package centrifugo

import (
	"bytes"
	"crypto/subtle"
	"encoding/json"
	"log/slog"
	"net/http"
	"sort"

	"git.golem15.com/golem15/summercms/modules/bouncer"
	"git.golem15.com/golem15/summercms/modules/lighthouse"
	"git.golem15.com/golem15/summercms/modules/surf"
)

type errorBody struct {
	Error string `json:"error"`
}

type tokenBody struct {
	Token string `json:"token"`
}

// TokenHandler issues the connection token of the signed-in user. It must
// be mounted behind a user guard (the UserAuth surface).
//
//   - no principal, or no user for it: 401 {"error":"Unauthorized"}
//   - no token secret: 503 with the WinterCMS not-configured error body
//   - otherwise 200 {"token":"…"} (see TokenIssuer.ForUser)
func TokenHandler(svc *lighthouse.Service, issuer *TokenIssuer) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		p, ok := bouncer.User(r.Context())
		if !ok || p == nil || p.ID == 0 {
			writeJSON(w, http.StatusUnauthorized, errorBody{Error: "Unauthorized"})
			return
		}
		u, found, err := svc.User(r.Context(), p.ID)
		if err != nil || !found {
			writeJSON(w, http.StatusUnauthorized, errorBody{Error: "Unauthorized"})
			return
		}
		if !issuer.Configured() {
			writeJSON(w, http.StatusServiceUnavailable, errorBody{Error: "WebSocket not configured"})
			return
		}
		tok, err := issuer.ForUser(u)
		if err != nil {
			svc.Logger().Error("realtime: token signing failed", "error", err)
			writeJSON(w, http.StatusInternalServerError, errorBody{Error: "Internal server error"})
			return
		}
		writeJSON(w, http.StatusOK, tokenBody{Token: tok})
	}
}

// writeJSON writes v with no trailing newline and no HTML escaping, plus the
// Content-Type and Cache-Control headers of a Laravel JSON response.
func writeJSON(w http.ResponseWriter, status int, v any) {
	var buf bytes.Buffer
	enc := json.NewEncoder(&buf)
	enc.SetEscapeHTML(false)
	if err := enc.Encode(v); err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		return
	}
	h := w.Header()
	h.Set("Content-Type", "application/json")
	h.Set("Cache-Control", "no-cache, private")
	w.WriteHeader(status)
	_, _ = w.Write(bytes.TrimSuffix(buf.Bytes(), []byte("\n")))
}

// maxProxyBody caps a subscribe proxy request body.
const maxProxyBody = 64 << 10

// denyAnswer is the one answer every denied subscribe gets. Centrifugo
// reads a non-200 status as internal error 100, so a deny is HTTP 200 with
// an error body; it never reveals why.
var denyAnswer = json.RawMessage(`{"error":{"code":403,"message":"` + accessDenied + `"}}`)

// accessDenied is the generic deny message, also logged when an authorizer
// gives no reason.
const accessDenied = "Access denied"

// proxyRequest is the part of Centrifugo's subscribe proxy body the
// handler reads.
type proxyRequest struct {
	User    json.RawMessage `json:"user"`
	Channel *string         `json:"channel"`
	Client  string          `json:"client"`
}

// ProxyHandler is the Centrifugo subscribe proxy endpoint, the WinterCMS
// ProxyController::subscribe. Every subscribe is re-authorized:
//
//  1. X-Centrifugo-Secret must equal cfg.ProxySecret (constant-time; an
//     empty configured secret denies everything);
//  2. an empty or "0" user denies;
//  3. the namespace comes from lighthouse.ParseChannel and must have a
//     registered authorizer;
//  4. the authorizer gets the user id (PHP (int) cast, negative as 0) and
//     the full original channel, with the client id in ctx.
//
// An allow answers {"result":{"info":…}} with info [] when empty; a
// presence channel also gets "allow" (the authorizer's capabilities or
// ["prs"]) and "override" (presence and join_leave true,
// force_push_join_leave false, then the authorizer's overrides). Every
// deny answers the same HTTP 200 body and logs the reason at Warn.
func ProxyHandler(svc *lighthouse.Service, cfg Config) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		log := svc.Logger()
		provided := r.Header.Get("X-Centrifugo-Secret")
		if cfg.ProxySecret == "" || subtle.ConstantTimeCompare([]byte(cfg.ProxySecret), []byte(provided)) != 1 {
			deny(w, log, "Invalid or missing proxy secret", slog.String("ip", surf.ClientIP(r, cfg.TrustedProxies)))
			return
		}
		var req proxyRequest
		dec := json.NewDecoder(http.MaxBytesReader(w, r.Body, maxProxyBody))
		dec.UseNumber()
		if err := dec.Decode(&req); err != nil {
			deny(w, log, "Malformed proxy request", slog.String("ip", surf.ClientIP(r, cfg.TrustedProxies)))
			return
		}
		user := userInput(req.User)
		channel := ""
		if req.Channel != nil {
			channel = *req.Channel
		}
		if user == "" || user == "0" {
			deny(w, log, "Authentication required", slog.String("channel", channel), slog.String("client", req.Client))
			return
		}
		if req.Channel == nil || channel == "" {
			// Centrifugo always sends a channel; WinterCMS would fail with
			// a TypeError here. Denying is deliberate hardening.
			deny(w, log, "Missing channel", slog.String("user", user), slog.String("client", req.Client))
			return
		}
		namespace, presence := lighthouse.ParseChannel(channel)
		authorizer, ok := svc.Registry().Get(namespace)
		if !ok {
			deny(w, log, "Unknown channel namespace",
				slog.String("namespace", namespace), slog.String("channel", channel),
				slog.String("user", user), slog.String("client", req.Client))
			return
		}
		id := lighthouse.PHPInt(user)
		if id < 0 {
			id = 0
		}
		ctx := lighthouse.WithClientID(r.Context(), req.Client)
		res := authorizer.Authorize(ctx, uint(id), channel)
		if !res.Allowed {
			reason := res.Reason()
			if reason == "" {
				reason = accessDenied
			}
			deny(w, log, reason,
				slog.String("user", user), slog.String("channel", channel),
				slog.String("client", req.Client), slog.String("internal_reason", res.Reason()))
			return
		}
		allow(w, res, presence)
	}
}

// userInput returns the user field as PHP's $request->input('user') string
// form: a JSON string as is, a JSON number as its literal. Anything else is
// "" (treated as empty).
func userInput(raw json.RawMessage) string {
	raw = bytes.TrimSpace(raw)
	if len(raw) == 0 {
		return ""
	}
	switch raw[0] {
	case '"':
		var s string
		if err := json.Unmarshal(raw, &s); err != nil {
			return ""
		}
		return s
	case '-', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
		var n json.Number
		if err := json.Unmarshal(raw, &n); err != nil {
			return ""
		}
		if f, err := n.Float64(); err == nil && f == 0 {
			return "0" // PHP empty(0) and empty(0.0)
		}
		return n.String()
	default:
		return ""
	}
}

func deny(w http.ResponseWriter, log *slog.Logger, reason string, attrs ...slog.Attr) {
	args := make([]any, 0, len(attrs)+1)
	args = append(args, slog.String("reason", reason))
	for _, a := range attrs {
		args = append(args, a)
	}
	log.Warn("Subscription denied", args...)
	writeRaw(w, denyAnswer)
}

func allow(w http.ResponseWriter, res lighthouse.Result, presence bool) {
	var buf bytes.Buffer
	buf.WriteString(`{"result":{"info":`)
	if len(res.Info) == 0 {
		buf.WriteString(`[]`)
	} else if b, err := marshal(res.Info); err == nil {
		buf.Write(b)
	} else {
		writeRaw(w, denyAnswer)
		return
	}
	if presence {
		caps := res.Capabilities
		if caps == nil {
			caps = []string{"prs"}
		}
		b, err := marshal(caps)
		if err != nil {
			writeRaw(w, denyAnswer)
			return
		}
		buf.WriteString(`,"allow":`)
		buf.Write(b)
		o, err := overrideJSON(res.Overrides)
		if err != nil {
			writeRaw(w, denyAnswer)
			return
		}
		buf.WriteString(`,"override":`)
		buf.Write(o)
	}
	buf.WriteString(`}}`)
	writeRaw(w, buf.Bytes())
}

// overrideJSON is PHP array_merge of the presence defaults with the
// authorizer's overrides: the default keys keep their order and take the
// authorizer's value when it names them; extra keys follow, sorted.
func overrideJSON(overrides map[string]any) ([]byte, error) {
	defaults := []struct {
		key   string
		value any
	}{
		{"presence", map[string]bool{"value": true}},
		{"join_leave", map[string]bool{"value": true}},
		{"force_push_join_leave", map[string]bool{"value": false}},
	}
	var buf bytes.Buffer
	buf.WriteByte('{')
	seen := map[string]bool{}
	write := func(key string, value any) error {
		k, err := marshal(key)
		if err != nil {
			return err
		}
		v, err := marshal(value)
		if err != nil {
			return err
		}
		if buf.Len() > 1 {
			buf.WriteByte(',')
		}
		buf.Write(k)
		buf.WriteByte(':')
		buf.Write(v)
		return nil
	}
	for _, d := range defaults {
		v := d.value
		if o, ok := overrides[d.key]; ok {
			v = o
		}
		seen[d.key] = true
		if err := write(d.key, v); err != nil {
			return nil, err
		}
	}
	extra := make([]string, 0, len(overrides))
	for k := range overrides {
		if !seen[k] {
			extra = append(extra, k)
		}
	}
	sort.Strings(extra)
	for _, k := range extra {
		if err := write(k, overrides[k]); err != nil {
			return nil, err
		}
	}
	buf.WriteByte('}')
	return buf.Bytes(), nil
}

func writeRaw(w http.ResponseWriter, body []byte) {
	h := w.Header()
	h.Set("Content-Type", "application/json")
	h.Set("Cache-Control", "no-cache, private")
	w.WriteHeader(http.StatusOK)
	_, _ = w.Write(bytes.TrimSuffix(body, []byte("\n")))
}