import struct
import numpy as np
from PIL import Image, ImageDraw
import os


def parse_stl(file_path: str):
    """Parse an STL file (binary or ASCII) and return mesh data + metadata."""
    with open(file_path, 'rb') as f:
        header = f.read(80)

    is_binary = False
    if not header.startswith(b'solid'):
        is_binary = True
    else:
        # Some binary files also start with 'solid', check further
        with open(file_path, 'rb') as f:
            f.read(80)
            tri_count_bytes = f.read(4)
            if len(tri_count_bytes) == 4:
                tri_count = struct.unpack('<I', tri_count_bytes)[0]
                file_size = os.path.getsize(file_path)
                expected = 80 + 4 + tri_count * 50
                if file_size == expected:
                    is_binary = True

    if is_binary:
        return _parse_binary(file_path)
    else:
        return _parse_ascii(file_path)


def _parse_binary(file_path: str):
    with open(file_path, 'rb') as f:
        f.read(80)  # skip header
        tri_count = struct.unpack('<I', f.read(4))[0]

        vertices = []
        for _ in range(tri_count):
            f.read(12)  # normal
            v1 = struct.unpack('<3f', f.read(12))
            v2 = struct.unpack('<3f', f.read(12))
            v3 = struct.unpack('<3f', f.read(12))
            f.read(2)   # attribute byte count
            vertices.extend([v1, v2, v3])

    vertices = np.array(vertices, dtype=np.float32)
    return _compute_metadata(vertices, tri_count)


def _parse_ascii(file_path: str):
    vertices = []
    with open(file_path, 'r', encoding='utf-8', errors='ignore') as f:
        for line in f:
            line = line.strip().lower()
            if line.startswith('vertex'):
                parts = line.split()
                if len(parts) >= 4:
                    v = [float(parts[1]), float(parts[2]), float(parts[3])]
                    vertices.append(v)

    vertices = np.array(vertices, dtype=np.float32)
    tri_count = len(vertices) // 3
    return _compute_metadata(vertices, tri_count)


def _compute_metadata(vertices: np.ndarray, tri_count: int):
    if len(vertices) == 0:
        return {
            'vertices': vertices,
            'faces': 0,
            'width': 0.0,
            'height': 0.0,
            'depth': 0.0,
        }

    min_v = vertices.min(axis=0)
    max_v = vertices.max(axis=0)
    dims = max_v - min_v

    return {
        'vertices': vertices,
        'faces': tri_count,
        'width': float(dims[0]),
        'height': float(dims[1]),
        'depth': float(dims[2]),
    }


def generate_thumbnail(vertices: np.ndarray, output_path: str, size: int = 256):
    """Generate a simple orthographic thumbnail from vertices."""
    if len(vertices) == 0:
        img = Image.new('RGB', (size, size), color=(30, 30, 30))
        img.save(output_path)
        return

    # Project to XY plane, normalize to image coords
    min_v = vertices.min(axis=0)
    max_v = vertices.max(axis=0)
    dims = max_v - min_v
    scale = max(dims[0], dims[1])
    if scale == 0:
        scale = 1.0

    margin = 20
    img_size = size - 2 * margin

    img = Image.new('RGB', (size, size), color=(30, 30, 30))
    draw = ImageDraw.Draw(img)

    # Draw triangles
    for i in range(0, len(vertices), 3):
        tri = vertices[i:i+3]
        pts = []
        for v in tri:
            x = margin + int(((v[0] - min_v[0]) / scale) * img_size)
            y = margin + int(((1.0 - (v[1] - min_v[1]) / scale)) * img_size)
            pts.append((x, y))
        if len(pts) == 3:
            # Simple shading based on Z
            z_avg = sum(v[2] for v in tri) / 3.0
            z_norm = (z_avg - min_v[2]) / (dims[2] if dims[2] > 0 else 1)
            brightness = int(80 + z_norm * 120)
            color = (brightness, brightness, int(brightness * 1.1))
            draw.polygon(pts, fill=color, outline=(50, 50, 60))

    img.save(output_path, 'PNG')