Create a structure for different diff strategies, starting with unified (#55)

src/core/diff/strategies/unified.ts

@@ -0,0 +1,114 @@
+import { applyPatch } from "diff"
+import { DiffStrategy } from "../types"
+
+export class UnifiedDiffStrategy implements DiffStrategy {
+    getToolDescription(cwd: string): string {
+        return `## apply_diff
+Description: Apply a unified diff to a file at the specified path. This tool is useful when you need to make specific modifications to a file based on a set of changes provided in unified diff format (diff -U3).
+
+Parameters:
+- path: (required) The path of the file to apply the diff to (relative to the current working directory ${cwd})
+- diff: (required) The diff content in unified format to apply to the file.
+
+Format Requirements:
+
+1. Header (REQUIRED):
+    \`\`\`
+    --- path/to/original/file
+    +++ path/to/modified/file
+    \`\`\`
+    - Must include both lines exactly as shown
+    - Use actual file paths
+    - NO timestamps after paths
+
+2. Hunks:
+    \`\`\`
+    @@ -lineStart,lineCount +lineStart,lineCount @@
+    -removed line
+    +added line
+    \`\`\`
+    - Each hunk starts with @@ showing line numbers for changes
+    - Format: @@ -originalStart,originalCount +newStart,newCount @@
+    - Use - for removed/changed lines
+    - Use + for new/modified lines
+    - Indentation must match exactly
+
+Complete Example:
+
+Original file (with line numbers):
+\`\`\`
+1 | import { Logger } from '../logger';
+2 | 
+3 | function calculateTotal(items: number[]): number {
+4 |   return items.reduce((sum, item) => {
+5 |     return sum + item;
+6 |   }, 0);
+7 | }
+8 | 
+9 | export { calculateTotal };
+\`\`\`
+
+After applying the diff, the file would look like:
+\`\`\`
+1 | import { Logger } from '../logger';
+2 | 
+3 | function calculateTotal(items: number[]): number {
+4 |   const total = items.reduce((sum, item) => {
+5 |     return sum + item * 1.1;  // Add 10% markup
+6 |   }, 0);
+7 |   return Math.round(total * 100) / 100;  // Round to 2 decimal places
+8 | }
+9 | 
+10 | export { calculateTotal };
+\`\`\`
+
+Diff to modify the file:
+\`\`\`
+--- src/utils/helper.ts
++++ src/utils/helper.ts
+@@ -1,9 +1,10 @@
+ import { Logger } from '../logger';
+ 
+ function calculateTotal(items: number[]): number {
+-  return items.reduce((sum, item) => {
+-    return sum + item;
++  const total = items.reduce((sum, item) => {
++    return sum + item * 1.1;  // Add 10% markup
+   }, 0);
++  return Math.round(total * 100) / 100;  // Round to 2 decimal places
+ }
+ 
+ export { calculateTotal };
+\`\`\`
+
+Common Pitfalls:
+1. Missing or incorrect header lines
+2. Incorrect line numbers in @@ lines
+3. Wrong indentation in changed lines
+4. Incomplete context (missing lines that need changing)
+5. Not marking all modified lines with - and +
+
+Best Practices:
+1. Replace entire code blocks:
+    - Remove complete old version with - lines
+    - Add complete new version with + lines
+    - Include correct line numbers
+2. Moving code requires two hunks:
+    - First hunk: Remove from old location
+    - Second hunk: Add to new location
+3. One hunk per logical change
+4. Verify line numbers match the line numbers you have in the file
+
+Usage:
+<apply_diff>
+<path>File path here</path>
+<diff>
+Your diff here
+</diff>
+</apply_diff>`
+    }
+
+    applyDiff(originalContent: string, diffContent: string): string | false {
+        return applyPatch(originalContent, diffContent) as string | false
+    }
+}