// Package router assigns queued tasks to registered, reachable herdrs.
package router

import (
	"encoding/json"
	"fmt"
	"errors"
	"orchestra/internal/authz"
	"orchestra/internal/domain"
	"orchestra/internal/registry"
	"orchestra/internal/store"
	"sort"
	"strings"
	"sync"
	"time"
)

type Availability interface{ Available(h registry.Herdr) bool }

// ProjectAvailability is an optional stricter availability contract used by
// federated workers, whose local checkout configuration is authoritative.
type ProjectAvailability interface {
	Supports(h registry.Herdr, project string) bool
}
// ReasonedAvailability is an optional contract that names why a herdr was
// refused. Without it every refusal collapses into one string, which told an
// operator "stale heartbeat" while the heartbeat was one second old and the
// real refusal came from the quota gate. Found on burn-in run 2, 2026-08-26.
type ReasonedAvailability interface {
	// Unavailable returns "" when the herdr may be leased, otherwise the
	// specific reason.
	Unavailable(h registry.Herdr) string
}
type AlwaysAvailable struct{}

func (AlwaysAvailable) Available(registry.Herdr) bool { return true }

// QuotaWindowLimits are the two independent caps the spec (§7.2) requires:
// the subscription pool's 5-hour rolling window and its weekly window. They
// are tracked and evaluated separately — a harness deep into its 5h window
// but fine on the week, or vice versa, must still be excluded.
type QuotaWindowLimits struct {
	FiveHour float64
	Weekly   float64
}

const (
	fiveHourWindow = 5 * time.Hour
	weeklyWindow   = 7 * 24 * time.Hour
	// quotaConservativeFraction is the degrade-safe default from spec §7.2/§9
	// item 1: since no quota pool is authoritative, treat 80% reported as
	// full rather than trusting the exact number.
	quotaConservativeFraction = 0.8
)

// QuotaAvailability applies the conservative 80% rule independently to the
// 5-hour rolling window and the weekly window, per harness. Receipts are
// additive across rotations; a cumulative session total must never replace
// earlier rotations' receipts (spec §5.2.1) — summing native per-report
// `consumed` deltas is what keeps this correct across rotation.
type QuotaAvailability struct {
	Store  *store.Store
	Limits map[string]QuotaWindowLimits
	Now    func() time.Time
}

func (q QuotaAvailability) sumSince(harnessID string, since time.Time) (float64, bool) {
	return q.Store.QuotaSince(harnessID, since)
}

func (q QuotaAvailability) Available(h registry.Herdr) bool {
	if q.Store == nil {
		return false
	}
	limits, bounded := q.Limits[h.ID]
	if !bounded || (limits.FiveHour <= 0 && limits.Weekly <= 0) {
		return true
	}
	now := time.Now()
	if q.Now != nil {
		now = q.Now()
	}
	if limits.FiveHour > 0 {
		used, known := q.sumSince(h.ID, now.Add(-fiveHourWindow))
		if !known || used >= limits.FiveHour*quotaConservativeFraction {
			return false
		}
	}
	if limits.Weekly > 0 {
		used, known := q.sumSince(h.ID, now.Add(-weeklyWindow))
		if !known || used >= limits.Weekly*quotaConservativeFraction {
			return false
		}
	}
	return true
}

func (q QuotaAvailability) Unavailable(h registry.Herdr) string {
	if q.Store == nil {
		return "quota unavailable: no receipt store"
	}
	limits, bounded := q.Limits[h.ID]
	if !bounded || (limits.FiveHour <= 0 && limits.Weekly <= 0) {
		return ""
	}
	now := time.Now()
	if q.Now != nil {
		now = q.Now()
	}
	windows := []struct {
		name  string
		limit float64
		since time.Time
	}{
		{"5h", limits.FiveHour, now.Add(-fiveHourWindow)},
		{"weekly", limits.Weekly, now.Add(-weeklyWindow)},
	}
	for _, w := range windows {
		if w.limit <= 0 {
			continue
		}
		used, known := q.sumSince(h.ID, w.since)
		if !known {
			return "quota unavailable: " + w.name + " usage unknown"
		}
		if cap := w.limit * quotaConservativeFraction; used >= cap {
			return fmt.Sprintf("quota exhausted: %s window %.0f/%.0f conservative limit (of %.0f)", w.name, used, cap, w.limit)
		}
	}
	return ""
}

// unavailableReason prefers a specific reason when the availability supports
// one, and never lets a bare Available disagree with it.
func unavailableReason(a Availability, h registry.Herdr) string {
	if ra, ok := a.(ReasonedAvailability); ok {
		return ra.Unavailable(h)
	}
	if a.Available(h) {
		return ""
	}
	return "worker unavailable"
}

type RetryPolicy struct {
	MaxAttempts int
	Backoff     time.Duration
}
type Router struct {
	Store        *store.Store
	Registry     registry.Registry
	Reachability registry.Reachability
	Availability Availability
	Timeout      time.Duration
	Retry        RetryPolicy
	Now          func() time.Time
	OnLease      func(domain.Event) error
	// HealthTTL bounds re-use of a successful or failed reachability probe.
	// A scheduling pass always has a coherent health snapshot; this cache also
	// prevents bursts of TaskCreated events from repeatedly dialing the same
	// herdr between passes.
	HealthTTL  time.Duration
	healthMu   sync.Mutex
	health     map[string]healthProbe
	rejectMu   sync.Mutex
	rejections []Rejection
}

// Rejection is why one scheduling pass did not give one task to one herdr.
// Every eligibility gate records one, because a silent `continue` is
// indistinguishable from "nothing was queued": during burn-in a task sat
// queued while every gate checked out by hand, and the router said nothing.
type Rejection struct {
	TaskID  string `json:"task_id"`
	HerdrID string `json:"herdr_id,omitempty"`
	Reason  string `json:"reason"`
}

// maxRejections bounds the recorded set so a large queue cannot grow it without
// limit. The newest pass always fits, because the list is reset per pass.
const maxRejections = 200

func (r *Router) reject(taskID, herdrID, reason string) {
	r.rejectMu.Lock()
	defer r.rejectMu.Unlock()
	if len(r.rejections) >= maxRejections {
		return
	}
	r.rejections = append(r.rejections, Rejection{TaskID: taskID, HerdrID: herdrID, Reason: reason})
}

// Rejections returns why the most recent scheduling pass assigned nothing to
// the tasks it could not place.
func (r *Router) Rejections() []Rejection {
	r.rejectMu.Lock()
	defer r.rejectMu.Unlock()
	return append([]Rejection(nil), r.rejections...)
}

func (r *Router) resetRejections() {
	r.rejectMu.Lock()
	r.rejections = nil
	r.rejectMu.Unlock()
}

type healthProbe struct {
	reachable bool
	until     time.Time
}

func (r *Router) init() {
	if r.Availability == nil {
		r.Availability = AlwaysAvailable{}
	}
	if r.Now == nil {
		r.Now = time.Now
	}
	if r.HealthTTL <= 0 {
		r.HealthTTL = 5 * time.Second
	}
}

// HandleEvent evaluates the sink after creation and after a lease is freed.
func (r *Router) HandleEvent(e domain.Event) ([]domain.Event, error) {
	r.init()
	if e.Type != "TaskCreated" && e.Type != "TaskReleased" {
		return nil, nil
	}
	return r.AssignPending()
}

func (r *Router) AssignPending() ([]domain.Event, error) {
	r.init()
	if r.Store == nil {
		return nil, errors.New("router: store required")
	}
	now := r.Now()
	r.resetRejections()
	snapshot := r.Store.SchedulingSnapshot()
	var queued []domain.Task
	for _, t := range snapshot.Tasks {
		if t.State != domain.StateQueued {
			continue
		}
		if !t.NextRetryAt.IsZero() && now.Before(t.NextRetryAt) {
			// A queued task the pass never even considers is the most
			// confusing state of all: it looks assignable and nothing is
			// recorded against it. Say so.
			r.reject(t.ID, "", "retry backoff until "+t.NextRetryAt.UTC().Format(time.RFC3339))
			continue
		}
		queued = append(queued, t)
	}
	sort.SliceStable(queued, func(i, j int) bool { return importance(queued[i], now).Before(importance(queued[j], now)) })
	health := r.healthSnapshot(now)
	candidates := make(map[string][]registry.Herdr)
	availability := make(map[string]string)
	availabilityKnown := make(map[string]bool)
	projectSupport := make(map[string]bool)
	projectSupportKnown := make(map[string]bool)
	activeLeases := snapshot.ActiveLeases
	var out []domain.Event
	for _, t := range queued {
		if r.Retry.MaxAttempts > 0 && t.Attempt >= r.Retry.MaxAttempts {
			e, err := r.fail(t)
			if err != nil {
				return out, err
			}
			out = append(out, e)
			continue
		}
		cs, found := candidates[t.Project]
		if !found {
			var err error
			cs, err = r.Registry.CandidatesWithHealth(t.Project, health)
			if err != nil {
				r.reject(t.ID, "", "no candidate herdr for project "+t.Project+": "+err.Error())
				continue
			}
			candidates[t.Project] = cs
		}
		if len(cs) == 0 {
			r.reject(t.ID, "", "no candidate herdr for project "+t.Project+" (affinity, capability or reachability)")
			continue
		}
		placed := false
		for _, h := range cs {
			projectKey := h.ID + "\x00" + t.Project
			projectOK, checked := projectSupport[projectKey], projectSupportKnown[projectKey]
			if !checked {
				projectOK = true
				if projects, ok := r.Availability.(ProjectAvailability); ok {
					projectOK = projects.Supports(h, t.Project)
				}
				projectSupport[projectKey], projectSupportKnown[projectKey] = projectOK, true
			}
			if !projectOK {
				r.reject(t.ID, h.ID, "worker has not declared project "+t.Project)
				continue
			}
			if !matches(t.Capability, h.Capabilities) {
				r.reject(t.ID, h.ID, "capability mismatch")
				continue
			}
			reason, checked := availability[h.ID], availabilityKnown[h.ID]
			if !checked {
				reason = unavailableReason(r.Availability, h)
				availability[h.ID], availabilityKnown[h.ID] = reason, true
			}
			if reason != "" {
				r.reject(t.ID, h.ID, reason)
				continue
			}
			if occupiedCount(activeLeases[h.ID], h.Concurrency) {
				r.reject(t.ID, h.ID, "no free concurrency")
				continue
			}
			e, err := r.Store.Lease(t.ID, h.ID, 30*time.Minute)
			if err != nil {
				// Includes a pre-lease reconciliation refusal, which is the
				// one gate that fails closed on purpose.
				r.reject(t.ID, h.ID, "lease refused: "+err.Error())
				continue
			}
			placed = true
			out = append(out, e)
			activeLeases[h.ID]++
			if r.OnLease != nil {
				if err := r.OnLease(e); err != nil {
					return out, err
				}
			}
			break
		}
		if !placed {
			r.reject(t.ID, "", "no candidate accepted the task")
		}
	}
	return out, nil
}

func matches(need, have []string) bool {
	set := map[string]bool{}
	for _, x := range have {
		set[strings.ToLower(x)] = true
	}
	for _, x := range need {
		if !set[strings.ToLower(x)] {
			return false
		}
	}
	return true
}
func occupiedCount(count, limit int) bool {
	return limit > 0 && count >= limit
}

func (r *Router) healthSnapshot(now time.Time) map[string]bool {
	herdrs := r.Registry.Herdrs()
	health := make(map[string]bool, len(herdrs))
	if r.Reachability == nil {
		for _, h := range herdrs {
			health[h.ID] = true
		}
		return health
	}
	type target struct {
		key     string
		id      string
		address string
	}
	var probes []target
	r.healthMu.Lock()
	if r.health == nil {
		r.health = make(map[string]healthProbe)
	}
	for _, h := range herdrs {
		key := h.ID + "\x00" + r.Registry.Endpoint(h)
		if cached, ok := r.health[key]; ok && now.Before(cached.until) {
			health[h.ID] = cached.reachable
			continue
		}
		probes = append(probes, target{key: key, id: h.ID, address: r.Registry.Endpoint(h)})
	}
	r.healthMu.Unlock()
	var wg sync.WaitGroup
	var mu sync.Mutex
	for _, target := range probes {
		target := target
		wg.Add(1)
		go func() {
			defer wg.Done()
			reachable := r.Reachability.Reachable(target.address, r.Timeout)
			mu.Lock()
			health[target.id] = reachable
			mu.Unlock()
		}()
	}
	wg.Wait()
	if len(probes) > 0 {
		r.healthMu.Lock()
		for _, target := range probes {
			r.health[target.key] = healthProbe{reachable: health[target.id], until: now.Add(r.HealthTTL)}
		}
		r.healthMu.Unlock()
	}
	return health
}
func importance(t domain.Task, now time.Time) time.Time {
	if t.Due != nil {
		return t.Due.Add(-time.Duration(t.InherentPriority) * time.Hour)
	}
	return now.Add(-time.Duration(t.InherentPriority) * time.Hour)
}
func (r *Router) fail(t domain.Task) (domain.Event, error) {
	b, _ := json.Marshal(map[string]any{"reason": "retry_limit", "attempts": t.Attempt, "failure_class": t.FailureClass})
	e := domain.Event{ID: domain.NewID(), Type: "TaskFailed", TaskID: t.ID, Version: t.Version + 1, Payload: b, Surface: string(authz.System)}
	return e, r.Store.Append(e)
}