import numpy as np
import torch
from sentence_transformers import SentenceTransformer
import nltk.data
import nltk
import os

# Set NLTK data path to project directory
PROJECT_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
NLTK_DATA_DIR = os.path.join(PROJECT_DIR, 'nltk_data')

# Add to NLTK's search path
nltk.data.path.insert(0, NLTK_DATA_DIR)

# Download to the custom location
# Using punkt_tab (the modern tab-separated format introduced in NLTK 3.8+)
# instead of the older punkt pickle format
# The punkt_tab model version depends on the NLTK Python package version
# Check your NLTK version with: uv pip show nltk
nltk.download('punkt_tab', download_dir=NLTK_DATA_DIR)

# Available models for the demo
AVAILABLE_MODELS = {
    'all-mpnet-base-v2': 'all-mpnet-base-v2', # Dec 2020
    'gte-large-en-v1.5': 'Alibaba-NLP/gte-large-en-v1.5', # Jan 2024
    # 'qwen3-embedding-4b': 'Qwen/Qwen3-Embedding-4B', # April 2025
    'mxbai-embed-large-v1': 'mixedbread-ai/mxbai-embed-large-v1',
}

# On clustering
# mixedbread-ai/mxbai-embed-large-v1:   46.71
# gte-large-en-v1.5:                    47.95
# Qwen/Qwen3-Embedding-0.6B:            52.33
# Qwen/Qwen3-Embedding-4B:              57.15

# On STS
# gte-large-en-v1.5:                    81.43
# Qwen/Qwen3-Embedding-0.6B:            76.17
# Qwen/Qwen3-Embedding-4B:              80.86
# mixedbread-ai/mxbai-embed-large-v1:   85.00

# Load all models into memory
print("Loading sentence transformer models...")
models = {}

models['all-mpnet-base-v2'] = SentenceTransformer('all-mpnet-base-v2')
print("Loading Alibaba-NLP/gte-large-en-v1.5")
models['gte-large-en-v1.5'] = SentenceTransformer('Alibaba-NLP/gte-large-en-v1.5', trust_remote_code=True)
#print("Loading Qwen/Qwen3-Embedding-4B")
#models['qwen3-embedding-4b'] = SentenceTransformer('Qwen/Qwen3-Embedding-4B', trust_remote_code=True)
print("Loading mixedbread-ai/mxbai-embed-large-v1")
models["mxbai-embed-large-v1"] = SentenceTransformer('mixedbread-ai/mxbai-embed-large-v1')
print("All models loaded!")

sent_detector = nltk.data.load('tokenizers/punkt/english.pickle')

def cos_sim(a, b):
    sims = a @ b.T
    a_norm = np.linalg.norm(a, axis=-1)
    b_norm = np.linalg.norm(b, axis=-1)
    a_normalized = (sims.T / a_norm.T).T
    sims = a_normalized / b_norm
    return sims

def degree_power(A, k):
    degrees = np.power(np.array(A.sum(1)), k).ravel()
    D = np.diag(degrees)
    return D

def normalized_adjacency(A):
    normalized_D = degree_power(A, -0.5)
    return torch.from_numpy(normalized_D.dot(A).dot(normalized_D))

def get_sentences(source_text):
    sentence_ranges = list(sent_detector.span_tokenize(source_text))
    sentences = [source_text[start:end] for start, end in sentence_ranges]
    return sentences, sentence_ranges

def text_rank(sentences, model_name='all-mpnet-base-v2'):
    model = models[model_name]
    vectors = model.encode(sentences)
    adjacency = torch.tensor(cos_sim(vectors, vectors)).fill_diagonal_(0.)
    adjacency[adjacency < 0] = 0
    return normalized_adjacency(adjacency)

def extract(source_text, model_name='all-mpnet-base-v2'):
    """
    Main API function that extracts sentence positions and computes normalized adjacency matrix.

    Returns:
        sentence_ranges: List of (start, end) tuples for each sentence's character position
        adjacency: (N × N) normalized adjacency matrix where N is the number of sentences.
                   Each entry (i,j) represents the normalized similarity between sentences i and j.
                   This matrix is returned to the frontend, which raises it to a power and computes
                   the final salience scores via random walk simulation.
    """
    sentences, sentence_ranges = get_sentences(source_text)
    adjacency = text_rank(sentences, model_name)
    return sentence_ranges, adjacency


# =============================================================================
# Unused/Debugging Code
# =============================================================================

def terminal_distr(adjacency, initial=None):
    sample = initial if initial is not None else torch.full((adjacency.shape[0],), 1.)
    scores = sample.matmul(torch.matrix_power(adjacency, 10)).numpy().tolist()
    return scores

def get_results(sentences, adjacency):
    scores = terminal_distr(adjacency)
    for score, sentence in sorted(zip(scores, sentences), key=lambda xs: xs[0]):
        if score > 1.1:
            print('{:0.2f}: {}'.format(score, sentence))