package middleware

import (
	"bufio"
	"crypto/rand"
	"errors"
	"log/slog"
	"net"
	"net/http"
	"time"

	"git.avsdev.uk/Go/job-search/internal/httpx"
)

// responseRecorder captures status and size while staying transparent to
// http.ResponseController (Unwrap) and to code that type-asserts for
// http.Hijacker / http.Flusher (needed by the WebSocket upgrade).
type responseRecorder struct {
	http.ResponseWriter
	status   int
	bytes    int64
	hijacked bool
	// beforeHeader, if set, runs once just before headers are written.
	beforeHeader func(http.Header)
}

// WriteHeader records the status, running beforeHeader the first time, and
// writes it.
func (w *responseRecorder) WriteHeader(code int) {
	if w.status == 0 {
		w.status = code
		if w.beforeHeader != nil {
			w.beforeHeader(w.Header())
		}
	}
	w.ResponseWriter.WriteHeader(code)
}

// Write writes data, writing a 200 status first if none has been, and counts
// the bytes written.
func (w *responseRecorder) Write(data []byte) (int, error) {
	if w.status == 0 {
		w.WriteHeader(http.StatusOK)
	}

	written, err := w.ResponseWriter.Write(data)
	w.bytes += int64(written)

	return written, err
}

// Unwrap returns the wrapped ResponseWriter, for http.ResponseController.
func (w *responseRecorder) Unwrap() http.ResponseWriter {
	return w.ResponseWriter
}

// Flush writes a 200 status first if none has been, then flushes the
// wrapped ResponseWriter if it can.
func (w *responseRecorder) Flush() {
	if w.status == 0 {
		w.WriteHeader(http.StatusOK)
	}
	http.NewResponseController(w.ResponseWriter).Flush() //nolint:errcheck,gosec // none returned
}

// Hijack takes over the connection, recording it as hijacked with status 101
// (switching protocols) if no status was written.
func (w *responseRecorder) Hijack() (net.Conn, *bufio.ReadWriter, error) {
	conn, readWriter, err := http.NewResponseController(w.ResponseWriter).Hijack()
	if err == nil {
		w.hijacked = true
		if w.status == 0 {
			w.status = http.StatusSwitchingProtocols
		}
	}
	return conn, readWriter, err
}

// RequestID assigns each request an ID, exposed as X-Request-ID. An incoming
// X-Request-ID is only accepted from trusted proxies and only if well formed.
func RequestID(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		id := ""
		if Client(r).ViaProxy {
			if incoming := r.Header.Get("X-Request-ID"); validRequestID(incoming) {
				id = incoming
			}
		}
		if id == "" {
			id = rand.Text()
		}

		w.Header().Set("X-Request-ID", id)
		next.ServeHTTP(w, r.WithContext(httpx.WithRequestID(r.Context(), id)))
	})
}

// validRequestID reports whether id is an acceptable request ID: 1 to 64
// characters, each a letter, digit, '-', '_' or '.'.
func validRequestID(id string) bool {
	if id == "" || len(id) > 64 {
		return false
	}
	for i := 0; i < len(id); i++ {
		if !isRequestIDChar(id[i]) {
			return false
		}
	}
	return true
}

// isRequestIDChar reports whether char may appear in a request ID.
func isRequestIDChar(char byte) bool {
	switch {
	case char >= 'a' && char <= 'z',
		char >= 'A' && char <= 'Z',
		char >= '0' && char <= '9':
		return true
	}
	return char == '-' || char == '_' || char == '.'
}

// Logger logs one line per request. The query string is deliberately not
// logged, as it may carry secrets. It logs to slog.Default() unless given
// WithLogger.
func Logger(opts ...Option) func(http.Handler) http.Handler {
	settings := applyOptions(opts)
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			start := time.Now()
			recorder := &responseRecorder{
				ResponseWriter: w,
			}

			defer func() {
				status := recorder.status
				if status == 0 {
					status = http.StatusOK
				}

				level := slog.LevelInfo
				switch {
				case status >= 500:
					level = slog.LevelError
				case status >= 400:
					level = slog.LevelWarn
				}

				settings.logger("http").LogAttrs(
					r.Context(),
					level,
					"request",
					slog.String("method", r.Method),
					slog.String("path", r.URL.Path),
					slog.Int("status", status),
					slog.Int64("bytes", recorder.bytes),
					slog.Duration("duration", time.Since(start)),
					slog.String("ip", ClientIP(r)),
					slog.String("proto", r.Proto),
					slog.String("request_id", httpx.RequestID(r.Context())),
					slog.Bool("hijacked", recorder.hijacked),
				)
			}()

			next.ServeHTTP(recorder, r)
		})
	}
}

// Recoverer turns panics into 500 responses and logs them. It logs to
// slog.Default() unless given WithLogger.
func Recoverer(opts ...Option) func(http.Handler) http.Handler {
	settings := applyOptions(opts)
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			defer func() {
				if recovered := recover(); recovered != nil {
					err, isErr := recovered.(error)
					if isErr && errors.Is(err, http.ErrAbortHandler) {
						panic(recovered)
					}

					settings.logger("http").Error(
						"panic",
						"error", recovered,
						"path", r.URL.Path,
						"request_id", httpx.RequestID(r.Context()),
					)
					httpx.WriteProblem(w, r, http.StatusInternalServerError, "")
				}
			}()
			next.ServeHTTP(w, r)
		})
	}
}