#![doc = include_str!("../README.md")]

mod components;
use std::collections::BTreeSet;

use bevy_app::prelude::*;
use bevy_ecs::prelude::*;
pub use components::*;
use tracing::{debug, warn};
use valence_server::client::{Client, OldVisibleEntityLayers, VisibleEntityLayers};
use valence_server::entity::EntityLayerId;
use valence_server::layer::UpdateLayersPreClientSet;
use valence_server::protocol::packets::play::scoreboard_display_s2c::ScoreboardPosition;
use valence_server::protocol::packets::play::scoreboard_objective_update_s2c::{
    ObjectiveMode, ObjectiveRenderType,
};
use valence_server::protocol::packets::play::scoreboard_player_update_s2c::ScoreboardPlayerUpdateAction;
use valence_server::protocol::packets::play::{
    ScoreboardDisplayS2c, ScoreboardObjectiveUpdateS2c, ScoreboardPlayerUpdateS2c,
};
use valence_server::protocol::{VarInt, WritePacket};
use valence_server::text::IntoText;
use valence_server::{Despawned, EntityLayer};

/// Provides all necessary systems to manage scoreboards.
pub struct ScoreboardPlugin;

impl Plugin for ScoreboardPlugin {
    fn build(&self, app: &mut App) {
        app.configure_sets(PostUpdate, ScoreboardSet.before(UpdateLayersPreClientSet));

        app.add_systems(
            PostUpdate,
            (
                create_or_update_objectives,
                display_objectives.after(create_or_update_objectives),
            )
                .in_set(ScoreboardSet),
        )
        .add_systems(
            PostUpdate,
            remove_despawned_objectives.in_set(ScoreboardSet),
        )
        .add_systems(PostUpdate, handle_new_clients.in_set(ScoreboardSet))
        .add_systems(
            PostUpdate,
            update_scores
                .after(create_or_update_objectives)
                .after(handle_new_clients)
                .in_set(ScoreboardSet),
        );
    }
}

#[derive(SystemSet, Copy, Clone, PartialEq, Eq, Hash, Debug)]
pub struct ScoreboardSet;

fn create_or_update_objectives(
    objectives: Query<
        (
            Ref<Objective>,
            &ObjectiveDisplay,
            &ObjectiveRenderType,
            &EntityLayerId,
        ),
        Or<(Changed<ObjectiveDisplay>, Changed<ObjectiveRenderType>)>,
    >,
    mut layers: Query<&mut EntityLayer>,
) {
    for (objective, display, render_type, entity_layer) in objectives.iter() {
        if objective.name().is_empty() {
            warn!("Objective name is empty");
        }
        let mode = if objective.is_added() {
            ObjectiveMode::Create {
                objective_display_name: (&display.0).into_cow_text(),
                render_type: *render_type,
            }
        } else {
            ObjectiveMode::Update {
                objective_display_name: (&display.0).into_cow_text(),
                render_type: *render_type,
            }
        };

        let Ok(mut layer) = layers.get_mut(entity_layer.0) else {
            warn!(
                "No layer found for entity layer ID {:?}, can't update scoreboard objective",
                entity_layer
            );
            continue;
        };

        layer.write_packet(&ScoreboardObjectiveUpdateS2c {
            objective_name: &objective.0,
            mode,
        });
    }
}

/// Must occur after `create_or_update_objectives`.
fn display_objectives(
    objectives: Query<
        (&Objective, Ref<ScoreboardPosition>, &EntityLayerId),
        Changed<ScoreboardPosition>,
    >,
    mut layers: Query<&mut EntityLayer>,
) {
    for (objective, position, entity_layer) in objectives.iter() {
        let packet = ScoreboardDisplayS2c {
            score_name: &objective.0,
            position: *position,
        };

        let Ok(mut layer) = layers.get_mut(entity_layer.0) else {
            warn!(
                "No layer found for entity layer ID {:?}, can't update scoreboard display",
                entity_layer
            );
            continue;
        };

        layer.write_packet(&packet);
    }
}

fn remove_despawned_objectives(
    mut commands: Commands,
    objectives: Query<(Entity, &Objective, &EntityLayerId), With<Despawned>>,
    mut layers: Query<&mut EntityLayer>,
) {
    for (entity, objective, entity_layer) in objectives.iter() {
        commands.entity(entity).despawn();
        let Ok(mut layer) = layers.get_mut(entity_layer.0) else {
            warn!(
                "No layer found for entity layer ID {:?}, can't remove scoreboard objective",
                entity_layer
            );
            continue;
        };

        layer.write_packet(&ScoreboardObjectiveUpdateS2c {
            objective_name: &objective.0,
            mode: ObjectiveMode::Remove,
        });
    }
}

fn handle_new_clients(
    mut clients: Query<
        (&mut Client, &VisibleEntityLayers, &OldVisibleEntityLayers),
        Or<(Added<Client>, Changed<VisibleEntityLayers>)>,
    >,
    objectives: Query<
        (
            &Objective,
            &ObjectiveDisplay,
            &ObjectiveRenderType,
            &ScoreboardPosition,
            &ObjectiveScores,
            &EntityLayerId,
        ),
        Without<Despawned>,
    >,
) {
    // Remove objectives from the old visible layers that are not in the new visible
    // layers.
    for (mut client, visible_layers, old_visible_layers) in &mut clients {
        let removed_layers: BTreeSet<_> = old_visible_layers
            .get()
            .difference(&visible_layers.0)
            .collect();

        for (objective, _, _, _, _, layer) in objectives.iter() {
            if !removed_layers.contains(&layer.0) {
                continue;
            }
            client.write_packet(&ScoreboardObjectiveUpdateS2c {
                objective_name: &objective.0,
                mode: ObjectiveMode::Remove,
            });
        }
    }

    // Add objectives from the new visible layers that are not in the old visible
    // layers, or send all objectives if the client is new.
    for (mut client, visible_layers, old_visible_layers) in &mut clients {
        // not sure how to avoid the clone here
        let added_layers = if client.is_added() {
            debug!("client is new, sending all objectives");
            visible_layers.0.clone()
        } else {
            visible_layers
                .0
                .difference(old_visible_layers.get())
                .copied()
                .collect::<BTreeSet<_>>()
        };

        for (objective, display, render_type, position, scores, layer) in objectives.iter() {
            if !added_layers.contains(&layer.0) {
                continue;
            }

            client.write_packet(&ScoreboardObjectiveUpdateS2c {
                objective_name: &objective.0,
                mode: ObjectiveMode::Create {
                    objective_display_name: (&display.0).into_cow_text(),
                    render_type: *render_type,
                },
            });
            client.write_packet(&ScoreboardDisplayS2c {
                score_name: &objective.0,
                position: *position,
            });

            for (key, score) in &scores.0 {
                let packet = ScoreboardPlayerUpdateS2c {
                    entity_name: key,
                    action: ScoreboardPlayerUpdateAction::Update {
                        objective_name: &objective.0,
                        objective_score: VarInt(*score),
                    },
                };

                client.write_packet(&packet);
            }
        }
    }
}

fn update_scores(
    mut objectives: Query<
        (
            &Objective,
            &ObjectiveScores,
            &mut OldObjectiveScores,
            &EntityLayerId,
        ),
        (Changed<ObjectiveScores>, Without<Despawned>),
    >,
    mut layers: Query<&mut EntityLayer>,
) {
    for (objective, scores, mut old_scores, entity_layer) in &mut objectives {
        let Ok(mut layer) = layers.get_mut(entity_layer.0) else {
            warn!(
                "No layer found for entity layer ID {:?}, can't update scores",
                entity_layer
            );
            continue;
        };

        for changed_key in old_scores.diff(scores) {
            let action = match scores.0.get(changed_key) {
                Some(score) => ScoreboardPlayerUpdateAction::Update {
                    objective_name: &objective.0,
                    objective_score: VarInt(*score),
                },
                None => ScoreboardPlayerUpdateAction::Remove {
                    objective_name: &objective.0,
                },
            };

            let packet = ScoreboardPlayerUpdateS2c {
                entity_name: changed_key,
                action,
            };

            layer.write_packet(&packet);
        }

        old_scores.0.clone_from(&scores.0);
    }
}