use std::fmt::Display;
use std::io::Write;

/// An SVG document
pub struct SVG {
    stuff: Vec<Box<dyn AsSVG>>,
    size: (f64, f64),
}

fn xml_tag(w: &mut Vec<u8>, name: &str, attrs: &[(&str, &dyn Display)]) {
    write!(w, "<{}", name);
    for (k, v) in attrs {
        write!(w, " {}=\"{}\"", k, v);
    }
    writeln!(w, "/>");
}

fn xml_open(w: &mut Vec<u8>, name: &str, attrs: &[(&str, &dyn Display)]) {
    write!(w, "<{}", name);
    for (k, v) in attrs {
        write!(w, " {}=\"{}\"", k, v);
    }
    writeln!(w, ">");
}

fn xml_close(w: &mut Vec<u8>, name: &str) {
    write!(w, "<{}/>", name);
}

/// Create a new empty SVG document of the specified width and height
pub fn svg(w: f64, h: f64) -> SVG {
    SVG {
        stuff: Vec::new(),
        size: (w, h),
    }
}

impl SVG {
    /// Print this SVG document to stdout
    pub fn to_stdout(self) {
        let buf = self.to_bytes();
        println!("{}", String::from_utf8(buf).unwrap());
    }

    /// Write this SVG document to a file
    pub fn to_file<W: Write>(self, w: &mut W) -> Result<(), std::io::Error> {
        let buf = self.to_bytes();
        w.write(&buf)?;
        Ok(())
    }

    pub fn to_bytes(self) -> Vec<u8> {
        let mut buf = Vec::new();
        let (w, h) = self.size;
        writeln!(buf, "<?xml version=\"1.0\" encoding=\"UTF-8\" ?>");
        xml_open(
            &mut buf, "svg",
            &[("xmlns", &"http://www.w3.org/2000/svg"),
              ("version", &"1.1"),
              ("width", &w),
              ("height", &h),
            ],
        );
        for elem in self.stuff {
            elem.draw_svg(&mut buf);
        }
        xml_close(&mut buf, "svg");
        buf
    }

    /// Add a new drawable thing to this SVG document
    pub fn add<T: AsSVG>(&mut self, t: T) {
        self.stuff.push(t.consume())
    }
}



/// The AsSVG trait represents things which can be rendered to an SVG
/// canvas.
pub trait AsSVG {
    fn draw_svg(&self, buf: &mut Vec<u8>);
    // This is a bit of a hack to make sure that all of our types live
    // long enough: it's now on the implementer of AsSVG to box it up
    // and make sure that we can keep a trait object around.
    fn consume(self) -> Box<AsSVG>;
}

/// A Line is a sequence of points. It'll be represented as a single
/// dot if it has only one point, and otherwise will be drawn as a
/// line between them.
pub struct Line {
    start: (f64, f64),
    points: Vec<(f64, f64)>,
}

impl AsSVG for Line {
    fn draw_svg(&self, buf: &mut Vec<u8>) {
        if self.points.len() == 0 {
            // if there are no later points, then we just draw a
            // 'point' at the starting position, which is just a tiny
            // circle
            let (x, y) = self.start;
            xml_tag(
                buf, "circle",
                &[("cx", &x),
                  ("cy", &y),
                  ("r", &"0.5"),
                  ("fill", &"black"),
                ],
            );
        } else {
            // Otherwise, we draw a path, which mean assembling this
            // somewhat wonky path field

            let path = {
                let mut path = Vec::new();
                let (x, y) = self.start;
                write!(&mut path, "M{} {}", x, y);
                for (x, y) in self.points.iter() {
                    write!(&mut path, " L{} {}", x, y);
                }
                String::from_utf8(path).unwrap()
            };

            xml_tag(
                buf, "path",
                &[("d", &path), ("stroke", &"black")],
            );
        }
    }

    fn consume(self) -> Box<AsSVG> {
        Box::new(self)
    }
}

/// Create a new line at the given starting point
pub fn line(x: f64, y: f64) -> Line {
    Line::new(x, y)
}

impl Line {
    /// Create a new line at the given starting point
    pub fn new(x: f64, y: f64) -> Line {
        Line {
            start: (x, y),
            points: Vec::new(),
        }
    }

    /// Draw a line segment from this point to another point
    pub fn draw_to(mut self, x: f64, y: f64) -> Line {
        self.points.push((x, y));
        self
    }
}

pub struct Rect {
    position: (f64, f64),
    size: (f64, f64),
}

pub fn rect(position: (f64, f64), size: (f64, f64)) -> Rect {
    Rect { position, size }
}

impl AsSVG for Rect {
    fn draw_svg(&self, buf: &mut Vec<u8>) {
        let (x, y) = self.position;
        let (w, h) = self.size;
        xml_tag(
            buf, "rect",
            &[("x", &x),
              ("y", &y),
              ("width", &w),
              ("height", &h),
              ("stroke", &"black"),
              ("fill", &"white"),
            ]
        );
    }

    fn consume(self) -> Box<AsSVG> {
        Box::new(self)
    }
}


pub struct Circle {
    position: (f64, f64),
    radius: f64,
}

pub fn circle(position: (f64, f64), radius: f64) -> Circle {
    Circle { position, radius }
}

impl AsSVG for Circle {
    fn draw_svg(&self, buf: &mut Vec<u8>) {
        let (x, y) = self.position;
        let r = self.radius;
        xml_tag(
            buf, "circle",
            &[("cx", &x),
              ("cy", &y),
              ("r", &r),
              ("stroke", &"black"),
              ("fill", &"white"),
            ]
        );
    }

    fn consume(self) -> Box<AsSVG> {
        Box::new(self)
    }
}