startup

local coalSide = "left"
local saplingSide = "right"

-- More Settings
local fuelSlot = 15
local saplingSlot = 16
local travelDistance = 16
local dirtQuantity = 4

-- Directionality Stuff
local facing = 2

local function getFacing(f)
    if f == nil then f = facing end

    if f == 0 then return "north" end
    if f == 1 then return "east" end
    if f == 2 then return "south" end
    return "west"
end

local function getDirectionForSide(side)
    local offset = 0
    if side == "right" then offset = 1 end
    if side == "back" then offset = 2 end
    if side == "left" then offset = 3 end

    local f = facing + offset
    if f > 4 then f = f - 4 end
    return getFacing(f)
end

local function turnLeft(count)
    if count == nil then count = 1 end
    for i=1,count do
        if turtle.turnLeft() then
            facing = facing - 1
            if facing < 1 then facing = facing + 4 end
        end
    end
    return facing
end

local function turnRight(count)
    if count == nil then count = 1 end
    for i=1,count do
        if turtle.turnRight() then
            facing = facing + 1
            if facing > 4 then facing = facing - 4 end
        end
    end
    return facing
end

local function forward(count)
    if count == nil then count = 1 end
    for i=1,count do
        if not turtle.forward() then
            error("Could not move.")
        end
    end
end

local function up(count)
    if count == nil then count = 1 end
    for i=1,count do
        if not turtle.up() then
            error("Could not move.")
        end
    end
end

local function down(count)
    if count == nil then count = 1 end
    for i=1,count do
        if not turtle.down() then
            error("Could not move.")
        end
    end
end

local function getOpposite(side)
    if side == "north" then return "south" end
    if side == "east" then return "west" end
    if side == "south" then return "north" end
    if side == "west" then return "east" end
    if side == "up" then return "down" end
    return "up"
end

local select = turtle.select
local placeDown = turtle.placeDown

-- Inventory Management

local function getFromContainer(side, slot, quantity)
    peripheral.call(side, "pushItem", getOpposite(getDirectionForSide(side)), 1, quantity, slot)
end

local function getFuel()
    print("Checking fuel...")
    if turtle.getFuelLevel() < travelDistance then
        print("Refueling.")
        getFromContainer(coalSide, fuelSlot, 1)
        select(fuelSlot)
        turtle.refuel(1)
        select(1)
    end
end

local function getSapling()
    print("Checking saplings...")
    local count = turtle.getItemCount(saplingSlot)
    if count < 4 then
        print("Getting saplings.")
        getFromContainer(saplingSide, saplingSlot, 4-count)
    end
end

-- Plant Saplings
local function plant()
    print("Planting...")

    turnRight(2)
    forward(4)

    -- Place Dirt
    select(1)
    placeDown()
    forward()
    placeDown()
    turnRight()
    forward()
    placeDown()
    turnRight()
    forward()
    placeDown()

    -- Place Saplings
    select(saplingSlot)
    turnRight(2)
    up()
    placeDown()
    forward()
    placeDown()
    turnLeft()
    forward()
    placeDown()
    turnLeft()
    forward()
    placeDown()

    -- Return to Start
    forward(4)
    down()
    select(1)
end

-- The Loop
print("Getting started...")
while true do
    print("Waiting for inventory event...")
    local event, p1 = os.pullEvent("turtle_inventory")
    if turtle.getItemCount(1) == dirtQuantity then
        print("Found a tree! Sleeping...")

        -- Time to Harvest
        sleep(15)

        -- Now, Work
        getFuel()
        getSapling()
        plant()
    else
        print("Not what we wanted.")
    end
end