# uniq.awk --- do uniq in awk
#
# Requires getopt() and join() library functions
#
# Arnold Robbins, arnold@skeeve.com, Public Domain
# May 1993
# Updated August 2020 to current POSIX

function usage()
{
    print("Usage: uniq [-udc [-f fields] [-s chars]] " \
          "[ in [ out ]]") > "/dev/stderr"
    exit 1
}

# -c    count lines. overrides -d and -u
# -d    only repeated lines
# -u    only nonrepeated lines
# -f n  skip n fields
# -s n  skip n characters, skip fields first
# As of 2020, '+' can be used as the option character in addition to '-'
# Previously allowed use of -N to skip fields and +N to skip
# characters is no longer allowed, and not supported by this version.

BEGIN {
    # Convert + to - so getopt can handle things
    for (i = 1; i < ARGC; i++) {
        first = substr(ARGV[i], 1, 1)
        if (ARGV[i] == "--" || (first != "-" && first != "+"))
            break
        else if (first == "+")
            # Replace "+" with "-"
            ARGV[i] = "-" substr(ARGV[i], 2)
    }
}
BEGIN {
    count = 1
    outputfile = "/dev/stdout"
    opts = "udcf:s:"
    while ((c = getopt(ARGC, ARGV, opts)) != -1) {
        if (c == "u")
            non_repeated_only++
        else if (c == "d")
            repeated_only++
        else if (c == "c")
            do_count++
        else if (c == "f")
            fcount = Optarg + 0
        else if (c == "s")
            charcount = Optarg + 0
        else
            usage()
    }

    for (i = 1; i < Optind; i++)
        ARGV[i] = ""

    if (repeated_only == 0 && non_repeated_only == 0)
        repeated_only = non_repeated_only = 1

    if (ARGC - Optind == 2) {
        outputfile = ARGV[ARGC - 1]
        ARGV[ARGC - 1] = ""
    }
}
function are_equal(    n, m, clast, cline, alast, aline)
{
    if (fcount == 0 && charcount == 0)
        return (last == $0)

    if (fcount > 0) {
        n = split(last, alast)
        m = split($0, aline)
        clast = join(alast, fcount+1, n)
        cline = join(aline, fcount+1, m)
    } else {
        clast = last
        cline = $0
    }
    if (charcount) {
        clast = substr(clast, charcount + 1)
        cline = substr(cline, charcount + 1)
    }

    return (clast == cline)
}
NR == 1 {
    last = $0
    next
}

{
    equal = are_equal()

    if (do_count) {    # overrides -d and -u
        if (equal)
            count++
        else {
            printf("%4d %s\n", count, last) > outputfile
            last = $0
            count = 1    # reset
        }
        next
    }

    if (equal)
        count++
    else {
        if ((repeated_only && count > 1) ||
            (non_repeated_only && count == 1))
                print last > outputfile
        last = $0
        count = 1
    }
}

END {
    if (do_count)
        printf("%4d %s\n", count, last) > outputfile
    else if ((repeated_only && count > 1) ||
            (non_repeated_only && count == 1))
        print last > outputfile
    close(outputfile)
}