"""Preview module for generating image previews of patterns.

Uses ProcessPoolExecutor to run CPU-intensive preview generation in separate
processes, completely eliminating Python GIL contention with the motion control thread.
"""
import os
import math
import asyncio
import logging
from io import BytesIO
from modules.core import process_pool as pool_module

logger = logging.getLogger(__name__)


def _generate_preview_in_process(pattern_file, format='WEBP'):
    """Generate preview for a pattern file, optimized for 300x300 view.
    
    Runs in a separate process with its own GIL, avoiding contention
    with the motion control thread.
    
    All imports are done inside the function to ensure they happen
    in the worker process, not the main process.
    
    Note: Worker CPU affinity/priority is configured once at pool init via initializer.
    """
    # Import dependencies in the worker process
    from PIL import Image, ImageDraw
    from modules.core.pattern_manager import parse_theta_rho_file, THETA_RHO_DIR
    
    file_path = os.path.join(THETA_RHO_DIR, pattern_file)
    coordinates = parse_theta_rho_file(file_path)
    
    # Image generation parameters
    RENDER_SIZE = 2048  # Use 2048x2048 for high quality rendering
    DISPLAY_SIZE = 512  # Final display size
    
    if not coordinates:
        # Create an image with "No pattern data" text
        img = Image.new('RGBA', (DISPLAY_SIZE, DISPLAY_SIZE), (255, 255, 255, 0))  # Transparent background
        draw = ImageDraw.Draw(img)
        text = "No pattern data"
        try:
            bbox = draw.textbbox((0, 0), text)
            text_width = bbox[2] - bbox[0]
            text_height = bbox[3] - bbox[1]
            text_x = (DISPLAY_SIZE - text_width) / 2
            text_y = (DISPLAY_SIZE - text_height) / 2
        except:
            text_x = DISPLAY_SIZE / 4 
            text_y = DISPLAY_SIZE / 2
        draw.text((text_x, text_y), text, fill="black")
        
        img_byte_arr = BytesIO()
        img.save(img_byte_arr, format=format)
        img_byte_arr.seek(0)
        return img_byte_arr.getvalue()

    # Create image and draw pattern
    img = Image.new('RGBA', (RENDER_SIZE, RENDER_SIZE), (255, 255, 255, 0))  # Transparent background
    draw = ImageDraw.Draw(img)
    
    # Image drawing parameters
    CENTER = RENDER_SIZE / 2.0
    SCALE_FACTOR = (RENDER_SIZE / 2.0) - 10.0 
    LINE_COLOR = "black" 
    STROKE_WIDTH = 2  # Increased stroke width for better visibility after scaling

    points_to_draw = []
    for theta, rho in coordinates:
        x = CENTER - rho * SCALE_FACTOR * math.cos(theta)
        y = CENTER - rho * SCALE_FACTOR * math.sin(theta)
        points_to_draw.append((x, y))
    
    if len(points_to_draw) > 1:
        draw.line(points_to_draw, fill=LINE_COLOR, width=STROKE_WIDTH, joint="curve")
    elif len(points_to_draw) == 1:
        r = 4  # Larger radius for single point to remain visible after scaling
        x, y = points_to_draw[0]
        draw.ellipse([(x-r, y-r), (x+r, y+r)], fill=LINE_COLOR)

    # Scale down to display size with high-quality resampling
    img = img.resize((DISPLAY_SIZE, DISPLAY_SIZE), Image.Resampling.LANCZOS)
    # Rotate the image 180 degrees
    img = img.rotate(180)

    # Save to bytes
    img_byte_arr = BytesIO()
    img.save(img_byte_arr, format=format, lossless=False, alpha_quality=20, method=0)
    img_byte_arr.seek(0)
    return img_byte_arr.getvalue()


async def generate_preview_image(pattern_file, format='WEBP'):
    """Generate a preview for a pattern file.
    
    Runs in a separate process via ProcessPoolExecutor to completely
    eliminate GIL contention with the motion control thread.
    """
    loop = asyncio.get_running_loop()
    pool = pool_module.get_pool()
    
    try:
        # Run preview generation in a separate process (separate GIL)
        result = await loop.run_in_executor(
            pool,
            _generate_preview_in_process,
            pattern_file,
            format
        )
        return result
    except Exception as e:
        logger.error(f"Error generating preview for {pattern_file}: {e}")
        return None