OpenSecurity Sentry

local component = require "component"
local dtec = component.os_entdetector
local turr = component.os_energyturret

turr.powerOn()
turr.extendShaft(2)
turr.setArmed(true)

local mob_names = {
    "Creeper",
    "Zombie",
    "Skeleton",
    "Spider"
}
local mob_lookup = {}
for _, mob in pairs(mob_names) do
    mob_lookup[mob] = true
end

local function get_direction(entity)
    local x, y, z = entity.x, entity.y, entity.z
    local pitch = -math.atan2(y, math.sqrt(x * x + z * z))
    local yaw = math.atan2(-x, z)
    return pitch, yaw
end

local function fire(entity)
    print("TARGET", entity.name)
    turr.moveToRadians(entity.yaw, entity.pitch)
    repeat
        os.sleep(0.05)
    until turr.isOnTarget()
    print "FIRING"
    turr.fire()
end

while true do
    local entities = dtec.scanEntities(32)
    local nearest
    for _, entity in pairs(entities) do
        if mob_lookup[entity.name] and (nearest == nil or entity.range < nearest.range) then
            local pitch, yaw = get_direction(entity)
            entity.pitch = pitch
            entity.yaw = yaw
            entity.y = entity.y + 1
            entity.z = entity.z + 1
            local degpitch = math.deg(pitch)
            print(entity.name, degpitch)
            if degpitch > -25 and degpitch < 50 then
                print("NEAR", degpitch, entity.name)
                nearest = entity
            end
        end
    end
    if nearest then
        fire(nearest)
    end
    os.sleep(0.1)
end