#!/usr/bin/env python3

import unittest
import random

import numpy as np
import torch
from torch import nn
from torch import optim

import learn2learn as l2l


def accuracy(predictions, targets):
    predictions = predictions.argmax(dim=1).view(targets.shape)
    return (predictions == targets).sum().float() / targets.size(0)


def fast_adapt(batch, learner, loss, adaptation_steps, shots, ways, device):
    data, labels = batch
    data, labels = data.to(device), labels.to(device)

    # Separate data into adaptation/evalutation sets
    adaptation_indices = np.zeros(data.size(0), dtype=bool)
    adaptation_indices[np.arange(shots*ways) * 2] = True
    evaluation_indices = torch.from_numpy(~adaptation_indices)
    adaptation_indices = torch.from_numpy(adaptation_indices)
    adaptation_data, adaptation_labels = data[adaptation_indices], labels[adaptation_indices]
    evaluation_data, evaluation_labels = data[evaluation_indices], labels[evaluation_indices]

    # Adapt the model
    for step in range(adaptation_steps):
        train_error = loss(learner(adaptation_data), adaptation_labels)
        train_error /= len(adaptation_data)
        learner.adapt(train_error)

    # Evaluate the adapted model
    predictions = learner(evaluation_data)
    valid_error = loss(predictions, evaluation_labels)
    valid_error /= len(evaluation_data)
    valid_accuracy = accuracy(predictions, evaluation_labels)
    return valid_error, valid_accuracy


def main(
        ways=5,
        shots=5,
        meta_lr=0.003,
        fast_lr=0.5,
        meta_batch_size=32,
        adaptation_steps=1,
        num_iterations=60000,
        cuda=True,
        seed=42,
):
    random.seed(seed)
    np.random.seed(seed)
    torch.manual_seed(seed)
    device = torch.device('cpu')
    if cuda and torch.cuda.device_count():
        torch.cuda.manual_seed(seed)
        device = torch.device('cuda')

    # Create Datasets
    train_dataset = l2l.vision.datasets.MiniImagenet(root='~/data', mode='train')
    valid_dataset = l2l.vision.datasets.MiniImagenet(root='~/data', mode='validation')
    test_dataset = l2l.vision.datasets.MiniImagenet(root='~/data', mode='test')
    train_dataset = l2l.data.MetaDataset(train_dataset)
    valid_dataset = l2l.data.MetaDataset(valid_dataset)
    test_dataset = l2l.data.MetaDataset(test_dataset)

    train_transforms = [
        l2l.data.transforms.NWays(train_dataset, ways),
        l2l.data.transforms.KShots(train_dataset, 2*shots),
        l2l.data.transforms.LoadData(train_dataset),
        l2l.data.transforms.RemapLabels(train_dataset),
        l2l.data.transforms.ConsecutiveLabels(train_dataset),
    ]
    train_tasks = l2l.data.Taskset(
        train_dataset,
        task_transforms=train_transforms,
        num_tasks=20000,
    )

    valid_transforms = [
        l2l.data.transforms.NWays(valid_dataset, ways),
        l2l.data.transforms.KShots(valid_dataset, 2*shots),
        l2l.data.transforms.LoadData(valid_dataset),
        l2l.data.transforms.ConsecutiveLabels(train_dataset),
        l2l.data.transforms.RemapLabels(valid_dataset),
    ]
    valid_tasks = l2l.data.Taskset(
        valid_dataset,
        task_transforms=valid_transforms,
        num_tasks=600,
    )

    test_transforms = [
        l2l.data.transforms.NWays(test_dataset, ways),
        l2l.data.transforms.KShots(test_dataset, 2*shots),
        l2l.data.transforms.LoadData(test_dataset),
        l2l.data.transforms.RemapLabels(test_dataset),
        l2l.data.transforms.ConsecutiveLabels(train_dataset),
    ]
    test_tasks = l2l.data.Taskset(
        test_dataset,
        task_transforms=test_transforms,
        num_tasks=600,
    )

    # Create model
    model = l2l.vision.models.MiniImagenetCNN(ways)
    model.to(device)
    maml = l2l.algorithms.MAML(model, lr=fast_lr, first_order=False)
    opt = optim.Adam(maml.parameters(), meta_lr)
    loss = nn.CrossEntropyLoss(size_average=True, reduction='mean')

    for iteration in range(num_iterations):
        opt.zero_grad()
        meta_train_error = 0.0
        meta_train_accuracy = 0.0
        meta_valid_error = 0.0
        meta_valid_accuracy = 0.0
        meta_test_error = 0.0
        meta_test_accuracy = 0.0
        for task in range(meta_batch_size):
            # Compute meta-training loss
            learner = maml.clone()
            batch = train_tasks.sample()
            evaluation_error, evaluation_accuracy = fast_adapt(batch,
                                                               learner,
                                                               loss,
                                                               adaptation_steps,
                                                               shots,
                                                               ways,
                                                               device)
            evaluation_error.backward()
            meta_train_error += evaluation_error.item()
            meta_train_accuracy += evaluation_accuracy.item()

            # Compute meta-validation loss
            learner = maml.clone()
            batch = valid_tasks.sample()
            evaluation_error, evaluation_accuracy = fast_adapt(batch,
                                                               learner,
                                                               loss,
                                                               adaptation_steps,
                                                               shots,
                                                               ways,
                                                               device)
            meta_valid_error += evaluation_error.item()
            meta_valid_accuracy += evaluation_accuracy.item()

            # Compute meta-testing loss
            learner = maml.clone()
            batch = test_tasks.sample()
            evaluation_error, evaluation_accuracy = fast_adapt(batch,
                                                               learner,
                                                               loss,
                                                               adaptation_steps,
                                                               shots,
                                                               ways,
                                                               device)
            meta_test_error += evaluation_error.item()
            meta_test_accuracy += evaluation_accuracy.item()

        # Print some metrics
        print('\n')
        print('Iteration', iteration)
        print('Meta Train Error', meta_train_error / meta_batch_size)
        print('Meta Train Accuracy', meta_train_accuracy / meta_batch_size)
        print('Meta Valid Error', meta_valid_error / meta_batch_size)
        print('Meta Valid Accuracy', meta_valid_accuracy / meta_batch_size)
        print('Meta Test Error', meta_test_error / meta_batch_size)
        print('Meta Test Accuracy', meta_test_accuracy / meta_batch_size)

        # Average the accumulated gradients and optimize
        for p in maml.parameters():
            p.grad.data.mul_(1.0 / meta_batch_size)
        opt.step()
    return meta_train_accuracy, meta_valid_accuracy, meta_test_accuracy

class MAMLMiniImagenetIntegrationTests(unittest.TestCase):

    def setUp(self):
        pass

    def tearDown(self):
        pass

    def test_final_accuracy(self):
        train_acc, valid_acc, test_acc = main(num_iterations=1)
        self.assertTrue(train_acc >= 0.2)
        self.assertTrue(valid_acc >= 0.2)
        self.assertTrue(test_acc >= 0.2)


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