// Package health probes backends with a status ping, caching their server-list
// response and tracking whether each one is up.
package health

import (
	"context"
	"encoding/json"
	"log/slog"
	"net"
	"sort"
	"sync"
	"time"

	"git.veillax.com/Veillax/spinner/internal/config"
	"git.veillax.com/Veillax/spinner/internal/protocol"
)

type State struct {
	Name      string    `json:"name"`
	Up        bool      `json:"up"`
	LastCheck time.Time `json:"last_check"`
	LatencyMS int64     `json:"latency_ms"`
	Error     string    `json:"error,omitempty"`
	Version   string    `json:"version,omitempty"`
	Online    int       `json:"online"`
	Max       int       `json:"max"`
	status    string
}

type Tracker struct {
	mu  sync.RWMutex
	st  map[string]*State
	log *slog.Logger
}

func New(log *slog.Logger) *Tracker {
	return &Tracker{st: map[string]*State{}, log: log}
}

// Cached returns the backend's last status JSON if it is up and the probe is
// no older than maxAge.
func (t *Tracker) Cached(name string, maxAge time.Duration) (string, bool) {
	t.mu.RLock()
	defer t.mu.RUnlock()
	s := t.st[name]
	if s == nil || !s.Up || s.status == "" || time.Since(s.LastCheck) > maxAge {
		return "", false
	}
	return s.status, true
}

func (t *Tracker) Snapshot() []State {
	t.mu.RLock()
	defer t.mu.RUnlock()
	out := make([]State, 0, len(t.st))
	for _, s := range t.st {
		out = append(out, *s)
	}
	sort.Slice(out, func(i, j int) bool { return out[i].Name < out[j].Name })
	return out
}

// Run probes every server immediately and then on each interval until ctx ends.
func (t *Tracker) Run(ctx context.Context, m *config.Manager) {
	for {
		cfg := m.Current()
		t.probeAll(ctx, cfg)
		select {
		case <-ctx.Done():
			return
		case <-time.After(cfg.ProbeInterval()):
		}
	}
}

func (t *Tracker) probeAll(ctx context.Context, cfg *config.Config) {
	var wg sync.WaitGroup
	for i := range cfg.Servers {
		wg.Add(1)
		go func(s *config.Server) {
			defer wg.Done()
			t.record(s.Name, Probe(ctx, s, cfg.ConnectTimeout()))
		}(&cfg.Servers[i])
	}
	wg.Wait()

	names := map[string]bool{}
	for _, s := range cfg.Servers {
		names[s.Name] = true
	}
	t.mu.Lock()
	for n := range t.st {
		if !names[n] {
			delete(t.st, n)
		}
	}
	t.mu.Unlock()
}

// Result is the outcome of one probe.
type Result struct {
	Status  string
	Latency time.Duration
	Err     error
}

// Probe tries each of the server's addresses in order and returns the first success.
func Probe(ctx context.Context, s *config.Server, timeout time.Duration) Result {
	var last Result
	for _, addr := range s.Addresses {
		start := time.Now()
		d := net.Dialer{Timeout: timeout}
		conn, err := d.DialContext(ctx, "tcp", addr)
		if err != nil {
			last = Result{Err: err}
			continue
		}
		host, port := protocol.SplitHostPort(addr)
		js, err := protocol.QueryStatus(conn, host, port, timeout)
		conn.Close()
		if err != nil {
			last = Result{Err: err}
			continue
		}
		return Result{Status: js, Latency: time.Since(start)}
	}
	return last
}

func (t *Tracker) record(name string, r Result) {
	s := State{Name: name, Up: r.Err == nil, LastCheck: time.Now(), LatencyMS: r.Latency.Milliseconds(), status: r.Status}
	if r.Err != nil {
		s.Error = r.Err.Error()
	} else {
		var parsed struct {
			Version struct{ Name string }     `json:"version"`
			Players struct{ Online, Max int } `json:"players"`
		}
		if json.Unmarshal([]byte(r.Status), &parsed) == nil {
			s.Version, s.Online, s.Max = parsed.Version.Name, parsed.Players.Online, parsed.Players.Max
		}
	}
	t.mu.Lock()
	prev := t.st[name]
	t.st[name] = &s
	t.mu.Unlock()
	if prev == nil || prev.Up != s.Up {
		if s.Up {
			t.log.Info("backend up", "server", name, "latency_ms", s.LatencyMS)
		} else {
			t.log.Warn("backend down", "server", name, "err", s.Error)
		}
	}
}