package engine

type collectionPolicy struct {
	identityFields      []string
	identityPresent     bool
	identityLocation    *Location
	explicitMode        sequenceMode
	explicitModePresent bool
	modeLocation        *Location
	recordOrder         []*collectionRecordOwner
	recordPolicies      map[*collectionRecordOwner]collectionPolicyScope
}

type collectionPolicyResolution struct {
	policy                     collectionPolicy
	operation                  sequenceMode
	declarations               []sequenceDeclarationSpec
	declarationsPresent        bool
	identityDeclarationPresent bool
	modeDeclarationPresent     bool
	applicationIdentityFields  []string
	applicationIdentityPresent bool
	effectiveIdentityFields    []string
}

// resolveCollectionPolicy reconciles declarations for one destination before
// peers are composed. The caller supplies only lower policy that is applicable
// to this destination; record survival and ownership are resolved elsewhere.
func resolveCollectionPolicy(
	destination Path,
	declarations []sequenceDeclarationSpec,
	applicationIdentityFields []string,
	lower *collectionPolicy,
) (collectionPolicyResolution, []Diagnostic) {
	normalizedDeclarations := cloneSequenceDeclarations(declarations)
	for index := range normalizedDeclarations {
		declaration := &normalizedDeclarations[index]
		if !declaration.identityPresent {
			continue
		}
		fields, err := normalizeSequenceIdentityFields(declaration.identityFields)
		if err != nil {
			return collectionPolicyResolution{}, []Diagnostic{{
				Code: CodeSequenceInvalid, Severity: SeverityError, Path: destination.clone(),
				Message: "collection identity declaration requires at least one field",
				Primary: collectionDeclarationLocation(declaration.identityLocation, declaration.location),
			}}
		}
		declaration.identityFields = fields
	}
	normalizedApplicationIdentityFields := cloneStrings(applicationIdentityFields)
	if len(applicationIdentityFields) != 0 {
		var err error
		normalizedApplicationIdentityFields, err = normalizeSequenceIdentityFields(applicationIdentityFields)
		if err != nil {
			return collectionPolicyResolution{}, []Diagnostic{{
				Code: CodeOptionsInvalid, Severity: SeverityError, Path: destination.clone(),
				Message: "application collection identity fields are invalid",
			}}
		}
	}
	result := collectionPolicyResolution{
		declarations:               normalizedDeclarations,
		declarationsPresent:        len(normalizedDeclarations) != 0,
		applicationIdentityFields:  normalizedApplicationIdentityFields,
		applicationIdentityPresent: len(normalizedApplicationIdentityFields) != 0,
	}

	var diagnostics []Diagnostic
	var declaredIdentityFields []string
	var declaredIdentityLocation *Location
	var declaredMode sequenceMode
	var declaredModeLocation *Location
	for _, declaration := range normalizedDeclarations {
		if declaration.identityPresent {
			result.identityDeclarationPresent = true
			if declaredIdentityFields == nil {
				declaredIdentityFields = cloneStrings(declaration.identityFields)
				declaredIdentityLocation = collectionDeclarationLocation(declaration.identityLocation, declaration.location)
			} else if !equalSequenceIdentityFields(declaredIdentityFields, declaration.identityFields) {
				diagnostics = append(diagnostics, collectionPolicyConflictDiagnostic(
					destination, declaredIdentityLocation,
					collectionDeclarationLocation(declaration.identityLocation, declaration.location),
					"collection identity declarations conflict",
				))
			}
		}
		if declaration.modePresent {
			result.modeDeclarationPresent = true
			if declaredMode == 0 {
				declaredMode = declaration.mode
				declaredModeLocation = collectionDeclarationLocation(declaration.modeLocation, declaration.location)
			} else if declaredMode != declaration.mode {
				diagnostics = append(diagnostics, collectionPolicyConflictDiagnostic(
					destination, declaredModeLocation,
					collectionDeclarationLocation(declaration.modeLocation, declaration.location),
					"collection operation declarations conflict",
				))
			}
		}
	}
	if len(diagnostics) != 0 {
		return collectionPolicyResolution{}, canonicalDiagnostics(diagnostics)
	}

	if lower != nil && lower.identityPresent && declaredIdentityFields != nil && !equalSequenceIdentityFields(lower.identityFields, declaredIdentityFields) {
		diagnostics = append(diagnostics, collectionPolicyConflictDiagnostic(
			destination, declaredIdentityLocation,
			collectionDeclarationLocation(lower.identityLocation, Location{}),
			"collection identity declaration conflicts with retained identity",
		))
	}
	if result.applicationIdentityPresent {
		if declaredIdentityFields != nil && !equalSequenceIdentityFields(normalizedApplicationIdentityFields, declaredIdentityFields) {
			diagnostics = append(diagnostics, collectionPolicyConflictDiagnostic(
				destination, declaredIdentityLocation, nil,
				"collection identity declaration conflicts with application constraint",
			))
		}
		if lower != nil && lower.identityPresent && !equalSequenceIdentityFields(normalizedApplicationIdentityFields, lower.identityFields) {
			diagnostics = append(diagnostics, collectionPolicyConflictDiagnostic(
				destination, declaredIdentityLocation,
				collectionDeclarationLocation(lower.identityLocation, Location{}),
				"retained collection identity conflicts with application constraint",
			))
		}
	}
	if len(diagnostics) != 0 {
		return collectionPolicyResolution{}, canonicalDiagnostics(diagnostics)
	}

	if declaredIdentityFields != nil {
		result.policy.identityFields = declaredIdentityFields
		result.policy.identityPresent = true
		result.policy.identityLocation = cloneLocation(declaredIdentityLocation)
	} else if lower != nil && lower.identityPresent {
		result.policy.identityFields = cloneStrings(lower.identityFields)
		result.policy.identityPresent = true
		result.policy.identityLocation = cloneLocation(lower.identityLocation)
	}
	if result.applicationIdentityPresent {
		result.effectiveIdentityFields = cloneStrings(normalizedApplicationIdentityFields)
	} else if result.policy.identityPresent {
		result.effectiveIdentityFields = cloneStrings(result.policy.identityFields)
	}

	if result.modeDeclarationPresent {
		result.policy.explicitMode = declaredMode
		result.policy.explicitModePresent = true
		result.policy.modeLocation = cloneLocation(declaredModeLocation)
	} else if lower != nil && lower.explicitModePresent {
		result.policy.explicitMode = lower.explicitMode
		result.policy.explicitModePresent = true
		result.policy.modeLocation = cloneLocation(lower.modeLocation)
	}
	result.operation = collectionOperationMode(declaredMode, result.policy.explicitMode, len(result.effectiveIdentityFields) != 0)

	return result, nil
}

func collectionOperationMode(current, retained sequenceMode, identified bool) sequenceMode {
	if current != 0 {
		return current
	}
	if retained != 0 {
		return retained
	}
	if identified {
		return sequenceModeUpsert
	}
	return sequenceModeReplace
}

func cloneSequenceDeclarations(declarations []sequenceDeclarationSpec) []sequenceDeclarationSpec {
	if declarations == nil {
		return nil
	}
	cloned := make([]sequenceDeclarationSpec, len(declarations))
	for index, declaration := range declarations {
		cloned[index] = declaration
		cloned[index].path = declaration.path.clone()
		cloned[index].destination = declaration.destination.clone()
		cloned[index].identityFields = cloneStrings(declaration.identityFields)
		cloned[index].identityLocation = cloneLocation(declaration.identityLocation)
		cloned[index].modeLocation = cloneLocation(declaration.modeLocation)
	}
	return cloned
}

func collectionDeclarationLocation(specific *Location, fallback Location) *Location {
	if specific != nil {
		return cloneLocation(specific)
	}
	if fallback != (Location{}) {
		return cloneLocation(&fallback)
	}
	return nil
}

func collectionPolicyConflictDiagnostic(path Path, primary, related *Location, message string) Diagnostic {
	diagnostic := Diagnostic{
		Code: CodeSequenceConflict, Severity: SeverityError,
		Path: path.clone(), Message: message, Primary: cloneLocation(primary),
	}
	if related != nil {
		diagnostic.Related = []Location{*cloneLocation(related)}
	}
	return diagnostic
}