{ depot, pkgs, lib, ... }:

# ytextr is a wrapper arount yt-dlp (previously youtube-dl)
# that extracts a single video according to my preferred settings.
#
# It will be sandboxed to the current directory, since I don’t particularly
# trust the massive codebase of that tool (with hundreds of contributors).
#
# Since the rules for downloading videos is usually against the wishes
# of proprietary vendors, and a video is many megabytes anyway,
# it will be fetched from the most recent nixpkgs unstable channel before running.

let
  bins = depot.nix.getBins pkgs.nix [ "nix-build" ]
      // depot.nix.getBins pkgs.bubblewrap [ "bwrap" ];

  # Run a command, with the given packages in scope, and `packageNamesAtRuntime` being fetched at the start in the given nix `channel`.
  nix-run-with-channel = {
    # The channel to get `packageNamesAtRuntime` from
    channel,
    # executable to run with `packageNamesAtRuntime` in PATH
    # and the argv
    executable,
    # A list of nixpkgs package attribute names that should be put into PATH when running `command`.
    packageNamesAtRuntime,
  }: depot.nix.writeExecline "nix-run-with-channel-${channel}" {} [
    # TODO: prevent race condition by writing a temporary gc root
    "backtick" "-iE" "storepath" [
      bins.nix-build
        "-I" "nixpkgs=channel:${channel}"
        "--arg"
          "packageNamesAtRuntimeJsonPath"
          (pkgs.writeText "packageNamesAtRuntime.json" (builtins.toJSON packageNamesAtRuntime))
        ./create-symlink-farm.nix
    ]
    "importas" "-ui" "PATH" "PATH"
    "export" "PATH" "\${storepath}/bin:\${PATH}"
    executable "$@"
  ];

in nix-run-with-channel {
  channel = "nixos-unstable";
  packageNamesAtRuntime = [ "yt-dlp" ];
  executable = depot.nix.writeExecline "ytextr" { readNArgs = 1; } [
    "getcwd" "-E" "cwd"
    bins.bwrap
      "--ro-bind" "/nix/store" "/nix/store"
      "--ro-bind" "/etc" "/etc"
      "--bind" "$cwd" "$cwd"
        "yt-dlp"
        "--no-playlist"
        "--write-sub"
        "--all-subs"
        "--embed-subs"
        "--merge-output-format" "mkv"
        "-f" "bestvideo[height<=?1080]+bestaudio/best"
        "$1"
  ];
}