fp-go/v2/samples/lens/example_test.go

// Copyright (c) 2023 - 2025 IBM Corp.
// All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package lens

import (
	"testing"

	F "github.com/IBM/fp-go/v2/function"
	L "github.com/IBM/fp-go/v2/optics/lens"
	O "github.com/IBM/fp-go/v2/option"
	"github.com/stretchr/testify/assert"
)

func TestPersonLens(t *testing.T) {
	// Create a person
	person := Person{
		Name:  "Alice",
		Age:   30,
		Email: "alice@example.com",
	}

	// Create lenses
	lenses := MakePersonLenses()

	// Test Get
	assert.Equal(t, "Alice", lenses.Name.Get(person))
	assert.Equal(t, 30, lenses.Age.Get(person))
	assert.Equal(t, "alice@example.com", lenses.Email.Get(person))

	// Test Set
	updated := lenses.Name.Set("Bob")(person)
	assert.Equal(t, "Bob", updated.Name)
	assert.Equal(t, 30, updated.Age)      // Other fields unchanged
	assert.Equal(t, "Alice", person.Name) // Original unchanged

	// Test Modify
	incrementAge := F.Pipe1(
		lenses.Age,
		L.Modify[Person](func(age int) int { return age + 1 }),
	)
	incremented := incrementAge(person)
	assert.Equal(t, 31, incremented.Age)
	assert.Equal(t, 30, person.Age) // Original unchanged
}

func TestCompanyLens(t *testing.T) {
	// Create a company with nested structures
	company := Company{
		Name: "Acme Corp",
		Address: Address{
			Street:  "123 Main St",
			City:    "Springfield",
			ZipCode: "12345",
			Country: "USA",
		},
		CEO: Person{
			Name:  "John Doe",
			Age:   45,
			Email: "john@acme.com",
		},
	}

	// Create lenses
	companyLenses := MakeCompanyLenses()
	addressLenses := MakeAddressLenses()
	personLenses := MakePersonLenses()

	// Test simple field access
	assert.Equal(t, "Acme Corp", companyLenses.Name.Get(company))

	// Test nested field access using composition
	cityLens := F.Pipe1(
		companyLenses.Address,
		L.Compose[Company](addressLenses.City),
	)
	assert.Equal(t, "Springfield", cityLens.Get(company))

	// Test nested field update
	updatedCompany := cityLens.Set("New York")(company)
	assert.Equal(t, "New York", updatedCompany.Address.City)
	assert.Equal(t, "Springfield", company.Address.City) // Original unchanged

	// Test deeply nested field access
	ceoNameLens := F.Pipe1(
		companyLenses.CEO,
		L.Compose[Company](personLenses.Name),
	)
	assert.Equal(t, "John Doe", ceoNameLens.Get(company))

	// Test deeply nested field update
	updatedCompany2 := ceoNameLens.Set("Jane Smith")(company)
	assert.Equal(t, "Jane Smith", updatedCompany2.CEO.Name)
	assert.Equal(t, "John Doe", company.CEO.Name) // Original unchanged
}

func TestLensComposition(t *testing.T) {
	company := Company{
		Name: "Tech Inc",
		Address: Address{
			Street:  "456 Oak Ave",
			City:    "Boston",
			ZipCode: "02101",
			Country: "USA",
		},
		CEO: Person{
			Name:  "Alice Johnson",
			Age:   50,
			Email: "alice@techinc.com",
		},
	}

	companyLenses := MakeCompanyLenses()
	personLenses := MakePersonLenses()

	// Compose lenses to access CEO's email
	ceoEmailLens := F.Pipe1(
		companyLenses.CEO,
		L.Compose[Company](personLenses.Email),
	)

	// Get the CEO's email
	email := ceoEmailLens.Get(company)
	assert.Equal(t, "alice@techinc.com", email)

	// Update the CEO's email
	updated := ceoEmailLens.Set("alice.johnson@techinc.com")(company)
	assert.Equal(t, "alice.johnson@techinc.com", updated.CEO.Email)
	assert.Equal(t, "alice@techinc.com", company.CEO.Email) // Original unchanged

	// Modify the CEO's age
	ceoAgeLens := F.Pipe1(
		companyLenses.CEO,
		L.Compose[Company](personLenses.Age),
	)

	modifyAge := F.Pipe1(
		ceoAgeLens,
		L.Modify[Company](func(age int) int { return age + 5 }),
	)
	olderCEO := modifyAge(company)
	assert.Equal(t, 55, olderCEO.CEO.Age)
	assert.Equal(t, 50, company.CEO.Age) // Original unchanged
}

func TestPersonRefLensesIdempotent(t *testing.T) {
	// Create a person pointer
	person := &Person{
		Name:  "Alice",
		Age:   30,
		Email: "alice@example.com",
	}

	// Create ref lenses
	refLenses := MakePersonRefLenses()

	// Test that setting the same value returns the identical pointer (idempotent)
	// This works because Name, Age, and Email use MakeLensStrict which has equality optimization

	// Test Name field - setting same value should return same pointer
	sameName := refLenses.Name.Set("Alice")(person)
	assert.Same(t, person, sameName, "Setting Name to same value should return identical pointer")

	// Test Age field - setting same value should return same pointer
	sameAge := refLenses.Age.Set(30)(person)
	assert.Same(t, person, sameAge, "Setting Age to same value should return identical pointer")

	// Test Email field - setting same value should return same pointer
	sameEmail := refLenses.Email.Set("alice@example.com")(person)
	assert.Same(t, person, sameEmail, "Setting Email to same value should return identical pointer")

	// Test that setting a different value creates a new pointer
	differentName := refLenses.Name.Set("Bob")(person)
	assert.NotSame(t, person, differentName, "Setting Name to different value should return new pointer")
	assert.Equal(t, "Bob", differentName.Name)
	assert.Equal(t, "Alice", person.Name, "Original should be unchanged")

	differentAge := refLenses.Age.Set(31)(person)
	assert.NotSame(t, person, differentAge, "Setting Age to different value should return new pointer")
	assert.Equal(t, 31, differentAge.Age)
	assert.Equal(t, 30, person.Age, "Original should be unchanged")

	differentEmail := refLenses.Email.Set("bob@example.com")(person)
	assert.NotSame(t, person, differentEmail, "Setting Email to different value should return new pointer")
	assert.Equal(t, "bob@example.com", differentEmail.Email)
	assert.Equal(t, "alice@example.com", person.Email, "Original should be unchanged")
}

func TestPersonRefLensesOptionalIdempotent(t *testing.T) {
	// Test that setting an optional field to the same value returns the identical pointer
	// This is important for performance and correctness in functional programming

	// Test with Phone field set to a value
	phoneValue := "555-1234"
	person := &Person{
		Name:  "Alice",
		Age:   30,
		Email: "alice@example.com",
		Phone: &phoneValue,
	}

	refLenses := MakePersonRefLenses()

	// Test that setting Phone to the same value returns the same pointer
	samePhone := refLenses.Phone.Set(O.Some(&phoneValue))(person)
	assert.Same(t, person, samePhone, "Setting Phone to same value should return identical pointer")

	// Test with Phone field set to nil
	personNoPhone := &Person{
		Name:  "Bob",
		Age:   25,
		Email: "bob@example.com",
		Phone: nil,
	}

	// Setting Phone to None when it's already nil should return same pointer
	sameNilPhone := refLenses.Phone.Set(O.None[*string]())(personNoPhone)
	assert.Same(t, personNoPhone, sameNilPhone, "Setting Phone to None when already nil should return identical pointer")

	// Test that setting to a different value creates a new pointer
	newPhoneValue := "555-5678"
	differentPhone := refLenses.Phone.Set(O.Some(&newPhoneValue))(person)
	assert.NotSame(t, person, differentPhone, "Setting Phone to different value should return new pointer")
	assert.Equal(t, &newPhoneValue, differentPhone.Phone)
	assert.Equal(t, &phoneValue, person.Phone, "Original should be unchanged")

	// Test setting from nil to Some creates new pointer
	somePhone := refLenses.Phone.Set(O.Some(&phoneValue))(personNoPhone)
	assert.NotSame(t, personNoPhone, somePhone, "Setting Phone from nil to Some should return new pointer")
	assert.Equal(t, &phoneValue, somePhone.Phone)
	assert.Nil(t, personNoPhone.Phone, "Original should be unchanged")

	// Test setting from Some to None creates new pointer
	nonePhone := refLenses.Phone.Set(O.None[*string]())(person)
	assert.NotSame(t, person, nonePhone, "Setting Phone from Some to None should return new pointer")
	assert.Nil(t, nonePhone.Phone)
	assert.Equal(t, &phoneValue, person.Phone, "Original should be unchanged")
}

func TestAddressRefLensesOptionalIdempotent(t *testing.T) {
	// Test Address.State optional field idempotency

	stateValue := "California"
	address := &Address{
		Street:  "123 Main St",
		City:    "Los Angeles",
		ZipCode: "90001",
		Country: "USA",
		State:   &stateValue,
	}

	refLenses := MakeAddressRefLenses()

	// Test that setting State to the same value returns the same pointer
	sameState := refLenses.State.Set(O.Some(&stateValue))(address)
	assert.Same(t, address, sameState, "Setting State to same value should return identical pointer")

	// Test with State field set to nil
	addressNoState := &Address{
		Street:  "456 Oak Ave",
		City:    "Boston",
		ZipCode: "02101",
		Country: "USA",
		State:   nil,
	}

	// Setting State to None when it's already nil should return same pointer
	sameNilState := refLenses.State.Set(O.None[*string]())(addressNoState)
	assert.Same(t, addressNoState, sameNilState, "Setting State to None when already nil should return identical pointer")

	// Test that setting to a different value creates a new pointer
	newStateValue := "New York"
	differentState := refLenses.State.Set(O.Some(&newStateValue))(address)
	assert.NotSame(t, address, differentState, "Setting State to different value should return new pointer")
	assert.Equal(t, &newStateValue, differentState.State)
	assert.Equal(t, &stateValue, address.State, "Original should be unchanged")
}

func TestCompanyRefLensesOptionalIdempotent(t *testing.T) {
	// Test Company.Website optional field idempotency

	websiteValue := "https://example.com"
	company := &Company{
		Name: "Tech Inc",
		Address: Address{
			Street:  "789 Tech Blvd",
			City:    "San Francisco",
			ZipCode: "94102",
			Country: "USA",
		},
		CEO: Person{
			Name:  "Jane Doe",
			Age:   45,
			Email: "jane@techinc.com",
		},
		Website: &websiteValue,
	}

	refLenses := MakeCompanyRefLenses()

	// Test that setting Website to the same value returns the same pointer
	sameWebsite := refLenses.Website.Set(O.Some(&websiteValue))(company)
	assert.Same(t, company, sameWebsite, "Setting Website to same value should return identical pointer")

	// Test with Website field set to nil
	companyNoWebsite := &Company{
		Name: "Startup LLC",
		Address: Address{
			Street:  "101 Innovation Way",
			City:    "Austin",
			ZipCode: "78701",
			Country: "USA",
		},
		CEO: Person{
			Name:  "John Smith",
			Age:   35,
			Email: "john@startup.com",
		},
	}

	// Setting Website to None when it's already nil should return same pointer
	sameNilWebsite := refLenses.Website.Set(O.None[*string]())(companyNoWebsite)
	assert.Same(t, companyNoWebsite, sameNilWebsite, "Setting Website to None when already nil should return identical pointer")

	// Test that setting to a different value creates a new pointer
	newWebsiteValue := "https://newsite.com"
	differentWebsite := refLenses.Website.Set(O.Some(&newWebsiteValue))(company)
	assert.NotSame(t, company, differentWebsite, "Setting Website to different value should return new pointer")
	assert.Equal(t, &newWebsiteValue, differentWebsite.Website)
	assert.Equal(t, &websiteValue, company.Website, "Original should be unchanged")
}