package api

import (
	"context"
	"encoding/json"
	"log"
	"net/http"
	"net/url"
	"path"
	"strings"
	"time"

	"github.com/danielgtaylor/huma/v2"
	"github.com/rs/cors"

	v0 "github.com/modelcontextprotocol/registry/internal/api/handlers/v0"
	"github.com/modelcontextprotocol/registry/internal/api/router"
	"github.com/modelcontextprotocol/registry/internal/config"
	"github.com/modelcontextprotocol/registry/internal/service"
	"github.com/modelcontextprotocol/registry/internal/telemetry"
)

// NulByteValidationMiddleware rejects requests containing NUL bytes in URL path or query parameters.
// This prevents PostgreSQL encoding errors (SQLSTATE 22021) and returns a proper 400 Bad Request.
// Checks for both literal NUL bytes (\x00) and URL-encoded form (%00).
func NulByteValidationMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// Check URL path for literal NUL bytes or URL-encoded %00
		// Path needs %00 check because handlers call url.PathUnescape() which would decode it
		if containsNulByte(r.URL.Path) {
			writeErrorResponse(w, http.StatusBadRequest, "Invalid request: URL path contains null bytes")
			return
		}

		// Check raw query string for literal NUL bytes or URL-encoded %00
		if containsNulByte(r.URL.RawQuery) {
			writeErrorResponse(w, http.StatusBadRequest, "Invalid request: query parameters contain null bytes")
			return
		}

		next.ServeHTTP(w, r)
	})
}

// writeErrorResponse writes a JSON error response using huma's ErrorModel format
// for consistency with the rest of the API.
func writeErrorResponse(w http.ResponseWriter, status int, detail string) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)

	errModel := &huma.ErrorModel{
		Title:  http.StatusText(status),
		Status: status,
		Detail: detail,
	}
	_ = json.NewEncoder(w).Encode(errModel)
}

// containsNulByte checks if a string contains a NUL byte, either as a literal \x00
// or URL-encoded as %00.
func containsNulByte(s string) bool {
	// Check for literal NUL byte
	if strings.ContainsRune(s, '\x00') {
		return true
	}
	// Check for URL-encoded NUL byte (%00)
	// Using Contains directly since %00 has no case variation (both hex digits are 0)
	return strings.Contains(s, "%00")
}

// TrailingSlashMiddleware redirects requests with trailing slashes to their canonical form
func TrailingSlashMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// Only redirect if the path is not "/" and ends with a "/"
		if r.URL.Path != "/" && strings.HasSuffix(r.URL.Path, "/") {
			// Build the target from the path and query alone, dropping any
			// scheme/host the client may have supplied in an absolute-form
			// request URI ("GET http://evil.com/foo/ HTTP/1.1"), which would
			// otherwise be echoed back as an off-site redirect.
			//
			// path.Clean both removes the trailing slash and collapses any
			// leading "//" to "/", which prevents an open-redirect via a
			// protocol-relative path like "//evil.com/" (GHSA-v8vw-gw5j-w7m6).
			newURL := url.URL{
				Path:     path.Clean(r.URL.Path),
				RawQuery: r.URL.RawQuery,
			}

			// Use 308 Permanent Redirect to preserve the request method
			http.Redirect(w, r, newURL.String(), http.StatusPermanentRedirect)
			return
		}

		next.ServeHTTP(w, r)
	})
}

// Server represents the HTTP server
type Server struct {
	config   *config.Config
	registry service.RegistryService
	humaAPI  huma.API
	server   *http.Server
}

// NewServer creates a new HTTP server
func NewServer(cfg *config.Config, registryService service.RegistryService, metrics *telemetry.Metrics, versionInfo *v0.VersionBody) *Server {
	// Create HTTP mux and Huma API
	mux := http.NewServeMux()

	api := router.NewHumaAPI(cfg, registryService, mux, metrics, versionInfo)

	// Configure CORS with permissive settings for public API
	corsHandler := cors.New(cors.Options{
		AllowedOrigins: []string{"*"},
		AllowedMethods: []string{
			http.MethodGet,
			http.MethodPost,
			http.MethodPut,
			http.MethodPatch,
			http.MethodDelete,
			http.MethodOptions,
		},
		AllowedHeaders:   []string{"*"},
		ExposedHeaders:   []string{"Content-Type", "Content-Length"},
		AllowCredentials: false, // Must be false when AllowedOrigins is "*"
		MaxAge:           86400, // 24 hours
	})

	// Wrap the mux with middleware stack
	// Order: NulByteValidation -> TrailingSlash -> CORS -> Mux
	handler := NulByteValidationMiddleware(TrailingSlashMiddleware(corsHandler.Handler(mux)))

	server := &Server{
		config:   cfg,
		registry: registryService,
		humaAPI:  api,
		server: &http.Server{
			Addr:              cfg.ServerAddress,
			Handler:           handler,
			ReadHeaderTimeout: 10 * time.Second,
			ReadTimeout:       30 * time.Second,
			// WriteTimeout intentionally not set: the publish path runs
			// outbound package validators sequentially (npm/pypi/nuget up to
			// 10s each, OCI up to 30s), so any tight cap could cut off a
			// legitimate multi-package publish mid-response — surfacing as a
			// truncated read to the publisher even when the DB commit
			// succeeded. Slow-response-read DoS is bounded upstream by
			// NGINX ingress timeouts and the per-IP rate limit. Revisit once
			// validators are parallelised or per-request package counts are
			// bounded.
			IdleTimeout: 120 * time.Second,
		},
	}

	return server
}

// Handler returns the fully wrapped HTTP handler (middleware stack plus routes).
// Exposed so tests can exercise the middleware, e.g. CORS, without binding a port.
func (s *Server) Handler() http.Handler {
	return s.server.Handler
}

// Start begins listening for incoming HTTP requests
func (s *Server) Start() error {
	log.Printf("HTTP server starting on %s", s.config.ServerAddress)
	return s.server.ListenAndServe()
}

// Shutdown gracefully shuts down the server
func (s *Server) Shutdown(ctx context.Context) error {
	return s.server.Shutdown(ctx)
}