// 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. The names are primed silently, so the bundle starting again does not
// say every name again; the watch's restarts are not — a restart made while the bundle was down is said when
// it starts (the watch keeps the last hour's). Nothing is remembered as said until its emit succeeded.
type Announcer struct {
	names  map[string]string
	primed bool
	// said is every restart said, by when it was made; judged every one whose outcome was said.
	said, judged map[time.Time]bool
}

// Event is one event to emit, and what saying it records.
type Event struct {
	Type string
	Body map[string]any
	said func()
}

// Next is what to say 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;
// restarts the watch made (`restarted`), with why; and, once the looks after a restart decide it, whether it
// helped (`restart-judged`). read says the roster was read: an unreadable roster says nothing about names,
// rather than every name removed. An event is remembered by Said, once it was emitted.
func (a *Announcer) Next(names []Named, read bool, s State) []Event {
	if a.said == nil {
		a.said, a.judged, a.names = map[time.Time]bool{}, map[time.Time]bool{}, map[string]string{}
	}
	var out []Event
	if read {
		now := map[string]string{}
		for _, n := range names {
			now[n.Name] = n.Address
		}
		if !a.primed {
			a.names, a.primed = now, true
		} else {
			for name, address := range now {
				if _, had := a.names[name]; !had {
					out = append(out, Event{"name.added", map[string]any{"name": name, "address": address},
						func() { a.names[name] = address }})
				}
			}
			for name := range a.names {
				if _, has := now[name]; !has {
					out = append(out, Event{"name.removed", map[string]any{"name": name}, func() { delete(a.names, name) }})
				}
			}
		}
	}
	for _, r := range s.Restarts {
		at := r.At
		if !a.said[at] {
			body := map[string]any{"unit": Unit, "at": at, "why": r.Why}
			if r.Error != "" {
				body["error"] = r.Error
			}
			out = append(out, Event{"restarted", body, func() { a.said[at] = true }})
		}
		if r.Helped != nil && !a.judged[at] {
			out = append(out, Event{"restart-judged", map[string]any{"unit": Unit, "at": at, "helped": *r.Helped},
				func() { a.judged[at] = true }})
		}
	}
	return out
}

// Said remembers an event as said.
func (e Event) Said() {
	if e.said != nil {
		e.said()
	}
}

// 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 {
		Tell(m, &a, emit)
		time.Sleep(AnnounceEvery)
	}
}

// Tell is one read and what it says: an event that could not be emitted is said again at the next read.
func Tell(m *Machine, a *Announcer, emit func(string, any, ...stdio.EmitOptions) error) {
	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, said again at the next read: %v\n", e.Type, err)
			continue
		}
		e.Said()
	}
}