# os.ludic — Os.* environment interface. args/env/platform are non-deterministic
# host input, so instead of fixed answers we assert the invariants that must hold
# regardless of where it runs: an env var round-trips, env_or falls back when a
# var is unset, unset removes it, args() agrees with arg_count(), and the host
# facts and known folders are all non-empty. Running it prints: 1 2 3 4 5 6 7 8 9 10 11 12 13 14
program Os {
  entry {
    # environment variables round-trip through set/get
    if Os.set_env("LUDIC_OS_TEST", "42") { print(1) }
    if Os.env("LUDIC_OS_TEST") == "42" { print(2) }
    if Os.has_env("LUDIC_OS_TEST") { print(3) }

    # env_or returns the fallback for a variable that is not set
    if Os.env_or("LUDIC_OS_DEFINITELY_UNSET", "fallback") == "fallback" { print(4) }

    # unset removes the variable
    if Os.unset_env("LUDIC_OS_TEST") { print(5) }
    if not Os.has_env("LUDIC_OS_TEST") { print(6) }

    # the argument vector always carries at least the program path, and args()
    # is a []string of exactly arg_count() elements
    if Os.arg_count() >= 1 { print(7) }
    if len(Os.args()) == Os.arg_count() { print(8) }

    # platform and arch are non-empty host facts
    if len(Os.platform()) > 0 { print(9) }
    if len(Os.arch()) > 0 { print(10) }

    # per-user known folders resolve to non-empty paths
    if len(Os.save_dir("MyGame")) > 0 { print(11) }
    if len(Os.temp_dir()) > 0 { print(12) }

    # the process id is a live, positive OS handle
    if Os.pid() > 0 { print(13) }

    # diagnostics go to stderr, so they never disturb this program's stdout
    Os.stderr_write("os.ludic: hello from stderr\n")
    print(14)
  }
}