use bevy::prelude::*;
use bevy::tasks::AsyncComputeTaskPool;
use bevy_platform::time::Instant;
use noise::{NoiseFn, Perlin};
use std::sync::{Arc, Mutex};

use crate::{
    config::TileRegistry,
    constants::{SEED, TILE_SIZE},
    world::{
        tiles::{ChunkData, FloorTileData, TileMap, TerrainSpriteState, CurrentWorldSpriteState},
        ChunkForrestryEvent, ChunkTerrainEvent, FloorTilePrefab, TileOcclusionEvent, CHUNK_SIZE,
        Z_ABOVE, Z_BELOW, ChunkMap, ChunkOwner,
    },
};

/// Thread-safe storage for completed terrain blobs.
/// Uses type erasure to avoid Debug bounds on TerrainBlob.
type BlobStorage = Arc<Mutex<Box<dyn Send + Sync>>>;

/// Typed wrapper for terrain blob storage.
#[derive(Resource)]
pub struct TerrainBlobStorage {
    pub blobs: Arc<Mutex<Vec<TerrainBlob>>>,
}

impl Default for TerrainBlobStorage {
    fn default() -> Self {
        Self {
            blobs: Arc::new(Mutex::new(Vec::new())),
        }
    }
}

impl Clone for TerrainBlobStorage {
    fn clone(&self) -> Self {
        Self {
            blobs: self.blobs.clone(),
        }
    }
}

/// Result of async terrain generation for a single chunk.
/// Contains all data needed to spawn entities and update TileMap on main thread.
pub struct TerrainBlob {
    pub chunk_pos: IVec2,
    pub chunk_data: ChunkData,
    pub tile_updates: Vec<(IVec3, FloorTileData)>,
    pub surface_positions: Vec<(Vec3, String)>,
    pub tile_spawns: Vec<(Vec3, FloorTilePrefab)>,
}

pub fn generate_surface_terrain(x: i32, y: i32) -> f32 {
    let noise = Perlin::new(SEED);
    let mut noise_value = 0.0;
    let mut amplitude = 1.0;
    let mut frequency = 0.008;

    for _ in 0..6 {
        noise_value += noise.get([x as f64 * frequency, y as f64 * frequency]) * amplitude;
        amplitude *= 0.6;
        frequency *= 1.8;
    }
    (noise_value * 2.5) as f32
}

/// Async terrain generation - runs on AsyncComputeTaskPool.
/// Computes all terrain data without ECS access, returns blob for main thread.
fn generate_terrain_blob(chunk_pos: IVec2) -> TerrainBlob {
    let cave_noise = Perlin::new(SEED);
    let start_x = chunk_pos.x * CHUNK_SIZE;
    let start_y = chunk_pos.y * CHUNK_SIZE;
    let registry = TileRegistry::global();

    let mut chunk_data = ChunkData::new(chunk_pos);
    let mut tile_updates: Vec<(IVec3, FloorTileData)> = Vec::new();
    let mut surface_positions: Vec<(Vec3, String)> = Vec::new();
    let mut tile_spawns: Vec<(Vec3, FloorTilePrefab)> = Vec::new();

    for local_y in 0..CHUNK_SIZE {
        for local_x in 0..CHUNK_SIZE {
            let world_x = start_x + local_x;
            let world_y = start_y + local_y;

            let noise_position = Vec3::new(
                (world_x as f32 * TILE_SIZE).round(),
                (world_y as f32 * TILE_SIZE).round(),
                (generate_surface_terrain(world_x, world_y) * TILE_SIZE).round(),
            );

            for z in -Z_BELOW as isize..=Z_ABOVE as isize {
                let position = Vec3::new(
                    (world_x as f32 * TILE_SIZE).round(),
                    (world_y as f32 * TILE_SIZE).round(),
                    (z as f32 * TILE_SIZE).round(),
                );
                let pos_ivec = position.as_ivec3();
                let local_z = z as i32;
                let surface_height =
                    (generate_surface_terrain(world_x, world_y) * TILE_SIZE).round();

                if z < -5 {
                    let cave_value = cave_noise.get([
                        world_x as f64 * 0.05,
                        world_y as f64 * 0.05,
                        z as f64 * 0.05,
                    ]);
                    if cave_value < -0.75 {
                        let tile = registry.floor("air");
                        tile_spawns.push((position, FloorTilePrefab::air(position)));
                        tile_updates.push((
                            pos_ivec,
                            FloorTileData::new(
                                tile.id,
                                tile.can_stand_in,
                                tile.can_stand_on,
                                tile.transparent,
                                tile.astar_weight,
                                [0; 8],
                            ),
                        ));
                        chunk_data.set_floor_tile(
                            local_x,
                            local_y,
                            local_z,
                            tile.id,
                            tile.can_stand_in,
                            tile.can_stand_on,
                            tile.astar_weight,
                        );
                    } else if cave_value < 0.8 {
                        let tile = registry.floor("rock");
                        tile_spawns.push((position, FloorTilePrefab::rock(position)));
                        tile_updates.push((
                            pos_ivec,
                            FloorTileData::new(
                                tile.id,
                                tile.can_stand_in,
                                tile.can_stand_on,
                                tile.transparent,
                                tile.astar_weight,
                                [0; 8],
                            ),
                        ));
                        chunk_data.set_floor_tile(
                            local_x,
                            local_y,
                            local_z,
                            tile.id,
                            tile.can_stand_in,
                            tile.can_stand_on,
                            tile.astar_weight,
                        );
                    } else {
                        let tile = registry.floor("dirt");
                        tile_spawns.push((position, FloorTilePrefab::dirt(position)));
                        tile_updates.push((
                            pos_ivec,
                            FloorTileData::new(
                                tile.id,
                                tile.can_stand_in,
                                tile.can_stand_on,
                                tile.transparent,
                                tile.astar_weight,
                                [0; 8],
                            ),
                        ));
                        chunk_data.set_floor_tile(
                            local_x,
                            local_y,
                            local_z,
                            tile.id,
                            tile.can_stand_in,
                            tile.can_stand_on,
                            tile.astar_weight,
                        );
                    }
                } else if noise_position.z > position.z {
                    if surface_height <= position.z + TILE_SIZE {
                        let tile = registry.floor("grass");
                        tile_spawns.push((position, FloorTilePrefab::grass(position)));
                        tile_updates.push((
                            pos_ivec,
                            FloorTileData::new(
                                tile.id,
                                tile.can_stand_in,
                                tile.can_stand_on,
                                tile.transparent,
                                tile.astar_weight,
                                [0; 8],
                            ),
                        ));
                        chunk_data.set_floor_tile(
                            local_x,
                            local_y,
                            local_z,
                            tile.id,
                            tile.can_stand_in,
                            tile.can_stand_on,
                            tile.astar_weight,
                        );
                        surface_positions.push((position, "grass".to_string()));
                    } else {
                        let tile = registry.floor("dirt");
                        tile_spawns.push((position, FloorTilePrefab::dirt(position)));
                        tile_updates.push((
                            pos_ivec,
                            FloorTileData::new(
                                tile.id,
                                tile.can_stand_in,
                                tile.can_stand_on,
                                tile.transparent,
                                tile.astar_weight,
                                [0; 8],
                            ),
                        ));
                        chunk_data.set_floor_tile(
                            local_x,
                            local_y,
                            local_z,
                            tile.id,
                            tile.can_stand_in,
                            tile.can_stand_on,
                            tile.astar_weight,
                        );
                    }
                } else {
                    let tile = registry.floor("air");
                    tile_spawns.push((position, FloorTilePrefab::air(position)));
                    tile_updates.push((
                        pos_ivec,
                        FloorTileData::new(
                            tile.id,
                            tile.can_stand_in,
                            tile.can_stand_on,
                            tile.transparent,
                            tile.astar_weight,
                            [0; 8],
                        ),
                    ));
                    chunk_data.set_floor_tile(
                        local_x,
                        local_y,
                        local_z,
                        tile.id,
                        tile.can_stand_in,
                        tile.can_stand_on,
                        tile.astar_weight,
                    );
                }
            }
        }
    }

    TerrainBlob {
        chunk_pos,
        chunk_data,
        tile_updates,
        surface_positions,
        tile_spawns,
    }
}

/// Spawns async terrain generation tasks on AsyncComputeTaskPool.
/// Fast - just reads events and spawns tasks.
pub fn spawn_terrain_tasks(
    mut events: MessageReader<ChunkTerrainEvent>,
    mut cwss: ResMut<CurrentWorldSpriteState>,
    blob_storage: Res<TerrainBlobStorage>,
) {
    let start = Instant::now();
    let count = events.len();

    if count == 0 {
        return;
    }

    let task_pool = AsyncComputeTaskPool::get();
    let blobs = blob_storage.blobs.clone();

    for event in events.read() {
        let chunk_pos = event.chunk_position;
        let blobs_clone = blobs.clone();
        task_pool.spawn(async move {
            let blob = generate_terrain_blob(chunk_pos);
            blobs_clone.lock().unwrap().push(blob);
        }).detach();
    }

    cwss.state = TerrainSpriteState::WaitingForRender;
    println!("{} terrain tasks spawned in {:.2?}", count, start.elapsed());
}

/// Applies completed terrain blobs on main thread.
/// Spawns entities, updates TileMap, sends occlusion events.
pub fn apply_terrain_blobs(
    mut commands: Commands,
    blob_storage: Res<TerrainBlobStorage>,
    mut tilemap: ResMut<TileMap>,
    mut chunk_map: ResMut<ChunkMap>,
    mut forrestry_event_writer: MessageWriter<ChunkForrestryEvent>,
    mut occlusion_event_writer: MessageWriter<TileOcclusionEvent>,
) {
    let start = Instant::now();
    let mut applied_count = 0;

    let completed: Vec<TerrainBlob> = blob_storage.blobs.lock().unwrap().drain(..).collect();

    for blob in completed {
        let new_positions: Vec<IVec3> = blob
            .tile_updates
            .into_iter()
            .map(|(pos, data)| {
                tilemap.insert_floor(pos, data);
                pos
            })
            .collect();

        tilemap.chunks.insert(blob.chunk_pos, blob.chunk_data);

        for (_position, prefab) in blob.tile_spawns {
            let entity = prefab.spawn(&mut commands);
            commands.entity(entity).insert(ChunkOwner(blob.chunk_pos));
            chunk_map
                .chunk_entity_index
                .entry(blob.chunk_pos)
                .or_default()
                .push(entity);
        }

        for pos in new_positions {
            occlusion_event_writer.write(TileOcclusionEvent { tile_position: pos });
        }

        forrestry_event_writer.write(ChunkForrestryEvent {
            chunk_position: blob.chunk_pos,
            floor_tiles: blob.surface_positions,
        });

        applied_count += 1;
    }

    if applied_count > 0 {
        println!("{} terrain blobs applied in {:.2?}", applied_count, start.elapsed());
    }
}

pub fn generate_chunk_weathering_and_precipitation() {
    // TODO: Generate weathering and precipitation
    // Temperature and humidity
    // Erosion
    // Hadley lines/cells etc
    // Biomes
}