use std::{
    io::{BufWriter, Write},
    path::Path,
};

use pulldown_cmark::{CowStr, Options, Parser};

pub fn compile_markdown(
    src: impl AsRef<Path>,
    html: impl AsRef<Path>,
    gmi: impl AsRef<Path>,
) -> std::io::Result<()> {
    let src_text = std::fs::read_to_string(src)?;

    let mut html = create_file(html)?;
    let mut gmi = create_file(gmi)?;

    let mut state = State::Start;
    let mut counter: u64 = 0;
    let mut links: Vec<GmiLink<'_>> = vec![];

    for event in Parser::new_ext(&src_text, Options::all()) {
        use pulldown_cmark::Event::*;

        match event {
            Start(tag) => {
                use pulldown_cmark::{CodeBlockKind, HeadingLevel, Tag::*};

                match tag {
                    Paragraph => {
                        html.write_all(b"<p>")?;
                        if state != State::Start {
                            gmi.write_all(b"\r\n\r\n")?;
                        }
                    }

                    Heading { level, id, .. } => {
                        if let Some(id) = id {
                            html.write_fmt(format_args!("<{} id=\"{}\">", level, id))?;
                        } else {
                            html.write_fmt(format_args!("<{}>", level))?;
                        }

                        let hashes = match level {
                            HeadingLevel::H1 => "# ",
                            HeadingLevel::H2 => "## ",
                            _ => "### ",
                        };
                        gmi.write_all(hashes.as_bytes())?;
                        state = State::GmiPrefix(hashes);
                    }

                    BlockQuote(_kind) => {
                        html.write_all(b"<blockquote>")?;
                        gmi.write_all(b"> ")?;
                        state = State::GmiPrefix("> ");
                    }

                    CodeBlock(CodeBlockKind::Fenced(lang)) => {
                        html.write_all(b"<pre><code>")?;
                        // TODO: highlighting with syntect
                        gmi.write_fmt(format_args!("```{}\r\n", lang))?;
                    }

                    CodeBlock(CodeBlockKind::Indented) => {
                        html.write_all(b"<pre><code>")?;
                        gmi.write_all(b"```")?;
                    }

                    List(None) => {
                        html.write_all(b"<ul>")?;
                    }

                    List(Some(counter_start)) => {
                        counter = counter_start;
                        if counter_start == 1 {
                            html.write_all(b"<ol>")?;
                        } else {
                            html.write_fmt(format_args!("<ol start=\"{}\">", counter_start))?;
                        }
                    }

                    Item => {
                        html.write_all(b"<li>")?;
                        gmi.write_fmt(format_args!("{}. ", counter))?;
                        counter += 1;
                    }

                    Strong => {
                        html.write_all(b"<b>")?;
                        gmi.write_all(b"**")?;
                    }

                    Emphasis => {
                        html.write_all(b"<i>")?;
                        gmi.write_all(b"*")?;
                    }

                    Strikethrough => {
                        html.write_all(b"<s>")?;
                        gmi.write_all(b"~")?;
                    }

                    Link {
                        dest_url, title, ..
                    } => {
                        html.write_fmt(format_args!("<a href=\"{}\">{}</a>", dest_url, title))?;

                        gmi.write_fmt(format_args!("{}[{}]", &title, links.len() + 1))?;
                        links.push(GmiLink {
                            title,
                            url: dest_url,
                        });
                    }

                    Image {
                        dest_url, title, ..
                    } => {
                        html.write_fmt(format_args!(
                            "<img src=\"{}\" alt=\"{}\">",
                            dest_url, title
                        ))?;

                        gmi.write_fmt(format_args!("{}[{}]", &title, links.len() + 1))?;
                        links.push(GmiLink {
                            title,
                            url: dest_url,
                        });
                    }

                    Table(_align) => {
                        html.write_all(b"<table>")?;
                        // gmi ??
                    }

                    TableHead => {
                        html.write_all(b"<thead><tr>")?;
                        state = State::TableHead;
                    }

                    TableRow => {
                        html.write_all(b"<tr>")?;
                    }

                    TableCell => {
                        if state == State::TableHead {
                            html.write_all(b"<th>")?;
                        } else {
                            html.write_all(b"<td>")?;
                        }
                    }

                    other => {
                        eprintln!("Unsupported tag: {:?}", other);
                    }
                }
            }

            End(tag) => {
                use pulldown_cmark::TagEnd::*;

                match tag {
                    Paragraph => {
                        html.write_all(b"</p>")?;

                        if !links.is_empty() {
                            gmi.write_all(b"\r\n\r\n")?;
                            for (i, link) in links.iter().enumerate() {
                                gmi.write_fmt(format_args!(
                                    "=> {} [{}]: {}",
                                    link.url, i, link.title,
                                ))?;
                            }
                            links.clear();
                        }
                    }
                    Heading(level) => html.write_fmt(format_args!("<{}>", level))?,
                    BlockQuote(_) => html.write_all(b"</blockquote>")?,
                    CodeBlock => {
                        html.write_all(b"</code></pre>")?;
                        gmi.write_all(b"```")?;
                    }
                    List(ordered) => {
                        if ordered {
                            html.write_all(b"</ol>")?;
                        } else {
                            html.write_all(b"</ul>")?;
                        }
                    }
                    Item => html.write_all(b"</li>")?,
                    Strong => {
                        html.write_all(b"</b>")?;
                        gmi.write_all(b"**")?;
                    }
                    Emphasis => {
                        html.write_all(b"</i>")?;
                        gmi.write_all(b"*")?;
                    }
                    Strikethrough => {
                        html.write_all(b"</s>")?;
                        gmi.write_all(b"~")?;
                    }
                    Link => {}
                    TableHead => html.write_all(b"</tr></thead><tbody>")?,
                    TableRow => html.write_all(b"</tr>")?,
                    TableCell => {
                        if state == State::TableHead {
                            html.write_all(b"</th>")?
                        } else {
                            html.write_all(b"</td>")?
                        }
                    }
                    Table => html.write_all(b"</tbody></table>")?,
                    _ => {}
                }

                state = State::Paragraph;
            }

            Text(text) => {
                html.write_all(text.as_bytes())?;
                gmi.write_all(text.as_bytes())?;
            }

            Code(code) => {
                html.write_all(b"<code>")?;
                html.write_all(code.as_bytes())?;
                html.write_all(b"</code>")?;

                gmi.write_all(b"`")?;
                gmi.write_all(code.as_bytes())?;
                gmi.write_all(b"`")?;
            }

            SoftBreak => {}

            HardBreak => {
                html.write_all(b"<br>")?;
                gmi.write_all(b"\r\n")?;
                if let State::GmiPrefix(prefix) = state {
                    gmi.write_all(prefix.as_bytes())?;
                }
            }

            Rule => {
                html.write_all(b"<hr>")?;
                gmi.write_all(b"---")?;
            }

            TaskListMarker(state) => {
                if state {
                    html.write_all(b"<input type=checkbox checked disabled>")?;
                    gmi.write_all(b"[x]")?;
                } else {
                    html.write_all(b"<input type=checkbox disabled>")?;
                    gmi.write_all(b"[ ]")?;
                }
            }

            other => {
                eprintln!("Unsupported event: {:?}", other);
            }
        }
    }

    html.flush()?;
    gmi.flush()?;

    Ok(())
}

#[inline(always)]
fn create_file(path: impl AsRef<Path>) -> std::io::Result<BufWriter<std::fs::File>> {
    let f = std::fs::OpenOptions::new()
        .create(true)
        .write(true)
        .open(path)?;
    Ok(BufWriter::new(f))
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum State {
    Start,
    Paragraph,
    GmiPrefix(&'static str),
    TableHead,
}

struct GmiLink<'link> {
    title: CowStr<'link>,
    url: CowStr<'link>,
}