/* The Computer Language Benchmarks Game
   http://benchmarksgame.alioth.debian.org/
   contributed by Isaac Gouy
   Modified slightly by Erik Little
*/

import Glibc

struct Body {
    var x, y, z, vx, vy, vz, mass : Double
}

let PI = 3.141592653589793
let SOLAR_MASS = 4 * PI * PI
let DAYS_PER_YEAR = 365.24

var bodies: [Body] = [
    Body (
        x: 0.0,
        y: 0.0,
        z: 0.0,
        vx: 0.0,
        vy: 0.0,
        vz: 0.0,
        mass: SOLAR_MASS
    ),

    Body (
        x: 4.84143144246472090e+00,
        y: -1.16032004402742839e+00,
        z: -1.03622044471123109e-01,
        vx: 1.66007664274403694e-03 * DAYS_PER_YEAR,
        vy: 7.69901118419740425e-03 * DAYS_PER_YEAR,
        vz: -6.90460016972063023e-05 * DAYS_PER_YEAR,
        mass: 9.54791938424326609e-04 * SOLAR_MASS
    ),

    Body (
        x: 8.34336671824457987e+00,
        y: 4.12479856412430479e+00,
        z: -4.03523417114321381e-01,
        vx: -2.76742510726862411e-03 * DAYS_PER_YEAR,
        vy: 4.99852801234917238e-03 * DAYS_PER_YEAR,
        vz: 2.30417297573763929e-05 * DAYS_PER_YEAR,
        mass: 2.85885980666130812e-04 * SOLAR_MASS
    ),

    Body (
        x: 1.28943695621391310e+01,
        y: -1.51111514016986312e+01,
        z: -2.23307578892655734e-01,
        vx: 2.96460137564761618e-03 * DAYS_PER_YEAR,
        vy: 2.37847173959480950e-03 * DAYS_PER_YEAR,
        vz: -2.96589568540237556e-05 * DAYS_PER_YEAR,
        mass: 4.36624404335156298e-05 * SOLAR_MASS
    ),

    Body (
        x: 1.53796971148509165e+01,
        y: -2.59193146099879641e+01,
        z: 1.79258772950371181e-01,
        vx: 2.68067772490389322e-03 * DAYS_PER_YEAR,
        vy: 1.62824170038242295e-03 * DAYS_PER_YEAR,
        vz: -9.51592254519715870e-05 * DAYS_PER_YEAR,
        mass: 5.15138902046611451e-05 * SOLAR_MASS
    )
]


func offsetMomentum() {
    var px = 0.0
    var py = 0.0
    var pz = 0.0

    for body in bodies {
        px += body.vx * body.mass
        py += body.vy * body.mass
        pz += body.vz * body.mass
    }

    bodies[0].vx = -px / SOLAR_MASS;
    bodies[0].vy = -py / SOLAR_MASS;
    bodies[0].vz = -pz / SOLAR_MASS;
}


func energy() -> Double {
    var dx, dy, dz, distance: Double
    var e = 0.0

    for i in 0..<bodies.count {
        e += 0.5 * bodies[i].mass *
            ( bodies[i].vx * bodies[i].vx
                + bodies[i].vy * bodies[i].vy
                + bodies[i].vz * bodies[i].vz )

        for j in i+1..<bodies.count {
            dx = bodies[i].x - bodies[j].x
            dy = bodies[i].y - bodies[j].y
            dz = bodies[i].z - bodies[j].z

            distance = sqrt(dx*dx + dy*dy + dz*dz)
            e -= (bodies[i].mass * bodies[j].mass) / distance
        }
    }
    return e
}


func advance(dt: Double) {
    var dx, dy, dz, distance, mag: Double

    for i in 0..<bodies.count {
        for j in i+1..<bodies.count {
            dx = bodies[i].x - bodies[j].x
            dy = bodies[i].y - bodies[j].y
            dz = bodies[i].z - bodies[j].z

            distance = sqrt(dx*dx + dy*dy + dz*dz)
            mag = dt / (distance * distance * distance)

            bodies[i].vx -= dx * bodies[j].mass * mag
            bodies[i].vy -= dy * bodies[j].mass * mag
            bodies[i].vz -= dz * bodies[j].mass * mag

            bodies[j].vx += dx * bodies[i].mass * mag
            bodies[j].vy += dy * bodies[i].mass * mag
            bodies[j].vz += dz * bodies[i].mass * mag
        }
    }

    for i in 0..<bodies.count {
        bodies[i].x += dt * bodies[i].vx
        bodies[i].y += dt * bodies[i].vy
        bodies[i].z += dt * bodies[i].vz
    }
}


let n = Int(Process.arguments[1])!
offsetMomentum()
print( energy() )
for _ in 1...n {
    advance(0.01)
}
print( energy() )
