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

import { z } from "zod";
import sharp from "sharp";
import archiver from "archiver";
import type { FastifyInstance } from "fastify";
import { randomUUID } from "node:crypto";
import { basename, extname } from "node:path";

const settingsSchema = z.object({
  columns: z.number().min(1).max(10).default(2),
  rows: z.number().min(1).max(10).default(2),
});

/**
 * Split an image into grid parts and return as ZIP.
 */
export function registerSplit(app: FastifyInstance) {
  app.post(
    "/api/v1/tools/split",
    async (request, reply) => {
      let fileBuffer: Buffer | null = null;
      let filename = "image";
      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);
            }
            fileBuffer = Buffer.concat(chunks);
            filename = basename(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 (!fileBuffer || fileBuffer.length === 0) {
        return reply.status(400).send({ error: "No image file 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: result.error.issues });
        }
        settings = result.data;
      } catch {
        return reply.status(400).send({ error: "Settings must be valid JSON" });
      }

      try {
        const metadata = await sharp(fileBuffer).metadata();
        const fullW = metadata.width ?? 0;
        const fullH = metadata.height ?? 0;
        const cellW = Math.floor(fullW / settings.columns);
        const cellH = Math.floor(fullH / settings.rows);
        const ext = extname(filename) || ".png";
        const baseName = filename.replace(ext, "");

        const jobId = randomUUID();

        // Set up response headers for ZIP
        reply.hijack();
        reply.raw.writeHead(200, {
          "Content-Type": "application/zip",
          "Content-Disposition": `attachment; filename="split-${jobId.slice(0, 8)}.zip"`,
          "Transfer-Encoding": "chunked",
        });

        const archive = archiver("zip", { zlib: { level: 5 } });
        archive.pipe(reply.raw);

        for (let row = 0; row < settings.rows; row++) {
          for (let col = 0; col < settings.columns; col++) {
            const left = col * cellW;
            const top = row * cellH;
            // Ensure we don't go out of bounds on the last row/col
            const w = col === settings.columns - 1 ? fullW - left : cellW;
            const h = row === settings.rows - 1 ? fullH - top : cellH;

            const partBuffer = await sharp(fileBuffer)
              .extract({ left, top, width: w, height: h })
              .toBuffer();

            archive.append(partBuffer, {
              name: `${baseName}_r${row + 1}_c${col + 1}${ext}`,
            });
          }
        }

        await archive.finalize();
      } catch (err) {
        if (!reply.raw.headersSent) {
          return reply.status(422).send({
            error: "Split failed",
            details: err instanceof Error ? err.message : "Unknown error",
          });
        }
      }
    },
  );
}