// mavend/routingtrace.go — persisting the per-turn decision record (V-629).
//
// internal/decision keeps a 25-turn in-memory ring and persisted nothing, on the
// argument that a turn record is read minutes later or never. The owner reversed
// that on 06-08-2026, because the routing heads (V-546) cannot be fitted or
// calibrated without real utterances and there is no other source of them. The
// reversal is written down in docs/plans/21-persisting-the-routing-trace.md.
//
// The ring stays. It is what /trace reads, it is fast, and it is what a test that
// wired no store still gets. This file is the second sink beside it, and it is
// nil unless the daemon has a database — no store, no trace, no error.
package main

import (
	"context"
	"encoding/json"
	"log"
	"strings"
	"time"

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

// traceWriter is the seam the handler persists through. store.Store satisfies
// it. nil ⇒ the ring is the only sink, which is the pre-V-629 behaviour exactly.
type traceWriter interface {
	WriteRoutingTrace(ctx context.Context, tr store.RoutingTrace) (int64, error)
}

// traceSink wraps the store, or returns nil when there is none. A typed nil
// pointer assigned straight into the interface would be non-nil and would panic
// on the first turn, which is the classic shape of this bug.
func traceSink(s *store.Store) traceWriter {
	if s == nil {
		return nil
	}
	return s
}

// pruneTracesOnStart enforces retention once at wiring time. Pruning on write
// alone is not enough: a box that goes quiet for a month keeps every row until
// the next sixty-fourth turn, and "kept for fourteen days" would then be true
// only of a box in daily use. Called for its effect and never blocks a start.
func pruneTracesOnStart(s *store.Store, now time.Time) {
	if s == nil {
		return
	}
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()
	if err := s.PruneRoutingTraces(ctx, now.Add(-store.RoutingTraceRetention)); err != nil {
		log.Printf("routing trace: prune on start: %v", err)
	}
}

// persistDecision writes one finished record. It takes the same *decision.Record
// the ring takes, so the two sinks cannot disagree about what the turn did.
//
// Errors are logged and swallowed. A trace is diagnostic and training data, and
// a failed insert must never change what the owner hears.
func (h *reactiveHandler) persistDecision(ctx context.Context, rec *decision.Record, src turnSource) {
	if h.traces == nil || rec == nil || strings.TrimSpace(rec.Utterance) == "" {
		return
	}
	// Detached from the turn's context, and bounded on its own. Two reasons, and
	// the first is the one that matters: the turn is over by the time this runs,
	// so a caller that hung up or timed out would cancel the insert, and the turn
	// he abandoned halfway is exactly the one worth having. The second is that a
	// write must not hold the reply, so it gets a second and no more.
	ctx, cancel := context.WithTimeout(context.WithoutCancel(ctx), time.Second)
	defer cancel()
	claims, err := json.Marshal(rec.Claims)
	if err != nil {
		log.Printf("routing trace: marshal claims: %v", err)
		return
	}
	tr := store.RoutingTrace{
		Ts:                rec.Ts,
		Utterance:         rec.Utterance,
		Source:            string(src),
		Winner:            rec.Winner,
		Intent:            wonIntent(rec),
		ClaimedBeforeHead: claimedBeforeHead(rec),
		EncoderID:         h.encoderID,
		Outcome:           wonAt(rec, decision.StageAction),
		Claims:            claims,
	}
	if _, err := h.traces.WriteRoutingTrace(ctx, tr); err != nil {
		log.Printf("routing trace: write: %v", err)
	}
}

// wonIntent — what the winning claimant made the turn. Read from the claim
// rather than from the route, because a pre-route resolver wins without routing
// and its intent is the honest answer to "what was this turn".
func wonIntent(rec *decision.Record) string {
	for _, c := range rec.Claims {
		if c.Outcome == decision.Won && c.Intent != "" {
			return c.Intent
		}
	}
	return ""
}

// wonAt — the claimant that won at one stage. The action stage is what actually
// produced the reply, which is a different question from what was routed: a
// route that reached a gap and a route that ran are not the same turn.
func wonAt(rec *decision.Record, stage string) string {
	for _, c := range rec.Claims {
		if c.Stage == stage && c.Outcome == decision.Won {
			return c.Claimant
		}
	}
	return ""
}

// claimedBeforeHead — a pre-route resolver or a stage-0 grammar answered, so the
// turn teaches nothing about the classifier. Those are a large share of real
// traffic, and fitting a head on them would fit it to the grammars rather than
// to him. Recorded per turn rather than filtered on write, because which share
// that is happens to be the number V-632 needs to know.
func claimedBeforeHead(rec *decision.Record) bool {
	stage, _, ok := strings.Cut(rec.Winner, ":")
	if !ok {
		return false
	}
	return stage == decision.StagePreRoute || stage == decision.StageZero
}