#!/bin/awk -f
#
# Copyright © 2022 Nick Bowler
#
# Partial implementation of POSIX "join" command.  No options are supported.
#
# License WTFPL2: Do What The Fuck You Want To Public License, version 2.
# This is free software: you are free to do what the fuck you want to.
# There is NO WARRANTY, to the extent permitted by law.

BEGIN {
  if (ARGC != 3) {
    exit 1;
  }

  file2 = ARGV[2];
  delete ARGV[2];

  advance_rhs();
}

$1 == lhs_prev {
  # Rewind RHS as we have duplicate keys in LHS.
  close(file2);
  advance_rhs();
}

$1 < rhs[1] { next }
{
  while ($1 > rhs[1]) {
    if (advance_rhs() == 0)
      exit(0);
  }
}

$1 == rhs[1] {
  lhs_prev = $1 = $1;
  do {
    print_match();
    advance_rhs();
  } while ($1 == rhs[1]);
}

function advance_rhs(raw, rc)
{
  rc = getline raw < file2;
  if (rc < 0)
    exit(1);

  split(raw, rhs);
  return rc;
}

function print_match(i)
{
  printf "%s", $0
  for (i = 2; i in rhs; i++) {
    printf " %s", rhs[i];
  }
  print ""
}