package main

import (
	"context"
	"database/sql"
	"encoding/json"
	"flag"
	"fmt"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"

	_ "github.com/mattn/go-sqlite3"
)

type Server struct {
	registryRoot string
	selfPC       string
	opsDB        *sql.DB

	mu      sync.RWMutex
	targets []Target
}

func main() {
	addr := flag.String("bind", "127.0.0.1:8485", "HTTP bind address")
	registry := flag.String("registry", defaultRegistryRoot(), "fn_registry root")
	opsPath := flag.String("db", "", "operations.db path (default: <app_dir>/operations.db)")
	interval := flag.Duration("interval", 15*time.Second, "check loop interval")
	once := flag.Bool("once", false, "run one check cycle and exit (smoke test)")
	flag.Parse()

	if *opsPath == "" {
		exe, _ := os.Executable()
		*opsPath = filepath.Join(filepath.Dir(exe), "operations.db")
	}

	selfPC := readSelfPC()
	log.Printf("services_api: selfPC=%q registry=%q ops=%q", selfPC, *registry, *opsPath)

	db, err := openOpsDB(*opsPath)
	if err != nil {
		log.Fatalf("open ops db: %v", err)
	}
	defer db.Close()

	srv := &Server{registryRoot: *registry, selfPC: selfPC, opsDB: db}
	if err := srv.refreshTargets(); err != nil {
		log.Fatalf("load targets: %v", err)
	}

	if *once {
		srv.runOneCycle()
		log.Printf("once: completed %d checks", len(srv.targets))
		return
	}

	// Background loop.
	go srv.checkLoop(*interval)

	mux := http.NewServeMux()
	mux.HandleFunc("/api/health", srv.handleHealth)
	mux.HandleFunc("/api/services", srv.handleServices)
	mux.HandleFunc("/api/check", srv.handleForceCheck)
	mux.HandleFunc("/api/pcs", srv.handlePCs)
	mux.HandleFunc("/api/action/", srv.handleAction)

	log.Printf("services_api listening on %s", *addr)
	if err := http.ListenAndServe(*addr, mux); err != nil {
		log.Fatal(err)
	}
}

func defaultRegistryRoot() string {
	if v := os.Getenv("FN_REGISTRY_ROOT"); v != "" {
		return v
	}
	exe, _ := os.Executable()
	// Walk up looking for registry.db.
	dir := filepath.Dir(exe)
	for i := 0; i < 6; i++ {
		if _, err := os.Stat(filepath.Join(dir, "registry.db")); err == nil {
			return dir
		}
		parent := filepath.Dir(dir)
		if parent == dir {
			break
		}
		dir = parent
	}
	return "/home/lucas/fn_registry"
}

func readSelfPC() string {
	home, _ := os.UserHomeDir()
	b, err := os.ReadFile(filepath.Join(home, ".fn_pc"))
	if err != nil {
		return "unknown"
	}
	return strings.TrimSpace(string(b))
}

func (s *Server) refreshTargets() error {
	ts, err := loadTargets(s.registryRoot)
	if err != nil {
		return err
	}
	s.mu.Lock()
	s.targets = ts
	s.mu.Unlock()
	return nil
}

func (s *Server) runOneCycle() {
	s.mu.RLock()
	targets := append([]Target(nil), s.targets...)
	s.mu.RUnlock()

	// Parallel probes (each remote SSH call can stall up to ~10s).
	// Cap concurrency to avoid overwhelming SSH agent / sockets.
	const maxParallel = 8
	sem := make(chan struct{}, maxParallel)
	results := make(chan ServiceCheck, len(targets))
	var wg sync.WaitGroup

	for _, t := range targets {
		wg.Add(1)
		sem <- struct{}{}
		go func(tt Target) {
			defer wg.Done()
			defer func() { <-sem }()
			done := make(chan ServiceCheck, 1)
			go func() { done <- probeTarget(tt, s.selfPC) }()
			select {
			case c := <-done:
				results <- c
			case <-time.After(20 * time.Second):
				results <- ServiceCheck{
					AppID:        tt.AppID,
					PCID:         tt.PCID,
					SystemdState: "timeout",
					Error:        "probe exceeded 20s",
					Overall:      "no-route",
				}
			}
		}(t)
	}

	go func() { wg.Wait(); close(results) }()

	for c := range results {
		if err := upsertState(s.opsDB, c); err != nil {
			log.Printf("upsert %s/%s: %v", c.AppID, c.PCID, err)
		}
	}
}

func (s *Server) checkLoop(interval time.Duration) {
	tick := time.NewTicker(interval)
	defer tick.Stop()
	// First cycle immediately, then on interval.
	s.runOneCycle()
	refreshEvery := 5 * time.Minute
	lastRefresh := time.Now()
	for {
		<-tick.C
		if time.Since(lastRefresh) > refreshEvery {
			if err := s.refreshTargets(); err != nil {
				log.Printf("refresh targets: %v", err)
			}
			lastRefresh = time.Now()
		}
		s.runOneCycle()
	}
}

// HTTP handlers ------------------------------------------------------------

func (s *Server) handleHealth(w http.ResponseWriter, r *http.Request) {
	writeJSON(w, http.StatusOK, map[string]any{"status": "ok", "self_pc": s.selfPC})
}

func (s *Server) handleServices(w http.ResponseWriter, r *http.Request) {
	s.mu.RLock()
	targets := append([]Target(nil), s.targets...)
	s.mu.RUnlock()

	rows, err := loadStates(s.opsDB, targets, s.selfPC)
	if err != nil {
		writeJSON(w, http.StatusInternalServerError, map[string]any{"error": err.Error()})
		return
	}

	// Compute reachable per PC: a PC is unreachable when all its services
	// returned no-route (we never got systemd state) AND it is not selfPC.
	noRouteByPC := map[string]int{}
	totalByPC := map[string]int{}
	for _, r := range rows {
		totalByPC[r.PCID]++
		if r.Overall == "no-route" {
			noRouteByPC[r.PCID]++
		}
	}
	reachableByPC := map[string]bool{}
	for pc, total := range totalByPC {
		if pc == s.selfPC {
			reachableByPC[pc] = true
			continue
		}
		reachableByPC[pc] = noRouteByPC[pc] < total
	}
	for i := range rows {
		rows[i].Reachable = reachableByPC[rows[i].PCID]
	}

	writeJSON(w, http.StatusOK, map[string]any{
		"self_pc":  s.selfPC,
		"services": rows,
		"ts":       time.Now().Unix(),
		"pcs":      pcsSummary(reachableByPC, totalByPC, s.selfPC),
	})
}

// pcsSummary builds the array used in /api/services and /api/pcs.
func pcsSummary(reachable map[string]bool, total map[string]int, selfPC string) []map[string]any {
	out := make([]map[string]any, 0, len(total))
	for pc, n := range total {
		out = append(out, map[string]any{
			"pc_id":          pc,
			"is_self":        pc == selfPC,
			"reachable":      reachable[pc],
			"services_count": n,
		})
	}
	return out
}

func (s *Server) handleForceCheck(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		w.WriteHeader(http.StatusMethodNotAllowed)
		return
	}
	ctx, cancel := context.WithTimeout(r.Context(), 60*time.Second)
	defer cancel()
	done := make(chan struct{})
	go func() {
		s.runOneCycle()
		close(done)
	}()
	select {
	case <-done:
		s.handleServices(w, r)
	case <-ctx.Done():
		writeJSON(w, http.StatusGatewayTimeout, map[string]any{"error": "check loop timed out"})
	}
}

// handleAction handles POST /api/action/{app_id}/{pc_id}/restart.
// Currently the only supported action is "restart"; we keep the URL
// shape general for stop/start in v2.
func (s *Server) handleAction(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		w.WriteHeader(http.StatusMethodNotAllowed)
		return
	}
	// URL: /api/action/{app_id}/{pc_id}/{verb}
	path := strings.TrimPrefix(r.URL.Path, "/api/action/")
	parts := strings.Split(path, "/")
	if len(parts) != 3 {
		writeJSON(w, http.StatusBadRequest, map[string]any{
			"error": "expected /api/action/{app_id}/{pc_id}/{verb}",
		})
		return
	}
	appID, pcID, verb := parts[0], parts[1], parts[2]
	if verb != "restart" {
		writeJSON(w, http.StatusBadRequest, map[string]any{
			"error": "unsupported verb (allowed: restart)",
		})
		return
	}

	// Lookup target.
	s.mu.RLock()
	var t *Target
	for i := range s.targets {
		if s.targets[i].AppID == appID && s.targets[i].PCID == pcID {
			t = &s.targets[i]
			break
		}
	}
	s.mu.RUnlock()
	if t == nil {
		writeJSON(w, http.StatusNotFound, map[string]any{
			"error": "target not found",
		})
		return
	}

	stdout, stderr, code, err := restartTarget(*t, s.selfPC)
	if err != nil && code == -1 {
		writeJSON(w, http.StatusInternalServerError, map[string]any{
			"app_id":     appID,
			"pc_id":      pcID,
			"verb":       verb,
			"error":      err.Error(),
			"stderr":     stderr,
			"exit_code":  code,
		})
		return
	}
	status := http.StatusOK
	if code != 0 {
		status = http.StatusBadGateway
	}
	// Trigger a check cycle so UI refresh shows the new state immediately.
	go s.runOneCycle()

	writeJSON(w, status, map[string]any{
		"app_id":    appID,
		"pc_id":     pcID,
		"verb":      verb,
		"exit_code": code,
		"stdout":    strings.TrimSpace(stdout),
		"stderr":    strings.TrimSpace(stderr),
	})
}

func (s *Server) handlePCs(w http.ResponseWriter, r *http.Request) {
	s.mu.RLock()
	targets := append([]Target(nil), s.targets...)
	s.mu.RUnlock()

	counts := map[string]int{}
	for _, t := range targets {
		counts[t.PCID]++
	}
	out := make([]map[string]any, 0, len(counts))
	for pc, n := range counts {
		out = append(out, map[string]any{
			"pc_id":           pc,
			"is_self":         pc == s.selfPC,
			"services_count":  n,
		})
	}
	writeJSON(w, http.StatusOK, map[string]any{"pcs": out, "self_pc": s.selfPC})
}

func writeJSON(w http.ResponseWriter, code int, v any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(code)
	enc := json.NewEncoder(w)
	enc.SetIndent("", "  ")
	_ = enc.Encode(v)
}

// stub to silence unused import
var _ = fmt.Sprintf