package metrics

import (
	"context"
	_ "embed"
	"fmt"
	"net"
	"net/http"

	"github.com/prometheus/client_golang/prometheus/promhttp"

	"git.warky.dev/wdevs/pgsql-broker/pkg/broker/adapter"
)

//go:embed page.html
var dashboardHTML []byte

// Server is the embedded HTTP server exposing /metrics (standard Prometheus
// exposition format) and / (a single-page HTML dashboard that polls
// /metrics).
type Server struct {
	httpServer *http.Server
	listener   net.Listener
	logger     adapter.Logger
}

// NewServer builds a Server bound to addr (e.g. "127.0.0.1:9469"). Binding
// happens immediately so a port conflict is reported to the caller rather
// than surfacing later in a background goroutine.
func NewServer(m *Metrics, addr string, logger adapter.Logger) (*Server, error) {
	listener, err := net.Listen("tcp", addr)
	if err != nil {
		return nil, fmt.Errorf("failed to bind metrics server to %s: %w", addr, err)
	}

	mux := http.NewServeMux()
	mux.Handle("/metrics", promhttp.HandlerFor(m.Registry, promhttp.HandlerOpts{}))
	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		if r.URL.Path != "/" {
			http.NotFound(w, r)
			return
		}
		w.Header().Set("Content-Type", "text/html; charset=utf-8")
		_, _ = w.Write(dashboardHTML)
	})

	return &Server{
		httpServer: &http.Server{Handler: mux},
		listener:   listener,
		logger:     logger.With("component", "metrics-server"),
	}, nil
}

// Addr returns the actual bound address (useful when addr was given with a
// ":0" port).
func (s *Server) Addr() string {
	return s.listener.Addr().String()
}

// Start serves in the background. It returns immediately; Serve errors
// (other than a clean Shutdown) are logged.
func (s *Server) Start() {
	s.logger.Info("metrics server listening", "addr", s.Addr())
	go func() {
		if err := s.httpServer.Serve(s.listener); err != nil && err != http.ErrServerClosed {
			s.logger.Error("metrics server stopped unexpectedly", "error", err)
		}
	}()
}

// Stop gracefully shuts down the server.
func (s *Server) Stop(ctx context.Context) error {
	return s.httpServer.Shutdown(ctx)
}