ReCo.jl/src/Particle.jl

using StaticArrays: SVector
using LoopVectorization: @turbo

mutable struct Particle
    id::Int64

    c::Vector{Float64} # Center
    tmp_c::Vector{Float64} # Temporary center

    φ::Float64 # Angle

    function Particle(; id::Int64, c::Vector{Float64}, φ::Float64)
        return new(id, c, copy(c), φ)
    end
end

function restrict_coordinate(value::Float64; l::Float64)
    if value < -l
        value += 2 * l
    elseif value >= l
        value -= 2 * l
    end

    return value
end

function restrict_coordinates!(p::Particle; l::Float64)
    @simd for i in 1:2
        p.tmp_c[i] = restrict_coordinate(p.tmp_c[i]; l=l)
    end

    return nothing
end

function minimum_image_coordinate(value::Float64; l::Float64)
    if value <= -l
        value += 2 * l
    elseif value > l
        value -= 2 * l
    end

    return value
end

function minimum_image(v::SVector{2,Float64}; l::Float64)
    return SVector(minimum_image_coordinate(v[1]; l=l), minimum_image_coordinate(v[2]; l=l))
end

function are_overlapping(p1::Particle, p2::Particle, overlapping_r²::Float64, l::Float64)
    r⃗₁₂ = SVector(p2.c[1] - p1.c[1], p2.c[2] - p1.c[2]) # 1 -> 2

    r⃗₁₂ = minimum_image(r⃗₁₂; l=l)

    distance² = r⃗₁₂[1]^2 + r⃗₁₂[2]^2

    overlapping = distance² < overlapping_r²

    return (; overlapping, r⃗₁₂, distance²)
end

function update!(p::Particle)
    @turbo for i in 1:2
        p.c[i] = p.tmp_c[i]
    end

    return nothing
end