use std::cell::RefCell;
use std::cmp::Ordering;
use std::io;
use std::fs;
use std::fs::DirEntry;
use std::path::{Component, Path, PathBuf};
use std::rc::Rc;
use std::ops::Deref;

use gio;
use gio::prelude::*;
use gtk;
use gtk::MenuExt;
use gtk::prelude::*;

use neovim_lib::NeovimApi;

use nvim::{ErrorReport, NeovimClient, NeovimRef};
use shell;

const ICON_FOLDER_CLOSED: &str = "folder-symbolic";
const ICON_FOLDER_OPEN: &str = "folder-open-symbolic";
const ICON_FILE: &str = "text-x-generic-symbolic";

struct Components {
    dir_list_model: gtk::TreeStore,
    dir_list: gtk::ComboBox,
    context_menu: gtk::Menu,
    show_hidden_checkbox: gtk::CheckMenuItem,
    cd_action: gio::SimpleAction,
}

struct State {
    current_dir: String,
    show_hidden: bool,
    selected_path: Option<String>,
}

pub struct FileBrowserWidget {
    store: gtk::TreeStore,
    tree: gtk::TreeView,
    widget: gtk::Box,
    nvim: Option<Rc<NeovimClient>>,
    comps: Components,
    state: Rc<RefCell<State>>,
}

impl Deref for FileBrowserWidget {
    type Target = gtk::Box;

    fn deref(&self) -> &gtk::Box {
        &self.widget
    }
}

#[derive(Copy, Clone, Debug)]
enum FileType {
    File,
    Dir,
}

#[allow(dead_code)]
enum Column {
    Filename,
    Path,
    FileType,
    IconName,
}

impl FileBrowserWidget {
    pub fn new() -> Self {
        let builder = gtk::Builder::new_from_string(include_str!("../resources/side-panel.ui"));
        let widget: gtk::Box = builder.get_object("file_browser").unwrap();
        let tree: gtk::TreeView = builder.get_object("file_browser_tree_view").unwrap();
        let store: gtk::TreeStore = builder.get_object("file_browser_tree_store").unwrap();
        let dir_list_model: gtk::TreeStore = builder.get_object("dir_list_model").unwrap();
        let dir_list: gtk::ComboBox = builder.get_object("dir_list").unwrap();
        let context_menu: gtk::Menu = builder.get_object("file_browser_context_menu").unwrap();
        let show_hidden_checkbox: gtk::CheckMenuItem = builder
            .get_object("file_browser_show_hidden_checkbox")
            .unwrap();

        let file_browser = FileBrowserWidget {
            store,
            tree,
            widget,
            nvim: None,
            comps: Components {
                dir_list_model,
                dir_list,
                context_menu,
                show_hidden_checkbox,
                cd_action: gio::SimpleAction::new("cd", None),
            },
            state: Rc::new(RefCell::new(State {
                current_dir: "".to_owned(),
                show_hidden: false,
                selected_path: None,
            })),
        };
        file_browser
    }

    fn nvim(&self) -> Option<NeovimRef> {
        self.nvim.as_ref().unwrap().nvim()
    }

    pub fn init(&mut self, shell_state: &shell::State) {
        // Initialize values.
        let nvim = shell_state.nvim_clone();
        self.nvim = Some(nvim);
        let dir = get_current_dir(&mut self.nvim().unwrap());
        update_dir_list(&dir, &self.comps.dir_list_model, &self.comps.dir_list);
        self.state.borrow_mut().current_dir = dir;

        // Populate tree.
        tree_reload(&self.store, &self.state.borrow());

        let store = &self.store;
        let state_ref = &self.state;
        self.tree.connect_test_expand_row(clone!(store, state_ref => move |_, iter, _| {
            store.set(&iter, &[Column::IconName as u32], &[&ICON_FOLDER_OPEN]);
            // We cannot recursively populate all directories. Instead, we have prepared a single
            // empty child entry for all non-empty directories, so the row will be expandable. Now,
            // when a directory is expanded, populate its children.
            let state = state_ref.borrow();
            if let Some(child) = store.iter_children(iter) {
                let filename = store.get_value(&child, Column::Filename as i32);
                if filename.get::<&str>().is_none() {
                    store.remove(&child);
                    let dir_value = store.get_value(&iter, Column::Path as i32);
                    if let Some(dir) = dir_value.get() {
                        populate_tree_nodes(&store, &state, dir, Some(iter));
                    }
                } else {
                    // This directory is already populated, i.e. it has been expanded and collapsed
                    // again. Rows further down the tree might have been silently collapsed without
                    // getting an event. Update their folder icon.
                    let mut tree_path = store.get_path(&child).unwrap();
                    while let Some(iter) = store.get_iter(&tree_path) {
                        tree_path.next();
                        let file_type = store
                            .get_value(&iter, Column::FileType as i32)
                            .get::<u8>();
                        if file_type == Some(FileType::Dir as u8) {
                            store.set(&iter, &[Column::IconName as u32], &[&ICON_FOLDER_CLOSED]);
                        }
                    }
                }
            }
            Inhibit(false)
        }));

        self.tree.connect_row_collapsed(clone!(store => move |_, iter, _| {
            store.set(&iter, &[Column::IconName as u32], &[&ICON_FOLDER_CLOSED]);
        }));

        // Further initialization.
        self.init_actions();
        self.init_subscriptions(shell_state);
        self.connect_events();
    }

    fn init_actions(&self) {
        let actions = gio::SimpleActionGroup::new();

        let store = &self.store;
        let state_ref = &self.state;
        let nvim_ref = self.nvim.as_ref().unwrap();

        let reload_action = gio::SimpleAction::new("reload", None);
        reload_action.connect_activate(clone!(store, state_ref => move |_, _| {
            tree_reload(&store, &state_ref.borrow());
        }));
        actions.add_action(&reload_action);

        let cd_action = &self.comps.cd_action;
        cd_action.connect_activate(clone!(state_ref, nvim_ref => move |_, _| {
            let mut nvim = nvim_ref.nvim().unwrap();
            if let Some(ref path) = state_ref.borrow().selected_path {
                nvim.set_current_dir(&path).report_err();
            }
        }));
        actions.add_action(cd_action);

        self.comps
            .context_menu
            .insert_action_group("filebrowser", &actions);
    }

    fn init_subscriptions(&self, shell_state: &shell::State) {
        // Always set the current working directory as the root of the file browser.
        let store = &self.store;
        let state_ref = &self.state;
        let dir_list_model = &self.comps.dir_list_model;
        let dir_list = &self.comps.dir_list;
        shell_state.subscribe(
            "DirChanged",
            &["getcwd()"],
            clone!(store, state_ref, dir_list_model, dir_list => move |args| {
                let dir = args.into_iter().next().unwrap();
                let mut state = state_ref.borrow_mut();
                if dir != *state.current_dir {
                    update_dir_list(&dir, &dir_list_model, &dir_list);
                    state.current_dir = dir;
                    tree_reload(&store, &state);
                }
            }),
        );

        // Reveal the file of an entered buffer in the file browser and select the entry.
        let tree = &self.tree;
        let subscription = shell_state.subscribe(
            "BufEnter",
            &["getcwd()", "expand('%:p')"],
            clone!(tree, store => move |args| {
                let mut args_iter = args.into_iter();
                let dir = args_iter.next().unwrap();
                let file_path = args_iter.next().unwrap();
                let could_reveal =
                    if let Ok(rel_path) = Path::new(&file_path).strip_prefix(&Path::new(&dir)) {
                        reveal_path_in_tree(&store, &tree, &rel_path)
                    } else {
                        false
                    };
                if !could_reveal {
                    tree.get_selection().unselect_all();
                }
            }),
        );
        shell_state.run_now(&subscription);
    }

    fn connect_events(&self) {
        // Open file / go to dir, when user clicks on an entry.
        let store = &self.store;
        let nvim_ref = self.nvim.as_ref().unwrap();
        self.tree.connect_row_activated(clone!(store, nvim_ref => move |tree, path, _| {
            let mut nvim = nvim_ref.nvim().unwrap();
            let iter = store.get_iter(path).unwrap();
            let file_type = store
                .get_value(&iter, Column::FileType as i32)
                .get::<u8>()
                .unwrap();
            let file_path = store
                .get_value(&iter, Column::Path as i32)
                .get::<String>()
                .unwrap();
            if file_type == FileType::Dir as u8 {
                let expanded = tree.row_expanded(path);
                if expanded {
                    tree.collapse_row(path);
                } else {
                    tree.expand_row(path, false);
                }
            } else {
                // FileType::File
                let dir = get_current_dir(&mut nvim);
                let dir = Path::new(&dir);
                let file_path = if let Some(rel_path) = Path::new(&file_path)
                    .strip_prefix(&dir)
                    .ok()
                    .and_then(|p| p.to_str())
                {
                    rel_path
                } else {
                    &file_path
                };
                nvim.command(&format!(":e {}", file_path)).report_err();
            }
        }));

        // Connect directory list.
        let nvim_ref = self.nvim.as_ref().unwrap();
        self.comps.dir_list.connect_changed(clone!(nvim_ref => move |dir_list| {
            if let Some(iter) = dir_list.get_active_iter() {
                let model = dir_list.get_model().unwrap();
                if let Some(dir) = model.get_value(&iter, 2).get::<&str>() {
                    let mut nvim = nvim_ref.nvim().unwrap();
                    nvim.set_current_dir(dir).report_err();
                }
            }
        }));

        let store = &self.store;
        let state_ref = &self.state;
        let context_menu = &self.comps.context_menu;
        let cd_action = &self.comps.cd_action;
        self.tree.connect_button_press_event(
            clone!(store, state_ref, context_menu, cd_action => move |tree, ev_btn| {
                // Open context menu on right click.
                if ev_btn.get_button() == 3 {
                    context_menu.popup_at_pointer(&**ev_btn);
                    let (pos_x, pos_y) = ev_btn.get_position();
                    let iter = tree
                        .get_path_at_pos(pos_x as i32, pos_y as i32)
                        .and_then(|(path, _, _, _)| path)
                        .and_then(|path| store.get_iter(&path));
                    let file_type = iter
                        .as_ref()
                        .and_then(|iter| {
                            store
                                .get_value(&iter, Column::FileType as i32)
                                .get::<u8>()
                        });
                    // Enable the "Go To Directory" action only if the user clicked on a folder.
                    cd_action.set_enabled(file_type == Some(FileType::Dir as u8));
                    let path = iter
                        .and_then(|iter| {
                            store
                                .get_value(&iter, Column::Path as i32)
                                .get::<String>()
                        });
                    state_ref.borrow_mut().selected_path = path;
                }
                Inhibit(false)
            }),
        );

        // Show / hide hidden files when corresponding menu item is toggled.
        self.comps.show_hidden_checkbox.connect_toggled(clone!(state_ref, store => move |ev| {
            let mut state = state_ref.borrow_mut();
            state.show_hidden = ev.get_active();
            tree_reload(&store, &state);
        }));
    }
}

/// Compare function for dir entries.
///
/// Sorts directories above files.
fn cmp_dirs_first(lhs: &DirEntry, rhs: &DirEntry) -> io::Result<Ordering> {
    let lhs_metadata = fs::metadata(lhs.path())?;
    let rhs_metadata = fs::metadata(rhs.path())?;
    if lhs_metadata.file_type() == rhs_metadata.file_type() {
        Ok(lhs.path().cmp(&rhs.path()))
    } else {
        if lhs_metadata.is_dir() {
            Ok(Ordering::Less)
        } else {
            Ok(Ordering::Greater)
        }
    }
}

/// Clears an repopulate the entire tree.
fn tree_reload(store: &gtk::TreeStore, state: &State) {
    let dir = &state.current_dir;
    store.clear();
    populate_tree_nodes(store, state, dir, None);
}

/// Updates the dirctory list on top of the file browser.
///
/// The list represents the path the the current working directory.  If the new cwd is a parent of
/// the old one, the list is kept and only the active entry is updated. Otherwise, the list is
/// replaced with the new path and the last entry is marked active.
fn update_dir_list(dir: &str, dir_list_model: &gtk::TreeStore, dir_list: &gtk::ComboBox) {
    // The current working directory path.
    let complete_path = Path::new(dir);
    let mut path = PathBuf::new();
    let mut components = complete_path.components();
    let mut next = components.next();

    // Iterator over existing dir_list model.
    let mut dir_list_iter = dir_list_model.get_iter_first();

    // Whether existing entries up to the current position of dir_list_iter are a prefix of the
    // new current working directory path.
    let mut is_prefix = true;

    // Iterate over components of the cwd. Simultaneously move dir_list_iter forward.
    while let Some(dir) = next {
        next = components.next();
        let dir_name = &*dir.as_os_str().to_string_lossy();
        // Assemble path up to current component.
        path.push(Path::new(&dir));
        let path_str = path.to_str().unwrap_or_else(|| {
            error!(
                "Could not convert path to string: {}\n
                    Directory chooser will not work for that entry.",
                path.to_string_lossy()
            );
            ""
        });
        // Use the current entry of dir_list, if any, otherwise append a new one.
        let current_iter = dir_list_iter.unwrap_or_else(|| dir_list_model.append(None));
        // Check if the current entry is still part of the new cwd.
        if is_prefix && dir_list_model.get_value(&current_iter, 0).get::<&str>() != Some(&dir_name)
        {
            is_prefix = false;
        }
        if next.is_some() {
            // Update dir_list entry.
            dir_list_model.set(
                &current_iter,
                &[0, 1, 2],
                &[&dir_name, &ICON_FOLDER_CLOSED, &path_str],
            );
        } else {
            // We reached the last component of the new cwd path. Set the active entry of dir_list
            // to this one.
            dir_list_model.set(
                &current_iter,
                &[0, 1, 2],
                &[&dir_name, &ICON_FOLDER_OPEN, &path_str],
            );
            dir_list.set_active_iter(&current_iter);
        };
        // Advance dir_list_iter.
        dir_list_iter = if dir_list_model.iter_next(&current_iter) {
            Some(current_iter)
        } else {
            None
        }
    }
    // We updated the dir list to the point of the current working directory.
    if let Some(iter) = dir_list_iter {
        if is_prefix {
            // If we didn't change any entries to this point and the list contains further entries,
            // the remaining ones are subdirectories of the cwd and we keep them.
            loop {
                dir_list_model.set(&iter, &[1], &[&ICON_FOLDER_CLOSED]);
                if !dir_list_model.iter_next(&iter) {
                    break;
                }
            }
        } else {
            // If we needed to change entries, the following ones are not directories under the
            // cwd and we clear them.
            while dir_list_model.remove(&iter) {}
        }
    }
}

/// Populates one level, i.e. one directory of the file browser tree.
fn populate_tree_nodes(
    store: &gtk::TreeStore,
    state: &State,
    dir: &str,
    parent: Option<&gtk::TreeIter>,
) {
    let path = Path::new(dir);
    let iter = path.read_dir()
        .expect("read dir failed")
        .filter_map(Result::ok);
    let mut entries: Vec<DirEntry> = if state.show_hidden {
        iter.collect()
    } else {
        iter.filter(|entry| !entry.file_name().to_string_lossy().starts_with("."))
            .filter(|entry| !entry.file_name().to_string_lossy().ends_with("~"))
            .collect()
    };
    entries.sort_unstable_by(|lhs, rhs| cmp_dirs_first(lhs, rhs).unwrap_or(Ordering::Equal));
    for entry in entries {
        let path = if let Some(path) = entry.path().to_str() {
            path.to_owned()
        } else {
            // Skip paths that contain invalid unicode.
            continue;
        };
        let filename = entry.file_name().to_str().unwrap().to_owned();
        let file_type = if let Ok(metadata) = fs::metadata(entry.path()) {
            let file_type = metadata.file_type();
            if file_type.is_dir() {
                FileType::Dir
            } else if file_type.is_file() {
                FileType::File
            } else {
                continue;
            }
        } else {
            // In case of invalid symlinks, we cannot obtain metadata.
            continue;
        };
        let icon = match file_type {
            FileType::Dir => ICON_FOLDER_CLOSED,
            FileType::File => ICON_FILE,
        };
        // When we get until here, we want to show the entry. Append it to the tree.
        let iter = store.append(parent);
        store.set(
            &iter,
            &[0, 1, 2, 3],
            &[&filename, &path, &(file_type as u8), &icon],
        );
        // For directories, check whether the directory is empty. If not, append a single empty
        // entry, so the expand arrow is shown. Its contents are dynamically populated when
        // expanded (see `init`).
        if let FileType::Dir = file_type {
            let not_empty = if let Ok(mut dir) = entry.path().read_dir() {
                dir.next().is_some()
            } else {
                false
            };
            if not_empty {
                let iter = store.append(&iter);
                store.set(&iter, &[], &[]);
            }
        }
    }
}

fn get_current_dir(nvim: &mut NeovimRef) -> String {
    nvim.eval("getcwd()")
        .as_ref()
        .ok()
        .and_then(|s| s.as_str())
        .expect("Couldn't get working directory")
        .to_owned()
}

/// Reveals and selects the given file in the file browser.
///
/// Returns `true` if the file could be successfully revealed.
fn reveal_path_in_tree(store: &gtk::TreeStore, tree: &gtk::TreeView, rel_file_path: &Path) -> bool {
    let mut tree_path = gtk::TreePath::new();
    'components: for component in rel_file_path.components() {
        if let Component::Normal(component) = component {
            tree_path.down();
            while let Some(iter) = store.get_iter(&tree_path) {
                let entry_value = store.get_value(&iter, Column::Filename as i32);
                let entry = entry_value.get::<&str>().unwrap();
                if component == entry {
                    tree.expand_row(&tree_path, false);
                    continue 'components;
                }
                tree_path.next();
            }
            return false;
        } else {
            return false;
        }
    }
    if tree_path.get_depth() == 0 {
        return false;
    }
    tree.set_cursor(&tree_path, None, false);
    true
}