# decoder.py
import numpy as np
from utils import index_to_char
from codebook import construct_codebook

def decode_message(Y, codebook):
    Y1, Y2 = Y[::2], Y[1::2]
    scores = []
    for i, c in enumerate(codebook):
        c1, c2 = c[::2], c[1::2]
        s1 = np.sqrt(10) * np.dot(Y1, c1) + np.dot(Y2, c2)
        s2 = np.dot(Y1, c1) + np.sqrt(10) * np.dot(Y2, c2)
        scores.append(max(s1, s2))
    return np.argmax(scores)

def signal_to_text(Y, codebook, r=6):
    _, n, _, _ = construct_codebook(r, 1)
    seg_len = n
    text = ''
    for i in range(40):
        seg = Y[i * seg_len:(i + 1) * seg_len]
        index = decode_message(seg, codebook)
        if index in index_to_char:
            text += index_to_char[index]
        else:
            text += '?'  # Unknown character
    return text