use std::path::Path;
use regex::Regex;

use errors::*;

use super::{Preprocessor, PreprocessorContext};
use book::{Book, BookItem};

/// A preprocessor for converting file name `README.md` to `index.md` since
/// `README.md` is the de facto index file in a markdown-based documentation.
pub struct IndexPreprocessor;

impl IndexPreprocessor {
    /// Create a new `IndexPreprocessor`.
    pub fn new() -> Self {
        IndexPreprocessor
    }
}

impl Preprocessor for IndexPreprocessor {
    fn name(&self) -> &str {
        "index"
    }

    fn run(&self, ctx: &PreprocessorContext, book: &mut Book) -> Result<()> {
        let source_dir = ctx.root.join(&ctx.config.book.src);
        book.for_each_mut(|section: &mut BookItem| {
            if let BookItem::Chapter(ref mut ch) = *section {
                if is_readme_file(&ch.path) {
                    let index_md = source_dir
                        .join(ch.path.with_file_name("index.md"));
                    if index_md.exists() {
                        warn_readme_name_conflict(&ch.path, &index_md);
                    }

                    ch.path.set_file_name("index.md");
                }
            }
        });

        Ok(())
    }
}

fn warn_readme_name_conflict<P: AsRef<Path>>(readme_path: P, index_path: P) {
    let file_name = readme_path.as_ref().file_name().unwrap_or_default();
    let parent_dir = index_path.as_ref().parent().unwrap_or(index_path.as_ref());
    warn!("It seems that there are both {:?} and index.md under \"{}\".", file_name, parent_dir.display());
    warn!("mdbook converts {:?} into index.html by default. It may cause", file_name);
    warn!("unexpected behavior if putting both files under the same directory.");
    warn!("To solve the warning, try to rearrange the book structure or disable");
    warn!("\"index\" preprocessor to stop the conversion.");
}

fn is_readme_file<P: AsRef<Path>>(path: P) -> bool {
    lazy_static! {
        static ref RE: Regex = Regex::new(r"(?i)^readme$").unwrap();
    }
    RE.is_match(
        path.as_ref()
            .file_stem()
            .and_then(|s| s.to_str())
            .unwrap_or_default()
    )
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn file_stem_exactly_matches_readme_case_insensitively() {
        let path = "path/to/Readme.md";
        assert!(is_readme_file(path));

        let path = "path/to/README.md";
        assert!(is_readme_file(path));

        let path = "path/to/rEaDmE.md";
        assert!(is_readme_file(path));

        let path = "path/to/README.markdown";
        assert!(is_readme_file(path));

        let path = "path/to/README";
        assert!(is_readme_file(path));

        let path = "path/to/README-README.md";
        assert!(!is_readme_file(path));
    }
}