Step 5: Analyze with Claude

// src/reviewer.ts
// ==========================================
// Claude Integration — Analyze Code Diffs
// and Return Structured Review Feedback
// ==========================================
 
import Anthropic from "@anthropic-ai/sdk";
import { ReviewResult, ReviewComment } from "./types";
 
// ------------------------------------------
// Initialize the Anthropic client
// ------------------------------------------
const anthropic = new Anthropic({
  apiKey: process.env.ANTHROPIC_API_KEY,
});
 
// ------------------------------------------
// System prompt — this is the most important
// part of the entire bot. It defines how
// Claude reviews code.
// ------------------------------------------
const SYSTEM_PROMPT = `You are a senior software engineer performing a code review on a pull request. Your job is to identify real issues — bugs, security problems, performance concerns, and maintainability risks.
 
Rules for your review:
1. Focus on REAL issues, not style preferences. Do not nitpick formatting, naming conventions, or minor style choices unless they cause confusion.
2. Every comment must be actionable. Say what is wrong AND how to fix it.
3. Be concise. One to three sentences per comment. No essays.
4. Use severity levels: "critical" for bugs and security issues, "warning" for performance and logic concerns, "suggestion" for improvements that are not urgent.
5. If the code looks good, say so. Do not invent problems to seem thorough.
6. Review each file independently. Reference the specific file path and line number.
 
Respond ONLY with valid JSON in this exact format:
{
  "summary": "Brief overall assessment of the PR (1-2 sentences)",
  "approved": true/false,
  "comments": [
    {
      "path": "src/example.ts",
      "line": 42,
      "body": "**warning**: This array lookup can return undefined when the index is out of bounds. Add a bounds check or use optional chaining.",
      "severity": "warning"
    }
  ]
}
 
If there are no issues, return an empty comments array and set approved to true.`;
 
// ------------------------------------------
// Send the diff to Claude and parse the
// structured response
// ------------------------------------------
export async function reviewDiff(
  diff: string,
  prTitle: string,
  prBody: string
): Promise<ReviewResult> {
  const userMessage = [
    `## Pull Request: ${prTitle}`,
    "",
    prBody ? `### Description\n${prBody}` : "",
    "",
    "### Changed Files",
    "",
    diff,
  ]
    .filter(Boolean)
    .join("\n");
 
  // ------------------------------------------
  // Call the Claude API with the diff
  // ------------------------------------------
  const response = await anthropic.messages.create({
    model: "claude-sonnet-4-20250514",
    max_tokens: 4096,
    system: SYSTEM_PROMPT,
    messages: [
      {
        role: "user",
        content: userMessage,
      },
    ],
  });
 
  // ------------------------------------------
  // Extract the text content from the response
  // ------------------------------------------
  const textBlock = response.content.find((block) => block.type === "text");
  if (!textBlock || textBlock.type !== "text") {
    throw new Error("No text response from Claude");
  }
 
  return parseReviewResponse(textBlock.text);
}
 
// ------------------------------------------
// Parse Claude's JSON response into our
// ReviewResult type. Handles edge cases
// like markdown code fences in the response.
// ------------------------------------------
function parseReviewResponse(raw: string): ReviewResult {
  // ------------------------------------------
  // Claude sometimes wraps JSON in ```json
  // code fences — strip them if present
  // ------------------------------------------
  let cleaned = raw.trim();
  if (cleaned.startsWith("```")) {
    cleaned = cleaned.replace(/^```(?:json)?\n?/, "").replace(/\n?```$/, "");
  }
 
  try {
    const parsed = JSON.parse(cleaned);
 
    // ------------------------------------------
    // Validate the structure matches our types
    // ------------------------------------------
    const result: ReviewResult = {
      summary: parsed.summary ?? "No summary provided.",
      approved: parsed.approved ?? false,
      comments: [],
    };
 
    if (Array.isArray(parsed.comments)) {
      result.comments = parsed.comments
        .filter(
          (c: any) =>
            typeof c.path === "string" &&
            typeof c.line === "number" &&
            typeof c.body === "string"
        )
        .map((c: any): ReviewComment => ({
          path: c.path,
          line: c.line,
          body: c.body,
          severity: ["critical", "warning", "suggestion"].includes(c.severity)
            ? c.severity
            : "suggestion",
        }));
    }
 
    return result;
  } catch (error) {
    // ------------------------------------------
    // If JSON parsing fails, return the raw
    // text as a summary with no inline comments
    // ------------------------------------------
    console.error("Failed to parse Claude response as JSON:", error);
    return {
      summary: raw,
      comments: [],
      approved: false,
    };
  }
}

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