use std::iter;
use std::ops::{Deref, Range};

use itertools::Itertools;

use crate::error::{mk_err, mk_errv, OrcRes, Reporter};
use crate::interner::{intern, Tok};
use crate::location::Pos;
use crate::name::VPath;
use crate::tree::{AtomRepr, ExtraTok, Paren, TokTree, Token};
use crate::{api, intern};

pub fn name_start(c: char) -> bool { c.is_alphabetic() || c == '_' }
pub fn name_char(c: char) -> bool { name_start(c) || c.is_numeric() }
pub fn op_char(c: char) -> bool { !name_char(c) && !c.is_whitespace() && !"()[]{}\\".contains(c) }
pub fn unrep_space(c: char) -> bool { c.is_whitespace() && !"\r\n".contains(c) }

#[derive(Debug)]
pub struct Snippet<'a, 'b, A: AtomRepr, X: ExtraTok> {
  prev: &'a TokTree<'b, A, X>,
  cur: &'a [TokTree<'b, A, X>],
}
impl<'a, 'b, A: AtomRepr, X: ExtraTok> Snippet<'a, 'b, A, X> {
  pub fn new(prev: &'a TokTree<'b, A, X>, cur: &'a [TokTree<'b, A, X>]) -> Self {
    Self { prev, cur }
  }
  pub fn split_at(self, pos: u32) -> (Self, Self) {
    let fst = Self { prev: self.prev, cur: &self.cur[..pos as usize] };
    let new_prev = if pos == 0 { self.prev } else { &self.cur[pos as usize - 1] };
    let snd = Self { prev: new_prev, cur: &self.cur[pos as usize..] };
    (fst, snd)
  }
  pub fn find_idx(self, mut f: impl FnMut(&Token<'b, A, X>) -> bool) -> Option<u32> {
    self.cur.iter().position(|t| f(&t.tok)).map(|t| t as u32)
  }
  pub fn get(self, idx: u32) -> Option<&'a TokTree<'b, A, X>> { self.cur.get(idx as usize) }
  pub fn len(self) -> u32 { self.cur.len() as u32 }
  pub fn prev(self) -> &'a TokTree<'b, A, X> { self.prev }
  pub fn pos(self) -> Range<u32> {
    (self.cur.first().map(|f| f.range.start..self.cur.last().unwrap().range.end))
      .unwrap_or(self.prev.range.clone())
  }
  pub fn pop_front(self) -> Option<(&'a TokTree<'b, A, X>, Self)> {
    self.cur.first().map(|r| (r, self.split_at(1).1))
  }
  pub fn pop_back(self) -> Option<(Self, &'a TokTree<'b, A, X>)> {
    self.cur.last().map(|r| (self.split_at(self.len() - 1).0, r))
  }
  pub fn split_once(self, f: impl FnMut(&Token<'b, A, X>) -> bool) -> Option<(Self, Self)> {
    let idx = self.find_idx(f)?;
    Some((self.split_at(idx).0, self.split_at(idx + 1).1))
  }
  pub fn split(
    mut self,
    mut f: impl FnMut(&Token<'b, A, X>) -> bool,
  ) -> impl Iterator<Item = Self> {
    iter::from_fn(move || {
      self.is_empty().then_some(())?;
      let (ret, next) = self.split_once(&mut f).unwrap_or(self.split_at(self.len()));
      self = next;
      Some(ret)
    })
  }
  pub fn is_empty(self) -> bool { self.len() == 0 }
  pub fn skip_fluff(self) -> Self {
    let non_fluff_start = self.find_idx(|t| !matches!(t, Token::NS | Token::Comment(_)));
    self.split_at(non_fluff_start.unwrap_or(self.len())).1
  }
}
impl<'a, 'b, A: AtomRepr, X: ExtraTok> Copy for Snippet<'a, 'b, A, X> {}
impl<'a, 'b, A: AtomRepr, X: ExtraTok> Clone for Snippet<'a, 'b, A, X> {
  fn clone(&self) -> Self { *self }
}
impl<'a, 'b, A: AtomRepr, X: ExtraTok> Deref for Snippet<'a, 'b, A, X> {
  type Target = [TokTree<'b, A, X>];
  fn deref(&self) -> &Self::Target { self.cur }
}

/// Remove tokens that aren't meaningful in expression context, such as comments
/// or line breaks
pub fn strip_fluff<'a, A: AtomRepr, X: ExtraTok>(
  tt: &TokTree<'a, A, X>,
) -> Option<TokTree<'a, A, X>> {
  let tok = match &tt.tok {
    Token::BR => return None,
    Token::Comment(_) => return None,
    Token::LambdaHead(arg) => Token::LambdaHead(arg.iter().filter_map(strip_fluff).collect()),
    Token::S(p, b) => Token::S(*p, b.iter().filter_map(strip_fluff).collect()),
    t => t.clone(),
  };
  Some(TokTree { tok, range: tt.range.clone() })
}

#[derive(Clone, Debug)]
pub struct Comment {
  pub text: Tok<String>,
  pub pos: Pos,
}
impl Comment {
  pub fn to_api(&self) -> api::Comment {
    api::Comment { location: self.pos.to_api(), text: self.text.to_api() }
  }
  pub fn from_api(api: &api::Comment) -> Self {
    Self { pos: Pos::from_api(&api.location), text: Tok::from_api(api.text) }  
  }
}

pub fn line_items<'a, 'b, A: AtomRepr, X: ExtraTok>(
  snip: Snippet<'a, 'b, A, X>,
) -> Vec<Parsed<'a, 'b, Vec<Comment>, A, X>> {
  let mut items = Vec::new();
  let mut comments = Vec::new();
  for mut line in snip.split(|t| matches!(t, Token::BR)) {
    match &line.cur {
      [TokTree { tok: Token::S(Paren::Round, tokens), .. }] => line.cur = tokens,
      [] => continue,
      _ => (),
    }
    match line.find_idx(|t| !matches!(t, Token::Comment(_))) {
      None => comments.extend(line.cur),
      Some(i) => {
        let (cmts, tail) = line.split_at(i);
        let comments = Vec::from_iter(comments.drain(..).chain(cmts.cur).map(|t| match &t.tok {
          Token::Comment(c) => Comment { text: intern(&**c), pos: Pos::Range(t.range.clone()) },
          _ => unreachable!("All are comments checked above"),
        }));
        items.push(Parsed { output: comments, tail });
      },
    }
  }
  items
}

pub fn try_pop_no_fluff<'a, 'b, A: AtomRepr, X: ExtraTok>(
  snip: Snippet<'a, 'b, A, X>,
) -> ParseRes<'a, 'b, &'a TokTree<'b, A, X>, A, X> {
  snip.skip_fluff().pop_front().map(|(output, tail)| Parsed { output, tail }).ok_or_else(|| {
    mk_errv(
      intern!(str: "Unexpected end"),
      "Pattern ends abruptly",
      [Pos::Range(snip.pos()).into()],
    )
  })
}

pub fn expect_end(snip: Snippet<'_, '_, impl AtomRepr, impl ExtraTok>) -> OrcRes<()> {
  match snip.skip_fluff().get(0) {
    Some(surplus) => Err(mk_errv(
      intern!(str: "Extra code after end of line"),
      "Code found after the end of the line",
      [Pos::Range(surplus.range.clone()).into()],
    )),
    None => Ok(()),
  }
}

pub fn expect_tok<'a, 'b, A: AtomRepr, X: ExtraTok>(
  snip: Snippet<'a, 'b, A, X>,
  tok: Tok<String>,
) -> ParseRes<'a, 'b, (), A, X> {
  let Parsed { output: head, tail } = try_pop_no_fluff(snip)?;
  match &head.tok {
    Token::Name(n) if *n == tok => Ok(Parsed { output: (), tail }),
    t => Err(mk_errv(
      intern!(str: "Expected specific keyword"),
      format!("Expected {tok} but found {t}"),
      [Pos::Range(head.range.clone()).into()],
    )),
  }
}

pub struct Parsed<'a, 'b, T, A: AtomRepr, X: ExtraTok> {
  pub output: T,
  pub tail: Snippet<'a, 'b, A, X>,
}

pub type ParseRes<'a, 'b, T, A, X> = OrcRes<Parsed<'a, 'b, T, A, X>>;

pub fn parse_multiname<'a, 'b, A: AtomRepr, X: ExtraTok>(
  ctx: &impl Reporter,
  tail: Snippet<'a, 'b, A, X>,
) -> ParseRes<'a, 'b, Vec<(Import, Pos)>, A, X> {
  let ret = rec(ctx, tail);
  #[allow(clippy::type_complexity)] // it's an internal function
  pub fn rec<'a, 'b, A: AtomRepr, X: ExtraTok>(
    ctx: &impl Reporter,
    tail: Snippet<'a, 'b, A, X>,
  ) -> ParseRes<'a, 'b, Vec<(Vec<Tok<String>>, Option<Tok<String>>, Pos)>, A, X> {
    let comma = intern!(str: ",");
    let globstar = intern!(str: "*");
    let (name, tail) = tail.skip_fluff().pop_front().ok_or_else(|| {
      mk_err(intern!(str: "Expected name"), "Expected a name, a list of names, or a globstar.", [
        Pos::Range(tail.pos()).into(),
      ])
    })?;
    if let Some((Token::NS, tail)) = tail.skip_fluff().pop_front().map(|(tt, s)| (&tt.tok, s)) {
      let n = match &name.tok {
        Token::Name(n) if n.starts_with(name_start) => Ok(n),
        _ => Err(mk_err(intern!(str: "Unexpected name prefix"), "Only names can precede ::", [
          Pos::Range(name.range.clone()).into(),
        ])),
      };
      match (rec(ctx, tail), n) {
        (Err(ev), n) => Err(ev.extended(n.err())),
        (Ok(Parsed { tail, .. }), Err(e)) => {
          ctx.report(e);
          Ok(Parsed { output: vec![], tail })
        },
        (Ok(Parsed { tail, output }), Ok(pre)) => Ok(Parsed {
          output: output.into_iter().update(|i| i.0.push(pre.clone())).collect_vec(),
          tail,
        }),
      }
    } else {
      let output = match &name.tok {
        Token::Name(ntok) => {
          let nopt = match ntok {
            n if *n == globstar => None,
            n if n.starts_with(op_char) =>
              return Err(mk_errv(
                intern!(str: "Unescaped operator in multiname"),
                "Operators in multinames should be enclosed in []",
                [Pos::Range(name.range.clone()).into()],
              )),
            n => Some(n.clone()),
          };
          vec![(vec![], nopt, Pos::Range(name.range.clone()))]
        },
        Token::S(Paren::Square, b) => {
          let mut ok = Vec::new();
          b.iter().for_each(|tt| match &tt.tok {
            Token::Name(n) if n.starts_with(op_char) =>
              ok.push((vec![], Some(n.clone()), Pos::Range(tt.range.clone()))),
            Token::BR | Token::Comment(_) => (),
            _ => ctx.report(mk_err(
              intern!(str: "Non-operator in escapement in multiname"),
              "In multinames, [] functions as a literal name list reserved for operators",
              [Pos::Range(name.range.clone()).into()],
            )),
          });
          ok
        },
        Token::S(Paren::Round, b) => {
          let mut ok = Vec::new();
          let body = Snippet::new(name, b);
          for csent in body.split(|n| matches!(n, Token::Name(n) if *n == comma)) {
            match rec(ctx, csent) {
              Err(e) => ctx.report(e),
              Ok(Parsed { output, tail }) => match tail.get(0) {
                None => ok.extend(output),
                Some(t) => ctx.report(mk_err(
                  intern!(str: "Unexpected token in multiname group"),
                  "Unexpected token. Likely missing a :: or , or wanted [] instead of ()",
                  [Pos::Range(t.range.clone()).into()],
                )),
              },
            }
          }
          ok
        },
        t =>
          return Err(mk_errv(
            intern!(str: "Unrecognized name end"),
            format!("Names cannot end with {t} tokens"),
            [Pos::Range(name.range.clone()).into()],
          )),
      };
      Ok(Parsed { output, tail })
    }
  }
  ret.map(|Parsed { output, tail }| {
    let output = (output.into_iter())
      .map(|(p, name, pos)| (Import { path: VPath::new(p.into_iter().rev()), name }, pos))
      .collect_vec();
    Parsed { output, tail }
  })
}

/// A compound name, possibly ending with a globstar
#[derive(Debug, Clone)]
pub struct Import {
  pub path: VPath,
  pub name: Option<Tok<String>>,
}
impl Import {
  // pub fn from_api(i: api::CompName) -> Self {
  //   Self { path: VPath::new(i.path.into_iter().map(deintern)), name: i.name.map(deintern) }
  // }
  // pub fn to_api(&self) -> api::CompName {
  //   api::CompName {
  //     path: self.path.iter().map(|t| t.marker()).collect(),
  //     name: self.name.as_ref().map(|t| t.marker()),
  //   }
  // }
}

#[cfg(test)]
mod test {
  use never::Never;

  use super::Snippet;

  fn _covary_snip_a<'a, 'b>(
    x: Snippet<'static, 'b, Never, Never>,
  ) -> Snippet<'a, 'b, Never, Never> {
    x
  }
  fn _covary_snip_b<'a, 'b>(
    x: Snippet<'a, 'static, Never, Never>,
  ) -> Snippet<'a, 'b, Never, Never> {
    x
  }
}