use egui::Rect;
use re_format::format_f32;
use re_types::blueprint::components::VisualBounds2D;
use re_ui::UiExt;
use re_viewer_context::ViewState;

use crate::layout::{ForceLayoutParams, ForceLayoutProvider, Layout, LayoutRequest};

/// View state for the custom view.
///
/// This state is preserved between frames, but not across Viewer sessions.
#[derive(Default)]
pub struct GraphViewState {
    pub layout_state: LayoutState,
    pub visual_bounds: Option<VisualBounds2D>,
    pub rect_in_ui: Option<Rect>,
}

impl GraphViewState {
    pub fn layout_ui(&self, ui: &mut egui::Ui) {
        let Some(rect) = self.layout_state.bounding_rect() else {
            return;
        };
        ui.grid_left_hand_label("Bounding box")
            .on_hover_text("The bounding box encompassing all entities in the view right now");
        ui.vertical(|ui| {
            ui.style_mut().wrap_mode = Some(egui::TextWrapMode::Extend);
            let egui::Rect { min, max } = rect;
            ui.label(format!("x [{} - {}]", format_f32(min.x), format_f32(max.x),));
            ui.label(format!("y [{} - {}]", format_f32(min.y), format_f32(max.y),));
        });
        ui.end_row();
    }

    pub fn simulation_ui(&mut self, ui: &mut egui::Ui) {
        if ui.button("Reset simulation").clicked() {
            self.layout_state.reset();
        }
    }
}

impl ViewState for GraphViewState {
    fn as_any(&self) -> &dyn std::any::Any {
        self
    }

    fn as_any_mut(&mut self) -> &mut dyn std::any::Any {
        self
    }
}

/// The following is a simple state machine that keeps track of the different
/// layouts and if they need to be recomputed. It also holds the state of the
/// force-based simulation.
#[derive(Default)]
pub enum LayoutState {
    #[default]
    None,
    InProgress {
        layout: Layout,
        provider: ForceLayoutProvider,
        params: ForceLayoutParams,
    },
    Finished {
        layout: Layout,
        provider: ForceLayoutProvider,
        params: ForceLayoutParams,
    },
}

impl LayoutState {
    pub fn bounding_rect(&self) -> Option<Rect> {
        match self {
            Self::None => None,
            Self::Finished { layout, .. } | Self::InProgress { layout, .. } => {
                Some(layout.bounding_rect())
            }
        }
    }

    pub fn reset(&mut self) {
        *self = Self::None;
    }

    pub fn is_none(&self) -> bool {
        matches!(self, Self::None)
    }

    pub fn is_in_progress(&self) -> bool {
        matches!(self, Self::InProgress { .. })
    }

    /// A simple state machine that keeps track of the different stages and if the layout needs to be recomputed.
    fn update(self, new_request: LayoutRequest, new_params: ForceLayoutParams) -> Self {
        match self {
            // Layout is up to date, nothing to do here.
            Self::Finished {
                ref provider,
                ref params,
                ..
            } if (provider.request == new_request) && (params == &new_params) => {
                self // no op
            }
            // We need to recompute the layout.
            Self::None => {
                let mut provider = ForceLayoutProvider::new(new_request, &new_params);
                let layout = provider.tick();
                Self::InProgress {
                    layout,
                    provider,
                    params: new_params,
                }
            }
            Self::Finished { layout, .. } => {
                let mut provider =
                    ForceLayoutProvider::new_with_previous(new_request, &layout, &new_params);
                let layout = provider.tick();
                Self::InProgress {
                    layout,
                    provider,
                    params: new_params,
                }
            }
            Self::InProgress {
                layout, provider, ..
            } if provider.request != new_request => {
                let mut provider =
                    ForceLayoutProvider::new_with_previous(new_request, &layout, &new_params);
                let layout = provider.tick();

                Self::InProgress {
                    layout,
                    provider,
                    params: new_params,
                }
            }
            // We keep iterating on the layout until it is stable.
            Self::InProgress {
                mut provider,
                layout,
                params: old_params,
            } => match (provider.is_finished(), new_params == old_params) {
                (true, true) => Self::Finished {
                    layout,
                    provider,
                    params: new_params,
                },
                (false, true) => Self::InProgress {
                    layout: provider.tick(),
                    provider,
                    params: new_params,
                },
                _ => {
                    let mut provider =
                        ForceLayoutProvider::new_with_previous(new_request, &layout, &new_params);
                    let layout = provider.tick();

                    Self::InProgress {
                        layout,
                        provider,
                        params: new_params,
                    }
                }
            },
        }
    }

    /// This method is lazy. A new layout is only computed if the current timestamp requires it.
    pub fn get(&mut self, request: LayoutRequest, params: ForceLayoutParams) -> &mut Layout {
        *self = std::mem::take(self).update(request, params);

        match self {
            Self::Finished { layout, .. } | Self::InProgress { layout, .. } => layout,
            Self::None => unreachable!(), // We just set the state to `Self::Current` above.
        }
    }
}