// loop/gather.go — the ONE impure piece in the loop.
//
// Gather builds a State snapshot under the store lock at the start of each
// tick. From there, every predicate and the gate are pure functions over State.
//
// Why centralize the I/O: the loop is "dumb + deterministic", the spec
// repeatedly enforces a no-I/O contract on predicates. Centralizing read here
// makes the contract checkable (anywhere outside gather.go doing I/O is a bug).
package loop

import (
	"context"
	"time"

	"github.com/kami/maven/internal/store"
)

// Gatherer — holds nothing mutable; the Store is the only dependency. The
// daemon runs one Gatherer per tick.
type Gatherer struct {
	store *store.Store
	rules []Rule
}

func NewGatherer(s *store.Store, rules []Rule) *Gatherer {
	return &Gatherer{store: s, rules: rules}
}

// GatherState — reads the store ONCE and assembles the snapshot the pure Tick
// will operate on.
//
// Reads the loop needs:
//   - presence: probes (ts per signal key), current bucket, compute score, resolve.
//   - facts: every key any rule's Predicate OR InertWhenNoData names.
//   - last nudge per rule (for cooldown).
//   - due reminders (the loop reuses the loop for reminders; we gather them here).
//   - env flags QuietHours / CalendarBusy — read as facts (kind=config/env).
//
// All reads share a single read-only transaction for a consistent snapshot.
func (g *Gatherer) GatherState(ctx context.Context, now time.Time) (State, []store.Reminder, error) {
	// presence first — pure function over probes. the gate checks the bucket;
	// delivery (later) checks the score.
	probes, err := g.store.PresenceProbes(ctx)
	if err != nil {
		return State{}, nil, err
	}
	lastBucket, _, _, err := g.store.LoadPresenceState(ctx)
	if err != nil {
		return State{}, nil, err
	}
	score := store.PresenceScore(now, probes)
	bucket := store.Resolve(score, lastBucket)

	// collect every key any rule references (predicate + inert list).
	// Daemon rules are small (≤ ~30, per the "revisit at 30 rules" line);
	// a single map over rules per tick is negligible at 60s cadence.
	wanted := make(map[string]struct{})
	for _, r := range g.rules {
		// We don't introspect the predicate closure (Go can't); the rule author
		// declares InertWhenNoData for keys the predicate reads. Reuse that list.
		for _, k := range r.InertWhenNoData {
			wanted[k] = struct{}{}
		}
	}
	// presence signal keys live in facts too — included via the probes path,
	// but also surface via Fact() for rules that want direct access (e.g. break).
	for _, sig := range store.PresenceSignals {
		wanted[sig.Key] = struct{}{}
	}

	facts := make(map[string]store.Fact, len(wanted))
	for k := range wanted {
		f, err := g.store.LatestFact(ctx, k)
		if err == nil {
			facts[k] = f
			continue
		}
		if err == store.ErrNoFact {
			continue // missing ⇒ shut up; the gate handles it
		}
		return State{}, nil, err
	}

	// last nudge per rule + cooldown-until derived from the active cooldown.
	// "active" = the feedback tuner's persisted base if one exists, else the
	// rule's static Base. LatestFactBySource is the trust-by-provenance read
	// (a module that doesn't own the `feedback` source can't poison a rule's
	// cooldown once the auth source-scope lands — same shape as ServiceDownRule).
	lastNudge := make(map[string]store.Nudge, len(g.rules))
	cooldownUntil := make(map[string]time.Time, len(g.rules))
	for _, r := range g.rules {
		base := r.Cooldown.Base
		if f, err := g.store.LatestFactBySource(ctx, FeedbackKey(r), FeedbackSource); err == nil {
			if tuned, ok := ParseCooldownFact(f); ok {
				base = tuned
			}
		} else if err != store.ErrNoFact {
			return State{}, nil, err
		}
		n, err := g.store.LastNudge(ctx, r.Name)
		if err == nil {
			lastNudge[r.Name] = n
			cooldownUntil[r.Name] = CooldownFor(base, n.Ts)
			continue
		}
		if err == store.ErrNudgeNotFound {
			continue // never fired → no cooldown
		}
		return State{}, nil, err
	}

	// env flags — QuietHours / CalendarBusy as config facts.
	// QuietHours: presence != reachability, sleep/quiet-hours handled separately
	// in the gate. We read a config `quiet_hours` fact for the boolean.
	var quiet bool
	if f, ok := readFact(ctx, g.store, "quiet_hours"); ok {
		quiet = f.Value == "true" || f.Value == `"true"`
	}
	var calBusy bool
	if f, ok := readFact(ctx, g.store, "calendar_busy"); ok {
		calBusy = f.Value == "true" || f.Value == `"true"`
	}

	// due reminders — gate-bypassing class. read here, the daemon emits them.
	due, err := g.store.DueReminders(ctx, now)
	if err != nil {
		return State{}, nil, err
	}

	s := State{
		Now:           now,
		Presence:      bucket,
		PresenceScore: score,
		Facts:         facts,
		LastNudge:     lastNudge,
		SnoozeUntil:   nil, // no snooze persistence yet — daemon wires in
		CooldownUntil: cooldownUntil,
		QuietHours:    quiet,
		CalendarBusy:  calBusy,
	}
	return s, due, nil
}

func readFact(ctx context.Context, s *store.Store, key string) (store.Fact, bool) {
	f, err := s.LatestFact(ctx, key)
	if err != nil {
		return store.Fact{}, false
	}
	return f, true
}