package agent

import (
	"os"

	"reasonix/internal/event"
	"reasonix/internal/evidence"
)

// ebmBlindThreshold is the Evidence-Before-More-Mutation trigger: three
// mutations since the last discriminating observation. Healthy trajectories
// peak at two (edit, edit, check); the one recorded failure peaked at five.
const ebmBlindThreshold = 3

// ebmNudge deliberately permits finishing a coherent multi-file change first —
// the goal is discriminating feedback, not a mechanical test-after-every-edit.
const ebmNudge = "[evidence nudge] You have made several unverified mutations. Before making further " +
	"changes, obtain the cheapest discriminating evidence available for the current hypothesis. " +
	"If the workspace is not yet in a verifiable state, finish only the minimum coherent change " +
	"needed to make such a check possible."

// ebmEnabled gates enforcement for the A/B experiment; eligibility is always
// recorded so baseline arms carry the same shadow. Env-scoped on purpose —
// graduation to config waits on the experiment's verdict.
var ebmEnabled = os.Getenv("REASONIX_EXPERIMENT_EBM") == "1"

type ebmState struct {
	fired        bool
	captureArmed bool
	captured     bool
	captureRound int
}

// applyEBM stamps eligibility on the round's sample and, when the experiment
// arm is active, asks once per turn for the cheapest discriminating check.
func (a *Agent) applyEBM(sample *evidence.OutcomeSample, outcomes []toolOutcome) intervention {
	if sample.DebtAge == 0 || sample.BlindMutations < ebmBlindThreshold {
		return intervention{}
	}
	sample.EBMEligible = true
	a.armForkCapture(*sample)
	if !ebmEnabled || a.task.ebm.fired || len(outcomes) == 0 {
		return intervention{}
	}
	a.task.ebm.fired = true
	a.task.ebm.captureArmed = false
	sample.EBMFired = true
	return intervention{
		verdict:  verdictAdvise,
		guidance: ebmNudge,
		notice: noticeFor(event.NoticeCodeEvidenceNudge, event.LevelInfo,
			"Several mutations are unverified; asking for the cheapest discriminating check.",
			"evidence nudge: verification debt open with blind mutations at threshold"),
	}
}