mod components;
pub mod indexing;

use std::collections::HashSet;

use azalea_block::{BlockState, BlockTrait, fluid_state::FluidKind, properties};
use azalea_core::{
    entity_id::MinecraftEntityId,
    position::{BlockPos, ChunkPos},
    tick::GameTick,
};
use azalea_registry::{builtin::BlockKind, tags};
use azalea_world::{ChunkStorage, WorldName, Worlds};
use bevy_app::{App, Plugin, PostUpdate, Update};
use bevy_ecs::prelude::*;
pub use components::*;
use derive_more::{Deref, DerefMut};
use indexing::EntityUuidIndex;
use tracing::debug;

use crate::{
    FluidOnEyes, LookDirection, Physics, Pose, Position,
    dimensions::{EntityDimensions, calculate_dimensions},
    metadata::{self, Health, Player},
};

/// A Bevy [`SystemSet`] for various types of entity updates.
#[derive(Clone, Debug, Eq, Hash, PartialEq, SystemSet)]
pub enum EntityUpdateSystems {
    /// Create search indexes for entities.
    Index,
    /// Remove despawned entities from search indexes.
    Deindex,
}

/// Plugin handling some basic entity functionality.
pub struct EntityPlugin;
impl Plugin for EntityPlugin {
    fn build(&self, app: &mut App) {
        // entities get added pre-update
        // added to indexes during update (done by this plugin)
        // modified during update
        // despawned post-update (done by this plugin)
        app.add_systems(
            PostUpdate,
            indexing::remove_despawned_entities_from_indexes.in_set(EntityUpdateSystems::Deindex),
        )
        .add_systems(
            Update,
            (
                (
                    indexing::update_entity_chunk_positions,
                    indexing::insert_entity_chunk_position,
                )
                    .chain()
                    .in_set(EntityUpdateSystems::Index),
                (
                    debug_new_entity,
                    add_dead,
                    clamp_look_direction,
                    update_on_climbable,
                    (update_dimensions, update_bounding_box).chain(),
                    update_crouching,
                ),
            ),
        )
        .add_systems(GameTick, (update_in_loaded_chunk, update_fluid_on_eyes))
        .init_resource::<EntityUuidIndex>();
    }
}

fn debug_new_entity(query: Query<(Entity, Option<&LocalEntity>), Added<MinecraftEntityId>>) {
    for (entity, local) in query.iter() {
        if local.is_some() {
            debug!("new local entity: {:?}", entity);
        } else {
            debug!("new entity: {:?}", entity);
        }
    }
}

/// System that adds the [`Dead`] marker component if an entity's health is set
/// to 0 (or less than 0).
///
/// This will be present if an entity is doing the death animation.
///
/// Entities that are dead cannot be revived.
pub fn add_dead(mut commands: Commands, query: Query<(Entity, &Health), Changed<Health>>) {
    for (entity, health) in query.iter() {
        if **health <= 0.0 {
            commands.entity(entity).insert(Dead);
        }
    }
}

pub fn update_fluid_on_eyes(
    mut query: Query<
        (&mut FluidOnEyes, &Position, &EntityDimensions, &WorldName),
        With<metadata::AbstractLiving>,
    >,
    worlds: Res<Worlds>,
) {
    query
        .par_iter_mut()
        .for_each(|(mut fluid_on_eyes, position, dimensions, world_name)| {
            let Some(world) = worlds.get(world_name) else {
                return;
            };

            let adjusted_eye_y = position.y + (dimensions.eye_height as f64) - 0.1111111119389534;
            let eye_block_pos = BlockPos::from(position.with_y(adjusted_eye_y));
            let fluid_at_eye = world
                .read()
                .get_fluid_state(eye_block_pos)
                .unwrap_or_default();
            let fluid_cutoff_y = (eye_block_pos.y as f32 + fluid_at_eye.height()) as f64;
            if fluid_cutoff_y > adjusted_eye_y {
                **fluid_on_eyes = fluid_at_eye.kind;
            } else {
                **fluid_on_eyes = FluidKind::Empty;
            }
        });
}

pub fn update_on_climbable(
    mut query: Query<(&mut OnClimbable, &Position, &WorldName), With<LocalEntity>>,
    worlds: Res<Worlds>,
) {
    for (mut on_climbable, position, world_name) in query.iter_mut() {
        // TODO: there's currently no gamemode component that can be accessed from here,
        // maybe LocalGameMode should be replaced with two components, maybe called
        // EntityGameMode and PreviousGameMode?

        // if game_mode == GameMode::Spectator {
        //     continue;
        // }

        let Some(world) = worlds.get(world_name) else {
            continue;
        };

        let world = world.read();

        let block_pos = BlockPos::from(position);
        let block_state_at_feet = world.get_block_state(block_pos).unwrap_or_default();
        let block_at_feet = Box::<dyn BlockTrait>::from(block_state_at_feet);
        let registry_block_at_feet = block_at_feet.as_block_kind();

        **on_climbable = tags::blocks::CLIMBABLE.contains(&registry_block_at_feet)
            || (tags::blocks::TRAPDOORS.contains(&registry_block_at_feet)
                && is_trapdoor_usable_as_ladder(block_state_at_feet, block_pos, &world));
    }
}

fn is_trapdoor_usable_as_ladder(
    block_state: BlockState,
    block_pos: BlockPos,
    world: &azalea_world::World,
) -> bool {
    // trapdoor must be open
    if !block_state
        .property::<properties::Open>()
        .unwrap_or_default()
    {
        return false;
    }

    // block below must be a ladder
    let block_below = world.get_block_state(block_pos.down(1)).unwrap_or_default();
    let registry_block_below = block_below.as_block_kind();
    if registry_block_below != BlockKind::Ladder {
        return false;
    }
    // and the ladder must be facing the same direction as the trapdoor
    let ladder_facing = block_below
        .property::<properties::FacingCardinal>()
        .expect("ladder block must have facing property");
    let trapdoor_facing = block_state
        .property::<properties::FacingCardinal>()
        .expect("trapdoor block must have facing property");
    if ladder_facing != trapdoor_facing {
        return false;
    }

    true
}

/// A component that lists all the local player entities that have this entity
/// loaded.
///
/// If this is empty, the entity will be removed from the ECS.
#[derive(Clone, Component, Deref, DerefMut)]
pub struct LoadedBy(pub HashSet<Entity>);

pub fn clamp_look_direction(mut query: Query<&mut LookDirection>) {
    for mut look_direction in &mut query {
        *look_direction = look_direction.clamped();
    }
}

/// Sets the position of the entity.
///
/// This doesn't update the cache in azalea-world, and should only be used
/// within azalea-world.
///
/// # Safety
///
/// Cached position in the world must be updated.
#[allow(clippy::type_complexity)]
pub fn update_bounding_box(
    mut query: Query<
        (&mut Physics, &Position, &EntityDimensions),
        Or<(Changed<Position>, Changed<EntityDimensions>)>,
    >,
) {
    for (mut physics, position, dimensions) in query.iter_mut() {
        let bounding_box = dimensions.make_bounding_box(**position);
        physics.bounding_box = bounding_box;
    }
}

#[allow(clippy::type_complexity)]
pub fn update_dimensions(
    mut query: Query<
        (&mut EntityDimensions, &EntityKindComponent, &Pose),
        Or<(Changed<EntityKindComponent>, Changed<Pose>)>,
    >,
) {
    for (mut dimensions, kind, pose) in query.iter_mut() {
        *dimensions = calculate_dimensions(**kind, *pose);
    }
}

#[allow(clippy::type_complexity)]
pub fn update_crouching(
    query: Query<(&mut Crouching, &Pose), (Without<LocalEntity>, With<Player>)>,
) {
    for (mut crouching, pose) in query {
        let new_crouching = *pose == Pose::Crouching;
        // avoid triggering change detection
        if **crouching != new_crouching {
            **crouching = new_crouching;
        }
    }
}

/// Marks an entity that's in a loaded chunk. This is updated at the beginning
/// of every tick.
///
/// Internally, this is only used for player physics. Not to be confused with
/// the somewhat similarly named [`LoadedBy`].
#[derive(Clone, Component, Copy, Debug)]
pub struct InLoadedChunk;

/// Update the [`InLoadedChunk`] component for all entities in the world.
pub fn update_in_loaded_chunk(
    mut commands: bevy_ecs::system::Commands,
    query: Query<(Entity, &WorldName, &Position, Option<&InLoadedChunk>)>,
    worlds: Res<Worlds>,
) {
    for (entity, world_name, position, last_in_loaded_chunk) in &query {
        let player_chunk_pos = ChunkPos::from(position);
        let Some(world_lock) = worlds.get(world_name) else {
            commands.entity(entity).remove::<InLoadedChunk>();
            continue;
        };

        let in_loaded_chunk = world_lock.read().chunks.get(&player_chunk_pos).is_some();
        if in_loaded_chunk {
            if last_in_loaded_chunk.is_none() {
                commands.entity(entity).insert(InLoadedChunk);
            }
        } else {
            if last_in_loaded_chunk.is_some() {
                commands.entity(entity).remove::<InLoadedChunk>();
            }
        }
    }
}

/// Get the position of the block below the entity, but a little lower.
pub fn on_pos_legacy(chunk_storage: &ChunkStorage, position: Position) -> BlockPos {
    on_pos(0.2, chunk_storage, position)
}

// int x = Mth.floor(this.position.x);
// int y = Mth.floor(this.position.y - (double)var1);
// int z = Mth.floor(this.position.z);
// BlockPos var5 = new BlockPos(x, y, z);
// if (this.level.getBlockState(var5).isAir()) {
//    BlockPos var6 = var5.below();
//    BlockState var7 = this.level.getBlockState(var6);
//    if (var7.is(BlockTags.FENCES) || var7.is(BlockTags.WALLS) ||
// var7.getBlock() instanceof FenceGateBlock) {       return var6;
//    }
// }
// return var5;
pub fn on_pos(offset: f32, chunk_storage: &ChunkStorage, pos: Position) -> BlockPos {
    let x = pos.x.floor() as i32;
    let y = (pos.y - offset as f64).floor() as i32;
    let z = pos.z.floor() as i32;
    let pos = BlockPos { x, y, z };

    // TODO: check if block below is a fence, wall, or fence gate
    let block_pos = pos.down(1);
    let block_state = chunk_storage.get_block_state(block_pos);
    if block_state == Some(BlockState::AIR) {
        let block_pos_below = block_pos.down(1);
        let block_state_below = chunk_storage.get_block_state(block_pos_below);
        if let Some(_block_state_below) = block_state_below {
            // if block_state_below.is_fence()
            //     || block_state_below.is_wall()
            //     || block_state_below.is_fence_gate()
            // {
            //     return block_pos_below;
            // }
        }
    }

    pos
}

#[cfg(test)]
mod tests {
    use azalea_block::{
        blocks::{Ladder, OakTrapdoor},
        properties::{FacingCardinal, TopBottom},
    };
    use azalea_core::position::{BlockPos, ChunkPos};
    use azalea_registry::builtin::BlockKind;
    use azalea_world::{Chunk, ChunkStorage, PartialWorld, World};

    use super::is_trapdoor_usable_as_ladder;

    #[test]
    fn test_is_trapdoor_useable_as_ladder() {
        let mut partial_world = PartialWorld::default();
        let mut chunks = ChunkStorage::default();
        partial_world.chunks.set(
            &ChunkPos { x: 0, z: 0 },
            Some(Chunk::default()),
            &mut chunks,
        );
        partial_world.chunks.set_block_state(
            BlockPos::new(0, 0, 0),
            BlockKind::Stone.into(),
            &chunks,
        );

        let ladder = Ladder {
            facing: FacingCardinal::East,
            waterlogged: false,
        };
        partial_world
            .chunks
            .set_block_state(BlockPos::new(0, 0, 0), ladder.into(), &chunks);

        let trapdoor = OakTrapdoor {
            facing: FacingCardinal::East,
            half: TopBottom::Bottom,
            open: true,
            powered: false,
            waterlogged: false,
        };
        partial_world
            .chunks
            .set_block_state(BlockPos::new(0, 1, 0), trapdoor.into(), &chunks);

        let world = World::from(chunks);
        let trapdoor_matches_ladder = is_trapdoor_usable_as_ladder(
            world
                .get_block_state(BlockPos::new(0, 1, 0))
                .unwrap_or_default(),
            BlockPos::new(0, 1, 0),
            &world,
        );

        assert!(trapdoor_matches_ladder);
    }
}