import io
import os
import uuid
import re

import numpy as np
import pandas as pd
from fastapi import HTTPException
from scipy import signal
import math

from .config import MAX_CSV_BYTES, MAX_PLOT_POINTS, MAX_ROWS

TEMP_CSV_DIR = "temp_csv"
os.makedirs(TEMP_CSV_DIR, exist_ok=True)

def get_cached_file_path(file_id):
    if file_id == "00000000-0000-0000-0000-000000000000":
        preset_path = "static/preset_signals.csv"
        if os.path.exists(preset_path):
            return preset_path

    if not re.match(r'^[0-9a-f\-]{36}$', file_id):
        raise HTTPException(status_code=400, detail="無效的檔案ID")
    file_path = os.path.join(TEMP_CSV_DIR, f"{file_id}.csv")
    if not os.path.exists(file_path):
        raise HTTPException(status_code=404, detail="找不到快取的 CSV 檔案，請重新上傳")
    return file_path


def downsample_for_plot(index, original, filtered_float, filtered_fixed):
    total = len(index)
    if total <= MAX_PLOT_POINTS:
        return index, original, filtered_float, filtered_fixed, 1
    step = int(np.ceil(total / MAX_PLOT_POINTS))
    return index[::step], original[::step], filtered_float[::step], filtered_fixed[::step], step


async def save_csv_upload(file):
    filename = (file.filename or "").lower()
    if filename and not filename.endswith(".csv"):
        raise HTTPException(status_code=400, detail="請上傳 CSV 檔案")
    contents = await file.read(MAX_CSV_BYTES + 1)
    if len(contents) > MAX_CSV_BYTES:
        raise HTTPException(status_code=413, detail=f"CSV 檔案不可超過 {MAX_CSV_BYTES // (1024 * 1024)}MB")
    if not contents.strip():
        raise HTTPException(status_code=400, detail="CSV 不可為空")
    
    file_id = str(uuid.uuid4())
    file_path = os.path.join(TEMP_CSV_DIR, f"{file_id}.csv")
    with open(file_path, "wb") as f:
        f.write(contents)
    return file_id


def integer_lfilter(b_int, a_int, x_float, shift_in, shift_out, shift_b, shift_a, use_round=False):
    """
    全整數差分方程式模擬 (Mimic DSP hardware)
    高精度狀態變數架構：前饋不位移，保留小數精度於狀態變數中。
    支援硬體 Rounding (四捨五入) vs Floor (無條件捨去向下取整)。
    """
    b_int = np.asarray(b_int, dtype=np.int64)
    a_int = np.asarray(a_int, dtype=np.int64)
    x_int = np.round(x_float * (2**shift_in)).astype(np.int64)
    
    # y_hist 將保留在 Q_{in + b} 格式以降低 Truncation Error
    y_hist = np.zeros(len(x_int), dtype=np.int64)
    y_out = np.zeros(len(x_int), dtype=np.int64)
    
    nb = len(b_int)
    na = len(a_int)
    
    A0 = int(a_int[0])
    if A0 == 0: A0 = 1
    
    # 輸出所需的總位移量
    out_shift = shift_in + shift_b - shift_out
    
    # 預先計算四捨五入的補償值 (+0.5)
    # 韌體開發提示 (C Implementation / RISC-V):
    # 1. 標準 RISC-V (RV32I/IMAC) 的 SRA 指令是純 Floor (無條件捨去)，沒有硬體 Rounding shift。
    #    (除非具備 'P' DSP Extension 才可能有 1-cycle 的硬體 rounding shift)。
    # 2. 演算法秘技：在 C 語言中要實現 1-clock 的四捨五入，不要呼叫 float 的 round()。
    #    請使用 `y = (acc + (1 << (shift - 1))) >> shift`。
    #    編譯器會將 (1 << (shift - 1)) 編譯為常數，整體只消耗 1 個 ADD 指令，極大消除了 DC Bias。
    round_offset_a = (A0 >> 1) if use_round else 0
    round_offset_out = (1 << (out_shift - 1)) if (use_round and out_shift > 0) else 0

    for n in range(len(x_int)):
        sum_b = 0
        # Feedforward: 前饋完全不位移，結果為 Q_{in + b}
        for i in range(nb):
            if n - i >= 0:
                sum_b += b_int[i] * x_int[n - i]
                
        # Feedback: 歷史紀錄為 Q_{in + b}，係數為 Q_a，乘積為 Q_{in + b + a}
        sum_a = 0
        for j in range(1, na):
            if n - j >= 0:
                sum_a += a_int[j] * y_hist[n - j]
                
        # Feedback 縮放：前提 A0 = 1 (或者代表放大了 Q_a 倍的常數)，除以 A0 (即 >> shift_a) 歸一化
        # Python 的 // 等同於硬體的 SRA (Arithmetic Right Shift)，會向負無窮大 Floor
        sum_a_scaled = (sum_a + round_offset_a) // A0
        
        acc = sum_b - sum_a_scaled
        
        # 將超高精度的 acc 直接存入歷史變數
        y_hist[n] = acc
        
        # 最終輸出再針對 Q_out 進行位移縮放
        if out_shift > 0:
            y_out[n] = (acc + round_offset_out) >> out_shift
        elif out_shift < 0:
            y_out[n] = acc << (-out_shift)
        else:
            y_out[n] = acc

    return y_out.astype(float) / (2**shift_out)


def filter_preview_response(file_id, b_vals, a_vals, col_idx, b_int=None, a_int=None, shift_in=14, shift_out=14, shift_b=14, shift_a=14, use_round=False, stages=None, start_idx=None, end_idx=None):
    path = get_cached_file_path(file_id)
    
    # 預先讀取欄位名稱，避免用 usecols 讀取後找不到原始索引
    cols = pd.read_csv(path, nrows=0).columns.tolist()
    if col_idx < 0 or col_idx >= len(cols):
        raise HTTPException(status_code=400, detail="欄位索引超出範圍")
    col_to_filter = cols[col_idx]
    
    # 精準讀取單一欄位，並加上筆數限制 (極大降低記憶體用量與時間)
    df = pd.read_csv(path, usecols=[col_idx], nrows=MAX_ROWS)
    
    # Check if there are non-numeric strings coerced to NaN
    original_nans = df[col_to_filter].isna()
    x_signal = pd.to_numeric(df[col_to_filter], errors="coerce")
    numeric_nans = x_signal.isna()
    if (numeric_nans & ~original_nans).any():
        raise HTTPException(status_code=400, detail=f"欄位 {col_to_filter} 含有非數值資料")
    
    # Drop trailing/all NaN empty cells to support different sequence lengths natively
    x_signal = x_signal.dropna()
    if len(x_signal) == 0:
        raise HTTPException(status_code=400, detail=f"欄位 {col_to_filter} 沒有任何有效數值")
        
    x_values = x_signal.to_numpy(dtype=float)
    if not np.isfinite(x_values).all():
        raise HTTPException(status_code=400, detail=f"欄位 {col_to_filter} 含有非有限數值")

    # 運算路徑：若有提供 stages 則依序級聯，否則使用單一濾波器
    if stages is not None:
        y_float = x_values
        y_fixed = x_values
        any_active = False
        for s in stages:
            if not s.get("isActive", True):
                continue
            any_active = True
            y_float = signal.lfilter(s["b"], s["a"], y_float)
            y_fixed = integer_lfilter(
                s["b_int"], s["a_int"], y_fixed,
                s["shift_in"], s["shift_out"], s["shift_b"], s["shift_a"],
                s["use_round"]
            )
        if not any_active:
            y_float = x_values
            y_fixed = x_values
    else:
        # 路徑 1: 理想浮點數路徑
        y_float = signal.lfilter(b_vals, a_vals, x_values)

        # 路徑 2: 整數模擬路徑
        if b_int is not None and a_int is not None:
            y_fixed = integer_lfilter(b_int, a_int, x_values, shift_in, shift_out, shift_b, shift_a, use_round)
        else:
            y_fixed = y_float

    total_len = len(x_values)
    
    # Robust type checking to bypass FastAPI Form object default values in python unit tests
    start_idx_clean = start_idx if isinstance(start_idx, (int, float, str)) else None
    end_idx_clean = end_idx if isinstance(end_idx, (int, float, str)) else None
    
    s_idx = max(0, int(start_idx_clean)) if start_idx_clean is not None else 0
    e_idx = min(total_len, int(end_idx_clean)) if end_idx_clean is not None else total_len
    if s_idx >= e_idx:
        s_idx = 0
        e_idx = total_len

    x_sliced = x_values[s_idx:e_idx]
    y_float_sliced = y_float[s_idx:e_idx]
    y_fixed_sliced = y_fixed[s_idx:e_idx]
    idx_sliced = x_signal.index.to_numpy()[s_idx:e_idx]

    index, original, filtered_float, filtered_fixed, step = downsample_for_plot(idx_sliced, x_sliced, y_float_sliced, y_fixed_sliced)

    return {
        "index": index.tolist(),
        "original": original.tolist(),
        "filtered": filtered_float.tolist(),
        "filtered_fixed": filtered_fixed.tolist(),
        "col_name": col_to_filter,
        "total_points": int(len(x_signal)),
        "plot_points": int(len(index)),
        "downsample_step": int(step),
    }


def filtered_csv_text(file_id, b_vals, a_vals, col_idx, b_int=None, a_int=None, shift_in=14, shift_out=14, shift_b=14, shift_a=14, use_round=False, stages=None, fs=100000.0):
    path = get_cached_file_path(file_id)
    # 匯出時需要原始所有欄位，但仍受限於 MAX_ROWS
    df = pd.read_csv(path, nrows=MAX_ROWS)
    
    if col_idx < 0 or col_idx >= len(df.columns):
        raise HTTPException(status_code=400, detail="欄位索引超出範圍")
    col_to_filter = df.columns[col_idx]
    
    # Check if there are non-numeric strings coerced to NaN
    original_nans = df[col_to_filter].isna()
    x_signal = pd.to_numeric(df[col_to_filter], errors="coerce")
    numeric_nans = x_signal.isna()
    if (numeric_nans & ~original_nans).any():
        raise HTTPException(status_code=400, detail=f"欄位 {col_to_filter} 含有非數值資料")
    
    # Drop NaNs to process shorter signals properly
    x_signal_clean = x_signal.dropna()
    x_values = x_signal_clean.to_numpy(dtype=float)
    
    if stages is not None:
        y_float = x_values
        y_fixed = x_values
        any_active = False
        for s in stages:
            if not s.get("isActive", True):
                continue
            any_active = True
            y_float = signal.lfilter(s["b"], s["a"], y_float)
            y_fixed = integer_lfilter(
                s["b_int"], s["a_int"], y_fixed,
                s["shift_in"], s["shift_out"], s["shift_b"], s["shift_a"],
                s["use_round"]
            )
        if not any_active:
            y_float = x_values
            y_fixed = x_values
    else:
        y_float = signal.lfilter(b_vals, a_vals, x_values)
        if b_int is not None and a_int is not None:
            y_fixed = integer_lfilter(b_int, a_int, x_values, shift_in, shift_out, shift_b, shift_a, use_round)
        else:
            y_fixed = y_float
        
    # Build a brand-new DataFrame containing exactly the 4 requested columns
    time_values = x_signal_clean.index.to_numpy(dtype=float) / fs
    
    export_df = pd.DataFrame({
        "Time (s)": time_values,
        col_to_filter: x_values,
        f"{col_to_filter}_filtered_ideal": y_float,
        f"{col_to_filter}_filtered_fixed": y_fixed
    })
    
    csv_buffer = io.StringIO()
    export_df.to_csv(csv_buffer, index=False)
    return csv_buffer.getvalue()