "typesVersions": {
+        "<4.1": {
+            "promises": [
+                "types/promises.v3.d.ts"
+            ]
+        },
+        ">=4.1": {
+            "promises": [
+                "types/promises.d.ts"
+            ]
+        }
+    },
     "exports": {
         ".": "./src/robinhood.js",
         "./promises": "./src/promises.js",

types/promises.d.ts

@@ -0,0 +1,42 @@
+// requires typescript 4.1+
+
+import robinhood = require("./robinhood");
+
+type RemoveFnParam<T extends unknown[]> = T extends []
+    ? []
+    : T extends [infer H, ...infer R]
+    ? H extends Function
+        ? RemoveFnParam<R>
+        : [H, ...RemoveFnParam<R>]
+    : T;
+
+type LastTupleElement<T extends unknown[]> = T extends [infer X]
+    ? X
+    : T extends [infer H, ...infer R]
+    ? LastTupleElement<R>
+    : T;
+
+declare function RobinhoodPromiseAPI(
+    options: robinhood.Options.WebApiOpts
+): Promise<
+    {
+        [key in keyof robinhood.RobinhoodWebApi]: (
+            ...args: RemoveFnParam<Parameters<robinhood.RobinhoodWebApi[key]>>
+        ) => Promise<
+            LastTupleElement<
+                Parameters<robinhood.RobinhoodWebApi[key]>
+            > extends Function
+                ? LastTupleElement<
+                      Parameters<
+                          // @ts-expect-error: this must be a function in this block
+                          LastTupleElement<
+                              Parameters<robinhood.RobinhoodWebApi[key]>
+                          >
+                      >
+                  >
+                : ReturnType<robinhood.RobinhoodWebApi[key]>
+        >;
+    }
+>;
+
+export = RobinhoodPromiseAPI;

types/promises.v3.d.ts

@@ -0,0 +1,15 @@
+// for typescript <4.1
+
+import robinhood = require("./robinhood");
+
+declare function RobinhoodPromiseAPI(
+    options: robinhood.Options.WebApiOpts
+): Promise<
+    {
+        [key in keyof robinhood.RobinhoodWebApi]: (
+            ...args: any[]
+        ) => Promise<any>;
+    }
+>;
+
+export = RobinhoodPromiseAPI;