feat: Gemini infographic generation service (Task 4)

New infographic generation service using Imagen 4 Fast via @google/genai SDK.\n\nExports: generateInfographic, generateInfographicBatch, generateInfographicsForTopic, buildInfographicPrompt.\nModel + instructions from Sanity config. Deterministic seeds for brand consistency.\nPer-item fault isolation. ~$0.10 per topic (5 images).

Author: codercatdev

lib/services/gemini-infographics.ts

@@ -0,0 +1,283 @@
+/**
+ * Gemini Infographic Generation Service
+ *
+ * Generates brand-consistent infographics using Google's Imagen 4 Fast model
+ * via the @google/genai SDK. Designed for the CodingCat.dev automated video
+ * pipeline — produces visual assets from research data for use in videos and
+ * blog posts.
+ *
+ * Pricing: Imagen 4 Fast — $0.02/image
+ * Supports seed-based reproducibility for brand consistency.
+ *
+ * @module lib/services/gemini-infographics
+ */
+
+import { GoogleGenAI } from "@google/genai";
+import { getConfigValue } from "@/lib/config";
+
+// ---------------------------------------------------------------------------
+// Types
+// ---------------------------------------------------------------------------
+
+/** A single generated infographic result. */
+export interface InfographicResult {
+  /** Base64-encoded PNG image bytes. */
+  imageBase64: string;
+  /** MIME type — always "image/png" for Imagen. */
+  mimeType: string;
+  /** The prompt used to generate this image. */
+  prompt: string;
+  /** Seed used (if provided), for reproducibility. */
+  seed?: number;
+}
+
+/** Options for a single infographic generation request. */
+export interface InfographicRequest {
+  /** Text prompt describing the infographic to generate. */
+  prompt: string;
+  /** Aspect ratio. Defaults to "16:9" for video pipeline use. */
+  aspectRatio?: "1:1" | "3:4" | "4:3" | "9:16" | "16:9";
+  /** Optional seed for reproducibility (not compatible with watermarks). */
+  seed?: number;
+  /** Negative prompt — what to avoid in the image. */
+  negativePrompt?: string;
+}
+
+/** Options for batch infographic generation. */
+export interface InfographicBatchOptions {
+  /** Override the Imagen model (defaults to pipeline_config.infographicModel or "imagen-4-fast"). */
+  model?: string;
+  /** Number of images per prompt (1–4). Defaults to 1. */
+  numberOfImages?: number;
+}
+
+/** Result of a batch generation run. */
+export interface InfographicBatchResult {
+  /** Successfully generated infographics. */
+  results: InfographicResult[];
+  /** Prompts that failed, with error messages. */
+  errors: Array<{ prompt: string; error: string }>;
+}
+
+// ---------------------------------------------------------------------------
+// Internal: lazy client
+// ---------------------------------------------------------------------------
+
+let _ai: GoogleGenAI | null = null;
+
+function getAI(): GoogleGenAI {
+  if (!_ai) {
+    const apiKey = process.env.GEMINI_API_KEY ?? "";
+    _ai = new GoogleGenAI({ apiKey });
+  }
+  return _ai;
+}
+
+// ---------------------------------------------------------------------------
+// Core: single image generation
+// ---------------------------------------------------------------------------
+
+/**
+ * Generate a single infographic image using Imagen 4 Fast.
+ *
+ * @param request - Prompt and generation options.
+ * @param model - Imagen model ID (e.g. "imagen-4-fast").
+ * @returns InfographicResult with base64 image bytes.
+ * @throws If the API call fails or no image is returned.
+ */
+export async function generateInfographic(
+  request: InfographicRequest,
+  model: string = "imagen-4-fast",
+): Promise<InfographicResult> {
+  const ai = getAI();
+
+  const response = await ai.models.generateImages({
+    model,
+    prompt: request.prompt,
+    config: {
+      numberOfImages: 1,
+      aspectRatio: request.aspectRatio ?? "16:9",
+      ...(request.seed !== undefined && { seed: request.seed }),
+      ...(request.negativePrompt && { negativePrompt: request.negativePrompt }),
+    },
+  });
+
+  const generated = response.generatedImages?.[0];
+  if (!generated?.image?.imageBytes) {
+    const reason = generated?.raiFilteredReason ?? "unknown";
+    throw new Error(
+      `Imagen returned no image for prompt "${request.prompt.slice(0, 80)}…" — RAI reason: ${reason}`,
+    );
+  }
+
+  const imageBytes = generated.image.imageBytes;
+  // imageBytes may be a Uint8Array or base64 string depending on SDK version
+  const imageBase64 =
+    typeof imageBytes === "string"
+      ? imageBytes
+      : Buffer.from(imageBytes).toString("base64");
+
+  return {
+    imageBase64,
+    mimeType: "image/png",
+    prompt: request.prompt,
+    ...(request.seed !== undefined && { seed: request.seed }),
+  };
+}
+
+// ---------------------------------------------------------------------------
+// Batch: generate multiple infographics
+// ---------------------------------------------------------------------------
+
+/**
+ * Generate a batch of infographics from an array of prompts.
+ *
+ * Processes requests sequentially to avoid rate-limit issues.
+ * Failed individual images are collected in `errors` rather than throwing.
+ *
+ * @param requests - Array of infographic requests (prompts + options).
+ * @param options - Batch-level options (model override, numberOfImages).
+ * @returns InfographicBatchResult with successes and failures.
+ *
+ * @example
+ * ```ts
+ * const { results, errors } = await generateInfographicBatch([
+ *   { prompt: "A clean infographic showing React hooks lifecycle, dark theme, CodingCat.dev branding" },
+ *   { prompt: "Comparison chart: REST vs GraphQL vs tRPC, developer-friendly, purple accent" },
+ * ]);
+ * console.log(`Generated ${results.length} images, ${errors.length} failed`);
+ * ```
+ */
+export async function generateInfographicBatch(
+  requests: InfographicRequest[],
+  options: InfographicBatchOptions = {},
+): Promise<InfographicBatchResult> {
+  const model =
+    options.model ??
+    (await getConfigValue("pipeline_config", "infographicModel", "imagen-4-fast"));
+
+  const results: InfographicResult[] = [];
+  const errors: Array<{ prompt: string; error: string }> = [];
+
+  for (const request of requests) {
+    try {
+      const result = await generateInfographic(request, model);
+      results.push(result);
+    } catch (err) {
+      const message = err instanceof Error ? err.message : String(err);
+      errors.push({ prompt: request.prompt, error: message });
+    }
+  }
+
+  return { results, errors };
+}
+
+// ---------------------------------------------------------------------------
+// Helpers
+// ---------------------------------------------------------------------------
+
+/**
+ * Build a brand-consistent infographic prompt for CodingCat.dev.
+ *
+ * Wraps a topic description with standard brand guidelines so all generated
+ * infographics share a consistent visual identity.
+ *
+ * @param topic - The subject matter (e.g. "React Server Components").
+ * @param style - Visual style hint (default: "dark tech").
+ * @returns A fully-formed Imagen prompt string.
+ */
+export function buildInfographicPrompt(
+  topic: string,
+  style: string = "dark tech",
+): string {
+  return (
+    `Create a professional, visually striking infographic about: ${topic}. ` +
+    `Style: ${style}, purple and teal accent colors, clean sans-serif typography, ` +
+    `CodingCat.dev brand aesthetic. ` +
+    `Layout: structured sections with icons, data visualizations, and clear hierarchy. ` +
+    `No watermarks. High information density. Developer audience.`
+  );
+}
+
+// ---------------------------------------------------------------------------
+// Default instructions (blueprint style from spec)
+// ---------------------------------------------------------------------------
+
+/** Default infographic instructions if Sanity contentConfig is not set up */
+const DEFAULT_INSTRUCTIONS: string[] = [
+  'Create a technical architecture sketch using white "hand-drawn" ink lines on a deep navy blue background (#003366). Use rough-sketched server and database icons with visible "marker" strokes, handwritten labels in a casual font, and a subtle grid pattern. Style: blueprint meets whiteboard doodle.',
+  'Create a comparison chart on a vibrant blue background (#004080) with hand-inked white headers and uneven, sketchy borders. Use white cross-hatching and doodle-style checkmarks to highlight feature differences. Include hand-drawn arrows and annotations. Style: technical chalkboard.',
+  'Create a step-by-step workflow "blueprint" on a dark blue canvas (#003366). Use hand-drawn white arrows connecting rough-sketched boxes, simple "stick-figure" style worker avatars, and handwritten-style labels with a slight chalk texture. Add a subtle grid background. Style: engineering whiteboard.',
+  'Create a hand-sketched timeline using a jagged white line on a royal blue background. Represent milestones with simple, iconic white doodles that look like they were quickly sketched during a brainstorming session. Use handwritten dates and labels. Style: notebook sketch on blue paper.',
+  'Create a pros and cons summary with a "lo-fi" aesthetic. Use hand-drawn white thumbs-up/down icons and rough-sketched containers on a deep blue background (#003366). Add hand-drawn underlines and circled keywords. Style: high-contrast ink-on-blueprint with cyan accent highlights.',
+];
+
+// ---------------------------------------------------------------------------
+// High-level API: generate all infographics for a topic
+// ---------------------------------------------------------------------------
+
+/**
+ * Generate a deterministic seed from a topic + instruction index.
+ * Ensures the same topic always produces the same seed per instruction,
+ * enabling brand-consistent regeneration.
+ */
+function generateSeed(topic: string, index: number): number {
+  let hash = 0;
+  const str = `${topic}-infographic-${index}`;
+  for (let i = 0; i < str.length; i++) {
+    const char = str.charCodeAt(i);
+    hash = ((hash << 5) - hash) + char;
+    hash = hash & hash;
+  }
+  return Math.abs(hash) % 2147483647;
+}
+
+/**
+ * Generate all infographics for a research topic using instructions
+ * from Sanity contentConfig.
+ *
+ * This is the main entry point for the check-research cron route.
+ * Reads infographic instructions from contentConfig.infographicInstructions,
+ * appends topic context to each, and generates images with deterministic
+ * seeds for brand consistency.
+ *
+ * @param topic - The research topic (e.g. "React Server Components")
+ * @param briefing - Optional research briefing text for additional context
+ * @returns InfographicBatchResult with generated images and any errors
+ */
+export async function generateInfographicsForTopic(
+  topic: string,
+  briefing?: string,
+): Promise<InfographicBatchResult> {
+  const instructions = await getConfigValue(
+    "content_config", "infographicInstructions", DEFAULT_INSTRUCTIONS
+  );
+
+  const model = await getConfigValue(
+    "pipeline_config", "infographicModel", "imagen-4-fast"
+  );
+
+  const contextSuffix = briefing
+    ? `\n\nTopic: ${topic}\nContext: ${briefing.slice(0, 500)}`
+    : `\n\nTopic: ${topic}`;
+
+  const requests: InfographicRequest[] = instructions.map(
+    (instruction, index) => ({
+      prompt: `${instruction}${contextSuffix}`,
+      seed: generateSeed(topic, index),
+      aspectRatio: "16:9" as const,
+    })
+  );
+
+  console.log(
+    `[infographics] Generating ${requests.length} infographics for "${topic}" with ${model}`
+  );
+
+  const result = await generateInfographicBatch(requests, { model });
+
+  console.log(
+    `[infographics] Complete: ${result.results.length} generated, ${result.errors.length} failed`
+  );
+
+  return result;
+}