import win32api, win32con
import os, os.path
import struct
import math

def checkPath(path, mode):
    if not os.path.exists(path) or not os.path.isfile(path):
        raise ValueError("{0} does not exist or isn't a file.".format(path))
    if not os.access(path, mode):
        raise ValueError("Insufficient permissions: {0}".format(path))

def updateExecutableIcon(executablePath, iconPath):
    """
    Updates the icon of a Windows executable file.
    """

    checkPath(executablePath, os.W_OK)
    checkPath(iconPath, os.R_OK)

    handle = win32api.BeginUpdateResource(executablePath, False)

    icon = open(iconPath, "rb")

    fileheader = icon.read(6)

    # Read icon data
    image_type, image_count = struct.unpack("xxHH", fileheader)
    print "Icon file has type {0} and contains {1} images.".format(image_type, image_count)

    icon_group_desc = struct.pack("<HHH", 0, image_type, image_count)
    icon_sizes = []
    icon_offsets = []

    # Read data of all included icons
    for i in range(1, image_count + 1):
        imageheader = icon.read(16)
        width, height, colors, panes, bits_per_pixel, image_size, offset =\
            struct.unpack("BBBxHHLL", imageheader)
        print "Image is {0}x{1}, has {2} colors in the palette, {3} planes, {4} bits per pixel.".format(
            width, height, colors, panes, bits_per_pixel);
        print "Image size is {0}, the image content has an offset of {1}".format(image_size, offset);

        icon_group_desc = icon_group_desc + struct.pack("<BBBBHHIH",
            width,          # Icon width
            height,         # Icon height
            colors,         # Colors (0 for 256 colors)
            0,              # Reserved2 (must be 0)
            panes,          # Color planes
            bits_per_pixel, # Bits per pixel
            image_size,     # ImageSize
            i               # Resource ID
        )
        icon_sizes.append(image_size)
        icon_offsets.append(offset)

    # Read icon content and write it to executable file
    for i in range(1, image_count + 1):
        icon_content = icon.read(icon_sizes[i - 1])
        print "Read {0} bytes for image #{1}".format(len(icon_content), i)
        win32api.UpdateResource(handle, win32con.RT_ICON, i, icon_content)

    win32api.UpdateResource(handle, win32con.RT_GROUP_ICON, "MAINICON", icon_group_desc)

    win32api.EndUpdateResource(handle, False)

# Use some files I found lying around
updateExecutableIcon("example.exe", "test.ico")