use nom::bytes::complete::tag;
use nom::character::complete::line_ending;
use nom::character::complete::one_of;
use nom::combinator::recognize;
use nom::multi::many0;

use super::Context;
use crate::error::CustomError;
use crate::error::MyError;
use crate::error::Res;
use crate::parser::util::get_consumed;
use crate::parser::util::get_current_line_before_position;
use crate::parser::util::get_one_before;
use crate::parser::LineBreak;

#[cfg_attr(feature = "tracing", tracing::instrument(ret, level = "debug"))]
pub fn line_break<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, LineBreak<'s>> {
    let (remaining, _) = pre(context, input)?;
    let (remaining, _) = tag(r#"\\"#)(remaining)?;
    let (remaining, _) = recognize(many0(one_of(" \t")))(remaining)?;
    let (remaining, _) = line_ending(remaining)?;
    let source = get_consumed(input, remaining);
    Ok((remaining, LineBreak { source }))
}

#[cfg_attr(feature = "tracing", tracing::instrument(ret, level = "debug"))]
fn pre<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, ()> {
    let document_root = context.get_document_root().unwrap();
    let preceding_character = get_one_before(document_root, input)
        .map(|slice| slice.chars().next())
        .flatten();
    match preceding_character {
        // If None, we are at the start of the file
        None | Some('\\') => {
            return Err(nom::Err::Error(CustomError::MyError(MyError(
                "Not a valid pre character for line break.",
            ))));
        }
        _ => {}
    };
    let current_line = get_current_line_before_position(document_root, input);
    match current_line {
        Some(line) => {
            let is_non_empty_line = line.chars().any(|c| !c.is_whitespace());
            if !is_non_empty_line {
                return Err(nom::Err::Error(CustomError::MyError(MyError(
                    "Not a valid pre line for line break.",
                ))));
            }
        }
        None => {
            return Err(nom::Err::Error(CustomError::MyError(MyError(
                "No preceding line for line break.",
            ))));
        }
    }

    Ok((input, ()))
}