use super::Image;

pub fn parse(file_data: &[u8]) -> Result<Image, String> {
    use orbclient::Color;

    let get = |i: usize| -> u8 {
        match file_data.get(i) {
            Some(byte) => *byte,
            None => 0,
        }
    };

    let getw = |i: usize| -> u16 { (get(i) as u16) + ((get(i + 1) as u16) << 8) };

    let getd = |i: usize| -> u32 {
        (get(i) as u32) + ((get(i + 1) as u32) << 8) + ((get(i + 2) as u32) << 16) +
        ((get(i + 3) as u32) << 24)
    };

    let gets = |start: usize, len: usize| -> String {
        (start..start + len).map(|i| get(i) as char).collect::<String>()
    };

    if gets(0, 2) == "BM" {
        // let file_size = getd(2);
        let offset = getd(0xA);
        // let header_size = getd(0xE);
        let width = getd(0x12);
        let height = getd(0x16);
        let depth = getw(0x1C) as u32;

        let bytes = (depth + 7) / 8;
        let row_bytes = (depth * width + 31) / 32 * 4;

        let mut blue_mask = 0xFF;
        let mut green_mask = 0xFF00;
        let mut red_mask = 0xFF0000;
        let mut alpha_mask = 0xFF000000;
        if getd(0x1E) == 3 {
            red_mask = getd(0x36);
            green_mask = getd(0x3A);
            blue_mask = getd(0x3E);
            alpha_mask = getd(0x42);
        }

        let mut blue_shift = 0;
        while blue_mask > 0 && blue_shift < 32 && (blue_mask >> blue_shift) & 1 == 0 {
            blue_shift += 1;
        }

        let mut green_shift = 0;
        while green_mask > 0 && green_shift < 32 && (green_mask >> green_shift) & 1 == 0 {
            green_shift += 1;
        }

        let mut red_shift = 0;
        while red_mask > 0 && red_shift < 32 && (red_mask >> red_shift) & 1 == 0 {
            red_shift += 1;
        }

        let mut alpha_shift = 0;
        while alpha_mask > 0 && alpha_shift < 32 && (alpha_mask >> alpha_shift) & 1 == 0 {
            alpha_shift += 1;
        }

        let mut data = Vec::with_capacity(width as usize * height as usize);

        for y in 0..height {
            for x in 0..width {
                let pixel_offset = offset + (height - y - 1) * row_bytes + x * bytes;

                let pixel_data = getd(pixel_offset as usize);
                let red = ((pixel_data & red_mask) >> red_shift) as u8;
                let green = ((pixel_data & green_mask) >> green_shift) as u8;
                let blue = ((pixel_data & blue_mask) >> blue_shift) as u8;
                let alpha = ((pixel_data & alpha_mask) >> alpha_shift) as u8;
                if bytes == 3 {
                    data.push(Color::rgb(red, green, blue));
                } else if bytes == 4 {
                    data.push(Color::rgba(red, green, blue, alpha));
                }
            }
        }

        // This is not Ok(Image::from...) because Image started to return an Option
        // It shouldn't ever return an Err in this case, unless there's an error somewhere
        // above
        Image::from_data(width, height, data.into_boxed_slice())
    }else{
        Err("BMP: invalid signature".to_string())
    }
}
