// The config package is responsible for loading and validating the
// configuration.
package config

import (
	"fmt"
	"strings"

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

// Config is the configuration that comes from loading a collection
// of Terraform templates.
type Config struct {
	Variables map[string]Variable
	Resources []*Resource
}

// A resource represents a single Terraform resource in the configuration.
// A Terraform resource is something that represents some component that
// can be created and managed, and has some properties associated with it.
type Resource struct {
	Name      string
	Type      string
	Config    map[string]interface{}
	Variables map[string]InterpolatedVariable
}

type Variable struct {
	Default     string
	Description string
}

// An InterpolatedVariable is a variable that is embedded within a string
// in the configuration, such as "hello ${world}" (world in this case is
// an interpolated variable).
//
// These variables can come from a variety of sources, represented by
// implementations of this interface.
type InterpolatedVariable interface {
	FullKey() string
}

// A ResourceVariable is a variable that is referencing the field
// of a resource, such as "${aws_instance.foo.ami}"
type ResourceVariable struct {
	Type  string
	Name  string
	Field string

	key string
}

// A UserVariable is a variable that is referencing a user variable
// that is inputted from outside the configuration. This looks like
// "${var.foo}"
type UserVariable struct {
	Name string

	key string
}

// A unique identifier for this resource.
func (r *Resource) Id() string {
	return fmt.Sprintf("%s.%s", r.Type, r.Name)
}

// ResourceGraph returns a dependency graph of the resources from this
// Terraform configuration.
func (c *Config) ResourceGraph() *depgraph.Graph {
	nouns := make(map[string]*depgraph.Noun)
	for _, r := range c.Resources {
		noun := &depgraph.Noun{
			Name: r.Id(),
			Meta: r,
		}
		nouns[noun.Name] = noun
	}

	for _, noun := range nouns {
		r := noun.Meta.(*Resource)
		for _, v := range r.Variables {
			// Only resource variables impose dependencies
			rv, ok := v.(*ResourceVariable)
			if !ok {
				continue
			}

			// Build the dependency
			dep := &depgraph.Dependency{
				Name:   rv.ResourceId(),
				Source: noun,
				Target: nouns[rv.ResourceId()],
			}

			noun.Deps = append(noun.Deps, dep)
		}
	}

	// Create the list of nouns that the depgraph.Graph struct expects
	nounsList := make([]*depgraph.Noun, 0, len(nouns))
	for _, n := range nouns {
		nounsList = append(nounsList, n)
	}

	// Create a root that just depends on everything else finishing.
	root := &depgraph.Noun{Name: "root"}
	for _, n := range nounsList {
		root.Deps = append(root.Deps, &depgraph.Dependency{
			Name:   n.Name,
			Source: root,
			Target: n,
		})
	}
	nounsList = append(nounsList, root)

	return &depgraph.Graph{
		Name:  "resources",
		Nouns: nounsList,
	}
}

func NewResourceVariable(key string) (*ResourceVariable, error) {
	parts := strings.SplitN(key, ".", 3)
	return &ResourceVariable{
		Type:  parts[0],
		Name:  parts[1],
		Field: parts[2],
		key:   key,
	}, nil
}

func (v *ResourceVariable) ResourceId() string {
	return fmt.Sprintf("%s.%s", v.Type, v.Name)
}

func (v *ResourceVariable) FullKey() string {
	return v.key
}

func NewUserVariable(key string) (*UserVariable, error) {
	name := key[len("var."):]
	return &UserVariable{
		key:  key,
		Name: name,
	}, nil
}

func (v *UserVariable) FullKey() string {
	return v.key
}