// Package web implements the NaviWatcher HTTP dashboard: a net/http server with
// embedded templates, basic-auth protection, and a dashboard that lists
// monitored artists with their missing-release counts.
package web

import (
	"context"
	"crypto/subtle"
	"encoding/base64"
	"fmt"
	"log"
	"net/http"
	"net/url"
	"strings"
	"time"

	"naviwatcher/internal/config"
	"naviwatcher/internal/database"
	"naviwatcher/internal/scanner"
)

// Server is the NaviWatcher web dashboard HTTP server.
type Server struct {
	cfg *config.ServerConfig
	db  *database.DB
	mux *http.ServeMux

	// uiBaseURL is the externally reachable base URL of the dashboard (scheme +
	// host), used to build links in notifications and elsewhere. Optional.
	uiBaseURL string

	// threshold is the fuzzy-similarity cutoff used when scanning for missing
	// releases; 0 means use the scanner default.
	threshold float64
}

// NewServer constructs a dashboard Server bound to the given DB and server
// config. uiBaseURL is the externally reachable origin (e.g.
// "http://localhost:8080") used when rendering absolute links; pass "" to omit.
// threshold is the fuzzy-similarity cutoff (0 → scanner default).
func NewServer(cfg *config.ServerConfig, db *database.DB, uiBaseURL string, threshold float64) *Server {
	s := &Server{
		cfg:       cfg,
		db:        db,
		uiBaseURL: strings.TrimRight(uiBaseURL, "/"),
		threshold: threshold,
	}
	// Warn loudly when auth is disabled but the server is reachable from outside
	// the host: Basic auth is silently skipped when Username/Password are empty,
	// so an operator who forgets credentials on a non-loopback bind would expose
	// DB-mutating POST routes (ignore/restore/toggle) to the network.
	if (cfg.Username == "" || cfg.Password == "") && cfg.Host != "localhost" && cfg.Host != "127.0.0.1" && cfg.Host != "::1" {
		log.Printf("WARNING: Web UI authentication is DISABLED (server.username/password empty) and the server is bound to %q. The dashboard and its state-changing routes are exposed to the network. Set credentials or bind to localhost.", cfg.Host)
	}
	mux := http.NewServeMux()
	mux.HandleFunc("/", s.handleDashboard)
	mux.HandleFunc("/artist/{id}", s.handleArtist)
	mux.HandleFunc("/artist/{id}/ignore", s.ignoreOrRestore)
	mux.HandleFunc("/artist/{id}/restore", s.ignoreOrRestore)
	mux.HandleFunc("/artist/{id}/ignore-singles", s.toggleIgnoreSingles)
	mux.HandleFunc("/archive", s.handleArchive)
	s.mux = mux
	return s
}

// Handler returns the http.Handler (auth-wrapped mux) for the server. It is
// exported so callers can embed the dashboard in a larger handler tree or test
// it directly via httptest.
func (s *Server) Handler() http.Handler {
	return s.authMiddleware(s.mux)
}

// Addr returns the listen address ("host:port") for this server.
func (s *Server) Addr() string {
	return fmt.Sprintf("%s:%d", s.cfg.Host, s.cfg.Port)
}

// Start begins listening and serving until the context is cancelled, then shuts
// down gracefully. It returns any unrecoverable serve error (a clean shutdown
// due to ctx cancellation returns nil).
func (s *Server) Start(ctx context.Context) error {
	srv := &http.Server{
		Addr:              s.Addr(),
		Handler:           s.Handler(),
		ReadTimeout:       15 * time.Second,
		ReadHeaderTimeout: 10 * time.Second,
		WriteTimeout:      30 * time.Second,
		IdleTimeout:       120 * time.Second,
	}

	go func() {
		<-ctx.Done()
		shutdownCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
		defer cancel()
		if err := srv.Shutdown(shutdownCtx); err != nil {
			log.Printf("web server shutdown error: %v", err)
		}
	}()

	log.Printf("Web UI listening on %s", s.Addr())
	if err := srv.ListenAndServe(); err != nil && err != http.ErrServerClosed {
		return fmt.Errorf("web server serve: %w", err)
	}
	return nil
}

// authMiddleware enforces HTTP Basic auth per RFC 7617 using a constant-time
// comparison of the base64-encoded "user:pass" credential. When either
// Username or Password is empty, auth is disabled (useful for local/dev).
func (s *Server) authMiddleware(next http.Handler) http.Handler {
	user := s.cfg.Username
	pass := s.cfg.Password
	if user == "" || pass == "" {
		return next
	}

	// Precompute the expected Authorization header value once.
	want := "Basic " + base64.StdEncoding.EncodeToString([]byte(user+":"+pass))

	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		header := r.Header.Get("Authorization")
		if header == "" {
			unauthorized(w)
			return
		}
		// Constant-time compare of the full header value.
		if subtle.ConstantTimeCompare([]byte(header), []byte(want)) != 1 {
			unauthorized(w)
			return
		}
		next.ServeHTTP(w, r)
	})
}

// unauthorized writes a 401 with a Basic auth challenge.
func unauthorized(w http.ResponseWriter) {
	w.Header().Set("WWW-Authenticate", `Basic realm="NaviWatcher"`)
	w.WriteHeader(http.StatusUnauthorized)
	_, _ = w.Write([]byte("401 Unauthorized\n"))
}

// sameOrigin returns true when the request's Origin (or, lacking that, Referer)
// header matches the server's own origin. State-changing POST routes use this
// as a lightweight CSRF defense: a cross-site request from a logged-in
// operator's browser will carry a different Origin/Referer and be rejected.
// When the header is absent (e.g. a same-origin form POST from older browsers
// or curl), the request is allowed rather than blocked, since the dashboard
// only ever issues same-origin form posts.
func (s *Server) sameOrigin(r *http.Request) bool {
	origin := r.Header.Get("Origin")
	if origin == "" {
		origin = r.Header.Get("Referer")
	}
	if origin == "" {
		return true
	}
	got, err := url.Parse(origin)
	if err != nil || got.Host == "" {
		return false
	}
	// Accept the actual Host the client reached (covers 0.0.0.0 bind with
	// localhost/127.0.0.1 access) as well as the configured bind address.
	gotHost := got.Host
	reqHost := r.Host
	if reqHost == "" {
		reqHost = s.Addr()
	}
	return gotHost == reqHost || gotHost == s.Addr()
}

// ArtistSummary is the dashboard projection of a single monitored artist and
// its missing-release count.
type ArtistSummary struct {
	ID              string
	Name            string
	MBID            string
	MissingCount    int
	Monitored       bool
}

// DashboardData is the view model passed to the dashboard template.
type DashboardData struct {
	Artists []ArtistSummary
	// TotalMissing is the sum of all artists' missing counts.
	TotalMissing int
	// UIBaseURL is the externally reachable origin, for building links.
	UIBaseURL string
}

// buildDashboardData computes the dashboard view model: every monitored artist
// joined with its current missing-release count (from the scanner).
func (s *Server) buildDashboardData(ctx context.Context, threshold float64) (*DashboardData, error) {
	settings, err := database.GetAllArtistSettings(s.db)
	if err != nil {
		return nil, fmt.Errorf("load artist settings: %w", err)
	}

	// Compute missing releases once and group by artist.
	missing, err := scanner.ScanAll(ctx, s.db, threshold)
	if err != nil {
		return nil, fmt.Errorf("scan: %w", err)
	}
	missingByArtist := make(map[string]int)
	for _, m := range missing {
		missingByArtist[m.ArtistID]++
	}

	data := &DashboardData{UIBaseURL: s.uiBaseURL}
	for _, a := range settings {
		if !a.Monitored {
			continue
		}
		count := missingByArtist[a.ID]
		data.Artists = append(data.Artists, ArtistSummary{
			ID:           a.ID,
			Name:         a.Name,
			MBID:         a.MBID,
			MissingCount: count,
			Monitored:    true,
		})
		data.TotalMissing += count
	}
	return data, nil
}