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// License: see LICENSE file at root directory of `master` branch

//! # Root

use std::{
    fs::{self, ReadDir},
    io,
    path::{Path, PathBuf},
};

/// # Path filter
pub trait PathFilter {

    /// # Returns `true` to accept given path, `false` to ignore it
    fn accept(&self, path: &Path) -> bool;

}

/// # A [filter][::PathFilter] that accepts all paths
///
/// [::PathFilter]: trait.PathFilter.html
#[derive(Debug)]
pub struct AllPaths {

    /// # Lock
    _lock: (),

}

impl AllPaths {

    /// # Makes new instance
    pub fn new() -> Self {
        Self {
            _lock: (),
        }
    }

}

impl PathFilter for AllPaths {

    fn accept(&self, _: &Path) -> bool {
        true
    }

}

/// # File discovery
///
/// ## Notes
///
/// - You can make this struct by [`::find_files()`][::find_files()].
/// - If sub directories are symlinks, they will be ignored.
/// - If an [entry][rust::DirEntry] is neither a file or a directory, it will be ignored.
///
/// [::find_files()]: fn.find_files.html
/// [rust::DirEntry]: https://doc.rust-lang.org/std/fs/struct.DirEntry.html
#[derive(Debug)]
pub struct FileDiscovery<F> where F: PathFilter {

    /// # Path filter
    path_filter: F,

    /// # Recursive
    recursive: bool,

    /// # Current
    current: ReadDir,

    /// # Sub directories
    sub_dirs: Option<Vec<PathBuf>>,

}

impl<F> Iterator for FileDiscovery<F> where F: PathFilter {

    type Item = io::Result<PathBuf>;

    fn next(&mut self) -> Option<Self::Item> {
        loop {
            match self.current.next() {
                Some(entry) => match entry {
                    Ok(entry) => match entry.file_type() {
                        Ok(file_type) => {
                            if file_type.is_dir() {
                                if self.recursive == false || file_type.is_symlink() {
                                    continue;
                                }

                                let dir = entry.path();
                                if self.path_filter.accept(&dir) == false {
                                    continue;
                                }

                                match self.sub_dirs.as_mut() {
                                    Some(sub_dirs) => sub_dirs.push(dir),
                                    None => self.sub_dirs = Some(vec![dir]),
                                };
                            } else if file_type.is_file() {
                                let file = entry.path();
                                if self.path_filter.accept(&file) == false {
                                    continue;
                                }
                                return Some(Ok(file));
                            }
                        },
                        Err(err) => return Some(Err(err)),
                    },
                    Err(err) => return Some(Err(err)),
                },
                None => match self.sub_dirs.as_mut() {
                    None => return None,
                    Some(sub_dirs) => match sub_dirs.len() {
                        0 => return None,
                        _ => match fs::read_dir(sub_dirs.remove(0)) {
                            Ok(new) => self.current = new,
                            Err(err) => return Some(Err(err)),
                        },
                    },
                },
            };
        }
    }

}

/// # Finds files
///
/// This function makes new instance of [`FileDiscovery`][::FileDiscovery]. You should refer to that struct for notes on usage.
///
/// [::FileDiscovery]: struct.FileDiscovery.html
pub fn find_files<P, F>(dir: P, recursive: bool, path_filter: F) -> io::Result<FileDiscovery<F>> where P: AsRef<Path>, F: PathFilter {
    Ok(FileDiscovery {
        path_filter,
        recursive,
        current: fs::read_dir(dir)?,
        sub_dirs: None,
    })
}