extern crate nom;

use std::rc::Rc;
use std::str::FromStr;

use nom::IResult;
use nom::character::complete::{one_of, space0, alphanumeric0};
use nom::bytes::complete::{tag, take, take_while, take_while1, take_until};
use nom::combinator::{cut, cond, map, map_res, value, opt, verify};
use nom::multi::{separated_list, separated_nonempty_list, many1, many0};
use nom::error::{context, ParseError, VerboseError};
use nom::branch::alt;
use nom::sequence::{pair, tuple, delimited, preceded};

use crate::ast::*;
use crate::builtin::Builtin;

type ParseResult<'a, T> = IResult<&'a str, T, VerboseError<&'a str>>;

pub fn ws<I, O, E: ParseError<I>, F>(parser: F) -> impl Fn(I) -> IResult<I, O, E>
where
    I: nom::InputTakeAtPosition,
    <I as nom::InputTakeAtPosition>::Item: nom::AsChar + Clone,
    F: Fn(I) -> IResult<I, O, E>,
    {
      delimited(space0, parser, space0)
    }

fn statement_sep(text: &str) -> ParseResult<()> {
  value((), one_of("\n;"))(text)
}

fn single_alphabetic_character(text: &str) -> ParseResult<char> {
  let p = verify(take(1usize), |s: &str| s.chars().nth(0).map(|c| c.is_alphabetic()).unwrap_or(false));
  map(p, |s: &str| s.chars().nth(0).unwrap())(text)
}

fn single_alphanumeric_character(text: &str) -> ParseResult<char> {
  let p = verify(take(1usize), |s: &str| s.chars().nth(0).map(|c| c.is_alphanumeric() || c == '_').unwrap_or(false));
  map(p, |s: &str| s.chars().nth(0).unwrap())(text)
}

fn identifier(text: &str) -> ParseResult<Rc<String>> {
  use nom::character::complete::char;
  map(alt((
    pair(char('_'), many1(single_alphanumeric_character)),
    pair(single_alphabetic_character, many0(single_alphanumeric_character))
  )),
  |(first, rest): (char, Vec<char>)| Rc::new(format!("{}{}", first, rest.into_iter().collect::<String>()))
  )(text)
}

const OPERATOR_CHARS: &'static str = "~`!@#$%^&*-+=<>?/|";
fn operator(text: &str) -> ParseResult<Vec<char>> {
  many1(one_of(OPERATOR_CHARS))(text)
}

fn binop(text: &str) -> ParseResult<BinOp> {
  context("Binop", map(
      operator,
      |op| BinOp::from_sigil(&op.into_iter().collect::<String>())
  ))(text)
}

fn bool_literal(text: &str) -> ParseResult<ExpressionKind> {
  let p = alt((
    value(true, tag("true")),
    value(false, tag("false"))
  ));
  map(p, ExpressionKind::BoolLiteral)(text)
}

fn number_literal(text: &str) -> ParseResult<ExpressionKind> {
  let num_lit = many1(alt((
    map(one_of("1234567890"), |s: char| Some(s)),
    value(None, nom::character::complete::char('_')),
  )));

  let (text, n) = map_res(num_lit,
    |digits: Vec<Option<char>>| {
      let num_str: String = digits.into_iter().filter_map(|x| x).collect();
      u64::from_str_radix(&num_str, 10)
    })(text)?;

  Ok((text, ExpressionKind::NatLiteral(n)))
}

fn binary_literal(text: &str) -> ParseResult<ExpressionKind> {
  let p = preceded(tag("0b"), cut(take_while1(|c: char| c == '0' || c == '1')));
  let (rest, n): (&str, u64) = map_res(
    p, |hex_str: &str| u64::from_str_radix(hex_str, 2)
  )(text)?;
  let expr = ExpressionKind::NatLiteral(n);
  Ok((rest, expr))
}

fn hex_literal(text: &str) -> ParseResult<ExpressionKind> {
  let p = preceded(tag("0x"), cut(take_while1(|c: char| c.is_digit(16))));
  let (rest, n): (&str, u64) = map_res(
    p, |hex_str: &str| u64::from_str_radix(hex_str, 16)
  )(text)?;
  let expr = ExpressionKind::NatLiteral(n);
  Ok((rest, expr))
}

fn string_literal(text: &str) -> ParseResult<ExpressionKind> {
  use nom::character::complete::char;
  let (text, string_output) = delimited(
    char('"'), take_until("\""), char('"')
  )(text)?;
  let expr = ExpressionKind::StringLiteral(Rc::new(string_output.to_string()));
  Ok((text, expr))
}

fn literal(text: &str) -> ParseResult<ExpressionKind> {
  alt((
    string_literal,
    hex_literal,
    binary_literal,
    number_literal,
    bool_literal,
  ))(text)
}

fn paren_expr(text: &str) -> ParseResult<ExpressionKind> {
  use nom::character::complete::char;
  context("Paren expression", delimited(char('('), expression_kind, char(')')))(text)
}

fn prefix_op(text: &str) -> ParseResult<PrefixOp> {
  use nom::character::complete::char;
  let p = alt((char('+'), char('-'), char('!')));
  map(p, |sigil| PrefixOp::from_str(&sigil.to_string()).unwrap())(text)
}

fn qualified_name(text: &str) -> ParseResult<QualifiedName> {
  map(
    separated_nonempty_list(tag("::"), identifier),
    |components| QualifiedName { id: ItemId::new(0), components }
  )(text)
}

fn identifier_expr(text: &str) -> ParseResult<ExpressionKind> {
  map(qualified_name, ExpressionKind::Value)(text)
}

fn primary_expr(text: &str) -> ParseResult<ExpressionKind> {
  // primary := literal | paren_expr | if_expr | for_expr | while_expr | identifier_expr | lambda_expr | anonymous_struct | list_expr

  alt((
    if_expr,
    for_expr,
    literal,
    paren_expr,
    identifier_expr,
  ))(text)
}

fn for_expr(text: &str) -> ParseResult<ExpressionKind> {
  //TODO do I need something like no struct literal here?
  let en = alt((
    map(enumerator, |e| vec![e]),
    delimited(tag("{"), enumerators, tag("}"))
  ));
  preceded(tag("for"),
    map(tuple((en, for_expr_body)),
    |(enumerators, body)| ExpressionKind::ForExpression { enumerators, body: Box::new(body) }
  ))(text)
}

fn enumerators(text: &str) -> ParseResult<Vec<Enumerator>> {
  separated_nonempty_list(alt((value((), tag(",")), statement_sep)),
    enumerator)(text)
}

fn enumerator(text: &str) -> ParseResult<Enumerator> {
  map(
    tuple((identifier, tag("<-"), expression)),
  |(id, _, generator)| Enumerator { id, generator }
  )(text)
}

fn for_expr_body(text: &str) -> ParseResult<ForBody> {
  unimplemented!()
}

fn invocation_argument(text: &str) -> ParseResult<InvocationArgument> {
  use nom::character::complete::char;
  alt((
    value(InvocationArgument::Ignored, pair(char('_'), alphanumeric0)),
    map(expression_kind, |kind: ExpressionKind| InvocationArgument::Positional(
        Expression {  id: ItemId::new(0), kind, type_anno: None }))
    //map(identifier, |id: Rc<String>| 
  ))(text)
}

fn if_expr(text: &str) -> ParseResult<ExpressionKind> {
  let p = preceded(tag("if"), pair(ws(discriminator), ws(if_expr_body)));
  map(p, |(discriminator, body)| {
    let discriminator = discriminator.map(Box::new);
    let body = Box::new(body);
    ExpressionKind::IfExpression { discriminator, body }
  }) (text)
}

fn discriminator(text: &str) -> ParseResult<Option<Expression>> {
  use nom::combinator::verify;
  cond(text.chars().next().map(|c| c != '{').unwrap_or(true),
    expression
  )(text)
}

fn if_expr_body(text: &str) -> ParseResult<IfExpressionBody> {
  alt((
    preceded(tag("then"), simple_conditional),
    preceded(tag("is"), simple_pattern_match),
    cond_block,
  ))(text)
}

fn simple_conditional(text: &str) -> ParseResult<IfExpressionBody> {
  map(
    pair(expr_or_block, else_case),
    |(then_case, else_case)| IfExpressionBody::SimpleConditional { then_case, else_case }
  )(text)
}

fn else_case(text: &str) -> ParseResult<Option<Block>> {
  opt(preceded(tag("else"), expr_or_block))(text)
}

fn simple_pattern_match(text: &str) -> ParseResult<IfExpressionBody> {
  let p = tuple((pattern, tag("then"), expr_or_block, else_case));
  map(p, |(pattern, _, then_case, else_case)| 
    IfExpressionBody::SimplePatternMatch { pattern, then_case, else_case }
  )(text)
}

fn pattern(text: &str) -> ParseResult<Pattern> {
  use nom::character::complete::char;

  let t = delimited(char('('), 
    separated_nonempty_list(char(','), pattern),
    char(')')
  );

  alt((
    map(t, |patterns| Pattern::TuplePattern(patterns)),
    simple_pattern,
  ))(text)
}

fn simple_pattern(text: &str) -> ParseResult<Pattern> {
  alt((
    value(Pattern::Ignored, tag("_")),
    tuple_struct_pattern,
    record_pattern,
    map(pattern_literal, Pattern::Literal),
    map(qualified_name, Pattern::VarOrName),
  ))(text)
}

fn tuple_struct_pattern(text: &str) -> ParseResult<Pattern> {
  unimplemented!()
}

fn record_pattern(text: &str) -> ParseResult<Pattern> {
  unimplemented!()
}

fn pattern_literal(text: &str) -> ParseResult<PatternLiteral> {
  use PatternLiteral::*;
  use nom::character::complete::char;
  alt((
    value(BoolPattern(true), tag("true")),
    value(BoolPattern(false), tag("false")),
    map(delimited(char('"'), take_until("\""), char('"')), |s: &str| StringPattern(Rc::new(s.to_string()))),
  ))(text)
    //TODO handle signed_number_literal
}

fn cond_block(text: &str) -> ParseResult<IfExpressionBody> {
  use nom::character::complete::char;
  //TODO maybe change this bit of syntax
  let comma_or_delimitor = alt((value((), char(',')), statement_sep));
  let p = delimited(char('{'),
    separated_nonempty_list(comma_or_delimitor, cond_arm),
  char('}'));
  map(p, IfExpressionBody::CondList)(text)
}

fn cond_arm(text: &str) -> ParseResult<ConditionArm> {
  let variant_1 = map(
    tuple((condition, guard, tag("then"), expr_or_block)),
    |(condition, guard, _, body)| ConditionArm { condition, guard, body }
  );
  let variant_2 = map(
    preceded(tag("else"), expr_or_block),
    |body| ConditionArm { condition: Condition::Else, guard: None, body }
  );
  alt((variant_1, variant_2))(text)
}

fn condition(text: &str) -> ParseResult<Condition> {
  alt((
    map(preceded(tag("is"), pattern), Condition::Pattern),
    map(tuple((binop, expression)), |(op, expr)|
      Condition::TruncatedOp(op, expr)),
    map(expression, Condition::Expression),
  ))(text)
}

fn guard(text: &str) -> ParseResult<Option<Expression>> {
  opt(preceded(tag("if"), expression))(text)
}

fn expr_or_block(text: &str) -> ParseResult<Block> {
  //TODO fix
  alt((block, map(expression, |expr| vec![Statement { id: ItemId::new(0), kind: StatementKind::Expression(expr)}])))(text)
}

fn block(text: &str) -> ParseResult<Block> {
  use nom::character::complete::char;
  //TODO fix this so it can handle nested statements
  delimited(char('{'),
    separated_nonempty_list(statement_sep,
      map(expression, |e| Statement { id: ItemId::new(0), kind: StatementKind::Expression(e) })
    ),
  char('}'))(text)
}

fn call_expr(text: &str) -> ParseResult<ExpressionKind> {
  use nom::character::complete::char;
  let parse_call = opt(
    delimited(char('('), separated_list(char(','), invocation_argument), char(')'))
  );
  let p = pair(primary_expr, parse_call);
  map(p, |(expr, call_part)| if let Some(arguments) = call_part {
    let f = bx!(Expression { id: ItemId::new(0), kind: expr, type_anno: None }); 
    ExpressionKind::Call { f, arguments }
  } else {
    expr
  })(text)
}

fn prefix_expr(text: &str) -> ParseResult<ExpressionKind> {
  let (text, pfx) = ws(opt(prefix_op))(text)?;
  let (text, result) = call_expr(text)?;
  match pfx {
    None => Ok((text, result)),
    Some(pfx) => {
      let exp = Expression { id: ItemId::new(0), kind: result, type_anno: None }; 
      Ok((text, ExpressionKind::PrefixExp(pfx, Box::new(exp))))
    }
  }
}

// this implements Pratt parsing, see http://journal.stuffwithstuff.com/2011/03/19/pratt-parsers-expression-parsing-made-easy/
fn precedence_expr(text: &str) -> ParseResult<ExpressionKind> {
  fn inner_precedence_expr(input: &str, precedence: i32) -> ParseResult<ExpressionKind> {
    let (mut outer_rest, mut lhs) = prefix_expr(input)?;
    loop {
      let (rest, _) = space0(outer_rest)?;
      let (rest, maybe_binop) = opt(binop)(rest)?;
      let (new_precedence, binop) = match maybe_binop {
        Some(binop) => (binop.precedence(), binop),
        None => break,
      };

      if precedence >= new_precedence {
        break;
      }
      let (rest, _) = space0(rest)?;
      let (rest, rhs) = inner_precedence_expr(rest, new_precedence)?;
      outer_rest = rest;
      lhs = ExpressionKind::BinExp(binop,
        bx!(Expression::new(ItemId::new(0), lhs)),
        bx!(Expression::new(ItemId::new(0), rhs))
      );
    }
    Ok((outer_rest, lhs))
  }
  context("Precedence expression",
    |input| inner_precedence_expr(input, BinOp::min_precedence())
  )(text)
}

fn expression_kind(text: &str) -> ParseResult<ExpressionKind> {
  context("Expression kind", precedence_expr)(text)
}

fn type_anno(text: &str) -> ParseResult<TypeIdentifier> {
  use nom::character::complete::char;
  preceded(ws(char(':')), ws(type_name))(text)
}

fn type_name(text: &str) -> ParseResult<TypeIdentifier> {
  //TODO incomplete
  let (text, name) = identifier(text)?;
  let id = TypeIdentifier::Singleton(TypeSingletonName { name, params: vec![] });
  Ok((text, id))
}

fn expression(text: &str) -> ParseResult<Expression> {
  let (rest, (kind, type_anno)) = pair(expression_kind, opt(type_anno))(text)?;
  let expr = Expression { id: ItemId::new(0), kind, type_anno };
  Ok((rest, expr))
}

pub fn perform_parsing(input: &str) -> Result<String, String> {
  let output = match expression(input) {
    Ok((rest, ast)) => format!("{:?} (rest: {})", ast, rest),
    Err(nom::Err::Incomplete(needed)) => format!("Incomplete: {:?}" ,needed),
    Err(nom::Err::Error(verbose_error) | nom::Err::Failure(verbose_error)) => {
      format!("Verbose Error: ` {:?} `", verbose_error)
      //nom::error::convert_error(input, verbose_error)
    }
  };
      
  Ok(output)
}