-- Based on excavate from the original computercraft distribution
-- written by hildenae
rubberwood=1
tool=2

local depth = 0
local xPos,zPos = 0,0
local xDir,zDir = 0,1

local function turnLeft()
    turtle.turnLeft()
    xDir, zDir = -zDir, xDir
end

local function turnRight()
    turtle.turnRight()
    xDir, zDir = zDir, -xDir
end

function goTo( x, y, z, xd, zd )
    while depth > y do
        if turtle.up() then
            depth = depth - 1
        else
            return false
        end
    end

    if xPos > x then
        while xDir ~= -1 do
            turnLeft()
        end
        while xPos > x do
            if turtle.forward() then
                xPos = xPos - 1
            else
                return false
            end
        end
    elseif xPos < x then
        while xDir ~= 1 do
            turnLeft()
        end
        while xPos < x do
            if turtle.forward() then
                xPos = xPos + 1
            else
                return false
            end
        end
    end

    if zPos > z then
        while zDir ~= -1 do
            turnLeft()
        end
        while zPos > z do
            if turtle.forward() then
                zPos = zPos - 1
            else
                return false
            end
        end
    elseif zPos < z then
        while zDir ~= 1 do
            turnLeft()
        end
        while zPos < z do
            if turtle.forward() then
                zPos = zPos + 1
            else
                return false
            end
        end
    end
    while depth < y do
        if turtle.down() then
            depth = depth + 1
        else
            return false
        end
    end
    while zDir ~= zd or xDir ~= xd do
        turnLeft()
    end
    return true
end

local function forward()
    turtle.forward()
    xPos = xPos + xDir
    zPos = zPos + zDir
    return true
end

local function down()
    if turtle.down() then
        depth = depth + 1
        return true
    else
        return false
    end
end

local function harvest()
    if turtle.compareTo(rubberwood) then
        turtle.select(tool)
        turtle.place()
    end
end

local function downTree()
    local x,y,z,xd,zd = xPos,depth,zPos,xDir,zDir
    while(down()) do
        harvest()
    end
    goTo( x,y,z,xd,zd )
end

local function moveRight()
    turnRight()
    forward()
    turnLeft()
end
local function moveLeft()
    turnLeft()
    forward()
    turnRight()
end
run = true
while run do
    forward()
    downTree()
    moveRight()
    downTree()
    moveRight()
    downTree()
    -- go to charge station
    goTo(0,0,0,0,1)
    run = false
end