package httpapi

import (
	"encoding/json"
	"fmt"
	"io"
	"log/slog"
	"net/http"
	"net/url"
	"strings"
	"time"

	"github.com/go-jose/go-jose/v4"
	"github.com/go-jose/go-jose/v4/jwt"
)

// PROJECT_BRIEF.md §2 keeps the browser path on standard OIDC PKCE. Backend
// proxies the token endpoint so the browser doesn't need a CORS-friendly OIDC
// provider; the access_token still flows back to the browser unchanged.

type authConfigResp struct {
	AuthMode     string `json:"auth_mode"`
	AuthorizeURL string `json:"authorize_url"`
	// TokenURL is published so native clients (the desktop app) can run their
	// own loopback PKCE flow directly against the provider, reusing this same
	// client_id. The browser doesn't need it — it proxies through /api/auth/exchange.
	TokenURL    string `json:"token_url"`
	ClientID    string `json:"client_id"`
	RedirectURI string `json:"redirect_uri"`
	Scopes      string `json:"scopes"`
}

// handleAuthConfig publishes everything the frontend needs to start the PKCE
// authorize redirect. No auth required (it's all public OIDC metadata).
func (s *Server) handleAuthConfig(w http.ResponseWriter, _ *http.Request) {
	writeJSON(w, http.StatusOK, authConfigResp{
		AuthMode:     s.cfg.AuthMode,
		AuthorizeURL: s.cfg.OIDCAuthorizeURL,
		TokenURL:     s.cfg.OIDCTokenURL,
		ClientID:     s.cfg.OIDCClientID,
		RedirectURI:  s.cfg.OIDCRedirectURI,
		Scopes:       s.cfg.OIDCScopes,
	})
}

type exchangeReq struct {
	Code         string `json:"code"`
	CodeVerifier string `json:"code_verifier"`
}

type tokenResp struct {
	AccessToken  string `json:"access_token"`
	RefreshToken string `json:"refresh_token"`
	IDToken      string `json:"id_token"`
	ExpiresIn    int    `json:"expires_in"`
	TokenType    string `json:"token_type"`
}

type userResp struct {
	ID     string `json:"id"`
	Name   string `json:"name"`
	Avatar string `json:"avatar,omitempty"`
}

type exchangeResp struct {
	AccessToken  string   `json:"access_token"`
	RefreshToken string   `json:"refresh_token"`
	ExpiresIn    int      `json:"expires_in"`
	User         userResp `json:"user"`
}

func (s *Server) handleAuthExchange(w http.ResponseWriter, r *http.Request) {
	var req exchangeReq
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "invalid json"})
		return
	}
	if req.Code == "" || req.CodeVerifier == "" {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "missing code or code_verifier"})
		return
	}
	if s.cfg.OIDCTokenURL == "" {
		writeJSON(w, http.StatusInternalServerError,
			map[string]string{"error": "OIDC token URL not configured"})
		return
	}

	form := url.Values{}
	form.Set("grant_type", "authorization_code")
	form.Set("code", req.Code)
	form.Set("code_verifier", req.CodeVerifier)
	form.Set("client_id", s.cfg.OIDCClientID)
	form.Set("redirect_uri", s.cfg.OIDCRedirectURI)
	// Casdoor's "cdrop" application is a confidential client; PKCE is layered
	// on top of the standard secret. Skip the secret if not configured to keep
	// public-client OIDC providers happy.
	if s.cfg.OIDCClientSecret != "" {
		form.Set("client_secret", s.cfg.OIDCClientSecret)
	}

	tr, err := postOIDCToken(r.Context(), s.cfg.OIDCTokenURL, form)
	if err != nil {
		slog.Warn("oidc exchange failed", "err", err)
		writeJSON(w, http.StatusBadGateway, map[string]string{"error": err.Error()})
		return
	}

	user, err := extractUser(tr.IDToken, tr.AccessToken)
	if err != nil {
		writeJSON(w, http.StatusBadGateway,
			map[string]string{"error": "extract user: " + err.Error()})
		return
	}

	writeJSON(w, http.StatusOK, exchangeResp{
		AccessToken:  tr.AccessToken,
		RefreshToken: tr.RefreshToken,
		ExpiresIn:    tr.ExpiresIn,
		User:         user,
	})
}

type refreshReq struct {
	RefreshToken string `json:"refresh_token"`
}

type refreshResp struct {
	AccessToken  string `json:"access_token"`
	RefreshToken string `json:"refresh_token"`
	ExpiresIn    int    `json:"expires_in"`
}

func (s *Server) handleAuthRefresh(w http.ResponseWriter, r *http.Request) {
	var req refreshReq
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "invalid json"})
		return
	}
	if req.RefreshToken == "" {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "missing refresh_token"})
		return
	}
	if s.cfg.OIDCTokenURL == "" {
		writeJSON(w, http.StatusInternalServerError,
			map[string]string{"error": "OIDC token URL not configured"})
		return
	}

	form := url.Values{}
	form.Set("grant_type", "refresh_token")
	form.Set("refresh_token", req.RefreshToken)
	form.Set("client_id", s.cfg.OIDCClientID)
	if s.cfg.OIDCClientSecret != "" {
		form.Set("client_secret", s.cfg.OIDCClientSecret)
	}

	tr, err := postOIDCToken(r.Context(), s.cfg.OIDCTokenURL, form)
	if err != nil {
		slog.Warn("oidc refresh failed", "err", err)
		writeJSON(w, http.StatusUnauthorized, map[string]string{"error": err.Error()})
		return
	}
	writeJSON(w, http.StatusOK, refreshResp{
		AccessToken:  tr.AccessToken,
		RefreshToken: tr.RefreshToken,
		ExpiresIn:    tr.ExpiresIn,
	})
}

var oidcHTTPClient = &http.Client{Timeout: 10 * time.Second}

func postOIDCToken(ctx interface{ Done() <-chan struct{} }, tokenURL string, form url.Values) (*tokenResp, error) {
	req, err := http.NewRequest(http.MethodPost, tokenURL, strings.NewReader(form.Encode()))
	if err != nil {
		return nil, fmt.Errorf("build request: %w", err)
	}
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
	req.Header.Set("Accept", "application/json")
	resp, err := oidcHTTPClient.Do(req)
	if err != nil {
		return nil, fmt.Errorf("oidc unreachable: %w", err)
	}
	defer resp.Body.Close()

	body, _ := io.ReadAll(resp.Body)
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("oidc status %d: %s", resp.StatusCode, truncate(string(body), 200))
	}

	var tr tokenResp
	if err := json.Unmarshal(body, &tr); err != nil {
		return nil, fmt.Errorf("oidc malformed: %w", err)
	}
	if tr.AccessToken == "" {
		return nil, fmt.Errorf("oidc returned no access_token")
	}
	return &tr, nil
}

// extractUser parses {sub, preferred_username | name} from the id_token if
// available, else falls back to access_token. We DON'T verify the signature
// here — the backend's auth middleware verifies access_token on every API
// call via the JWKS cache, so any tamper would surface there.
func extractUser(idToken, accessToken string) (userResp, error) {
	pick := idToken
	if pick == "" {
		pick = accessToken
	}
	parsed, err := jwt.ParseSigned(pick, []jose.SignatureAlgorithm{
		jose.RS256, jose.RS384, jose.RS512,
		jose.ES256, jose.ES384, jose.ES512,
		jose.HS256,
	})
	if err != nil {
		return userResp{}, err
	}
	var std jwt.Claims
	custom := map[string]any{}
	if err := parsed.UnsafeClaimsWithoutVerification(&std, &custom); err != nil {
		return userResp{}, err
	}
	u := userResp{ID: std.Subject}
	if v, ok := custom["preferred_username"].(string); ok && v != "" {
		u.Name = v
	} else if v, ok := custom["name"].(string); ok && v != "" {
		u.Name = v
	} else if v, ok := custom["email"].(string); ok && v != "" {
		u.Name = v
	} else {
		u.Name = u.ID
	}
	// Casdoor 的 OIDC id_token 暴露 avatar(自定义) 与 picture(标准 claim) 两种字段；
	// 不同 IdP 实现各异，所以都查一遍。值为空字符串视为未提供，前端落到字母方块回退。
	if v, ok := custom["avatar"].(string); ok && v != "" {
		u.Avatar = v
	} else if v, ok := custom["picture"].(string); ok && v != "" {
		u.Avatar = v
	}
	return u, nil
}

func truncate(s string, n int) string {
	if len(s) <= n {
		return s
	}
	return s[:n] + "…"
}