#![feature(proc_macro_diagnostic)]

use std::ops::ControlFlow;
use proc_macro::TokenStream;
use proc_macro2::{ TokenStream as Quoted };
use std::fmt::Debug;
use quote::quote;
use syn::{
  parse_macro_input,
  parenthesized,
  parse::{
    Parse,
    Result,
    ParseStream,
    discouraged::Speculative
  },
  Error,
  Ident,
  LitStr
};

fn _parsed<T: Parse>(
  input: ParseStream
) -> Result<T> {
  let _input = input.fork();
  match _input.parse::<T>() {
    Err(error) => Err(error),
    Ok(result) => {
      input.advance_to(&_input);
      Ok(result)
    }
  }
}

fn _parse_any<T>(
  input: ParseStream,
  parsers: Vec<fn(ParseStream) -> Result<T>>
) -> Result<T> {
  let result = parsers.iter().try_fold(Vec::new(), |mut errors, parser| {
    let _input = input.fork();
    match parser(&_input) {
      Ok(value) => {
        input.advance_to(&_input);
        ControlFlow::Break(value)
      }
      Err(new_error) => {
        errors.push(new_error);
        ControlFlow::Continue(errors)
      }
    }
  });
  match result {
    ControlFlow::Break(value) => Ok(value),
    ControlFlow::Continue(errors) => {
      let error = Error::new(input.span(), "Failed to parse any");
      Err(errors.iter().cloned().fold(error, |mut out_error, in_error| {
        out_error.combine(in_error);
        out_error
      }))
    }
  }
}

fn _parse_group<T>(
  input: ParseStream,
  parser: fn(ParseStream) -> Result<T>
) -> Result<T> {
  let content;
  parenthesized!(content in input);
  parser(&content)
}

#[derive(Debug, Clone)]
enum UnaryOp {
  Fix,
  Grp,
  Seq,
  Nest,
  Pack
}

fn _parse_unary_op(
  input: ParseStream
) -> Result<UnaryOp> {
  let item: Ident = input.parse()?;
  match item.to_string().as_str() {
    "fix" => Ok(UnaryOp::Fix),
    "grp" => Ok(UnaryOp::Grp),
    "seq" => Ok(UnaryOp::Seq),
    "nest" => Ok(UnaryOp::Nest),
    "pack" => Ok(UnaryOp::Pack),
    _ => Err(Error::new(item.span(), "Expected a unary operator"))
  }
}

mod binary_tokens {
  use syn::custom_punctuation;
  custom_punctuation!(Unpadded, &);
  custom_punctuation!(Padded, +);
  custom_punctuation!(FixedUnpadded, !&);
  custom_punctuation!(FixedPadded, !+);
  custom_punctuation!(Newline, @);
  custom_punctuation!(DoubleNewline, @@);
}

#[derive(Debug, Clone)]
enum BinaryOp {
  Unpadded,
  Padded,
  FixedUnpadded,
  FixedPadded,
  Newline,
  DoubleNewline
}

fn _parse_binary_op(
  input: ParseStream
) -> Result<BinaryOp> {
  use binary_tokens::*;
  _parse_any(input, vec![
    |input| _parsed::<Unpadded>(input).map(|_| BinaryOp::Unpadded),
    |input| _parsed::<Padded>(input).map(|_| BinaryOp::Padded),
    |input| _parsed::<FixedUnpadded>(input).map(|_| BinaryOp::FixedUnpadded),
    |input| _parsed::<FixedPadded>(input).map(|_| BinaryOp::FixedPadded),
    |input| _parsed::<DoubleNewline>(input).map(|_| BinaryOp::DoubleNewline),
    |input| _parsed::<Newline>(input).map(|_| BinaryOp::Newline),
  ])
}

#[derive(Debug, Clone)]
enum AST {
  Null,
  Variable(Ident),
  Text(String),
  Unary(UnaryOp, Box<AST>),
  Binary(BinaryOp, Box<AST>, Box<AST>)
}

fn _parse_null(
  input: ParseStream
) -> Result<Box<AST>> {
  let item: Ident = input.parse()?;
  match item.to_string().as_str() {
    "null" => Ok(Box::new(AST::Null)),
    _ => Err(Error::new(item.span(), "Expected a unary operator"))
  }
}

fn _parse_variable(
  input: ParseStream
) -> Result<Box<AST>> {
  let name = _parsed::<Ident>(input)?;
  Ok(Box::new(AST::Variable(name)))
}

fn _parse_text(
  input: ParseStream
) -> Result<Box<AST>> {
  let data = _parsed::<LitStr>(input)?;
  Ok(Box::new(AST::Text(data.value())))
}

fn _parse_group_ast(
  input: ParseStream
) -> Result<Box<AST>> {
  _parse_group(input, _parse_ast)
}

fn _parse_primary(
  input: ParseStream
) -> Result<Box<AST>> {
  _parse_any(input, vec![
    _parse_null,
    _parse_variable,
    _parse_text,
    _parse_group_ast
  ])
}

fn _parse_atom(
  input: ParseStream
) -> Result<Box<AST>> {
  _parse_any(input, vec![
    _parse_unary,
    _parse_primary
  ])
}

fn _parse_unary(
  input: ParseStream
) -> Result<Box<AST>> {
  let op = _parse_unary_op(input)?;
  let ast = _parse_primary(input)?;
  Ok(Box::new(AST::Unary(op, ast)))
}

fn _parse_binary(
  input: ParseStream
) -> Result<Box<AST>> {
  let left = _parse_atom(input)?;
  let op = _parse_binary_op(input)?;
  let right = _parse_ast(input)?;
  Ok(Box::new(AST::Binary(op, left, right)))
}

fn _parse_ast(
  input: ParseStream
) -> Result<Box<AST>> {
  _parse_any(input, vec![
    _parse_binary,
    _parse_atom
  ])
}

impl Parse for Box<AST> {
  fn parse(input: ParseStream) -> Result<Self> {
    let _input = input.fork();
    match _parse_ast(&_input) {
      Err(error) => Err(error),
      Ok(result) => {
        input.advance_to(&_input);
        if input.is_empty() {
          Ok(result)
        } else {
          Err(Error::new(
            input.span(),
            format!("Failed to parse layout:\n{}", input.to_string())
          ))
        }
      }
    }
  }
}

fn _reify_layout(ast: Box<AST>) -> Quoted {
  match *ast {
    AST::Null => quote! { typeset::null() },
    AST::Variable(name) => quote! { #name.clone() },
    AST::Text(data) => quote! { typeset::text(#data.to_string()) },
    AST::Unary(UnaryOp::Fix, ast1) => {
      let layout = _reify_layout(ast1);
      quote! { typeset::fix(#layout) }
    }
    AST::Unary(UnaryOp::Grp, ast1) => {
      let layout = _reify_layout(ast1);
      quote! { typeset::grp(#layout) }
    }
    AST::Unary(UnaryOp::Seq, ast1) => {
      let layout = _reify_layout(ast1);
      quote! { typeset::seq(#layout) }
    }
    AST::Unary(UnaryOp::Nest, ast1) => {
      let layout = _reify_layout(ast1);
      quote! { typeset::nest(#layout) }
    }
    AST::Unary(UnaryOp::Pack, ast1) => {
      let layout = _reify_layout(ast1);
      quote! { typeset::pack(#layout) }
    }
    AST::Binary(BinaryOp::Unpadded, left, right) => {
      let left_layout = _reify_layout(left);
      let right_layout = _reify_layout(right);
      quote! {
        typeset::comp(
          #left_layout,
          #right_layout,
          false,
          false
        )
      }
    }
    AST::Binary(BinaryOp::Padded, left, right) => {
      let left_layout = _reify_layout(left);
      let right_layout = _reify_layout(right);
      quote! {
        typeset::comp(
          #left_layout,
          #right_layout,
          true,
          false
        )
      }
    }
    AST::Binary(BinaryOp::FixedUnpadded, left, right) => {
      let left_layout = _reify_layout(left);
      let right_layout = _reify_layout(right);
      quote! {
        typeset::comp(
          #left_layout,
          #right_layout,
          false,
          true
        )
      }
    }
    AST::Binary(BinaryOp::FixedPadded, left, right) => {
      let left_layout = _reify_layout(left);
      let right_layout = _reify_layout(right);
      quote! {
        typeset::comp(
          #left_layout,
          #right_layout,
          true,
          true
        )
      }
    }
    AST::Binary(BinaryOp::Newline, left, right) => {
      let left_layout = _reify_layout(left);
      let right_layout = _reify_layout(right);
      quote! {
        typeset::line(
          #left_layout,
          #right_layout
        )
      }
    }
    AST::Binary(BinaryOp::DoubleNewline, left, right) => {
      let left_layout = _reify_layout(left);
      let right_layout = _reify_layout(right);
      quote! {
        typeset::line(
          #left_layout,
          typeset::line(
            typeset::null(),
            #right_layout
          )
        )
      }
    }
  }
}

#[proc_macro]
pub fn layout(input: TokenStream) -> TokenStream {
  let ast = parse_macro_input!(input as Box<AST>);
  let output = _reify_layout(ast);
  quote! { #output }.into()
}