local programParam = { ... }
local startLoc = { 0, 0, 0, 1 }
local lastGoodLoc = { 0, 0, 0, 1 }
local currentLoc = { 0, 0, 0, 1 }
local hitBedrock = false
local doneMining = false
local rtnToStart = false

local needFuel, returnAndUnload, travelTo, turnRight, turnLeft, unloadInv

-- Save current location for later use
local function saveLoc()
    local newSaveLoc = {};
    newSaveLoc[1] = currentLoc[1]
    newSaveLoc[2] = currentLoc[2]
    newSaveLoc[3] = currentLoc[3]
    newSaveLoc[4] = currentLoc[4]
    return newSaveLoc
end

-- When out of fuel, go back to start and wait for fuel
local function goWaitForFuel()
    lastGoodLoc = saveLoc()
    rtnToStart = true
    travelTo(startLoc)
    turnRight()
    turnRight()
    unloadInv()
    turnLeft()
    turnLeft()
    print("NEED MOAR FUELS!")
    while needFuel() do
        os.pullEvent("turtle_inventory")
    end
    rtnToStart = false
    travelTo(lastGoodLoc)
end

-- determine if fuel is needed
function needFuel()
    local fuelReq
    if rtnToStart then
        -- If traveling to starting location, calculate needed fuel by:
        fuelReq = (math.abs(currentLoc[1]) + math.abs(currentLoc[2]) + math.abs(currentLoc[3]) + 2)
    else
        -- If traveling to last saved location, calculate needed fuel by:
        fuelReq = (math.abs(lastGoodLoc[1]) + math.abs(lastGoodLoc[2]) + math.abs(lastGoodLoc[3]) + 2)
    end
    local fuelNeeded = false
    -- Check for unlimted fuel
    if turtle.getFuelLevel() == "unlimited" then
        return false
    else
        if fuelReq > turtle.getFuelLevel() then
            fuelNeeded = true
            for i = 1, 16 do
                if fuelNeeded then
                    -- Select one inventory slot at a time, then try and burn it.
                    -- If burn successful, repeat until enough fuel has been used.
                    if turtle.getItemCount(i) > 0 then
                        turtle.select(i)
                        if turtle.refuel(1) then
                            if turtle.getItemCount(i) > 0 then
                                while fuelReq > turtle.getFuelLevel() and turtle.refuel(1) do
                                end
                            end
                            if fuelReq < turtle.getFuelLevel() then
                                turtle.select(1)
                                fuelNeeded = false
                                break
                            end
                        end
                    end
                end
            end
            turtle.select(1)
        end
        -- Return result
        if fuelNeeded then
            return true
        else
            return false
        end
    end
end

-- Check inventory for free space
local function checkInvSpace()
    local invFull = true
    local totalItemCount = 0
    for i = 1, 16 do
        -- Look for empty inventory spaces
        local itemCount = turtle.getItemCount(i)
        if itemCount == 0 then
            invFull = false
        end
        totalItemCount = totalItemCount + itemCount
    end
    -- Return result
    if invFull then
        print("Inventory full.")
        return false
    else
        return true
    end
end

-- Update x, y, movement
local function updateLoc()
    if currentLoc[4] == 1 then
            currentLoc[2] = currentLoc[2] + 1
        elseif currentLoc[4] == 2 then
            currentLoc[1] = currentLoc[1] + 1
        elseif currentLoc[4] == 3 then
            currentLoc[2] = currentLoc[2] - 1
        else
            currentLoc[1] = currentLoc[1] - 1
    end
end

-- Forward mining movement
local function moveForward()
    if needFuel() then
        goWaitForFuel()
    end
    while not turtle.forward() do
            turtle.attack()
            turtle.dig()
            if not checkInvSpace() and not rtnToStart then
                returnAndUnload()
            end
            sleep(0.5)
    end
    local checkSucc, data = turtle.inspectDown()
    if data.name == "minecraft:bedrock" then
        hitBedrock = true
    end
    local checkSucc, data = turtle.inspect()
    if data.name == "minecraft:bedrock" then
        hitBedrock = true
        turtle.up()
        currentLoc[3] = currentLoc[3] + 1
    end
    -- Update location for movement
    updateLoc()
end

-- Upward mining movement
local function moveUp()
    if needFuel() then
        goWaitForFuel()
    end
    while not turtle.up() do
        turtle.attackUp()
        turtle.digUp()
        if not checkInvSpace() and not rtnToStart then
            returnAndUnload()
        end
        sleep(0.5)
    end
    -- Update location for movement
    currentLoc[3] = currentLoc[3] + 1
end

-- Downward mining movement
local function moveDown()
    if needFuel() then
        goWaitForFuel()
    end
    while not turtle.down() do
        turtle.attackDown()
        turtle.digDown()
        if not checkInvSpace() and not rtnToStart then
            returnAndUnload()
        end
        sleep(0.5)
    end
    -- Update location for movement
    currentLoc[3] = currentLoc[3] - 1
end

-- Rotate turtle counterclockwise
function turnLeft()
    if turtle.turnLeft() then
        currentLoc[4] = currentLoc[4] - 1
        if currentLoc[4] < 1 then
            currentLoc[4] = 4
        end
    else
        print("Error!  Unable to turn left.")
    end
end

-- Rotate turtle clockwise
function turnRight()
    if turtle.turnRight() then
        currentLoc[4] = currentLoc[4] + 1
        if currentLoc[4] > 4 then
            currentLoc[4] = 1
        end
    else
        print("Error!  Unable to turn right.")
    end
end

-- Unload inventory
function unloadInv()
    -- If mining is complete, unload everything
    if doneMining then
        for i = 1, 16 do
            turtle.select(i)
            turtle.drop()
        end
        turtle.select(1)
    else
        -- Unload only what can't be used as fuel
        for i = 1, 16 do
            turtle.select(i)
            if not turtle.refuel(1) then
                turtle.drop()
            end
        end
        turtle.select(1)
    end
end

-- Check if at start
local function isAtStart()
    return currentLoc[1] == startLoc[1] and currentLoc[2] ==startLoc[2] and currentLoc[3] == startLoc[3] and currentLoc[4] == startLoc[4]
end

-- Travel to a coordinate
function travelTo(locArrayIn)
    -- Below end location
    if currentLoc[3] < locArrayIn[3] then
        while currentLoc[3] ~= locArrayIn[3] do
            moveUp()
        end
    end

    -- If left of end location
    if currentLoc[1] < locArrayIn[1] then
        while currentLoc[4] ~= 2 do
            turnRight()
        end

        while currentLoc[1] ~= locArrayIn[1] do
            moveForward()
        end
    end

    -- If right of end location
    if currentLoc[1] > locArrayIn[1] then
        while currentLoc[4] ~= 4 do
            turnLeft()
        end

        while currentLoc[1] ~= locArrayIn[1] do
            moveForward()
        end
    end

    -- If behind end location
    if currentLoc[2] < locArrayIn[2] then
        while currentLoc[4] ~= 1 do
            turnRight()
        end
        while currentLoc[2] ~= locArrayIn[2] do
            moveForward()
        end
    end

    -- If in front of end location
    if currentLoc[2] > locArrayIn[2] then
        while currentLoc[4] ~= 3 do
            turnLeft()
        end
        while currentLoc[2] ~= locArrayIn[2] do
            moveForward()
        end
    end

    -- Above end location
    if currentLoc[3] > locArrayIn[3] then
        while currentLoc[3] ~= locArrayIn[3] do
            moveDown()
        end
    end

    -- Orient turtle to correct location
    while currentLoc[4] ~= locArrayIn[4] do
        turnRight()
    end
end

function returnAndUnload()
    lastGoodLoc = saveLoc()
    rtnToStart = true
    travelTo(startLoc)
    turnRight()
    turnRight()
    unloadInv()
    rtnToStart = false
    if not doneMining then
        turnLeft()
        turnLeft()
        travelTo(lastGoodLoc)
    end
end

-- Start digging that hole!
--
while true do
    -- Dig trench for however long required
    for i = 1, (tonumber(programParam[1])  - 1) do
        moveForward()
    end
    -- Finish the row
    -- See if dig is done
    if  hitBedrock then
        doneMining = true
        returnAndUnload()
        print("Job's done.")
        break
    else
        -- If not, turn around, go down, and continue
        turnRight()
        turnRight()
        moveDown()
    end
end