/**
 * Step 1 - Minimal LLM streaming client
 *
 * Goal:
 * - show the smallest useful Anthropic client wrapper
 * - stream text and tool-use events
 * - keep the code in one file for teaching purposes
 *
 * This file is intentionally simpler than easy-agent/src/services/api/*.
 */

import Anthropic from "@anthropic-ai/sdk";

export const DEFAULT_MODEL = process.env.ANTHROPIC_MODEL || "claude-sonnet-4-20250514";
export const DEFAULT_MAX_TOKENS = 4096;

// Create one shared SDK client.
export function getClient() {
  return new Anthropic({
    apiKey: process.env.ANTHROPIC_AUTH_TOKEN,
    baseURL: process.env.ANTHROPIC_BASE_URL,
  });
}

// Content blocks are the core message shape in Anthropic's Messages API.
export function textBlock(text = "") {
  return { type: "text", text };
}

export function toolUseBlock(id, name, input = {}) {
  return { type: "tool_use", id, name, input };
}

/**
 * Stream one assistant turn.
 *
 * Yields small events so the caller can render text in real time.
 * Returns the final assembled assistant message + usage.
 */
export async function* streamMessage({ messages, model = DEFAULT_MODEL, system, tools }) {
  const client = getClient();
  const stream = client.messages.stream({
    model,
    max_tokens: DEFAULT_MAX_TOKENS,
    messages,
    stream: true,
    ...(system ? { system } : {}),
    ...(tools?.length ? { tools } : {}),
  });

  const content = [];
  const usage = { input_tokens: 0, output_tokens: 0 };
  let stopReason = "end_turn";
  let pendingToolJson = "";

  for await (const event of stream) {
    switch (event.type) {
      case "message_start": {
        usage.input_tokens = event.message.usage?.input_tokens || 0;
        yield { type: "message_start", messageId: event.message.id };
        break;
      }

      case "content_block_start": {
        if (event.content_block.type === "text") {
          content[event.index] = textBlock("");
        }

        if (event.content_block.type === "tool_use") {
          content[event.index] = toolUseBlock(
            event.content_block.id,
            event.content_block.name,
            {},
          );
          pendingToolJson = "";
          yield {
            type: "tool_use_start",
            id: event.content_block.id,
            name: event.content_block.name,
          };
        }
        break;
      }

      case "content_block_delta": {
        if (event.delta.type === "text_delta") {
          content[event.index].text += event.delta.text;
          yield { type: "text", text: event.delta.text };
        }

        if (event.delta.type === "input_json_delta") {
          pendingToolJson += event.delta.partial_json;
        }
        break;
      }

      case "content_block_stop": {
        const block = content[event.index];
        if (block?.type === "tool_use" && pendingToolJson) {
          block.input = JSON.parse(pendingToolJson);
          pendingToolJson = "";
        }
        break;
      }

      case "message_delta": {
        usage.output_tokens = event.usage?.output_tokens || usage.output_tokens;
        stopReason = event.delta.stop_reason || stopReason;
        break;
      }

      case "message_stop": {
        yield { type: "message_done", stopReason, usage: { ...usage } };
        break;
      }

      default:
        break;
    }
  }

  return {
    assistantMessage: { role: "assistant", content },
    usage,
    stopReason,
  };
}