#!/bin/sh
# Sets your Mac's desktop picture to the image published next to this script.
#
# All the code is inside main() so that a partial download runs nothing.

die() {
  echo "bgmac: $1" >&2
  exit 1
}

main() {
  set -eu

  base_url="${BG_BASE_URL:-https://bgmac.pages.dev}"
  image="standard_pride-flagg.png"
  dry_run="${BG_DRY_RUN:-0}"

  [ "$(uname -s)" = "Darwin" ] || die "this only works on macOS for now."
  [ "$(id -u)" -ne 0 ] || die "run this without sudo, it changes your own desktop."

  dest_dir="$HOME/Library/Application Support/bgmac"
  tmp="$(mktemp -d)"
  trap 'rm -rf "$tmp"' EXIT

  echo "Downloading image..."
  curl -fsSL "$base_url/$image" -o "$tmp/wallpaper.png" \
    || die "could not download the image."

  sips -g pixelWidth "$tmp/wallpaper.png" 2>/dev/null | grep -q "pixelWidth: [0-9]" \
    || die "the downloaded file is not a valid image."

  # The picture has to stay on disk for macOS to keep showing it. The hash in
  # the name makes macOS notice when a new image is published.
  hash="$(shasum -a 256 "$tmp/wallpaper.png" | cut -c1-12)"
  dest="$dest_dir/wallpaper-$hash.png"
  mkdir -p "$dest_dir"
  mv -f "$tmp/wallpaper.png" "$dest"

  # NSWorkspace needs no Automation permission, unlike System Events or Finder.
  screens="$(osascript -l JavaScript - "$dest" "$dry_run" <<'JS'
ObjC.import('AppKit');

function run(argv) {
  var url = $.NSURL.fileURLWithPath(argv[0]);
  var dryRun = argv[1] === '1';
  var workspace = $.NSWorkspace.sharedWorkspace;
  var screens = $.NSScreen.screens;
  var count = screens.count;

  if (count === 0) throw new Error('no displays found');
  if (typeof workspace.setDesktopImageURLForScreenOptionsError !== 'function') {
    throw new Error('this macOS version does not offer the wallpaper API');
  }

  if (!dryRun) {
    for (var i = 0; i < count; i++) {
      var error = Ref();
      var ok = workspace.setDesktopImageURLForScreenOptionsError(
        url, screens.objectAtIndex(i), $.NSDictionary.alloc.init, error);
      if (!ok) throw new Error(ObjC.unwrap(error[0].localizedDescription));
    }
  }

  return count;
}
JS
  )" || die "macOS refused to change the desktop picture."

  if [ "$dry_run" = "1" ]; then
    echo "Dry run: found $screens display(s), nothing changed."
    return
  fi

  # Only our own older copies. The current one is still in use.
  find "$dest_dir" -maxdepth 1 -name 'wallpaper-*.png' ! -name "wallpaper-$hash.png" -delete

  echo "Done! New desktop picture on $screens display(s)."
}

main "$@"