use nom::branch::alt;
use nom::bytes::complete::tag;
use nom::character::complete::line_ending;
use nom::character::complete::space1;
use nom::combinator::eof;
use nom::combinator::not;
use nom::combinator::recognize;
use nom::multi::many1;
use nom::multi::many1_count;
use nom::sequence::tuple;

use crate::parser::error::CustomError;
use crate::parser::error::MyError;
use crate::parser::object::standard_set_object;
use crate::parser::parser_context::ChainBehavior;
use crate::parser::parser_context::ContextElement;
use crate::parser::parser_context::ContextTree;
use crate::parser::parser_context::ExitMatcherNode;

use super::element::Element;
use super::error::Res;
use super::object::Object;
use super::parser_with_context::parser_with_context;
use super::source::Source;
use super::Context;

#[derive(Debug)]
pub struct Document<'s> {
    pub source: &'s str,
    pub zeroth_section: Option<Section<'s>>,
    pub children: Vec<Heading<'s>>,
}

#[derive(Debug)]
pub struct Heading<'s> {
    pub source: &'s str,
    pub children: Vec<DocumentElement<'s>>,
}

#[derive(Debug)]
pub struct Section<'s> {
    pub source: &'s str,
    pub children: Vec<Element<'s>>,
}

#[derive(Debug)]
pub enum DocumentElement<'s> {
    Heading(Heading<'s>),
    Section(Section<'s>),
}

impl<'s> Source<'s> for Document<'s> {
    fn get_source(&'s self) -> &'s str {
        self.source
    }
}

impl<'s> Source<'s> for DocumentElement<'s> {
    fn get_source(&'s self) -> &'s str {
        match self {
            DocumentElement::Heading(obj) => obj.source,
            DocumentElement::Section(obj) => obj.source,
        }
    }
}

#[allow(dead_code)]
pub fn document(input: &str) -> Res<&str, Document> {
    let initial_context: ContextTree<'_, '_> = ContextTree::new();
    let document_context =
        initial_context.with_additional_node(ContextElement::DocumentRoot(input));

    todo!()
}

fn section<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, Section<'s>> {
    // TODO: The zeroth section is specialized so it probably needs its own parser
    let parser_context = context
        .with_additional_node(ContextElement::ExitMatcherNode(ExitMatcherNode {
            exit_matcher: ChainBehavior::AndParent(Some(&section_end)),
        }))
        .with_additional_node(ContextElement::Context("section"));
    not(|i| parser_context.check_exit_matcher(i))(input)?;
    todo!()
}

fn section_end<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, &'s str> {
    let heading_matcher = parser_with_context!(heading)(context);
    alt((recognize(heading_matcher), eof))(input)
}

fn heading<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, Heading<'s>> {
    not(|i| context.check_exit_matcher(i))(input)?;
    let (remaining, (star_count, _ws, title, _ws2)) = headline(context, input)?;
    todo!()
}

fn headline<'r, 's>(
    context: Context<'r, 's>,
    input: &'s str,
) -> Res<&'s str, (usize, &'s str, Vec<Object<'s>>, &'s str)> {
    let parser_context =
        context.with_additional_node(ContextElement::ExitMatcherNode(ExitMatcherNode {
            exit_matcher: ChainBehavior::AndParent(Some(&headline_end)),
        }));
    let standard_set_object_matcher = parser_with_context!(standard_set_object)(&parser_context);
    let start_of_line_matcher = parser_with_context!(start_of_line)(&parser_context);

    let (remaining, (_sol, star_count, ws, title, ws2)) = tuple((
        start_of_line_matcher,
        many1_count(tag("*")),
        space1,
        many1(standard_set_object_matcher),
        alt((line_ending, eof)),
    ))(input)?;
    Ok((remaining, (star_count, ws, title, ws2)))
}

fn headline_end<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, &'s str> {
    line_ending(input)
}

/// Check that we are at the start of a line
fn start_of_line<'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 {
        Some('\n') => {}
        Some(_) => {
            // Not at start of line, cannot be a heading
            return Err(nom::Err::Error(CustomError::MyError(MyError(
                "Not at start of line",
            ))));
        }
        // If None, we are at the start of the file which allows for headings
        None => {}
    };
    Ok((input, ()))
}

/// Get one character from before the current position.
fn get_one_before<'s>(document: &'s str, current_position: &'s str) -> Option<&'s str> {
    assert!(is_slice_of(document, current_position));
    if document.as_ptr() as usize == current_position.as_ptr() as usize {
        return None;
    }
    let offset = current_position.as_ptr() as usize - document.as_ptr() as usize;
    let previous_character_offset = document.floor_char_boundary(offset - 1);
    Some(&document[previous_character_offset..offset])
}

/// Check if the child string slice is a slice of the parent string slice.
fn is_slice_of(parent: &str, child: &str) -> bool {
    let parent_start = parent.as_ptr() as usize;
    let parent_end = parent_start + parent.len();
    let child_start = child.as_ptr() as usize;
    let child_end = child_start + child.len();
    child_start >= parent_start && child_end <= parent_end
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn get_one_before_unicode() {
        let input = "🧡💛💚💙💜";
        let (green_heart_index, _) = input.char_indices().skip(2).next().unwrap();
        let starting_with_green_heart = &input[green_heart_index..];
        let yellow_heart = get_one_before(input, starting_with_green_heart).unwrap();
        assert!(is_slice_of(input, yellow_heart));
        assert_eq!(yellow_heart, "💛");
    }
}