IE Excavator Placer

--------------------------------------
-- A program to place the excavator
-- from Immersive Engineering.
--
-- Needed items:
--  Slot 1: 23 Steel Scaffoldings
--  Slot 2: 21 Blocks of steel
--  Slot 3: 13 Heavy Engineering Blocks
--  Slot 4: 9 Light Engineering Blocks
--
-- Make sure you clear out a nice
-- 8x3x7 area.
--------------------------------------

local missingMessage = "Missing items: "
local matrix = {
    {{0, 0, 0, 0, 0, 0, 0, 0}, {0, 0, 0, 2, 0, 0, 0, 0}, {0, 0, 0, 0, 0, 0, 0, 0}},
    {{0, 0, 0, 0, 0, 0, 0, 0}, {0, 2, 1, 1, 1, 2, 0, 0}, {0, 0, 0, 0, 0, 0, 0, 0}},
    {{0, 0, 3, 3, 3, 2, 4, 2}, {0, 1, 1, 1, 1, 1, 0, 2}, {0, 0, 3, 4, 3, 2, 3, 3}},
    {{0, 0, 3, 3, 3, 2, 4, 2}, {2, 1, 1, 2, 1, 1, 2, 3}, {0, 0, 4, 4, 4, 2, 2, 4}},
    {{0, 0, 1, 1, 1, 2, 4, 2}, {0, 1, 1, 1, 1, 1, 0, 2}, {0, 0, 0, 4, 0, 2, 3, 3}},
    {{0, 0, 0, 0, 0, 0, 0, 0}, {0, 2, 1, 1, 1, 2, 0, 0}, {0, 0, 0, 0, 0, 0, 0, 0}},
    {{0, 0, 0, 0, 0, 0, 0, 0}, {0, 0, 0, 2, 0, 0, 0, 0}, {0, 0, 0, 0, 0, 0, 0, 0}}
}

local blocks = {
    {"Steel Scaffoldings", 23},
    {"Steel Blocks", 21},
    {"Heavy Engineering Blocks", 13},
    {"Light Engineering Blocks", 9}}

--------------------------------------
-- Don't touch things under here...
-- ... yeah you!
--------------------------------------
function tableLen(T)
  local cnt = 0
  for _ in pairs(T) do cnt = cnt + 1 end
  return cnt
end

local maxHeight = tableLen(matrix)
local maxWidth = tableLen(matrix[1])
local maxDepth = tableLen(matrix[1][1])

local position = {forward=1, right=1, up=0, face=1}
local facing = { "forward", "right", "back", "left" }

function _facingToNumber( direction )
    if direction == "forward" then return 1 end
    if direction == "right" then return 2 end
    if direction == "back" then return 3 end
    if direction == "left" then return 4 end
    return 0
end

function TurnTo( direction )
    local directionNum = _facingToNumber( direction )

    while facing[position.face] ~= direction do
        local difference = directionNum - position.face
        if difference == -1 or difference == 3 then
            turtle.turnLeft()
            position.face = position.face - 1
        else
            turtle.turnRight()
            position.face = position.face + 1
        end

        if position.face == 5 then position.face = 1 end
        if position.face == 0 then position.face = 4 end
    end
end

function Forward( amount )
    amount = amount or 1
    for i=1,amount do
        assert(turtle.forward(), "I got stuck! Give me more fuel next time and/or clear the area. You have to rerun me from the begining.")
        -- Update Position
        if position.face == 1 then position.forward = position.forward + 1 end
        if position.face == 3 then position.forward = position.forward - 1 end
        if position.face == 2 then position.right = position.right + 1 end
        if position.face == 4 then position.right = position.right - 1 end
    end
end

function Up( amount )
    amount = amount or 1
    for i=1,amount do
        assert(turtle.up(), "I got stuck! Give me more fuel next time and/or clear the area. You have to rerun me from the begining.")
        position.up = position.up + 1
    end
end

function Down( amount )
    amount = amount or 1
    for i=1,amount do
        turtle.down()
        position.up = position.up - 1
    end
end

function MoveTo(forward, right, up)
    local forwardMovement = forward - position.forward
    local rightMovement = right - position.right
    local upMovement = up - position.up

    if forwardMovement > 0 then
        TurnTo("forward")
        Forward(forwardMovement)
    end
    if forwardMovement < 0 then
        TurnTo("back")
        Forward(math.abs(forwardMovement))
    end
    if rightMovement > 0 then
        TurnTo("right")
        Forward(rightMovement)
    end
    if rightMovement < 0 then
        TurnTo("left")
        Forward(math.abs(rightMovement))
    end
    if upMovement < 0 then
        Down(upMovement)
    end
    if upMovement > 0 then
        Up(math.abs(upMovement))
    end
end

-- Intial Fun
term.clear()
term.setCursorPos(1,1)

function checkForNeeded()
    local toReturn = true
    local cnt = 1
    for i, v in pairs(blocks) do
        toReturn = checkSlot(i, v[2], v[1]) and toReturn
    end
    return toReturn
end

function checkSlot(slotNum, itemAmount, itemName)
    if turtle.getItemCount(slotNum) < itemAmount then
        missingMessage = missingMessage .. "\n - " .. itemAmount .. " " .. itemName .. " [Slot " .. slotNum .. "]"
        return false
    else
        return true
    end
end

function placeMatrix()
    for height = 1,maxHeight do
        for width = 1,maxWidth do
            for depth = 1,maxDepth do
                if matrix[height][width][depth] > 0 then
                    MoveTo(depth, width, height)
                    placeBlock(matrix[height][width][depth])
                end
            end
        end
    end
end

function placeBlock(slotNum)
    if slotNum > 0 then
        turtle.select(slotNum)
        assert(turtle.placeDown(), "Either clear the area or give me permission to place a block. You'll have to start over.")
    end
end

-- Do all the stuff!
if not checkForNeeded() then
    print(missingMessage)
    return
end

print("Running...")
placeMatrix()
print("Finished running...")