Init

src/main/java/me/lukasabbe/pastebooktext/mixin/SelectionManagerAccessors.java

@@ -0,0 +1,20 @@
+package me.lukasabbe.pastebooktext.mixin;
+
+import net.minecraft.client.util.SelectionManager;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.gen.Accessor;
+
+import java.util.function.Predicate;
+import java.util.function.Supplier;
+
+@Mixin(SelectionManager.class)
+public interface SelectionManagerAccessors {
+    @Accessor("stringFilter")
+    Predicate<String> getStringFilter();
+
+    @Accessor("stringGetter")
+    Supplier<String> getStringGetter();
+
+    @Accessor("selectionStart")
+    int selectionStartInt();
+}

src/main/java/me/lukasabbe/pastebooktext/mixin/WritableBookMixin.java

@@ -0,0 +1,70 @@
+package me.lukasabbe.pastebooktext.mixin;
+
+import net.minecraft.client.gui.screen.Screen;
+import net.minecraft.client.gui.screen.ingame.BookEditScreen;
+import net.minecraft.client.util.SelectionManager;
+import net.minecraft.text.Text;
+import org.spongepowered.asm.mixin.Final;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.Unique;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+
+import java.util.function.Predicate;
+
+@Mixin(BookEditScreen.class)
+public abstract class WritableBookMixin extends Screen {
+    @Shadow @Final private SelectionManager currentPageSelectionManager;
+
+    protected WritableBookMixin(Text title) {
+        super(title);
+    }
+
+    @Shadow protected abstract void openNextPage();
+
+    @Shadow protected abstract String getClipboard();
+
+    @Inject(method = "keyPressedEditMode", at= @At(value = "INVOKE", target = "Lnet/minecraft/client/util/SelectionManager;paste()V"), cancellable = true)
+    public void pasteInjects(int keyCode, int scanCode, int modifiers, CallbackInfoReturnable<Boolean> cir){
+        pasteText();
+        cir.setReturnValue(true);
+    }
+
+    @Unique
+    private void pasteText(){
+        final SelectionManagerAccessors currentPageAccessors = (SelectionManagerAccessors) currentPageSelectionManager;
+        String currentPageContent = currentPageAccessors.getStringGetter().get();
+        String clipboard = getClipboard();
+        final Predicate<String> test = currentPageAccessors.getStringFilter();
+
+        final int startInt = currentPageAccessors.selectionStartInt();
+        if(test.test(getTotalContent(currentPageContent, startInt,clipboard)) || currentPageAccessors.getStringGetter().get().length() != startInt){
+            currentPageSelectionManager.paste();
+            return;
+        }
+
+        while (!clipboard.isEmpty()){
+            currentPageContent = currentPageAccessors.getStringGetter().get();
+            if(test.test(getTotalContent(currentPageContent,currentPageAccessors.selectionStartInt(),clipboard))){
+                currentPageSelectionManager.insert(clipboard);
+                break;
+            }
+
+            for(int i = clipboard.length() - 1 ; i >=0; i--){
+                final String substring = clipboard.substring(0, i);
+                if(textRenderer.getWrappedLinesHeight(getTotalContent(currentPageContent, currentPageAccessors.selectionStartInt(), substring),114) > 127) continue;
+                currentPageSelectionManager.insert(substring);
+                clipboard = clipboard.substring(i);
+                openNextPage();
+                break;
+            }
+
+        }
+    }
+    @Unique
+    String getTotalContent(final String currentPageContent, final int selectionInt, final String clipboard){
+        return (new StringBuilder(currentPageContent)).insert(selectionInt, clipboard).toString();
+    }
+}

src/main/resources/fabric.mod.json

@@ -0,0 +1,20 @@
+{
+  "schemaVersion": 1,
+  "id": "pastebooktext",
+  "version": "${version}",
+  "name": "PasteBookText",
+  "description": "Paste an long text in to a book.",
+  "authors": ["lukasabbe"],
+  "contact": {},
+  "license": "MIT",
+  "icon": "assets/pastebooktext/icon.png",
+  "environment": "client",
+  "entrypoints": {},
+  "mixins": [
+    "pastebooktext.mixins.json"
+  ],
+  "depends": {
+    "fabricloader": ">=${loader_version}",
+    "minecraft": ">=1.21"
+  }
+}

src/main/resources/pastebooktext.mixins.json

@@ -0,0 +1,15 @@
+{
+  "required": true,
+  "minVersion": "0.8",
+  "package": "me.lukasabbe.pastebooktext.mixin",
+  "compatibilityLevel": "JAVA_21",
+  "mixins": [
+  ],
+  "client": [
+    "SelectionManagerAccessors",
+    "WritableBookMixin"
+  ],
+  "injectors": {
+    "defaultRequire": 1
+  }
+}