# Copper Farmers Migration Plan for Minecraft 26.2

## Overview
Porting the copper-farmers mod from 1.21.x Yarn mappings to Minecraft 26.2 where Yarn classes have been completely removed. The key insight is that both `MoveItemsTask` and `CopperGolemBrain` classes no longer exist in 26.2 - they've been replaced by entirely new class names and architecture.

## What Changed in Minecraft 26.2

### Class Removals and Replacements
- `MoveItemsTask` (entity.ai.brain.task) → **REMOVED** → replaced by `TransportItemsBetweenContainers` (ai.behavior)
- `CopperGolemBrain` (entity.passive) → **REMOVED** → replaced by `CopperGolemAi` (animal.golem)  
- `CopperGolemEntity` → `CopperGolem` (same package: animal.golem)

### Path Package Changes
| Old Path | New Path |
|---|---|
| `net.minecraft.entity.*` | `net.minecraft.world.entity.*` |
| `net.minecraft.entity.passive.*` | `net.minecraft.world.entity.animal.golem.*` |
| `net.minecraft.block.*` | `net.minecraft.world.level.block.*` |
| `net.minecraft.inventory.Inventory` | `net.minecraft.Container` (root pkg) |
| `net.minecraft.server.world.ServerWorld` | `net.minecraft.server.level.ServerLevel` |
| `net.minecraft.sound.SoundEvent` | `net.minecraft.sounds.SoundEvent` |
| `net.minecraft.util.math.Box/Vec3d` | `net.minecraft.world.phys.AABB/Vec3` |
| `net.minecraft.block.entity.*` | `net.minecraft.world.level.block.entity.*` |

### Inner Class Changes (on new classes)
- `MoveItemsTask.Storage` → `TransportItemTarget` nested in TBC
  - `.inventory()` renamed to `.container()` 
  - Still has `pos()`, `blockEntity()`, `state()` fields
- `MoveItemsTask.InteractionState` → `ContainerInteractionState` (TBC nested)
  - Same enum values: PICKUP_ITEM, PICKUP_NO_ITEM, PLACE_ITEM, PLACE_NO_ITEM

## Implementation Plan

### Files to Create/Modify

1. **TransportItemsBetweenContainersAccessor.java** (NEW - replaces MoveItemsTaskAccessor.java)
   - Mixin target: `TransportItemsBetweenContainers` 
   - @Invoker methods for TBC's static helper methods: `pickupItemFromContainer`, `addItemsToContainer`, `isPickingUpItems`
   - Uses `Container` instead of `Inventory`

2. **FarmlandPredicateMixin.java** (NEW - replaces MoveItemsTaskMixin.java core logic)
   - Mixin target: `CopperGolemAi` 
   - @WrapOperation on TBC constructor to add farmland support to source/destination predicates
   - Makes farmland valid for copper golems to interact with

3. **CopperGolemBehaviorHookMixin.java** (NEW - replaces CopperGolemBrainMixin.java)
   - Mixin target: `CopperGolemAi.getTargetReachedInteractions()`
   - @ModifyReturnValue to customize how farmland and chests are handled as storage
   - Handles chest open/close through Container interface on BlockEntity
   - Custom interaction callback for planting/harvesting

4. **CropRegistry.java** (NEW)
   - Central registry for what crops copper golems can plant
   - Default: wheat seeds, potatoes, carrots
   - API for other mods to register their own crop types as farmland-compatible

5. **copper-farmers.mixins.json** (MODIFY)
   - Update all class references to new package paths

### Key Technical Points for Farmland Support

The golem's behavior controller uses a `TransportItemsBetweenContainers` (TBC) that has:
- `sourceBlockType` predicate (what it can extract items FROM)
- `destinationBlockType` predicate (what it can insert items INTO)
- Both checked via `isWantedBlock(state)` during target search

The fix is to intercept TBC construction in CopperGolemAi and inject farmland into both predicates. The interaction callback is then modified to handle the two distinct scenarios:
1. **Container target**: container != null → do item transfer (existing TCB behavior)  
2. **Farmland target**: container == null, state == FARMLAND → place seeds / harvest grown crops

## Execution Order
1. Write TransportItemsBetweenContainersAccessor.java
2. Write CropRegistry.java (base registry with wheat/potato/carrot support)
3. Write FarmlandPredicateMixin.java (intercept TBC construction)
4. Write CopperGolemBehaviorHookMixin.java (interaction callbacks + chest detection)
5. Update copper-farmers.mixins.json
6. Verify compilation

## Complete File Contents for Each File

### 1. TransportItemsBetweenContainersAccessor.java (NEW - replaces MoveItemsTaskAccessor.java)
Package: `com.dynamitos.mixin`
Target: `@Mixin(TransportItemsBasedOnResearch)` 

```java
package com.dynamitos.mixin;

import org.spongepowered.asm.mixin.Mixin;
import org.spongepowered.asm.mixin.gen.Invoker;

import net.minecraft.Container;  // was Inventory
import net.minecraft.world.entity.PathfinderMob;  // was PathAwareEntity
import net.minecraft.world.entity.ai.behavior.TransportItemsBetweenContainers;
import net.minecraft.item.ItemStack;

@Mixin(TransportItemsBetweenContainers.class)
public interface TransportItemsBasedOnResearchAccessor {
    @Invoker("pickupItemFromContainer")
    ItemStack copperfarmers$pickupItem(Container inventory);

    @Invoker("addItemsToContainer")
    ItemStack copperfarmers$placeItem(PathfinderMob entity, Container inventory);

    @Invoker("isPickingUpItems")
    boolean copperfarmers$isPickingUpItems(PathfinderMob entity);

    @Invoker("matchesGettingItemsRequirement")
    boolean copperfarmers$matchesGettingItemsRequirement(Container inventory);

    @Invoker("hasItemMatchingHandItem")
    boolean copperfarmers$hasItemMatchingHandItem(PathfinderMob entity, Container inventory);

    @Invoker("getTransportTarget")
    java.util.Optional<TransportItemsBetweenContainers.TransportItemTarget> copperfarmers$getTransportTarget(
        net.minecraft.server.level.ServerLevel world, PathfinderMob entity);
}
```

### 2. CropRegistry.java (NEW)
Package: `com.dynamitos`

```java
package com.dynamitos;

import java.util.ArrayList;
import java.util.List;
import java.util.function.Predicate;

import net.minecraft.world.level.block.Block;
import net.minecraft.world.level.block.state.BlockState;
import net.minecraft.item.Items;

public class CopperFarmingRegistry {
    private static final List<CropType> CROP_TYPES = new ArrayList<>();

    public record CropType(Block block, Predicate<BlockState> statePredicate) {}

    public static void registerCrop(CropType cropType) {
        CROP_TYPES.add(cropType);
        Copperfarmers.LOGGER.info("Registered crop type: " + cropType.block());
    }

    /** Returns true if the block is farmland and the stack would be a compatible seed/crop */
    public static Predicate<BlockState> getFarmlandPredicate() {
        return state -> {
            if (!state.isOf(Blocks.FARMLAND)) {
                return false;
            }
            // Also register other farmable blocks registered by this mod and other mods
            for (var crop : CROP_TYPES) {
                if (state.isOf(crop.block())) {
                    return true;
                }
            }
            return false;
        };
    }

    static {
        // Register default crops: wheat, potatoes, carrots
        registerCrop(new CropType(Blocks.WHEAT, null));
        registerCrop(new PotatoType(), null);  // potato block/planted variant
        registerCrop(new CarrotType(), null);   // carrot block/planted variant
    }
    
    /** Get predicate for farmland destination (what goes on top of farmland) */
    public static Predicate<BlockState> getDestinationPredicate() {
        State -> state.isOf(Blocks.FARMLAND) && !CROP_TYPES.stream().anyMatch(crop -> crop.statePredicate().test(state));
    }

    /** Get predicate for source (what contains items the golem can extract) */
    public static Predicate<BlockState> getSourcePredicate() {
        State -> state.isOf(Blocks.FARMLAND);  // farmland is both source and destination
    }
    
    /** Check if a BlockState represents planted crops that are ready to harvest */
    public static boolean isCropsReadyToHarvest(BlockState state) {
        if (!state.isOf(Blocks.FARMLAND)) {
            return false;
        }
        // Check the block above farmland for fully-grown crops
        // TODO: This needs to match the grow state of wheat/potato/carrot blocks
    }
}
```

### 3. FarmlandPredicateMixin.java (NEW - replaces MoveItemsTaskMixin.java)
Package: `com.dynamitos.mixin`
Target: Mixin onto `CopperGolemAi` 

Key approach: Use @WrapOperation to intercept TBC construction and replace source/destination predicates with farmland-compatible ones. Target the constructor parameters where they are passed.

```java
package com.dynamitos.mixin;

import org.spongepowered.asm.mixin.Mixin;
import org.spongepowered.asm.mixin.injection.At;
import org.spongepowered.asm.mixin.injection.Inject;
import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
import org.spongepowered.asm.mixin.extra.injector.wrapoperation.Operation;
import org.spongepowered.asm.mixin.extra.injector.wrapoperation.WrapOperation;

import com.dynamitos.CropRegistry;
import net.minecraft.block.Blocks;
import net.minecraft.world.level.block.state.BlockState;
import java.util.function.Predicate;

@Mixin(CopperGolemAi.class)
public abstract class FarmlandPredicateMixin {

    /** Wrap the predicate lambdas in CopperGolemAi lambda$static$0 and lambda$static$1 to add farmland support */
    @WrapOperation(method = "initCoreActivity", at = @At(value = "INVOKE", target = "Lnet/minecraft/world/level/block/state/BlockState;isOf(Lnet/minecraft/world/level/block/;)Z"))
    private static boolean copperfarmers$wrapBlockCheck(BlockState $this, Block block, Operation<Boolean> original) {
        if (block == Blocks.FARMLAND) {
            return true;  // Always accept farmland regardless of what the original predicate checked
        }
        return original.call($this, block);
    }

    /** Alternative: Use @ModifyVariable on getTargetReachedInteractions to replace interaction map */    
    private static Predicate<BlockState> copperfarmers$createFarmlandPredicate() {
        return state -> 
            state.isOf(Blocks.FARMLAND) || 
            CopperFarmingRegistry.getDestinationPredicate().test(state); // Check registered crops
    }
}
```

### 4. CopperGolemBehaviorHookMixin.java (NEW - replaces CopperGolemBrainMixin.java)
Package: `com.dynamitos.mixin`
Target: Mixin onto `CopperGolemAi.getTargetReachedInteractions()` 

Callback now is `TriConsumer<PathfinderMob, TransportItemTarget, Integer>` (was previously: `(PathAwareEntity, Storage, int)`).

```java  
package com.dynamitos.mixin;

import org.spongepowered.asm.mixin.Mixin;
import org.spongepowered.asm.mixin.injection.At;
import org.spongepowered.asm.mixin.injection.Inject;
import org.spongepowered.asm.mixin.inition.callback.CallbackInfoReturnable;
import org.spongepowered.asm.mixin.extra.injector.ModifyReturnValue;

import com.dynamitos.Copperfarmers;
import net.minecraft.block.Blocks;
import net.minecraft.sounds.SoundEvents;  // was net.minecraft.sound.SoundEvent -> Sounds.SoundEvents

@Mixin(CopperGolemAi.class)
public abstract class CopperGolemBehaviorHookMixin {

    @ModifyReturnValue(method = "getTargetReachedInteractions")
    private static Map<TransportItemsBetweenContainers.ContainerInteractionState, TransportItemsBasedOnResearch$OnTargetReachedInteraction> 
        copperfarmers$modifyTargetReachedInter(Map original) {
        
        return state -> {
            switch (state) {
                case PLACE_ITEM:
                    // Farmland check - plant seeds if farmland block above is air
                    // Chest check - place item into chest inventory
                    break;
                case PICKUP_ITEM:
                    // Harvest crops from farmland
                    // Extract item from container
                    break;
            }
            return original.get(state);  // Fall back to default for unhandled cases
        };
    }

    /** Handle the actual planting logic (was in MoveItemsTask.placeStack2) */
    private static void handleFarmlandPlanting(
        PathfinderMob golem,
        TransportItemTarget target,
        int interactionTicks) {
        
        BlockPos pos = target.pos();
        World world = golem.getEntityWorld(); // was ServerWorld
        
        // Check farmland: state().isOf(FARMLAND) && world.isAir(pos.up())
        // Similar logic to original placeStack2 method
    }

    /** Handle chest open/close detection (was in moveItemsTaskMixin.tickInteracting) */
    private static boolean isContainerOpen(TransportItemTarget target, PathfinderMob golem) {
        BlockEntity be = target.blockEntity();
        if (be instanceof ChestBlockEntity chest) {
            return !chest.getEntitiesWithContainerOpen().isEmpty();  // was inventory.onViewingUsers()
        }
        return false;
    }
}
```

### 5. copper-farmers.mixins.json (UPDATE)

Replace these class references:
- `"CopperGolemBrainMixin"` → `"FarmlandPredicateMixin,"CopperGolemBehaviorHookMixin"` (split into two, or combine)
- `"MoveItemsTaskMixin"` → removed, replaced with above
- `"MoveItemsTaskAccessor"` → `"TransportItemsBasedOnResearchAccessor"` (or just update class name)

### 6. Move Items Between Containers.java (update package paths on imports):

**Full list of changes in every source file:**

#### MoveItemsTaskAccessor.java → TransportItemsBetweenContainersAccessor
- `import net.minecraft.block.BlockState` → `import net.minecraft.world.level.block.state.BlockState;`
- `import net.minecraft.entity.ai.brain.task.MoveItemsTask` → `import net.minecraft.world.entity.ai.behavior.TransportItemsBetweenContainers;`  
- `import net.minecraft.entity.mob.PathAwareEntity` → `import net.minecraft.world.entity.PathfinderMob;`
- `import net.minecraft.inventory.Inventory` → `import net.minecraft.Container;` (root package!)
- `@Mixin(MoveItemsTask.class)` → `@Mixin(TransportItemsBasedOnResearch.class)`
- Inner class refs: 
  - `MoveItemsTask.InteractionState` → `TBC$ContainerInteractionState` or just import the nested type
  - Method names change as noted above

#### CopperGolemBrainMixin.java → behavior hook mixin
- `import net.minecraft.block.Blocks` → `net.minecraft.world.level.block.Blocks;`
- `import net.minecraft.block.entity.ChestBlockEntity` → `net.minecraft.world.level.block.entity.ChestBlockEntity`
- `import net.minecraft.entity.passive.CopperGolemBrain` → **gone** - replaced by CopperGolemAi
- `import net.minecraft.entity.passive.CopperGolemEntity` → `net.minecraft.world.entity.animal.golem.CopperGolem;`
- `import net.minecraft.entity.passive.CopperGolemState` → `net.minecraft.world.entity.animal.golem.CopperGolemState` (still exists!)
- `@Mixin(CopperGolemBrain.class)` → `@Mixin(CopperGolemAi.class)`
- Methods:
  - `createInteractionCallback(...)` → `getTargetReachedInteractions()` (method renamed) 
  - Callback type change: `(PathAwareEntity, Storage, int) → (PathfinderMob, TransportItemTarget, Integer)`

#### Key Code Pattern Updates:

**Old pattern used by MoveItemsTaskAccessor:**
```java
MoveItemsTaskAccessor.copperfarmers$canPickUpItem(entity); // @Invoker on private method
entity.getEquippedStack(EquipmentSlot.MAINHAND).isOf(Items.WHEAT_SEEDS);
new Storage(pos, null, null, blockState);
```

**New pattern on top of 26.2:**
```java
TransportItemsBetweenContainersAccessor.copperfarmers$isPickingUpItems(entity);
// Inventory → Container: inventory is now called container() on target
target.container(); // Not .inventory() 

// Storage record was TransportItemTarget:
target; // Same record field access: pos(), container(), blockEntity(), state() 
```

**Chest detection pattern change:**
```java
// old (copperfarmersBrainMixin):
inventory.onOpen(copperGolemEntity);  // Inventory.onOpen  
inventory.getViewingUsers();            // Inventory.getViewingUsers()

// new: BlockEntity instead of Inventory
chestBlockEntity.triggerEvent(ChestBlockEntity.EVENT_SET_OPEN_COUNT, chestBlockEntity.getOpenCount());
chestBlockEntity.getEntitiesWithContainerOpenersCounter().startOpen(chestGolem);  // Or similar
chestBlockEntity.stopOpen(chestGolem);
chestBlockEntity.getEntitiesWithContainerOpen(); // Check who's viewing the container
```