#!/usr/bin/env bash

#
# Copyright (C) 2020, Maxim Lihachev, <envrm@yandex.ru>
#
# This program is free software: you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the Free
# Software Foundation, version 3.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
#

: <<'MAN'

=head1 NAME

kubectl-compare allows to juxtapose kubernetes resources with any diff-like utilities.

=head1 USAGE

  kubectl compare [-n|--namespace NAMESPACE] [-t|--type] [-e|--edit|-v|--visual] name1 name2
or
  kubectl compare [-e|--edit|-v|--visual] namespace/type/name1 namespace/type/name2
or
  kubectl compare [-e|--edit|-v|--visual] namespace/type/name1 namespace/type/name2 namespace/type/name3 ...

=head1 OPTIONS

  -n --namespace               Kubernetes namespace for search ('default' by default).
  -t --type                    Kubernetes resource's type, e.g. pod, svc, configmap, etc ('pod' by default).
  -e --edit, -v --visual       Open diff in visual editor (e.g. vimdiff).

Set B<VISUAL_DIFF_CMD> environment variable or provide its value in script's
file (kubectl-compare) to specify utility which will be used.

To specify main diff program set B<DIFF_CMD> variable (its default value is I<'diff
-u --color=always'>).

Use something like I<diff3> to compare 3 manifests.

=head1 EXAMPLE

  $ kubectl compare -n zookeeper -t pod zookeeper-0                zookeeper-1
  $ kubectl compare -n zookeeper    pod/zookeeper-0            pod/zookeeper-1
  $ kubectl compare       zookeeper/pod/zookeeper-0  zookeeper/pod/zookeeper-1
			     ^      ^   ^
	       [namespace]---+      |   |
			  [type]----+   |
			        [name]--+

  $ kubectl compare    zookeeper/pod/zookeeper-{0,1,2}

=head1 BUGS

If you find a bug, please report it at B<L<https://code.envrm.info/src/scripts-kubernetes>>.

=head1 AUTHORS

envrm B<L<https://code.envrm.info>>.

=cut
MAN


set -o pipefail

if [ -z "$DIFF_CMD" ]; then
	DIFF_CMD="diff -u --color=always"
fi

if [ -z "$VISUAL_DIFF_CMD" ]; then
	VISUAL_DIFF_CMD="vim -d --cmd 'autocmd BufRead * set filetype=yaml'"
fi

# Default Kubernetes namespace
NAMESPACE=default

# Default Kubernetes resource
TYPE=pod

usage() {
	sed -E -n '/^.*MAN/,/^MAN$/{//!p;}; /^MAN$/q' "$0" | sed -E 's/=head. |[LIBC]<|\b>*//g; /=cut/d'
	exit "${1:-0}"
}

die() {
	>&2 echo "ERROR: $*"
	exit 1
}

kubecmd() {
	IFS='/' read -r -a item <<< "$(sed -E 's:^/|/$::g' <<<"$1")"

	case ${#item[@]} in
		1) kubectl_cmd="kubectl --namespace $NAMESPACE get $TYPE      ${item[0]} -o yaml";;
		2) kubectl_cmd="kubectl --namespace $NAMESPACE get ${item[0]} ${item[1]} -o yaml";;
		3) kubectl_cmd="kubectl --namespace ${item[0]} get ${item[1]} ${item[2]} -o yaml";;
		*) exit 1;;
	esac

	echo "<(${kubectl_cmd[*]})"
}

#--------------------------------------------------------------------------

POSITIONAL=()

while [[ $# -gt 0 ]]; do
	key="$1"

	case $key in
		-h|--help) usage;;
		-e|--edit|-v|--visual) DIFF_CMD=$VISUAL_DIFF_CMD; shift;;
		-n|--namespace) NAMESPACE="$2"; shift; shift;;
		-t|--type) TYPE="$2"; shift; shift;;

		*) POSITIONAL+=("$1"); shift;;
	esac
done

set -- "${POSITIONAL[@]}"

diff_cmd=("$DIFF_CMD")

if [ $# -lt 2 ]; then
	usage 1
fi

for cmd in "$@"; do
	diff_cmd+=($(kubecmd "$cmd")) || die "Excessive nestedness of Kubernetes resource: $cmd"
done

eval "${diff_cmd[*]}"