from PIL import Image, ImageDraw
from pathlib import Path


def create_soft_edge_mask(width: int, height: int, transition_ratio: float = 0.02) -> Image:
    transition_height = int(height * transition_ratio)
    mask = Image.new("L", (width, height), 255)  # 默认全白（不透明）
    draw = ImageDraw.Draw(mask)
    draw.rectangle([0, 0, width, height // 2 - transition_height // 2], fill=0)  # 上半黑
    draw.rectangle([0, height // 2 + transition_height // 2, width, height], fill=255)  # 下半白

    # 顶部和底部之间 2% 的区域渐变
    for i in range(transition_height):
        alpha = int(255 * (i / transition_height))
        y = height // 2 - transition_height // 2 + i
        draw.line([(0, y), (width, y)], fill=alpha)

    return mask


def process_image(input_path: str | Path, output_path: str | Path):
    base_width, base_height = 800, 1000
    original = Image.open(input_path).convert("RGBA")

    # 缩放图像宽度适配底图宽度
    scale_ratio = base_width / original.width
    new_height = int(original.height * scale_ratio)
    resized = original.resize((base_width, new_height), Image.LANCZOS)

    # 创建底图并粘贴第一个图像（对齐顶部）
    base_image = Image.new("RGBA", (base_width, base_height), "white")
    base_image.paste(resized, (0, 0), resized)

    # 创建 A2 图层（对齐底部）
    A2 = resized.copy()
    A2_image = Image.new("RGBA", (base_width, base_height), (0, 0, 0, 0))
    A2_y = base_height - A2.height
    A2_image.paste(A2, (0, A2_y), A2)

    # 创建遮罩并加为 alpha 通道
    mask = create_soft_edge_mask(base_width, base_height, 0.02)
    A2_image.putalpha(mask)

    # 合成
    final = Image.alpha_composite(base_image, A2_image)
    final.convert("RGB").save(output_path, format="PNG")