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use std::borrow::Cow;
use std::cmp;
use std::io;
use std::ops::Deref;

pub use self::Doc::{Nil, Append, Space, Group, Nest, Newline, Text};

#[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
enum Mode {
    Break,
    Flat,
}

/// The concrete document type. This type is not meant to be used directly. Instead use the static
/// functions on `Doc` or the methods on an `DocAllocator`.
///
/// The `B` parameter is used to abstract over pointers to `Doc`. See `RefDoc` and `BoxDoc` for how
/// it is used
#[derive(Clone, Debug, Eq, Ord, PartialEq, PartialOrd)]
pub enum Doc<'a, B> {
    Nil,
    Append(B, B),
    Group(B),
    Nest(usize, B),
    Space,
    Newline,
    Text(Cow<'a, str>),
}

impl<'a, B, S> From<S> for Doc<'a, B>
    where S: Into<Cow<'a, str>>
{
    fn from(s: S) -> Doc<'a, B> {
        Doc::Text(s.into())
    }
}

impl<'a, B> Doc<'a, B> {
    /// Writes a rendered document.
    #[inline]
    pub fn render<'b, W: ?Sized + io::Write>(&'b self, width: usize, out: &mut W) -> io::Result<()>
        where B: Deref<Target = Doc<'b, B>>
    {
        best(self, width, out)
    }
}

type Cmd<'a, B> = (usize, Mode, &'a Doc<'a, B>);

fn write_newline<W: ?Sized + io::Write>(ind: usize, out: &mut W) -> io::Result<()> {
    try!(out.write_all(b"\n"));
    write_spaces(ind, out)
}

fn write_spaces<W: ?Sized + io::Write>(spaces: usize, out: &mut W) -> io::Result<()> {
    const SPACES: [u8; 100] = [b' '; 100];
    let mut inserted = 0;
    while inserted < spaces {
        let insert = cmp::min(100, spaces - inserted);
        inserted += try!(out.write(&SPACES[..insert]));
    }
    Ok(())
}

#[inline]
fn fitting<'a, B>(next: Cmd<'a, B>,
                  bcmds: &Vec<Cmd<'a, B>>,
                  fcmds: &mut Vec<Cmd<'a, B>>,
                  mut rem: isize)
                  -> bool
    where B: Deref<Target = Doc<'a, B>>
{
    let mut bidx = bcmds.len();
    fcmds.clear(); // clear from previous calls from best
    fcmds.push(next);
    while rem >= 0 {
        match fcmds.pop() {
            None => {
                if bidx == 0 {
                    // All commands have been processed
                    return true;
                } else {
                    fcmds.push(bcmds[bidx - 1]);
                    bidx -= 1;
                }
            }
            Some((ind, mode, doc)) => {
                match doc {
                    &Nil => {}
                    &Append(ref ldoc, ref rdoc) => {
                        fcmds.push((ind, mode, rdoc));
                        // Since appended documents often appear in sequence on the left side we
                        // gain a slight performance increase by batching these pushes (avoiding
                        // to push and directly pop `Append` documents)
                        let mut doc = ldoc;
                        while let Append(ref l, ref r) = **doc {
                            fcmds.push((ind, mode, r));
                            doc = l;
                        }
                        fcmds.push((ind, mode, doc));
                    }
                    &Group(ref doc) => {
                        fcmds.push((ind, mode, doc));
                    }
                    &Nest(off, ref doc) => {
                        fcmds.push((ind + off, mode, doc));
                    }
                    &Space => {
                        match mode {
                            Mode::Flat => {
                                rem -= 1;
                            }
                            Mode::Break => {
                                return true;
                            }
                        }
                    }
                    &Newline => return true,
                    &Text(ref str) => {
                        rem -= str.len() as isize;
                    }
                }
            }
        }
    }
    false
}

#[inline]
pub fn best<'a, W: ?Sized + io::Write, B>(doc: &'a Doc<'a, B>,
                                          width: usize,
                                          out: &mut W)
                                          -> io::Result<()>
    where B: Deref<Target = Doc<'a, B>>
{
    let mut pos = 0usize;
    let mut bcmds = vec![(0usize, Mode::Break, doc)];
    let mut fcmds = vec![];
    while let Some((ind, mode, doc)) = bcmds.pop() {
        match doc {
            &Nil => {}
            &Append(ref ldoc, ref rdoc) => {
                bcmds.push((ind, mode, rdoc));
                let mut doc = ldoc;
                while let Append(ref l, ref r) = **doc {
                    bcmds.push((ind, mode, r));
                    doc = l;
                }
                bcmds.push((ind, mode, doc));
            }
            &Group(ref doc) => {
                match mode {
                    Mode::Flat => {
                        bcmds.push((ind, Mode::Flat, doc));
                    }
                    Mode::Break => {
                        let next = (ind, Mode::Flat, &**doc);
                        let rem = width as isize - pos as isize;
                        if fitting(next, &bcmds, &mut fcmds, rem) {
                            bcmds.push(next);
                        } else {
                            bcmds.push((ind, Mode::Break, doc));
                        }
                    }
                }
            }
            &Nest(off, ref doc) => {
                bcmds.push((ind + off, mode, doc));
            }
            &Space => {
                match mode {
                    Mode::Flat => {
                        try!(write_spaces(1, out));
                    }
                    Mode::Break => {
                        try!(write_newline(ind, out));
                    }
                }
                pos = ind;
            }
            &Newline => {
                try!(write_newline(ind, out));
                pos = ind;
            }
            &Text(ref s) => {
                try!(out.write_all(&s.as_bytes()));
                pos += s.len();
            }
        }
    }
    Ok(())
}