package main

import (
	"encoding/json"
	"fmt"
	"net/http"
	"strconv"
)

// newAdminHandler exposes the rotation control surface. It is intended to bind
// to localhost only (WEIRCON_ADMIN_LISTEN) and is called by rotate.sh:
//
//	POST /drain?id=N    take slot N out of service; blocks until in-flight
//	                    drains (bounded by WEIRCON_DRAIN_TIMEOUT_SEC) + settle.
//	                    200 {"id":N,"drained":true,"inflight":0} on a clean drain,
//	                    "drained":false with the residual count on timeout.
//	POST /undrain?id=N  return slot N to service after the warmup window.
//	GET  /status        snapshot of every slot.
func newAdminHandler(cfg Config, mgr *proxyManager) http.Handler {
	mux := http.NewServeMux()

	slotID := func(w http.ResponseWriter, r *http.Request) (int, bool) {
		raw := r.URL.Query().Get("id")
		id, err := strconv.Atoi(raw)
		if err != nil || id < 0 || id >= mgr.n {
			http.Error(w, fmt.Sprintf("id must be 0-%d", mgr.n-1), http.StatusBadRequest)
			return 0, false
		}
		return id, true
	}
	writeJSON := func(w http.ResponseWriter, v any) {
		w.Header().Set("Content-Type", "application/json")
		_ = json.NewEncoder(w).Encode(v)
	}

	mux.HandleFunc("/drain", func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodPost {
			http.Error(w, "POST only", http.StatusMethodNotAllowed)
			return
		}
		id, ok := slotID(w, r)
		if !ok {
			return
		}
		residual := mgr.drain(id, cfg.DrainTimeout)
		writeJSON(w, map[string]any{"id": id, "drained": residual == 0, "inflight": residual})
	})

	mux.HandleFunc("/undrain", func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodPost {
			http.Error(w, "POST only", http.StatusMethodNotAllowed)
			return
		}
		id, ok := slotID(w, r)
		if !ok {
			return
		}
		mgr.undrain(id)
		writeJSON(w, map[string]any{"id": id, "warmup_sec": int(cfg.DrainWarmup.Seconds())})
	})

	mux.HandleFunc("/status", func(w http.ResponseWriter, r *http.Request) {
		writeJSON(w, mgr.snapshot())
	})

	return mux
}