ReCo.jl/src/Particle.jl

using StaticArrays: SVector

mutable struct Particle
    id::Int64

    c::SVector{2,Float64} # Center
    tmp_c::SVector{2,Float64} # Temporary center

    φ::Float64 # Angle

    function Particle(id::Int64, c::SVector{2,Float64}, φ::Float64)
        return new(id, c, 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!(v::SVector{2,Float64}, l::Float64)
    return SVector(restrict_coordinate(v[1], l), restrict_coordinate(v[2], l))
end

function restrict_coordinates!(p::Particle, l::Float64)
    p.tmp_c = restrict_coordinates!(p.tmp_c, l)

    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), minimum_image_coordinate(v[2], l))
end

function are_overlapping(
    c1::SVector{2,Float64}, c2::SVector{2,Float64}, overlapping_r²::Float64, l::Float64
)
    r⃗₁₂ = c2 - c1 # 1 -> 2

    r⃗₁₂ = minimum_image(r⃗₁₂, l)

    distance² = r⃗₁₂[1]^2 + r⃗₁₂[2]^2

    overlapping = distance² < overlapping_r²

    return (; overlapping, r⃗₁₂, distance²)
end