feat: add Perplexity Sonar provider with OpenAI fallback

src/lib/llm/providers/perplexity.ts

@@ -0,0 +1,117 @@
+import type { ComparisonRequest, ComparisonResult } from "../types";
+import type { SearchResult } from "./tavily";
+import { generateComparisonWithResearch } from "./openai";
+
+const PERPLEXITY_API_URL = "https://api.perplexity.ai/chat/completions";
+
+const SYSTEM_PROMPT = `You are a research synthesis engine. Given web search results for multiple items, produce a structured JSON comparison.
+
+You MUST respond with valid JSON matching this exact structure:
+{
+  "items": [
+    {
+      "name": "item name",
+      "description": "brief overview",
+      "overallScore": 7.5,
+      "dimensions": {
+        "Dimension Name": {
+          "score": 8,
+          "summary": "brief assessment",
+          "details": "detailed analysis",
+          "pros": ["pro 1"],
+          "cons": ["con 1"]
+        }
+      },
+      "pros": ["overall pro 1"],
+      "cons": ["overall con 1"],
+      "sources": [{ "title": "source", "url": "https://...", "snippet": "excerpt" }]
+    }
+  ],
+  "dimensions": ["Dimension 1", "Dimension 2"],
+  "summary": "comparison summary",
+  "recommendation": "clear recommendation"
+}`;
+
+export async function synthesizeResearch(
+  request: ComparisonRequest,
+  searchResults: Record<string, SearchResult[]>
+): Promise<ComparisonResult> {
+  const apiKey = process.env.PERPLEXITY_API_KEY;
+  if (!apiKey) {
+    return generateComparisonWithResearch(request, searchResults);
+  }
+
+  const allResults = Object.values(searchResults).flat();
+  if (allResults.length === 0) {
+    return generateComparisonWithResearch(request, searchResults);
+  }
+
+  let researchContext = "Search results for each item:\n\n";
+  for (const [itemName, results] of Object.entries(searchResults)) {
+    if (results.length === 0) continue;
+    researchContext += `=== ${itemName} ===\n`;
+    for (const r of results) {
+      researchContext += `- ${r.title}: ${r.content}\n  Source: ${r.url}\n`;
+    }
+    researchContext += "\n";
+  }
+
+  const userPrompt = `Compare: ${request.items.join(", ")}
+${request.query ? `Focus: ${request.query}` : ""}
+${request.dimensions?.length ? `Dimensions: ${request.dimensions.join(", ")}` : ""}
+
+${researchContext}`;
+
+  try {
+    const response = await fetch(PERPLEXITY_API_URL, {
+      method: "POST",
+      headers: {
+        Authorization: `Bearer ${apiKey}`,
+        "Content-Type": "application/json",
+      },
+      body: JSON.stringify({
+        model: "sonar",
+        messages: [
+          { role: "system", content: SYSTEM_PROMPT },
+          { role: "user", content: userPrompt },
+        ],
+        temperature: 0.3,
+      }),
+    });
+
+    if (!response.ok) {
+      console.error(
+        `Perplexity API error: ${response.status} ${response.statusText}`
+      );
+      return generateComparisonWithResearch(request, searchResults);
+    }
+
+    const data = await response.json();
+    const content = data.choices?.[0]?.message?.content;
+
+    if (!content) {
+      console.error("Empty response from Perplexity");
+      return generateComparisonWithResearch(request, searchResults);
+    }
+
+    const parsed: unknown = JSON.parse(content);
+
+    if (
+      !parsed ||
+      typeof parsed !== "object" ||
+      !Array.isArray((parsed as Record<string, unknown>).items) ||
+      !Array.isArray((parsed as Record<string, unknown>).dimensions)
+    ) {
+      console.error("Invalid structure from Perplexity, falling back to OpenAI");
+      return generateComparisonWithResearch(request, searchResults);
+    }
+
+    return parsed as ComparisonResult;
+  } catch (error) {
+    console.error(
+      "Perplexity synthesis failed, falling back to OpenAI:",
+      error instanceof Error ? error.message : error
+    );
+    return generateComparisonWithResearch(request, searchResults);
+  }
+}