"""Scene-based routing table (架构文档 §8.1 场景化路由).

``scene → (provider, model, temperature, max_tokens, timeout)`` is configuration,
so switching models never requires a code change (NFR-MAINT-05). Defaults live
here; ``LLM_SCENE_OVERRIDES_JSON`` overrides any field per scene at deploy time.

Token budgets follow 架构文档 §7.2: 输入合计 ≤ 3700, 输出 ≤ 800.
"""

from __future__ import annotations

from typing import Any

from packages.llm.errors import SceneNotRoutedError
from packages.llm.types import Scene, SceneConfig

_DEFAULTS: dict[Scene, dict[str, Any]] = {
    Scene.AGENT_CHAT: {
        "temperature": 0.7,
        "max_tokens": 800,
        "timeout_seconds": 30.0,
        "prompt_id": "agent_chat",
        "prompt_version": "v1",
        "critical": False,
    },
    Scene.INTENT_CLASSIFY: {
        "temperature": 0.0,
        "max_tokens": 128,
        "timeout_seconds": 10.0,
        "prompt_id": "intent_classify",
        "prompt_version": "v1",
        # Intent classification gates 越界拒答 (FR-AGT-02); degrading it silently
        # would let out-of-scope questions through, so it is never budget-gated.
        "critical": True,
    },
    Scene.PREFERENCE_EXTRACT: {
        "temperature": 0.0,
        "max_tokens": 256,
        "timeout_seconds": 15.0,
        "prompt_id": "preference_extract",
        "prompt_version": "v1",
        "critical": False,
    },
    Scene.REPORT_COPY: {
        "temperature": 0.6,
        "max_tokens": 3000,
        "timeout_seconds": 90.0,
        "prompt_id": "report_copy",
        "prompt_version": "v1",
        "critical": False,
    },
}


def build_scene_configs(
    *,
    primary_provider: str,
    backup_provider: str | None = None,
    structured_max_retries: int = 2,
    models: dict[str, str] | None = None,
    overrides: dict[str, dict[str, Any]] | None = None,
) -> dict[Scene, SceneConfig]:
    """Materialise the routing table from settings."""
    providers = tuple(p for p in (primary_provider, backup_provider) if p)
    configs: dict[Scene, SceneConfig] = {}
    for scene, defaults in _DEFAULTS.items():
        merged: dict[str, Any] = {
            **defaults,
            "structured_max_retries": structured_max_retries,
            **(overrides or {}).get(scene.value, {}),
        }
        configs[scene] = SceneConfig(
            scene=scene,
            providers=tuple(merged.pop("providers", providers)),
            models=dict(merged.pop("models", models or {})),
            **merged,
        )
    return configs


class SceneRouter:
    def __init__(self, configs: dict[Scene, SceneConfig]) -> None:
        self._configs = dict(configs)

    def resolve(self, scene: Scene) -> SceneConfig:
        config = self._configs.get(scene)
        if config is None:
            msg = f"no routing configured for scene {scene.value}"
            raise SceneNotRoutedError(msg)
        return config

    def scenes(self) -> tuple[Scene, ...]:
        return tuple(self._configs)