package terraform

import (
	"log"

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

// TargetsTransformer is a GraphTransformer that, when the user specifies a
// list of resources to target, limits the graph to only those resources and
// their dependencies.
type TargetsTransformer struct {
	// List of targeted resource names specified by the user
	Targets []string

	// List of parsed targets, provided by callers like ResourceCountTransform
	// that already have the targets parsed
	ParsedTargets []ResourceAddress

	// Set to true when we're in a `terraform destroy` or a
	// `terraform plan -destroy`
	Destroy bool
}

func (t *TargetsTransformer) Transform(g *Graph) error {
	if len(t.Targets) > 0 && len(t.ParsedTargets) == 0 {
		addrs, err := t.parseTargetAddresses()
		if err != nil {
			return err
		}
		t.ParsedTargets = addrs
	}
	if len(t.ParsedTargets) > 0 {
		targetedNodes, err := t.selectTargetedNodes(g, t.ParsedTargets)
		if err != nil {
			return err
		}

		for _, v := range g.Vertices() {
			removable := false
			if _, ok := v.(GraphNodeAddressable); ok {
				removable = true
			}
			if vr, ok := v.(RemovableIfNotTargeted); ok {
				removable = vr.RemoveIfNotTargeted()
			}
			if removable && !targetedNodes.Include(v) {
				log.Printf("[DEBUG] Removing %q, filtered by targeting.", dag.VertexName(v))
				g.Remove(v)
			}
		}
	}
	return nil
}

func (t *TargetsTransformer) parseTargetAddresses() ([]ResourceAddress, error) {
	addrs := make([]ResourceAddress, len(t.Targets))
	for i, target := range t.Targets {
		ta, err := ParseResourceAddress(target)
		if err != nil {
			return nil, err
		}
		addrs[i] = *ta
	}
	return addrs, nil
}

// Returns the list of targeted nodes. A targeted node is either addressed
// directly, or is an Ancestor of a targeted node. Destroy mode keeps
// Descendents instead of Ancestors.
func (t *TargetsTransformer) selectTargetedNodes(
	g *Graph, addrs []ResourceAddress) (*dag.Set, error) {
	targetedNodes := new(dag.Set)
	for _, v := range g.Vertices() {
		if t.nodeIsTarget(v, addrs) {
			targetedNodes.Add(v)

			// We inform nodes that ask about the list of targets - helps for nodes
			// that need to dynamically expand. Note that this only occurs for nodes
			// that are already directly targeted.
			if tn, ok := v.(GraphNodeTargetable); ok {
				tn.SetTargets(addrs)
			}

			var deps *dag.Set
			var err error
			if t.Destroy {
				deps, err = g.Descendents(v)

				// Select any variables that we depend on in case we need them later for
				// interpolating in the count
				ancestors, _ := g.Ancestors(v)
				for _, a := range ancestors.List() {
					if _, ok := a.(*GraphNodeConfigVariableFlat); ok {
						deps.Add(a)
					}
				}
			} else {
				deps, err = g.Ancestors(v)
			}
			if err != nil {
				return nil, err
			}

			for _, d := range deps.List() {
				targetedNodes.Add(d)
			}
		}
	}
	return targetedNodes, nil
}

func (t *TargetsTransformer) nodeIsTarget(
	v dag.Vertex, addrs []ResourceAddress) bool {
	r, ok := v.(GraphNodeAddressable)
	if !ok {
		return false
	}
	addr := r.ResourceAddress()
	for _, targetAddr := range addrs {
		if targetAddr.Equals(addr) {
			return true
		}
	}
	return false
}

// RemovableIfNotTargeted is a special interface for graph nodes that
// aren't directly addressable, but need to be removed from the graph when they
// are not targeted. (Nodes that are not directly targeted end up in the set of
// targeted nodes because something that _is_ targeted depends on them.) The
// initial use case for this interface is GraphNodeConfigVariable, which was
// having trouble interpolating for module variables in targeted scenarios that
// filtered out the resource node being referenced.
type RemovableIfNotTargeted interface {
	RemoveIfNotTargeted() bool
}