args = {...}
-- Make sure turtle is positioned correctly
term.clear()
term.setCursorPos(1,1)
print("I am set up to dig a rectangle downward in a forward-left direction. There should be a refuel chest to my right and a dropoff chest behind me. Is this how I am set up?")
print("\(y/n\)")
while true do
        local event, character = os.pullEvent()
        if event == "char" and character == "y" then
                print("Initializing...")
                sleep(1)
                break
        elseif event == "char" and character == "n" then
                print("Please set up correctly.")
                error()
        end
end

local function forward() --Forward movement
        --Move forward
        local i = 0 --Iterator for bedrock/strong player detection
        while not turtle.forward() do
                if not turtle.dig() then --Detect blocks
                        i = i + 1
                        turtle.attack() --Detect entities
                        if i == 30 then
                                return false --If movement fails
                        end
                end
        end
        --Clear above and below
        while turtle.detectUp() do
                turtle.digUp()
        end
        while turtle.detectDown() do
                turtle.digDown()
        end
        --Position tracking
        if currentpos.f == 0 then
                currentpos.z = currentpos.z + 1
        elseif currentpos.f == 1 then
                currentpos.x = currentpos.x - 1
        elseif currentpos.f == 2 then
                currentpos.z = currentpos.z - 1
        elseif currentpos.f == 3 then
                currentpos.x = currentpos.x + 1
        else
                running = false
                error("Something went wrong with the direction :P/>/>/>")
        end
        return true
end
local function turnRight() --Right turn with position tracking
        turtle.turnRight()
        if currentpos.f < 3 then
                currentpos.f = currentpos.f + 1
        else
                currentpos.f = 0
        end
end
local function turnLeft() --Left turn with position tracking
        turtle.turnLeft()
        if currentpos.f > 0 then
                currentpos.f = currentpos.f - 1
        else
                currentpos.f = 3
        end
end
local function down() --Downward movement
        --Move down
        local i = 0 --Iterator for bedrock detection
        while not turtle.down() do
                if not turtle.digDown() then --Detect blocks
                        i = i + 1
                        turtle.attackDown() --Detect entities
                        if i == 25 then
                                return false --If movement fails
                        end
                end
        end
        --Position tracking
        currentpos.y = currentpos.y - 1
        return true
end
local function mineDown() --Moves one layer downward
        if currentpos.y == edge.y + 2 then --If close to bottom (2 blocks away)
                if not down() then --If downward movement fails, return to start
                        shell.run("goto","special",0,0,0,0,currentpos.x,currentpos.y,currentpos.z,currentpos.f)
                        running = false
                        error("I think I tried to dig bedrock.")
                end
        elseif currentpos.y == edge.y + 3 then --If close to bottom (3 blocks away)
                for i=1,2 do
                        if not down() then --If downward movement fails, return to start
                                shell.run("goto","special",0,0,0,0,currentpos.x,currentpos.y,currentpos.z,currentpos.f)
                                running = false
                                error("I think I tried to dig bedrock.")
                        end
                end
        else --If far enough from bottom
                for i=1,3 do
                        if not down() then --If downward movement fails, return to start
                                shell.run("goto","special",0,0,0,0,currentpos.x,currentpos.y,currentpos.z,currentpos.f)
                                running = false
                                error("I think I tried to dig bedrock.")
                        end
                end
        end
end
local function getFuelLevel() --Check if fuel level is unlimited
        local fuelLevel = turtle.getFuelLevel()
        if type(fuelLevel) == "string" then
                fuelLevel = 9001e9001
        end
        return fuelLevel
end
local function findDistance(x,y,z,newx,newy,newz) --Find how many blocks to travel to get somewhere (non-diagonally)
        local distance = 0
        local xDist = 0
        local yDist = 0
        local zDist = 0
        if x > newx then
                xDist = x - newx
        elseif x < newx then
                xDist = newx - x
        end
        if y > newy then
                yDist = y - newy
        elseif y < newy then
                yDist = newy - y
        end
        if z > newz then
                zDist = z - newz
        elseif z < newz then
                zDist = newz - z
        end
        distance = xDist + yDist + zDist
        return distance
end
local function saveLoc()
        --Write variables to savefile
        local fPos = fs.open("GPSExcavateCurrentpos","w")
        fPos.writeLine(currentpos.x)
        fPos.writeLine(currentpos.y)
        fPos.writeLine(currentpos.z)
        fPos.writeLine(currentpos.f)
        fPos.writeLine(edge.x)
        fPos.writeLine(edge.y)
        fPos.writeLine(edge.z)
        fPos.writeLine(backwards)
        fPos.writeLine(totalMined)
        fPos.writeLine(lastSlot)
        fPos.close()
end
local function detectUnwanted()
        local unwantedSlots = 0
        for i=1, lastSlot do
                turtle.select(i)
                if turtle.compareTo(13) or turtle.compareTo(14) or turtle.compareTo(15) or turtle.compareTo(16) then
                        unwantedSlots = unwantedSlots + 1
                end
        end
        turtle.select(1)
        return unwantedSlots
end
local function dropUnwanted()
        local freeSlots = 0
        turtle.turnLeft()
        turtle.turnLeft()
        for i=1, lastSlot do
                turtle.select(i)
                if turtle.compareTo(13) or turtle.compareTo(14) or turtle.compareTo(15) or turtle.compareTo(16) then
                        turtle.drop()
                end
        end
        turtle.turnLeft()
        turtle.turnLeft()
        turtle.select(1)
end
local function dropAll() --Drop mined resources, display amounts
        local mined = 0
        turtle.turnRight()
        turtle.turnRight()
        for i=1,lastSlot do
                turtle.select(i)
                mined = mined + turtle.getItemCount(i)
                turtle.drop()
        end
        --This will send to rednet soon
        totalMined = totalMined + mined
        print("Minerals mined this run: "..mined)
        print("Total mined: "..totalMined)
        turtle.select(1)
        turtle.turnRight()
        turtle.turnRight()
end
local function refuel() --Refuel if needed
        turtle.turnRight()
        turtle.select(1)
        while getFuelLevel() < findDistance(currentpos.x,currentpos.y,currentpos.z,0,0,0) + 400 do --Enough to make it back to where he was digging and dig a bit
                turtle.suck()
                if turtle.getItemCount(1) == 0 then --If no fuel is in the box
                        print("Please put fuel in my top-left slot, then press space.")
                        while true do
                                local event, character = os.pullEvent()
                                if event == "key" and character == 57 then
                                        print("Refueling...")
                                        sleep(1)
                                        break
                                end
                        end
                end
                if not turtle.refuel() then --If item isn't fuel
                        print("This is not fuel! Please remove it, then press space.")
                        while true do
                                local event, character = os.pullEvent()
                                if event == "key" and character == 57 then
                                        print("Refueling...")
                                        sleep(1)
                                        break
                                end
                        end
                end
        end
        turtle.turnLeft()
end
local function dropRefuel()
        print("Dropping & refueling")
        shell.run("goto","special",0,0,0,0,currentpos.x,currentpos.y,currentpos.z,currentpos.f) --Return to start
        dropAll()
        refuel()
        shell.run("goto","special",currentpos.x,currentpos.y,currentpos.z,currentpos.f,0,0,0,0) --Return to where he left off
end
local function excavate() --The actual excavation process
        while running do --Make sure stop signal hasn't been sent
                turtle.select(1)
                if currentpos.x == 0 and currentpos.y == 0 and currentpos.z == 0 then --To start off a layer down
                        down()
                        turtle.digDown()
                end
                if ( currentpos.x == edge.x and currentpos.y == edge.y + 1 and currentpos.z == edge.z or currentpos.x == edge.x and currentpos.y == edge.y + 1 and currentpos.z == 0 ) and not backwards or ( currentpos.x == 0 and currentpos.y == edge.y + 1 and currentpos.z == 0 or currentpos.x == 0 and currentpos.y == edge.y + 1 and currentpos.z == edge.z ) and backwards then --Very long check to see if at the end of process
                        if lastSlot ~= 16 and detectUnwanted()  then
                                dropUnwanted()
                        end
                        shell.run("goto","special",0,0,0,0,currentpos.x,currentpos.y,currentpos.z,currentpos.f) --Return to start
                        dropAll()
                        print("Done digging a hole! Whew, that was hard work.")
                        done = true --Record that turtle is finished digging
                        running = false --Stop other "stopping" loop
                        break
                end
                if turtle.getItemCount(lastSlot) > 0 then --Check if inventory is full or fuel is low
                        if lastSlot ~= 16 then
                                dropUnwanted()
                                if detectUnwanted() < 3 then
                                        dropRefuel()
                                elseif turtle.getItemCount(lastSlot) > 0 then
                                        turtle.select(lastSlot)
                                        while turtle.getItemCount(lastSlot) > 0 do
                                                for i=1, lastSlot do
                                                        turtle.transferTo(i)
                                                end
                                        end
                                end
                        else
                                dropRefuel()
                        end
                end
                if getFuelLevel() < (findDistance(currentpos.x,currentpos.y,currentpos.z,0,0,0) + 16) then
                        if lastSlot ~= 16 then
                                dropUnwanted()
                        end
                        dropRefuel()
                end
                if ( currentpos.x == edge.x and currentpos.z == edge.z or currentpos.x == edge.x and currentpos.z == 0 ) and not backwards then --If at the end of a layer
                        mineDown()
                        turnRight()
                        turnRight()
                        backwards = true --Switching directions
                        turtle.digDown()
                elseif ( currentpos.x == 0 and currentpos.z == 0 or currentpos.x == 0 and currentpos.z == edge.z ) and backwards then --If at the end of a layer
                        mineDown()
                        turnLeft()
                        turnLeft()
                        backwards = false --Switching directions
                        turtle.digDown()
                elseif currentpos.z == edge.z then --If at edge, turn around and do next line
                        if backwards then
                                turnRight()
                                forward()
                                turnRight()
                        else
                                turnLeft()
                                forward()
                                turnLeft()
                        end
                elseif currentpos.z == 0 and currentpos.x ~= 0 then --If at edge, turn around and do next line
                        if backwards then
                                turnLeft()
                                forward()
                                turnLeft()
                        else
                                turnRight()
                                forward()
                                turnRight()
                        end
                end
                if not forward() then --If movement fails, return to start
                        shell.run("goto","special",0,0,0,0,currentpos.x,currentpos.y,currentpos.z,currentpos.f)
                        running = false
                        error("I think I tried to dig bedrock.")
                end
                saveLoc()
        end
end
local function stop() --Ability to stop turtle mid-excavation. This will wait until current action is done, then exit the excavate function
        while running do
                local event, data, message = os.pullEvent()
                if event == "char" and data == "p" then --If direct keypress
                        print("Stopping...")
                        running = false
                        break
                end
        end
end
local function restart() --To restart from previous digging
        print("Restarting from saved position...")
        if not fs.exists("GPSExcavateCurrentpos") then -- Check for save file
                error("Could not find saved position!")
        end
        --Read save file, change variables
        local fPos = fs.open("GPSExcavateCurrentpos","r")
        currentpos.x = tonumber(fPos.readLine())
        currentpos.y = tonumber(fPos.readLine())
        currentpos.z = tonumber(fPos.readLine())
        currentpos.f = tonumber(fPos.readLine())
        edge.x = tonumber(fPos.readLine())
        edge.y = tonumber(fPos.readLine())
        edge.z = tonumber(fPos.readLine())
        local backwardsString = fPos.readLine()
        if backwardsString == "true" then
                backwards = true
        else
                backwards = false
        end
        totalMined = tonumber(fPos.readLine())
        lastSlot = tonumber(fPos.readLine())
        fPos.close()
        shell.run("goto","special",currentpos.x,currentpos.y,currentpos.z,currentpos.f,0,0,0,0) --Go to position where turtle left off
        restarting = true
        print("Let the diggy-hole recommence!")
end

totalMined = 0 --Total mined out blocks over course of excavation
restarting = false --Whether turtle is restarting from save
done = false --Whether turtle has completed excavation
running = true --Whether turtle is currently digging
backwards = false --Which direction turtle is digging the layers currently
currentpos = {} --Current position storage. It's a table just because it is easier, no real need for it
edge = {} --Boundaries of hole. Same deal as currentpos, no real reason to have it as a table
id = -1 --Id of computer that sent the rednet message. This is so that it can reply when it has stopped
w, l, d = 0, 0, 0 --Width, length, depth of hole. This is just for input of numbers
currentpos.x, currentpos.y, currentpos.z, currentpos.f = 0, 0, 0, 0 --Initialise pieces of currentpos
lastSlot = 16 --Slot in which to make sure there are no blocks: this is to keep any comparing slots free

if #args == 1 and args[1] == "restart" then --If restarting from save
        restart()
elseif #args == 2 and tonumber(args[1]) > 1 and tonumber(args[2]) > 2 then --If a square hole is wanted
        w = tonumber(args[1])
        l = w
        d = tonumber(args[2])
elseif #args == 3 and tonumber(args[1]) > 1 and tonumber(args[2]) > 1 and tonumber(args[3]) > 2 then --If a non-square hole is wanted
        w = tonumber(args[1])
        l = tonumber(args[2])
        d = tonumber(args[3])
else --If arguments improperly input, print usage
        print("Usage: \"GPSExcavate <side> <depth>\" or \"GPSExcavate <width> <length> <depth>\"")
        print("Note: depth must be at least 3.")
        print("To restart digging, use: \"GPSExcavate restart\"")
        error()
end
if not restarting then --Input edge locations
        edge.x = w - 1
        edge.y = -(d - 1)
        edge.z = l - 1
        print("Would you like the turtle not to collect certain blocks?")
        print("\(y/n\)")
        while true do
                local event, character = os.pullEvent()
                if event == "char" and character == "y" then
                        lastSlot = 12
                        print("Please put unwanted blocks in the bottom four slots, then press space to continue.")
                        while true do
                                local event, character = os.pullEvent()
                                if event == "key" and character == 57 then
                                        print("Turtle will not collect these blocks.")
                                        break
                                end
                        end
                        break
                elseif event == "char" and character == "n" then
                        lastSlot = 16
                        break
                end
        end
        print("Let the diggy-hole commence! Digging a hole "..w.." by "..l.." by "..d.." meters.")
end
print("Press \"p\" to save and stop at any time.")
parallel.waitForAll(excavate,stop) --Actual running of program. This is to enable stopping mid-digging
if not done then --If turtle was stopped before the end
        print("Saving position and dimensions...")
        sleep(1)
        saveLoc()
        print("Position and dimensions saved. Returning to base...")
        shell.run("goto","special",0,0,0,0,currentpos.x,currentpos.y,currentpos.z,currentpos.f) --Return to start
        dropAll()
        print("Excavation stopped.")
        end
else --Get rid of save file if turtle is done excavating. I will find a way to have rednet in here too
        fs.delete("GPSExcavateCurrentpos")
end
print("Next hole please? :D/>/>/>")
--Delete variables so they don't persist
args, currentpos, edge, id, done, restarting, running, w, l, d, backwards, lastSlot = nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil