package rollout

import (
	"context"
	"time"

	"github.com/carlosframework/platform/internal/activator"
	"github.com/carlosframework/platform/internal/registry"
	"github.com/carlosframework/platform/internal/release"
)

// executeWorker runs one resolved attempt on a socketless host (spec §6.5,
// §7.9) through the activator's same-entry replacement. The host's good
// build, by its retained identity, goes with it as the fallback for a failed
// adoption in overlap mode; the activator decides whether it applies.
//
// While a hold-ran marker of the app stands on the host, the replacement
// carries no fallback (Astra R3 N5, spec §6.4): a hold build ran there
// without passing and may have migrated the database, so a failed
// replacement must not start the good build against it.
//
// An abandoned result (a staging refusal, a busy entry, a re-check that
// refused) is deferred by done(), as a refused swap is: while the attempt is
// still the host's newest it waits abandonDeferral, and one superseded by a
// newer desire does not wait at all.
func (s *scheduler) executeWorker(ctx context.Context, rt registry.Route, a activator.Attempt) activator.SwapResult {
	m := s.m
	var fallback *release.StagedIdentity
	acct := release.RouteAccount(rt)
	if _, marked := holdRanFor(m.d.Book, acct, rt.App, rt.Host); !marked {
		if g := rt.Good(); g.Version != "" && g.Digest != "" && g.Version != a.Build {
			fallback = &release.StagedIdentity{Version: g.Version, Digest: g.Digest, Demand: g.Demand,
				StagedPath: release.VersionPath(m.d.OptDir, acct, g.Version, rt.App)}
		}
	}
	m.emit(rt, EvSwapping, "info", textSwapping(a.Build, a.Cause))
	return m.d.Act.ReplaceWorker(ctx, a, fallback, s.newest)
}

// admitOne is admit for one host, for the recycle hook: the host's pending
// attempt, if it is a release-class attempt (an adoption) the queue would
// start right now. It honours everything admit does for that host: its
// waits, its cohort's canary and settle, a halt, and swap_concurrency. A
// restart or config attempt is not taken: the recycle runs on the serving
// build, and that attempt follows in its turn. The caller holds the
// scheduler's lock.
func (q *appQueue) admitOne(host string, now time.Time) (dispatch, bool) {
	h := q.hosts[host]
	if h == nil || h.running != nil || q.running >= q.concurrency {
		return dispatch{}, false
	}
	d, ok := q.gate(h, now)
	if !ok || d.Class != classAdopt {
		return dispatch{}, false
	}
	q.start(h, d)
	return d, true
}

// CoalesceRecycle is plan 4's Service.CoalesceRecycle (spec §7.9). The
// activator calls it under its own lock (activator.Service.mu), so it calls
// nothing in the activator and waits on nothing that could: it takes
// Manager.mu (schedulerOf) and then the scheduler's lock, the documented
// order, and the attempt it admits runs on its own goroutine. True means an
// attempt makes the spawn and the recycle is skipped: one admitted now, or
// one already running for the host (ReplaceWorker respawns that child
// itself, and its observation reads a crash as the build's). Once Close has
// begun it is also true, with nothing admitted.
func (m *Manager) CoalesceRecycle(host string) bool {
	s := m.schedulerOf(host)
	if s == nil {
		return false
	}
	s.mu.Lock()
	if h := s.q.hosts[host]; h != nil && h.running != nil {
		s.mu.Unlock()
		return true
	}
	// Counted before it is admitted, as the scheduler loop counts its
	// admissions, so Close joins its done() (spec §8.6, Task 11 fix round
	// 1). joinMu is a leaf, so it may be taken here under activator.Service.mu
	// and s.mu. Once Close has begun nothing is admitted and the recycle is
	// skipped: the agent is stopping, and the child goes with it.
	if !m.enter(true) {
		s.mu.Unlock()
		return true
	}
	d, ok := s.q.admitOne(host, m.d.Now())
	if !ok {
		m.leave()
		s.mu.Unlock()
		return false
	}
	s.mu.Unlock()
	go func() {
		defer m.leave()
		s.execute(m.ctx, d)
	}()
	return true
}