const fs = require("fs");
const cloudinary = require("../config/cloudinary");

const FOLDER = "aynwerd-courses";

// Public ID of the white Aynwerd logo, uploaded once (see
// scripts/uploadWatermarkLogo.js) as a plain, non-secret image asset —
// it's only ever used as an overlay layer, never served on its own.
const WATERMARK_LOGO_PUBLIC_ID = process.env.CLOUDINARY_WATERMARK_LOGO_PUBLIC_ID || "aynwerd_watermark_logo";

// Cloudinary's chunked `upload_large` is meant for genuinely large
// files (their own docs point to it for anything that risks a single
// request timing out or exceeding size limits — 100MB+ in practice).
// Using it unconditionally for every video was a bug: for small files
// its resolved result can come back missing fields (public_id,
// resource_type) that the plain, non-chunked upload always includes,
// which surfaced as a confusing Mongoose "required" validation error
// rather than a clear upload error. Only use it above this threshold.
const LARGE_UPLOAD_THRESHOLD_BYTES = 100 * 1024 * 1024; // 100MB

/**
 * Uploads a file from a local temp path to Cloudinary under private,
 * signed-only access. `type: "authenticated"` means the asset can
 * NEVER be fetched by its plain URL or by guessing the public ID —
 * every request must carry a valid signature that we only ever mint
 * for a verified, paying learner (see getSignedPlaybackUrl below).
 */
async function uploadFromPath(filePath, { resourceType, filenameHint }) {
  const options = {
    folder: FOLDER,
    resource_type: resourceType, // "video" | "image" | "raw"
    type: "authenticated",
    use_filename: true,
    unique_filename: true,
    filename_override: filenameHint,
  };

  const { size } = fs.statSync(filePath);
  const useLargeUpload = resourceType === "video" && size > LARGE_UPLOAD_THRESHOLD_BYTES;

  const result = useLargeUpload
    ? await cloudinary.uploader.upload_large(filePath, { ...options, chunk_size: 20 * 1024 * 1024 })
    : await cloudinary.uploader.upload(filePath, options);

  // Fail loudly and specifically here rather than letting an
  // incomplete result silently reach the database, where it would
  // otherwise surface as an opaque Mongoose validation error instead
  // of a clear "the upload didn't actually succeed" message.
  if (!result || !result.public_id || !result.resource_type) {
    throw new Error(
      `Cloudinary upload did not return the expected result (got: ${JSON.stringify(result)}). ` +
        "The file was not saved — please try again."
    );
  }

  return result;
}

function deleteAsset(publicId, resourceType) {
  return cloudinary.uploader.destroy(publicId, { resource_type: resourceType, type: "authenticated" });
}

const THUMBNAIL_FOLDER = "aynwerd-course-thumbnails";

/**
 * Uploads a course thumbnail image. Deliberately PUBLIC (type: "upload",
 * the Cloudinary default) — unlike lesson videos/documents, a
 * thumbnail's whole purpose is to be visible to any visitor browsing
 * the storefront before they've bought anything, so there's nothing to
 * gate here.
 */
async function uploadThumbnail(filePath, { filenameHint }) {
  const result = await cloudinary.uploader.upload(filePath, {
    folder: THUMBNAIL_FOLDER,
    resource_type: "image",
    type: "upload",
    use_filename: true,
    unique_filename: true,
    filename_override: filenameHint,
    // Keep thumbnails reasonably sized regardless of what the admin
    // uploads, so course cards load fast on the storefront.
    transformation: [{ width: 1024, height: 768, crop: "limit" }],
  });

  if (!result || !result.public_id || !result.secure_url) {
    throw new Error(`Cloudinary thumbnail upload did not return the expected result (got: ${JSON.stringify(result)}).`);
  }

  return result;
}

function deleteThumbnail(publicId) {
  return cloudinary.uploader.destroy(publicId, { resource_type: "image", type: "upload" });
}

/**
 * Builds the overlay layers that stamp a video with the Aynwerd logo
 * plus the viewing learner's email, so any leaked/recorded copy is
 * both clearly branded and traceable back to the account it leaked
 * from. Applied at request time, per viewer — nothing pre-baked, so
 * the same source video is watermarked differently for every learner
 * who opens it.
 *
 * Logo sits top-right (matching a standard, clearly-visible corner
 * bug like most watermarked platform videos), email sits bottom-left
 * — opposite corner, so the two marks don't overlap and a crop that
 * removes one is unlikely to remove both.
 */
function buildWatermarkTransformation({ email }) {
  return [
    {
      overlay: { public_id: WATERMARK_LOGO_PUBLIC_ID, resource_type: "image" },
      width: 160,
      opacity: 90,
      gravity: "north_east",
      x: 24,
      y: 24,
    },
    {
      overlay: {
        font_family: "Arial",
        font_size: 22,
        font_weight: "bold",
        text: email,
      },
      color: "white",
      opacity: 85,
      gravity: "south_west",
      x: 20,
      y: 20,
    },
  ];
}

/**
 * Mints a short-lived, signed URL for a specific lesson asset. Valid for
 * a couple of hours only, so a leaked link stops working quickly and
 * cannot be redistributed as a permanent download.
 *
 * When `viewer` is provided and the asset is a video, the URL also
 * carries a per-viewer watermark (Aynwerd logo + the learner's email —
 * see buildWatermarkTransformation above) — Cloudinary renders that
 * watermarked derivative on the fly and signs the transformed URL, so
 * the overlay can't be stripped without the original signed request.
 * Watermarking only applies to video; document/raw lessons (PDFs,
 * slides) are returned unmodified since Cloudinary can't overlay text
 * on a raw file delivery the same way.
 */
function getSignedPlaybackUrl(
  publicId,
  resourceType,
  { format, expiresInSeconds = 2 * 60 * 60, viewer } = {}
) {
  const expiresAt = Math.floor(Date.now() / 1000) + expiresInSeconds;
  const url = cloudinary.url(publicId, {
    resource_type: resourceType,
    type: "authenticated",
    sign_url: true,
    secure: true,
    expires_at: expiresAt,
    format: format || undefined,
    transformation: resourceType === "video" && viewer ? buildWatermarkTransformation(viewer) : undefined,
  });
  return { url, expiresAt };
}

/** Maps an uploaded file's mimetype to the Cloudinary resource_type bucket it belongs in. */
function resourceTypeForMimetype(mimetype) {
  if (mimetype.startsWith("video/")) return "video";
  if (mimetype.startsWith("image/")) return "image";
  return "raw"; // PDFs, docs, slides, zips, etc.
}

module.exports = {
  uploadFromPath,
  deleteAsset,
  getSignedPlaybackUrl,
  resourceTypeForMimetype,
  uploadThumbnail,
  deleteThumbnail,
};