// Package httpapi serves the Kamado REST API. WebSocket push and static
// UI serving land in a follow-up commit.
package httpapi

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

	"github.com/kamadopool/kamado-api/internal/state"
	"github.com/kamadopool/kamado-api/internal/webui"
)

type Server struct {
	Agg *state.Aggregator
	Hub *Hub
	Log *slog.Logger
}

func New(agg *state.Aggregator, log *slog.Logger) *Server {
	return &Server{Agg: agg, Hub: NewHub(), Log: log}
}

// Handler returns an http.Handler with all kamado routes mounted under
// /api and the embedded Svelte dashboard served under /. Unknown
// non-/api paths fall back to index.html for SPA-style routing.
func (s *Server) Handler() http.Handler {
	mux := http.NewServeMux()
	mux.HandleFunc("GET /api/health", s.health)
	mux.HandleFunc("GET /api/pool", s.pool)
	mux.HandleFunc("GET /api/users", s.users)
	mux.HandleFunc("GET /api/workers", s.workers)
	mux.HandleFunc("GET /api/clients", s.clients)
	mux.HandleFunc("GET /api/blocks", s.blocks)
	mux.HandleFunc("GET /api/snapshot", s.snapshot)
	mux.HandleFunc("GET /api/ws", s.handleWS)
	mux.Handle("/", spaHandler(webui.FS()))
	return mux
}

// spaHandler serves static files from the embedded dist tree and
// falls back to index.html on 404 so client-side routing works. It
// refuses anything under /api to keep the contract with mux patterns
// explicit (those routes register their own handlers above).
func spaHandler(root fs.FS) http.Handler {
	fileServer := http.FileServerFS(root)
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// Defence-in-depth — /api routes are matched by the mux first
		// with their GET patterns, but a bare POST /api/... would fall
		// through here. Return 404 so we don't accidentally shadow
		// API semantics with HTML.
		if strings.HasPrefix(r.URL.Path, "/api/") || r.URL.Path == "/api" {
			http.NotFound(w, r)
			return
		}

		// Fast path: exact file exists in the embed.
		clean := strings.TrimPrefix(r.URL.Path, "/")
		if clean == "" {
			clean = "index.html"
		}
		if _, err := fs.Stat(root, clean); err == nil {
			fileServer.ServeHTTP(w, r)
			return
		} else if !errors.Is(err, fs.ErrNotExist) {
			http.Error(w, "webui: "+err.Error(), http.StatusInternalServerError)
			return
		}

		// SPA fallback: serve index.html with a 200 so reloads on a
		// client-side route don't 404.
		r2 := r.Clone(r.Context())
		r2.URL.Path = "/"
		fileServer.ServeHTTP(w, r2)
	})
}

func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.Header().Set("Cache-Control", "no-store")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(v)
}

// ---- handlers ---------------------------------------------------------

func (s *Server) health(w http.ResponseWriter, r *http.Request) {
	snap := s.Agg.Snapshot()
	status := http.StatusOK

	// Submit-attempt gap: if we've tried to submit more blocks than have
	// been confirmed, surface the gap. A non-zero gap is a strong signal
	// even if everything else looks healthy.
	submitGap := snap.BlockSubmitAttempts - snap.BlockSubmitsConfirmed
	if submitGap < 0 {
		submitGap = 0
	}

	// ZMQ freshness: only meaningful if the operator enabled it. Stale
	// = no event in 30 minutes (typical mainnet block interval is 10
	// min, but spikes happen).
	zmqStale := false
	if snap.ZMQEnabled && snap.HasLastZMQEvent && snap.LastZMQEventAge > 1800 {
		zmqStale = true
	}

	overallOK := snap.CKPoolOK && snap.BitcoinOK && submitGap == 0 && !zmqStale
	if !snap.CKPoolOK || !snap.BitcoinOK {
		status = http.StatusServiceUnavailable
	}
	writeJSON(w, status, map[string]any{
		"ok":                       overallOK,
		"ckpool":                   snap.CKPoolOK,
		"bitcoin":                  snap.BitcoinOK,
		"submit_attempts":          snap.BlockSubmitAttempts,
		"submits_confirmed":        snap.BlockSubmitsConfirmed,
		"submit_gap":               submitGap,
		"fallback_submits_total":   snap.FallbackSubmitsTotal,
		"last_fallback_submit_at":  snap.LastFallbackSubmitAt,
		"last_fallback_via":        snap.LastFallbackVia,
		"zmq_enabled":              snap.ZMQEnabled,
		"zmq_event_age_seconds":    snap.LastZMQEventAge,
		"zmq_has_event":            snap.HasLastZMQEvent,
		"zmq_stale":                zmqStale,
		"last_error":               snap.LastError,
	})
}

func (s *Server) snapshot(w http.ResponseWriter, r *http.Request) {
	writeJSON(w, http.StatusOK, s.Agg.Snapshot())
}

func (s *Server) pool(w http.ResponseWriter, r *http.Request) {
	snap := s.Agg.Snapshot()
	writeJSON(w, http.StatusOK, map[string]any{
		"pool":                snap.Pool,
		"uptime_seconds":      snap.Uptime,
		"hashrate_hs_1m":      snap.HashrateHs,
		"hashrate_hs_5m":      snap.HashrateHs5m,
		"hashrate_hs_1h":      snap.HashrateHs1h,
		"hashrate_hs_24h":     snap.HashrateHs24h,
		"chain":               snap.Chain,
		"network_hashrate_hs": snap.NetworkHashrateHs,
	})
}

func (s *Server) users(w http.ResponseWriter, r *http.Request) {
	writeJSON(w, http.StatusOK, s.Agg.Snapshot().Users)
}

func (s *Server) workers(w http.ResponseWriter, r *http.Request) {
	writeJSON(w, http.StatusOK, s.Agg.Snapshot().Workers)
}

func (s *Server) clients(w http.ResponseWriter, r *http.Request) {
	writeJSON(w, http.StatusOK, s.Agg.Snapshot().Clients)
}

func (s *Server) blocks(w http.ResponseWriter, r *http.Request) {
	writeJSON(w, http.StatusOK, s.Agg.Blocks())
}