use feature_flags::{FeatureFlag, FeatureFlagAppExt as _};
use gpui::{
    Action, AppContext as _, Entity, EventEmitter, Focusable, NoAction, Subscription, WeakEntity,
};
use multi_buffer::{MultiBuffer, MultiBufferFilterMode};
use project::Project;
use ui::{
    App, Context, InteractiveElement as _, IntoElement as _, ParentElement as _, Render,
    Styled as _, Window, div,
};
use workspace::{
    ActivePaneDecorator, Item, ItemHandle, Pane, PaneGroup, SplitDirection, Workspace,
};

use crate::{Editor, EditorEvent};

struct SplitDiffFeatureFlag;

impl FeatureFlag for SplitDiffFeatureFlag {
    const NAME: &'static str = "split-diff";

    fn enabled_for_staff() -> bool {
        true
    }
}

#[derive(Clone, Copy, PartialEq, Eq, Action, Default)]
#[action(namespace = editor)]
struct SplitDiff;

#[derive(Clone, Copy, PartialEq, Eq, Action, Default)]
#[action(namespace = editor)]
struct UnsplitDiff;

pub struct SplittableEditor {
    primary_editor: Entity<Editor>,
    secondary: Option<SecondaryEditor>,
    panes: PaneGroup,
    workspace: WeakEntity<Workspace>,
    _subscriptions: Vec<Subscription>,
}

struct SecondaryEditor {
    editor: Entity<Editor>,
    pane: Entity<Pane>,
    has_latest_selection: bool,
    _subscriptions: Vec<Subscription>,
}

impl SplittableEditor {
    pub fn primary_editor(&self) -> &Entity<Editor> {
        &self.primary_editor
    }

    pub fn last_selected_editor(&self) -> &Entity<Editor> {
        if let Some(secondary) = &self.secondary
            && secondary.has_latest_selection
        {
            &secondary.editor
        } else {
            &self.primary_editor
        }
    }

    pub fn new_unsplit(
        buffer: Entity<MultiBuffer>,
        project: Entity<Project>,
        workspace: Entity<Workspace>,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) -> Self {
        let primary_editor =
            cx.new(|cx| Editor::for_multibuffer(buffer, Some(project.clone()), window, cx));
        let pane = cx.new(|cx| {
            let mut pane = Pane::new(
                workspace.downgrade(),
                project,
                Default::default(),
                None,
                NoAction.boxed_clone(),
                true,
                window,
                cx,
            );
            pane.set_should_display_tab_bar(|_, _| false);
            pane.add_item(primary_editor.boxed_clone(), true, true, None, window, cx);
            pane
        });
        let panes = PaneGroup::new(pane);
        // TODO(split-diff) we might want to tag editor events with whether they came from primary/secondary
        let subscriptions =
            vec![
                cx.subscribe(&primary_editor, |this, _, event: &EditorEvent, cx| {
                    if let EditorEvent::SelectionsChanged { .. } = event
                        && let Some(secondary) = &mut this.secondary
                    {
                        secondary.has_latest_selection = false;
                    }
                    cx.emit(event.clone())
                }),
            ];

        window.defer(cx, {
            let workspace = workspace.downgrade();
            let primary_editor = primary_editor.downgrade();
            move |window, cx| {
                workspace
                    .update(cx, |workspace, cx| {
                        primary_editor.update(cx, |editor, cx| {
                            editor.added_to_workspace(workspace, window, cx);
                        })
                    })
                    .ok();
            }
        });
        Self {
            primary_editor,
            secondary: None,
            panes,
            workspace: workspace.downgrade(),
            _subscriptions: subscriptions,
        }
    }

    fn split(&mut self, _: &SplitDiff, window: &mut Window, cx: &mut Context<Self>) {
        if !cx.has_flag::<SplitDiffFeatureFlag>() {
            return;
        }
        if self.secondary.is_some() {
            return;
        }
        let Some(workspace) = self.workspace.upgrade() else {
            return;
        };
        let project = workspace.read(cx).project().clone();
        let follower = self.primary_editor.update(cx, |primary, cx| {
            primary.buffer().update(cx, |buffer, cx| {
                let follower = buffer.get_or_create_follower(cx);
                buffer.set_filter_mode(Some(MultiBufferFilterMode::KeepInsertions));
                follower
            })
        });
        follower.update(cx, |follower, _| {
            follower.set_filter_mode(Some(MultiBufferFilterMode::KeepDeletions));
        });
        let secondary_editor = workspace.update(cx, |workspace, cx| {
            cx.new(|cx| {
                let mut editor = Editor::for_multibuffer(follower, Some(project), window, cx);
                // TODO(split-diff) this should be at the multibuffer level
                editor.set_use_base_text_line_numbers(true, cx);
                editor.added_to_workspace(workspace, window, cx);
                editor
            })
        });
        let secondary_pane = cx.new(|cx| {
            let mut pane = Pane::new(
                workspace.downgrade(),
                workspace.read(cx).project().clone(),
                Default::default(),
                None,
                NoAction.boxed_clone(),
                true,
                window,
                cx,
            );
            pane.set_should_display_tab_bar(|_, _| false);
            pane.add_item(
                ItemHandle::boxed_clone(&secondary_editor),
                false,
                false,
                None,
                window,
                cx,
            );
            pane
        });

        let subscriptions =
            vec![
                cx.subscribe(&secondary_editor, |this, _, event: &EditorEvent, cx| {
                    if let EditorEvent::SelectionsChanged { .. } = event
                        && let Some(secondary) = &mut this.secondary
                    {
                        secondary.has_latest_selection = true;
                    }
                    cx.emit(event.clone())
                }),
            ];
        self.secondary = Some(SecondaryEditor {
            editor: secondary_editor,
            pane: secondary_pane.clone(),
            has_latest_selection: false,
            _subscriptions: subscriptions,
        });
        let primary_pane = self.panes.first_pane();
        self.panes
            .split(&primary_pane, &secondary_pane, SplitDirection::Left)
            .unwrap();
        cx.notify();
    }

    fn unsplit(&mut self, _: &UnsplitDiff, _: &mut Window, cx: &mut Context<Self>) {
        let Some(secondary) = self.secondary.take() else {
            return;
        };
        self.panes.remove(&secondary.pane).unwrap();
        self.primary_editor.update(cx, |primary, cx| {
            primary.buffer().update(cx, |buffer, _| {
                buffer.set_filter_mode(None);
            });
        });
        cx.notify();
    }

    pub fn added_to_workspace(
        &mut self,
        workspace: &mut Workspace,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) {
        self.workspace = workspace.weak_handle();
        self.primary_editor.update(cx, |primary_editor, cx| {
            primary_editor.added_to_workspace(workspace, window, cx);
        });
        if let Some(secondary) = &self.secondary {
            secondary.editor.update(cx, |secondary_editor, cx| {
                secondary_editor.added_to_workspace(workspace, window, cx);
            });
        }
    }
}

impl EventEmitter<EditorEvent> for SplittableEditor {}
impl Focusable for SplittableEditor {
    fn focus_handle(&self, cx: &App) -> gpui::FocusHandle {
        self.primary_editor.read(cx).focus_handle(cx)
    }
}

impl Render for SplittableEditor {
    fn render(
        &mut self,
        window: &mut ui::Window,
        cx: &mut ui::Context<Self>,
    ) -> impl ui::IntoElement {
        let inner = if self.secondary.is_none() {
            self.primary_editor.clone().into_any_element()
        } else if let Some(active) = self.panes.panes().into_iter().next() {
            self.panes
                .render(
                    None,
                    &ActivePaneDecorator::new(active, &self.workspace),
                    window,
                    cx,
                )
                .into_any_element()
        } else {
            div().into_any_element()
        };
        div()
            .id("splittable-editor")
            .on_action(cx.listener(Self::split))
            .on_action(cx.listener(Self::unsplit))
            .size_full()
            .child(inner)
    }
}