Melon Farm

local delay = 0
local price = 16
local startsEven = false
local WHEREIS_CHANNEL = 420

local DIRECTION_CALIBRATION_BLOCK = "minecraft:sandstone"
local CROP_START_VARIANT = {
    [true] = "smooth_granite",
    [false] = "smooth_andesite"
}
local CROP_END_VARIANT = {
    [true] = "smooth_andesite",
    [false] = "smooth_granite"
}
local CROP_SWITCH_VARIANT = {
    [true] = "andesite",
    [false] = "granite"
}
local TRANSIT_VERTICAL_ENTER_VARIANT = "smooth_diorite"
local MELON_BLOCK = "minecraft:melon_block"
local CHEST_BLOCK = "minecraft:chest"
local STONE_BLOCK = "minecraft:stone"

local activities = {
    CHEST_LEAVE = 1, -- spin until sandstone, note as even direction. go forward one then CROP_FIRST.
    CROP_FIRST = 2, -- go along the crops until a wall
    CROP_SWITCH = 3, -- switch row until left is ditorite
    CROP_SECOND = 4, -- go along crops until granite (odd), andesite (even)
    TRANSIT_HORIZONTAL = 5, -- go toward chest until below is andesite (CROP_FIRST) or above is ditorite (turn and foward, then TRANSIT_VERTICAL_UP)
    TRANSIT_VERTICAL_UP = 6, -- go up until front is plank, rotate twice, switch odd/even then CROP_FIRST. otherwise, if above is blocked then
    TRANSIT_VERTICAL_UP_START = 7, -- go up one block to clear the previous level
    TRANSIT_VERTICAL_DOWN = 8, -- go down until blocked, then CHEST_RETURN
    CHEST_RETURN = 9, -- check below if chest, if so drop everything, else spin to not even direction and repeat
    CHEST_DROP = 10, -- check below if chest, if so drop everything, else spin to not even direction and repeat
}

local directions = {
    CROP_TOWARD = 0,
    CHEST_TOWARD = 1,
    CROP_AWAY = 2,
    CHEST_AWAY = 3
}

-- fix the modem bug
if not peripheral.find("modem") then
    -- first find an empty slot
    for i = 1, 16 do
        if turtle.getItemCount(i) == 0 then
            turtle.select(i)
            break
        elseif i == 16 then
            turtle.select(i)
            turtle.drop()
        end
    end
    turtle.equipLeft()
    turtle.equipLeft()
    turtle.equipRight()
    turtle.equipRight()
end

local state
local function loadState()
    local h = fs.open("melon.state", "r")
    if h then
        state = textutils.unserialise(h.readAll())
        h.close()
    else
        state = {
            activity = activities.CHEST_LEAVE,
            direction = directions.CROP_TOWARD,
            isEven = startsEven,
            startFuel = turtle.getFuelLevel()
        }
    end
end

local function saveState()
    local h = fs.open("melon.state", "w")
    if h then
        h.write(textutils.serialise(state))
        h.close()
    end
end

local function turnTo(direction)
    local difference = direction - state.direction
    if math.abs(difference) >= 3 then
        difference = (difference - 2 * (difference / math.abs(difference))) * -1
    end
    if difference > 0 then
        for i = 1, difference do
            turtle.turnLeft()
            state.direction = (state.direction + 1) % 4
            saveState()
        end
    elseif difference < 0 then
        for i = 1, math.abs(difference) do
            turtle.turnRight()
            state.direction = (state.direction - 1) % 4
            saveState()
        end
    end
end

local function setActivity(activity)
    if not activity then error('act') end
    state.activity = activity
    saveState()
end

local funcs = {}

local function activity(activity)
    setActivity(activity)
    return funcs[activity]()
end

funcs[activities.CHEST_LEAVE] = function()
    turnTo(directions.CROP_TOWARD)
    turtle.forward()
    return activity(activities.CROP_FIRST)
end

local function crop()
    while true do
        local isBlock, block = turtle.inspectDown()
        if isBlock and block.name == MELON_BLOCK then
            -- there's a melon below us, break it and til the ground
            turtle.digDown()
            turtle.digDown()
        elseif isBlock and block.name == STONE_BLOCK and block.state.variant == CROP_END_VARIANT[state.isEven] then
            -- we're at the end block, TRANSIT_HORIZONTAL
            return activity(activities.TRANSIT_HORIZONTAL)
        end
        if turtle.inspect() then
            -- there's a block in front of us, CROP_SWITCH
            return activity(activities.CROP_SWITCH)
        else
            turtle.forward()
        end
    end
end

funcs[activities.CROP_FIRST] = function()
    print("Collecting crop row #1...")
    turnTo(directions.CROP_TOWARD)
    return crop()
end

funcs[activities.CROP_SWITCH] = function()
    print("Switching crop row...")
    while true do
        turnTo(directions.CROP_TOWARD)
        local isBlock, block = turtle.inspect()
        if isBlock and block.name == STONE_BLOCK and block.state.variant == CROP_SWITCH_VARIANT[state.isEven] then
            -- we're at the block where the next row starts, CROP_SECOND
            return activity(activities.CROP_SECOND)
        else
            turnTo(state.isEven and directions.CHEST_TOWARD or directions.CHEST_AWAY)
            turtle.forward()
        end
    end
end

funcs[activities.CROP_SECOND] = function()
    print("Collecting crop row #2...")
    turnTo(directions.CROP_AWAY)
    return crop()
end

funcs[activities.TRANSIT_HORIZONTAL] = function()
    print("Travelling horizontally to next crop...")
    turnTo(state.isEven and directions.CHEST_TOWARD or directions.CHEST_AWAY)
    while true do
        local isBlock, block = turtle.inspectDown()
        if isBlock and block.name == STONE_BLOCK and block.state.variant == CROP_START_VARIANT[state.isEven] then
            -- we're at the block where the next crop starts, CROP_FIRST
            return activity(activities.CROP_FIRST)
        else
            local isBlockAbove, blockAbove = turtle.inspectUp()
            if isBlockAbove and blockAbove.name == STONE_BLOCK and blockAbove.state.variant == TRANSIT_VERTICAL_ENTER_VARIANT then
                -- we're at the end of the row, TRANSIT_VERTICAL_UP
                turnTo(directions.CROP_AWAY)
                turtle.forward()
                return activity(activities.TRANSIT_VERTICAL_UP_START)
            else
                turtle.forward()
            end
        end
    end
end

funcs[activities.TRANSIT_VERTICAL_UP_START] = function()
    -- we need to do this because otherwise if it reloads just after it moves into this spot it'll stay on the same level
    print("Leaving previous layer...")
    turtle.up()
    return activity(activities.TRANSIT_VERTICAL_UP)
end

funcs[activities.TRANSIT_VERTICAL_UP] = function()
    print("Travelling vertically to next crop layer...")
    turnTo(directions.CROP_TOWARD)
    while true do
        local isBlock, block = turtle.inspect()
        if not isBlock then
            -- we've arrived at the new level, CROP_FIRST
            state.isEven = not state.isEven
            return activity(activities.CROP_FIRST)
        else
            if turtle.inspectUp() then
                -- there's a block in the way, so we're at the maximum available layer, TRANSIT_VERTICAL_DOWN
                return activity(activities.TRANSIT_VERTICAL_DOWN)
            else
                turtle.up()
            end
        end
    end
end

funcs[activities.TRANSIT_VERTICAL_DOWN] = function()
    print("Travelling vertically back to the starting layer...")
    while true do
        local isBlock, block = turtle.inspectDown()
        if isBlock then
            -- we've arrived at the chest layer
            state.isEven = false
            if block.name == CHEST_BLOCK then
                -- we're right above the chest, CROP_DROP
                return activity(activities.CHEST_DROP)
            else
                -- we need to move along to the chest
                return activity(activities.CHEST_RETURN)
            end
        else
            turtle.down()
        end
    end
end

funcs[activities.CHEST_RETURN] = function()
    print("Travelling horizontally back to the chest...")
    turnTo(startsEven and directions.CHEST_AWAY or directions.CHEST_TOWARD)
    while true do
        local isBlock, block = turtle.inspectDown()
        if isBlock and block.name == CHEST_BLOCK then
            -- we're right above the chest, CROP_DROP
            return activity(activities.CHEST_DROP)
        else
            turtle.forward()
        end
    end
end

funcs[activities.CHEST_DROP] = function()
    print("Dropping the crop in the chest...")
    local count = 0
    for i = 1, 16 do
        count = count + turtle.getItemCount(i)
        turtle.select(i)
        turtle.dropDown()
    end
    print("Harvested " .. count .. " melon.")
    print(string.format("Value: $%.2f", (count / 64) * price))
    print("Fuel consumption: " .. state.startFuel - turtle.getFuelLevel())
    return
end

-- depart from the idle chest location
function resume()
    print("Resuming...")
    loadState()
    activity(state.activity)
end

parallel.waitForAll(function()
    resume()
    while true do
        sleep(delay)
        print("Starting fresh...")
        state.startFuel = turtle.getFuelLevel()
        state.isEven = startsEven
        saveState()
        activity(activities.CHEST_LEAVE)
    end
end, function()
    local modem = peripheral.find("modem")
    modem.open(WHEREIS_CHANNEL)
    while true do
        local event, side, channel, replyChannel, message = os.pullEvent("modem_message")
        if channel == WHEREIS_CHANNEL and message == "WHEREIS" then
            modem.transmit(replyChannel, channel, {os.getComputerID(), os.getComputerLabel(), gps.locate()})
        end
    end
end)