# Copyright (c) Facebook, Inc. and its affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.

import unittest

from fairseq.data import iterators, ListDataset


class TestIterators(unittest.TestCase):
    def test_counting_iterator_index(self, ref=None, itr=None):
        # Test the indexing functionality of CountingIterator
        if ref is None:
            assert itr is None
            ref = list(range(10))
            itr = iterators.CountingIterator(ref)
        else:
            assert len(ref) == 10
            assert itr is not None

        self.assertTrue(itr.has_next())
        self.assertEqual(itr.n, 0)
        self.assertEqual(next(itr), ref[0])
        self.assertEqual(itr.n, 1)
        self.assertEqual(next(itr), ref[1])
        self.assertEqual(itr.n, 2)
        itr.skip(3)
        self.assertEqual(itr.n, 5)
        self.assertEqual(next(itr), ref[5])
        itr.skip(2)
        self.assertEqual(itr.n, 8)
        self.assertEqual(list(itr), [ref[8], ref[9]])
        self.assertFalse(itr.has_next())

    def test_counting_iterator_length_mismatch(self):
        ref = list(range(10))
        # When the underlying iterable is longer than the CountingIterator,
        # the remaining items in the iterable should be ignored
        itr = iterators.CountingIterator(ref, total=8)
        self.assertEqual(list(itr), ref[:8])
        # When the underlying iterable is shorter than the CountingIterator,
        # raise an IndexError when the underlying iterable is exhausted
        itr = iterators.CountingIterator(ref, total=12)
        self.assertRaises(IndexError, list, itr)

    def test_counting_iterator_take(self):
        # Test the "take" method of CountingIterator
        ref = list(range(10))
        itr = iterators.CountingIterator(ref)
        itr.take(5)
        self.assertEqual(len(itr), len(list(iter(itr))))
        self.assertEqual(len(itr), 5)

        itr = iterators.CountingIterator(ref)
        itr.take(5)
        self.assertEqual(next(itr), ref[0])
        self.assertEqual(next(itr), ref[1])
        itr.skip(2)
        self.assertEqual(next(itr), ref[4])
        self.assertFalse(itr.has_next())

    def test_grouped_iterator(self):
        # test correctness
        x = list(range(10))
        itr = iterators.GroupedIterator(x, 1)
        self.assertEqual(list(itr), [[0], [1], [2], [3], [4], [5], [6], [7], [8], [9]])
        itr = iterators.GroupedIterator(x, 4)
        self.assertEqual(list(itr), [[0, 1, 2, 3], [4, 5, 6, 7], [8, 9]])
        itr = iterators.GroupedIterator(x, 5)
        self.assertEqual(list(itr), [[0, 1, 2, 3, 4], [5, 6, 7, 8, 9]])

        # test the GroupIterator also works correctly as a CountingIterator
        x = list(range(30))
        ref = list(iterators.GroupedIterator(x, 3))
        itr = iterators.GroupedIterator(x, 3)
        self.test_counting_iterator_index(ref, itr)

    def test_sharded_iterator(self):
        # test correctness
        x = list(range(10))
        itr = iterators.ShardedIterator(x, num_shards=1, shard_id=0)
        self.assertEqual(list(itr), x)
        itr = iterators.ShardedIterator(x, num_shards=2, shard_id=0)
        self.assertEqual(list(itr), [0, 2, 4, 6, 8])
        itr = iterators.ShardedIterator(x, num_shards=2, shard_id=1)
        self.assertEqual(list(itr), [1, 3, 5, 7, 9])
        itr = iterators.ShardedIterator(x, num_shards=3, shard_id=0)
        self.assertEqual(list(itr), [0, 3, 6, 9])
        itr = iterators.ShardedIterator(x, num_shards=3, shard_id=1)
        self.assertEqual(list(itr), [1, 4, 7, None])
        itr = iterators.ShardedIterator(x, num_shards=3, shard_id=2)
        self.assertEqual(list(itr), [2, 5, 8, None])

        # test CountingIterator functionality
        x = list(range(30))
        ref = list(iterators.ShardedIterator(x, num_shards=3, shard_id=0))
        itr = iterators.ShardedIterator(x, num_shards=3, shard_id=0)
        self.test_counting_iterator_index(ref, itr)

    def test_counting_iterator_buffered_iterator_take(self):
        ref = list(range(10))
        buffered_itr = iterators.BufferedIterator(2, ref)
        itr = iterators.CountingIterator(buffered_itr)
        itr.take(5)
        self.assertEqual(len(itr), len(list(iter(itr))))
        self.assertEqual(len(itr), 5)

        buffered_itr = iterators.BufferedIterator(2, ref)
        itr = iterators.CountingIterator(buffered_itr)
        itr.take(5)
        self.assertEqual(len(buffered_itr), 5)
        self.assertEqual(len(list(iter(buffered_itr))), 5)

        buffered_itr = iterators.BufferedIterator(2, ref)
        itr = iterators.CountingIterator(buffered_itr)
        itr.take(5)
        self.assertEqual(next(itr), ref[0])
        self.assertEqual(next(itr), ref[1])
        itr.skip(2)
        self.assertEqual(next(itr), ref[4])
        self.assertFalse(itr.has_next())
        self.assertRaises(StopIteration, next, buffered_itr)

        ref = list(range(4, 10))
        buffered_itr = iterators.BufferedIterator(2, ref)
        itr = iterators.CountingIterator(buffered_itr, start=4)
        itr.take(5)
        self.assertEqual(len(itr), 5)
        self.assertEqual(len(buffered_itr), 1)
        self.assertEqual(next(itr), ref[0])
        self.assertFalse(itr.has_next())
        self.assertRaises(StopIteration, next, buffered_itr)

    def test_epoch_batch_iterator_skip_remainder_batch(self):
        reference = [1, 2, 3]
        itr1 = _get_epoch_batch_itr(reference, 2, True)
        self.assertEqual(len(itr1), 1)
        itr2 = _get_epoch_batch_itr(reference, 2, False)
        self.assertEqual(len(itr2), 2)
        itr3 = _get_epoch_batch_itr(reference, 1, True)
        self.assertEqual(len(itr3), 2)
        itr4 = _get_epoch_batch_itr(reference, 1, False)
        self.assertEqual(len(itr4), 3)
        itr5 = _get_epoch_batch_itr(reference, 4, True)
        self.assertEqual(len(itr5), 0)
        self.assertFalse(itr5.has_next())
        itr6 = _get_epoch_batch_itr(reference, 4, False)
        self.assertEqual(len(itr6), 1)

    def test_grouped_iterator_skip_remainder_batch(self):
        reference = [1, 2, 3, 4, 5, 6, 7, 8, 9]
        itr1 = _get_epoch_batch_itr(reference, 3, False)
        grouped_itr1 = iterators.GroupedIterator(itr1, 2, True)
        self.assertEqual(len(grouped_itr1), 1)

        itr2 = _get_epoch_batch_itr(reference, 3, False)
        grouped_itr2 = iterators.GroupedIterator(itr2, 2, False)
        self.assertEqual(len(grouped_itr2), 2)

        itr3 = _get_epoch_batch_itr(reference, 3, True)
        grouped_itr3 = iterators.GroupedIterator(itr3, 2, True)
        self.assertEqual(len(grouped_itr3), 1)

        itr4 = _get_epoch_batch_itr(reference, 3, True)
        grouped_itr4 = iterators.GroupedIterator(itr4, 2, False)
        self.assertEqual(len(grouped_itr4), 1)

        itr5 = _get_epoch_batch_itr(reference, 5, True)
        grouped_itr5 = iterators.GroupedIterator(itr5, 2, True)
        self.assertEqual(len(grouped_itr5), 0)

        itr6 = _get_epoch_batch_itr(reference, 5, True)
        grouped_itr6 = iterators.GroupedIterator(itr6, 2, False)
        self.assertEqual(len(grouped_itr6), 1)


def _get_epoch_batch_itr(ref, bsz, skip_remainder_batch):
    dsz = len(ref)
    indices = range(dsz)
    starts = indices[::bsz]
    batch_sampler = [indices[s : s + bsz] for s in starts]
    dataset = ListDataset(ref)
    itr = iterators.EpochBatchIterator(
        dataset=dataset,
        collate_fn=dataset.collater,
        batch_sampler=batch_sampler,
        skip_remainder_batch=skip_remainder_batch,
    )
    return itr.next_epoch_itr()


if __name__ == "__main__":
    unittest.main()