use std::cmp::Ordering;

use crate::Vim;
use editor::{display_map::ToDisplayPoint, scroll::scroll_amount::ScrollAmount, Editor};
use gpui::{actions, AppContext, ViewContext};
use language::Bias;
use workspace::Workspace;

actions!(
    vim,
    [LineUp, LineDown, ScrollUp, ScrollDown, PageUp, PageDown,]
);

pub fn init(cx: &mut AppContext) {
    cx.add_action(|_: &mut Workspace, _: &LineDown, cx| {
        scroll(cx, |c| ScrollAmount::Line(c.unwrap_or(1.)))
    });
    cx.add_action(|_: &mut Workspace, _: &LineUp, cx| {
        scroll(cx, |c| ScrollAmount::Line(-c.unwrap_or(1.)))
    });
    cx.add_action(|_: &mut Workspace, _: &PageDown, cx| {
        scroll(cx, |c| ScrollAmount::Page(c.unwrap_or(1.)))
    });
    cx.add_action(|_: &mut Workspace, _: &PageUp, cx| {
        scroll(cx, |c| ScrollAmount::Page(-c.unwrap_or(1.)))
    });
    cx.add_action(|_: &mut Workspace, _: &ScrollDown, cx| {
        scroll(cx, |c| {
            if let Some(c) = c {
                ScrollAmount::Line(c)
            } else {
                ScrollAmount::Page(0.5)
            }
        })
    });
    cx.add_action(|_: &mut Workspace, _: &ScrollUp, cx| {
        scroll(cx, |c| {
            if let Some(c) = c {
                ScrollAmount::Line(-c)
            } else {
                ScrollAmount::Page(-0.5)
            }
        })
    });
}

fn scroll(cx: &mut ViewContext<Workspace>, by: fn(c: Option<f32>) -> ScrollAmount) {
    Vim::update(cx, |vim, cx| {
        let amount = by(vim.pop_number_operator(cx).map(|c| c as f32));
        vim.update_active_editor(cx, |editor, cx| scroll_editor(editor, &amount, cx));
    })
}

fn scroll_editor(editor: &mut Editor, amount: &ScrollAmount, cx: &mut ViewContext<Editor>) {
    let should_move_cursor = editor.newest_selection_on_screen(cx).is_eq();
    editor.scroll_screen(amount, cx);
    if should_move_cursor {
        let selection_ordering = editor.newest_selection_on_screen(cx);
        if selection_ordering.is_eq() {
            return;
        }

        let visible_rows = if let Some(visible_rows) = editor.visible_line_count() {
            visible_rows as u32
        } else {
            return;
        };

        let top_anchor = editor.scroll_manager.anchor().anchor;

        editor.change_selections(None, cx, |s| {
            s.replace_cursors_with(|snapshot| {
                let mut new_point = top_anchor.to_display_point(&snapshot);

                match selection_ordering {
                    Ordering::Less => {
                        new_point = snapshot.clip_point(new_point, Bias::Right);
                    }
                    Ordering::Greater => {
                        *new_point.row_mut() += visible_rows - 1;
                        new_point = snapshot.clip_point(new_point, Bias::Left);
                    }
                    Ordering::Equal => unreachable!(),
                }

                vec![new_point]
            })
        });
    }
}

#[cfg(test)]
mod test {
    use crate::{state::Mode, test::VimTestContext};
    use gpui::geometry::vector::vec2f;
    use indoc::indoc;

    #[gpui::test]
    async fn test_scroll(cx: &mut gpui::TestAppContext) {
        let mut cx = VimTestContext::new(cx, true).await;

        cx.set_state(indoc! {"ˇa\nb\nc\nd\ne\n"}, Mode::Normal);

        cx.update_editor(|editor, cx| {
            assert_eq!(editor.snapshot(cx).scroll_position(), vec2f(0., 0.))
        });
        cx.simulate_keystrokes(["ctrl-e"]);
        cx.update_editor(|editor, cx| {
            assert_eq!(editor.snapshot(cx).scroll_position(), vec2f(0., 1.))
        });
        cx.simulate_keystrokes(["2", "ctrl-e"]);
        cx.update_editor(|editor, cx| {
            assert_eq!(editor.snapshot(cx).scroll_position(), vec2f(0., 3.))
        });
        cx.simulate_keystrokes(["ctrl-y"]);
        cx.update_editor(|editor, cx| {
            assert_eq!(editor.snapshot(cx).scroll_position(), vec2f(0., 2.))
        });
    }
}