use nom::branch::alt;
use nom::combinator::eof;
use nom::combinator::recognize;
use nom::combinator::verify;
use nom::multi::many1;
use nom::multi::many_till;
use nom::sequence::tuple;

use crate::parser::error::CustomError;
use crate::parser::error::MyError;
use crate::parser::exiting::ExitClass;
use crate::parser::object::standard_set_object;
use crate::parser::parser_context::ContextElement;
use crate::parser::parser_context::ExitMatcherNode;
use crate::parser::parser_with_context::parser_with_context;
use crate::parser::util::exit_matcher_parser;
use crate::parser::util::immediate_in_section;
use crate::parser::util::maybe_consume_trailing_whitespace_if_not_exiting;
use crate::parser::util::start_of_line;

use super::element::non_paragraph_element;
use super::error::Res;
use super::lesser_element::Paragraph;
use super::util::blank_line;
use super::util::get_consumed;
use super::Context;

#[tracing::instrument(ret, level = "debug")]
pub fn paragraph<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, Paragraph<'s>> {
    if immediate_in_section(context, "paragraph") {
        return Err(nom::Err::Error(CustomError::MyError(MyError(
            "Cannot nest objects of the same element",
        ))));
    }
    let parser_context = context
        .with_additional_node(ContextElement::Context("paragraph"))
        .with_additional_node(ContextElement::ExitMatcherNode(ExitMatcherNode {
            class: ExitClass::Beta,
            exit_matcher: &paragraph_end,
        }));
    let standard_set_object_matcher = parser_with_context!(standard_set_object)(&parser_context);
    let exit_matcher = parser_with_context!(exit_matcher_parser)(&parser_context);

    let (remaining, (children, _exit_contents)) = verify(
        many_till(standard_set_object_matcher, exit_matcher),
        |(children, _exit_contents)| !children.is_empty(),
    )(input)?;

    // Not checking parent exit matcher because if there are any children matched then we have a valid paragraph.

    let (remaining, _trailing_ws) =
        maybe_consume_trailing_whitespace_if_not_exiting(context, remaining)?;

    let source = get_consumed(input, remaining);

    Ok((remaining, Paragraph { source, children }))
}

#[tracing::instrument(ret, level = "debug")]
fn paragraph_end<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, &'s str> {
    let non_paragraph_element_matcher = parser_with_context!(non_paragraph_element)(context);
    let start_of_line_matcher = parser_with_context!(start_of_line)(&context);
    alt((
        recognize(tuple((start_of_line_matcher, many1(blank_line)))),
        recognize(non_paragraph_element_matcher),
        eof,
    ))(input)
}

#[cfg(test)]
mod tests {
    use crate::parser::parser_context::ContextElement;
    use crate::parser::parser_context::ContextTree;
    use crate::parser::parser_with_context::parser_with_context;

    use super::*;

    #[test]
    fn two_paragraphs() {
        let input = "foo bar baz\n\nlorem ipsum";
        let initial_context: ContextTree<'_, '_> = ContextTree::new();
        let document_context =
            initial_context.with_additional_node(ContextElement::DocumentRoot(input));
        let paragraph_matcher = parser_with_context!(paragraph)(&document_context);
        let (remaining, first_paragraph) = paragraph_matcher(input).expect("Parse first paragraph");
        let (remaining, second_paragraph) =
            paragraph_matcher(remaining).expect("Parse second paragraph.");
        assert_eq!(remaining, "");
        assert_eq!(first_paragraph.source, "foo bar baz\n\n");
        assert_eq!(second_paragraph.source, "lorem ipsum");
    }
}