#[cfg(test)]
use std::fmt::Debug;

use unicode_xid::UnicodeXID;

use nom::Slice;
use nom::types::CompleteStr;
use nom_locate::LocatedSpan;
pub(crate) type StrSpan<'a> = LocatedSpan<CompleteStr<'a>>;


/// Like `ws!()`, but does not allow newlines.
macro_rules! ws_nonl (
  ($i:expr, $($args:tt)*) => (
    {
      use nom::Convert;
      use nom::Err;

      match sep!($i, $crate::helpers::spaces_nonl, $($args)*) {
        Err(e) => Err(e),
        Ok((i1,o))    => {
          match $crate::helpers::spaces_nonl(i1) {
            Err(e) => Err(Err::convert(e)),
            Ok((i2,_))    => Ok((i2, o))
          }
        }
      }
    }
  )
);

/// Like `ws!()`, but ignores comments as well
macro_rules! ws_comm (
  ($i:expr, $($args:tt)*) => (
    {
      use nom::Convert;
      use nom::Err;

      match sep!($i, $crate::helpers::spaces_nl, $($args)*) {
        Err(e) => Err(e),
        Ok((i1,o))    => {
          match $crate::helpers::spaces_nl(i1) {
            Err(e) => Err(Err::convert(e)),
            Ok((i2,_))    => Ok((i2, o))
          }
        }
      }
    }
  )
);

named!(escaped_newline<StrSpan, ()>,
  map!(terminated!(char!('\\'), char!('\n')), |_| ())
);

named!(pub spaces_nl<StrSpan, ()>,
  map!(many0!(alt!(one_of!(" \t\x0c") => { |_|() } | escaped_newline | newline)), |_| ())
);

// Bottleneck:
// named!(pub spaces_nonl<StrSpan, ()>,
//   map!(many0!(alt!(one_of!(" \t\x0c") => { |_| () }|escaped_newline)), |_| ())
// );
// Rewritten as:
pub fn spaces_nonl(i: StrSpan) -> Result<(StrSpan, ()), ::nom::Err<StrSpan>> {
    let mut it = i.fragment.chars().enumerate().peekable();
    while let Some((index, c)) = it.next() {
        let next_char = it.peek().map(|(_,c)|*c);
        match c {
            ' ' | '\t' | '\x0c' => (),
            '\\' if next_char.unwrap_or(' ') == '\n' => {it.next();},
            _ => {
                if index == 0 {
                    return Ok((i, ()))
                }
                else {
                    return Ok((i.slice(index..), ()))
                }
            },
        }
    }
    Ok((i.slice(i.fragment.len()..), ()))
}

named!(pub space_sep_nl<StrSpan, ()>,
  map!(many1!(alt!(one_of!(" \t\x0c") => { |_|() } | escaped_newline | newline)), |_| ())
);

named!(pub space_sep_nonl<StrSpan, ()>,
  map!(many1!(alt!(one_of!(" \t\x0c") => { |_| () } | escaped_newline)), |_| ())
);

// Let me explain this ugliness.
//
// We allow newlines in expressions if and only if the newline is
// wrapped in parenthesis, square brackets, or curly brackets.
// As any given subparser can be used either in or out one of these
// pairs, we need either:
//
// 1. a boolean argument to the subparser telling whether it is wrapped
//    in one of these pairs or not
// 2. two versions of each subparser
//
// The first version has the downside of requiring run-time checks, whereas
// the second one resolves everything at compile-time.
//
// Since I do not want to write each subparser twice, I'm writing them
// in the impl{} of a polymorphic structure, which has a static boolean
// argument corresponding to newlines, so monomorphing the structure
// generates the two subparsers. Then, a simple constant propagation
// is able to get rid of the runtime checks for this boolean.
pub(crate) trait AreNewlinesSpaces { const VALUE: bool; }
pub(crate) struct NewlinesAreSpaces; impl AreNewlinesSpaces for NewlinesAreSpaces { const VALUE: bool = true; }
pub(crate) struct NewlinesAreNotSpaces; impl AreNewlinesSpaces for NewlinesAreNotSpaces { const VALUE: bool = false; }

macro_rules! spaces {
    ( $i:expr, $($args:tt)* ) => {
        match ANS::VALUE {
            true => call!($i, $crate::helpers::spaces_nl, $($args)*),
            false => call!($i, $crate::helpers::spaces_nonl, $($args)*),
        }
    }
}

macro_rules! ws_auto {
    ( $i:expr, $($args:tt)* ) => {
        delimited!($i, spaces!(), $($args)*, spaces!())
    }
}

macro_rules! space_sep {
    ( $i:expr, $($args:tt)* ) => {
        match ANS::VALUE {
            true => call!($i, $crate::helpers::space_sep_nl, $($args)*),
            false => call!($i, $crate::helpers::space_sep_nonl, $($args)*),
        }
    }
}

const KEYWORDS: [&'static str; 2] = ["yield", "import"];
named!(pub name<StrSpan, String>,
  do_parse!(
    name: map!(
      tuple!(
        alt!(char!('_') | verify!(call!(::nom::anychar), |c| UnicodeXID::is_xid_start(c))),
        take_while!(call!(|c| UnicodeXID::is_xid_continue(c)))
      ), |(c, s)| format!("{}{}", c, s.fragment)
    ) >>
    verify!(tag!(""), |_| !KEYWORDS.contains(&&name[..])) >>
    (name)
  )
);

named!(pub word_end<StrSpan, ()>,
  not!(verify!(peek!(::nom::anychar), |c| UnicodeXID::is_xid_continue(c)))
);

macro_rules! keyword {
    ($i:expr, $kw:expr) => { terminated!($i, tag!($kw), word_end) }
}

named!(pub newline<StrSpan, ()>,
  map!(
    many1!(
      tuple!(
        spaces_nonl,
        opt!(preceded!(char!('#'), many0!(none_of!("\n")))),
        char!('\n')
      )
    ),
    |_| ()
  )
);

named!(pub semicolon<StrSpan, ()>,
  map!(ws_nonl!(char!(';')), |_| ())
);

/// Helper to make an instance of `StrSpan`, that can be used as the argument
/// to other parsers.
pub fn make_strspan(s: &str) -> StrSpan {
    StrSpan::new(CompleteStr(s))
}

#[cfg(test)]
pub(crate) fn assert_parse_eq<T: Debug + PartialEq>(
        left:  Result<(StrSpan, T), ::nom::Err<StrSpan>>,
        right: Result<(StrSpan, T), ::nom::Err<StrSpan>>,
        ) {
    use nom::Context;
    match (left, right) {
        (Ok((left_span, left_tree)), Ok((right_span, right_tree))) =>
            assert_eq!(((left_span.fragment, left_tree)), ((right_span.fragment, right_tree))),
        (Err(::nom::Err::Failure(Context::Code(left_span, left_code))), Err(::nom::Err::Failure(Context::Code(right_span, right_code)))) =>
            assert_eq!((left_span.fragment, left_code), (right_span.fragment, right_code)),
        (Err(::nom::Err::Incomplete(_)), _) => unreachable!(),
        (_, Err(::nom::Err::Incomplete(_))) => panic!("We're only using complete strings here!"),
        (l, r) => assert_eq!(l, r),
    }
}

pub(crate) fn first_word(i: StrSpan) -> Result<(StrSpan, &str), ::nom::Err<StrSpan>> {
    match ::nom::alpha(i) {
        Ok((i, s)) => Ok((i, s.fragment.0)),
        Err(e) => Err(e),
    }
}