// Package api is the inbound HTTP adapter for the /api/v1 surface.
package api

import (
	"crypto/rand"
	"encoding/base64"
	"encoding/json"
	"errors"
	"net/http"
	"strings"
	"time"

	"github.com/snip/backend/internal/config"
	"github.com/snip/backend/internal/domain"
	"github.com/snip/backend/internal/port"
	"github.com/snip/backend/internal/service"
)

const (
	sessionCookie = "snip_session"
	stateCookie   = "snip_oauth_state"
)

// API wires the link and auth use cases to HTTP.
type API struct {
	links    *service.LinkService
	auth     *service.AuthService
	sessions port.SessionManager
	cfg      config.Config
}

func New(links *service.LinkService, auth *service.AuthService, sessions port.SessionManager, cfg config.Config) *API {
	return &API{links: links, auth: auth, sessions: sessions, cfg: cfg}
}

// Handler returns the routed, CORS-wrapped /api/v1 handler.
func (a *API) Handler() http.Handler {
	mux := http.NewServeMux()
	mux.HandleFunc("/api/v1/healthz", a.health)
	mux.HandleFunc("/api/v1/config", a.config)
	mux.HandleFunc("/api/v1/links/stats", a.linkStats) // exact: wins over /links/
	mux.HandleFunc("/api/v1/links", a.linksCollection)
	mux.HandleFunc("/api/v1/links/", a.linkItem)
	mux.HandleFunc("/api/v1/auth/", a.authRoutes)
	return cors(mux)
}

func (a *API) health(w http.ResponseWriter, _ *http.Request) {
	writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
}

// config exposes client-relevant, non-secret settings (e.g. the short domain),
// so the frontend doesn't hardcode them.
func (a *API) config(w http.ResponseWriter, _ *http.Request) {
	writeJSON(w, http.StatusOK, map[string]string{"shortDomain": a.cfg.ShortDomain})
}

// --- helpers ---

func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(v)
}

func writeError(w http.ResponseWriter, err error) {
	status := http.StatusInternalServerError
	switch {
	case errors.Is(err, domain.ErrUnauthorized):
		status = http.StatusUnauthorized
	case errors.Is(err, domain.ErrForbidden):
		status = http.StatusForbidden
	case errors.Is(err, domain.ErrNotFound):
		status = http.StatusNotFound
	case errors.Is(err, domain.ErrCodeTaken), errors.Is(err, domain.ErrReserved):
		status = http.StatusConflict
	case errors.Is(err, domain.ErrInvalidURL), errors.Is(err, domain.ErrInvalidAlias),
		errors.Is(err, domain.ErrInvalidPin), errors.Is(err, domain.ErrPinInvalid),
		errors.Is(err, domain.ErrPinRequired):
		status = http.StatusBadRequest
	}
	writeJSON(w, status, map[string]string{"error": err.Error()})
}

// userID extracts and verifies the caller's session, or "" if anonymous.
func (a *API) userID(r *http.Request) string {
	c, err := r.Cookie(sessionCookie)
	if err != nil {
		return ""
	}
	id, err := a.sessions.Verify(c.Value)
	if err != nil {
		return ""
	}
	return id
}

func (a *API) setSession(w http.ResponseWriter, token string) {
	http.SetCookie(w, &http.Cookie{
		Name:     sessionCookie,
		Value:    token,
		Path:     "/",
		HttpOnly: true,
		Secure:   a.cfg.CookieSecure,
		SameSite: http.SameSiteLaxMode,
		Expires:  time.Now().Add(30 * 24 * time.Hour),
	})
}

func (a *API) clearCookie(w http.ResponseWriter, name string) {
	http.SetCookie(w, &http.Cookie{
		Name: name, Value: "", Path: "/", HttpOnly: true,
		Secure: a.cfg.CookieSecure, SameSite: http.SameSiteLaxMode, MaxAge: -1,
	})
}

func randomState() string {
	b := make([]byte, 24)
	_, _ = rand.Read(b)
	return base64.RawURLEncoding.EncodeToString(b)
}

func decode(r *http.Request, v any) error {
	defer r.Body.Close()
	return json.NewDecoder(r.Body).Decode(v)
}

// cors reflects the request Origin and allows credentials (cookies). In
// production the SPA and API are same-origin behind a gateway; this keeps local
// dev (vite :5173 → api :8080) working.
func cors(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		origin := r.Header.Get("Origin")
		if origin != "" {
			w.Header().Set("Access-Control-Allow-Origin", origin)
			w.Header().Set("Vary", "Origin")
			w.Header().Set("Access-Control-Allow-Credentials", "true")
			w.Header().Set("Access-Control-Allow-Methods", "GET,POST,PATCH,PUT,DELETE,OPTIONS")
			w.Header().Set("Access-Control-Allow-Headers", "Content-Type")
		}
		if r.Method == http.MethodOptions {
			w.WriteHeader(http.StatusNoContent)
			return
		}
		next.ServeHTTP(w, r)
	})
}

// pathTail returns the part of the request path after a prefix.
func pathTail(path, prefix string) string {
	return strings.TrimPrefix(path, prefix)
}