from __future__ import annotations

from typing import Literal, Optional

from fastapi import APIRouter, Request
from fastapi.responses import HTMLResponse
from pydantic import BaseModel, HttpUrl

from app.core.config import get_settings
from app.legal_docs import PRIVACY_POLICY_MD, TERMS_OF_USE_MD, choose_content_by_lang, render_as_simple_html


router = APIRouter(prefix="/v1/legal", tags=["legal"])

INTERNAL_SENTINEL = "__internal__"


# 当前多语言仅支持 EN / TC（繁体）
ResolvedLang = Literal["en", "tc"]


class LegalLinksResponse(BaseModel):
    privacyPolicyUrl: HttpUrl
    termsOfUseUrl: HttpUrl
    resolvedLang: ResolvedLang


def _resolve_lang(accept_language: Optional[str]) -> ResolvedLang:
    """
    从 Accept-Language 里做一个轻量语言解析。

    说明：
    - 只关心：en / tc（繁体）
    - 解析失败或缺失：回退 en
    """

    if not accept_language:
        return "en"
    s = accept_language.lower()

    # 目前只支持 EN / TC：只要是中文或显式 tc，都归到 tc
    if "tc" in s:
        return "tc"
    if "zh" in s or "hant" in s or "tw" in s or "hk" in s or "mo" in s:
        return "tc"

    return "en"


def _pick_urls(lang: ResolvedLang) -> tuple[str, str, ResolvedLang]:
    settings = get_settings()

    if lang == "tc":
        privacy = settings.legal_privacy_url_tc or settings.legal_privacy_url_en
        terms = settings.legal_terms_url_tc or settings.legal_terms_url_en
        # 如果未配置 tc 链接：
        # - 若走内置页面（__internal__），可直接展示 tc 内容，因此 resolved=tc
        # - 否则回退到 en 链接，因此 resolved=en
        if settings.legal_privacy_url_tc or settings.legal_terms_url_tc:
            resolved: ResolvedLang = "tc"
        elif privacy == INTERNAL_SENTINEL or terms == INTERNAL_SENTINEL:
            resolved = "tc"
        else:
            resolved = "en"
        return privacy, terms, resolved

    return settings.legal_privacy_url_en, settings.legal_terms_url_en, "en"


def _join_base_url(base_url: str, path: str) -> str:
    base = (base_url or "").rstrip("/")
    p = (path or "").strip()
    if not p.startswith("/"):
        p = "/" + p
    return base + p


def _normalize_internal_url(request: Request, url: str, internal_path: str) -> str:
    """
    将内置哨兵值替换为当前服务的可访问绝对 URL。
    """

    if url != INTERNAL_SENTINEL:
        return url
    return _join_base_url(str(request.base_url), internal_path)


@router.get("/links", response_model=LegalLinksResponse)
async def get_legal_links(request: Request) -> LegalLinksResponse:
    """
    获取协议链接（隐私协议 / 使用协议）。

    - 语言来源：Accept-Language
    - 默认兜底：en
    """

    accept_language = request.headers.get("accept-language")
    lang = _resolve_lang(accept_language)
    privacy, terms, resolved = _pick_urls(lang)
    privacy = _normalize_internal_url(request, privacy, "/v1/legal/privacy")
    terms = _normalize_internal_url(request, terms, "/v1/legal/terms")
    return LegalLinksResponse(privacyPolicyUrl=privacy, termsOfUseUrl=terms, resolvedLang=resolved)


@router.get("/privacy", response_class=HTMLResponse)
async def get_privacy_policy(request: Request) -> HTMLResponse:
    """
    内置隐私协议页面（用于未配置外部托管链接时的兜底）。
    """

    accept_language = request.headers.get("accept-language")
    lang = _resolve_lang(accept_language)
    content, resolved = choose_content_by_lang(PRIVACY_POLICY_MD, lang)
    title = "Dear Mama | Privacy Policy" if resolved == "en" else "Dear Mama｜隱私權政策"
    page = render_as_simple_html(title=title, content=content)
    return HTMLResponse(content=page, headers={"Content-Language": "en" if resolved == "en" else "zh-Hant"})


@router.get("/terms", response_class=HTMLResponse)
async def get_terms_of_use(request: Request) -> HTMLResponse:
    """
    内置使用协议页面（用于未配置外部托管链接时的兜底）。
    """

    accept_language = request.headers.get("accept-language")
    lang = _resolve_lang(accept_language)
    content, resolved = choose_content_by_lang(TERMS_OF_USE_MD, lang)
    title = "Dear Mama – Terms of Use" if resolved == "en" else "Dear Mama 使用條款"
    page = render_as_simple_html(title=title, content=content)
    return HTMLResponse(content=page, headers={"Content-Language": "en" if resolved == "en" else "zh-Hant"})