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use std::io::{Read,Seek};

use crate::nom::{
    IResult,
    all_consuming,
    alt,
    is_alphanumeric,
    line_ending,
    many0,
    many1,
    multispace0,
    opt,
    space1,
    take_while1,
    tag,
    tuple,
};

use crate::{
    Decode,
    Def,
    DefItem,
    Definition,
    Error,
    ErrorKind,
    ScriptExpression,
};

impl Decode for Def {
    fn decode<Source>(source: &mut Source) -> Result<Def, Error> where
        Source: Read + Seek
    {
        let mut input = Vec::new();
        source.read_to_end(&mut input)?;
        let (_, def) = all_consuming(Def::decode_def)(&input)?;
        Ok(def)
    }
}

impl Def {
    fn decode_def(input: &[u8]) -> IResult<&[u8], Def, Error> {
        let (input, body) = many0(Self::decode_def_item)(input)?;
        let (input, _) = multispace0(input)?;
        Ok((input, Def { body }))
    }

    fn decode_def_item(input: &[u8]) -> IResult<&[u8], DefItem, Error> {
        let (input, _) = multispace0(input)?;
        alt((
            Self::decode_def_item_definition,
            Self::decode_def_item_between,
        ))(input)
    }

    fn decode_def_item_definition(input: &[u8]) -> IResult<&[u8], DefItem, Error> {
        let (input, definition) = Self::decode_definition(input)?;
        Ok((input, DefItem::Definition(definition)))
    }

    /// Everything between definitions is ignored. Evidenced by numerous syntax errors.
    fn decode_def_item_between(input: &[u8]) -> IResult<&[u8], DefItem, Error> {
        if input.len() < 11 {
            return Err(nom::Err::Error(Error::Fable(ErrorKind::NotEnoughSpaceForParser)))
        }

        let mut should = true;
        let mut ending = 0;

        loop {
            if &input[ending..ending+2] == b"//" {
                should = false;
                ending += 2;
            } else if let Ok((_, m)) = line_ending::<&[u8], Error>(&input[ending..ending+2]) {
                should = true;
                ending += m.len();
            } else if should && &input[ending..ending+11] == b"#definition" {
                break
            } else {
                ending += 1;
            }
        }

        let between = &input[..ending];

        let between = match String::from_utf8(between.to_vec()) {
            Ok(s) => s,
            _ => return Err(nom::Err::Error(Error::Utf8Error))
        };

        let input = &input[ending..];

        Ok((input, DefItem::Between(between)))
    }

    fn decode_definition(input: &[u8]) -> IResult<&[u8], Definition, Error> {
        // println!("definition start {:?}", String::from_utf8(input[..10].to_vec()));

        let (input, directive) = alt((tag("#definition_template"), tag("#definition")))(input)?;

        let is_template = match std::str::from_utf8(&directive) {
            Ok("#definition_template") => true,
            _ => false,
        };

        let (input, _) = space1(input)?;

        let (input, group) = Self::decode_definition_name(input)?;

        let group = match String::from_utf8(group.to_vec()) {
            Ok(group) => group,
            _ => return Err(nom::Err::Error(Error::Utf8Error))
        };

        let (input, _) = space1(input)?;

        let (input, name) = Self::decode_definition_name(input)?;

        let name = match String::from_utf8(name.to_vec()) {
            Ok(name) => name,
            _ => return Err(nom::Err::Error(Error::Utf8Error))
        };

        let (input, specializes) = opt(tuple((space1, tag("specialises"), space1, Self::decode_definition_name)))(input)?;

        let specializes = match specializes {
            Some((_space1, _specializes, _space2, specializes)) => {
                match String::from_utf8(specializes.to_vec()) {
                    Ok(specializes) => Some(specializes),
                    _ => return Err(nom::Err::Error(Error::Utf8Error))
                }
            },
            None => None,
        };

        // println!("definition {} ({}) specializes {:?}", name, group, specializes);

        let (input, body) = ScriptExpression::decode_expression_list(input)?;

        // println!("definition {:#?}", body);
        // println!("definition {:?}", String::from_utf8(input[..10].to_vec()));

        // There's potientially stray "#end_definition" that do nothing.
        let (input, _) = many1(tuple((multispace0, tag("#end_definition"), opt(tag(";")))))(input)?;

        Ok(
            (
                input,
                Definition {
                    is_template: is_template,
                    group: group,
                    name: name,
                    specializes: specializes,
                    body: body,
                }
            )
        )
    }

    pub fn decode_definition_name(input: &[u8]) -> IResult<&[u8], &[u8], Error> {
        take_while1(|c| is_alphanumeric(c) || c == b'_')(input)
    }
}