use anyhow::bail;
use anyhow::Context;
use anyhow::Error;
use orgize::elements::Timestamp;
use orgize::{
    export::{DefaultHtmlHandler, HtmlHandler},
    Element, Org,
};
use std::io::Write;
use syntect::{
    highlighting::{Theme, ThemeSet},
    html::highlighted_html_for_string,
    parsing::SyntaxSet,
};
use time::macros::format_description;
use time::Date;

pub trait Parser<T> {
    fn start(&mut self, _: &Element) -> anyhow::Result<()>;
    fn end(&mut self, _: &Element) -> anyhow::Result<()>;
    fn render(self) -> anyhow::Result<T>;
}

pub fn parse<T, P: Parser<T>>(mut p: P, org: &str) -> anyhow::Result<T> {
    for e in Org::parse(org).iter() {
        match e {
            orgize::Event::Start(ele) => p.start(ele)?,
            orgize::Event::End(ele) => p.end(ele)?,
        }
    }

    p.render()
}

pub struct CustomHtmlHandler {
    fallback: DefaultHtmlHandler,
    ps: SyntaxSet,
    theme: Theme,
}

impl Default for CustomHtmlHandler {
    fn default() -> Self {
        let mut ts = ThemeSet::load_defaults();

        Self {
            fallback: Default::default(),
            ps: SyntaxSet::load_defaults_newlines(),
            theme: ts
                .themes
                .remove("base16-eighties.dark")
                .expect("Could not load theme"),
        }
    }
}

impl HtmlHandler<Error> for CustomHtmlHandler {
    fn start<W: Write>(&mut self, mut w: W, element: &Element) -> Result<(), Error> {
        match element {
            Element::SourceBlock(block) => {
                let syntax = self
                    .ps
                    .find_syntax_by_token(&block.language)
                    .with_context(|| format!("Unknown language {}", block.language))?;

                let html =
                    highlighted_html_for_string(&block.contents, &self.ps, syntax, &self.theme)?;

                write!(w, "{html}")?;
            }
            Element::SpecialBlock(block) => match block.name.as_ref() {
                "JUSTIFYRIGHT" => {
                    write!(w, r#"<div class="justify-right">"#)?;
                }
                _ => bail!("Unrecognized special block name {}", block.name),
            },
            Element::Timestamp(Timestamp::Active { start, .. }) => {
                let date = Date::from_calendar_date(
                    start.year.into(),
                    start.month.try_into()?,
                    start.day,
                )?;

                date.format_into(
                    &mut w,
                    format_description!("[day] [month repr:short] [year]"),
                )?;
            }
            // fallback to default handler
            _ => self.fallback.start(w, element)?,
        }

        Ok(())
    }

    fn end<W: Write>(&mut self, mut w: W, element: &Element) -> Result<(), Error> {
        match element {
            Element::SpecialBlock(block) => match block.name.as_ref() {
                "JUSTIFYRIGHT" => {
                    write!(w, "</div>")?;
                }
                _ => bail!("Unrecognized special block name {}", block.name),
            },

            // fallback to default handler
            _ => self.fallback.end(w, element)?,
        }

        Ok(())
    }
}