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use std::fs::File;
use std::io::prelude::*;

const COMMENT_BEGIN: &str = "<!-- BEGIN mktoc -->";
const COMMENT_END: &str = "<!-- END mktoc -->";

/// reads a file into a mutable string
fn read_file(file_path: String) -> Result<String, ::std::io::Error> {
    let mut file = File::open(file_path)?;
    let mut contents = String::new();
    file.read_to_string(&mut contents)?;

    Ok(contents)
}

fn text_to_url(text: &str) -> String {
    text.trim()
        .replace(" ", "-")
        .replace("(", "")
        .replace(")", "")
        .replace("`", "")
        .replace("´", "")
        .replace("'", "")
        .replace("\"", "")
        .replace("[", "")
        .replace("]", "")
        .replace("{", "")
        .replace("}", "")
        .replace("?", "")
        .replace("¿", "")
        .replace("!", "")
        .replace("¡", "")
        .replace(".", "")
        .replace(",", "")
        .replace("\\", "")
        .replace("/", "")
        .replace(":", "")
        .replace(";", "")
        .replace("§", "")
        .replace("$", "")
        .replace("%", "")
        .replace("&", "")
        .replace("=", "")
        .replace("^", "")
        .replace("°", "")
        .replace("#", "")
        .replace("+", "")
        .replace("*", "")
        .replace("<", "")
        .replace(">", "")
        .to_ascii_lowercase()
}

/// parses a string and extracts all headlines to build a table of contents
///
/// Uses a basic regex "((#{1,6}\s))((.*))" to parse headings out of the
pub fn generate_toc(original_content: String, min_depth: i32, max_depth: i32) -> String {
    let mut already_found_code_open = false;
    let mut code_block_found = false;
    let mut new_toc = String::from(COMMENT_BEGIN);
    let re = regex::Regex::new(r"((#{1,6}\s))((.*))").unwrap();
    for line in original_content.lines() {
        let line_s: String = line.chars().take(3).collect();
        if line_s == "```".to_owned() {
            code_block_found = true;
        }

        if !code_block_found && !already_found_code_open {
            if line.starts_with("#") {
                // Check if the regex matches, if it doesn't continue skip (continue) the loop.
                let caps = match re.captures(line) {
                    Some(matched) => matched,
                    None => { continue; }
                };
                
                let level: i32 = (caps.get(2).unwrap().as_str().chars().count() - 1) as i32;
                
                if level < min_depth {
                    continue;
                }

                if level > max_depth {
                    continue;
                }

                let text = caps.get(3).unwrap().as_str();
                let link = text_to_url(text);
                let spaces = match level {
                    3 => String::from("  "),
                    4 => String::from("    "),
                    5 => String::from("      "),
                    6 => String::from("        "),
                    _ => String::from(""),
                };

                new_toc = format!(
                    "{old}\n{spaces}- [{text}](#{link})",
                    old = new_toc.as_str(),
                    spaces = spaces,
                    text = text,
                    link = link
                );
            }
        }

        if code_block_found && already_found_code_open {
            code_block_found = false;
            already_found_code_open = false;
        }

        if line.starts_with("```") {
            already_found_code_open = true;
        }
    }

    new_toc = format!("{}\n{}", new_toc, COMMENT_END);

    new_toc
}

/// takes a file path as `String` and returns a table of contents for the file
pub fn make_toc(
    file_path_in: String,
    min_depth: i32,
    max_depth: i32,
) -> Result<String, ::std::io::Error> {
    let content = read_file(file_path_in)?;
    let new_toc = generate_toc(content.to_owned(), min_depth, max_depth);
    let re_toc =
        regex::Regex::new(r"(?ms)^(<!-- BEGIN mktoc -->)(.*?)(<!-- END mktoc -->)").unwrap();
    let res: String = re_toc
        .replacen(content.as_str(), 1, new_toc.as_str())
        .into_owned();

    Ok(res)
}