terraform/helper/schema/resource_diff.go

package schema

import (
	"fmt"
	"reflect"
	"strings"
	"sync"

	"github.com/hashicorp/terraform/terraform"
)

// newValueWriter is a minor re-implementation of MapFieldWriter to include
// keys that should be marked as computed, to represent the new part of a
// pseudo-diff.
type newValueWriter struct {
	*MapFieldWriter

	// A list of keys that should be marked as computed.
	computedKeys map[string]bool

	// A lock to prevent races on writes. The underlying writer will have one as
	// well - this is for computed keys.
	lock sync.Mutex
}

// WriteField overrides MapValueWriter's WriteField, adding the ability to flag
// the address as computed.
func (w *newValueWriter) WriteField(address []string, value interface{}, computed bool) error {
	if err := w.MapFieldWriter.WriteField(address, value); err != nil {
		return err
	}

	w.lock.Lock()
	defer w.lock.Unlock()
	if w.result == nil {
		w.computedKeys = make(map[string]bool)
	}

	if computed {
		w.computedKeys[strings.Join(address, ".")] = true
	}
	return nil
}

// ComputedKeysMap returns the underlying computed keys map.
func (w *newValueWriter) ComputedKeysMap() map[string]bool {
	w.lock.Lock()
	defer w.lock.Unlock()
	if w.result == nil {
		w.computedKeys = make(map[string]bool)
	}
	return w.computedKeys
}

// newValueReader is a minor re-implementation of MapFieldReader and is the
// read counterpart to MapValueWriter, allowing the read of keys flagged as
// computed to accommodate the diff override logic in ResourceDiff.
type newValueReader struct {
	*MapFieldReader

	// The list of computed keys from a newValueWriter.
	computedKeys map[string]bool
}

// ReadField reads the values from the underlying writer, returning the
// computed value if it is found as well.
func (r *newValueReader) ReadField(address []string) (FieldReadResult, error) {
	v, err := r.MapFieldReader.ReadField(address)
	if err != nil {
		return FieldReadResult{}, err
	}
	if _, ok := r.computedKeys[strings.Join(address, ".")]; ok {
		v.Computed = true
	}

	return v, nil
}

// ResourceDiff is used to query and make custom changes to an in-flight diff.
// It can be used to veto particular changes in the diff, customize the diff
// that has been created, or diff values not controlled by config.
//
// The object functions similar to ResourceData, however most notably lacks
// Set, SetPartial, and Partial, as it should be used to change diff values
// only.  Most other frist-class ResourceData functions exist, namely Get,
// GetOk, HasChange, and GetChange exist.
//
// All functions in ResourceDiff, save for ForceNew, can only be used on
// computed fields.
type ResourceDiff struct {
	// The schema for the resource being worked on.
	schema map[string]*Schema

	// The current config for this resource.
	config *terraform.ResourceConfig

	// The state for this resource as it exists post-refresh, after the initial
	// diff.
	state *terraform.InstanceState

	// The diff created by Terraform. This diff is used, along with state,
	// config, and custom-set diff data, to provide a multi-level reader
	// experience similar to ResourceData.
	diff *terraform.InstanceDiff

	// The internal reader structure that contains the state, config, the default
	// diff, and the new diff.
	multiReader *MultiLevelFieldReader

	// A writer that writes overridden old fields.
	oldWriter *MapFieldWriter

	// A writer that writes overridden new fields.
	newWriter *newValueWriter
}

// newResourceDiff creates a new ResourceDiff instance.
func newResourceDiff(schema map[string]*Schema, config *terraform.ResourceConfig, state *terraform.InstanceState, diff *terraform.InstanceDiff) *ResourceDiff {
	d := &ResourceDiff{
		config: config,
		state:  state,
		diff:   diff,
	}
	// Duplicate the passed in schema to ensure that any changes we make with
	// functions like ForceNew don't affect the referenced schema.
	for k, v := range schema {
		newSchema := *v
		d.schema[k] = &newSchema
	}

	d.oldWriter = &MapFieldWriter{Schema: d.schema}
	d.newWriter = &newValueWriter{
		MapFieldWriter: &MapFieldWriter{Schema: d.schema},
	}
	readers := make(map[string]FieldReader)
	var stateAttributes map[string]string
	if d.state != nil {
		stateAttributes = d.state.Attributes
		readers["state"] = &MapFieldReader{
			Schema: d.schema,
			Map:    BasicMapReader(stateAttributes),
		}
	}
	if d.config != nil {
		readers["config"] = &ConfigFieldReader{
			Schema: d.schema,
			Config: d.config,
		}
	}
	if d.diff != nil {
		readers["diff"] = &DiffFieldReader{
			Schema: d.schema,
			Diff:   d.diff,
			Source: &MultiLevelFieldReader{
				Levels:  []string{"state", "config"},
				Readers: readers,
			},
		}
	}
	readers["newDiffOld"] = &MapFieldReader{
		Schema: d.schema,
		Map:    BasicMapReader(d.oldWriter.Map()),
	}
	readers["newDiffNew"] = &newValueReader{
		MapFieldReader: &MapFieldReader{
			Schema: d.schema,
			Map:    BasicMapReader(d.newWriter.Map()),
		},
		computedKeys: d.newWriter.ComputedKeysMap(),
	}
	d.multiReader = &MultiLevelFieldReader{
		Levels: []string{
			"state",
			"config",
			"diff",
			"newDiffOld",
			"newDiffNew",
		},

		Readers: readers,
	}

	return d
}

// ClearAll wipes the current diff. This cannot be undone - use only if you
// need to create a whole new diff from scatch, such as when you are leaning on
// the provider completely to create the diff.
//
// Note that this does not wipe overrides.
func (d *ResourceDiff) ClearAll() {
	d.diff = new(terraform.InstanceDiff)
}

// Clear wipes the diff for a particular key. It is called by SetDiff to remove
// any possibility of conflicts, but can be called on its own to just remove a
// specific key from the diff completely.
//
// Note that this does not wipe an override.
func (d *ResourceDiff) Clear(key string) error {
	// Check the schema to make sure that this key exists first.
	if _, ok := d.schema[key]; !ok {
		return fmt.Errorf("%s is not a valid key", key)
	}
	for k := range d.diff.Attributes {
		if strings.HasPrefix(k, key) {
			delete(d.diff.Attributes, k)
		}
	}
	return nil
}

// diffChange helps to implement resourceDiffer and derives its change values
// from ResourceDiff's own change data, in addition to existing diff, config, and state.
func (d *ResourceDiff) diffChange(key string) (interface{}, interface{}, bool, bool) {
	old, new := d.getChange(key)

	if !old.Exists {
		old.Value = nil
	}
	if !new.Exists {
		new.Value = nil
	}

	return old.Value, new.Value, !reflect.DeepEqual(old.Value, new.Value), new.Computed
}

// SetNew is used to set a new diff value for the mentioned key. The value must
// be correct for the attribute's schema (mostly relevant for maps, lists, and
// sets). The original value from the state is used as the old value.
//
// This function is only allowed on computed attributes.
//
// It is an unsupported operation to set invalid values with this function -
// doing so will taint any existing diff for this key and will remove it from
// the catalog.
func (d *ResourceDiff) SetNew(key string, value interface{}) error {
	return d.SetDiff(key, d.Get(key), value, false)
}

// SetNewComputed functions like SetNew, except that it sets the new value to
// the zero value and flags the attribute's diff as computed.
//
// This function is only allowed on computed keys.
func (d *ResourceDiff) SetNewComputed(key string) error {
	return d.SetDiff(key, d.Get(key), d.schema[key].ZeroValue(), true)
}

// SetDiff allows the setting of both old and new values for the diff
// referenced by a given key. This can be used to completely override
// Terraform's own diff behaviour, and can be used in conjunction with Clear or
// ClearAll to construct a compleletely new diff based off of provider logic
// alone.
//
// This function is only allowed on computed keys.
func (d *ResourceDiff) SetDiff(key string, old, new interface{}, computed bool) error {
	if !d.schema[key].Computed {
		return fmt.Errorf("SetNew, SetNewComputed, and SetDiff are allowed on computed attributes only - %s is not one", key)
	}

	if err := d.Clear(key); err != nil {
		return err
	}

	if err := d.oldWriter.WriteField(strings.Split(key, "."), old); err != nil {
		return fmt.Errorf("Cannot set old diff value for key %s: %s", key, err)
	}

	if err := d.newWriter.WriteField(strings.Split(key, "."), new, computed); err != nil {
		return fmt.Errorf("Cannot set new diff value for key %s: %s", key, err)
	}

	return nil
}

// ForceNew force-flags ForceNew in the schema for a specific key, and
// re-calculates its diff. This function is a no-op/error if there is no diff.
//
// Note that the change to schema is permanent for the lifecycle of this
// specific ResourceDiff instance, until ClearAll or Reset is called to start
// anew.
func (d *ResourceDiff) ForceNew(key string) error {
	if !d.HasChange(key) {
		return fmt.Errorf("ResourceDiff.ForceNew: No changes for %s", key)
	}

	old, new := d.GetChange(key)
	d.schema[key].ForceNew = true
	return d.SetDiff(key, old, new, false)
}

// Get hands off to ResourceData.Get.
func (d *ResourceDiff) Get(key string) interface{} {
	r, _ := d.GetOk(key)
	return r
}

// GetChange gets the change between the state and diff, checking first to see
// if a overridden diff exists.
//
// This implementation differs from ResourceData's in the way that we first get
// results from the exact levels for the new diff, then from state and diff as
// per normal.
func (d *ResourceDiff) GetChange(key string) (interface{}, interface{}) {
	old, new := d.getChange(key)
	return old.Value, new.Value
}

// GetOk functions the same way as ResourceData.GetOk, but it also checks the
// new diff levels to provide data consistent with the current state of the
// customized diff.
func (d *ResourceDiff) GetOk(key string) (interface{}, bool) {
	r := d.get(strings.Split(key, "."), "newDiffNew")
	exists := r.Exists && !r.Computed
	if exists {
		// If it exists, we also want to verify it is not the zero-value.
		value := r.Value
		zero := r.Schema.Type.Zero()

		if eq, ok := value.(Equal); ok {
			exists = !eq.Equal(zero)
		} else {
			exists = !reflect.DeepEqual(value, zero)
		}
	}

	return r.Value, exists
}

// HasChange checks to see if there is a change between state and the diff, or
// in the overridden diff.
func (d *ResourceDiff) HasChange(key string) bool {
	old, new := d.GetChange(key)

	// If the type implements the Equal interface, then call that
	// instead of just doing a reflect.DeepEqual. An example where this is
	// needed is *Set
	if eq, ok := old.(Equal); ok {
		return !eq.Equal(new)
	}

	return !reflect.DeepEqual(old, new)
}

// Id returns the ID of this resource.
//
// Note that technically, ID does not change during diffs (it either has
// already changed in the refresh, or will change on update), hence we do not
// support updating the ID or fetching it from anything else other than state.
func (d *ResourceDiff) Id() string {
	var result string

	if d.state != nil {
		result = d.state.ID
	}
	return result
}

// getChange gets values from two different levels, designed for use in
// diffChange, HasChange, and GetChange.
//
// This implementation differs from ResourceData's in the way that we first get
// results from the exact levels for the new diff, then from state and diff as
// per normal.
func (d *ResourceDiff) getChange(key string) (getResult, getResult) {
	old := d.getExact(strings.Split(key, "."), "newDiffOld")
	new := d.getExact(strings.Split(key, "."), "newDiffNew")

	if old.Exists && new.Exists {
		// Both values should exist if SetDiff operated on this key.
		// TODO: Maybe verify this. Zero values might be an issue here.
		return old, new
	}

	// If we haven't set this in the new diff, then we want to get the default
	// levels as if we were using ResourceData normally.
	old = d.get(strings.Split(key, "."), "state")
	new = d.get(strings.Split(key, "."), "diff")
	return old, new
}

// get performs the appropriate multi-level reader logic for ResourceDiff,
// starting at source. Refer to newResourceDiff for the level order.
func (d *ResourceDiff) get(addr []string, source string) getResult {
	result, err := d.multiReader.ReadFieldMerge(addr, source)
	if err != nil {
		panic(err)
	}

	return d.finalizeResult(addr, result)
}

// getExact gets an attribute from the exact level referenced by source.
func (d *ResourceDiff) getExact(addr []string, source string) getResult {
	result, err := d.multiReader.ReadFieldExact(addr, source)
	if err != nil {
		panic(err)
	}

	return d.finalizeResult(addr, result)
}

// finalizeResult does some post-processing of the result produced by get and getExact.
func (d *ResourceDiff) finalizeResult(addr []string, result FieldReadResult) getResult {
	// If the result doesn't exist, then we set the value to the zero value
	var schema *Schema
	if schemaL := addrToSchema(addr, d.schema); len(schemaL) > 0 {
		schema = schemaL[len(schemaL)-1]
	}

	if result.Value == nil && schema != nil {
		result.Value = result.ValueOrZero(schema)
	}

	// Transform the FieldReadResult into a getResult. It might be worth
	// merging these two structures one day.
	return getResult{
		Value:          result.Value,
		ValueProcessed: result.ValueProcessed,
		Computed:       result.Computed,
		Exists:         result.Exists,
		Schema:         schema,
	}
}