#!/bin/sh

# The MIT License (MIT)
#
# Copyright (c) 2026 pacman64
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.


# regsort [option...] [regex...] [files...]
#
# Regular Expression Group SORT groups/sorts lines according to common results
# of matching the extended-mode regular-expression given. Each match group
# starts appearing in the output depending on the order the first line matching
# it appeared in the input.
#
# The options are, available both in single and double-dash versions
#
#   -i, -ins, -insensitive    match the regex given case-insensitively
#   -h, -help                 show this help message


case "$1" in
    -h|--h|-help|--help)
        awk '/^# +regsort /, /^$/ { gsub(/^# ?/, ""); print }' "$0"
        exit 0
    ;;
esac

case_insensitive=0
case "$1" in
    -i|--i|-ins|--ins|-insensitive|--insensitive)
        case_insensitive=1
        shift
    ;;
esac

[ "$1" = '--' ] && shift

if [ $# -eq 0 ]; then
    awk '/^# +regsort /, /^$/ { gsub(/^# ?/, ""); print }' "$0" >&2
    exit 1
fi
regex="$1"
shift

# show all non-existing files given
failed=0
for arg in "$@"; do
    if [ "${arg}" = "-" ]; then
        continue
    fi
    if [ ! -e "${arg}" ]; then
        printf "no file named \"%s\"\n" "${arg}" >&2
        failed=1
    fi
done

if [ "${failed}" -gt 0 ]; then
    exit 2
fi

flush=0
if [ -p /dev/stdout ] || [ -t 1 ]; then
    flush=1
fi

awk -v ci="${case_insensitive}" -v regex="${regex}" -v flush="${flush}" '
    BEGIN {
        if (SUBSEP == "") SUBSEP = "\034"

        if (ci == 1 && IGNORECASE == "") {
            m = "your `awk` command lacks case-insensitive regex-matching"
            print(m) > "/dev/stderr"
            exit 125
        }
        if (ci == 1) IGNORECASE = 1
    }

    {
        k = match($0, regex) ? substr($0, RSTART, RLENGTH) : ""

        if (numkeys == 0) {
            first = k
            numkeys++
        }

        # the first group is the only one which can be shown right away
        if (numkeys > 0 && k == first) {
            print
            if (flush) fflush()
            next
        }

        if (tally[k]++ == 0) ordkeys[++numkeys] = k
        groups[k SUBSEP tally[k]] = $0
    }

    END {
        for (i = 2; i <= numkeys; i++) {
            k = ordkeys[i]
            n = tally[k]
            for (j = 1; j <= n; j++) print groups[k SUBSEP j]
        }
    }
' "$@"