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use std::fs::File;
use std::io::prelude::*;

// Data buffer for image
#[derive(Clone)]
pub struct Ppm {
    pub width: usize,
    pub height: usize,
    pub data: Vec<u8>,
}

impl Ppm {
    pub fn new(width: usize, height: usize) -> Ppm {
        Ppm {
            width,
            height,
            data: vec![0; width * height * 3],
        }
    }

    pub fn read(filename: String) -> Result<Ppm, std::io::Error> {
        // Open the file
        let file = File::open(filename)?;
        let mut reader = std::io::BufReader::new(file);

        let mut line = String::new();
        let _ = reader.read_line(&mut line)?;

        // Check the file type
        if line.len() < 2 || &line[0..2] != "P3" {
            return Err(std::io::Error::new(std::io::ErrorKind::Other, "Invalid image header - only P3 is supported"));
        }

        // Read dimensions from header
        line.clear();
        while line.is_empty() {
            let _ = reader.read_line(&mut line)?;
        }
        let dimensions = line.split_whitespace().collect::<Vec<&str>>();
        if dimensions.len() < 2 {
            return Err(std::io::Error::new(std::io::ErrorKind::Other, "Invalid image dimensions"));
        }
        let width: usize = dimensions[0].parse().unwrap_or(0);
        let height: usize = dimensions[1].parse().unwrap_or(0);
        if width == 0 || height == 0 {
            return Err(std::io::Error::new(std::io::ErrorKind::Other, "Invalid image dimensions"));
        }

        // Read max field value
        line.clear();
        while line.is_empty() {
            let _ = reader.read_line(&mut line)?;
        }
        if line.len() < 3 || &line[0..3] != "255" {
            return Err(std::io::Error::new(std::io::ErrorKind::Other, "Invalid pixel type, only '255' is supported"));
        }

        let mut ppm = Ppm::new(width, height);

        // Now load the image data
        let mut row : usize = 0;
        loop {
            line.clear();
            let len = reader.read_line(&mut line)?;
            if len == 0 { break; }

            let bytes = line.split_whitespace().collect::<Vec<&str>>();
            let mut index : usize = 0;
            for byte in bytes {
                ppm.data[(row * ppm.width * 3) + index] = byte.parse().unwrap_or(0);
                index += 1;
            }

            row += 1;
        }

        Ok(ppm)
    }

    pub fn write(&self, filename: String) -> std::io::Result<()> {
        let mut file = File::create(filename)?;

        // Colours are ascii
        write!(&mut file, "P3\n")?;
        // Columns, Rows
        write!(&mut file, "{} {}\n", self.width, self.height)?;
        // Maximum value of a colour
        write!(&mut file, "255\n")?;

        for y in 0..self.height {
            for x in 0..self.width {
                let offset = (y * self.width * 3) + x * 3;
                write!(&mut file, "{} {} {} ", 
                        self.data[offset + 0],
                        self.data[offset + 1],
                        self.data[offset + 2]
                        )?;
            }
            write!(&mut file, "\n")?;
        }

        Ok(())
    }

    pub fn set_pixel(&mut self, x: usize, y: usize, r: u8, g: u8, b: u8) {
        let offset = (y * self.width * 3) + x * 3;
        self.data[offset + 0] = r;
        self.data[offset + 1] = g;
        self.data[offset + 2] = b;
    }

    pub fn get_pixel(&self, x: usize, y: usize) -> (u8, u8, u8) {
        let offset = (y * self.width * 3) + x * 3;
        (
            self.data[offset + 0],
            self.data[offset + 1],
            self.data[offset + 2],
        )
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn round_trip() {
        // Make an image
        let width = 10;
        let height = 5;
        let mut orig = Ppm::new(width, height);
        for y in 0..height {
            for x in 0..width {
                orig.set_pixel(x, y, x as u8, y as u8, 0x22);
            }
        }

        // Save it
        let filename = "/tmp/test.ppm";
        orig.write(String::from(filename)).unwrap();
        
        // Load it
        let read_back = Ppm::read(String::from(filename)).unwrap();

        // And verify
        assert_eq!(read_back.width, width);
        assert_eq!(read_back.height, height);
        assert_eq!(read_back.data, orig.data);

        for y in 0..height {
            for x in 0..width {
                let (r,g,b) = read_back.get_pixel(x, y);
                assert_eq!(r, x as u8);
                assert_eq!(g, y as u8);
                assert_eq!(b, 0x22);
            }
        }
    }
}