// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package reflectlite

import (
	"unsafe"
)

// Field returns the i'th field of the struct v.
// It panics if v's Kind is not Struct or i is out of range.
func Field(v Value, i int) Value {
	if v.kind() != Struct {
		panic(&ValueError{"reflect.Value.Field", v.kind()})
	}
	tt := (*structType)(unsafe.Pointer(v.typ))
	if uint(i) >= uint(len(tt.fields)) {
		panic("reflect: Field index out of range")
	}
	field := &tt.fields[i]
	typ := field.typ

	// Inherit permission bits from v, but clear flagEmbedRO.
	fl := v.flag&(flagStickyRO|flagIndir|flagAddr) | flag(typ.Kind())
	// Using an unexported field forces flagRO.
	if !field.name.isExported() {
		if field.embedded() {
			fl |= flagEmbedRO
		} else {
			fl |= flagStickyRO
		}
	}
	// Either flagIndir is set and v.ptr points at struct,
	// or flagIndir is not set and v.ptr is the actual struct data.
	// In the former case, we want v.ptr + offset.
	// In the latter case, we must have field.offset = 0,
	// so v.ptr + field.offset is still the correct address.
	ptr := add(v.ptr, field.offset(), "same as non-reflect &v.field")
	return Value{typ, ptr, fl}
}

func TField(typ Type, i int) Type {
	t := typ.(*rtype)
	if t.Kind() != Struct {
		panic("reflect: Field of non-struct type")
	}
	tt := (*structType)(unsafe.Pointer(t))

	return StructFieldType(tt, i)
}

// Field returns the i'th struct field.
func StructFieldType(t *structType, i int) Type {
	if i < 0 || i >= len(t.fields) {
		panic("reflect: Field index out of bounds")
	}
	p := &t.fields[i]
	return toType(p.typ)
}

// Zero returns a Value representing the zero value for the specified type.
// The result is different from the zero value of the Value struct,
// which represents no value at all.
// For example, Zero(TypeOf(42)) returns a Value with Kind Int and value 0.
// The returned value is neither addressable nor settable.
func Zero(typ Type) Value {
	if typ == nil {
		panic("reflect: Zero(nil)")
	}
	t := typ.(*rtype)
	fl := flag(t.Kind())
	if ifaceIndir(t) {
		return Value{t, unsafe_New(t), fl | flagIndir}
	}
	return Value{t, nil, fl}
}

// ToInterface returns v's current value as an interface{}.
// It is equivalent to:
//	var i interface{} = (v's underlying value)
// It panics if the Value was obtained by accessing
// unexported struct fields.
func ToInterface(v Value) (i any) {
	return valueInterface(v)
}

type EmbedWithUnexpMeth struct{}

func (EmbedWithUnexpMeth) f() {}

type pinUnexpMeth interface {
	f()
}

var pinUnexpMethI = pinUnexpMeth(EmbedWithUnexpMeth{})

func FirstMethodNameBytes(t Type) *byte {
	_ = pinUnexpMethI

	ut := t.uncommon()
	if ut == nil {
		panic("type has no methods")
	}
	m := ut.methods()[0]
	mname := t.(*rtype).nameOff(m.name)
	if *mname.data(0, "name flag field")&(1<<2) == 0 {
		panic("method name does not have pkgPath *string")
	}
	return mname.bytes
}

type Buffer struct {
	buf []byte
}
