// Copyright (c) 2026, Pim van Pelt <pim@ipng.ch>

package main

import (
	"encoding/json"
	"fmt"
	"io/fs"
	"log/slog"
	"net/http"
	"strings"
	"time"

	buildinfo "git.ipng.ch/ipng/vpp-maglev/cmd"
)

func registerHandlers(mux *http.ServeMux, clients []*maglevClient, broker *Broker) {
	byName := make(map[string]*maglevClient, len(clients))
	for _, c := range clients {
		byName[c.name] = c
	}

	mux.HandleFunc("/healthz", func(w http.ResponseWriter, _ *http.Request) {
		_, _ = w.Write([]byte("ok\n"))
	})

	mux.HandleFunc("/view/api/version", func(w http.ResponseWriter, _ *http.Request) {
		writeJSON(w, VersionInfo{
			Version: buildinfo.Version(),
			Commit:  buildinfo.Commit(),
			Date:    buildinfo.Date(),
		})
	})

	mux.HandleFunc("/view/api/maglevds", func(w http.ResponseWriter, _ *http.Request) {
		infos := make([]MaglevdInfo, 0, len(clients))
		for _, c := range clients {
			infos = append(infos, c.Info())
		}
		writeJSON(w, infos)
	})

	mux.HandleFunc("/view/api/state", func(w http.ResponseWriter, _ *http.Request) {
		out := make([]*StateSnapshot, 0, len(clients))
		for _, c := range clients {
			out = append(out, c.Snapshot())
		}
		writeJSON(w, out)
	})

	mux.HandleFunc("/view/api/state/", func(w http.ResponseWriter, r *http.Request) {
		name := strings.TrimPrefix(r.URL.Path, "/view/api/state/")
		c, ok := byName[name]
		if !ok {
			http.NotFound(w, r)
			return
		}
		writeJSON(w, c.Snapshot())
	})

	mux.HandleFunc("/view/api/events", func(w http.ResponseWriter, r *http.Request) {
		serveSSE(w, r, broker)
	})

	mux.HandleFunc("/admin/", func(w http.ResponseWriter, _ *http.Request) {
		http.Error(w, "admin mode not implemented", http.StatusNotImplemented)
	})

	// Static SPA served from the embedded dist fs, mounted under /view/.
	staticFS, err := fs.Sub(webFS, "web/dist")
	if err != nil {
		slog.Error("embed-subfs", "err", err)
		return
	}
	fileServer := http.FileServer(http.FS(staticFS))
	mux.Handle("/view/", http.StripPrefix("/view/", fileServer))
	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		if r.URL.Path == "/" {
			http.Redirect(w, r, "/view/", http.StatusFound)
			return
		}
		http.NotFound(w, r)
	})
}

func writeJSON(w http.ResponseWriter, v any) {
	w.Header().Set("Content-Type", "application/json")
	enc := json.NewEncoder(w)
	enc.SetEscapeHTML(false)
	if err := enc.Encode(v); err != nil {
		slog.Error("json-encode", "err", err)
	}
}

// serveSSE handles the long-lived /view/api/events stream. The operational
// requirements (retry hint, heartbeat, flush-after-write, X-Accel-Buffering,
// context-done teardown) are documented in PLAN_FRONTEND.md §SSE operational
// requirements.
func serveSSE(w http.ResponseWriter, r *http.Request, broker *Broker) {
	flusher, ok := w.(http.Flusher)
	if !ok {
		http.Error(w, "streaming unsupported", http.StatusInternalServerError)
		return
	}

	h := w.Header()
	h.Set("Content-Type", "text/event-stream")
	h.Set("Cache-Control", "no-cache")
	h.Set("Connection", "keep-alive")
	h.Set("X-Accel-Buffering", "no")
	w.WriteHeader(http.StatusOK)

	// Reconnect hint: EventSource default is 3–5s; 2s feels livelier.
	fmt.Fprintf(w, "retry: 2000\n\n")
	flusher.Flush()

	result := broker.Subscribe(r.Header.Get("Last-Event-ID"))
	defer broker.Unsubscribe(result.Channel)

	if result.NeedResync {
		// No id: line — the browser keeps whatever Last-Event-ID it had,
		// so subsequent reconnects compare against a real event ID.
		fmt.Fprintf(w, "event: resync\ndata: {}\n\n")
		flusher.Flush()
	}
	for _, ev := range result.ReplayEvents {
		if err := writeEvent(w, ev); err != nil {
			return
		}
		flusher.Flush()
	}

	heartbeat := time.NewTicker(15 * time.Second)
	defer heartbeat.Stop()

	for {
		select {
		case <-r.Context().Done():
			return
		case ev, ok := <-result.Channel:
			if !ok {
				return
			}
			if err := writeEvent(w, ev); err != nil {
				return
			}
			flusher.Flush()
		case <-heartbeat.C:
			if _, err := fmt.Fprintf(w, ": ping\n\n"); err != nil {
				return
			}
			flusher.Flush()
		}
	}
}

func writeEvent(w http.ResponseWriter, ev deliveredEvent) error {
	body, err := json.Marshal(ev.Event)
	if err != nil {
		return err
	}
	_, err = fmt.Fprintf(w, "id: %s\ndata: %s\n\n", ev.ID, body)
	return err
}