refactor IPromptObject return from build method

package.json

@@ -1,6 +1,6 @@
 {
   "name": "langtail",
-  "version": "0.3.2-beta-0",
+  "version": "0.4.0-beta-0",
   "description": "",
   "main": "./dist/LangtailNode.js",
   "packageManager": "pnpm@8.15.6",

src/LangtailPrompts.spec.ts

@@ -195,15 +195,15 @@ describe(
           }
         `)
 
-        const openAiBody = ltLocal.build(playgroundState, {
+        const promptObj = ltLocal.build(playgroundState, {
           stream: true,
           variables: {
             optionalExtra: "This is an optional extra",
           },
 
         })
 
-        expect(openAiBody).toMatchInlineSnapshot(`
+        expect(promptObj.toOpenAI()).toMatchInlineSnapshot(`
           {
             "frequency_penalty": 0,
             "max_tokens": 800,

src/LangtailPrompts.ts

@@ -5,7 +5,7 @@ import {
 import { ChatCompletionChunk } from "openai/resources/chat/completions"
 
 import { Stream } from "openai/streaming"
-import { ILangtailExtraProps } from "./LangtailNode"
+import { ILangtailExtraProps, LangtailNode } from "./LangtailNode"
 import { Fetch } from "openai/core"
 import { userAgent } from "./userAgent"
 import queryString from "query-string"
@@ -50,16 +50,29 @@ interface IRequestParamsStream extends IRequestParams {
   stream: boolean
 }
 
+interface IPromptObject {
+  promptConfig: PlaygroundState
+  variables: Record<string, string> | undefined
+  toOpenAI: () => ReturnType<typeof getOpenAIBody>
+}
+
 export class LangtailPrompts {
   apiKey: string
   baseUrl: string
   options: Options
+  ltNode: LangtailNode
 
   constructor(options: Options) {
     const { apiKey, baseURL: baseUrl } = options
     this.apiKey = apiKey
     this.baseUrl = baseUrl ?? "https://api.langtail.com"
     this.options = options
+
+    this.ltNode = new LangtailNode({
+      apiKey,
+      fetch: options.fetch,
+      onResponse: options.onResponse,
+    })
   }
 
   _createPromptPath({
@@ -205,8 +218,23 @@ export class LangtailPrompts {
     return res.json()
   }
 
-  build(completionConfig: PlaygroundState, parsedBody: OpenAiBodyType) {
-    return getOpenAIBody(completionConfig, parsedBody)
+  build(
+    completionConfig: PlaygroundState,
+    parsedBody: OpenAiBodyType,
+  ): IPromptObject {
+    const openAiBody = getOpenAIBody(completionConfig, parsedBody)
+    return {
+      promptConfig: completionConfig,
+      variables: parsedBody.variables,
+      toOpenAI: () => openAiBody,
+    }
+  }
+
+  completions = {
+    create: async (prompt: IPromptObject) => {
+      // @ts-expect-error
+      return this.ltNode.chat.completions.create(prompt.toOpenAI())
+    },
   }
 
   async _record(