// Package admin serves the REST API, Prometheus metrics and the embedded UI.
package admin

import (
	"crypto/sha256"
	"crypto/subtle"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"strings"

	"git.veillax.com/Veillax/spinner/internal/config"
	"git.veillax.com/Veillax/spinner/internal/health"
	"git.veillax.com/Veillax/spinner/internal/proxy"
	"git.veillax.com/Veillax/spinner/web"
)

type Admin struct {
	Cfg    *config.Manager
	Health *health.Tracker
	Proxy  *proxy.Proxy
	Token  string
}

func (a *Admin) Handler() http.Handler {
	mux := http.NewServeMux()
	mux.HandleFunc("GET /{$}", func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "text/html; charset=utf-8")
		w.Header().Set("Content-Security-Policy", "default-src 'self'; style-src 'unsafe-inline'; script-src 'unsafe-inline'")
		w.Write(web.Index)
	})
	mux.HandleFunc("GET /api/overview", a.auth(a.overview))
	mux.HandleFunc("GET /api/config", a.auth(a.getConfig))
	mux.HandleFunc("PUT /api/config", a.auth(a.putConfig))
	mux.HandleFunc("GET /metrics", a.auth(a.metrics))
	return mux
}

func (a *Admin) auth(next http.HandlerFunc) http.HandlerFunc {
	want := sha256.Sum256([]byte(a.Token))
	return func(w http.ResponseWriter, r *http.Request) {
		got := sha256.Sum256([]byte(strings.TrimPrefix(r.Header.Get("Authorization"), "Bearer ")))
		if subtle.ConstantTimeCompare(got[:], want[:]) != 1 {
			w.Header().Set("WWW-Authenticate", `Bearer realm="spinner"`)
			http.Error(w, "unauthorized", http.StatusUnauthorized)
			return
		}
		next(w, r)
	}
}

func writeJSON(w http.ResponseWriter, v any) {
	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(v)
}

type serverView struct {
	config.Server
	Health *health.State         `json:"health,omitempty"`
	Stats  *proxy.ServerSnapshot `json:"stats,omitempty"`
}

func (a *Admin) overview(w http.ResponseWriter, r *http.Request) {
	snap := a.Proxy.Stats.Snapshot()
	states := map[string]health.State{}
	for _, s := range a.Health.Snapshot() {
		states[s.Name] = s
	}
	stats := map[string]proxy.ServerSnapshot{}
	for _, s := range snap.Servers {
		stats[s.Name] = s
	}
	var servers []serverView
	for _, s := range a.Cfg.Current().Servers {
		v := serverView{Server: s}
		if h, ok := states[s.Name]; ok {
			v.Health = &h
		}
		if st, ok := stats[s.Name]; ok {
			v.Stats = &st
		}
		servers = append(servers, v)
	}
	snap.Servers = nil
	writeJSON(w, map[string]any{"totals": snap, "servers": servers})
}

func (a *Admin) getConfig(w http.ResponseWriter, r *http.Request) { writeJSON(w, a.Cfg.Current()) }

func (a *Admin) putConfig(w http.ResponseWriter, r *http.Request) {
	body, err := io.ReadAll(io.LimitReader(r.Body, 1<<20))
	if err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}
	cfg, err := config.Parse(body)
	if err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}
	if err := a.Cfg.Save(cfg); err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	writeJSON(w, cfg)
}

func esc(s string) string {
	return strings.NewReplacer(`\`, `\\`, `"`, `\"`, "\n", `\n`).Replace(s)
}

func (a *Admin) metrics(w http.ResponseWriter, r *http.Request) {
	snap := a.Proxy.Stats.Snapshot()
	w.Header().Set("Content-Type", "text/plain; version=0.0.4")
	p := func(format string, args ...any) { fmt.Fprintf(w, format+"\n", args...) }
	p("# TYPE spinner_uptime_seconds gauge\nspinner_uptime_seconds %d", snap.UptimeSecs)
	p("# TYPE spinner_connections_active gauge\nspinner_connections_active %d", snap.Active)
	p("# TYPE spinner_connections_total counter\nspinner_connections_total %d", snap.Total)
	p("# TYPE spinner_connections_rejected_total counter\nspinner_connections_rejected_total %d", snap.Rejected)
	p("# TYPE spinner_unknown_host_total counter\nspinner_unknown_host_total %d", snap.Unknown)
	for _, s := range snap.Servers {
		l := fmt.Sprintf(`{server="%s"}`, esc(s.Name))
		p("spinner_server_connections_active%s %d", l, s.Active)
		p("spinner_server_connections_total%s %d", l, s.Total)
		p("spinner_server_failures_total%s %d", l, s.Failures)
		p("spinner_server_bytes_in_total%s %d", l, s.BytesIn)
		p("spinner_server_bytes_out_total%s %d", l, s.BytesOut)
	}
	for _, h := range a.Health.Snapshot() {
		up := 0
		if h.Up {
			up = 1
		}
		l := fmt.Sprintf(`{server="%s"}`, esc(h.Name))
		p("spinner_server_up%s %d", l, up)
		p("spinner_server_latency_ms%s %d", l, h.LatencyMS)
		p("spinner_server_players_online%s %d", l, h.Online)
	}
}