// The dnsmasq module's Go bundle: one of the mesh's resolvers (novox/hq ADR 0194, 0223).
//
// Started with no arguments it is served by the node's runtime as the operator account, over MCP on stdio
// (ADR 0188, ADR 0193): the module's tools and its health, and beside them the events the resolver's
// answers give — a machine's name it now answers or no longer does, and a restart the watch made. Started
// as `dnsmasq-tools watch` it is the module's long-running process, as root: it asks the resolver a real
// question on every listen address and restarts it, within a budget, when it stops answering (watch.go,
// novox/hq issue 348). stdout is the MCP channel; everything else is said on stderr.
package main

import (
	"context"
	"fmt"
	"os"
	"os/signal"
	"syscall"
	"time"

	stdio "git.novox.be/novox/mesh-sdk/go"
)

func main() {
	if len(os.Args) > 1 {
		if os.Args[1] != "watch" || len(os.Args) != 2 {
			fmt.Fprintln(os.Stderr, "usage: dnsmasq-tools [watch]")
			os.Exit(2)
		}
		ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGTERM, os.Interrupt)
		defer stop()
		m := Here()
		if err := m.Watch(ctx, ExecRunner, m.WriteState); err != nil {
			fmt.Fprintln(os.Stderr, err)
			os.Exit(1)
		}
		return
	}
	m := Here()
	go Announce(m, stdio.Emit)
	if err := stdio.Serve("", Tools(m)); err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
}

// AnnounceEvery is how often the bundle reads the roster and the watch for what to say.
var AnnounceEvery = 30 * time.Second

// Announcer remembers what was said, primed silently so a restart of the bundle does not say every name
// and every restart again.
type Announcer struct {
	names    map[string]string
	restarts map[time.Time]bool
	// primed says the names were read once; heard that the watch's restarts were.
	primed, heard bool
}

// Event is one event to emit.
type Event struct {
	Type string
	Body map[string]any
}

// Next is what changed since the last read: names the resolver now answers (`name.added`) or no longer
// does (`name.removed`) — the mesh's names having reached this resolver, apart from the controller's own
// events — and restarts the watch made (`restarted`), each with why and whether it helped once known.
//
// read says the roster was read: an unreadable roster says nothing about names, rather than every name
// removed.
func (a *Announcer) Next(names []Named, read bool, s State) []Event {
	now := map[string]string{}
	for _, n := range names {
		now[n.Name] = n.Address
	}
	var out []Event
	if a.primed && read {
		for name, address := range now {
			if _, had := a.names[name]; !had {
				out = append(out, Event{"name.added", map[string]any{"name": name, "address": address}})
			}
		}
		for name := range a.names {
			if _, has := now[name]; !has {
				out = append(out, Event{"name.removed", map[string]any{"name": name}})
			}
		}
	}
	if a.restarts == nil {
		a.restarts = map[time.Time]bool{}
	}
	for _, r := range s.Restarts {
		if a.restarts[r.At] {
			continue
		}
		a.restarts[r.At] = true
		if a.heard {
			body := map[string]any{"unit": Unit, "at": r.At, "why": r.Why}
			if r.Error != "" {
				body["error"] = r.Error
			}
			out = append(out, Event{"restarted", body})
		}
	}
	a.heard = true
	if read {
		a.names, a.primed = now, true
	}
	return out
}

// Announce says the events for as long as the bundle runs.
func Announce(m *Machine, emit func(string, any, ...stdio.EmitOptions) error) {
	time.Sleep(2 * time.Second) // the SDK reaches the bus once Serve runs
	var a Announcer
	for {
		var names []Named
		text, err := m.read(NodesFile)
		if err == nil {
			names = AnsweredNames(text)
		}
		s, _, _ := m.ReadState()
		for _, e := range a.Next(names, err == nil, s) {
			if err := emit(e.Type, e.Body); err != nil {
				fmt.Fprintf(os.Stderr, "dnsmasq: %s not said: %v\n", e.Type, err)
			}
		}
		time.Sleep(AnnounceEvery)
	}
}