#!/usr/bin/env python

"""gosh: use Golang as a shell scripting language.

This is written in Python so that I don't have to commit any binaries to my
dotfiles repo, and my Go shell scripts can also remain in source form.

Usage: write a Go program with this shebang comment on top immediately before
the `package main` statement:

    #!/usr/bin/env gosh
    package main

And make it executable and run it like any shell script.
"""

import codecs
import os
import subprocess
import sys
import tempfile

def main():
    if len(sys.argv) == 1:
        die("Usage: gosh <file.go>")

    # Get the Go source file from the command line.
    source = sys.argv[1]
    argv   = sys.argv[2:]
    if not os.path.isfile(source):
        die("{}: not a file".format(source))

    # Make a temp file that lacks the shebang line of the input file.
    with codecs.open(source, "r", "utf-8") as fh:
        # Get the shebang off and sanity check it.
        shebang = fh.readline()
        if not "gosh" in shebang:
            die("{}: doesn't appear to be a Go script".format(source))

        # Write it to a temp file, sans shebang.
        temp = tempfile.NamedTemporaryFile(delete=False, suffix=".go")
        temp.write(fh.read().strip())
        temp.close()

        # Call it.
        subprocess.call(["go", "run", temp.name] + argv)

        # Clean up.
        os.unlink(temp.name)

def die(message):
    print(message)
    sys.exit(1)

if __name__ == "__main__":
    main()