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

//! # Root

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

use crate::filter::Filter;

/// # File discovery
///
/// ## Notes
///
/// - You can make this struct by [`find_files()`][::find_files()].
/// - If sub directories are symlinks, they will be ignored.
///
/// [::find_files()]: fn.find_files.html
#[derive(Debug)]
pub struct FileDiscovery<F> where F: Filter {

    /// # Root directory
    root: PathBuf,

    /// # Filter
    filter: F,

    /// # Recursive
    recursive: bool,

    /// # Current
    current: ReadDir,

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

    /// # Max depth
    max_depth: Option<usize>,

}

impl<F> FileDiscovery<F> where F: Filter {

    /// # Makes new instance
    pub fn make<P>(dir: P, recursive: bool, filter: F, max_depth: Option<usize>) -> io::Result<Self> where P: AsRef<Path> {
        Ok(Self {
            root: dir.as_ref().canonicalize()?,
            filter,
            recursive,
            current: fs::read_dir(dir)?,
            sub_dirs: None,
            max_depth,
        })
    }

}

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

    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) => {
                            let path = entry.path();
                            let is_symlink = file_type.is_symlink();
                            if file_type.is_dir() || (is_symlink && path.is_dir()) {
                                // If we accept symlinks, update code that calls ancestors()!
                                if self.recursive == false || is_symlink {
                                    continue;
                                }

                                if let Some(max_depth) = self.max_depth.as_ref() {
                                    match path.canonicalize() {
                                        // Symlinks are ignored, so using ancestors() is safe.
                                        Ok(path) => match depth_from(&self.root, &path) {
                                            Ok(depth) => if &depth >= max_depth {
                                                continue;
                                            },
                                            Err(err) => return Some(Err(err)),
                                        },
                                        Err(err) => return Some(Err(err)),
                                    };
                                }

                                if self.filter.accept(&path) == false {
                                    continue;
                                }

                                match self.sub_dirs.as_mut() {
                                    Some(sub_dirs) => sub_dirs.push(path),
                                    None => self.sub_dirs = Some(vec![path]),
                                };
                            } else if file_type.is_file() || (is_symlink && path.is_file()) {
                                if self.filter.accept(&path) == false {
                                    continue;
                                }
                                return Some(Ok(path));
                            }
                        },
                        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)),
                        },
                    },
                },
            };
        }
    }

}

/// # Calculates depth of path from a root directory
///
/// ## Notes
///
/// - [`canonicalize()`][r://PathBuf/canonicalize()] is _not_ called on input paths.
///
/// [r://PathBuf/canonicalize()]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.canonicalize
fn depth_from<P>(root_dir: P, path: P) -> io::Result<usize> where P: AsRef<Path> {
    let root_dir = root_dir.as_ref();
    let path = path.as_ref();

    let mut depth: usize = 0;
    let mut found_root = false;
    for a in path.ancestors().skip(1) {
        match a == root_dir {
            true => {
                found_root = true;
                break;
            },
            false => match depth.checked_add(1) {
                Some(new_depth) => depth = new_depth,
                None => return Err(Error::new(ErrorKind::Other, format!("Directory level of {:?} is too deep: {}", path, depth))),
            },
        };
    }

    match found_root {
        true => Ok(depth),
        false => Err(Error::new(ErrorKind::Other, format!("{:?} was expected to be inside of {:?}, but not", path, root_dir))),
    }
}

/// # 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, filter: F) -> io::Result<FileDiscovery<F>> where P: AsRef<Path>, F: Filter {
    FileDiscovery::make(dir, recursive, filter, None)
}