Tree Farmer

local sideLength = 7
local inspectAttempts = 5
local desiredFuelPercent = 0.5

local move = {
    forward = function()
        while not turtle.forward() do
            turtle.dig()
        end
    end,
    up = function()
        while not turtle.up() do
            turtle.digUp()
        end
    end,
    down = function()
        while not turtle.down() do
            turtle.digDown()
        end
    end
}

local checkBlock = {
    forward = function(name)
        local i
        for i = 1, inspectAttempts do
            local success, blockData = turtle.inspect()
            if success then
                return blockData.name:find(name) ~= nil
            end
        end
    end,
    up = function(name)
        local i
        for i = 1, inspectAttempts do
            local success, blockData = turtle.inspectUp()
            if success then
                return blockData.name:find(name) ~= nil
            end
        end
    end,
    down = function(name)
        local i
        for i = 1, inspectAttempts do
            local success, blockData = turtle.inspectDown()
            if success then
                return blockData.name:find(name) ~= nil
            end
        end
    end
}

local function checkItem(name, slot)
    local item = turtle.getItemDetail(slot)
    return item and item.name:find(name)
end

local function selectItem(name)
    local i
    for i = 1, 16 do
        if checkItem(name, i) then
            turtle.select(i)
            return
        end
    end
end

local function chopTreeIfExists()
    if checkBlock.down('log') then
        turtle.digDown()
        selectItem('sapling')
        turtle.placeDown()
    end
    local height, i = 0
    while checkBlock.up('log') do
        move.up()
        height = height + 1
    end
    for i = 1, height do
        move.down()
    end
end

local function transferItem(name, slot)
    local i
    if not checkItem(name, slot) and turtle.getItemCount(slot) > 0 then
        turtle.select(slot)
        for i = 1, 16 do
            if i ~= slot and turtle.getItemCount(i) == 0 then
                turtle.transferTo(i)
                break
            end
        end
    end
    for i = 1, 16 do
        if checkItem(name, i) then
            turtle.select(i)
            turtle.transferTo(slot)
        end
    end
end

while true do
    move.forward()
    chopTreeIfExists()

    local i, j
    for i = 1, sideLength do
        for j = 1, sideLength - 1 do
            move.forward()
            chopTreeIfExists()
        end
        if i < sideLength then
            if i % 2 == 1 then
                turtle.turnRight()
                move.forward()
                chopTreeIfExists()
                turtle.turnRight()
            else
                turtle.turnLeft()
                move.forward()
                chopTreeIfExists()
                turtle.turnLeft()
            end
        end
    end

    move.forward()
    transferItem('sapling', 1)
    if checkBlock.down('barrel') then
        for i = 2, 16 do
            if turtle.getItemCount(i) > 0 then
                turtle.select(i)
                turtle.dropDown()
            end
        end
    end
    if checkBlock.forward('pedestal') then
        turtle.select(1)
        turtle.suck(turtle.getItemSpace(1))
    end
    turtle.turnRight()
    if
        turtle.getFuelLevel() ~= 'unlimited' and checkBlock.forward('pedestal') and
            turtle.getFuelLevel() < turtle.getFuelLimit() * desiredFuelPercent
     then
        turtle.select(16)
        turtle.suck()
        turtle.refuel()
    end
    turtle.turnRight()
    sleep(60)
end