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pub mod ppm_loader {
    use std::fs::File;
    use std::io::{Read, BufRead};
    use std::io::BufReader;

    /// Reads specified .ppm file
    /// Returns (width: usize, height: usize, pixels: Vec<u32>)
    ///
    /// 24bpp bitmaps are converted to 32 bit, so it is easy to push them to framebuffer.
    ///
    /// # Examples
    /// ```rust, no_run
    /// extern crate tinyppm;
    ///
    /// // some code here...
    ///
    /// fn my_function(filename: String) {
    ///     let (width, height, image) = tinyppm:ppm_loader::read_image_data(filename);
    ///     // `image` contains 32bit image data
    /// }
    ///
    /// ```
    pub fn read_image_data(image_name: &String) -> (usize, usize, Vec<u32>) {
        let file = File::open(image_name).unwrap();
        let mut reader = std::io::BufReader::new(file);
        let (width, height) = read_image_info(&mut reader);

        let mut rgb_buffer: Vec<u8> = Vec::with_capacity(width * height * 3);
        let read_bytes = reader.read_to_end(rgb_buffer.as_mut()).unwrap();

        if read_bytes != width * height * 3 {
            println!("error while reading image data");
            std::process::exit(5);
        }

        let buffer = convert_rgb_to_argb(width, height, &mut rgb_buffer);
        (width, height, buffer)
    }

    fn convert_rgb_to_argb(width: usize, height: usize, rgb_buffer: &mut Vec<u8>) -> Vec<u32> {
        let mut buffer: Vec<u32> = vec![0; width * height];
        for index in 0..width * height {
            let pixel = index * 3;
            let r = rgb_buffer[pixel] as u32;
            let g = rgb_buffer[pixel + 1] as u32;
            let b = rgb_buffer[pixel + 2] as u32;
            let color = b + (g << 8) + (r << 16);
            buffer[index] = color;
        }
        buffer
    }

    fn read_image_info(reader: &mut BufReader<File>) -> (usize, usize) {
        let mut string_buffer = String::new();
        for _i in 0..3 {
            reader.read_line(&mut string_buffer).unwrap();
        }

        let ppm_id = string_buffer.lines().nth(0usize).unwrap();
        validate_ppm_image(ppm_id);

        let image_size = string_buffer.lines().nth(1usize).unwrap().to_string().clone();
        let (width, height) = extract_image_size(image_size);

        let color_depth = string_buffer.lines().nth(2usize).unwrap().to_string().clone();
        validate_color_depth(color_depth);

        (width, height)
    }

    fn validate_color_depth(bpp_str: String) {
        let bpp = bpp_str.parse::<usize>().expect("image bit depth should be a number");
        if bpp != 255usize {
            println!("only 8bpp RGB images are supported!");
            std::process::exit(4);
        }
    }

    fn validate_ppm_image(ppm_id: &str) {
        if ppm_id.to_string() != "P6" {
            println!("invalid header");
            std::process::exit(3);
        }
    }

    fn extract_image_size(size: String) -> (usize, usize) {
        let image_size: Vec<String> = size.split_whitespace().into_iter().map(|w| w.to_string()).collect();
        let width = image_size.first().unwrap()
            .parse::<usize>()
            .expect("image width should be a number");
        let height = image_size.last().unwrap().
            parse::<usize>()
            .expect("image height should be a number");
        (width, height)
    }
}