// Package federationapi is the Server-Server API as a running component:
// the inbound endpoints other servers call, the outbound queue that sends
// them this server's events, and the Module that starts and stops it all
// with the federation switch.
//
// The protocol itself — X-Matrix signing, server discovery, the HTTP
// client, keys — is in package federation. This package is where that
// protocol meets the roomserver and the sync API, which is why it is
// separate: the roomserver uses the protocol, and this package uses the
// roomserver.
package federationapi

import (
	"context"
	"log/slog"
	"sync"
)

// Module is the switchable part of federation: everything that runs in the
// background and talks to other servers on its own initiative.
//
// The inbound endpoints are not in it. They are behind the gate, which
// reads the switch on every request, so they need nothing started or
// stopped. What does is the outbound queue — the only thing in Warp that
// opens connections to other servers unprompted — and turning federation
// off stops it mid-flight, leaving what it had not sent in the database for
// when federation comes back on.
//
// Requests a component makes on a client's behalf — a join, a key fetch,
// a profile lookup — need nothing stopping either: the client refuses
// every request while the switch is off.
type Module struct {
	queue *Queue
	log   *slog.Logger

	mu      sync.Mutex
	running bool
}

// NewModule builds a stopped module.
func NewModule(queue *Queue, log *slog.Logger) *Module {
	if log == nil {
		log = slog.Default()
	}
	return &Module{queue: queue, log: log}
}

// Start brings federation up. Starting a running module does nothing.
func (m *Module) Start(ctx context.Context) error {
	m.mu.Lock()
	defer m.mu.Unlock()
	if m.running {
		return nil
	}
	if err := m.queue.Start(ctx); err != nil {
		m.queue.Stop()
		return err
	}
	m.running = true
	m.log.Info("federation started")
	return nil
}

// Stop takes federation down and waits for in-flight sends to finish or
// be cancelled. Stopping a stopped module does nothing.
func (m *Module) Stop() {
	m.mu.Lock()
	defer m.mu.Unlock()
	if !m.running {
		return
	}
	m.queue.Stop()
	m.running = false
	m.log.Info("federation stopped")
}

// Apply starts or stops the module to match the switch.
func (m *Module) Apply(ctx context.Context, enabled bool) {
	if enabled {
		if err := m.Start(ctx); err != nil {
			m.log.Error("could not start federation", "error", err)
		}
		return
	}
	m.Stop()
}

// Running reports whether the module is up.
func (m *Module) Running() bool {
	m.mu.Lock()
	defer m.mu.Unlock()
	return m.running
}

// Queue exposes the outbound queue, for the admin API.
func (m *Module) Queue() *Queue { return m.queue }