package merge

import (
	"fmt"
	"reflect"
	"sort"
	"strings"

	"github.com/go-openapi/spec"
	"k8s.io/kube-openapi/pkg/util"
)

const gvkKey = "x-kubesphere-group-version-kind"

// usedDefinitionForSpec returns a map with all used definitions in the provided spec as keys and true as values.
func usedDefinitionForSpec(root *spec.Swagger) map[string]bool {
	usedDefinitions := map[string]bool{}
	walkOnAllReferences(func(ref *spec.Ref) {
		if refStr := ref.String(); refStr != "" && strings.HasPrefix(refStr, definitionPrefix) {
			usedDefinitions[refStr[len(definitionPrefix):]] = true
		}
	}, root)
	return usedDefinitions
}

// FilterSpecByPathsWithoutSideEffects removes unnecessary paths and definitions used by those paths.
// i.e. if a Path removed by this function, all definitions used by it and not used
// anywhere else will also be removed.
// It does not modify the input, but the output shares data structures with the input.
func FilterSpecByPathsWithoutSideEffects(sp *spec.Swagger, keepPathPrefixes []string) *spec.Swagger {
	if sp.Paths == nil {
		return sp
	}

	// Walk all references to find all used definitions. This function
	// want to only deal with unused definitions resulted from filtering paths.
	// Thus a definition will be removed only if it has been used before but
	// it is unused because of a path prune.
	initialUsedDefinitions := usedDefinitionForSpec(sp)

	// First remove unwanted paths
	prefixes := util.NewTrie(keepPathPrefixes)
	ret := *sp
	ret.Paths = &spec.Paths{
		VendorExtensible: sp.Paths.VendorExtensible,
		Paths:            map[string]spec.PathItem{},
	}
	for path, pathItem := range sp.Paths.Paths {
		if !prefixes.HasPrefix(path) {
			continue
		}
		ret.Paths.Paths[path] = pathItem
	}

	// Walk all references to find all definition references.
	usedDefinitions := usedDefinitionForSpec(&ret)

	// Remove unused definitions
	ret.Definitions = spec.Definitions{}
	for k, v := range sp.Definitions {
		if usedDefinitions[k] || !initialUsedDefinitions[k] {
			ret.Definitions[k] = v
		}
	}

	return &ret
}

// renameDefinitions renames definition references, without mutating the input.
// The output might share data structures with the input.
func renameDefinitions(s *spec.Swagger, renames map[string]string) *spec.Swagger {
	refRenames := make(map[string]string, len(renames))
	foundOne := false
	for k, v := range renames {
		refRenames[definitionPrefix+k] = definitionPrefix + v
		if _, ok := s.Definitions[k]; ok {
			foundOne = true
		}
	}

	if !foundOne {
		return s
	}

	ret := &spec.Swagger{}
	*ret = *s

	ret = ReplaceReferences(func(ref *spec.Ref) *spec.Ref {
		refName := ref.String()
		if newRef, found := refRenames[refName]; found {
			ret := spec.MustCreateRef(newRef)
			return &ret
		}
		return ref
	}, ret)

	renamedDefinitions := make(spec.Definitions, len(ret.Definitions))
	for k, v := range ret.Definitions {
		if newRef, found := renames[k]; found {
			k = newRef
		}
		renamedDefinitions[k] = v
	}
	ret.Definitions = renamedDefinitions

	return ret
}

// renameParameters renames parameter references, without mutating the input.
// The output might share data structures with the input.
func renameParameters(s *spec.Swagger, renames map[string]string) *spec.Swagger {
	refRenames := make(map[string]string, len(renames))
	foundOne := false
	for k, v := range renames {
		refRenames[parameterPrefix+k] = parameterPrefix + v
		if _, ok := s.Parameters[k]; ok {
			foundOne = true
		}
	}

	if !foundOne {
		return s
	}

	ret := &spec.Swagger{}
	*ret = *s

	ret = ReplaceReferences(func(ref *spec.Ref) *spec.Ref {
		refName := ref.String()
		if newRef, found := refRenames[refName]; found {
			ret := spec.MustCreateRef(newRef)
			return &ret
		}
		return ref
	}, ret)

	renamed := make(map[string]spec.Parameter, len(ret.Parameters))
	for k, v := range ret.Parameters {
		if newRef, found := renames[k]; found {
			k = newRef
		}
		renamed[k] = v
	}
	ret.Parameters = renamed

	return ret
}

// MergeSpecsIgnorePathConflictRenamingDefinitionsAndParameters is the same as
// MergeSpecs except it will ignore any path conflicts by keeping the paths of
// destination. It will rename definition and parameter conflicts.
func MergeSpecsIgnorePathConflictRenamingDefinitionsAndParameters(dest, source *spec.Swagger) error {
	return mergeSpecs(dest, source, true, true, true)
}

// mergeSpecs merges source into dest while resolving conflicts.
// The source is not mutated.
func mergeSpecs(dest, source *spec.Swagger, renameModelConflicts, renameParameterConflicts, ignorePathConflicts bool) (err error) {
	// Paths may be empty, due to [ACL constraints](http://goo.gl/8us55a#securityFiltering).
	if source.Paths == nil {
		// When a source spec does not have any path, that means none of the definitions
		// are used thus we should not do anything
		return nil
	}
	if dest.Paths == nil {
		dest.Paths = &spec.Paths{}
	}
	if ignorePathConflicts {
		keepPaths := []string{}
		hasConflictingPath := false
		for k := range source.Paths.Paths {
			if _, found := dest.Paths.Paths[k]; !found {
				keepPaths = append(keepPaths, k)
			} else {
				hasConflictingPath = true
			}
		}
		if len(keepPaths) == 0 {
			// There is nothing to merge. All paths are conflicting.
			return nil
		}
		if hasConflictingPath {
			source = FilterSpecByPathsWithoutSideEffects(source, keepPaths)
		}
	}

	// Check for model conflicts and rename to make definitions conflict-free (modulo different GVKs)
	usedNames := map[string]bool{}
	for k := range dest.Definitions {
		usedNames[k] = true
	}
	renames := map[string]string{}
DEFINITIONLOOP:
	for k, v := range source.Definitions {
		existing, found := dest.Definitions[k]
		if !found || deepEqualDefinitionsModuloGVKs(&existing, &v) {
			// skip for now, we copy them after the rename loop
			continue
		}

		if !renameModelConflicts {
			return fmt.Errorf("model name conflict in merging OpenAPI spec: %s", k)
		}

		// Reuse previously renamed model if one exists
		var newName string
		i := 1
		for found {
			i++
			newName = fmt.Sprintf("%s_v%d", k, i)
			existing, found = dest.Definitions[newName]
			if found && deepEqualDefinitionsModuloGVKs(&existing, &v) {
				renames[k] = newName
				continue DEFINITIONLOOP
			}
		}

		_, foundInSource := source.Definitions[newName]
		for usedNames[newName] || foundInSource {
			i++
			newName = fmt.Sprintf("%s_v%d", k, i)
			_, foundInSource = source.Definitions[newName]
		}
		renames[k] = newName
		usedNames[newName] = true
	}
	source = renameDefinitions(source, renames)

	// Check for parameter conflicts and rename to make parameters conflict-free
	usedNames = map[string]bool{}
	for k := range dest.Parameters {
		usedNames[k] = true
	}
	renames = map[string]string{}
PARAMETERLOOP:
	for k, p := range source.Parameters {
		existing, found := dest.Parameters[k]
		if !found || reflect.DeepEqual(&existing, &p) {
			// skip for now, we copy them after the rename loop
			continue
		}

		if !renameParameterConflicts {
			return fmt.Errorf("parameter name conflict in merging OpenAPI spec: %s", k)
		}

		// Reuse previously renamed parameter if one exists
		var newName string
		i := 1
		for found {
			i++
			newName = fmt.Sprintf("%s_v%d", k, i)
			existing, found = dest.Parameters[newName]
			if found && reflect.DeepEqual(&existing, &p) {
				renames[k] = newName
				continue PARAMETERLOOP
			}
		}

		_, foundInSource := source.Parameters[newName]
		for usedNames[newName] || foundInSource {
			i++
			newName = fmt.Sprintf("%s_v%d", k, i)
			_, foundInSource = source.Parameters[newName]
		}
		renames[k] = newName
		usedNames[newName] = true
	}
	source = renameParameters(source, renames)

	// Now without conflict (modulo different GVKs), copy definitions to dest
	for k, v := range source.Definitions {
		if existing, found := dest.Definitions[k]; !found {
			if dest.Definitions == nil {
				dest.Definitions = make(spec.Definitions, len(source.Definitions))
			}
			dest.Definitions[k] = v
		} else if merged, changed, err := mergedGVKs(&existing, &v); err != nil {
			return err
		} else if changed {
			existing.Extensions[gvkKey] = merged
		}
	}

	// Now without conflict, copy parameters to dest
	for k, v := range source.Parameters {
		if _, found := dest.Parameters[k]; !found {
			if dest.Parameters == nil {
				dest.Parameters = make(map[string]spec.Parameter, len(source.Parameters))
			}
			dest.Parameters[k] = v
		}
	}

	// Check for path conflicts
	for k, v := range source.Paths.Paths {
		if _, found := dest.Paths.Paths[k]; found {
			return fmt.Errorf("unable to merge: duplicated path %s", k)
		}
		// PathItem may be empty, due to [ACL constraints](http://goo.gl/8us55a#securityFiltering).
		if dest.Paths.Paths == nil {
			dest.Paths.Paths = map[string]spec.PathItem{}
		}
		dest.Paths.Paths[k] = v
	}

	return nil
}

// deepEqualDefinitionsModuloGVKs compares s1 and s2, but ignores the x-kubernetes-group-version-kind extension.
func deepEqualDefinitionsModuloGVKs(s1, s2 *spec.Schema) bool {
	if s1 == nil {
		return s2 == nil
	} else if s2 == nil {
		return false
	}
	if !reflect.DeepEqual(s1.Extensions, s2.Extensions) {
		for k, v := range s1.Extensions {
			if k == gvkKey {
				continue
			}
			if !reflect.DeepEqual(v, s2.Extensions[k]) {
				return false
			}
		}
		len1 := len(s1.Extensions)
		len2 := len(s2.Extensions)
		if _, found := s1.Extensions[gvkKey]; found {
			len1--
		}
		if _, found := s2.Extensions[gvkKey]; found {
			len2--
		}
		if len1 != len2 {
			return false
		}

		if s1.Extensions != nil {
			shallowCopy := *s1
			s1 = &shallowCopy
			s1.Extensions = nil
		}
		if s2.Extensions != nil {
			shallowCopy := *s2
			s2 = &shallowCopy
			s2.Extensions = nil
		}
	}

	return reflect.DeepEqual(s1, s2)
}

// mergedGVKs merges the x-kubernetes-group-version-kind slices and returns the result, and whether
// s1's x-kubernetes-group-version-kind slice was changed at all.
func mergedGVKs(s1, s2 *spec.Schema) (interface{}, bool, error) {
	gvk1, found1 := s1.Extensions[gvkKey]
	gvk2, found2 := s2.Extensions[gvkKey]

	if !found1 {
		return gvk2, found2, nil
	}
	if !found2 {
		return gvk1, false, nil
	}

	slice1, ok := gvk1.([]interface{})
	if !ok {
		return nil, false, fmt.Errorf("expected slice of GroupVersionKinds, got: %+v", slice1)
	}
	slice2, ok := gvk2.([]interface{})
	if !ok {
		return nil, false, fmt.Errorf("expected slice of GroupVersionKinds, got: %+v", slice2)
	}

	ret := make([]interface{}, len(slice1), len(slice1)+len(slice2))
	keys := make([]string, 0, len(slice1)+len(slice2))
	copy(ret, slice1)
	seen := make(map[string]bool, len(slice1))
	for _, x := range slice1 {
		gvk, ok := x.(map[string]interface{})
		if !ok {
			return nil, false, fmt.Errorf(`expected {"group": <group>, "kind": <kind>, "version": <version>}, got: %#v`, x)
		}
		k := fmt.Sprintf("%s/%s.%s", gvk["group"], gvk["version"], gvk["kind"])
		keys = append(keys, k)
		seen[k] = true
	}
	changed := false
	for _, x := range slice2 {
		gvk, ok := x.(map[string]interface{})
		if !ok {
			return nil, false, fmt.Errorf(`expected {"group": <group>, "kind": <kind>, "version": <version>}, got: %#v`, x)
		}
		k := fmt.Sprintf("%s/%s.%s", gvk["group"], gvk["version"], gvk["kind"])
		if seen[k] {
			continue
		}
		ret = append(ret, x)
		keys = append(keys, k)
		changed = true
	}

	if changed {
		sort.Sort(byKeys{ret, keys})
	}

	return ret, changed, nil
}

type byKeys struct {
	values []interface{}
	keys   []string
}

func (b byKeys) Len() int {
	return len(b.values)
}

func (b byKeys) Less(i, j int) bool {
	return b.keys[i] < b.keys[j]
}

func (b byKeys) Swap(i, j int) {
	b.values[i], b.values[j] = b.values[j], b.values[i]
	b.keys[i], b.keys[j] = b.keys[j], b.keys[i]
}

func ReplaceReferences(walkRef func(ref *spec.Ref) *spec.Ref, sp *spec.Swagger) *spec.Swagger {
	walker := &Walker{RefCallback: walkRef, SchemaCallback: SchemaCallBackNoop}
	return walker.WalkRoot(sp)
}

type Walker struct {
	// SchemaCallback will be called on each schema, taking the original schema,
	// and before any other callbacks of the Walker.
	// If the schema needs to be mutated, DO NOT mutate it in-place,
	// always create a copy, mutate, and return it.
	SchemaCallback func(schema *spec.Schema) *spec.Schema

	// RefCallback will be called on each ref.
	// If the ref needs to be mutated, DO NOT mutate it in-place,
	// always create a copy, mutate, and return it.
	RefCallback func(ref *spec.Ref) *spec.Ref
}

type SchemaCallbackFunc func(schema *spec.Schema) *spec.Schema
type RefCallbackFunc func(ref *spec.Ref) *spec.Ref

var SchemaCallBackNoop SchemaCallbackFunc = func(schema *spec.Schema) *spec.Schema {
	return schema
}
var RefCallbackNoop RefCallbackFunc = func(ref *spec.Ref) *spec.Ref {
	return ref
}

func (w *Walker) WalkRoot(swagger *spec.Swagger) *spec.Swagger {
	if swagger == nil {
		return nil
	}

	orig := swagger
	cloned := false
	clone := func() {
		if !cloned {
			cloned = true
			swagger = &spec.Swagger{}
			*swagger = *orig
		}
	}

	parametersCloned := false
	for k, v := range swagger.Parameters {
		if p := w.walkParameter(&v); p != &v {
			if !parametersCloned {
				parametersCloned = true
				clone()
				swagger.Parameters = make(map[string]spec.Parameter, len(orig.Parameters))
				for k2, v2 := range orig.Parameters {
					swagger.Parameters[k2] = v2
				}
			}
			swagger.Parameters[k] = *p
		}
	}

	responsesCloned := false
	for k, v := range swagger.Responses {
		if r := w.walkResponse(&v); r != &v {
			if !responsesCloned {
				responsesCloned = true
				clone()
				swagger.Responses = make(map[string]spec.Response, len(orig.Responses))
				for k2, v2 := range orig.Responses {
					swagger.Responses[k2] = v2
				}
			}
			swagger.Responses[k] = *r
		}
	}

	definitionsCloned := false
	for k, v := range swagger.Definitions {
		if s := w.WalkSchema(&v); s != &v {
			if !definitionsCloned {
				definitionsCloned = true
				clone()
				swagger.Definitions = make(spec.Definitions, len(orig.Definitions))
				for k2, v2 := range orig.Definitions {
					swagger.Definitions[k2] = v2
				}
			}
			swagger.Definitions[k] = *s
		}
	}

	if swagger.Paths != nil {
		if p := w.walkPaths(swagger.Paths); p != swagger.Paths {
			clone()
			swagger.Paths = p
		}
	}

	return swagger
}

func (w *Walker) WalkSchema(schema *spec.Schema) *spec.Schema {
	if schema == nil {
		return nil
	}

	orig := schema
	clone := func() {
		if orig == schema {
			schema = &spec.Schema{}
			*schema = *orig
		}
	}

	// Always run callback on the whole schema first
	// so that SchemaCallback can take the original schema as input.
	schema = w.SchemaCallback(schema)

	if r := w.RefCallback(&schema.Ref); r != &schema.Ref {
		clone()
		schema.Ref = *r
	}

	definitionsCloned := false
	for k, v := range schema.Definitions {
		if s := w.WalkSchema(&v); s != &v {
			if !definitionsCloned {
				definitionsCloned = true
				clone()
				schema.Definitions = make(spec.Definitions, len(orig.Definitions))
				for k2, v2 := range orig.Definitions {
					schema.Definitions[k2] = v2
				}
			}
			schema.Definitions[k] = *s
		}
	}

	propertiesCloned := false
	for k, v := range schema.Properties {
		if s := w.WalkSchema(&v); s != &v {
			if !propertiesCloned {
				propertiesCloned = true
				clone()
				schema.Properties = make(map[string]spec.Schema, len(orig.Properties))
				for k2, v2 := range orig.Properties {
					schema.Properties[k2] = v2
				}
			}
			schema.Properties[k] = *s
		}
	}

	patternPropertiesCloned := false
	for k, v := range schema.PatternProperties {
		if s := w.WalkSchema(&v); s != &v {
			if !patternPropertiesCloned {
				patternPropertiesCloned = true
				clone()
				schema.PatternProperties = make(map[string]spec.Schema, len(orig.PatternProperties))
				for k2, v2 := range orig.PatternProperties {
					schema.PatternProperties[k2] = v2
				}
			}
			schema.PatternProperties[k] = *s
		}
	}

	allOfCloned := false
	for i := range schema.AllOf {
		if s := w.WalkSchema(&schema.AllOf[i]); s != &schema.AllOf[i] {
			if !allOfCloned {
				allOfCloned = true
				clone()
				schema.AllOf = make([]spec.Schema, len(orig.AllOf))
				copy(schema.AllOf, orig.AllOf)
			}
			schema.AllOf[i] = *s
		}
	}

	anyOfCloned := false
	for i := range schema.AnyOf {
		if s := w.WalkSchema(&schema.AnyOf[i]); s != &schema.AnyOf[i] {
			if !anyOfCloned {
				anyOfCloned = true
				clone()
				schema.AnyOf = make([]spec.Schema, len(orig.AnyOf))
				copy(schema.AnyOf, orig.AnyOf)
			}
			schema.AnyOf[i] = *s
		}
	}

	oneOfCloned := false
	for i := range schema.OneOf {
		if s := w.WalkSchema(&schema.OneOf[i]); s != &schema.OneOf[i] {
			if !oneOfCloned {
				oneOfCloned = true
				clone()
				schema.OneOf = make([]spec.Schema, len(orig.OneOf))
				copy(schema.OneOf, orig.OneOf)
			}
			schema.OneOf[i] = *s
		}
	}

	if schema.Not != nil {
		if s := w.WalkSchema(schema.Not); s != schema.Not {
			clone()
			schema.Not = s
		}
	}

	if schema.AdditionalProperties != nil && schema.AdditionalProperties.Schema != nil {
		if s := w.WalkSchema(schema.AdditionalProperties.Schema); s != schema.AdditionalProperties.Schema {
			clone()
			schema.AdditionalProperties = &spec.SchemaOrBool{Schema: s, Allows: schema.AdditionalProperties.Allows}
		}
	}

	if schema.AdditionalItems != nil && schema.AdditionalItems.Schema != nil {
		if s := w.WalkSchema(schema.AdditionalItems.Schema); s != schema.AdditionalItems.Schema {
			clone()
			schema.AdditionalItems = &spec.SchemaOrBool{Schema: s, Allows: schema.AdditionalItems.Allows}
		}
	}

	if schema.Items != nil {
		if schema.Items.Schema != nil {
			if s := w.WalkSchema(schema.Items.Schema); s != schema.Items.Schema {
				clone()
				schema.Items = &spec.SchemaOrArray{Schema: s}
			}
		} else {
			itemsCloned := false
			for i := range schema.Items.Schemas {
				if s := w.WalkSchema(&schema.Items.Schemas[i]); s != &schema.Items.Schemas[i] {
					if !itemsCloned {
						clone()
						schema.Items = &spec.SchemaOrArray{
							Schemas: make([]spec.Schema, len(orig.Items.Schemas)),
						}
						itemsCloned = true
						copy(schema.Items.Schemas, orig.Items.Schemas)
					}
					schema.Items.Schemas[i] = *s
				}
			}
		}
	}

	return schema
}

func (w *Walker) walkParameter(param *spec.Parameter) *spec.Parameter {
	if param == nil {
		return nil
	}

	orig := param
	cloned := false
	clone := func() {
		if !cloned {
			cloned = true
			param = &spec.Parameter{}
			*param = *orig
		}
	}

	if r := w.RefCallback(&param.Ref); r != &param.Ref {
		clone()
		param.Ref = *r
	}
	if s := w.WalkSchema(param.Schema); s != param.Schema {
		clone()
		param.Schema = s
	}
	if param.Items != nil {
		if r := w.RefCallback(&param.Items.Ref); r != &param.Items.Ref {
			param.Items.Ref = *r
		}
	}

	return param
}

func (w *Walker) walkParameters(params []spec.Parameter) ([]spec.Parameter, bool) {
	if params == nil {
		return nil, false
	}

	orig := params
	cloned := false
	clone := func() {
		if !cloned {
			cloned = true
			params = make([]spec.Parameter, len(params))
			copy(params, orig)
		}
	}

	for i := range params {
		if s := w.walkParameter(&params[i]); s != &params[i] {
			clone()
			params[i] = *s
		}
	}

	return params, cloned
}

func (w *Walker) walkResponse(resp *spec.Response) *spec.Response {
	if resp == nil {
		return nil
	}

	orig := resp
	cloned := false
	clone := func() {
		if !cloned {
			cloned = true
			resp = &spec.Response{}
			*resp = *orig
		}
	}

	if r := w.RefCallback(&resp.Ref); r != &resp.Ref {
		clone()
		resp.Ref = *r
	}
	if s := w.WalkSchema(resp.Schema); s != resp.Schema {
		clone()
		resp.Schema = s
	}

	return resp
}

func (w *Walker) walkResponses(resps *spec.Responses) *spec.Responses {
	if resps == nil {
		return nil
	}

	orig := resps
	cloned := false
	clone := func() {
		if !cloned {
			cloned = true
			resps = &spec.Responses{}
			*resps = *orig
		}
	}

	if r := w.walkResponse(resps.ResponsesProps.Default); r != resps.ResponsesProps.Default {
		clone()
		resps.Default = r
	}

	responsesCloned := false
	for k, v := range resps.ResponsesProps.StatusCodeResponses {
		if r := w.walkResponse(&v); r != &v {
			if !responsesCloned {
				responsesCloned = true
				clone()
				resps.ResponsesProps.StatusCodeResponses = make(map[int]spec.Response, len(orig.StatusCodeResponses))
				for k2, v2 := range orig.StatusCodeResponses {
					resps.ResponsesProps.StatusCodeResponses[k2] = v2
				}
			}
			resps.ResponsesProps.StatusCodeResponses[k] = *r
		}
	}

	return resps
}

func (w *Walker) walkOperation(op *spec.Operation) *spec.Operation {
	if op == nil {
		return nil
	}

	orig := op
	cloned := false
	clone := func() {
		if !cloned {
			cloned = true
			op = &spec.Operation{}
			*op = *orig
		}
	}

	parametersCloned := false
	for i := range op.Parameters {
		if s := w.walkParameter(&op.Parameters[i]); s != &op.Parameters[i] {
			if !parametersCloned {
				parametersCloned = true
				clone()
				op.Parameters = make([]spec.Parameter, len(orig.Parameters))
				copy(op.Parameters, orig.Parameters)
			}
			op.Parameters[i] = *s
		}
	}

	if r := w.walkResponses(op.Responses); r != op.Responses {
		clone()
		op.Responses = r
	}

	return op
}

func (w *Walker) walkPathItem(pathItem *spec.PathItem) *spec.PathItem {
	if pathItem == nil {
		return nil
	}

	orig := pathItem
	cloned := false
	clone := func() {
		if !cloned {
			cloned = true
			pathItem = &spec.PathItem{}
			*pathItem = *orig
		}
	}

	if p, changed := w.walkParameters(pathItem.Parameters); changed {
		clone()
		pathItem.Parameters = p
	}
	if op := w.walkOperation(pathItem.Get); op != pathItem.Get {
		clone()
		pathItem.Get = op
	}
	if op := w.walkOperation(pathItem.Head); op != pathItem.Head {
		clone()
		pathItem.Head = op
	}
	if op := w.walkOperation(pathItem.Delete); op != pathItem.Delete {
		clone()
		pathItem.Delete = op
	}
	if op := w.walkOperation(pathItem.Options); op != pathItem.Options {
		clone()
		pathItem.Options = op
	}
	if op := w.walkOperation(pathItem.Patch); op != pathItem.Patch {
		clone()
		pathItem.Patch = op
	}
	if op := w.walkOperation(pathItem.Post); op != pathItem.Post {
		clone()
		pathItem.Post = op
	}
	if op := w.walkOperation(pathItem.Put); op != pathItem.Put {
		clone()
		pathItem.Put = op
	}

	return pathItem
}

func (w *Walker) walkPaths(paths *spec.Paths) *spec.Paths {
	if paths == nil {
		return nil
	}

	orig := paths
	cloned := false
	clone := func() {
		if !cloned {
			cloned = true
			paths = &spec.Paths{}
			*paths = *orig
		}
	}

	pathsCloned := false
	for k, v := range paths.Paths {
		if p := w.walkPathItem(&v); p != &v {
			if !pathsCloned {
				pathsCloned = true
				clone()
				paths.Paths = make(map[string]spec.PathItem, len(orig.Paths))
				for k2, v2 := range orig.Paths {
					paths.Paths[k2] = v2
				}
			}
			paths.Paths[k] = *p
		}
	}

	return paths
}