"""Engine gateway HTTP and SSE contract.

Keep this module adapter-neutral. The Python API client, the current Python
gateway, and a future Node.js gateway must preserve these shapes.
"""

from __future__ import annotations

import json
from typing import Any, Literal, Optional

from pydantic import BaseModel, Field

AIRole = Literal["client", "counselor", "evaluator"]
EngineMessageRole = Literal["system", "user", "assistant"]
EngineGatewaySseEvent = Literal["token", "done", "error"]

ENGINE_GATEWAY_SSE_TOKEN: EngineGatewaySseEvent = "token"
ENGINE_GATEWAY_SSE_DONE: EngineGatewaySseEvent = "done"
ENGINE_GATEWAY_SSE_ERROR: EngineGatewaySseEvent = "error"
ENGINE_GATEWAY_SSE_EVENTS: tuple[EngineGatewaySseEvent, ...] = (
    ENGINE_GATEWAY_SSE_TOKEN,
    ENGINE_GATEWAY_SSE_DONE,
    ENGINE_GATEWAY_SSE_ERROR,
)


class EngineMessage(BaseModel):
    role: EngineMessageRole
    content: str
    cache: bool = False


class GenerateRequest(BaseModel):
    ai_role: AIRole = "client"
    messages: list[EngineMessage]
    model: Optional[str] = None
    max_tokens: int = 1024
    temperature: float = 0.7
    structured_schema: Optional[dict[str, Any]] = None
    session_id: Optional[str] = None
    metadata: dict[str, Any] = Field(default_factory=dict)


class StreamRequest(GenerateRequest):
    """SSE stream request for live client AI turns."""


class GenerateResponse(BaseModel):
    text: str
    model: str
    provider: str
    tokens_in: int = 0
    tokens_out: int = 0
    cost_usd: float = 0.0
    inference_geo: Optional[str] = None
    structured: Optional[dict[str, Any]] = None


class StreamTokenEvent(BaseModel):
    text: str


class StreamDoneEvent(BaseModel):
    provider: str
    model: str
    tokens_in: int = 0
    tokens_out: int = 0
    cost_usd: float = 0.0
    turns: int = 0


class StreamErrorEvent(BaseModel):
    detail: str


def sse_frame(event: EngineGatewaySseEvent, payload: BaseModel | dict[str, Any]) -> str:
    if isinstance(payload, BaseModel):
        body = payload.model_dump()
    else:
        body = payload
    return f"event: {event}\ndata: {json.dumps(body, ensure_ascii=False)}\n\n"