//! VFS stands for Virtual File System.
//!
//! When doing analysis, we don't want to do any IO, we want to keep all source
//! code in memory. However, the actual source code is stored on disk, so you
//! need to get it into the memory in the first place somehow. VFS is the
//! component which does this.
//!
//! It is also responsible for watching the disk for changes, and for merging
//! editor state (modified, unsaved files) with disk state.
//! TODO: Some LSP clients support watching the disk, so this crate should
//! to support custom watcher events (related to https://github.com/rust-analyzer/rust-analyzer/issues/131)
//!
//! VFS is based on a concept of roots: a set of directories on the file system
//! which are watched for changes. Typically, there will be a root for each
//! Cargo package.
mod io;

use std::{
    cmp::Reverse,
    fmt, fs, mem,
    ops::{Deref, DerefMut},
    path::{Path, PathBuf},
    sync::Arc,
    thread,
};

use crossbeam_channel::Receiver;
use ra_arena::{impl_arena_id, Arena, RawId};
use relative_path::{Component, RelativePath, RelativePathBuf};
use rustc_hash::{FxHashMap, FxHashSet};
use walkdir::DirEntry;

pub use crate::io::TaskResult as VfsTask;
use io::{TaskResult, Worker};

/// `RootFilter` is a predicate that checks if a file can belong to a root. If
/// several filters match a file (nested dirs), the most nested one wins.
pub(crate) struct RootFilter {
    root: PathBuf,
    filter: fn(&Path, &RelativePath) -> bool,
    excluded_dirs: Vec<PathBuf>,
}

impl RootFilter {
    fn new(root: PathBuf, excluded_dirs: Vec<PathBuf>) -> RootFilter {
        RootFilter {
            root,
            filter: default_filter,
            excluded_dirs,
        }
    }
    /// Check if this root can contain `path`. NB: even if this returns
    /// true, the `path` might actually be conained in some nested root.
    pub(crate) fn can_contain(&self, path: &Path) -> Option<RelativePathBuf> {
        let rel_path = path.strip_prefix(&self.root).ok()?;
        let rel_path = RelativePathBuf::from_path(rel_path).ok()?;
        if !(self.filter)(path, rel_path.as_relative_path()) {
            return None;
        }
        Some(rel_path)
    }

    pub(crate) fn entry_filter<'a>(&'a self) -> impl FnMut(&DirEntry) -> bool + 'a {
        move |entry: &DirEntry| {
            if entry.path().is_dir() && self.excluded_dirs.iter().any(|it| it == entry.path()) {
                // do not walk nested roots
                false
            } else {
                self.can_contain(entry.path()).is_some()
            }
        }
    }
}

pub(crate) fn default_filter(path: &Path, rel_path: &RelativePath) -> bool {
    if path.is_dir() {
        for (i, c) in rel_path.components().enumerate() {
            if let Component::Normal(c) = c {
                // TODO hardcoded for now
                if (i == 0 && c == "target") || c == ".git" || c == "node_modules" {
                    return false;
                }
            }
        }
        true
    } else {
        rel_path.extension() == Some("rs")
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct VfsRoot(pub RawId);
impl_arena_id!(VfsRoot);

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct VfsFile(pub RawId);
impl_arena_id!(VfsFile);

struct VfsFileData {
    root: VfsRoot,
    path: RelativePathBuf,
    is_overlayed: bool,
    text: Arc<String>,
}

pub(crate) struct Roots {
    roots: Arena<VfsRoot, Arc<RootFilter>>,
}

impl Roots {
    pub(crate) fn new(mut paths: Vec<PathBuf>) -> Roots {
        let mut roots = Arena::default();
        // A hack to make nesting work.
        paths.sort_by_key(|it| Reverse(it.as_os_str().len()));
        for (i, path) in paths.iter().enumerate() {
            let nested_roots = paths[..i]
                .iter()
                .filter(|it| it.starts_with(path))
                .map(|it| it.clone())
                .collect::<Vec<_>>();

            let root_filter = Arc::new(RootFilter::new(path.clone(), nested_roots));

            roots.alloc(root_filter.clone());
        }
        Roots { roots }
    }
    pub(crate) fn find(&self, path: &Path) -> Option<(VfsRoot, RelativePathBuf)> {
        self.roots
            .iter()
            .find_map(|(root, data)| data.can_contain(path).map(|it| (root, it)))
    }
}

impl Deref for Roots {
    type Target = Arena<VfsRoot, Arc<RootFilter>>;
    fn deref(&self) -> &Self::Target {
        &self.roots
    }
}

impl DerefMut for Roots {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.roots
    }
}

pub struct Vfs {
    roots: Arc<Roots>,
    files: Arena<VfsFile, VfsFileData>,
    root2files: FxHashMap<VfsRoot, FxHashSet<VfsFile>>,
    pending_changes: Vec<VfsChange>,
    worker: Worker,
}

impl fmt::Debug for Vfs {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.write_str("Vfs { ... }")
    }
}

impl Vfs {
    pub fn new(roots: Vec<PathBuf>) -> (Vfs, Vec<VfsRoot>) {
        let roots = Arc::new(Roots::new(roots));
        let worker = io::Worker::start(roots.clone());
        let mut root2files = FxHashMap::default();

        for (root, filter) in roots.iter() {
            root2files.insert(root, Default::default());
            worker
                .sender()
                .send(io::Task::AddRoot {
                    root,
                    filter: filter.clone(),
                })
                .unwrap();
        }
        let res = Vfs {
            roots,
            files: Arena::default(),
            root2files,
            worker,
            pending_changes: Vec::new(),
        };
        let vfs_roots = res.roots.iter().map(|(id, _)| id).collect();
        (res, vfs_roots)
    }

    pub fn root2path(&self, root: VfsRoot) -> PathBuf {
        self.roots[root].root.clone()
    }

    pub fn path2file(&self, path: &Path) -> Option<VfsFile> {
        if let Some((_root, _path, Some(file))) = self.find_root(path) {
            return Some(file);
        }
        None
    }

    pub fn file2path(&self, file: VfsFile) -> PathBuf {
        let rel_path = &self.files[file].path;
        let root_path = &self.roots[self.files[file].root].root;
        rel_path.to_path(root_path)
    }

    pub fn file_for_path(&self, path: &Path) -> Option<VfsFile> {
        if let Some((_root, _path, Some(file))) = self.find_root(path) {
            return Some(file);
        }
        None
    }

    pub fn load(&mut self, path: &Path) -> Option<VfsFile> {
        if let Some((root, rel_path, file)) = self.find_root(path) {
            return if let Some(file) = file {
                Some(file)
            } else {
                let text = fs::read_to_string(path).unwrap_or_default();
                let text = Arc::new(text);
                let file = self.add_file(root, rel_path.clone(), Arc::clone(&text), false);
                let change = VfsChange::AddFile {
                    file,
                    text,
                    root,
                    path: rel_path,
                };
                self.pending_changes.push(change);
                Some(file)
            };
        }
        None
    }

    pub fn task_receiver(&self) -> &Receiver<io::TaskResult> {
        self.worker.receiver()
    }

    pub fn handle_task(&mut self, task: io::TaskResult) {
        match task {
            TaskResult::BulkLoadRoot { root, files } => {
                let mut cur_files = Vec::new();
                // While we were scanning the root in the backgound, a file might have
                // been open in the editor, so we need to account for that.
                let exising = self.root2files[&root]
                    .iter()
                    .map(|&file| (self.files[file].path.clone(), file))
                    .collect::<FxHashMap<_, _>>();
                for (path, text) in files {
                    if let Some(&file) = exising.get(&path) {
                        let text = Arc::clone(&self.files[file].text);
                        cur_files.push((file, path, text));
                        continue;
                    }
                    let text = Arc::new(text);
                    let file = self.add_file(root, path.clone(), Arc::clone(&text), false);
                    cur_files.push((file, path, text));
                }

                let change = VfsChange::AddRoot {
                    root,
                    files: cur_files,
                };
                self.pending_changes.push(change);
            }
            TaskResult::AddSingleFile { root, path, text } => {
                self.do_add_file(root, path, text, false);
            }
            TaskResult::ChangeSingleFile { root, path, text } => {
                if let Some(file) = self.find_file(root, &path) {
                    self.do_change_file(file, text, false);
                } else {
                    self.do_add_file(root, path, text, false);
                }
            }
            TaskResult::RemoveSingleFile { root, path } => {
                if let Some(file) = self.find_file(root, &path) {
                    self.do_remove_file(root, path, file, false);
                }
            }
        }
    }

    fn do_add_file(
        &mut self,
        root: VfsRoot,
        path: RelativePathBuf,
        text: String,
        is_overlay: bool,
    ) -> Option<VfsFile> {
        let text = Arc::new(text);
        let file = self.add_file(root, path.clone(), text.clone(), is_overlay);
        self.pending_changes.push(VfsChange::AddFile {
            file,
            root,
            path,
            text,
        });
        Some(file)
    }

    fn do_change_file(&mut self, file: VfsFile, text: String, is_overlay: bool) {
        if !is_overlay && self.files[file].is_overlayed {
            return;
        }
        let text = Arc::new(text);
        self.change_file(file, text.clone(), is_overlay);
        self.pending_changes
            .push(VfsChange::ChangeFile { file, text });
    }

    fn do_remove_file(
        &mut self,
        root: VfsRoot,
        path: RelativePathBuf,
        file: VfsFile,
        is_overlay: bool,
    ) {
        if !is_overlay && self.files[file].is_overlayed {
            return;
        }
        self.remove_file(file);
        self.pending_changes
            .push(VfsChange::RemoveFile { root, path, file });
    }

    pub fn add_file_overlay(&mut self, path: &Path, text: String) -> Option<VfsFile> {
        if let Some((root, rel_path, file)) = self.find_root(path) {
            if let Some(file) = file {
                self.do_change_file(file, text, true);
                Some(file)
            } else {
                self.do_add_file(root, rel_path, text, true)
            }
        } else {
            None
        }
    }

    pub fn change_file_overlay(&mut self, path: &Path, new_text: String) {
        if let Some((_root, _path, file)) = self.find_root(path) {
            let file = file.expect("can't change a file which wasn't added");
            self.do_change_file(file, new_text, true);
        }
    }

    pub fn remove_file_overlay(&mut self, path: &Path) -> Option<VfsFile> {
        if let Some((root, path, file)) = self.find_root(path) {
            let file = file.expect("can't remove a file which wasn't added");
            let full_path = path.to_path(&self.roots[root].root);
            if let Ok(text) = fs::read_to_string(&full_path) {
                self.do_change_file(file, text, true);
            } else {
                self.do_remove_file(root, path, file, true);
            }
            Some(file)
        } else {
            None
        }
    }

    pub fn commit_changes(&mut self) -> Vec<VfsChange> {
        mem::replace(&mut self.pending_changes, Vec::new())
    }

    /// Sutdown the VFS and terminate the background watching thread.
    pub fn shutdown(self) -> thread::Result<()> {
        self.worker.shutdown()
    }

    fn add_file(
        &mut self,
        root: VfsRoot,
        path: RelativePathBuf,
        text: Arc<String>,
        is_overlayed: bool,
    ) -> VfsFile {
        let data = VfsFileData {
            root,
            path,
            text,
            is_overlayed,
        };
        let file = self.files.alloc(data);
        self.root2files.get_mut(&root).unwrap().insert(file);
        file
    }

    fn change_file(&mut self, file: VfsFile, new_text: Arc<String>, is_overlayed: bool) {
        let mut file_data = &mut self.files[file];
        file_data.text = new_text;
        file_data.is_overlayed = is_overlayed;
    }

    fn remove_file(&mut self, file: VfsFile) {
        //FIXME: use arena with removal
        self.files[file].text = Default::default();
        self.files[file].path = Default::default();
        let root = self.files[file].root;
        let removed = self.root2files.get_mut(&root).unwrap().remove(&file);
        assert!(removed);
    }

    fn find_root(&self, path: &Path) -> Option<(VfsRoot, RelativePathBuf, Option<VfsFile>)> {
        let (root, path) = self.roots.find(&path)?;
        let file = self.find_file(root, &path);
        Some((root, path, file))
    }

    fn find_file(&self, root: VfsRoot, path: &RelativePath) -> Option<VfsFile> {
        self.root2files[&root]
            .iter()
            .map(|&it| it)
            .find(|&file| self.files[file].path == path)
    }
}

#[derive(Debug, Clone)]
pub enum VfsChange {
    AddRoot {
        root: VfsRoot,
        files: Vec<(VfsFile, RelativePathBuf, Arc<String>)>,
    },
    AddFile {
        root: VfsRoot,
        file: VfsFile,
        path: RelativePathBuf,
        text: Arc<String>,
    },
    RemoveFile {
        root: VfsRoot,
        file: VfsFile,
        path: RelativePathBuf,
    },
    ChangeFile {
        file: VfsFile,
        text: Arc<String>,
    },
}