#![cfg_attr(docsrs, feature(doc_auto_cfg))]
#![deny(
    unreachable_pub,
    missing_debug_implementations,
    clippy::pedantic,
    clippy::perf
)]
#![allow(clippy::too_many_lines, clippy::too_many_arguments)]

use colored::Colorize;
use kvarn_utils::prelude::*;
use pulldown_cmark::{html, CowStr, Event, Options, Parser, Tag};
use std::collections::HashMap;
use std::ffi::OsStr;
use std::fmt::{self, Display, Formatter};
use std::io;
use std::path::Path;
use unicode_categories::UnicodeCategories;

mod highlight;

#[derive(Debug, Clone, Copy, Eq, PartialEq)]
pub enum ContinueBehaviour {
    /// Asks the user for confirmation.
    Ask,
    /// Continues with the default.
    Default,
    /// Continues with `yes`.
    Yes,
    /// Continues with `no`.
    No,
}

pub fn exit_with_message(message: impl AsRef<str>) -> ! {
    error!("{}", message.as_ref());
    // Wait in Windows, if we run a md file with kvarn-chute and CMD pops up, use this to make it
    // remain open.
    #[cfg(windows)]
    wait_for("Press enter to close...");
    std::process::exit(1)
}

pub(crate) mod filesystem {
    use super::{exit_with_message, io, read_continue_behaviour, warn, ContinueBehaviour, Path};
    use std::{
        fs::{File, Metadata, OpenOptions},
        io::ErrorKind,
    };
    pub(crate) fn open_file_with_metadata<P: AsRef<Path>>(path: P) -> io::Result<(File, Metadata)> {
        match File::open(path).and_then(|file| file.metadata().map(|metadata| (file, metadata))) {
            Ok(file) => Ok(file),
            Err(err) => match err.kind() {
                ErrorKind::NotFound => {
                    exit_with_message("File not found, please check the entered path.")
                }
                ErrorKind::PermissionDenied => Err(err),
                _ => exit_with_message("Encountered an unknown error reading the file specified."),
            },
        }
    }
    pub(crate) fn create_file<P: AsRef<Path>>(
        path: P,
        continue_behaviour: ContinueBehaviour,
    ) -> File {
        fn open<P: AsRef<Path>>(
            options: &OpenOptions,
            path: P,
            continue_behaviour: ContinueBehaviour,
        ) -> File {
            match options.open(&path) {
                Ok(file) => file,
                Err(err) => match err.kind() {
                    ErrorKind::AlreadyExists => {
                        if let ContinueBehaviour::Yes | ContinueBehaviour::Default =
                            continue_behaviour
                        {
                            warn!("Overriding file.");
                        }
                        if !read_continue_behaviour(
                            "The existing HTML file will be overridden.",
                            true,
                            continue_behaviour,
                        ) {
                            exit_with_message("Aborted conversion.")
                        };
                        open(
                            OpenOptions::new().write(true).create(true).truncate(true),
                            path,
                            continue_behaviour,
                        )
                    }
                    ErrorKind::NotFound => {
                        exit_with_message("File not found, please check the entered path.")
                    }
                    ErrorKind::PermissionDenied => {
                        exit_with_message("You do not have permission to read the file specified.")
                    }
                    _ => exit_with_message(
                        "Encountered an unknown error reading the file specified.",
                    ),
                },
            }
        }
        open(
            OpenOptions::new()
                .write(true)
                .create_new(true)
                .truncate(true),
            path,
            continue_behaviour,
        )
    }
}

/// The message is in the beginning of the print so it should be capitalized and contain a punctuation marking the end of a sentence (e.g. `.?!`).
///
/// The message should not contain the word continue, since it is used extensively in this fn.
#[must_use = "you have promted the user for input, so use it"]
pub fn read_continue_behaviour(
    message: impl AsRef<str>,
    default: bool,
    behaviour: ContinueBehaviour,
) -> bool {
    match behaviour {
        ContinueBehaviour::No => false,
        ContinueBehaviour::Yes => true,
        ContinueBehaviour::Default => default,
        ContinueBehaviour::Ask => read_continue(message, default),
    }
}
#[must_use = "you have promted the user for input, so use it"]
/// The message is in the beginning of the print so it should be
/// capitalized and contain a punctuation marking the end of a sentence (e.g. `.?!`).
///
/// The message should not contain the word continue, since it is used extensively in this fn.
pub fn read_continue(message: impl AsRef<str>, default: bool) -> bool {
    let message = message.as_ref();
    // Don't output to normal out.
    eprint!(
        "{} {} ",
        message,
        format!(
            "Do you want to continue ({} or {})?",
            if default { "Y" } else { "y" }.green(),
            if default { "n" } else { "N" }.red(),
        )
        .bold(),
    );
    io::stdout()
        .lock()
        .flush()
        .unwrap_or_else(|e| exit_with_message(format!("Failed to flush stdout {:?}", e)));

    loop {
        let mut buffer = [0; 64];
        let read = if let Ok(read) = io::stdin().lock().read(&mut buffer) {
            read
        } else {
            error!("Failed to read stdin for confirmation.");
            return false;
        };
        let read = match buffer.get(read.saturating_sub(2)) {
            Some(byte) if *byte == chars::CR => read - 2,
            Some(_) if buffer.get(read - 1) == Some(&chars::LF) => read - 1,
            _ => read,
        };
        if let Ok(s) = str::from_utf8(&buffer[..read]) {
            if s.trim().is_empty() {
                return default;
            }
            if s.eq_ignore_ascii_case("y")
                || s.eq_ignore_ascii_case("yes")
                || s.eq_ignore_ascii_case("true")
            {
                return true;
            }
            if s.eq_ignore_ascii_case("n")
                || s.eq_ignore_ascii_case("no")
                || s.eq_ignore_ascii_case("false")
            {
                return false;
            }

            eprintln!(
                "Could not detect your intent. Please try again. {}",
                message
            );
        } else {
            error!("Input isn't UTF-8");
        }
    }
}

/// Process the document at the given path.
///
/// If a Kvarn extension resides in the beginning of the header, make sure
/// it has a newline in the end if only extension declaration; else parsing will fail.
///
/// # Errors
///
/// Prints an error if writing to the output file failed or if the file
/// specified cannot be accessed (privileges, if it's a folder).
/// Should not panic.
///
/// The returned result indicates whether everything went fine.
#[allow(clippy::result_unit_err)]
pub fn process_document<P: AsRef<Path>>(
    path: P,
    header_pre_meta: &[u8],
    header_post_meta: &[u8],
    footer: &[u8],
    ignored_extensions: &[&str],
    continue_behaviour: ContinueBehaviour,
    theme: &str,
    syntax_highlighting: bool,
) -> Result<(), ()> {
    match process_inner(
        path,
        header_pre_meta,
        header_post_meta,
        footer,
        ignored_extensions,
        continue_behaviour,
        theme,
        syntax_highlighting,
    ) {
        Ok(()) => Ok(()),
        Err(ref err) if err.kind() == io::ErrorKind::PermissionDenied => {
            error!("You do not have permission to read the file specified.",);
            Err(())
        }
        Err(_) => {
            error!("Failed to write to output file.");
            Err(())
        }
    }
}

#[cfg(feature = "date")]
static FORMAT: &[time::format_description::FormatItem] = time::macros::format_description!(
    "[weekday repr:short], \
    [year]-[month repr:numerical]-[day], \
    [hour]:[minute] [offset_hour sign:mandatory]:[offset_minute]"
);

#[allow(clippy::too_many_lines)]
fn process_inner<P: AsRef<Path>>(
    path: P,
    header_pre_meta: &[u8],
    header_post_meta: &[u8],
    footer: &[u8],
    ignored_extensions: &[&str],
    continue_behaviour: ContinueBehaviour,
    theme: &str,
    syntax_highlighting: bool,
) -> io::Result<()> {
    let path = path.as_ref();
    if path.extension().and_then(OsStr::to_str).map(|s| s == "md") == Some(false)
        && !read_continue_behaviour(
            "Specified file does not have the Markdown extension.",
            false,
            continue_behaviour,
        )
    {
        exit_with_message("Aborted conversion.");
    }
    let (mut file, metadata) = filesystem::open_file_with_metadata(path)?;
    let new_path = {
        let mut path = path.to_owned();
        let ext = path.extension().and_then(OsStr::to_str);

        if ext.map_or(false, |ext| ext == "md") {
            path.set_extension("html");
        } else if let Some(ext) = ext {
            let ext = format!("{}.html", ext);
            path.set_extension(ext);
        } else {
            path.set_extension("html");
        }
        info!("Creating file {}", path.display());
        path
    };
    let mut write_file = filesystem::create_file(new_path, continue_behaviour);

    // We'll run out of memory before we hit the usize limit.
    #[allow(clippy::cast_possible_truncation)]
    let mut buffer = WriteableBytes::with_capacity(metadata.len() as usize);
    if let Err(err) = io::copy(&mut file, &mut buffer) {
        exit_with_message(format!(
            "Encountered an error reading the contents of the file specified: {:?}",
            err
        ))
    }
    let buffer = buffer.into_inner().freeze();

    let hardcoded_extensions =
        kvarn_utils::PresentExtensions::new(Bytes::copy_from_slice(header_pre_meta));

    let mut extension_list = hardcoded_extensions
        .as_ref()
        .map_or_else(Vec::new, |ext| ext.iter_clone().collect());

    let file_extensions = kvarn_utils::PresentExtensions::new(buffer.clone());
    let mut file_content_start = file_extensions
        .as_ref()
        .map_or(0, kvarn_utils::PresentExtensions::data_start);

    if let Some(file_extensions) = file_extensions {
        let mut ignored_extensions = ignored_extensions.to_vec();

        'extension_loop: for extension in file_extensions {
            // Check for ignored extensions, and skip pushing it to main extensions if matched
            if let Some(pos) = ignored_extensions
                .iter()
                .position(|ext| *ext == extension.name())
            {
                ignored_extensions.remove(pos);
                continue 'extension_loop;
            }
            // Push to main extension list
            extension_list.insert(0, extension);
        }
    }
    if let Ok(string) = std::str::from_utf8(&buffer[file_content_start..]) {
        let white_space_chars = string.len() - string.trim_start().len();

        file_content_start += white_space_chars;
    }

    // Write all extensions
    for (position, extension) in extension_list.iter().enumerate() {
        match position {
            // Write !> in first iteration, &> in the rest!
            0 => {
                write_file.write_all(b"!> ")?;
            }
            _ => {
                write_file.write_all(b" &> ")?;
            }
        }
        write_file.write_all(extension.name().as_bytes())?;
        for arg in extension {
            write_file.write_all(b" ")?;
            write_file.write_all(arg.as_bytes())?;
        }
    }
    // Write newline after extensions
    write_file.write_all(b"\n")?;

    // Write rest of header before meta
    write_file
        .write_all(&header_pre_meta[hardcoded_extensions.map_or(0, |ext| ext.data_start())..])?;

    // If we have a head tag
    let file_content_start = if buffer[file_content_start..].starts_with(b"<head>") {
        let buffer = &buffer[file_content_start..];
        let end = buffer
            .windows(7)
            .position(|slice| slice == b"</head>")
            .unwrap_or(buffer.len());

        write_file.write_all(&buffer[6..end])?;

        file_content_start + end + 7
    } else {
        file_content_start
    };

    // Write header after meta
    write_file.write_all(header_post_meta)?;

    let input = std::str::from_utf8(&buffer[file_content_start..]).expect(
        "we tried to split the beginning of MarkDown on a \
        character boundary, or the input file isn't valid UTF-8",
    );

    let mut headers = Vec::new();
    get_headers(&mut headers, input);

    let mut tags: Tags = HashMap::new();
    tags.insert(
        "toc".to_owned(),
        Box::new(|_inner, mut ext| {
            use fmt::Write;

            struct MarginDisplay<'a> {
                counter: &'a IndentCounter,
                multiplier: usize,
            }
            impl<'a> Display for MarginDisplay<'a> {
                fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
                    let margin = self.counter.left_margin(self.multiplier);

                    if margin == 0 {
                        Ok(())
                    } else {
                        write!(f, "<span style=\"margin-left: {}em\"></span>", margin)
                    }
                }
            }

            let mut indent_counter = IndentCounter::new();
            writeln!(
                ext,
                "<table id=\"toc\"><thead><tr><th>Contents</th></tr></thead><tbody>"
            )
            .unwrap();
            for Header {
                name,
                anchor,
                indent,
            } in &headers
            {
                indent_counter.add(*indent);
                let margin = MarginDisplay {
                    counter: &indent_counter,
                    multiplier: 2,
                };

                writeln!(
                    ext,
                    "<tr><td>{}<a href=\"#{}\">{} {}</a></td></tr>",
                    margin, anchor, indent_counter, name
                )
                .unwrap();
            }
            writeln!(ext, "</tbody></table>").unwrap();
        }),
    );

    #[cfg(feature = "date")]
    tags.insert(
        "date".to_owned(),
        Box::new(|inner, mut ext| {
            use fmt::Write;
            use time_tz::OffsetDateTimeExt;

            let now = time::OffsetDateTime::now_utc();
            let offset = time_tz::system::get_timezone();
            let date = offset.map_or(now, |offset| now.to_timezone(offset));
            let s = if inner.trim().is_empty() {
                date.format(FORMAT).expect("failed to format datetime")
            } else if let Ok(f) = time::format_description::parse(inner.trim()) {
                date.format(&f).expect("failed to format datetime")
            } else {
                error!(
                    "Failed to parse time description ({inner:?}). \
                    See https://time-rs.github.io/book/api/format-description.html"
                );
                date.format(FORMAT).expect("failed to format datetime")
            };
            write!(ext, "{}", s).expect("failed to push to string");
        }),
    );

    let input = replace_tags(input, &tags);

    // Parse CMark
    let parser = Parser::new_ext(&input, Options::all());

    let mut parser_header_index = 0;
    let parser = parser.map(|event| match event {
        Event::Start(Tag::Heading { level, classes, .. }) => {
            let Header { anchor, .. } = &headers[parser_header_index];
            parser_header_index += 1;

            let class = if classes.is_empty() {
                String::new()
            } else {
                const START: &str = " class=\"";
                const END: &str = r#"""#;
                let mut s = String::with_capacity(
                    classes.iter().fold(START.len() + END.len(), |acc, class| {
                        acc + class.len() + " ".len()
                    }),
                );

                s.push_str(START);
                for class in &classes {
                    s.push_str(class);
                    s.push(' ');
                }
                s.push_str(END);

                s
            };

            let html = format!("<{} id=\"{}\"{}>", level, anchor, class);
            Event::Html(CowStr::Boxed(html.into_boxed_str()))
        }
        _ => event,
    });
    let parser = highlight::SyntaxPreprocessor {
        parent: parser,
        theme,
        skip: !syntax_highlighting,
    };

    let mut output = Vec::with_capacity(input.len() * 2);

    // Write HTML from specified file to output file (buffered for performance)
    html::write_html(&mut output, parser)?;

    // Write output
    write_file.write_all(&output)?;

    // Writes footer
    write_file.write_all(footer)?;
    write_file.flush()?;

    Ok(())
}

/// Watch the given directory.
///
/// If a Kvarn extension resides in the beginning of the header,
/// make sure it has a newline in the end if only extension declaration;
/// else parsing will fail.
///
/// # Errors
///
/// Prints an error if writing to the output file failed or if
/// the file specified cannot be accessed (privileges, if it's a folder).
/// Should not panic.
pub fn watch<P: AsRef<Path>>(
    path: P,
    header_pre_meta: &[u8],
    header_post_meta: &[u8],
    footer: &[u8],
    ignored_extensions: &[&str],
    mut continue_behaviour: ContinueBehaviour,
    theme: &str,
    syntax_highlighting: bool,
) {
    use notify_debouncer_full::{
        new_debouncer,
        notify::{RecursiveMode, Watcher},
    };
    use std::sync::mpsc::channel;

    let path = path.as_ref();

    // Create a channel to receive the events.
    let (tx, rx) = channel();

    // Create a watcher object, delivering debounced events.
    // The notification back-end is selected based on the platform.
    let mut watcher = if let Ok(w) = new_debouncer(Duration::from_millis(100), None, tx) {
        w
    } else {
        error!("Failed to create a watcher.");
        return;
    };

    // Add a path to be watched. All files and directories at that path and
    // below will be monitored for changes.
    if watcher
        .watcher()
        .watch(path, RecursiveMode::Recursive)
        .is_err()
    {
        error!("Failed to start watching {}.", path.display());
        return;
    }

    if let ContinueBehaviour::Ask = continue_behaviour {
        continue_behaviour = ContinueBehaviour::Default;
    }

    loop {
        if let Ok(Ok(events)) = rx.recv() {
            for event in events {
                let path = &event.paths[0];
                if path.exists() && path.extension().and_then(OsStr::to_str) == Some("md") {
                    let r = process_document(
                        path,
                        header_pre_meta,
                        header_post_meta,
                        footer,
                        ignored_extensions,
                        continue_behaviour,
                        theme,
                        syntax_highlighting,
                    );
                    if r.is_ok() {
                        let local_path = if let Ok(wd) = std::env::current_dir() {
                            path.strip_prefix(wd).unwrap_or(path)
                        } else {
                            path
                        };
                        info!("Converted {} to HTML.", local_path.display());
                    }
                }
            }
        } else {
            error!("Got an error watching the specified directory.");
            return;
        }
    }
}

/// Blocks while waiting for the user to press enter, displaying the message specified.
#[inline]
pub fn wait_for(message: &str) {
    // Don't write to normal output.
    eprintln!("{}", message);
    drop(io::stdin().read(&mut [0; 0]));
}

/// It's safe to unwrap on the [`fmt::Write`] trait; we're writing to a [`String`].
#[derive(Debug)]
pub struct Extendible<'a> {
    inner: &'a mut String,
}
impl<'a> Extendible<'a> {
    pub fn extend(&mut self, string: &str) {
        self.inner.push_str(string);
    }
}
impl<'a> fmt::Write for Extendible<'a> {
    fn write_fmt(&mut self, args: fmt::Arguments<'_>) -> fmt::Result {
        self.inner.write_fmt(args)
    }
    fn write_str(&mut self, s: &str) -> fmt::Result {
        self.inner.push_str(s);
        Ok(())
    }
}

#[must_use]
pub fn make_anchor(headers: &[Header], title: &str) -> String {
    fn is_parenthesis(c: char) -> bool {
        matches!(c, '(' | ')' | '[' | ']' | '{' | '}')
    }
    let lowercase = title.to_lowercase();
    let mut a = String::with_capacity(lowercase.len());
    let mut in_parenthesis = false;
    for char in lowercase.chars() {
        match char {
            ' ' if !in_parenthesis => a.push('-'),
            _ if is_parenthesis(char) => in_parenthesis = !in_parenthesis,
            _ if !in_parenthesis && char.is_ascii_alphanumeric() => a.push(char),
            _ => {}
        }
    }
    {
        let mut last_number = 0_u32;
        let mut last_number_length = 0_u32;
        while headers.iter().any(|header| header.anchor == a) {
            if last_number_length == 0 {
                a.push_str("-1");
            } else {
                for _ in 0..last_number_length {
                    a.pop();
                }
                let number = (last_number + 1).to_string();

                a.push_str(&number);

                // As we're formatting a number, I guarantee that doesn't take more space than we
                // have memory...
                #[allow(clippy::cast_possible_truncation)]
                {
                    last_number_length = number.len() as u32;
                }
                last_number += 1;
            }
        }
    }
    a
}

pub type Tags<'a> = HashMap<String, Box<dyn Fn(&'a str, Extendible) + 'a>>;

#[allow(clippy::missing_panics_doc)]
#[must_use]
pub fn replace_tags<'a>(text: &'a str, tags: &Tags<'a>) -> String {
    let mut string = String::with_capacity(text.len() + 64);

    let mut in_tag = false;
    let mut escaped_tag = false;

    for (index, char) in text.char_indices() {
        let text = unsafe { text.get_unchecked(index..) };
        if let Some(after_opening) = text.strip_prefix("${") {
            if !escaped_tag {
                if let Some((name, func)) = after_opening
                    .split(|c| c == ' ' || c == '}')
                    .next()
                    .and_then(|name| tags.get_key_value(name))
                {
                    let tag_len = text.find('}').unwrap_or(name.len() + 2);
                    if !in_tag {
                        // For unwrap, see above.
                        let inner = text.get(2 + name.len() + 1..tag_len).unwrap_or("");
                        let extendible = Extendible { inner: &mut string };
                        func(inner, extendible);
                        in_tag = true;
                    }
                }
            }
            if escaped_tag {
                string.pop();
            }
        }
        if in_tag {
            if char == '\\' && text.starts_with("\\{") {
                warn!("Just know you cannot escape closing brackets for tags");
            }
            if char == '}' {
                in_tag = false;
            }
        } else {
            string.push(char);
        }
        if char == '\\' {
            escaped_tag = !escaped_tag;
        } else {
            escaped_tag = false;
        }
    }
    string
}

#[derive(Debug)]
pub struct Header<'a> {
    name: &'a str,
    anchor: String,
    indent: u8,
}
pub fn get_headers<'a>(headers: &mut Vec<Header<'a>>, input: &'a str) {
    fn is_parenthesis(c: char) -> bool {
        matches!(c, '(' | ')' | '[' | ']' | '{' | '}')
    }
    let mut in_code = false;
    for (line, next_line) in input
        .lines()
        .zip(input.lines().skip(1).map(Some).chain(std::iter::once(None)))
    {
        let trimmed = line.trim();
        let header_trimmed = trimmed.trim_start_matches('#');
        let indent = (trimmed.len() - header_trimmed.len())
            .wrapping_sub(1)
            .min(next_line.map_or(usize::MAX, |next_line| {
                if !trimmed.is_empty()
                    && (next_line.trim().starts_with("---") || next_line.trim().starts_with("==="))
                {
                    0
                } else {
                    usize::MAX
                }
            }))
            .wrapping_add(1);

        if trimmed.starts_with("```") {
            in_code = !in_code;
        }

        if !in_code && indent > 0 {
            let heavily_trimmed = header_trimmed.trim_start_matches(|c: char| !c.is_alphabetic());
            let split_using_parentheses = header_trimmed.contains("](");
            let heavily_trimmed = heavily_trimmed
                .split(|c: char| {
                    !(c.is_alphanumeric()
                        || c.is_ascii_punctuation()
                        || c.is_whitespace()
                        || c.is_punctuation())
                        || (split_using_parentheses && is_parenthesis(c))
                })
                .next()
                .unwrap_or(heavily_trimmed);

            let anchor = make_anchor(headers, heavily_trimmed);
            // Ehm no, it doesn't!
            #[allow(clippy::cast_possible_truncation)]
            let indent = indent.min(255) as u8;

            headers.push(Header {
                name: heavily_trimmed,
                anchor,
                indent,
            });
        }
    }
}
#[derive(Debug)]
#[must_use]
pub struct IndentCounter {
    indent_index: [u8; 6],
    last_indent: u8,
}
impl IndentCounter {
    pub fn new() -> Self {
        Self {
            indent_index: [0; 6],
            last_indent: 0,
        }
    }
    pub fn add(&mut self, indent: u8) {
        let indent = indent - 1;
        if self.last_indent > indent {
            self.indent_index[self.last_indent as usize] = 0;
        }
        self.indent_index[indent as usize] += 1;
        self.last_indent = indent;
    }
    pub fn indent(&self) -> IndentIndenter {
        IndentIndenter { data: self }
    }
    #[must_use]
    pub fn left_margin(&self, multiplier: usize) -> usize {
        self.last_indent as usize * multiplier
    }
}
impl Default for IndentCounter {
    fn default() -> Self {
        Self::new()
    }
}
impl Display for IndentCounter {
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        for i in 0..self.last_indent {
            write!(f, "{}.", self.indent_index[i as usize])?;
        }
        write!(f, "{}", self.indent_index[self.last_indent as usize])
    }
}
#[derive(Debug)]
#[must_use]
pub struct IndentIndenter<'a> {
    data: &'a IndentCounter,
}
impl<'a> Display for IndentIndenter<'a> {
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        for _ in 0..self.data.last_indent {
            write!(f, "    ")?;
        }
        Ok(())
    }
}