struct_copier_test.go

package deepcopy

import (
	"testing"
	"time"

	"github.com/stretchr/testify/assert"
)

func Test_Copy_struct(t *testing.T) {
	t.Run("#1: copy fields directly", func(t *testing.T) {
		type SS struct {
			I int
			U uint
		}
		type DD struct {
			I int
			U uint
		}

		var s SS = SS{I: 1, U: 2}
		var d DD
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, U: 2}, d)
	})

	t.Run("#2: copy fields with conversion", func(t *testing.T) {
		type SS struct {
			I int
			F float32
		}
		type DD struct {
			I IntT
			F uint
		}

		var s SS = SS{I: 1, F: 2.2}
		var d DD
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, F: 2}, d)
	})

	t.Run("#3: copy fields with lossy conversion (int -> int8)", func(t *testing.T) {
		type SS struct {
			I int
			F float32
			X string
		}
		type DD struct {
			I int8
			F uint
			Y bool
		}

		var s SS = SS{I: 128, F: 2.2}
		var d DD
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: -128, F: 2}, d)
	})

	t.Run("#4: copy fields with conversion (ptr -> value)", func(t *testing.T) {
		type SS struct {
			I *int
			F float32
		}
		type DD struct {
			I int
			F uint
		}

		var s SS = SS{I: ptrOf(1), F: 2.2}
		var d DD
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, F: 2}, d)
	})

	t.Run("#5: copy fields with conversion (value -> ptr)", func(t *testing.T) {
		type SS struct {
			I int
			F float32
		}
		type DD struct {
			I *int8
			F uint
		}

		var s SS = SS{I: 128, F: 2.2}
		var d DD
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: ptrOf(int8(-128)), F: 2}, d)
	})

	t.Run("#6: copy fields with conversion (slice -> array)", func(t *testing.T) {
		type SS struct {
			I []int
			F float32
		}
		type DD struct {
			I [5]int8
			F uint
		}

		var s SS = SS{I: []int{126, 127, 128}, F: 2.2}
		var d DD = DD{I: [5]int8{1, 2, 3, 4, 5}}
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: [5]int8{126, 127, -128, 0, 0}, F: 2}, d)
	})

	t.Run("#7: struct-in-struct", func(t *testing.T) {
		type SS2 struct {
			I int
			X bool
		}
		type SS struct {
			I  int
			SS SS2
		}
		type DD2 struct {
			I int
			Y string
		}
		type DD struct {
			I  int
			DD *DD2 `copy:"SS"`
		}

		var s SS = SS{I: 1, SS: SS2{I: 11, X: true}}
		var d DD
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, DD: &DD2{I: 11}}, d)
	})

	t.Run("#8: with src field is ignored", func(t *testing.T) {
		type SS struct {
			I int `copy:"-"`
			F float32
		}
		type DD struct {
			I int
			F uint
		}

		var s SS = SS{I: 1, F: 2.2}
		var d DD = DD{I: 100}
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 100, F: 2}, d)
	})

	t.Run("#9: with dst field is ignored", func(t *testing.T) {
		type SS struct {
			I int
			F float32
		}
		type DD struct {
			I int `copy:"-"`
			F uint
		}

		var s SS = SS{I: 1, F: 2.2}
		var d DD = DD{I: 100}
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 100, F: 2}, d)
	})

	t.Run("#10: structs have fields of type function", func(t *testing.T) {
		type SS struct {
			I  int
			Fn func(int) string `copy:"fn"`
		}
		type DD struct {
			I  int
			Fn func(int) string `copy:"fn"`
		}

		fn := func(int) string { return "abc" }

		var s SS = SS{I: 1, Fn: fn}
		var d DD = DD{I: 100}
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.NotNil(t, d.Fn)
		assert.Equal(t, "abc", d.Fn(1))
	})

	t.Run("#11: cycle reference", func(t *testing.T) {
		type SS struct {
			I   int
			Ref *SS
		}
		type DD struct {
			I   int
			Ref *DD
		}

		var s SS = SS{I: 1, Ref: &SS{I: 2, Ref: &SS{I: 3}}}
		var d DD = DD{}
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, Ref: &DD{I: 2, Ref: &DD{I: 3}}}, d)
	})
}

func Test_Copy_struct_error(t *testing.T) {
	t.Run("#1: struct -> slice (error)", func(t *testing.T) {
		type SS struct {
			I int
		}
		var s SS = SS{111}
		var d []int
		err := Copy(&d, s)
		assert.ErrorIs(t, err, ErrTypeNonCopyable)
	})

	t.Run("#2: src required but no equivalent dst field", func(t *testing.T) {
		type SS struct {
			I int `copy:",required"`
			U uint
		}
		type DD struct {
			U uint
		}

		var s SS = SS{I: 1, U: 2}
		var d DD
		err := Copy(&d, s)
		assert.ErrorIs(t, err, ErrFieldRequireCopying)
	})

	t.Run("#3: dst required but no equivalent src field", func(t *testing.T) {
		type SS struct {
			I int
		}
		type DD struct {
			U uint `copy:",required"`
		}

		var s SS = SS{I: 1}
		var d DD
		err := Copy(&d, s)
		assert.ErrorIs(t, err, ErrFieldRequireCopying)
	})

	t.Run("#4: struct -> slice (ignore error)", func(t *testing.T) {
		type SS struct {
			I int
		}
		var s SS = SS{111}
		var d []int
		err := Copy(&d, s, IgnoreNonCopyableTypes(true))
		assert.Nil(t, err)
	})

	t.Run("#5: src ignore non-copyable but set 'required'", func(t *testing.T) {
		type SS struct {
			I int `copy:",required"`
			U uint
		}
		type DD struct {
			I []string
			U uint
		}

		var s SS = SS{I: 1, U: 2}
		var d DD
		err := Copy(&d, s, IgnoreNonCopyableTypes(true))
		assert.ErrorIs(t, err, ErrFieldRequireCopying)
	})

	t.Run("#6: dst ignore non-copyable but set 'required'", func(t *testing.T) {
		type SS struct {
			I int
			U uint
		}
		type DD struct {
			I []string `copy:",required"`
			U uint
		}

		var s SS = SS{I: 1, U: 2}
		var d DD
		err := Copy(&d, s, IgnoreNonCopyableTypes(true))
		assert.ErrorIs(t, err, ErrFieldRequireCopying)
	})

	t.Run("#7: non-copyable between src and dst fields", func(t *testing.T) {
		type SS struct {
			I []float32
			U uint
		}
		type DD struct {
			I []string
			U uint
		}

		var s SS = SS{I: []float32{1}, U: 2}
		var d DD
		err := Copy(&d, s)
		assert.ErrorIs(t, err, ErrTypeNonCopyable)
	})
}

func Test_Copy_struct_unexported(t *testing.T) {
	t.Run("#1: unexported -> unexported", func(t *testing.T) {
		type SS struct {
			I int
			u uint
		}
		type DD struct {
			I int
			u uint `copy:",required"`
		}

		var s SS = SS{I: 1, u: 2}
		var d DD
		err := Copy(&d, &s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, u: 2}, d)
	})

	t.Run("#2: unexported -> exported", func(t *testing.T) {
		type SS struct {
			I int
			u uint
		}
		type DD struct {
			I int
			U uint `copy:"u,required"`
		}

		var s SS = SS{I: 1, u: 2}
		var d DD
		err := Copy(&d, &s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, U: 2}, d)
	})

	t.Run("#3: exported -> unexported", func(t *testing.T) {
		type SS struct {
			I int
			U uint
		}
		type DD struct {
			I int
			u uint `copy:"U,required"`
		}

		var s SS = SS{I: 1, U: 2}
		var d DD
		err := Copy(&d, &s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, u: 2}, d)
	})

	t.Run("#4: exported -> unexported with conversion", func(t *testing.T) {
		type SS struct {
			I int
			U uint
		}
		type DD struct {
			i IntT `copy:"I,required"`
			U uint
		}

		var s SS = SS{I: 1, U: 2}
		var d DD
		err := Copy(&d, &s)
		assert.Nil(t, err)
		assert.Equal(t, DD{i: 1, U: 2}, d)
	})

	t.Run("#5: unexported -> unexported with conversion", func(t *testing.T) {
		type SS struct {
			i int `copy:"I,required"`
			U uint
		}
		type DD struct {
			i *int `copy:"I,required"`
			U uint
		}

		var s SS = SS{i: 1, U: 2}
		var d DD
		err := Copy(&d, &s)
		assert.Nil(t, err)
		assert.Equal(t, DD{i: ptrOf(1), U: 2}, d)
	})
}

func Test_Copy_struct_unexported_error(t *testing.T) {
	t.Run("#1: src is unaddressable", func(t *testing.T) {
		type SS struct {
			I int
			u uint
		}
		type DD struct {
			I int
			u uint `copy:",required"`
		}

		var s SS = SS{I: 1, u: 2}
		var d DD
		err := Copy(&d, s)
		assert.ErrorIs(t, err, ErrValueUnaddressable)
	})
}

type testD1 struct {
	x1 int
	x2 int
	x3 int
	x4 uint
	U  uint
}

func (d *testD1) CopyI1(i1 int) error {
	d.x1 = i1 * 2
	return nil
}
func (d *testD1) CopyI2(i2 int) { // incorrect method prototype (no return error)
	d.x2 = i2 * 2
}
func (d *testD1) CopyI3(i3 int, v string) error { // incorrect method prototype (2 input args)
	d.x3 = i3 * 2
	return nil
}
func (d *testD1) CopyI4(i4 uint) error { // incorrect method prototype (unmatched input type)
	d.x4 = i4 * 2
	return nil
}
func (d *testD1) CopyI5(i5 int) string { // incorrect method prototype (not return error type)
	return ""
}
func (d *testD1) CopyI6(i6 int) error { // incorrect method prototype (unmatched input type)
	return errTest
}
func (d *testD1) NotCopy(i6 int) error { // not a copying method
	return errTest
}

func Test_Copy_struct_method(t *testing.T) {
	t.Run("#1: field -> dst method", func(t *testing.T) {
		type SS struct {
			I1 int
			U  uint
		}

		var s SS = SS{I1: 1, U: 2}
		var d testD1
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, testD1{x1: 2, U: 2}, d)
	})

	t.Run("#2: unexported field -> dst method", func(t *testing.T) {
		type SS struct {
			i1 int `copy:"I1,required"`
			U  uint
		}

		var s SS = SS{i1: 1, U: 2}
		var d testD1
		err := Copy(&d, &s)
		assert.Nil(t, err)
		assert.Equal(t, testD1{x1: 2, U: 2}, d)
	})

	t.Run("#3: incorrect method prototype (CopyI2())", func(t *testing.T) {
		type SS struct {
			I2 int
			U  uint
		}

		var s SS = SS{I2: 1, U: 2}
		var d testD1
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, testD1{U: 2}, d)
	})

	t.Run("#4: not allow copying from field -> method", func(t *testing.T) {
		type SS struct {
			I1 int
			U  uint
		}

		var s SS = SS{I1: 1, U: 2}
		var d testD1
		err := Copy(&d, s, CopyBetweenStructFieldAndMethod(false))
		assert.Nil(t, err)
		assert.Equal(t, testD1{U: 2}, d)
	})

	t.Run("#5: copy from src embedded field", func(t *testing.T) {
		type SBase struct {
			I1 int
		}
		type SS struct {
			SBase
			U uint
		}

		var s SS = SS{U: 2, SBase: SBase{I1: 123}}
		var d testD1
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, testD1{U: 2, x1: 246}, d)
	})

	t.Run("#6: copy from src embedded field, but field value can't be retrieved due to nil ptr", func(t *testing.T) {
		type SBase struct {
			I1 int
		}
		type SS struct {
			*SBase
			U uint
		}

		var s SS = SS{U: 2}
		var d testD1
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, testD1{U: 2}, d)
	})
}

func Test_Copy_struct_method_error(t *testing.T) {
	t.Run("#1: unexported field -> dst method", func(t *testing.T) {
		type SS struct {
			i1 int `copy:"I1,required"`
			U  uint
		}

		var s SS = SS{i1: 1, U: 2}
		var d testD1
		err := Copy(&d, s)
		assert.ErrorIs(t, err, ErrValueUnaddressable)
	})

	t.Run("#2: incorrect method prototype (CopyI2())", func(t *testing.T) {
		type SS struct {
			I2 int `copy:",required"`
			U  uint
		}

		var s SS = SS{I2: 1, U: 2}
		var d testD1
		err := Copy(&d, s)
		assert.ErrorIs(t, err, ErrFieldRequireCopying)
	})

	t.Run("#3: incorrect method prototype (CopyI3())", func(t *testing.T) {
		type SS struct {
			I3 int `copy:",required"`
			U  uint
		}

		var s SS = SS{I3: 1, U: 2}
		var d testD1
		err := Copy(&d, s)
		assert.ErrorIs(t, err, ErrFieldRequireCopying)
	})

	t.Run("#4: incorrect method prototype (CopyI4())", func(t *testing.T) {
		type SS struct {
			I4 int `copy:",required"`
			U  uint
		}

		var s SS = SS{I4: 1, U: 2}
		var d testD1
		err := Copy(&d, s)
		assert.ErrorIs(t, err, ErrMethodInvalid)
	})

	t.Run("#5: incorrect method prototype (CopyI5())", func(t *testing.T) {
		type SS struct {
			I5 int `copy:",required"`
			U  uint
		}

		var s SS = SS{I5: 1, U: 2}
		var d testD1
		err := Copy(&d, s)
		assert.ErrorIs(t, err, ErrFieldRequireCopying)
	})

	t.Run("#6: copy method return error (CopyI6())", func(t *testing.T) {
		type SS struct {
			I6 int `copy:",required"`
			U  uint
		}

		var s SS = SS{I6: 1, U: 2}
		var d testD1
		err := Copy(&d, s)
		assert.ErrorIs(t, err, errTest)
	})
}

func Test_Copy_struct_with_embedded_struct(t *testing.T) {
	type SBase1 struct {
		I int
	}
	type SBase2 struct {
		SBase1
		S string
	}

	type DBase1 struct {
		I int
	}
	type DBase2 struct {
		DBase1
		S string
	}

	t.Run("#1: both src and dst have equivalent embedded fields", func(t *testing.T) {
		type SS struct {
			SBase2
			U uint `copy:",required"`
		}
		type DD struct {
			DBase2
			U uint `copy:",required"`
		}

		s := SS{U: 100, SBase2: SBase2{S: "abc", SBase1: SBase1{I: 11}}}
		d := DD{}
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{U: 100, DBase2: DBase2{S: "abc", DBase1: DBase1{I: 11}}}, d)

		// With some tags
		type SS2 struct {
			SBase2 `copy:"base,required"`
			U      uint `copy:",required"`
		}
		type DD2 struct {
			DBase2 `copy:"base,required"`
			U      uint `copy:",required"`
		}

		s2 := SS2{U: 100, SBase2: SBase2{S: "abc", SBase1: SBase1{I: 11}}}
		d2 := DD2{}
		err = Copy(&d2, s2)
		assert.Nil(t, err)
		assert.Equal(t, DD2{U: 100, DBase2: DBase2{S: "abc", DBase1: DBase1{I: 11}}}, d2)
	})

	t.Run("#2: both src and dst have same embedded struct", func(t *testing.T) {
		type SS struct {
			SBase2
			U uint `copy:",required"`
		}
		type DD struct {
			SBase2
			U uint `copy:",required"`
		}

		s := SS{U: 100, SBase2: SBase2{S: "abc", SBase1: SBase1{I: 11}}}
		d := DD{U: 123, SBase2: SBase2{S: "xyz", SBase1: SBase1{I: 111}}}
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{U: 100, SBase2: SBase2{S: "abc", SBase1: SBase1{I: 11}}}, d)
	})

	t.Run("#3: both src and dst have equivalent embedded fields, but src embeds ptr of struct", func(t *testing.T) {
		type SS struct {
			*SBase2
			U uint `copy:",required"`
		}
		type DD struct {
			DBase2
			U uint `copy:",required"`
		}

		// Ptr has value set
		s := SS{U: 100, SBase2: &SBase2{S: "abc", SBase1: SBase1{I: 11}}}
		d := DD{}
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{U: 100, DBase2: DBase2{S: "abc", DBase1: DBase1{I: 11}}}, d)

		// Ptr is nil
		s = SS{U: 100}
		d = DD{}
		err = Copy(&d, &s)
		assert.Nil(t, err)
		assert.Equal(t, DD{U: 100}, d)
	})

	t.Run("#4: both src and dst have equivalent embedded fields, but dst embeds ptr of struct", func(t *testing.T) {
		type SS struct {
			SBase2
			U uint
		}
		type DD struct {
			*DBase2
			U uint
		}

		s := SS{U: 100, SBase2: SBase2{S: "abc", SBase1: SBase1{I: 11}}}
		d := DD{}
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{U: 100, DBase2: &DBase2{S: "abc", DBase1: DBase1{I: 11}}}, d)
	})

	t.Run("#5: src has embedded struct, dst doesn't (flattening the copy)", func(t *testing.T) {
		type SS struct {
			SBase2
			U uint
		}
		type DD struct {
			I int    `copy:",required"`
			S string `copy:",required"`
			U uint   `copy:",required"`
		}

		s := SS{U: 100, SBase2: SBase2{S: "abc", SBase1: SBase1{I: 11}}}
		d := DD{S: "xyz"}
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{U: 100, S: "abc", I: 11}, d)

		// With ignoring a field
		type DD2 struct {
			I int    `copy:",required"`
			S string `copy:"-"`
			U uint   `copy:",required"`
		}

		d2 := DD2{}
		err = Copy(&d2, s)
		assert.Nil(t, err)
		assert.Equal(t, DD2{U: 100, I: 11}, d2)
	})

	t.Run("#6: src has embedded struct ptr, dst doesn't (flattening the copy)", func(t *testing.T) {
		type SS struct {
			*SBase2
			U uint
		}
		type DD struct {
			I int    `copy:",required"`
			S string `copy:",required"`
			U uint   `copy:",required"`
		}

		// Ptr has a value set
		s := SS{U: 100, SBase2: &SBase2{S: "abc", SBase1: SBase1{I: 11}}}
		d := DD{S: "xyz"}
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{U: 100, S: "abc", I: 11}, d)

		// Ptr is nil
		s = SS{U: 100}
		d = DD{S: "xyz"}
		err = Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{U: 100}, d)

		// With ignoring a field
		type DD2 struct {
			I int    `copy:",required"`
			S string `copy:"-"`
			U uint   `copy:",required"`
		}

		s = SS{U: 100, SBase2: &SBase2{S: "abc", SBase1: SBase1{I: 11}}}
		d2 := DD2{S: "xyz"}
		err = Copy(&d2, s)
		assert.Nil(t, err)
		assert.Equal(t, DD2{U: 100, S: "xyz", I: 11}, d2)
	})

	t.Run("#7: dst has embedded struct, src doesn't (flattening the copy)", func(t *testing.T) {
		type SS struct {
			I int    `copy:",required"`
			S string `copy:",required"`
			U uint   `copy:",required"`
		}
		type DD struct {
			DBase2
			U uint
		}

		s := SS{U: 100, S: "abc", I: 11}
		d := DD{U: 123, DBase2: DBase2{S: "xyz"}}
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{U: 100, DBase2: DBase2{S: "abc", DBase1: DBase1{I: 11}}}, d)
	})

	t.Run("#8: dst has embedded struct ptr, src doesn't (flattening the copy)", func(t *testing.T) {
		type SS struct {
			I int    `copy:",required"`
			S string `copy:",required"`
			U uint   `copy:",required"`
		}
		type DD struct {
			*DBase2
			U uint
		}

		// Ptr has value set
		s := SS{U: 100, S: "abc", I: 11}
		d := DD{U: 123, DBase2: &DBase2{S: "xyz"}}
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{U: 100, DBase2: &DBase2{S: "abc", DBase1: DBase1{I: 11}}}, d)

		// Ptr is nil initially
		s = SS{U: 100, S: "abc", I: 11}
		d = DD{U: 123}
		err = Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{U: 100, DBase2: &DBase2{S: "abc", DBase1: DBase1{I: 11}}}, d)
	})
}

func Test_Copy_struct_with_embedded_struct_error(t *testing.T) {
	t.Run("#1: src inherited field requires copying", func(t *testing.T) {
		type SBase struct {
			I int `copy:",required"`
		}
		type SS struct {
			SBase
			U uint
		}
		type DD struct {
			U uint
		}

		s := SS{U: 100, SBase: SBase{I: 11}}
		d := DD{}
		err := Copy(&d, s)
		assert.ErrorIs(t, err, ErrFieldRequireCopying)
	})

	t.Run("#2: dst inherited field requires copying", func(t *testing.T) {
		type SS struct {
			U uint
		}
		type DBase struct {
			I int `copy:",required"`
		}
		type DD struct {
			DBase
			U uint
		}

		s := SS{U: 100}
		d := DD{}
		err := Copy(&d, s)
		assert.ErrorIs(t, err, ErrFieldRequireCopying)
	})
}

func Test_Copy_struct_with_set_nil_on_zero(t *testing.T) {
	t.Run("#1: primitive type", func(t *testing.T) {
		type SS struct {
			I int
			U uint
		}
		type DD struct {
			I int
			U *uint `copy:",nilonzero"`
		}

		// Source field is not zero
		s := SS{I: 1, U: 11}
		d := DD{}
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, U: ptrOf(uint(11))}, d)

		// Source field is zero
		s = SS{I: 1, U: 0}
		d = DD{}
		err = Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, U: nil}, d)
	})

	t.Run("#2: string type", func(t *testing.T) {
		type SS struct {
			I int
			S string
		}
		type DD struct {
			I int
			S *string `copy:",nilonzero"`
		}

		// Source field is not zero
		s := SS{I: 1, S: "x"}
		d := DD{}
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, S: ptrOf("x")}, d)

		// Source field is zero
		s = SS{I: 1, S: ""}
		d = DD{}
		err = Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, S: nil}, d)
	})

	t.Run("#3: time.Time type", func(t *testing.T) {
		type SS struct {
			I    int
			Time time.Time
		}
		type DD struct {
			I    int
			Time *time.Time `copy:",nilonzero"`
		}

		// Source field is not zero
		dt := time.Now()
		s := SS{I: 1, Time: dt}
		d := DD{}
		err := Copy(&d, &s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, Time: ptrOf(dt)}, d)

		// Source field is zero
		s = SS{I: 1, Time: time.Time{}}
		d = DD{}
		err = Copy(&d, &s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, Time: nil}, d)
	})

	t.Run("#3b: time.Time type with deeper level", func(t *testing.T) {
		type SS struct {
			I    int
			Time time.Time
		}
		type DD struct {
			I    int
			Time ***time.Time `copy:",nilonzero"`
		}

		// Source field is not zero
		dt := time.Now()
		s := SS{I: 1, Time: dt}
		d := DD{}
		err := Copy(&d, &s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, Time: ptrOf(ptrOf(ptrOf(dt)))}, d)

		// Source field is zero
		s = SS{I: 1, Time: time.Time{}}
		d = DD{}
		err = Copy(&d, &s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, Time: nil}, d)
	})

	t.Run("#4: custom struct type", func(t *testing.T) {
		type StructType struct {
			I int
			S *string
		}
		type SS struct {
			I  int
			ST StructType
		}
		type DD struct {
			I  int
			ST *StructType `copy:",nilonzero"`
		}

		s := SS{I: 1, ST: StructType{}}
		d := DD{}
		err := Copy(&d, &s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, ST: nil}, d)
	})

	t.Run("#5: dst field is interface type", func(t *testing.T) {
		type SS struct {
			I    int
			Time time.Time
		}
		type DD struct {
			I    int
			Time any `copy:",nilonzero"`
		}

		// Source field is not zero
		dt := time.Now()
		s := SS{I: 1, Time: dt}
		d := DD{}
		err := Copy(&d, &s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, Time: dt}, d)

		// Source field is zero
		s = SS{I: 1, Time: time.Time{}}
		d = DD{}
		err = Copy(&d, &s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, Time: nil}, d)
	})

	t.Run("#6: dst field is map type", func(t *testing.T) {
		type SS struct {
			I int
			M map[int]string
		}
		type DD struct {
			I int
			M map[int]string `copy:",nilonzero"`
		}

		// Source field is not zero
		s := SS{I: 1, M: map[int]string{1: "a", 2: "b"}}
		d := DD{}
		err := Copy(&d, &s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, M: map[int]string{1: "a", 2: "b"}}, d)

		// Source field is zero
		s = SS{I: 1, M: map[int]string{}}
		d = DD{}
		err = Copy(&d, &s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, M: nil}, d)
	})

	t.Run("#7: dst field is slice type", func(t *testing.T) {
		type SS struct {
			I int
			S []any
		}
		type DD struct {
			I int
			S []any `copy:",nilonzero"`
		}

		// Source field is not zero
		s := SS{I: 1, S: []any{1, "a"}}
		d := DD{}
		err := Copy(&d, &s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, S: []any{1, "a"}}, d)

		// Source field is zero
		s = SS{I: 1, S: make([]any, 0, 10)}
		d = DD{}
		err = Copy(&d, &s)
		assert.Nil(t, err)
		assert.Equal(t, DD{I: 1, S: nil}, d)
	})
}

type testS2 struct {
	I int
	S string
}

type testD2 struct {
	I int
	S string
}

func (d *testD2) PostCopy(src any) error {
	testS2, _ := src.(testS2)
	if testS2.I == 100 {
		return errTest
	}
	d.I *= 2
	d.S += d.S
	return nil
}

type testD22 struct {
	I int
	S string
}

func (d *testD22) PostCopy(src any) any {
	d.I *= 2
	d.S += d.S
	return nil
}

type testD23 struct {
	I int
	S string
}

// PostCopy is defined within struct value, not pointer
func (d testD23) PostCopy(src any) error {
	d.I *= 2
	d.S += d.S
	return nil
}

func Test_Copy_struct_with_post_copy_event(t *testing.T) {
	t.Run("#1: success without error", func(t *testing.T) {
		s := testS2{I: 1, S: "a"}
		d := testD2{}
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, testD2{I: 2, S: "aa"}, d)
	})

	t.Run("#2: PostCopy returns error", func(t *testing.T) {
		s := testS2{I: 100, S: "a"} // When testS2.I == 100, PostCopy returns error
		d := testD2{}
		err := Copy(&d, s)
		assert.NotNil(t, err)
		assert.ErrorIs(t, err, errTest)
	})

	t.Run("#3: dstStruct.PostCopy not satisfied", func(t *testing.T) {
		s := testS2{I: 1, S: "a"}
		d := testD22{}
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, testD22{I: 1, S: "a"}, d)
	})

	t.Run("#4: dstStruct.PostCopy is defined on struct value, not pointer", func(t *testing.T) {
		s := testS2{I: 1, S: "a"}
		d := testD23{}
		err := Copy(&d, s)
		assert.Nil(t, err)
		assert.Equal(t, testD23{I: 1, S: "a"}, d) // won't work
	})
}