package domain

import (
	"errors"
	"strings"

	"git.cin.su/m/Assistant/contracts/capability"
)

var ErrInvalidSkillProfile = errors.New("invalid skill profile")
var ErrInvalidFastPathInput = errors.New("invalid fast path input")
var ErrInsufficientSkillEvidence = errors.New("insufficient independent skill evidence")

func ValidateSkillProfile(value capability.SkillProfile) error {
	if value.ID == "" || value.Revision < 1 || strings.TrimSpace(value.Name) == "" ||
		strings.TrimSpace(value.Description) == "" || value.Status == "" ||
		value.ConfidenceMillis < 0 || value.ConfidenceMillis > 1000 || value.RecordedAtUnixMillis < 1 {
		return ErrInvalidSkillProfile
	}
	switch value.Status {
	case capability.SkillCandidate, capability.SkillEvaluating, capability.SkillValidated, capability.SkillActive, capability.SkillDegraded, capability.SkillSuspended, capability.SkillRetired:
	default:
		return ErrInvalidSkillProfile
	}
	return nil
}

// CandidateFromVerifiedExperience starts a reusable approach but deliberately
// does not validate or activate it. Evidence stays in Epistemics by reference.
func CandidateFromVerifiedExperience(profile capability.SkillProfile, experience capability.SkillEvidenceRef, verified bool, recordedAt int64) (capability.SkillProfile, error) {
	if err := ValidateSkillProfile(profile); err != nil || experience == "" || !verified || recordedAt < 1 {
		return capability.SkillProfile{}, ErrInvalidSkillProfile
	}
	next := profile
	next.Revision++
	next.Status = capability.SkillCandidate
	next.SupportingExperienceRefs = appendEvidenceRef(next.SupportingExperienceRefs, experience)
	next.VerifiedOutcomeCount++
	next.RecordedAtUnixMillis = recordedAt
	return next, nil
}

// ValidateSkill requires repeatable verified outcomes plus evidence produced by
// an evaluator other than the candidate creator. It never activates a Skill.
func ValidateSkill(profile capability.SkillProfile, evaluation capability.SkillEvidenceRef, independent bool, mustNotWorsen bool, recordedAt int64) (capability.SkillProfile, error) {
	if err := ValidateSkillProfile(profile); err != nil || evaluation == "" || !independent || !mustNotWorsen || recordedAt < 1 {
		return capability.SkillProfile{}, ErrInsufficientSkillEvidence
	}
	if profile.VerifiedOutcomeCount < 2 || len(profile.SupportingExperienceRefs) < 2 {
		return capability.SkillProfile{}, ErrInsufficientSkillEvidence
	}
	next := profile
	next.Revision++
	next.Status = capability.SkillValidated
	next.ValidationEvidenceRefs = appendEvidenceRef(next.ValidationEvidenceRefs, evaluation)
	next.IndependentEvaluationRefs = appendEvidenceRef(next.IndependentEvaluationRefs, evaluation)
	next.MustNotWorsenSatisfied = true
	next.LastValidatedUnixMillis = recordedAt
	next.RecordedAtUnixMillis = recordedAt
	return next, nil
}

func ActivateSkill(profile capability.SkillProfile, recordedAt int64) (capability.SkillProfile, error) {
	if err := ValidateSkillProfile(profile); err != nil || profile.Status != capability.SkillValidated || len(profile.IndependentEvaluationRefs) == 0 || !profile.MustNotWorsenSatisfied || recordedAt < 1 {
		return capability.SkillProfile{}, ErrInsufficientSkillEvidence
	}
	next := profile
	next.Revision++
	next.Status = capability.SkillActive
	next.RecordedAtUnixMillis = recordedAt
	return next, nil
}

func ObserveSkillOutcome(profile capability.SkillProfile, observation capability.SkillOutcomeObservation) (capability.SkillProfile, error) {
	if err := ValidateSkillProfile(profile); err != nil {
		return capability.SkillProfile{}, err
	}
	if observation.ExperienceRef == "" || observation.ObservedAtUnixMillis < 1 {
		return capability.SkillProfile{}, ErrInvalidSkillProfile
	}
	next := profile
	next.Revision++
	next.RecordedAtUnixMillis = observation.ObservedAtUnixMillis
	switch observation.Outcome {
	case capability.UsageSucceeded:
		next.SupportingExperienceRefs = appendEvidenceRef(next.SupportingExperienceRefs, observation.ExperienceRef)
		next.ConfidenceMillis = clampConfidence(next.ConfidenceMillis + 25)
	case capability.UsageFailed:
		next.KnownFailureExperienceRefs = appendEvidenceRef(next.KnownFailureExperienceRefs, observation.ExperienceRef)
		next.ObservedFailureCount++
		next.ConfidenceMillis = clampConfidence(next.ConfidenceMillis - 150)
	case capability.UsageUnknown, capability.UsageSkipped:
		// UNKNOWN and SKIPPED are evidence of incomplete observation or a safe
		// non-application, not evidence that the skill itself failed.
	default:
		return capability.SkillProfile{}, ErrInvalidSkillProfile
	}
	if observation.UserCorrected {
		next.ObservedCorrectionCount++
		next.KnownFailureExperienceRefs = appendEvidenceRef(next.KnownFailureExperienceRefs, observation.ExperienceRef)
		next.ConfidenceMillis = clampConfidence(next.ConfidenceMillis - 200)
	}
	if (next.Status == capability.SkillValidated || next.Status == capability.SkillActive) && (next.ObservedFailureCount >= 3 || next.ObservedCorrectionCount >= 2 || next.ConfidenceMillis < 500) {
		next.Status = capability.SkillDegraded
	}
	if next.Status == capability.SkillDegraded && next.ConfidenceMillis < 250 {
		next.Status = capability.SkillSuspended
	}
	return next, nil
}

func DecideFastPath(profile capability.SkillProfile, supported bool, confidenceMillis int64, environmentVersionChanged bool, conflict bool, observedAtUnixMillis int64) (capability.FastPathDecision, error) {
	if err := ValidateSkillProfile(profile); err != nil {
		return capability.FastPathDecision{}, err
	}
	if confidenceMillis < 0 || confidenceMillis > 1000 || observedAtUnixMillis < 1 {
		return capability.FastPathDecision{}, ErrInvalidFastPathInput
	}
	decision := capability.FastPathDecision{
		SkillProfileID:       profile.ID,
		Decision:             capability.FastPathApplied,
		Explanation:          "validated fast path applied",
		ObservedAtUnixMillis: observedAtUnixMillis,
	}
	switch {
	case profile.Status == capability.SkillSuspended || profile.Status == capability.SkillRetired || profile.Status == capability.SkillDegraded:
		return decline(decision, capability.FastPathStale, "skill profile is not eligible for fast-path use"), nil
	case environmentVersionChanged:
		return decline(decision, capability.FastPathStale, "environment or implementation version changed since validation"), nil
	case conflict:
		return decline(decision, capability.FastPathConflict, "input conflicts with known fast-path assumptions"), nil
	case !supported:
		return decline(decision, capability.FastPathOutOfDistribution, "input is outside supported semantics"), nil
	case confidenceMillis < 700 || profile.ConfidenceMillis < 700:
		return decline(decision, capability.FastPathLowConfidence, "confidence is too low for optimized path"), nil
	case profile.Status != capability.SkillActive:
		return decline(decision, capability.FastPathNotApplicable, "skill is not validated"), nil
	default:
		return decision, nil
	}
}

func decline(decision capability.FastPathDecision, reason capability.FastPathDeclineReason, explanation string) capability.FastPathDecision {
	decision.Decision = capability.FastPathEscalate
	decision.DeclineReason = reason
	decision.RequiresCognition = true
	decision.Explanation = explanation
	return decision
}

func appendEvidenceRef(values []capability.SkillEvidenceRef, ref capability.SkillEvidenceRef) []capability.SkillEvidenceRef {
	for _, value := range values {
		if value == ref {
			return values
		}
	}
	return append(values, ref)
}

func clampConfidence(value int64) int64 {
	if value < 0 {
		return 0
	}
	if value > 1000 {
		return 1000
	}
	return value
}