// Package monitor implements the local HTTP server that
// HarborForge.Monitor (a separate native daemon on the same host)
// queries for telemetry. Mirrors the OpenclawPlugin monitor-bridge:
//
//	GET /telemetry  → JSON Snapshot
//	GET /health     → {"ok":true}
//
// The bridge runs as a goroutine started at plugin Init time; ctx
// cancellation tears it down. Bind address is 127.0.0.1 only —
// HarborForge.Monitor is expected on the same host. Configured port
// comes from config.json's monitor_port; zero/missing disables the
// bridge entirely (the plugin still serves tools + calendar).

package monitor

import (
	"context"
	"encoding/json"
	"fmt"
	"net"
	"net/http"
	"sync"
	"time"

	"git.hangman-lab.top/zhi/HarborForge.PlexumPlugin/internal/telemetry"
)

// Bridge owns the HTTP listener + last-query state.
type Bridge struct {
	port    int
	collect func() telemetry.Snapshot
	log     LogFunc

	mu        sync.Mutex
	lastQuery time.Time
	lastSnap  telemetry.Snapshot
	queries   uint64
	server    *http.Server
}

// LogFunc is the plugin's log adapter — kept narrow so the bridge
// doesn't depend on the SDK directly.
type LogFunc func(level, msg string, attrs map[string]any)

// New constructs an idle Bridge. Call Start to actually listen.
func New(port int, collect func() telemetry.Snapshot, log LogFunc) *Bridge {
	return &Bridge{port: port, collect: collect, log: log}
}

// Start the HTTP server in a background goroutine. Returns nil even
// when the port is 0 (bridge disabled by config) so callers don't
// need to guard. Stop cancels via context.
func (b *Bridge) Start(ctx context.Context) error {
	if b.port <= 0 {
		b.log("info", "monitor bridge disabled (monitor_port=0)", nil)
		return nil
	}
	addr := fmt.Sprintf("127.0.0.1:%d", b.port)
	ln, err := net.Listen("tcp", addr)
	if err != nil {
		return fmt.Errorf("monitor bridge listen %s: %w", addr, err)
	}
	mux := http.NewServeMux()
	mux.HandleFunc("/telemetry", b.handleTelemetry)
	mux.HandleFunc("/health", b.handleHealth)
	srv := &http.Server{Handler: mux, ReadHeaderTimeout: 5 * time.Second}
	b.server = srv
	go func() {
		<-ctx.Done()
		shutCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
		defer cancel()
		_ = srv.Shutdown(shutCtx)
	}()
	b.log("info", "monitor bridge listening", map[string]any{"addr": addr})
	go func() {
		if err := srv.Serve(ln); err != nil && err != http.ErrServerClosed {
			b.log("warn", "monitor bridge exited", map[string]any{"err": err.Error()})
		}
	}()
	return nil
}

func (b *Bridge) handleTelemetry(w http.ResponseWriter, _ *http.Request) {
	snap := b.collect()
	b.mu.Lock()
	b.lastQuery = time.Now()
	b.lastSnap = snap
	b.queries++
	b.mu.Unlock()
	w.Header().Set("Content-Type", "application/json")
	_ = json.NewEncoder(w).Encode(snap)
}

func (b *Bridge) handleHealth(w http.ResponseWriter, _ *http.Request) {
	w.Header().Set("Content-Type", "application/json")
	_ = json.NewEncoder(w).Encode(map[string]bool{"ok": true})
}

// Stats returns a copy of the bridge's last-query state — used by the
// harborforge_status / harborforge_monitor_telemetry tools.
func (b *Bridge) Stats() Stats {
	b.mu.Lock()
	defer b.mu.Unlock()
	return Stats{
		Port:      b.port,
		Listening: b.server != nil,
		LastQuery: b.lastQuery,
		LastSnap:  b.lastSnap,
		Queries:   b.queries,
	}
}

// Stats is the introspection shape returned by Bridge.Stats.
type Stats struct {
	Port      int
	Listening bool
	LastQuery time.Time
	LastSnap  telemetry.Snapshot
	Queries   uint64
}