feat(mod_format): Add check-only formatting with interactive diff preview; make formatting default to dry-run and extend formatting API

ts/mod_format/classes.baseformatter.ts

@@ -1,6 +1,6 @@
 import * as plugins from './mod.plugins.js';
 import { FormatContext } from './classes.formatcontext.js';
-import type { IPlannedChange } from './interfaces.format.js';
+import type { IPlannedChange, ICheckResult } from './interfaces.format.js';
 import { Project } from '../classes.project.js';
 
 export abstract class BaseFormatter {
@@ -79,4 +79,94 @@ export abstract class BaseFormatter {
   protected async shouldProcessFile(filepath: string): Promise<boolean> {
     return true;
   }
+
+  /**
+   * Check for diffs without applying changes
+   * Returns information about what would change
+   */
+  async check(): Promise<ICheckResult> {
+    const changes = await this.analyze();
+    const diffs: ICheckResult['diffs'] = [];
+
+    for (const change of changes) {
+      // Skip generic changes that don't have actual content
+      if (change.path === '<various files>') {
+        continue;
+      }
+
+      if (change.type === 'modify' || change.type === 'create') {
+        // Read current content if file exists
+        let currentContent: string | undefined;
+        try {
+          currentContent = await plugins.smartfs.file(change.path).encoding('utf8').read() as string;
+        } catch {
+          // File doesn't exist yet
+          currentContent = undefined;
+        }
+
+        const newContent = change.content;
+
+        // Check if there's an actual diff
+        if (currentContent !== newContent && newContent !== undefined) {
+          diffs.push({
+            path: change.path,
+            type: change.type,
+            before: currentContent,
+            after: newContent,
+          });
+        }
+      } else if (change.type === 'delete') {
+        // Check if file exists before marking for deletion
+        try {
+          const currentContent = await plugins.smartfs.file(change.path).encoding('utf8').read() as string;
+          diffs.push({
+            path: change.path,
+            type: 'delete',
+            before: currentContent,
+            after: undefined,
+          });
+        } catch {
+          // File doesn't exist, nothing to delete
+        }
+      }
+    }
+
+    return {
+      hasDiff: diffs.length > 0,
+      diffs,
+    };
+  }
+
+  /**
+   * Display a single diff using smartdiff
+   */
+  displayDiff(diff: ICheckResult['diffs'][0]): void {
+    console.log(`\n--- ${diff.path}`);
+    if (diff.before && diff.after) {
+      console.log(plugins.smartdiff.formatLineDiffForConsole(diff.before, diff.after));
+    } else if (diff.after && !diff.before) {
+      console.log('  (new file)');
+      // Show first few lines of new content
+      const lines = diff.after.split('\n').slice(0, 10);
+      lines.forEach(line => console.log(`  + ${line}`));
+      if (diff.after.split('\n').length > 10) {
+        console.log('  ... (truncated)');
+      }
+    } else if (diff.before && !diff.after) {
+      console.log('  (file will be deleted)');
+    }
+  }
+
+  /**
+   * Display all diffs from a check result
+   */
+  displayAllDiffs(result: ICheckResult): void {
+    if (!result.hasDiff) {
+      console.log('  No changes detected');
+      return;
+    }
+    for (const diff of result.diffs) {
+      this.displayDiff(diff);
+    }
+  }
 }

ts/mod_format/index.ts

@@ -19,7 +19,8 @@ import { CopyFormatter } from './formatters/copy.formatter.js';
 
 export let run = async (
   options: {
-    dryRun?: boolean;
+    write?: boolean;      // Explicitly write changes (default: false, dry-mode)
+    dryRun?: boolean;     // Deprecated, kept for compatibility
     yes?: boolean;
     planOnly?: boolean;
     savePlan?: string;
@@ -35,7 +36,11 @@ export let run = async (
     setVerboseMode(true);
   }
 
-  const project = await Project.fromCwd();
+  // Determine if we should write changes
+  // Default is dry-mode (no writing) unless --write/-w is specified
+  const shouldWrite = options.write ?? (options.dryRun === false);
+
+  const project = await Project.fromCwd({ requireProjectType: false });
   const context = new FormatContext();
   // Cache system removed - no longer needed
   const planner = new FormatPlanner();
@@ -127,9 +132,9 @@ export let run = async (
       return;
     }
 
-    // Dry-run mode
-    if (options.dryRun) {
-      logger.log('info', 'Dry-run mode - no changes will be made');
+    // Dry-run mode (default behavior)
+    if (!shouldWrite) {
+      logger.log('info', 'Dry-run mode - use --write (-w) to apply changes');
       return;
     }
 
@@ -197,14 +202,27 @@ export const handleCleanBackups = async (): Promise<void> => {
   );
 };
 
+// Import the ICheckResult type for external use
+import type { ICheckResult } from './interfaces.format.js';
+export type { ICheckResult };
+
+// Formatters that don't require projectType to be set
+const formattersNotRequiringProjectType = ['npmextra', 'prettier', 'cleanup', 'packagejson'];
+
 /**
  * Run a single formatter by name (for use by other modules)
  */
 export const runFormatter = async (
   formatterName: string,
-  options: { silent?: boolean } = {}
-): Promise<void> => {
-  const project = await Project.fromCwd();
+  options: {
+    silent?: boolean;
+    checkOnly?: boolean;    // Only check for diffs, don't apply
+    showDiff?: boolean;     // Show the diff output
+  } = {}
+): Promise<ICheckResult | void> => {
+  // Determine if this formatter requires projectType
+  const requireProjectType = !formattersNotRequiringProjectType.includes(formatterName);
+  const project = await Project.fromCwd({ requireProjectType });
   const context = new FormatContext();
 
   // Map formatter names to classes
@@ -227,6 +245,17 @@ export const runFormatter = async (
   }
 
   const formatter = new FormatterClass(context, project);
+
+  // Check-only mode: just check for diffs and optionally display them
+  if (options.checkOnly) {
+    const result = await formatter.check();
+    if (result.hasDiff && options.showDiff) {
+      formatter.displayAllDiffs(result);
+    }
+    return result;
+  }
+
+  // Normal mode: analyze and apply changes
   const changes = await formatter.analyze();
 
   for (const change of changes) {

ts/mod_format/interfaces.format.ts

@@ -39,7 +39,18 @@ export type IPlannedChange = {
   path: string;
   module: string;
   description: string;
-  content?: string; // For create/modify operations
+  content?: string; // New content for create/modify operations
+  originalContent?: string; // Original content for comparison
   diff?: string;
   size?: number;
 };
+
+export interface ICheckResult {
+  hasDiff: boolean;
+  diffs: Array<{
+    path: string;
+    type: 'create' | 'modify' | 'delete';
+    before?: string;
+    after?: string;
+  }>;
+}