// 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 field

import (
	"database/sql"
	"database/sql/driver"
	"errors"
	"fmt"
	"math"
	"reflect"
	"regexp"
	"sort"
	"time"

	"github.com/facebook/ent/schema"
)

// String returns a new Field with type string.
func String(name string) *stringBuilder {
	return &stringBuilder{&Descriptor{
		Name: name,
		Info: &TypeInfo{Type: TypeString},
	}}
}

// Text returns a new string field without limitation on the size.
// In MySQL, it is the "longtext" type, but in SQLite and Gremlin it has not effect.
func Text(name string) *stringBuilder {
	return &stringBuilder{&Descriptor{
		Name: name,
		Size: math.MaxInt32,
		Info: &TypeInfo{Type: TypeString},
	}}
}

// Bytes returns a new Field with type bytes/buffer.
// In MySQL and SQLite, it is the "BLOB" type, and it does not support for Gremlin.
func Bytes(name string) *bytesBuilder {
	return &bytesBuilder{&Descriptor{
		Name: name,
		Info: &TypeInfo{Type: TypeBytes, Nillable: true},
	}}
}

// Bool returns a new Field with type bool.
func Bool(name string) *boolBuilder {
	return &boolBuilder{&Descriptor{
		Name: name,
		Info: &TypeInfo{Type: TypeBool},
	}}
}

// Time returns a new Field with type timestamp.
func Time(name string) *timeBuilder {
	return &timeBuilder{&Descriptor{
		Name: name,
		Info: &TypeInfo{Type: TypeTime, PkgPath: "time"},
	}}
}

// JSON returns a new Field with type json that is serialized to the given object.
// For example:
//
//	field.JSON("dirs", []http.Dir{}).
//		Optional()
//
//
//	field.JSON("info", &Info{}).
//		Optional()
//
func JSON(name string, typ interface{}) *jsonBuilder {
	t := reflect.TypeOf(typ)
	info := &TypeInfo{
		Type:    TypeJSON,
		Ident:   t.String(),
		PkgPath: t.PkgPath(),
	}
	switch t.Kind() {
	case reflect.Slice, reflect.Array, reflect.Ptr, reflect.Map:
		info.Nillable = true
		info.PkgPath = pkgPath(t)
	}
	return &jsonBuilder{&Descriptor{
		Name: name,
		Info: info,
	}}
}

// Strings returns a new JSON Field with type []string.
func Strings(name string) *jsonBuilder {
	return JSON(name, []string{})
}

// Ints returns a new JSON Field with type []int.
func Ints(name string) *jsonBuilder {
	return JSON(name, []int{})
}

// Floats returns a new JSON Field with type []float.
func Floats(name string) *jsonBuilder {
	return JSON(name, []float64{})
}

// Enum returns a new Field with type enum. An example for defining enum is as follows:
//
//	field.Enum("state").
//		Values(
//			"on",
//			"off",
//		).
//		Default("on")
//
func Enum(name string) *enumBuilder {
	return &enumBuilder{&Descriptor{
		Name: name,
		Info: &TypeInfo{Type: TypeEnum},
	}}
}

// UUID returns a new Field with type UUID. An example for defining UUID field is as follows:
//
//	field.UUID("id", uuid.New())
//
func UUID(name string, typ driver.Valuer) *uuidBuilder {
	rt := reflect.TypeOf(typ)
	return &uuidBuilder{&Descriptor{
		Name: name,
		Info: &TypeInfo{
			Type:     TypeUUID,
			Nillable: true,
			Ident:    rt.String(),
			PkgPath:  rt.PkgPath(),
		},
	}}
}

// stringBuilder is the builder for string fields.
type stringBuilder struct {
	desc *Descriptor
}

// Unique makes the field unique within all vertices of this type.
func (b *stringBuilder) Unique() *stringBuilder {
	b.desc.Unique = true
	return b
}

// Sensitive fields not printable and not serializable.
func (b *stringBuilder) Sensitive() *stringBuilder {
	b.desc.Sensitive = true
	return b
}

// Match adds a regex matcher for this field. Operation fails if the regex fails.
func (b *stringBuilder) Match(re *regexp.Regexp) *stringBuilder {
	b.desc.Validators = append(b.desc.Validators, func(v string) error {
		if !re.MatchString(v) {
			return errors.New("value does not match validation")
		}
		return nil
	})
	return b
}

// MinLen adds a length validator for this field.
// Operation fails if the length of the string is less than the given value.
func (b *stringBuilder) MinLen(i int) *stringBuilder {
	b.desc.Validators = append(b.desc.Validators, func(v string) error {
		if len(v) < i {
			return errors.New("value is less than the required length")
		}
		return nil
	})
	return b
}

// NotEmpty adds a length validator for this field.
// Operation fails if the length of the string is zero.
func (b *stringBuilder) NotEmpty() *stringBuilder {
	return b.MinLen(1)
}

// MaxLen adds a length validator for this field.
// Operation fails if the length of the string is greater than the given value.
func (b *stringBuilder) MaxLen(i int) *stringBuilder {
	b.desc.Size = i
	b.desc.Validators = append(b.desc.Validators, func(v string) error {
		if len(v) > i {
			return errors.New("value is greater than the required length")
		}
		return nil
	})
	return b
}

// Validate adds a validator for this field. Operation fails if the validation fails.
func (b *stringBuilder) Validate(fn func(string) error) *stringBuilder {
	b.desc.Validators = append(b.desc.Validators, fn)
	return b
}

// Default sets the default value of the field.
func (b *stringBuilder) Default(s string) *stringBuilder {
	b.desc.Default = s
	return b
}

// Nillable indicates that this field is a nillable.
// Unlike "Optional" only fields, "Nillable" fields are pointers in the generated field.
func (b *stringBuilder) Nillable() *stringBuilder {
	b.desc.Nillable = true
	return b
}

// Optional indicates that this field is optional on create.
// Unlike edges, fields are required by default.
func (b *stringBuilder) Optional() *stringBuilder {
	b.desc.Optional = true
	return b
}

// Immutable indicates that this field cannot be updated.
func (b *stringBuilder) Immutable() *stringBuilder {
	b.desc.Immutable = true
	return b
}

// Comment sets the comment of the field.
func (b *stringBuilder) Comment(string) *stringBuilder {
	return b
}

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

// StorageKey sets the storage key of the field.
// In SQL dialects is the column name and Gremlin is the property.
func (b *stringBuilder) StorageKey(key string) *stringBuilder {
	b.desc.StorageKey = key
	return b
}

// SchemaType overrides the default database type with a custom
// schema type (per dialect) for string.
//
//	field.String("name").
//		SchemaType(map[string]string{
//			dialect.MySQL:    "text",
//			dialect.Postgres: "varchar",
//		})
//
func (b *stringBuilder) SchemaType(types map[string]string) *stringBuilder {
	b.desc.SchemaType = types
	return b
}

// GoType overrides the default Go type with a custom one.
//
//	field.String("dir").
//		GoType(http.Dir("dir"))
//
func (b *stringBuilder) GoType(typ interface{}) *stringBuilder {
	b.desc.goType(typ, stringType)
	return b
}

// Annotations adds a list of annotations to the field object to be used by
// codegen extensions.
//
//	field.String("dir").
//		Annotations(entgql.Config{
//			Ordered: true,
//		})
//
func (b *stringBuilder) Annotations(annotations ...schema.Annotation) *stringBuilder {
	b.desc.Annotations = append(b.desc.Annotations, annotations...)
	return b
}

// Descriptor implements the ent.Field interface by returning its descriptor.
func (b *stringBuilder) Descriptor() *Descriptor {
	return b.desc
}

// timeBuilder is the builder for time fields.
type timeBuilder struct {
	desc *Descriptor
}

// Nillable indicates that this field is a nillable.
// Unlike "Optional" only fields, "Nillable" fields are pointers in the generated field.
func (b *timeBuilder) Nillable() *timeBuilder {
	b.desc.Nillable = true
	return b
}

// Optional indicates that this field is optional on create.
// Unlike edges, fields are required by default.
func (b *timeBuilder) Optional() *timeBuilder {
	b.desc.Optional = true
	return b
}

// Immutable indicates that this field cannot be updated.
func (b *timeBuilder) Immutable() *timeBuilder {
	b.desc.Immutable = true
	return b
}

// Comment sets the comment of the field.
func (b *timeBuilder) Comment(c string) *timeBuilder {
	return b
}

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

// Default sets the function that is applied to set default value
// of the field on creation. For example:
//
//	field.Time("created_at").
//		Default(time.Now)
//
func (b *timeBuilder) Default(f func() time.Time) *timeBuilder {
	b.desc.Default = f
	return b
}

// UpdateDefault sets the function that is applied to set default value
// of the field on update. For example:
//
//	field.Time("updated_at").
//		Default(time.Now).
//		UpdateDefault(time.Now),
//
func (b *timeBuilder) UpdateDefault(f func() time.Time) *timeBuilder {
	b.desc.UpdateDefault = f
	return b
}

// StorageKey sets the storage key of the field.
// In SQL dialects is the column name and Gremlin is the property.
func (b *timeBuilder) StorageKey(key string) *timeBuilder {
	b.desc.StorageKey = key
	return b
}

// GoType overrides the default Go type with a custom one.
//
//	field.Time("deleted_at").
//		GoType(&sql.NullTime{})
//
func (b *timeBuilder) GoType(typ interface{}) *timeBuilder {
	b.desc.goType(typ, timeType)
	return b
}

// Annotations adds a list of annotations to the field object to be used by
// codegen extensions.
//
//	field.Time("deleted_at").
//		Annotations(entgql.Config{
//			Ordered: true,
//		})
//
func (b *timeBuilder) Annotations(annotations ...schema.Annotation) *timeBuilder {
	b.desc.Annotations = append(b.desc.Annotations, annotations...)
	return b
}

// Descriptor implements the ent.Field interface by returning its descriptor.
func (b *timeBuilder) Descriptor() *Descriptor {
	return b.desc
}

// SchemaType overrides the default database type with a custom
// schema type (per dialect) for time.
//
//	field.Time("created_at").
//		SchemaType(map[string]string{
//			dialect.MySQL:    "datetime",
//			dialect.Postgres: "time with time zone",
//		})
//
func (b *timeBuilder) SchemaType(types map[string]string) *timeBuilder {
	b.desc.SchemaType = types
	return b
}

// boolBuilder is the builder for boolean fields.
type boolBuilder struct {
	desc *Descriptor
}

// Default sets the default value of the field.
func (b *boolBuilder) Default(v bool) *boolBuilder {
	b.desc.Default = v
	return b
}

// Nillable indicates that this field is a nillable.
// Unlike "Optional" only fields, "Nillable" fields are pointers in the generated field.
func (b *boolBuilder) Nillable() *boolBuilder {
	b.desc.Nillable = true
	return b
}

// Optional indicates that this field is optional on create.
// Unlike edges, fields are required by default.
func (b *boolBuilder) Optional() *boolBuilder {
	b.desc.Optional = true
	return b
}

// Immutable indicates that this field cannot be updated.
func (b *boolBuilder) Immutable() *boolBuilder {
	b.desc.Immutable = true
	return b
}

// Comment sets the comment of the field.
func (b *boolBuilder) Comment(c string) *boolBuilder {
	return b
}

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

// StorageKey sets the storage key of the field.
// In SQL dialects is the column name and Gremlin is the property.
func (b *boolBuilder) StorageKey(key string) *boolBuilder {
	b.desc.StorageKey = key
	return b
}

// GoType overrides the default Go type with a custom one.
//
//	field.Bool("deleted").
//		GoType(&sql.NullBool{})
//
func (b *boolBuilder) GoType(typ interface{}) *boolBuilder {
	b.desc.goType(typ, boolType)
	return b
}

// Annotations adds a list of annotations to the field object to be used by
// codegen extensions.
//
//	field.Bool("deleted").
//		Annotations(entgql.Config{
//			Ordered: true,
//		})
//
func (b *boolBuilder) Annotations(annotations ...schema.Annotation) *boolBuilder {
	b.desc.Annotations = append(b.desc.Annotations, annotations...)
	return b
}

// Descriptor implements the ent.Field interface by returning its descriptor.
func (b *boolBuilder) Descriptor() *Descriptor {
	return b.desc
}

// bytesBuilder is the builder for bytes fields.
type bytesBuilder struct {
	desc *Descriptor
}

// Default sets the default value of the field.
func (b *bytesBuilder) Default(v []byte) *bytesBuilder {
	b.desc.Default = v
	return b
}

// Nillable indicates that this field is a nillable.
// Unlike "Optional" only fields, "Nillable" fields are pointers in the generated field.
func (b *bytesBuilder) Nillable() *bytesBuilder {
	b.desc.Nillable = true
	return b
}

// Optional indicates that this field is optional on create.
// Unlike edges, fields are required by default.
func (b *bytesBuilder) Optional() *bytesBuilder {
	b.desc.Optional = true
	return b
}

// Immutable indicates that this field cannot be updated.
func (b *bytesBuilder) Immutable() *bytesBuilder {
	b.desc.Immutable = true
	return b
}

// Comment sets the comment of the field.
func (b *bytesBuilder) Comment(string) *bytesBuilder {
	return b
}

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

// MaxLen sets the max-length of the bytes type in the database.
// In MySQL, this affects the BLOB type (tiny 2^8-1, regular 2^16-1, medium 2^24-1, long 2^32-1).
// In SQLite, it does not have any effect on the type size, which is default to 1B bytes.
func (b *bytesBuilder) MaxLen(i int) *bytesBuilder {
	b.desc.Size = i
	return b
}

// StorageKey sets the storage key of the field.
// In SQL dialects is the column name and Gremlin is the property.
func (b *bytesBuilder) StorageKey(key string) *bytesBuilder {
	b.desc.StorageKey = key
	return b
}

// GoType overrides the default Go type with a custom one.
//
//	field.Bytes("ip").
//		GoType(net.IP("127.0.0.1"))
//
func (b *bytesBuilder) GoType(typ interface{}) *bytesBuilder {
	b.desc.goType(typ, bytesType)
	return b
}

// Annotations adds a list of annotations to the field object to be used by
// codegen extensions.
//
//	field.Bytes("ip").
//		Annotations(entgql.Config{
//			Ordered: true,
//		})
//
func (b *bytesBuilder) Annotations(annotations ...schema.Annotation) *bytesBuilder {
	b.desc.Annotations = append(b.desc.Annotations, annotations...)
	return b
}

// SchemaType overrides the default database type with a custom
// schema type (per dialect) for bytes.
//
//	field.Bytes("blob").
//		SchemaType(map[string]string{
//			dialect.MySQL:	"tinyblob",
//			dialect.SQLite:	"tinyblob",
//		})
//
func (b *bytesBuilder) SchemaType(types map[string]string) *bytesBuilder {
	b.desc.SchemaType = types
	return b
}

// Descriptor implements the ent.Field interface by returning its descriptor.
func (b *bytesBuilder) Descriptor() *Descriptor {
	return b.desc
}

// jsonBuilder is the builder for json fields.
type jsonBuilder struct {
	desc *Descriptor
}

// StorageKey sets the storage key of the field.
// In SQL dialects is the column name and Gremlin is the property.
func (b *jsonBuilder) StorageKey(key string) *jsonBuilder {
	b.desc.StorageKey = key
	return b
}

// Optional indicates that this field is optional on create.
// Unlike edges, fields are required by default.
func (b *jsonBuilder) Optional() *jsonBuilder {
	b.desc.Optional = true
	return b
}

// Immutable indicates that this field cannot be updated.
func (b *jsonBuilder) Immutable() *jsonBuilder {
	b.desc.Immutable = true
	return b
}

// Comment sets the comment of the field.
func (b *jsonBuilder) Comment(c string) *jsonBuilder {
	return b
}

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

// SchemaType overrides the default database type with a custom
// schema type (per dialect) for json.
//
//	field.JSON("json").
//		SchemaType(map[string]string{
//			dialect.MySQL:		"json",
//			dialect.Postgres:	"jsonb",
//		})
//
func (b *jsonBuilder) SchemaType(types map[string]string) *jsonBuilder {
	b.desc.SchemaType = types
	return b
}

// Annotations adds a list of annotations to the field object to be used by
// codegen extensions.
//
//	field.JSON("json").
//		Annotations(entgql.Config{
//			Ordered: true,
//		})
//
func (b *jsonBuilder) Annotations(annotations ...schema.Annotation) *jsonBuilder {
	b.desc.Annotations = append(b.desc.Annotations, annotations...)
	return b
}

// Descriptor implements the ent.Field interface by returning its descriptor.
func (b *jsonBuilder) Descriptor() *Descriptor {
	return b.desc
}

// enumBuilder is the builder for enum fields.
type enumBuilder struct {
	desc *Descriptor
}

// Values adds given values to the enum values.
//
//	field.Enum("priority").
//		Values("low", "mid", "high")
//
func (b *enumBuilder) Values(values ...string) *enumBuilder {
	for _, v := range values {
		b.desc.Enums = append(b.desc.Enums, struct{ N, V string }{N: v, V: v})
	}
	return b
}

// NamedValues adds the given name, value pairs to the enum value.
// The "name" defines the Go identifier of the enum, and the value
// defines the actual value in the database.
//
// NamedValues returns an error if given an odd number of arguments.
//
//	field.Enum("priority").
//		NamedValues(
//			"LOW", "low",
//			"MID", "mid",
//			"HIGH", "high",
//		)
//
func (b *enumBuilder) NamedValues(namevalue ...string) *enumBuilder {
	if len(namevalue)%2 == 1 {
		b.desc.err = fmt.Errorf("Enum.NamedValues: odd argument count")
		return b
	}
	for i := 0; i < len(namevalue); i += 2 {
		b.desc.Enums = append(b.desc.Enums, struct{ N, V string }{N: namevalue[i], V: namevalue[i+1]})
	}
	return b
}

// ValueMap adds the given values in the map to the enum value.
// The key in the map is the Go identifier and the value in the
// map is the actual enum value.
//
// If keys in not titled, ent codegen will change it to be exported.
//
// Deprecated: the ValueMap method predates the NamedValues method and it
// is planned be removed in v0.5.0. New code should use NamedValues instead.
func (b *enumBuilder) ValueMap(values map[string]string) *enumBuilder {
	enums := make([]struct{ N, V string }, 0, len(values))
	for k, v := range values {
		enums = append(enums, struct{ N, V string }{N: k, V: v})
	}
	sort.Slice(enums, func(i, j int) bool {
		return enums[i].V < enums[j].V
	})
	b.desc.Enums = append(b.desc.Enums, enums...)
	return b
}

// Default sets the default value of the field.
func (b *enumBuilder) Default(value string) *enumBuilder {
	b.desc.Default = value
	return b
}

// StorageKey sets the storage key of the field.
// In SQL dialects is the column name and Gremlin is the property.
func (b *enumBuilder) StorageKey(key string) *enumBuilder {
	b.desc.StorageKey = key
	return b
}

// Optional indicates that this field is optional on create.
// Unlike edges, fields are required by default.
func (b *enumBuilder) Optional() *enumBuilder {
	b.desc.Optional = true
	return b
}

// Immutable indicates that this field cannot be updated.
func (b *enumBuilder) Immutable() *enumBuilder {
	b.desc.Immutable = true
	return b
}

// Comment sets the comment of the field.
func (b *enumBuilder) Comment(c string) *enumBuilder {
	return b
}

// Nillable indicates that this field is a nillable.
// Unlike "Optional" only fields, "Nillable" fields are pointers in the generated field.
func (b *enumBuilder) Nillable() *enumBuilder {
	b.desc.Nillable = true
	return b
}

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

// SchemaType overrides the default database type with a custom
// schema type (per dialect) for enum.
//
//	field.Enum("enum").
//		SchemaType(map[string]string{
//			dialect.Postgres: "EnumType",
//		})
//
func (b *enumBuilder) SchemaType(types map[string]string) *enumBuilder {
	b.desc.SchemaType = types
	return b
}

// Annotations adds a list of annotations to the field object to be used by
// codegen extensions.
//
//	field.Enum("enum").
//		Annotations(entgql.Config{
//			Ordered: true,
//		})
//
func (b *enumBuilder) Annotations(annotations ...schema.Annotation) *enumBuilder {
	b.desc.Annotations = append(b.desc.Annotations, annotations...)
	return b
}

// EnumValues defines the interface for getting the enum values.
type EnumValues interface {
	Values() []string
}

// GoType overrides the default Go type with a custom one.
//
//	field.Enum("enum").
//		GoType(role.Enum("role"))
//
func (b *enumBuilder) GoType(ev EnumValues) *enumBuilder {
	b.Values(ev.Values()...)
	b.desc.goType(ev, stringType)
	return b
}

// Descriptor implements the ent.Field interface by returning its descriptor.
func (b *enumBuilder) Descriptor() *Descriptor {
	return b.desc
}

// uuidBuilder is the builder for uuid fields.
type uuidBuilder struct {
	desc *Descriptor
}

// StorageKey sets the storage key of the field.
// In SQL dialects is the column name and Gremlin is the property.
func (b *uuidBuilder) StorageKey(key string) *uuidBuilder {
	b.desc.StorageKey = key
	return b
}

// Optional indicates that this field is optional on create.
// Unlike edges, fields are required by default.
func (b *uuidBuilder) Optional() *uuidBuilder {
	b.desc.Optional = true
	return b
}

// Unique makes the field unique within all vertices of this type.
func (b *uuidBuilder) Unique() *uuidBuilder {
	b.desc.Unique = true
	return b
}

// Immutable indicates that this field cannot be updated.
func (b *uuidBuilder) Immutable() *uuidBuilder {
	b.desc.Immutable = true
	return b
}

// Comment sets the comment of the field.
func (b *uuidBuilder) Comment(c string) *uuidBuilder {
	return b
}

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

// Default sets the function that is applied to set default value
// of the field on creation. Codegen fails if the default function
// doesn't return the same concrete that was set for the UUID type.
//
//	field.UUID("id", uuid.UUID{}).
//		Default(uuid.New)
//
func (b *uuidBuilder) Default(fn interface{}) *uuidBuilder {
	typ := reflect.TypeOf(fn)
	if typ.Kind() != reflect.Func || typ.NumIn() != 0 || typ.NumOut() != 1 || typ.Out(0).String() != b.desc.Info.String() {
		b.desc.err = fmt.Errorf("expect type (func() %s) for uuid default value", b.desc.Info)
	}
	b.desc.Default = fn
	return b
}

// SchemaType overrides the default database type with a custom
// schema type (per dialect) for uuid.
//
//	field.UUID("id", uuid.New()).
//		SchemaType(map[string]string{
//			dialect.Postgres: "CustomUUID",
//		})
//
func (b *uuidBuilder) SchemaType(types map[string]string) *uuidBuilder {
	b.desc.SchemaType = types
	return b
}

// Annotations adds a list of annotations to the field object to be used by
// codegen extensions.
//
//	field.UUID("id", uuid.New()).
//		Annotations(entgql.Config{
//			Ordered: true,
//		})
//
func (b *uuidBuilder) Annotations(annotations ...schema.Annotation) *uuidBuilder {
	b.desc.Annotations = append(b.desc.Annotations, annotations...)
	return b
}

// Descriptor implements the ent.Field interface by returning its descriptor.
func (b *uuidBuilder) Descriptor() *Descriptor {
	return b.desc
}

// A Descriptor for field configuration.
type Descriptor struct {
	Tag           string                  // struct tag.
	Size          int                     // varchar size.
	Name          string                  // field name.
	Info          *TypeInfo               // field type info.
	Unique        bool                    // unique index of field.
	Nillable      bool                    // nillable struct field.
	Optional      bool                    // nullable field in database.
	Immutable     bool                    // create-only field.
	Default       interface{}             // default value on create.
	UpdateDefault interface{}             // default value on update.
	Validators    []interface{}           // validator functions.
	StorageKey    string                  // sql column or gremlin property.
	Enums         []struct{ N, V string } // enum values.
	Sensitive     bool                    // sensitive info string field.
	SchemaType    map[string]string       // override the schema type.
	Annotations   []schema.Annotation     // field annotations.
	err           error
}

// Err returns the error, if any, that was added by the field builder.
func (d *Descriptor) Err() error {
	return d.err
}

func (d *Descriptor) goType(typ interface{}, expectType reflect.Type) {
	t := reflect.TypeOf(typ)
	tv := indirect(t)
	info := &TypeInfo{
		Type:    d.Info.Type,
		Ident:   tv.String(),
		PkgPath: tv.PkgPath(),
		RType: &RType{
			Name:    tv.Name(),
			Kind:    tv.Kind(),
			PkgPath: tv.PkgPath(),
			Methods: make(map[string]struct{ In, Out []*RType }, t.NumMethod()),
		},
	}
	switch t.Kind() {
	case reflect.Slice, reflect.Array, reflect.Ptr, reflect.Map:
		info.Nillable = true
	}
	switch {
	case t.Kind() == expectType.Kind() && t.ConvertibleTo(expectType):
	case t.Implements(valueScannerType):
		n := t.NumMethod()
		for i := 0; i < n; i++ {
			m := t.Method(i)
			in := make([]*RType, m.Type.NumIn()-1)
			for j := range in {
				arg := m.Type.In(j + 1)
				in[j] = &RType{Name: arg.Name(), Kind: arg.Kind(), PkgPath: arg.PkgPath()}
			}
			out := make([]*RType, m.Type.NumOut())
			for j := range out {
				ret := m.Type.Out(j)
				out[j] = &RType{Name: ret.Name(), Kind: ret.Kind(), PkgPath: ret.PkgPath()}
			}
			info.RType.Methods[m.Name] = struct{ In, Out []*RType }{in, out}
		}
	default:
		d.err = fmt.Errorf("GoType must be a %q type or ValueScanner", expectType)
		if pt := reflect.PtrTo(t); pt.Implements(valueScannerType) {
			d.err = fmt.Errorf("%s. Use %s instead", d.err, pt)
		}
	}
	d.Info = info
}

var (
	boolType         = reflect.TypeOf(false)
	bytesType        = reflect.TypeOf([]byte(nil))
	timeType         = reflect.TypeOf(time.Time{})
	stringType       = reflect.TypeOf("")
	valueScannerType = reflect.TypeOf((*ValueScanner)(nil)).Elem()
)

// ValueScanner is the interface that groups the Value and the Scan methods.
type ValueScanner interface {
	driver.Valuer
	sql.Scanner
}

// indirect returns the type at the end of indirection.
func indirect(t reflect.Type) reflect.Type {
	for t.Kind() == reflect.Ptr {
		t = t.Elem()
	}
	return t
}

func pkgPath(t reflect.Type) string {
	pkg := t.PkgPath()
	if pkg != "" {
		return pkg
	}
	switch t.Kind() {
	case reflect.Slice, reflect.Array, reflect.Ptr, reflect.Map:
		return pkgPath(t.Elem())
	}
	return pkg
}