ai-analysis.ts

import * as fs from 'fs';

export interface AIAnalysisResult {
  analysis: string;
  provider: string;
  model: string;
}

function detectProvider(model: string): 'anthropic' | 'openai' {
  return model.toLowerCase().startsWith('claude') ? 'anthropic' : 'openai';
}

async function callAnthropicAPI(prompt: string, token: string, model: string): Promise<string> {
  const response = await fetch('https://api.anthropic.com/v1/messages', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'x-api-key': token,
      'anthropic-version': '2023-06-01',
    },
    body: JSON.stringify({
      model,
      max_tokens: 2048,
      messages: [{ role: 'user', content: prompt }],
    }),
  });

  if (!response.ok) {
    const error = await response.text();
    throw new Error(`Anthropic API error ${response.status}: ${error}`);
  }

  const data = await response.json() as any;
  return data.content[0].text as string;
}

async function callOpenAIAPI(prompt: string, token: string, model: string): Promise<string> {
  const response = await fetch('https://api.openai.com/v1/chat/completions', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'Authorization': `Bearer ${token}`,
    },
    body: JSON.stringify({
      model,
      max_tokens: 2048,
      messages: [{ role: 'user', content: prompt }],
    }),
  });

  if (!response.ok) {
    const error = await response.text();
    throw new Error(`OpenAI API error ${response.status}: ${error}`);
  }

  const data = await response.json() as any;
  return data.choices[0].message.content as string;
}

function buildPrompt(diffData: unknown): string {
  // Truncate large diff data to avoid token limits (~50k chars)
  const MAX_CHARS = 50000;
  let diffStr = JSON.stringify(diffData, null, 2);
  if (diffStr.length > MAX_CHARS) {
    diffStr = diffStr.substring(0, MAX_CHARS) + '\n... (truncated due to size)';
  }

  return `You are a frontend performance expert analyzing a JavaScript bundle size diff report generated by Rsdoctor (a Webpack/Rspack bundle analyzer).

Please analyze the following bundle diff JSON data and provide a concise report covering:

1. **Size Regression Summary**: Which assets/chunks increased significantly in size
2. **Root Cause Analysis**: Likely causes of size increases based on the diff data
3. **Risk Assessment**: Overall severity — Low / Medium / High — with a brief justification
4. **Optimization Recommendations**: Specific, actionable steps to reduce the regressions

Focus especially on:
- Assets or chunks with >5% or >10 KB size increase
- Newly added large assets or modules
- Changes to initial/entry chunks (highest priority)
- Potential duplicate dependencies

Bundle diff data:
\`\`\`json
${diffStr}
\`\`\`

Respond in concise GitHub-flavored Markdown suitable for a PR comment. If there are no regressions, say so clearly.`;
}

/**
 * Run AI degradation analysis on a bundle-diff JSON file.
 *
 * @param diffJsonPath  Path to the JSON file produced by `rsdoctor bundle-diff --json`
 * @param token         AI API key (Anthropic or OpenAI)
 * @param model         Model name — auto-detects provider from prefix (default: claude-3-5-haiku-latest)
 */
export async function analyzeWithAI(
  diffJsonPath: string,
  token: string,
  model = 'claude-3-5-haiku-latest',
): Promise<AIAnalysisResult | null> {
  if (!token) {
    console.log('ℹ️  No AI token provided, skipping AI analysis');
    return null;
  }

  if (!fs.existsSync(diffJsonPath)) {
    console.log(`⚠️  Bundle diff JSON not found at ${diffJsonPath}, skipping AI analysis`);
    return null;
  }

  try {
    const diffData: unknown = JSON.parse(fs.readFileSync(diffJsonPath, 'utf8'));
    const prompt = buildPrompt(diffData);
    const provider = detectProvider(model);

    console.log(`🤖 Running AI analysis with ${provider} (${model})...`);

    const analysis =
      provider === 'anthropic'
        ? await callAnthropicAPI(prompt, token, model)
        : await callOpenAIAPI(prompt, token, model);

    console.log('✅ AI analysis completed');
    return { analysis, provider, model };
  } catch (error) {
    console.warn(`⚠️ AI analysis failed: ${error}`);
    return null;
  }
}