import numpy as np
from keras.datasets import mnist
import matplotlib.pyplot as plt

# Load MNIST 
print("Loading MNIST...") # debugging
(X_train_raw, y_train), (X_test_raw, y_test) = mnist.load_data()

# print("X_train_raw[0]:")
# print(X_train_raw[0]) # output: 28x28 vector spelling 5
# print("y_train[0]:")
# print(y_train[0]) # output: 5
# print("X_test_raw[0]:")
# print(X_test_raw[0]) # output: 28x28 vector spelling 7
# print("y_test[0]:")
# print(y_test[0]) # output: 7

# Flatten images from (samples, 28, 28) to (samples, 784) -> one dimensional
X_train = X_train_raw.reshape(X_train_raw.shape[0], -1).astype(np.float32)
X_test = X_test_raw.reshape(X_test_raw.shape[0], -1).astype(np.float32)

print("Train:", X_train.shape, "Test:", X_test.shape)

# Select first 1000 prototype vectors
prototypes = X_train[:1000]
prototype_labels = y_train[:1000]

print("Using", len(prototypes), "prototype vectors.") # debugging

# kNN function with explicit loops for readability
def knn_predict_batch(X_batch, k=3):
    """
    Predicts labels for a batch of test vectors using kNN.
    X_batch: shape (batch_size, 784)
    returns: shape (batch_size,)
    """
    preds = []
    
    # For each test image
    for test_img in X_batch:
        distances = []
        
        # Euclidean distance to each prototype
        for prototype in prototypes:
            # distance = sqrt(sum((test_img - prototype)^2))
            diff = test_img - prototype
            distance = np.sqrt(np.sum(diff ** 2))
            distances.append(distance)
        
        # Find indices of k nearest neighbors (smallest distances)
        distances = np.array(distances)
        nearest_k_indices = np.argsort(distances)[:k] # returns indices of array with sorted distances
        
        # Get labels of the k nearest neighbors
        nearest_k_labels = prototype_labels[nearest_k_indices]
        
        # Majority vote
        prediction = np.bincount(nearest_k_labels, minlength=10).argmax()
        preds.append(prediction)
    
    return np.array(preds)


# Evaluate on first N_TEST test samples
N_TEST = 1000
print(f"Evaluating on {N_TEST} test samples...") # debugging

X_eval = X_test[:N_TEST]
y_eval = y_test[:N_TEST]

preds = knn_predict_batch(X_eval, k=5)

accuracy = np.mean(preds == y_eval)

print("Predictions:", preds[:20])
print("True labels:", y_eval[:20])
print("Accuracy:", accuracy)

# Visualize first 20 predictions
fig, axes = plt.subplots(4, 5, figsize=(12, 10))
axes = axes.flatten()

for i in range(0, 20):
    # Reshape flattened image back to 28x28
    img = X_eval[i].reshape(28, 28)
    axes[i].imshow(img, cmap='gray')
    axes[i].set_title(f"Pred: {preds[i]}, True: {y_eval[i]}")
    axes[i].axis('off')

plt.tight_layout()
plt.show()