import numpy as np
from fastapi import HTTPException

from .config import MAX_COEFFICIENTS, NYQUIST_MARGIN


def require_finite(value, name):
    if not np.isfinite(value):
        raise HTTPException(status_code=400, detail=f"{name} 必須是有限數值")
    return float(value)


def validate_frequency(name, value, fs, *, below_nyquist=True):
    value = require_finite(value, name)
    if value <= 0:
        raise HTTPException(status_code=400, detail=f"{name} 必須大於 0")
    if below_nyquist and value >= (fs / 2) * NYQUIST_MARGIN:
        raise HTTPException(status_code=400, detail=f"{name} 必須小於 Nyquist 頻率 ({fs / 2:g} Hz)")
    return value


def parse_coefficients(raw, name):
    try:
        values = [float(x.strip()) for x in raw.replace(",", " ").split() if x.strip()]
    except ValueError:
        raise HTTPException(status_code=400, detail=f"{name} 係數格式錯誤")
    return validate_coefficients(values, name)


def validate_coefficients(values, name):
    if len(values) == 0:
        raise HTTPException(status_code=400, detail=f"{name} 係數不可為空")
    if len(values) > MAX_COEFFICIENTS:
        raise HTTPException(status_code=400, detail=f"{name} 係數最多 {MAX_COEFFICIENTS} 個")
    coeffs = np.asarray(values, dtype=float)
    if not np.all(np.isfinite(coeffs)):
        raise HTTPException(status_code=400, detail=f"{name} 係數必須都是有限數值")
    if name == "a" and np.isclose(coeffs[0], 0.0):
        raise HTTPException(status_code=400, detail="a[0] 不可為 0")
    return coeffs


def normalize_coefficients(b_values, a_values):
    b_arr = validate_coefficients(b_values, "b")
    a_arr = validate_coefficients(a_values, "a")
    if not np.isclose(a_arr[0], 1.0):
        b_arr = b_arr / a_arr[0]
        a_arr = a_arr / a_arr[0]
    return b_arr, a_arr