// Copyright 2023 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use matter::matter;
use mdbook::book::{Book, BookItem};
use mdbook::preprocess::PreprocessorContext;

pub fn remove_frontmatter(
    ctx: &PreprocessorContext,
    book: &mut Book,
) -> anyhow::Result<()> {
    let is_html = ctx.renderer == "html";
    book.for_each_mut(|chapter| {
        let BookItem::Chapter(chapter) = chapter else {
            return;
        };
        if let Some((frontmatter, content)) = matter(&chapter.content) {
            if is_html {
                // For the moment, include the frontmatter in the slide in a floating <pre>, for review
                // purposes.
                let pre = format!(r#"<pre class="frontmatter">{frontmatter}</pre>"#);
                chapter.content = format!("{pre}\n\n{content}");
            } else {
                // For non-HTML renderers, just strip the frontmatter.
                chapter.content = content;
            }
        }
    });
    Ok(())
}