use editor::{scroll::Autoscroll, Anchor, Editor, ExcerptId};
use gpui::{
    actions, div, rems, uniform_list, AppContext, Div, EventEmitter, FocusHandle, FocusableView,
    Hsla, InteractiveElement, IntoElement, Model, MouseButton, MouseDownEvent, MouseMoveEvent,
    ParentElement, Render, SharedString, Styled, UniformListScrollHandle, View, ViewContext,
    VisualContext, WeakView, WindowContext,
};
use language::{Buffer, OwnedSyntaxLayer};
use std::{mem, ops::Range};
use theme::ActiveTheme;
use tree_sitter::{Node, TreeCursor};
use ui::{h_flex, ButtonLike, Color, ContextMenu, Label, LabelCommon, PopoverMenu};
use workspace::{
    item::{Item, ItemHandle},
    SplitDirection, ToolbarItemEvent, ToolbarItemLocation, ToolbarItemView, Workspace,
};

actions!(debug, [OpenSyntaxTreeView]);

pub fn init(cx: &mut AppContext) {
    cx.observe_new_views(|workspace: &mut Workspace, _| {
        workspace.register_action(|workspace, _: &OpenSyntaxTreeView, cx| {
            let active_item = workspace.active_item(cx);
            let workspace_handle = workspace.weak_handle();
            let syntax_tree_view =
                cx.new_view(|cx| SyntaxTreeView::new(workspace_handle, active_item, cx));
            workspace.split_item(SplitDirection::Right, Box::new(syntax_tree_view), cx)
        });
    })
    .detach();
}

pub struct SyntaxTreeView {
    workspace_handle: WeakView<Workspace>,
    editor: Option<EditorState>,
    list_scroll_handle: UniformListScrollHandle,
    selected_descendant_ix: Option<usize>,
    hovered_descendant_ix: Option<usize>,
    focus_handle: FocusHandle,
}

pub struct SyntaxTreeToolbarItemView {
    tree_view: Option<View<SyntaxTreeView>>,
    subscription: Option<gpui::Subscription>,
}

struct EditorState {
    editor: View<Editor>,
    active_buffer: Option<BufferState>,
    _subscription: gpui::Subscription,
}

#[derive(Clone)]
struct BufferState {
    buffer: Model<Buffer>,
    excerpt_id: ExcerptId,
    active_layer: Option<OwnedSyntaxLayer>,
}

impl SyntaxTreeView {
    pub fn new(
        workspace_handle: WeakView<Workspace>,
        active_item: Option<Box<dyn ItemHandle>>,
        cx: &mut ViewContext<Self>,
    ) -> Self {
        let mut this = Self {
            workspace_handle: workspace_handle.clone(),
            list_scroll_handle: UniformListScrollHandle::new(),
            editor: None,
            hovered_descendant_ix: None,
            selected_descendant_ix: None,
            focus_handle: cx.focus_handle(),
        };

        this.workspace_updated(active_item, cx);
        cx.observe(
            &workspace_handle.upgrade().unwrap(),
            |this, workspace, cx| {
                this.workspace_updated(workspace.read(cx).active_item(cx), cx);
            },
        )
        .detach();

        this
    }

    fn workspace_updated(
        &mut self,
        active_item: Option<Box<dyn ItemHandle>>,
        cx: &mut ViewContext<Self>,
    ) {
        if let Some(item) = active_item {
            if item.item_id() != cx.entity_id() {
                if let Some(editor) = item.act_as::<Editor>(cx) {
                    self.set_editor(editor, cx);
                }
            }
        }
    }

    fn set_editor(&mut self, editor: View<Editor>, cx: &mut ViewContext<Self>) {
        if let Some(state) = &self.editor {
            if state.editor == editor {
                return;
            }
            editor.update(cx, |editor, cx| {
                editor.clear_background_highlights::<Self>(cx)
            });
        }

        let subscription = cx.subscribe(&editor, |this, _, event, cx| {
            let did_reparse = match event {
                editor::EditorEvent::Reparsed(_) => true,
                editor::EditorEvent::SelectionsChanged { .. } => false,
                _ => return,
            };
            this.editor_updated(did_reparse, cx);
        });

        self.editor = Some(EditorState {
            editor,
            _subscription: subscription,
            active_buffer: None,
        });
        self.editor_updated(true, cx);
    }

    fn editor_updated(&mut self, did_reparse: bool, cx: &mut ViewContext<Self>) -> Option<()> {
        // Find which excerpt the cursor is in, and the position within that excerpted buffer.
        let editor_state = self.editor.as_mut()?;
        let editor = &editor_state.editor.read(cx);
        let selection_range = editor.selections.last::<usize>(cx).range();
        let multibuffer = editor.buffer().read(cx);
        let (buffer, range, excerpt_id) = multibuffer
            .range_to_buffer_ranges(selection_range, cx)
            .pop()?;

        // If the cursor has moved into a different excerpt, retrieve a new syntax layer
        // from that buffer.
        let buffer_state = editor_state
            .active_buffer
            .get_or_insert_with(|| BufferState {
                buffer: buffer.clone(),
                excerpt_id,
                active_layer: None,
            });
        let mut prev_layer = None;
        if did_reparse {
            prev_layer = buffer_state.active_layer.take();
        }
        if buffer_state.buffer != buffer || buffer_state.excerpt_id != excerpt_id {
            buffer_state.buffer = buffer.clone();
            buffer_state.excerpt_id = excerpt_id;
            buffer_state.active_layer = None;
        }

        let layer = match &mut buffer_state.active_layer {
            Some(layer) => layer,
            None => {
                let snapshot = buffer.read(cx).snapshot();
                let layer = if let Some(prev_layer) = prev_layer {
                    let prev_range = prev_layer.node().byte_range();
                    snapshot
                        .syntax_layers()
                        .filter(|layer| layer.language == &prev_layer.language)
                        .min_by_key(|layer| {
                            let range = layer.node().byte_range();
                            ((range.start as i64) - (prev_range.start as i64)).abs()
                                + ((range.end as i64) - (prev_range.end as i64)).abs()
                        })?
                } else {
                    snapshot.syntax_layers().next()?
                };
                buffer_state.active_layer.insert(layer.to_owned())
            }
        };

        // Within the active layer, find the syntax node under the cursor,
        // and scroll to it.
        let mut cursor = layer.node().walk();
        while cursor.goto_first_child_for_byte(range.start).is_some() {
            if !range.is_empty() && cursor.node().end_byte() == range.start {
                cursor.goto_next_sibling();
            }
        }

        // Ascend to the smallest ancestor that contains the range.
        loop {
            let node_range = cursor.node().byte_range();
            if node_range.start <= range.start && node_range.end >= range.end {
                break;
            }
            if !cursor.goto_parent() {
                break;
            }
        }

        let descendant_ix = cursor.descendant_index();
        self.selected_descendant_ix = Some(descendant_ix);
        self.list_scroll_handle.scroll_to_item(descendant_ix);

        cx.notify();
        Some(())
    }

    fn update_editor_with_range_for_descendant_ix(
        &self,
        descendant_ix: usize,
        cx: &mut ViewContext<Self>,
        mut f: impl FnMut(&mut Editor, Range<Anchor>, &mut ViewContext<Editor>),
    ) -> Option<()> {
        let editor_state = self.editor.as_ref()?;
        let buffer_state = editor_state.active_buffer.as_ref()?;
        let layer = buffer_state.active_layer.as_ref()?;

        // Find the node.
        let mut cursor = layer.node().walk();
        cursor.goto_descendant(descendant_ix);
        let node = cursor.node();
        let range = node.byte_range();

        // Build a text anchor range.
        let buffer = buffer_state.buffer.read(cx);
        let range = buffer.anchor_before(range.start)..buffer.anchor_after(range.end);

        // Build a multibuffer anchor range.
        let multibuffer = editor_state.editor.read(cx).buffer();
        let multibuffer = multibuffer.read(cx).snapshot(cx);
        let excerpt_id = buffer_state.excerpt_id;
        let range = multibuffer
            .anchor_in_excerpt(excerpt_id, range.start)
            .unwrap()
            ..multibuffer
                .anchor_in_excerpt(excerpt_id, range.end)
                .unwrap();

        // Update the editor with the anchor range.
        editor_state.editor.update(cx, |editor, cx| {
            f(editor, range, cx);
        });
        Some(())
    }

    fn render_node(cursor: &TreeCursor, depth: u32, selected: bool, cx: &AppContext) -> Div {
        let colors = cx.theme().colors();
        let mut row = h_flex();
        if let Some(field_name) = cursor.field_name() {
            row = row.children([Label::new(field_name).color(Color::Info), Label::new(": ")]);
        }

        let node = cursor.node();
        return row
            .child(if node.is_named() {
                Label::new(node.kind()).color(Color::Default)
            } else {
                Label::new(format!("\"{}\"", node.kind())).color(Color::Created)
            })
            .child(
                div()
                    .child(Label::new(format_node_range(node)).color(Color::Muted))
                    .pl_1(),
            )
            .text_bg(if selected {
                colors.element_selected
            } else {
                Hsla::default()
            })
            .pl(rems(depth as f32))
            .hover(|style| style.bg(colors.element_hover));
    }
}

impl Render for SyntaxTreeView {
    fn render(&mut self, cx: &mut gpui::ViewContext<'_, Self>) -> impl IntoElement {
        let mut rendered = div().flex_1();

        if let Some(layer) = self
            .editor
            .as_ref()
            .and_then(|editor| editor.active_buffer.as_ref())
            .and_then(|buffer| buffer.active_layer.as_ref())
        {
            let layer = layer.clone();
            rendered = rendered.child(uniform_list(
                cx.view().clone(),
                "SyntaxTreeView",
                layer.node().descendant_count(),
                move |this, range, cx| {
                    let mut items = Vec::new();
                    let mut cursor = layer.node().walk();
                    let mut descendant_ix = range.start;
                    cursor.goto_descendant(descendant_ix);
                    let mut depth = cursor.depth();
                    let mut visited_children = false;
                    while descendant_ix < range.end {
                        if visited_children {
                            if cursor.goto_next_sibling() {
                                visited_children = false;
                            } else if cursor.goto_parent() {
                                depth -= 1;
                            } else {
                                break;
                            }
                        } else {
                            items.push(
                                Self::render_node(
                                    &cursor,
                                    depth,
                                    Some(descendant_ix) == this.selected_descendant_ix,
                                    cx,
                                )
                                .on_mouse_down(
                                    MouseButton::Left,
                                    cx.listener(move |tree_view, _: &MouseDownEvent, cx| {
                                        tree_view.update_editor_with_range_for_descendant_ix(
                                            descendant_ix,
                                            cx,
                                            |editor, mut range, cx| {
                                                // Put the cursor at the beginning of the node.
                                                mem::swap(&mut range.start, &mut range.end);

                                                editor.change_selections(
                                                    Some(Autoscroll::newest()),
                                                    cx,
                                                    |selections| {
                                                        selections.select_ranges(vec![range]);
                                                    },
                                                );
                                            },
                                        );
                                    }),
                                )
                                .on_mouse_move(cx.listener(
                                    move |tree_view, _: &MouseMoveEvent, cx| {
                                        if tree_view.hovered_descendant_ix != Some(descendant_ix) {
                                            tree_view.hovered_descendant_ix = Some(descendant_ix);
                                            tree_view.update_editor_with_range_for_descendant_ix(descendant_ix, cx, |editor, range, cx| {
                                                editor.clear_background_highlights::<Self>(cx);
                                                editor.highlight_background::<Self>(
                                                    &[range],
                                                    |theme| theme.editor_document_highlight_write_background,
                                                    cx,
                                                );
                                            });
                                            cx.notify();
                                        }
                                    },
                                )),
                            );
                            descendant_ix += 1;
                            if cursor.goto_first_child() {
                                depth += 1;
                            } else {
                                visited_children = true;
                            }
                        }
                    }
                    items
                },
            )
            .size_full()
            .track_scroll(self.list_scroll_handle.clone())
            .text_bg(cx.theme().colors().background).into_any_element());
        }

        rendered
    }
}

impl EventEmitter<()> for SyntaxTreeView {}

impl FocusableView for SyntaxTreeView {
    fn focus_handle(&self, _: &AppContext) -> gpui::FocusHandle {
        self.focus_handle.clone()
    }
}

impl Item for SyntaxTreeView {
    type Event = ();

    fn to_item_events(_: &Self::Event, _: impl FnMut(workspace::item::ItemEvent)) {}

    fn tab_content_text(&self, _cx: &WindowContext) -> Option<SharedString> {
        Some("Syntax Tree".into())
    }

    fn telemetry_event_text(&self) -> Option<&'static str> {
        None
    }

    fn clone_on_split(
        &self,
        _: Option<workspace::WorkspaceId>,
        cx: &mut ViewContext<Self>,
    ) -> Option<View<Self>>
    where
        Self: Sized,
    {
        Some(cx.new_view(|cx| {
            let mut clone = Self::new(self.workspace_handle.clone(), None, cx);
            if let Some(editor) = &self.editor {
                clone.set_editor(editor.editor.clone(), cx)
            }
            clone
        }))
    }
}

impl SyntaxTreeToolbarItemView {
    pub fn new() -> Self {
        Self {
            tree_view: None,
            subscription: None,
        }
    }

    fn render_menu(&mut self, cx: &mut ViewContext<'_, Self>) -> Option<PopoverMenu<ContextMenu>> {
        let tree_view = self.tree_view.as_ref()?;
        let tree_view = tree_view.read(cx);

        let editor_state = tree_view.editor.as_ref()?;
        let buffer_state = editor_state.active_buffer.as_ref()?;
        let active_layer = buffer_state.active_layer.clone()?;
        let active_buffer = buffer_state.buffer.read(cx).snapshot();

        let view = cx.view().clone();
        Some(
            PopoverMenu::new("Syntax Tree")
                .trigger(Self::render_header(&active_layer))
                .menu(move |cx| {
                    ContextMenu::build(cx, |mut menu, cx| {
                        for (layer_ix, layer) in active_buffer.syntax_layers().enumerate() {
                            menu = menu.entry(
                                format!(
                                    "{} {}",
                                    layer.language.name(),
                                    format_node_range(layer.node())
                                ),
                                None,
                                cx.handler_for(&view, move |view, cx| {
                                    view.select_layer(layer_ix, cx);
                                }),
                            );
                        }
                        menu
                    })
                    .into()
                }),
        )
    }

    fn select_layer(&mut self, layer_ix: usize, cx: &mut ViewContext<Self>) -> Option<()> {
        let tree_view = self.tree_view.as_ref()?;
        tree_view.update(cx, |view, cx| {
            let editor_state = view.editor.as_mut()?;
            let buffer_state = editor_state.active_buffer.as_mut()?;
            let snapshot = buffer_state.buffer.read(cx).snapshot();
            let layer = snapshot.syntax_layers().nth(layer_ix)?;
            buffer_state.active_layer = Some(layer.to_owned());
            view.selected_descendant_ix = None;
            cx.notify();
            view.focus_handle.focus(cx);
            Some(())
        })
    }

    fn render_header(active_layer: &OwnedSyntaxLayer) -> ButtonLike {
        ButtonLike::new("syntax tree header")
            .child(Label::new(active_layer.language.name()))
            .child(Label::new(format_node_range(active_layer.node())))
    }
}

fn format_node_range(node: Node) -> String {
    let start = node.start_position();
    let end = node.end_position();
    format!(
        "[{}:{} - {}:{}]",
        start.row + 1,
        start.column + 1,
        end.row + 1,
        end.column + 1,
    )
}

impl Render for SyntaxTreeToolbarItemView {
    fn render(&mut self, cx: &mut ViewContext<'_, Self>) -> impl IntoElement {
        self.render_menu(cx)
            .unwrap_or_else(|| PopoverMenu::new("Empty Syntax Tree"))
    }
}

impl EventEmitter<ToolbarItemEvent> for SyntaxTreeToolbarItemView {}

impl ToolbarItemView for SyntaxTreeToolbarItemView {
    fn set_active_pane_item(
        &mut self,
        active_pane_item: Option<&dyn ItemHandle>,
        cx: &mut ViewContext<Self>,
    ) -> ToolbarItemLocation {
        if let Some(item) = active_pane_item {
            if let Some(view) = item.downcast::<SyntaxTreeView>() {
                self.tree_view = Some(view.clone());
                self.subscription = Some(cx.observe(&view, |_, _, cx| cx.notify()));
                return ToolbarItemLocation::PrimaryLeft;
            }
        }
        self.tree_view = None;
        self.subscription = None;
        ToolbarItemLocation::Hidden
    }
}