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#![forbid(unsafe_code)]
#![no_std]

extern crate alloc;
extern crate core;

use alloc::{borrow, fmt, format, string::String, vec, vec::Vec};

#[cfg(test)]
mod tests;

pub mod indention;
use indention::{Indented, Unindent};

#[derive(Clone, Debug)]
#[cfg_attr(any(feature = "extra-traits", test), derive(PartialEq))]
pub struct Block<S> {
    pub head: S,
    pub subs: Vec<Block<S>>,
}

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
#[cfg_attr(feature = "extra-traits", derive(PartialOrd, Ord, Hash))]
pub enum EmptyLinesMode {
    Skip,
    HonorIndent,
    PrevIndent,
}

impl<A> Block<A> {
    pub fn map_ref<B, F>(&self, mut f: F) -> Block<B>
    where
        F: FnMut(&A) -> B,
    {
        fn intern_<A, B, F: FnMut(&A) -> B>(this: &Block<A>, f: &mut F) -> Block<B> {
            let head = f(&this.head);
            Block {
                head,
                subs: this.subs.iter().map(move |i| intern_(i, f)).collect(),
            }
        }
        intern_(self, &mut f)
    }

    pub fn map<B, F>(self, mut f: F) -> Block<B>
    where
        F: FnMut(A) -> B,
    {
        fn intern_<A, B, F: FnMut(A) -> B>(this: Block<A>, f: &mut F) -> Block<B> {
            let Block { head, subs } = this;
            let head = f(head);
            Block {
                head,
                subs: subs.into_iter().map(move |i| intern_(i, f)).collect(),
            }
        }
        intern_(self, &mut f)
    }
}

impl<'a, T> Block<&'a T>
where
    T: borrow::ToOwned,
{
    #[inline(always)]
    pub fn to_owned(&self) -> Block<<T as borrow::ToOwned>::Owned> {
        self.map_ref(|&i| borrow::ToOwned::to_owned(i))
    }
}

impl<A: fmt::Display> Block<A> {
    pub fn append_to_string(&self, ret: &mut String, single_indent: &str, upper_indent: &str) {
        ret.push_str(upper_indent);
        *ret += &format!("{}\n", self.head);
        let new_indent = format!("{}{}", upper_indent, single_indent);
        for i in &self.subs {
            i.append_to_string(ret, single_indent, &new_indent);
        }
    }

    #[inline]
    pub fn to_string(&self, single_indent: &str) -> String {
        let mut ret = String::new();
        self.append_to_string(&mut ret, single_indent, "");
        ret
    }
}

/// This function splits a string into the indention (spaces before text) and the real text
fn get_indent(s: &str) -> Indented<&str> {
    let (indent, data) = s.split_at(
        s.chars()
            .take_while(|x| x.is_whitespace())
            .map(|x| x.len_utf8())
            .sum(),
    );
    Indented { indent, data }
}

pub fn parse_nested_blocks(
    s: &str,
    empty_lines_mode: EmptyLinesMode,
) -> Vec<Block<Indented<&str>>> {
    let mut base = vec![];
    let mut stack: Vec<Block<Indented<&str>>> = vec![];

    let mut lit = s
        .lines()
        .map(get_indent)
        .filter(|&Indented { data, .. }| {
            !(empty_lines_mode == EmptyLinesMode::Skip && data.is_empty())
        })
        .map(|head| Block {
            head,
            subs: Vec::new(),
        });

    loop {
        let i = lit.next();
        let i_indent = i
            .as_ref()
            .and_then(|j| match empty_lines_mode {
                _ if !j.head.data.is_empty() => Some(j),
                EmptyLinesMode::HonorIndent => Some(j),
                EmptyLinesMode::PrevIndent => stack.last(),
                EmptyLinesMode::Skip => unreachable!(),
            })
            .map(|x| x.head.indent)
            .unwrap_or("");

        // reduce scope if necessary
        while {
            stack
                .last()
                .map(|Block { ref head, .. }| {
                    !i_indent.starts_with(head.indent) || i_indent == head.indent
                })
                .unwrap_or(false)
        } {
            // merge block with parent
            let old_top = stack.pop().unwrap();
            stack
                .last_mut()
                .map(|top2| &mut top2.subs)
                .unwrap_or(&mut base)
                .push(old_top);
        }

        assert!(i_indent.starts_with(stack.last().map(|top| top.head.indent).unwrap_or("")));
        match i {
            Some(j) => stack.push(j),
            None => break,
        }
    }

    assert!(stack.is_empty());
    base
}

pub fn blocks_to_string<B>(blks: Vec<Block<B>>, single_indent: &str) -> String
where
    B: Unindent,
    <B as Unindent>::Item: fmt::Display,
{
    blks.into_iter()
        .map(Unindent::unindent)
        .fold(String::new(), |mut acc, x| {
            x.append_to_string(&mut acc, single_indent, "");
            acc
        })
}