Melon Farm

--By xXxMoNkEyMaNxXx
--Designed for a 2xN melon farm
--Put the turtle on the right ride facing the farm
--Put a chest of fuel to the right of the turtle
--Put a chest for melons behind the turtle


local tick=os.clock
local ceil=math.ceil
local floor=math.floor
local max=math.max
local min=math.min

local interval=2*60
local efficiency=0.5 --wait for 50% of melons to grow before harvesting
local probability=1/(1+floor(25/(2*0.75)))
local wait=math.log(1-efficiency)/(20*math.log(1-probability*3/(16*16*16)))

local farm_len=...
local s=1
turtle.select(s)
local function unload()
    if turtle.detect() then
        for i=1,16 do
            if turtle.getItemCount(i)>0 then
                turtle.select(i)
                turtle.drop()
            end
        end
    end
end

local function getRealFuel()
    local f=turtle.getFuelLevel()
    return type(f)=="number" and f or math.huge
end

local function fillTo(req,slot)
    turtle.select(slot)
    local ret
    local i=0
    local f_0=getRealFuel()
    print("Fuel: "..f_0)
    print("Required: "..req)
    if f_0<req then
            if turtle.detect() then
            print'Refuelling...'
            local t=1
            while turtle.getItemCount(t)>0 and t<=16 do
                t=t+1
            end
            if t<=16 and turtle.select(t) then
                while getRealFuel()<req and turtle.suck() do
                    local f0=getRealFuel()
                    local i0=turtle.getItemSpace(t)
                    assert(turtle.refuel(1),"That's not fuel!")
                    local f1=getRealFuel()
                    local i1=turtle.getItemSpace(t)

                    local df,di=f1-f0,i1-i0
                    local rate=df/di
                    local f_req=ceil((req-f1)/rate)

                    local c=turtle.getItemCount(t)
                    if c>0 then
                        assert(turtle.refuel(min(max(0,f_req),c)),"That's not fuel!")
                    end
                    i=i+turtle.getItemSpace(t)-i0
                    local c=turtle.getItemCount(t)
                    if c>0 then
                        if turtle.drop(c) then
                            break
                        else
                            turtle.turnRight()
                            turtle.turnRight()
                            turtle.drop(c)
                            turtle.turnLeft()
                            turtle.turnLeft()
                        end
                    end
                end
                turtle.select(s)
                local f_1=getRealFuel()
                print("Gained "..f_1-f_0.." fuel from "..i.." fuel items.")
                ret=f_1>=req
            else
                print'Unable to refuel.\n(No room in the turtle)'
                ret=false
            end
        end
        turtle.select(slot)
    else
        ret=true
    end
    turtle.select(s)
    return ret
end
local unfirst=false
turtle.turnRight()
local runs=0
local fuel=fillTo(2*(farm_len or 2^runs)+2,1)
local start
while fuel do
    turtle.turnLeft()
    --while farm_len and not turtle.detect() do sleep(1) end
    if unfirst then
        local delay=wait+start-tick()
        if delay>0 then
            local show_delay=floor(delay*10)/10
            print("Waiting "..show_delay.." second"..(show_delay==1 and "" or "s")..".")
            sleep(delay%interval)
            for d=floor(delay/interval),1,-1 do
                print("Harvesting in "..(d*interval/60).." min.")
                sleep(interval)
            end
        end
    else
        unfirst=true
    end
    start=tick()
    local distance=0
    while farm_len and distance<farm_len or turtle.detectDown() and distance+3<getRealFuel() do
        if turtle.getItemSpace(s)>0 then
            if turtle.detect() then
                turtle.dig()
            end
            if turtle.forward() then
                distance=distance+1
            end
        elseif s==16 then
            error'TOO MUCH WATERMELON FUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU'
            unload(2)
            s=2
            turtle.select(2)
        else
            s=s+1
            turtle.select(s)
        end
    end
    if not turtle.detectDown() then
        farm_len=distance-1
    end
    turtle.turnLeft()
    turtle.forward()
    turtle.turnLeft()
    local d=distance
    while d>0 do
        if turtle.getItemSpace(s)>0 then
            if turtle.detect() then
                turtle.dig()
            end
            if turtle.forward() then
                d=d-1
            end
        elseif s==16 then
            error'TOO MUCH WATERMELON FUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU'
            unload(2)
            s=2
            turtle.select(2)
        else
            s=s+1
            turtle.select(s)
        end
    end
    turtle.turnLeft()
    turtle.forward()
    turtle.turnRight()
    unload()
    turtle.turnLeft()
    runs=runs+1
    if farm_len then
        fuel=fillTo(2*farm_len+2,1)
    else
        fuel=fillTo(2*2^runs+2,1)
    end
end
turtle.turnLeft()
print'Out of fuel.'