package api

import (
	"bytes"
	"context"
	"crypto/hmac"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log"
	"mime"
	"net/http"
	"net/url"
	"os"
	"path"
	"strings"
	"sync"
	"time"

	"greencoast/internal/index"
)

// BlobStore is the minimal storage interface the API needs.
type BlobStore interface {
	Put(hash string, r io.Reader) error
	Get(hash string) (io.ReadCloser, int64, error)
	Delete(hash string) error
}

// optional capability for stores that can enumerate blobs
type blobWalker interface {
	Walk(func(hash string, size int64, mod time.Time) error) error
}

// -----------------------------
// Public wiring
// -----------------------------

type DiscordProvider struct {
	Enabled      bool
	ClientID     string
	ClientSecret string
	RedirectURI  string
}

type AuthProviders struct {
	SigningSecretHex string // HMAC secret in hex
	Discord          DiscordProvider

	GoogleEnabled   bool
	FacebookEnabled bool

	WebAuthnEnabled bool
	TOTPEnabled     bool
}

type Server struct {
	mux *http.ServeMux

	store BlobStore
	idx   *index.Index

	coarseTS  bool
	zeroTrust bool

	allowClientSignedTokens bool // accept self-signed tokens (no DB)
	signingKey              []byte

	// dev flags (from env)
	allowUnauth bool
	devBearer   string

	// SSE fanout (in-process)
	sseMu     sync.Mutex
	sseSubs   map[chan []byte]struct{}
	sseClosed bool

	// SSO ephemeral state
	stateMu sync.Mutex
	states  map[string]time.Time
}

// New constructs the API server and registers routes.
func New(store BlobStore, idx *index.Index, coarseTS bool, zeroTrust bool, providers AuthProviders) *Server {
	key, _ := hex.DecodeString(strings.TrimSpace(providers.SigningSecretHex))
	s := &Server{
		mux:                     http.NewServeMux(),
		store:                   store,
		idx:                     idx,
		coarseTS:                coarseTS,
		zeroTrust:               zeroTrust,
		allowClientSignedTokens: true,
		signingKey:              key,
		allowUnauth:             os.Getenv("GC_DEV_ALLOW_UNAUTH") == "true",
		devBearer:               os.Getenv("GC_DEV_BEARER"),
		sseSubs:                 make(map[chan []byte]struct{}),
		states:                  make(map[string]time.Time),
	}

	// MIME safety (minimal base images can be sparse)
	_ = mime.AddExtensionType(".js", "application/javascript; charset=utf-8")
	_ = mime.AddExtensionType(".css", "text/css; charset=utf-8")
	_ = mime.AddExtensionType(".html", "text/html; charset=utf-8")
	_ = mime.AddExtensionType(".map", "application/json; charset=utf-8")

	// Core
	s.mux.HandleFunc("/healthz", s.handleHealthz)

	// Objects
	s.mux.Handle("/v1/object", s.withCORS(http.HandlerFunc(s.handlePutObject)))
	s.mux.Handle("/v1/object/", s.withCORS(http.HandlerFunc(s.handleObjectByHash)))

	// Index + SSE
	s.mux.Handle("/v1/index", s.withCORS(http.HandlerFunc(s.handleIndex)))
	s.mux.Handle("/v1/index/stream", s.withCORS(http.HandlerFunc(s.handleIndexSSE)))

	// GDPR+policy endpoint (minimal; no PII)
	s.mux.Handle("/v1/gdpr/policy", s.withCORS(http.HandlerFunc(s.handleGDPRPolicy)))

	// Admin: reindex from disk if store supports Walk
	s.mux.Handle("/v1/admin/reindex", s.withCORS(http.HandlerFunc(s.handleAdminReindex)))

	// Discord SSO
	s.mux.Handle("/v1/auth/discord/start", s.withCORS(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		s.handleDiscordStart(w, r, providers.Discord)
	})))
	s.mux.Handle("/v1/auth/discord/callback", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		s.handleDiscordCallback(w, r, providers.Discord)
	}))

	return s
}

// ListenHTTP serves the API on addr.
func (s *Server) ListenHTTP(addr string) error {
	log.Printf("http listening on %s", addr)
	server := &http.Server{
		Addr:              addr,
		Handler:           s.withCORS(s.mux),
		ReadHeaderTimeout: 5 * time.Second,
	}
	return server.ListenAndServe()
}

// ListenHTTPS serves TLS directly.
func (s *Server) ListenHTTPS(addr, certFile, keyFile string) error {
	log.Printf("https listening on %s", addr)
	server := &http.Server{
		Addr:              addr,
		Handler:           s.withCORS(s.mux),
		ReadHeaderTimeout: 5 * time.Second,
	}
	return server.ListenAndServeTLS(certFile, keyFile)
}

// -----------------------------
// Middleware / headers
// -----------------------------

func (s *Server) secureHeaders(w http.ResponseWriter) {
	// Privacy / security posture
	w.Header().Set("Referrer-Policy", "no-referrer")
	w.Header().Set("Cross-Origin-Opener-Policy", "same-origin")
	w.Header().Set("Cross-Origin-Resource-Policy", "same-site")
	w.Header().Set("Permissions-Policy", "camera=(), microphone=(), geolocation=(), interest-cohort=(), browsing-topics=()")
	w.Header().Set("X-Frame-Options", "DENY")
	w.Header().Set("X-Content-Type-Options", "nosniff")
	// HSTS (harmless over HTTP; browsers only enforce under HTTPS)
	w.Header().Set("Strict-Transport-Security", "max-age=15552000; includeSubDomains; preload")
}

func (s *Server) withCORS(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		s.secureHeaders(w)
		w.Header().Set("Access-Control-Allow-Origin", "*")
		w.Header().Set("Access-Control-Allow-Methods", "GET, PUT, DELETE, OPTIONS")
		w.Header().Set("Access-Control-Allow-Headers", "Authorization, Content-Type, X-GC-Private, X-GC-3P-Assent, X-GC-TZ")

		if r.Method == http.MethodOptions {
			w.WriteHeader(http.StatusNoContent)
			return
		}
		next.ServeHTTP(w, r)
	})
}

// -----------------------------
// Health & policy
// -----------------------------

func (s *Server) handleHealthz(w http.ResponseWriter, r *http.Request) {
	s.secureHeaders(w)
	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
	io.WriteString(w, "ok")
}

func (s *Server) handleGDPRPolicy(w http.ResponseWriter, r *http.Request) {
	s.secureHeaders(w)
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	type policy struct {
		StoresPII  bool   `json:"stores_pii"`
		CollectIP  bool   `json:"collect_ip"`
		CollectUA  bool   `json:"collect_user_agent"`
		Timestamps string `json:"timestamps"`
		ZeroTrust  bool   `json:"zero_trust"`
	}
	resp := policy{
		StoresPII:  false,
		CollectIP:  false,
		CollectUA:  false,
		Timestamps: map[bool]string{true: "coarse_utc", false: "utc"}[s.coarseTS],
		ZeroTrust:  s.zeroTrust,
	}
	_ = json.NewEncoder(w).Encode(resp)
}

// -----------------------------
// Auth helpers
// -----------------------------

func (s *Server) requireAuth(w http.ResponseWriter, r *http.Request) bool {
	// Developer bypass
	if s.allowUnauth {
		return true
	}
	// Optional dev bearer
	if s.devBearer != "" {
		h := r.Header.Get("Authorization")
		if h == "Bearer "+s.devBearer {
			return true
		}
	}

	// Accept self-signed HMAC tokens if configured
	if s.allowClientSignedTokens && len(s.signingKey) > 0 {
		h := r.Header.Get("Authorization")
		if strings.HasPrefix(h, "Bearer ") {
			tok := strings.TrimSpace(strings.TrimPrefix(h, "Bearer "))
			if s.verifyToken(tok) == nil {
				return true
			}
		}
	}

	http.Error(w, "unauthorized", http.StatusUnauthorized)
	return false
}

func (s *Server) makeToken(subject string, ttl time.Duration) (string, error) {
	if len(s.signingKey) == 0 {
		return "", errors.New("signing key not set")
	}
	type claims struct {
		Sub string `json:"sub"`
		Exp int64  `json:"exp"`
		Iss string `json:"iss"`
	}
	c := claims{
		Sub: subject,
		Exp: time.Now().Add(ttl).Unix(),
		Iss: "greencoast",
	}
	body, _ := json.Marshal(c)
	mac := hmac.New(sha256.New, s.signingKey)
	mac.Write(body)
	sig := mac.Sum(nil)
	return "gc1." + base64.RawURLEncoding.EncodeToString(body) + "." + base64.RawURLEncoding.EncodeToString(sig), nil
}

func (s *Server) verifyToken(tok string) error {
	if !strings.HasPrefix(tok, "gc1.") {
		return errors.New("bad prefix")
	}
	parts := strings.Split(tok, ".")
	if len(parts) != 3 {
		return errors.New("bad parts")
	}
	body, err := base64.RawURLEncoding.DecodeString(parts[1])
	if err != nil {
		return err
	}
	want, err := base64.RawURLEncoding.DecodeString(parts[2])
	if err != nil {
		return err
	}
	mac := hmac.New(sha256.New, s.signingKey)
	mac.Write(body)
	if !hmac.Equal(want, mac.Sum(nil)) {
		return errors.New("bad sig")
	}
	var c struct {
		Sub string `json:"sub"`
		Exp int64  `json:"exp"`
	}
	if err := json.Unmarshal(body, &c); err != nil {
		return err
	}
	if time.Now().Unix() > c.Exp {
		return errors.New("expired")
	}
	return nil
}

// -----------------------------
// Objects & Index
// -----------------------------

func (s *Server) handlePutObject(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPut {
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}
	if !s.requireAuth(w, r) {
		return
	}

	isPrivate := r.Header.Get("X-GC-Private") == "1"
	creatorTZ := strings.TrimSpace(r.Header.Get("X-GC-TZ"))
	if creatorTZ != "" && !isReasonableTZ(creatorTZ) {
		creatorTZ = ""
	}

	// Write to store; compute hash while streaming
	var buf bytes.Buffer
	n, err := io.Copy(&buf, r.Body)
	if err != nil {
		http.Error(w, "read error", 500)
		return
	}
	sum := sha256.Sum256(buf.Bytes())
	hash := hex.EncodeToString(sum[:])

	// Persist
	if err := s.store.Put(hash, bytes.NewReader(buf.Bytes())); err != nil {
		http.Error(w, "store error", 500)
		return
	}

	// Index
	when := time.Now().UTC()
	if s.coarseTS {
		when = when.Truncate(time.Minute)
	}
	entry := index.Entry{
		Hash:      hash,
		Bytes:     n,
		StoredAt:  when.Format(time.RFC3339Nano),
		Private:   isPrivate,
		CreatorTZ: creatorTZ,
	}
	if err := s.idx.Put(entry); err != nil {
		http.Error(w, "index error", 500)
		return
	}
	s.sseBroadcast(map[string]interface{}{"event": "put", "data": entry})

	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	_ = json.NewEncoder(w).Encode(entry)
}

func (s *Server) handleObjectByHash(w http.ResponseWriter, r *http.Request) {
	// path: /v1/object/{hash}
	parts := strings.Split(strings.TrimPrefix(r.URL.Path, "/v1/object/"), "/")
	if len(parts) == 0 || parts[0] == "" {
		http.NotFound(w, r)
		return
	}
	hash := parts[0]

	switch r.Method {
	case http.MethodGet:
		if !s.requireAuth(w, r) {
			return
		}
		rc, n, err := s.store.Get(hash)
		if err != nil {
			http.Error(w, "not found", http.StatusNotFound)
			return
		}
		defer rc.Close()
		w.Header().Set("Content-Type", "application/octet-stream")
		if n > 0 {
			w.Header().Set("Content-Length", fmt.Sprintf("%d", n))
		}
		_, _ = io.Copy(w, rc)

	case http.MethodDelete:
		if !s.requireAuth(w, r) {
			return
		}
		if err := s.store.Delete(hash); err != nil {
			http.Error(w, "delete error", 500)
			return
		}
		// prune index if present
		_ = s.idx.Delete(hash)
		s.sseBroadcast(map[string]interface{}{"event": "delete", "data": map[string]string{"hash": hash}})
		w.WriteHeader(http.StatusNoContent)

	default:
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
	}
}

func (s *Server) handleIndex(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}
	if !s.requireAuth(w, r) {
		return
	}
	items, err := s.idx.List()
	if err != nil {
		http.Error(w, "index error", 500)
		return
	}
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	_ = json.NewEncoder(w).Encode(items)
}

// Simple in-process SSE fanout.
func (s *Server) handleIndexSSE(w http.ResponseWriter, r *http.Request) {
	if !s.requireAuth(w, r) {
		return
	}
	flusher, ok := w.(http.Flusher)
	if !ok {
		http.Error(w, "stream unsupported", http.StatusInternalServerError)
		return
	}
	w.Header().Set("Content-Type", "text/event-stream; charset=utf-8")
	w.Header().Set("Cache-Control", "no-store")
	w.Header().Set("Connection", "keep-alive")

	ch := make(chan []byte, 8)

	// subscribe
	s.sseMu.Lock()
	if s.sseClosed {
		s.sseMu.Unlock()
		http.Error(w, "closed", http.StatusGone)
		return
	}
	s.sseSubs[ch] = struct{}{}
	s.sseMu.Unlock()

	// Send a hello/heartbeat
	fmt.Fprintf(w, "data: %s\n\n", `{"event":"hello","data":"ok"}`)
	flusher.Flush()

	// pump
	ctx := r.Context()
	t := time.NewTicker(25 * time.Second)
	defer t.Stop()

	defer func() {
		s.sseMu.Lock()
		delete(s.sseSubs, ch)
		s.sseMu.Unlock()
		close(ch)
	}()

	for {
		select {
		case <-ctx.Done():
			return
		case b := <-ch:
			w.Write(b)
			w.Write([]byte("\n\n"))
			flusher.Flush()
		case <-t.C:
			w.Write([]byte("data: {}\n\n"))
			flusher.Flush()
		}
	}
}

func (s *Server) sseBroadcast(v interface{}) {
	b, _ := json.Marshal(v)
	s.sseMu.Lock()
	for ch := range s.sseSubs {
		select {
		case ch <- append([]byte("data: "), b...):
		default:
		}
	}
	s.sseMu.Unlock()
}

// -----------------------------
// Admin: reindex from disk
// -----------------------------

func (s *Server) handleAdminReindex(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}
	if !s.requireAuth(w, r) {
		return
	}
	walker, ok := s.store.(blobWalker)
	if !ok {
		http.Error(w, "store does not support walk", http.StatusNotImplemented)
		return
	}

	count := 0
	err := walker.Walk(func(hash string, size int64, mod time.Time) error {
		count++
		return s.idx.Put(index.Entry{
			Hash:     hash,
			Bytes:    size,
			StoredAt: mod.UTC().Format(time.RFC3339Nano),
			Private:  false,
		})
	})
	if err != nil {
		http.Error(w, "walk error: "+err.Error(), 500)
		return
	}
	items, _ := s.idx.List()
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	_ = json.NewEncoder(w).Encode(map[string]any{
		"walked":  count,
		"indexed": len(items),
	})
}

// -----------------------------
// Discord SSO (server-side code flow)
// -----------------------------

func (s *Server) handleDiscordStart(w http.ResponseWriter, r *http.Request, cfg DiscordProvider) {
	if !cfg.Enabled || cfg.ClientID == "" || cfg.ClientSecret == "" || cfg.RedirectURI == "" {
		http.Error(w, "discord sso disabled", http.StatusBadRequest)
		return
	}
	// Require explicit 3P assent (UI shows disclaimer)
	if r.Header.Get("X-GC-3P-Assent") != "1" {
		http.Error(w, "third-party provider not assented", http.StatusForbidden)
		return
	}

	state := s.newState(5 * time.Minute)
	v := url.Values{}
	v.Set("response_type", "code")
	v.Set("client_id", cfg.ClientID)
	v.Set("redirect_uri", cfg.RedirectURI)
	v.Set("scope", "identify")
	v.Set("prompt", "consent")
	v.Set("state", state)
	authURL := (&url.URL{
		Scheme:   "https",
		Host:     "discord.com",
		Path:     "/api/oauth2/authorize",
		RawQuery: v.Encode(),
	}).String()

	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	_ = json.NewEncoder(w).Encode(map[string]string{"url": authURL})
}

func (s *Server) handleDiscordCallback(w http.ResponseWriter, r *http.Request, cfg DiscordProvider) {
	if !cfg.Enabled {
		http.Error(w, "disabled", http.StatusBadRequest)
		return
	}

	q := r.URL.Query()
	code := q.Get("code")
	state := q.Get("state")
	if code == "" || state == "" || !s.consumeState(state) {
		http.Error(w, "invalid state/code", http.StatusBadRequest)
		return
	}

	// Exchange code for token
	form := url.Values{}
	form.Set("client_id", cfg.ClientID)
	form.Set("client_secret", cfg.ClientSecret)
	form.Set("grant_type", "authorization_code")
	form.Set("code", code)
	form.Set("redirect_uri", cfg.RedirectURI)

	req, _ := http.NewRequestWithContext(r.Context(), http.MethodPost, "https://discord.com/api/oauth2/token", strings.NewReader(form.Encode()))
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
	res, err := http.DefaultClient.Do(req)
	if err != nil {
		http.Error(w, "token exchange failed", 502)
		return
	}
	defer res.Body.Close()
	if res.StatusCode/100 != 2 {
		b, _ := io.ReadAll(res.Body)
		http.Error(w, "discord token error: "+string(b), 502)
		return
	}
	var tok struct {
		AccessToken string `json:"access_token"`
		TokenType   string `json:"token_type"`
		Scope       string `json:"scope"`
		ExpiresIn   int64  `json:"expires_in"`
	}
	if err := json.NewDecoder(res.Body).Decode(&tok); err != nil {
		http.Error(w, "token decode failed", 502)
		return
	}

	// Fetch user id (identify scope)
	ureq, _ := http.NewRequestWithContext(r.Context(), http.MethodGet, "https://discord.com/api/users/@me", nil)
	ureq.Header.Set("Authorization", tok.TokenType+" "+tok.AccessToken)
	ures, err := http.DefaultClient.Do(ureq)
	if err != nil {
		http.Error(w, "user fetch failed", 502)
		return
	}
	defer ures.Body.Close()
	if ures.StatusCode/100 != 2 {
		b, _ := io.ReadAll(ures.Body)
		http.Error(w, "discord user error: "+string(b), 502)
		return
	}
	var user struct {
		ID       string `json:"id"`
		Username string `json:"username"`
	}
	if err := json.NewDecoder(ures.Body).Decode(&user); err != nil {
		http.Error(w, "user decode failed", 502)
		return
	}

	// Mint self-signed bearer with Discord snowflake as subject
	bearer, err := s.makeToken("discord:"+user.ID, time.Hour*8)
	if err != nil {
		http.Error(w, "signing error", 500)
		return
	}

	// Redirect to frontend callback with bearer in fragment (not query)
	target := cfg.RedirectURI
	u, _ := url.Parse(target)
	u.Fragment = "bearer=" + url.QueryEscape(bearer) + "&next=/"
	http.Redirect(w, r, u.String(), http.StatusFound)
}

// simple in-memory state store
func (s *Server) newState(ttl time.Duration) string {
	s.stateMu.Lock()
	defer s.stateMu.Unlock()
	b := make([]byte, 12)
	now := time.Now().UnixNano()
	copy(b, []byte(fmt.Sprintf("%x", now)))
	val := base64.RawURLEncoding.EncodeToString(b)
	s.states[val] = time.Now().Add(ttl)
	return val
}

func (s *Server) consumeState(v string) bool {
	s.stateMu.Lock()
	defer s.stateMu.Unlock()
	exp, ok := s.states[v]
	if !ok {
		return false
	}
	delete(s.states, v)
	return time.Now().Before(exp)
}

// -----------------------------
// Utilities
// -----------------------------

func isReasonableTZ(tz string) bool {
	if !strings.Contains(tz, "/") || len(tz) > 64 {
		return false
	}
	for _, r := range tz {
		if !(r == '/' || r == '_' || r == '-' || (r >= 'A' && r <= 'Z') || (r >= 'a' && r <= 'z')) {
			return false
		}
	}
	return true
}

// -----------------------------
// Optional: graceful shutdown
// -----------------------------

func (s *Server) Shutdown(ctx context.Context) error {
	s.sseMu.Lock()
	s.sseClosed = true
	for ch := range s.sseSubs {
		close(ch)
	}
	s.sseSubs = make(map[chan []byte]struct{})
	s.sseMu.Unlock()
	return nil
}

// -----------------------------
// Helpers for static serving (optional use)
// -----------------------------

func fileExists(p string) bool {
	st, err := os.Stat(p)
	return err == nil && !st.IsDir()
}

func joinClean(dir, p string) (string, bool) {
	fp := path.Clean("/" + p)
	full := path.Clean(dir + fp)
	if !strings.HasPrefix(full, path.Clean(dir)) {
		return "", false
	}
	return full, true
}