import json
from collections.abc import Iterator

import httpx
from core_domain import ChatCompletionRequestContract, ChatCompletionResponseContract


class ModelGatewayClientError(Exception):
    pass


class ModelGatewayClient:
    def __init__(self, *, base_url: str, timeout_seconds: float = 60.0) -> None:
        self.base_url = base_url.rstrip("/")
        self.timeout_seconds = timeout_seconds

    def create_chat_completion(
        self,
        payload: ChatCompletionRequestContract) -> ChatCompletionResponseContract:
        try:
            with httpx.Client(timeout=self.timeout_seconds) as client:
                response = client.post(
                    f"{self.base_url}/models/chat-completions",
                    json=payload.model_dump(mode="json"))
                response.raise_for_status()
                return ChatCompletionResponseContract.model_validate(response.json())
        except httpx.HTTPError as exc:
            raise ModelGatewayClientError(f"model-gateway-service request failed: {exc}") from exc

    def stream_chat_completion(
        self,
        payload: ChatCompletionRequestContract) -> Iterator[str]:
        try:
            with httpx.Client(timeout=self.timeout_seconds) as client:
                with client.stream(
                    "POST",
                    f"{self.base_url}/models/chat-completions/stream",
                    json=payload.model_dump(mode="json")) as response:
                    response.raise_for_status()
                    for event_name, data in _iter_sse_events(response):
                        if event_name == "delta":
                            delta = data.get("delta")
                            if isinstance(delta, str):
                                yield delta
                        elif event_name == "error":
                            message = data.get("message")
                            raise ModelGatewayClientError(
                                str(message) if isinstance(message, str) else "model-gateway stream failed")
        except httpx.HTTPError as exc:
            raise ModelGatewayClientError(f"model-gateway-service stream failed: {exc}") from exc


def _iter_sse_events(response: httpx.Response) -> Iterator[tuple[str, dict[str, object]]]:
    event_name = "message"
    data_lines: list[str] = []
    for line in response.iter_lines():
        if line == "":
            if data_lines:
                yield event_name, _parse_json("\n".join(data_lines))
            event_name = "message"
            data_lines = []
            continue
        if line.startswith("event:"):
            event_name = line.removeprefix("event:").strip()
        elif line.startswith("data:"):
            data_lines.append(line.removeprefix("data:").strip())
    if data_lines:
        yield event_name, _parse_json("\n".join(data_lines))


def _parse_json(value: str) -> dict[str, object]:
    try:
        payload = json.loads(value)
    except json.JSONDecodeError:
        return {}
    return payload if isinstance(payload, dict) else {}