A simple forge mod I created in 2016 that would auto mine and repair the pickaxe on a server I used to play on.

automine.java

public class Main {
    static final String MODID = "Rab";
    static final String VERSION = "1.0";
    private Minecraft mc = Minecraft.getMinecraft();
    private boolean repair;

    @Mod.EventHandler
    public void init(final FMLPreInitializationEvent event) {
        MinecraftForge.EVENT_BUS.register(this);
    }

    @SubscribeEvent(priority = EventPriority.HIGHEST)
    public void onTick(TickEvent event) {
        EntityPlayerSP player = mc.thePlayer;
        if(player != null) {
            ItemStack currentItem = player.getCurrentEquippedItem();
            if (currentItem != null) {
                Item item = currentItem.getItem();
                if (!isPickaxe(item)) {
                    setMining(false);
                    return;
                }
                if (almostBroken(currentItem)) {
                    if (!repair) {
                        setMining(false);
                        repair = true;
                        mc.thePlayer.sendChatMessage("/drepair");
                    }
                    return;
                }
            }
            setMining(true);
        }
    }

    private void setMining(final boolean value) {
        KeyBinding.setKeyBindState(mc.gameSettings.keyBindAttack.getKeyCode(), value);
        KeyBinding.onTick(mc.gameSettings.keyBindAttack.getKeyCode());
    }

    @SubscribeEvent
    public void onReceivedMessage(ClientChatReceivedEvent event) {
        String isRequestIncoming = event.message.getUnformattedText();
        if (isRequestIncoming.equals("MINELINK You cannot use commands before you move!")) {
            mc.thePlayer.rotationYaw = mc.thePlayer.rotationYaw - 90;
            mc.thePlayer.rotationYaw = mc.thePlayer.rotationYaw + 90;
            repair = false;
        }
    }

    private static boolean almostBroken(ItemStack itemStack) {
        double damage = itemStack.getItemDamage() / itemStack.getMaxDamage();
        return damage > 0.1;
    }

    private static boolean isPickaxe(Item item) {
        return item == Items.diamond_pickaxe || item == Items.iron_pickaxe || item == Items.golden_pickaxe || item == Items.stone_pickaxe || item == Items.wooden_pickaxe;
    }
}