// Package httpapi is the HTTP layer: routing, middleware, and handlers.
//
// In Phase 0 it serves only health and version. Feature modules (auth, library,
// ebooks, comics, ...) mount their own routes onto the same mux via
// Server.Handle, so this package never imports a feature module.
package httpapi

import (
	"bufio"
	"context"
	"crypto/rand"
	"database/sql"
	"encoding/hex"
	"encoding/json"
	"io"
	"log/slog"
	"net"
	"net/http"
	"time"

	"github.com/mithral/vellum/internal/auth"
)

// Server holds the dependencies every handler needs.
type Server struct {
	db      *sql.DB
	log     *slog.Logger
	version string
	started time.Time
	mux     *http.ServeMux
	auth    *auth.Authenticator
}

// New builds a Server and registers the core routes.
func New(db *sql.DB, log *slog.Logger, version string) *Server {
	s := &Server{
		db:      db,
		log:     log,
		version: version,
		started: time.Now(),
		mux:     http.NewServeMux(),
	}
	s.routes()
	s.mountWeb()
	return s
}

// Mux exposes the root mux so feature modules can mount their own routes.
func (s *Server) Mux() *http.ServeMux { return s.mux }

// SetAuth installs the session middleware. Until it is set, no request carries
// a current user.
func (s *Server) SetAuth(a *auth.Authenticator) { s.auth = a }

// Handle lets a module mount routes on the shared mux.
func (s *Server) Handle(pattern string, h http.Handler) {
	s.mux.Handle(pattern, h)
}

func (s *Server) routes() {
	s.mux.HandleFunc("GET /healthz", s.handleHealth)
	s.mux.HandleFunc("GET /api/v1/version", s.handleVersion)
}

// Handler returns the fully wrapped root handler.
//
// Order matters. Security headers wrap the entire stack (outermost) so they are
// written before anything can commit a response, including the recovery
// middleware's 500 after a panic. Once a handler calls WriteHeader the header
// map is frozen, so a security middleware placed inside recovery would be too
// late for any panicking route. The request ID must be attached before the
// logging middleware runs, so the log line can include it. Session loading sits
// innermost so it runs after logging has started timing.
func (s *Server) Handler() http.Handler {
	var h http.Handler = s.mux
	if s.auth != nil {
		h = s.auth.Middleware(h)
	}
	return s.withSecurityHeaders(s.withRecovery(s.withRequestID(s.withRequestLogging(h))))
}

// ── Middleware ─────────────────────────────────────────────────────────

// withSecurityHeaders sets a baseline of hardening headers on every response.
//
// Vellum renders user-supplied EPUB content on its own origin, so a malicious
// EPUB is stored XSS unless the browser refuses to run foreign/inline script
// and to frame the app. The policy is checked against the actual frontend;
// each directive names the file that requires it. Keep it in sync when a
// reader adds a new origin.
//
// It must sit outermost (see Handler): the headers have to be in place before
// any handler — including the panic-recovery 500 — writes its status line.
func (s *Server) withSecurityHeaders(next http.Handler) http.Handler {
	// default-src 'self'           every bundled asset is same-origin (web/dist/index.html).
	// script-src  'self'           the bundled ES module (web/dist/index.html).
	//             'wasm-unsafe-eval'  EmulatorJS cores are WebAssembly (GamePlayer.svelte).
	//             https://cdn.emulatorjs.org  loader.js and core scripts (GamePlayer.svelte DATA_PATH).
	// style-src   'self'           the bundled stylesheet (web/dist/index.html).
	//             'unsafe-inline'     epub.js injects a <style> into the rendition iframe
	//                                 (epubjs rendition.injectStylesheet, contents.css).
	//             blob:               EPUB stylesheets are rewritten to blob: URLs
	//                                 (epubjs book.js replacements="blobUrl", resources.js).
	// img-src     'self'           covers, comic pages, photos (ComicReader/PhotoViewer/Card).
	//             data: blob:         EPUB images as data:/blob: URIs (epubjs resources.js).
	// media-src   'self' blob:      <audio> streams tracks via ServeContent (AudiobookPlayer.svelte).
	// connect-src 'self'           every API fetch() (web/src/lib/api.ts).
	//             https://cdn.emulatorjs.org  EmulatorJS fetches its wasm/data files (GamePlayer.svelte).
	// font-src    'self' data: blob:  bundled fonts plus EPUB-embedded fonts as data:/blob:
	//                                 (epubjs resources.js rewrites fonts to blob: URLs).
	// worker-src  'self' blob:      pdf.js worker is a same-origin asset, with a blob: fallback
	//                                 (PdfReader.svelte `?url`); EmulatorJS spawns a blob: worker.
	// frame-src   'self' blob:      epub.js renders each section in an iframe (Reader.svelte;
	//                                 epubjs iframe.js srcdoc/blobUrl). Nothing uses data:.
	// object-src  'none'            no plugin content is ever embedded.
	// base-uri/form-action/frame-ancestors  no <base> hijack, no cross-site form posts, never framed.
	const csp = "default-src 'self'; " +
		"script-src 'self' 'wasm-unsafe-eval' https://cdn.emulatorjs.org; " +
		"style-src 'self' 'unsafe-inline' blob:; " +
		"img-src 'self' data: blob:; " +
		"media-src 'self' blob:; " +
		"connect-src 'self' https://cdn.emulatorjs.org; " +
		"font-src 'self' data: blob:; " +
		"worker-src 'self' blob:; " +
		"frame-src 'self' blob:; " +
		"object-src 'none'; " +
		"base-uri 'self'; form-action 'self'; frame-ancestors 'none'"

	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		h := w.Header()
		h.Set("X-Content-Type-Options", "nosniff")
		h.Set("X-Frame-Options", "DENY")
		h.Set("Referrer-Policy", "no-referrer")
		h.Set("Content-Security-Policy", csp)
		next.ServeHTTP(w, r)
	})
}

type ctxKey string

const ctxRequestID ctxKey = "request_id"

func withValue(ctx context.Context, k ctxKey, v string) context.Context {
	return context.WithValue(ctx, k, v)
}

func valueString(ctx context.Context, k ctxKey) string {
	if v, ok := ctx.Value(k).(string); ok {
		return v
	}
	return ""
}

func (s *Server) withRequestID(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		id := r.Header.Get("X-Request-ID")
		if id == "" {
			var b [8]byte
			_, _ = rand.Read(b[:])
			id = hex.EncodeToString(b[:])
		}
		w.Header().Set("X-Request-ID", id)
		next.ServeHTTP(w, r.WithContext(withValue(r.Context(), ctxRequestID, id)))
	})
}

func (s *Server) withRequestLogging(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()
		rec := &statusRecorder{ResponseWriter: w, status: http.StatusOK}
		next.ServeHTTP(rec, r)
		s.log.Info("request",
			"method", r.Method,
			"path", r.URL.Path,
			"status", rec.status,
			"bytes", rec.bytes,
			"duration_ms", time.Since(start).Milliseconds(),
			"request_id", valueString(r.Context(), ctxRequestID),
		)
	})
}

func (s *Server) withRecovery(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		defer func() {
			if rec := recover(); rec != nil {
				s.log.Error("panic",
					"path", r.URL.Path,
					"recover", rec,
					"request_id", valueString(r.Context(), ctxRequestID),
				)
				writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "internal server error"})
			}
		}()
		next.ServeHTTP(w, r)
	})
}

// ── Helpers ────────────────────────────────────────────────────────────

// statusRecorder wraps a ResponseWriter to record the status code and byte
// count for logging.
//
// It MUST forward Flush, Hijack, and ReadFrom to the underlying writer.
// Wrapping a ResponseWriter without forwarding these silently disables
// streaming: http.ServeContent can no longer flush early (progressive
// audio/video stalls until the whole body is ready) and io.Copy can no longer
// reach the net/http ReaderFrom that drives kernel sendfile for multi-GB
// files. The type assertions below are the only reason media playback and
// downloads keep working once this middleware is installed.
type statusRecorder struct {
	http.ResponseWriter
	status      int
	bytes       int
	wroteHeader bool
}

// WriteHeader records the first status and ignores repeats. net/http logs a
// "superfluous WriteHeader" warning on a second call, and a handler that
// writes a body before setting a status would otherwise be recorded wrongly.
func (r *statusRecorder) WriteHeader(code int) {
	if r.wroteHeader {
		return
	}
	r.wroteHeader = true
	r.status = code
	r.ResponseWriter.WriteHeader(code)
}

func (r *statusRecorder) Write(b []byte) (int, error) {
	if !r.wroteHeader {
		r.WriteHeader(http.StatusOK)
	}
	n, err := r.ResponseWriter.Write(b)
	r.bytes += n
	return n, err
}

// Flush forwards to the underlying http.Flusher so handlers such as
// http.ServeContent can push bytes to the client before the body is complete.
func (r *statusRecorder) Flush() {
	if f, ok := r.ResponseWriter.(http.Flusher); ok {
		f.Flush()
	}
}

// Hijack forwards to the underlying http.Hijacker for protocols that take over
// the connection.
func (r *statusRecorder) Hijack() (net.Conn, *bufio.ReadWriter, error) {
	if hj, ok := r.ResponseWriter.(http.Hijacker); ok {
		return hj.Hijack()
	}
	return nil, nil, http.ErrNotSupported
}

// ReadFrom forwards to the underlying io.ReaderFrom so io.Copy keeps the
// sendfile fast path instead of looping through Write. The byte count is not
// updated on that path: wrapping src to count it would defeat the zero-copy
// transfer this method exists to preserve.
func (r *statusRecorder) ReadFrom(src io.Reader) (int64, error) {
	if !r.wroteHeader {
		r.WriteHeader(http.StatusOK)
	}
	if rf, ok := r.ResponseWriter.(io.ReaderFrom); ok {
		return rf.ReadFrom(src)
	}
	n, err := io.Copy(r.ResponseWriter, src)
	r.bytes += int(n)
	return n, err
}

func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(v)
}

func (s *Server) handleNotFound(w http.ResponseWriter, r *http.Request) {
	writeJSON(w, http.StatusNotFound, map[string]string{
		"error": "not found",
		"path":  r.URL.Path,
	})
}