"""CSV helpers for IO tracing.

This module provides lightweight helpers that append sent/received
position records to CSV files located in the application's Temp folder.
Behavior is governed by `target_simulator.config.DEBUG_CONFIG` (see keys
``enable_io_trace``, ``temp_folder_name``, and filename overrides).

These functions are intended for debugging and tracing; they return ``True``
when the append operation succeeded and ``False`` when disabled or on error.

PERFORMANCE: Uses asynchronous buffering to avoid blocking the simulation
thread. Rows are buffered in memory and flushed periodically by a background
thread, eliminating I/O overhead from the critical path.
"""

import csv
import os
import time
import threading
import atexit
from typing import Iterable, Any, Dict, List, Tuple
from collections import deque

from target_simulator.config import DEBUG_CONFIG

# --- Async CSV Buffer ---
_CSV_BUFFER_LOCK = threading.Lock()
_CSV_BUFFERS: Dict[str, deque] = {}  # filename -> deque of (row, headers)
_CSV_FLUSH_THREAD: threading.Thread = None
_CSV_STOP_EVENT = threading.Event()
_CSV_FLUSH_INTERVAL_S = 2.0  # Flush every 2 seconds
_CSV_MAX_BUFFER_SIZE = 1000  # Flush immediately if buffer exceeds this


def _ensure_temp_folder():
    temp_folder = DEBUG_CONFIG.get("temp_folder_name", "Temp")
    if not os.path.exists(temp_folder):
        try:
            os.makedirs(temp_folder, exist_ok=True)
        except Exception:
            # If we cannot create the folder, swallow the exception; callers
            # should handle absence of files gracefully.
            return None
    return temp_folder


def append_row(filename: str, row: Iterable[Any], headers: Iterable[str] | None = None):
    """Append a row to a CSV file stored under the Temp folder.

    If the file does not exist and ``headers`` is provided, the headers are
    written as the first row. The function is a no-op when tracing is
    disabled via DEBUG_CONFIG.

    Args:
        filename: Name of the target CSV file inside the Temp folder.
        row: Iterable of values to write as a CSV row.
        headers: Optional iterable of header names to write when creating a
            new file.

    Returns:
        True on success, False when tracing is disabled or an error occurred.
    """
    if not DEBUG_CONFIG.get("enable_io_trace", False):
        return False

    temp_folder = _ensure_temp_folder()
    if not temp_folder:
        return False

    file_path = os.path.join(temp_folder, filename)
    write_headers = not os.path.exists(file_path) and headers is not None

    try:
        with open(file_path, "a", newline="", encoding="utf-8") as csvfile:
            writer = csv.writer(csvfile)
            if write_headers:
                writer.writerow(list(headers))
            writer.writerow(list(row))
    except Exception:
        return False

    return True


def append_sent_position(
    timestamp: float, target_id: int, x: float, y: float, z: float, command: str
):
    """Append a sent-position entry for IO tracing.

    The row contains a timestamp, target id, position in feet and the issued
    command string.
    """
    filename = DEBUG_CONFIG.get("io_trace_sent_filename", "sent_positions.csv")
    headers = ["timestamp", "target_id", "x_ft", "y_ft", "z_ft", "command"]
    row = [timestamp, target_id, x, y, z, command]
    return append_row(filename, row, headers=headers)


def append_received_position(
    timestamp: float, target_id: int, x: float, y: float, z: float
):
    """Append a received-position entry for IO tracing.

    The row contains a timestamp, target id and position in feet.
    """
    filename = DEBUG_CONFIG.get("io_trace_received_filename", "received_positions.csv")
    headers = ["timestamp", "target_id", "x_ft", "y_ft", "z_ft"]
    row = [timestamp, target_id, x, y, z]
    return append_row(filename, row, headers=headers)