@LAZYGLOBAL OFF.

run once "lib/rocket".
run once "lib/warp".


function estimated_burn_duration {
    //
    // Calculate estimated burn duration for a maneuver node.
    // Based on:
    //  https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation
    //  https://space.stackexchange.com/questions/27375/how-do-i-calculate-a-rockets-burn-time-from-required-velocity
    //
    parameter node is NEXTNODE.
    
    local exhaust_velocity is isp_sum() * (CONSTANT:G * KERBIN:mass).
    return ((SHIP:mass * exhaust_velocity) / SHIP:maxthrust) * (1 - CONSTANT:E^(-node:deltav:mag/exhaust_velocity)).
}


function execute_node {
    //
    // Execute given maneuver node (the next one by default).
    //
    parameter node is NEXTNODE.
    
    local burn_duration is estimated_burn_duration(node).
    
    print "=== EXECUTE MANEUVER NODE ===".
    print "Estimated burn duration: " + ROUND(burn_duration, 1) + "s".
        
    print "Aligning ship with burn vector..".
    SAS off.
    lock STEERING to node:deltav.
    wait until vang(SHIP:facing:vector, node:deltav) < 0.5.
    
    print "Initializing warp".
    warp_for(MAX(0, node:eta - (burn_duration/2) - 5)).  // warp until 5s before node
    
    print "Approaching".
    wait until node:eta <= CEILING(burn_duration/2).  // CEILING instead of ROUND, since we'd rather start the burn too soon to have time for perfecting the burn
    
    print "Burn!".
    lock THROTTLE to 1.0.
    
    // Decrease throttle linearly when the burn duration is less than 1 second
    wait until estimated_burn_duration(node) <= 1.
    lock THROTTLE to MAX(0.01, estimated_burn_duration(node)).  // ensure we always finish by burning with at least 1% power
    
    // The burn vector will start to drift once we have very little left to burn. Therefore, take a "snapshot" of the burn vector as it is right now, and lock steering to it, instead of the dynamic vector
    local dv0 is node:deltav.
    lock STEERING to dv0.
    
    // Stop the burn once the "snapshot" vector dv0 and current burn vector start facing opposite directions
    wait until vdot(dv0, node:deltav) < 0.
    set THROTTLE to 0.0.
    
    print "=== MANEUVER NODE EXECUTED ===".
    print round(node:deltav:mag, 3) + "m/s delta-v remaining".
    unlock_control().
    wait 1.
    remove node.
}