// Copyright 2019-present Facebook Inc. All rights reserved.
// This source code is licensed under the Apache 2.0 license found
// in the LICENSE file in the root directory of this source tree.

package edge

import (
	"reflect"
)

// A Descriptor for edge configuration.
type Descriptor struct {
	Tag      string      // struct tag.
	Type     string      // edge type.
	Name     string      // edge name.
	RefName  string      // ref name; inverse only.
	Ref      *Descriptor // edge reference; to/from of the same type.
	Unique   bool        // unique edge.
	Inverse  bool        // inverse edge.
	Required bool        // required on creation.
}

// To defines an association edge between two vertices.
func To(name string, t interface{}) *assocBuilder {
	return &assocBuilder{desc: &Descriptor{Name: name, Type: typ(t)}}
}

// From represents a reversed-edge between two vertices that has a back-reference to its source edge.
func From(name string, t interface{}) *inverseBuilder {
	return &inverseBuilder{desc: &Descriptor{Name: name, Type: typ(t), Inverse: true}}
}

func typ(t interface{}) string {
	if rt := reflect.TypeOf(t); rt.NumIn() > 0 {
		return rt.In(0).Name()
	}
	return ""
}

// assocBuilder is the builder for assoc edges.
type assocBuilder struct {
	desc *Descriptor
}

// Unique sets the edge type to be unique. Basically, it's limited the ent to be one of the two:
// one2one or one2many. one2one applied if the inverse-edge is also unique.
func (b *assocBuilder) Unique() *assocBuilder {
	b.desc.Unique = true
	return b
}

// Required indicates that this edge is a required field on creation.
// Unlike fields, edges are optional by default.
func (b *assocBuilder) Required() *assocBuilder {
	b.desc.Required = true
	return b
}

// StructTag sets the struct tag of the assoc edge.
func (b *assocBuilder) StructTag(s string) *assocBuilder {
	b.desc.Tag = s
	return b
}

// Assoc creates an inverse-edge with the same type.
func (b *assocBuilder) From(name string) *inverseBuilder {
	return &inverseBuilder{desc: &Descriptor{Name: name, Type: b.desc.Type, Inverse: true, Ref: b.desc}}
}

// Comment used to put annotations on the schema.
func (b *assocBuilder) Comment(string) *assocBuilder {
	return b
}

// Descriptor implements the ent.Descriptor interface.
func (b *assocBuilder) Descriptor() *Descriptor {
	return b.desc
}

// inverseBuilder is the builder for inverse edges.
type inverseBuilder struct {
	desc *Descriptor
}

// Ref sets the referenced-edge of this inverse edge.
func (b *inverseBuilder) Ref(ref string) *inverseBuilder {
	b.desc.RefName = ref
	return b
}

// Unique sets the edge type to be unique. Basically, it's limited the ent to be one of the two:
// one2one or one2many. one2one applied if the inverse-edge is also unique.
func (b *inverseBuilder) Unique() *inverseBuilder {
	b.desc.Unique = true
	return b
}

// Required indicates that this edge is a required field on creation.
// Unlike fields, edges are optional by default.
func (b *inverseBuilder) Required() *inverseBuilder {
	b.desc.Required = true
	return b
}

// StructTag sets the struct tag of the inverse edge.
func (b *inverseBuilder) StructTag(s string) *inverseBuilder {
	b.desc.Tag = s
	return b
}

// Comment used to put annotations on the schema.
func (b *inverseBuilder) Comment(string) *inverseBuilder {
	return b
}

// Descriptor implements the ent.Descriptor interface.
func (b *inverseBuilder) Descriptor() *Descriptor {
	return b.desc
}