SnapOtter/apps/api/src/routes/tools/compose.ts

import { randomUUID } from "node:crypto";
import type { FastifyInstance } from "fastify";
import sharp from "sharp";
import { z } from "zod";
import { autoOrient } from "../../lib/auto-orient.js";
import { formatZodErrors } from "../../lib/errors.js";
import { validateImageBuffer } from "../../lib/file-validation.js";
import { sanitizeFilename } from "../../lib/filename.js";
import { decodeToSharpCompat, needsCliDecode } from "../../lib/format-decoders.js";
import { decodeHeic } from "../../lib/heic-converter.js";
import { putObject } from "../../lib/object-storage.js";
import { decompressSvgz, sanitizeSvg } from "../../lib/svg-sanitize.js";

async function decodeBuffer(inputBuffer: Buffer, filename: string): Promise<Buffer> {
  const validation = await validateImageBuffer(inputBuffer, filename);
  if (!validation.valid) {
    throw new Error(`Invalid image: ${validation.reason}`);
  }

  let decoded = inputBuffer;
  if (validation.format === "heif") {
    decoded = await decodeHeic(decoded);
  } else if (needsCliDecode(validation.format)) {
    const ext = filename.split(".").pop()?.toLowerCase();
    decoded = await decodeToSharpCompat(decoded, validation.format, ext);
  } else if (validation.format === "svg") {
    decoded = decompressSvgz(decoded);
    decoded = sanitizeSvg(decoded);
  }

  return autoOrient(decoded);
}

const settingsSchema = z.object({
  x: z.number().min(0).default(0),
  y: z.number().min(0).default(0),
  opacity: z.number().min(0).max(100).default(100),
  blendMode: z
    .enum([
      "over",
      "multiply",
      "screen",
      "overlay",
      "darken",
      "lighten",
      "hard-light",
      "soft-light",
      "difference",
      "exclusion",
    ])
    .default("over"),
});

export function registerCompose(app: FastifyInstance) {
  app.post("/api/v1/tools/image/compose", async (request, reply) => {
    let baseBuffer: Buffer | null = null;
    let overlayBuffer: Buffer | null = null;
    let filename = "image";
    let overlayFilename = "overlay";
    let settingsRaw: string | null = null;

    try {
      const parts = request.parts();
      for await (const part of parts) {
        if (part.type === "file") {
          const chunks: Buffer[] = [];
          for await (const chunk of part.file) {
            chunks.push(chunk);
          }
          const buf = Buffer.concat(chunks);
          if (part.fieldname === "overlay") {
            overlayBuffer = buf;
            overlayFilename = sanitizeFilename(part.filename ?? "overlay");
          } else {
            baseBuffer = buf;
            filename = sanitizeFilename(part.filename ?? "image");
          }
        } else if (part.fieldname === "settings") {
          settingsRaw = part.value as string;
        }
      }
    } catch (err) {
      return reply.status(400).send({
        error: "Failed to parse multipart request",
        details: err instanceof Error ? err.message : String(err),
      });
    }

    if (!baseBuffer || baseBuffer.length === 0) {
      return reply.status(400).send({ error: "No base image provided" });
    }
    if (!overlayBuffer || overlayBuffer.length === 0) {
      return reply.status(400).send({ error: "No overlay image provided" });
    }

    let settings: z.infer<typeof settingsSchema>;
    try {
      const parsed = settingsRaw ? JSON.parse(settingsRaw) : {};
      const result = settingsSchema.safeParse(parsed);
      if (!result.success) {
        return reply
          .status(400)
          .send({ error: "Invalid settings", details: formatZodErrors(result.error.issues) });
      }
      settings = result.data;
    } catch {
      return reply.status(400).send({ error: "Settings must be valid JSON" });
    }

    try {
      baseBuffer = await decodeBuffer(baseBuffer, filename);
      overlayBuffer = await decodeBuffer(overlayBuffer, overlayFilename);

      // Apply opacity to overlay if needed
      let processedOverlay = overlayBuffer;
      if (settings.opacity < 100) {
        const overlayImg = sharp(overlayBuffer).ensureAlpha();
        const overlayBuf = await overlayImg.toBuffer();
        const overlayMeta = await sharp(overlayBuf).metadata();
        const oW = overlayMeta.width ?? 100;
        const oH = overlayMeta.height ?? 100;

        const opacityMask = await sharp({
          create: {
            width: oW,
            height: oH,
            channels: 4,
            background: { r: 0, g: 0, b: 0, alpha: settings.opacity / 100 },
          },
        })
          .png()
          .toBuffer();

        processedOverlay = await sharp(overlayBuf)
          .composite([{ input: opacityMask, blend: "dest-in" }])
          .toBuffer();
      }

      const result = await sharp(baseBuffer)
        .composite([
          {
            input: processedOverlay,
            top: settings.y,
            left: settings.x,
            blend: settings.blendMode as sharp.Blend,
          },
        ])
        .toBuffer();

      const jobId = randomUUID();
      await putObject(`outputs/${jobId}/${filename}`, result);

      return reply.send({
        jobId,
        downloadUrl: `/api/v1/download/${jobId}/${encodeURIComponent(filename)}`,
        originalSize: baseBuffer.length,
        processedSize: result.length,
      });
    } catch (err) {
      return reply.status(422).send({
        error: "Processing failed",
        details: err instanceof Error ? err.message : "Image processing failed",
      });
    }
  });
}