-- dig5x5.lua
-- Mines a 5x5 shaft downward until bedrock.
-- Start at one corner of the 5x5, facing across the area.
-- Put a chest behind the turtle. Slot 16 is reserved for fuel.

local SIZE = 5
local FUEL_SLOT = 16
local START_FUEL_MIN = 50

-- Internal position tracking.
-- x/z are relative to the start corner.
-- depth is blocks below the start level.
-- dir: 0=east/forward from start, 1=south, 2=west, 3=north
local x, z, depth, dir = 0, 0, 0, 0

local inUnload = false

local goTo, safeDown, safeUp, checkInventory

local function isBedrock(data)
    return data and data.name == "minecraft:bedrock"
end

local function isLava(data)
    return data and (
        data.name == "minecraft:lava" or
        data.name == "minecraft:flowing_lava"
    )
end

local function isUnlimitedFuel()
    return turtle.getFuelLevel() == "unlimited"
end

local function ensureFuel(want)
    if isUnlimitedFuel() then return end

    while turtle.getFuelLevel() < want do
        local before = turtle.getFuelLevel()
        local selected = turtle.getSelectedSlot()

        for i = 1, 16 do
            if turtle.getItemCount(i) > 0 then
                turtle.select(i)
                turtle.refuel(1)
            end

            if turtle.getFuelLevel() >= want then
                break
            end
        end

        turtle.select(selected)

        if turtle.getFuelLevel() <= before then
            error("Out of fuel. Put coal/charcoal/etc in slot 16.", 0)
        end
    end
end

local function hasEmptyMiningSlot()
    for i = 1, FUEL_SLOT - 1 do
        if turtle.getItemCount(i) == 0 then
            return true
        end
    end
    return false
end

local function unloadItems()
    print("Unloading...")

    for i = 1, FUEL_SLOT - 1 do
        if turtle.getItemCount(i) > 0 then
            turtle.select(i)
            local ok, err = turtle.drop()

            if not ok and turtle.getItemCount(i) > 0 then
                error("Unload failed. Chest behind turtle may be full/missing: " .. tostring(err), 0)
            end
        end
    end

    turtle.select(1)
end

local function updateForwardPosition()
    if dir == 0 then
        x = x + 1
    elseif dir == 1 then
        z = z + 1
    elseif dir == 2 then
        x = x - 1
    elseif dir == 3 then
        z = z - 1
    end
end

local function turnLeft()
    turtle.turnLeft()
    dir = (dir + 3) % 4
end

local function turnRight()
    turtle.turnRight()
    dir = (dir + 1) % 4
end

local function face(want)
    while dir ~= want do
        local diff = (want - dir) % 4

        if diff == 1 then
            turnRight()
        elseif diff == 3 then
            turnLeft()
        else
            turnRight()
            turnRight()
        end
    end
end

local function clearFront(allowUnload)
    while turtle.detect() do
        local ok, data = turtle.inspect()

        if ok and isBedrock(data) then
            return false, "bedrock in front"
        end

        if ok and isLava(data) then
            error("Lava in front. Stopping for safety.", 0)
        end

        if allowUnload then
            checkInventory()
        end

        local dug, err = turtle.dig()
        if not dug and turtle.detect() then
            return false, "cannot dig front: " .. tostring(err)
        end

        sleep(0.2)
    end

    return true
end

local function safeForward(allowUnload)
    ensureFuel(1)

    local tries = 0

    while true do
        local ok, err = turtle.forward()

        if ok then
            updateForwardPosition()
            return true
        end

        local cleared, reason = clearFront(allowUnload)
        if not cleared then
            return false, reason
        end

        turtle.attack()
        tries = tries + 1

        if tries > 20 then
            error("Cannot move forward: " .. tostring(err), 0)
        end

        sleep(0.2)
    end
end

safeUp = function(allowUnload)
    ensureFuel(1)

    local tries = 0

    while true do
        local ok, err = turtle.up()

        if ok then
            depth = depth - 1
            return true
        end

        if turtle.detectUp() then
            local hasBlock, data = turtle.inspectUp()

            if hasBlock and isLava(data) then
                error("Lava above. Stopping for safety.", 0)
            end

            if allowUnload then
                checkInventory()
            end

            local dug, digErr = turtle.digUp()
            if not dug and turtle.detectUp() then
                error("Cannot dig up: " .. tostring(digErr), 0)
            end
        else
            turtle.attackUp()
            tries = tries + 1

            if tries > 20 then
                error("Cannot move up: " .. tostring(err), 0)
            end
        end

        sleep(0.2)
    end
end

safeDown = function(allowUnload)
    ensureFuel(1)

    local tries = 0

    while true do
        local ok, err = turtle.down()

        if ok then
            depth = depth + 1
            return true
        end

        if turtle.detectDown() then
            local hasBlock, data = turtle.inspectDown()

            if hasBlock and isBedrock(data) then
                return false, "bedrock below"
            end

            if hasBlock and isLava(data) then
                error("Lava below. Stopping for safety.", 0)
            end

            if allowUnload then
                checkInventory()
            end

            local dug, digErr = turtle.digDown()
            if not dug and turtle.detectDown() then
                hasBlock, data = turtle.inspectDown()

                if hasBlock and isBedrock(data) then
                    return false, "bedrock below"
                end

                error("Cannot dig down: " .. tostring(digErr), 0)
            end
        else
            turtle.attackDown()
            tries = tries + 1

            if tries > 20 then
                error("Cannot move down: " .. tostring(err), 0)
            end
        end

        sleep(0.2)
    end
end

goTo = function(tx, tz, allowUnload)
    while x < tx do
        face(0)
        local ok, reason = safeForward(allowUnload)
        if not ok then error("Path blocked east: " .. tostring(reason), 0) end
    end

    while x > tx do
        face(2)
        local ok, reason = safeForward(allowUnload)
        if not ok then error("Path blocked west: " .. tostring(reason), 0) end
    end

    while z < tz do
        face(1)
        local ok, reason = safeForward(allowUnload)
        if not ok then error("Path blocked south: " .. tostring(reason), 0) end
    end

    while z > tz do
        face(3)
        local ok, reason = safeForward(allowUnload)
        if not ok then error("Path blocked north: " .. tostring(reason), 0) end
    end
end

checkInventory = function()
    if inUnload then return end
    if hasEmptyMiningSlot() then return end

    inUnload = true

    local savedX = x
    local savedZ = z
    local savedDepth = depth
    local savedDir = dir

    print("Inventory full. Returning to unload.")

    goTo(0, 0, false)
    face(0)

    while depth > 0 do
        safeUp(false)
    end

    -- Chest should be behind the turtle's start position.
    face(2)
    unloadItems()

    -- Return to where we were.
    face(0)

    while depth < savedDepth do
        local ok, reason = safeDown(false)
        if not ok then
            error("Could not return to mining depth: " .. tostring(reason), 0)
        end
    end

    goTo(savedX, savedZ, false)
    face(savedDir)

    inUnload = false
end

local function mineStep()
    checkInventory()

    local ok, reason = safeForward(true)
    if not ok then
        return false, reason
    end

    return true
end

local function mineLayer()
    face(0)

    for row = 1, SIZE do
        for col = 1, SIZE - 1 do
            local ok, reason = mineStep()
            if not ok then return false, reason end
        end

        if row < SIZE then
            if row % 2 == 1 then
                turnRight()
                local ok, reason = mineStep()
                if not ok then return false, reason end
                turnRight()
            else
                turnLeft()
                local ok, reason = mineStep()
                if not ok then return false, reason end
                turnLeft()
            end
        end
    end

    return true
end

print("Starting 5x5 bedrock miner.")
print("Start at Y=60 corner, facing into the 5x5.")
print("Chest behind turtle. Fuel in slot 16.")

ensureFuel(START_FUEL_MIN)

while true do
    print("Mining layer, depth " .. depth)

    local fullLayer, reason = mineLayer()

    goTo(0, 0, false)
    face(0)

    checkInventory()

    if not fullLayer then
        print("Stopped while mining layer: " .. tostring(reason))
        break
    end

    local movedDown, downReason = safeDown(true)

    if not movedDown then
        print("Reached bedrock: " .. tostring(downReason))
        break
    end
end

print("Returning to surface...")

goTo(0, 0, false)
face(0)

while depth > 0 do
    safeUp(false)
end

face(2)
unloadItems()
face(0)

print("Done. Turtle is back at the start.")