# Test `AsyncBackend` class.

test_that("'AsyncBackend' creates and manages clusters correctly", {
    # Create a specification.
    specification <- Specification$new()

    # Set the number of cores.
    specification$set_cores(cores = 2)

    # Pick a cluster type.
    cluster_type <- pick_cluster_type(specification$types)

    # Let the specification determine the cluster type.
    specification$set_type(type = cluster_type)

    # Create a synchronous backend object.
    backend <- AsyncBackend$new()

    # Expect the backend to support progress tracking.
    expect_true(backend$supports_progress)

    # Start the cluster on the backend.
    backend$start(specification)

    # Expect the cluster to be an object of `callr` class.
    expect_true(is(backend$cluster, "r_session"))

    # Expect that the cluster is of correct size.
    expect_equal(backend$cluster$run(function() length(cluster)), specification$cores)

    # Expect that the cluster is of correct type.
    switch(cluster_type,
        "psock" = expect_true(all(tolower(backend$cluster$run(function() summary(cluster))[, 2]) == "socknode")),
        "fork" = expect_true(all(tolower(backend$cluster$run(function() summary(cluster))[, 2]) == "forknode"))
    )

    # Test backend states.
    tests_set_for_backend_states(backend, specification)

    # Expect error attempting to get the task state for an inactive backend.
    expect_error(backend$task_state, as_text(Exception$cluster_not_active()))

    # Expect error attempting to get the session for an inactive backend.
    expect_error(backend$session_state, as_text(Exception$cluster_not_active()))
})


test_that("'AsyncBackend' stops busy clusters correctly", {
    # Create a specification.
    specification <- Specification$new()

    # Set the number of cores.
    specification$set_cores(cores = 2)

    # Pick a cluster type.
    cluster_type <- pick_cluster_type(specification$types)

    # Let the specification determine the cluster type.
    specification$set_type(type = cluster_type)

    # Create a synchronous backend object.
    backend <- AsyncBackend$new()

    # Start the cluster on the backend.
    backend$start(specification)

    # Disable forceful stopping.
    set_option("stop_forceful", FALSE)

    # Make sure the backend is busy.
    backend$sapply(1:100, function(x) {
        while (TRUE) { }
    })

    # Expect error when stopping a busy backend while a task is running.
    expect_error(backend$stop(), as_text(Exception$stop_busy_backend_not_allowed()))

    # Enable forceful stopping.
    set_option("stop_forceful", TRUE)

    # Stop the cluster on the backend.
    backend$stop()

    # Expect the backend to be inactive.
    expect_false(backend$active)

    # Start the cluster on the backend.
    backend$start(specification)

    # Disable forceful stopping.
    set_option("stop_forceful", FALSE)

    # Make sure the backend has unread results.
    backend$sapply(1:100, function(x) x)

    # Block the main session until the task is finished.
    block_until_async_task_finished(backend)

    # Expect error when stopping backend with unread task results.
    expect_error(backend$stop(), as_text(Exception$stop_busy_backend_not_allowed()))

    # Enable forceful stopping.
    set_option("stop_forceful", TRUE)

    # Stop the cluster on the backend.
    backend$stop()

    # Expect the backend to be inactive.
    expect_false(backend$active)

    # Restore the default options.
    set_default_options()
})


test_that("'AsyncBackend' performs operations on the cluster correctly", {
    # Create a specification.
    specification <- Specification$new()

    # Set the number of cores.
    specification$set_cores(cores = 2)

    # Determine the cluster type.
    cluster_type <- pick_cluster_type(specification$types)

    # Determine the cluster type automatically.
    specification$set_type(type = cluster_type)

    # Create an asynchronous backend object.
    backend <- AsyncBackend$new()

    # Perform tests for asynchronous backend operations.
    tests_set_for_asynchronous_backend_operations(backend, specification, test_task)
})