[FEATURE REQUEST] Support for multiple files in side-by-side diff

[mydeveloperplanet]

Follow-up from #339

Support multiple files in the side-by-side diff. In v0.3.0 only one file is supported.
Test:

• Use the DevoxxGeniePlugin source code
• Add files `AddDirectoryAction' and 'AddFileAction'
• Select 'Simple Git Diff' in the settings
• Prompt: Add javadoc to both files
• Ollama with Llam3.2 is used

Git diff is: both files are present in the 'LLM suggested' side, the 'original code' of AddFileAction is present. So only these changes can be applied easily

LLM response is:

// Filename: AddDirectoryAction.java
package com.devoxx.genie.action;

import com.devoxx.genie.model.LanguageModel;
import com.devoxx.genie.model.ScanContentResult;
import com.devoxx.genie.model.enumarations.ModelProvider;
import com.devoxx.genie.service.DevoxxGenieSettingsService;
import com.devoxx.genie.service.FileListManager;
import com.devoxx.genie.service.LLMModelRegistryService;
import com.devoxx.genie.service.ProjectContentService;
import com.devoxx.genie.ui.settings.DevoxxGenieStateService;
import com.devoxx.genie.ui.util.NotificationUtil;
import com.devoxx.genie.ui.util.WindowContextFormatterUtil;
import com.intellij.openapi.actionSystem.ActionUpdateThread;
import com.intellij.openapi.actionSystem.AnActionEvent;
import com.intellij.openapi.actionSystem.CommonDataKeys;
import com.intellij.openapi.project.DumbAwareAction;
import com.intellij.openapi.project.Project;
import com.intellij.openapi.vfs.VirtualFile;
import org.jetbrains.annotations.NotNull;

/**
 * Action to add directory content to clipboard.
 */
public class AddDirectoryAction extends DumbAwareAction {

    @Override
    public void actionPerformed(@NotNull AnActionEvent e) {
        Project project = e.getProject();
        if (project == null) {
            return;
        }

        ensureToolWindowVisible(project);

        FileListManager fileListManager = FileListManager.getInstance();
        VirtualFile[] children = e.getData(CommonDataKeys.VIRTUAL_FILE_ARRAY);
        List<VirtualFile> filesToAdd = new ArrayList<>();

        for (VirtualFile child : children) {
            if (!child.isDirectory() && !fileListManager.contains(child)) {
                filesToAdd.add(child);
            }
        }

        if (!filesToAdd.isEmpty()) {
            fileListManager.addFiles(filesToAdd);
            NotificationUtil.sendNotification(project, "Added " + filesToAdd.size() + " file(s) to prompt context");
        } else {
            NotificationUtil.sendNotification(project, "No new files to add or only directories selected");
        }
    }

    @Override
    public void update(@NotNull AnActionEvent e) {
        VirtualFile[] files = e.getData(CommonDataKeys.VIRTUAL_FILE_ARRAY);
        e.getPresentation().setEnabledAndVisible(files != null && files.length > 0);
    }

    @Override
    public @NotNull ActionUpdateThread getActionUpdateThread() {
        return ActionUpdateThread.BGT;
    }

    @Override
    public boolean isDumbAware() {
        return true;
    }
}

// Filename: AddFileAction.java
package com.devoxx.genie.action;

import com.devoxx.genie.service.FileListManager;
import com.devoxx.genie.ui.util.NotificationUtil;
import com.intellij.openapi.actionSystem.ActionUpdateThread;
import com.intellij.openapi.actionSystem.AnActionEvent;
import com.intellij.openapi.actionSystem.CommonDataKeys;
import com.intellij.openapi.project.DumbAwareAction;
import com.intellij.openapi.project.Project;
import com.intellij.openapi.vfs.VirtualFile;
import org.jetbrains.annotations.NotNull;

/**
 * Action to add file(s) to prompt context.
 */
public class AddFileAction extends DumbAwareAction {

    @Override
    public void actionPerformed(@NotNull AnActionEvent e) {
        Project project = e.getProject();
        if (project == null) {
            return;
        }

        ensureToolWindowVisible(project);

        FileListManager fileListManager = FileListManager.getInstance();
        VirtualFile[] selectedFiles = e.getData(CommonDataKeys.VIRTUAL_FILE_ARRAY);

        if (selectedFiles != null && selectedFiles.length > 0) {
            List<VirtualFile> filesToAdd = new ArrayList<>();

            for (VirtualFile file : selectedFiles) {
                if (!file.isDirectory() && !fileListManager.contains(file)) {
                    filesToAdd.add(file);
                }
            }

            if (!filesToAdd.isEmpty()) {
                fileListManager.addFiles(filesToAdd);
                NotificationUtil.sendNotification(project, "Added " + filesToAdd.size() + " file(s) to prompt context");
            } else {
                NotificationUtil.sendNotification(project, "No new files to add or only directories selected");
            }
        } else {
            NotificationUtil.sendNotification(project, "No files selected");
        }
    }

    @Override
    public void update(@NotNull AnActionEvent e) {
        VirtualFile[] files = e.getData(CommonDataKeys.VIRTUAL_FILE_ARRAY);
        e.getPresentation().setEnabledAndVisible(files != null && files.length > 0);
    }

    @Override
    public @NotNull ActionUpdateThread getActionUpdateThread() {
        return ActionUpdateThread.BGT;
    }

    @Override
    public boolean isDumbAware() {
        return true;
    }
}