import numpy as np
from rank_bm25 import BM25Okapi

class SparseRetriever:
    def __init__(self, doc_texts):
        self.tokenized_corpus = [t.lower().split() for t in doc_texts]
        self.bm25 = BM25Okapi(self.tokenized_corpus)
        
    def retrieve(self, query_text, top_k=1000):
        tokens = query_text.lower().split()
        scores = self.bm25.get_scores(tokens)
        top_indices = np.argsort(scores)[::-1][:top_k]
        return [(int(i), float(scores[i])) for i in top_indices]