from typing import List, Optional

from ..schemas.llm import ChatMessage, ChatResponse, Usage


class MockProvider:
    """A simple echo-like provider for local testing.

    It takes the last user message and returns a prefixed reply.
    """

    def chat(
        self,
        messages: List[ChatMessage],
        *,
        model: Optional[str] = None,
        temperature: Optional[float] = None,
        max_tokens: Optional[int] = None,
    ) -> ChatResponse:
        last_user = next((m.content for m in reversed(messages) if m.role == "user"), "")
        content = f"[mock] You said: {last_user}"

        # Very rough word-count "tokens" approximation for demo purposes only
        prompt_tokens = sum(len(m.content.split()) for m in messages)
        completion_tokens = len(content.split())
        usage = Usage(
            prompt_tokens=prompt_tokens,
            completion_tokens=completion_tokens,
            total_tokens=prompt_tokens + completion_tokens,
        )

        return ChatResponse(content=content, model=model or "mock-echo-001", usage=usage)