-- media.lua — MIME metadata and content sniffing for uploaded files.
--
-- Uploads are stored as `docs` rows in the content table (slug, title,
-- mime_type, file_data) and served at /docs/:slug.  Images uploaded
-- from the post editor go through the same store.

local M = {}

M.MIME_EXT = {
  ["application/pdf"]      = ".pdf",
  ["application/epub+zip"] = ".epub",
  ["text/plain"]           = ".txt",
  ["application/zip"]      = ".zip",
  ["image/png"]            = ".png",
  ["image/jpeg"]           = ".jpg",
  ["image/gif"]            = ".gif",
  ["image/webp"]           = ".webp",
}

M.MIME_LABELS = {
  ["application/pdf"]          = "PDF Document",
  ["application/epub+zip"]     = "EPUB e-book",
  ["text/plain"]               = "Plain text",
  ["application/zip"]          = "ZIP archive",
  ["image/png"]                = "PNG image",
  ["image/jpeg"]               = "JPEG image",
  ["image/gif"]                = "GIF image",
  ["image/webp"]               = "WebP image",
  ["application/octet-stream"] = "Other binary",
}

--- Detect the MIME type of a binary blob from its magic bytes.
--- Returns a mime string, or nil when unrecognised.
function M.sniff(data)
  if not data or #data < 12 then return nil end
  local head = data:sub(1, 12)
  if head:sub(1, 8) == "\137PNG\r\n\26\10" then return "image/png" end
  if head:sub(1, 3) == "\255\216\255" then return "image/jpeg" end
  if head:sub(1, 6) == "GIF87a" or head:sub(1, 6) == "GIF89a" then return "image/gif" end
  if head:sub(1, 4) == "RIFF" and head:sub(9, 12) == "WEBP" then return "image/webp" end
  if head:sub(1, 5) == "%PDF-" then return "application/pdf" end
  if head:sub(1, 4) == "PK\3\4" then return "application/zip" end
  return nil
end

--- True for MIME types the editor's image-upload widget accepts.
function M.is_image(mime)
  return mime == "image/png" or mime == "image/jpeg"
      or mime == "image/gif" or mime == "image/webp"
end

return M