package google

import (
	"encoding/json"
)

type ComputeApiVersion uint8

const (
	v1 ComputeApiVersion = iota
	v0beta
)

var OrderedComputeApiVersions = []ComputeApiVersion{
	v0beta,
	v1,
}

// Convert between two types by converting to/from JSON. Intended to switch
// between multiple API versions, as they are strict supersets of one another.
// Convert loses information about ForceSendFields and NullFields.
func Convert(item, out interface{}) error {
	bytes, err := json.Marshal(item)
	if err != nil {
		return err
	}

	err = json.Unmarshal(bytes, out)
	if err != nil {
		return err
	}

	return nil
}

type TerraformResourceData interface {
	HasChange(string) bool
	GetOk(string) (interface{}, bool)
}

// Compare the fields set in schema against a list of features and their versions to determine
// what version of the API is required in order to manage the resource.
func getComputeApiVersion(d TerraformResourceData, resourceVersion ComputeApiVersion, features []Feature) ComputeApiVersion {
	versions := map[ComputeApiVersion]struct{}{resourceVersion: struct{}{}}
	for _, feature := range features {
		if feature.InUseBy(d) {
			versions[feature.Version] = struct{}{}
		}
	}

	return maxVersion(versions)
}

// Compare the fields set in schema against a list of features and their version, and a
// list of features that exist at the base resource version that can only be update at some other
// version, to determine what version of the API is required in order to update the resource.
func getComputeApiVersionUpdate(d TerraformResourceData, resourceVersion ComputeApiVersion, features, updateOnlyFields []Feature) ComputeApiVersion {
	versions := map[ComputeApiVersion]struct{}{resourceVersion: struct{}{}}
	schemaVersion := getComputeApiVersion(d, resourceVersion, features)
	versions[schemaVersion] = struct{}{}

	for _, feature := range updateOnlyFields {
		if feature.HasChangeBy(d) {
			versions[feature.Version] = struct{}{}
		}
	}

	return maxVersion(versions)
}

// A field of a resource and the version of the Compute API required to use it.
type Feature struct {
	Version ComputeApiVersion
	Item    string
}

// Returns true when a feature has been modified.
// This is most important when updating a resource to remove versioned feature usage; if the
// resource is reverting to its base version, it needs to perform a final update at the higher
// version in order to remove high version features.
func (s Feature) HasChangeBy(d TerraformResourceData) bool {
	return d.HasChange(s.Item)
}

// Return true when a feature appears in schema or has been modified.
func (s Feature) InUseBy(d TerraformResourceData) bool {
	_, ok := d.GetOk(s.Item)
	return ok || s.HasChangeBy(d)
}

func maxVersion(versionsInUse map[ComputeApiVersion]struct{}) ComputeApiVersion {
	for _, version := range OrderedComputeApiVersions {
		if _, ok := versionsInUse[version]; ok {
			return version
		}
	}

	// Fallback to the final, most stable version
	return OrderedComputeApiVersions[len(OrderedComputeApiVersions)-1]
}