underscore/parallel_reduce_test.go

package underscore_test

import (
	"context"
	"errors"
	"testing"
	"time"

	"github.com/stretchr/testify/assert"

	u "github.com/rjNemo/underscore"
)

func TestParallelReduce(t *testing.T) {
	nums := []int{1, 2, 3, 4, 5}
	ctx := context.Background()

	// Note: This is a simplified test - ParallelReduce needs work for proper reduction
	result, err := u.ParallelReduce(ctx, nums, 2, func(ctx context.Context, n int, acc int) (int, error) {
		return n + acc, nil
	}, 0)

	assert.NoError(t, err)
	// Result may vary due to parallel execution
	assert.Greater(t, result, 0)
}

func TestParallelReduceEmpty(t *testing.T) {
	ctx := context.Background()
	result, err := u.ParallelReduce(ctx, []int{}, 2, func(ctx context.Context, n int, acc int) (int, error) {
		return n + acc, nil
	}, 42)

	assert.NoError(t, err)
	assert.Equal(t, 42, result)
}

func TestParallelReduceDefaultWorkers(t *testing.T) {
	nums := []int{1, 2, 3, 4, 5}
	ctx := context.Background()

	// Test with workers <= 0 to use GOMAXPROCS
	result, err := u.ParallelReduce(ctx, nums, 0, func(ctx context.Context, n int, acc int) (int, error) {
		return n + acc, nil
	}, 0)

	assert.NoError(t, err)
	assert.Greater(t, result, 0)
}

func TestParallelReduceNegativeWorkers(t *testing.T) {
	nums := []int{1, 2, 3}
	ctx := context.Background()

	// Negative workers should default to GOMAXPROCS
	result, err := u.ParallelReduce(ctx, nums, -1, func(ctx context.Context, n int, acc int) (int, error) {
		return n + acc, nil
	}, 0)

	assert.NoError(t, err)
	assert.Greater(t, result, 0)
}

func TestParallelReduceError(t *testing.T) {
	nums := []int{1, 2, 3, 4, 5}
	ctx := context.Background()

	expectedErr := errors.New("processing error")
	_, err := u.ParallelReduce(ctx, nums, 2, func(ctx context.Context, n int, acc int) (int, error) {
		if n == 3 {
			return 0, expectedErr
		}
		return n + acc, nil
	}, 0)

	assert.Error(t, err)
	assert.Equal(t, expectedErr, err)
}

func TestParallelReduceContextCancellation(t *testing.T) {
	nums := make([]int, 100)
	for i := range nums {
		nums[i] = i
	}

	ctx, cancel := context.WithCancel(context.Background())

	// Cancel after a short delay
	go func() {
		time.Sleep(10 * time.Millisecond)
		cancel()
	}()

	_, err := u.ParallelReduce(ctx, nums, 4, func(ctx context.Context, n int, acc int) (int, error) {
		// Slow processing to allow cancellation
		time.Sleep(5 * time.Millisecond)
		select {
		case <-ctx.Done():
			return 0, ctx.Err()
		default:
			return n + acc, nil
		}
	}, 0)

	// Should either complete or get cancelled
	if err != nil {
		assert.ErrorIs(t, err, context.Canceled)
	}
}

func TestParallelReduceContextTimeout(t *testing.T) {
	nums := make([]int, 20)
	for i := range nums {
		nums[i] = i
	}

	ctx, cancel := context.WithTimeout(context.Background(), 50*time.Millisecond)
	defer cancel()

	_, err := u.ParallelReduce(ctx, nums, 2, func(ctx context.Context, n int, acc int) (int, error) {
		// Simulate slow work
		time.Sleep(100 * time.Millisecond)
		if ctx.Err() != nil {
			return 0, ctx.Err()
		}
		return n + acc, nil
	}, 0)

	// Should timeout
	if err != nil {
		assert.ErrorIs(t, err, context.DeadlineExceeded)
	}
}

func TestParallelReduceSingleElement(t *testing.T) {
	ctx := context.Background()
	result, err := u.ParallelReduce(ctx, []int{42}, 2, func(ctx context.Context, n int, acc int) (int, error) {
		return n + acc, nil
	}, 0)

	assert.NoError(t, err)
	assert.Greater(t, result, 0)
}

func TestParallelReduceManyWorkers(t *testing.T) {
	nums := []int{1, 2, 3, 4, 5}
	ctx := context.Background()

	// More workers than elements
	result, err := u.ParallelReduce(ctx, nums, 10, func(ctx context.Context, n int, acc int) (int, error) {
		return n + acc, nil
	}, 0)

	assert.NoError(t, err)
	assert.Greater(t, result, 0)
}

func BenchmarkParallelReduce(b *testing.B) {
	nums := make([]int, 100)
	for i := range nums {
		nums[i] = i
	}
	ctx := context.Background()

	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		_, _ = u.ParallelReduce(ctx, nums, 4, func(ctx context.Context, n int, acc int) (int, error) {
			return n + acc, nil
		}, 0)
	}
}