// SPDX-License-Identifier: AGPL-3.0-only

//! Chunk-space coordinates.

use super::CHUNK_SIZE;
use serde::{Deserialize, Serialize};

/// The three-dimensional spatial coordinates of a chunk in the world.
#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub struct ChunkPos {
    /// The X coordinate of the chunk.
    pub x: i32,
    /// The Y coordinate of the chunk.
    pub y: i32,
    /// The Z coordinate of the chunk.
    pub z: i32,
}

impl ChunkPos {
    /// Initializes a new chunk position.
    #[must_use]
    pub fn new(x: i32, y: i32, z: i32) -> Self {
        Self { x, y, z }
    }

    /// Initializes a new chunk position from a world-space position measured in blocks.
    #[must_use]
    #[expect(clippy::cast_possible_truncation, clippy::cast_possible_wrap)]
    pub fn from_world(x: f64, y: f64, z: f64) -> Self {
        ChunkPos {
            x: (x.floor() as i32).div_euclid(CHUNK_SIZE as i32),
            y: (y.floor() as i32).div_euclid(CHUNK_SIZE as i32),
            z: (z.floor() as i32).div_euclid(CHUNK_SIZE as i32),
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn from_world_maps_positive_positions() {
        // A block at 40 falls in chunk 1 (chunk 1 spans blocks 32..=63).
        assert_eq!(ChunkPos::from_world(40.0, 0.0, 0.0).x, 1);
        // The last block of chunk 0 (block 31) stays in chunk 0.
        assert_eq!(ChunkPos::from_world(31.0, 0.0, 0.0).x, 0);
    }

    #[test]
    fn from_world_floors_negative_positions() {
        // Block -1 belongs to chunk -1, not chunk 0: this is the div_euclid contract.
        assert_eq!(ChunkPos::from_world(-1.0, 0.0, 0.0).x, -1);
        // Block -33 belongs to chunk -2 (chunk -2 spans blocks -64..=-33).
        assert_eq!(ChunkPos::from_world(-33.0, 0.0, 0.0).x, -2);
    }

    #[test]
    fn from_world_floors_fractional_positions() {
        // A position of -0.5 lies inside block -1, which is in chunk -1.
        assert_eq!(ChunkPos::from_world(-0.5, 0.0, 0.0).x, -1);
    }
}