cal

#!/bin/sh
help() { cat <<'/help'
Wrapper for cal supporting month names, 9mo view, and relative/arbitrary dates
Usage: cal [OPTIONS] [+][-][MONTH] [+][-][YEAR]

  -1, --one          Display only the target month (default)
  -3, --three        Display a row of the prior, target, and next months
  -9, --nine         Display 3 rows centered on the target (like `-A 4 -B 4`)
  -A, --after=NUM    Show this many months after the target month
  -B, --before=NUM   Show this many months before the target month
  -d, --date=DATE    Change the target date from today to DATE (in any format)
  -j, --julian       Display days of the year (Julian days), e.g. Feb 1 = 32
  -m, --month=MONTH  Display the specified month. Aborts the wrapper.
  -W, --week=MIN     The first week of the year must contain MIN days

If just given a month, shows calendar for closest instance of given month.
When a month or year is prefixed with + or - or +-, it is considered an offset
relative to the current date.

/help
  version
}

self="${0##*/}"
url='https://github.com/adamhotep/misc-scripts'

version() {
  echo "Part of misc-scripts: $url"
  echo "cal-wrapper 0.4.20250711.0 copyright 2019+ by Adam Katz, GPL v2+"
  exit
}

die() { [ $# -gt 0 ] && printf "%s\n" "$@" >&2; exit 2; }
bb() { true; }	# we call this to warn about Busybox cal's limited options

if ! command -v ncal >/dev/null; then
  exe="/usr/bin/cal"
  if [ "$exe" != "$0" ] && [ -x "$exe" ]; then
    ncal() { shift; "$exe" "$@"; }
  elif command -v busybox >/dev/null && busybox cal --help >/dev/null 2>&1; then
    ncal() { shift; busybox cal "$@"; }
    bb() { die "Option \`-$OPT\` requires installing \`ncal\`"; }
  else
    die 'This script wraps either `ncal` or `busybox cal` but you lack both.' \
        'Maybe try `apt install ncal` or `apt install busybox`, etc.'
  fi
fi

run() {
  while [ -n "$arr" ]; do	# split (pop) options into $@
    OPT="${arr##*$sep}"
    arr="${arr%"$OPT"}"
    arr="${arr%"$sep"}"
    set -- "$OPT" "$@"
  done

  ncal -C "$@" ${month:+"$month"} ${year:+"$year"}
  exit $?
}

datefrom() {
  out=$(date -d "2000-$2-15" +"%$1") 2>/dev/null	# GNU or Busybox date
  if [ -z "$out" ]; then
    datefrom() {
      local out="$(date -jf %m $2 +"%$1")" 2>/dev/null || return 2  # BSD date
      printf %s "$out"
    }
    datefrom "$@" || die 'ERROR: missing `locale` & GNU/busybox/BSD `date`'
  fi
  printf %s "$out"
}

# Usage: month NAME
# Extract the locale's list of months and print the number for month NAME
month() {
  # POSIX requires locale, but here's a fallback using GNU/busybox/BSD date:
  { locale LC_TIME 2>/dev/null \
    || echo && for b in b B; do  # %b = abmon (abbreviated) and %B = mon (full)
      n=0 d='\n'
      while [ $((n+=1)) -le 12 ]; do
        printf "$d"
        datefrom $b $n
        d=';'
      done
    done
  } |awk -v name="$1" '
    BEGIN { name = tolower(name); len = length(name) }	# lowercase, length
    NR == 3 || NR == 4 {	# abbreviated month or full month
      split(tolower($0), list, ";")	# split lowercased list of names
      for (m=1; m<13; m++) if (name == list[m]) exit		# exact match
      if (len > 2) for (m=1; m<13; m++) if (1 == index(list[m], name)) exit
    }
  END { if (m == 13) exit 1; print m }	# exit with error if we failed to match
  '
}

# Usage: dateas [DATE_OPTIONS] [+DATESPEC]
# Convert the date (trumped by "$now") to DATESPEC format
# With BSD date, DATESTRING must itself use DATESPEC +%Y-%m-%d, e.g. 2024-07-28
dateas() {
  local ymd="%Y-%m-%d" tmp="${1#@}" now
  if [ "$1" != "$tmp" ]; then
    now="$tmp"
    shift
  fi
  if [ $# = 0 ]; then set -- +"$ymd"; fi
  if [ -n "$now" ]; then
    # GNU date (any format) or else BSD date (YYYY-MM-DD only)
    date -d "$now" "$@" 2>/dev/null || date -jf "$ymd" "$now" "$@"
  else
    date "$@"
  fi
}

if [ $# = 0 ]; then
  run
fi

sep="\`$TTY\`$$\`"
arr=""
push() { local i; for i in "$@"; do arr="$arr${arr:+$sep}$i"; done; }

needs_arg() { if [ -z "$OPTARG" ]; then die "No arg for --$OPT option"; fi; }

abort=
month=
year=

# official options disallowed with `ncal -C`: b e h(!) H(!) J M o p s S w W
while getopts 139A:B:Cd:hjm:vVW:y-: OPT; do
  if [ "$OPT" = - ]; then  # --long: https://stackoverflow.com/a/28466267/519360
    OPT="${OPTARG%%=*}" OPTARG="${OPTARG#"$OPT"}" OPTARG="${OPTARG#=}"
  fi
  case "$OPT" in
    ( 1 | one* )	bb; push -1 ;;
    ( 3 | three* )	bb; push -3 ;;
    ( 9 | nine* )	bb; push -A4 -B4 ;;
    ( A | after )	bb; needs_arg; push -A "$OPTARG" ;;
    ( B | before )	bb; needs_arg; push -B "$OPTARG" ;;
    ( C )		: "ignoring redundant -C" ;;
    ( d | date )	bb; needs_arg; push -d "$(dateas "@$OPTARG")" ;;
    ( h | help )	help ;;  # note, the other -h is somehow just for ncal
    ( j | julian )	push -j ;;
    ( m | month)	abort=abort; push -m "$OPTARG" ;;	# bypass script
    ( [Vv] | ver* )	version ;;
    ( W | week-min* )	bb; needs_arg; push -W "$OPTARG" ;;
    ( y | year* )	push -y ;;
    ( \? )		die ;; # bad short option (error reported via getopts)
    ( * )		die "Illegal option --$OPT" ;; # bad long option
  esac
done
shift $((OPTIND-1))

if [ "$abort" = abort ]; then
  run "$@"
fi

# Parse remaining parameters into $month and $year
abs="${1#+}"
if [ $# -gt 2 ]; then	# too many arguments
  m="$1" y="$2"
  shift 2
  die "Error: unexpected arguments after month \`$m\` and year \`$y\`: $*"
elif [ -n "$1" ] && ! [ "${abs#-}" -gt 0 ] 2>/dev/null; then # non-numeric month
  month="$(month "$1")" year="$2"
elif [ $# = 2 ]; then
  month="${1#0}" year="$2"	# remove month's leading zero if there is one
elif [ $# = 1 ]; then
  if [ "$abs" != "${1#-}" ]; then
    month="$1"
  else
    year="$1"
  fi
fi

# year by offset or as 2-digit abbrev (no conflicts: ncal only supports year 1+)
case "$year" in
  ( [+-]*[!0-9]* )	die "$self: not a valid year '$year'" ;;
  ( [+-]* )		year=$((${year#+} + $(dateas +%Y))) ;;	# year by offset
  ( \'[0-9][0-9] | [0-9][0-9] ) 			# 2-digit year
    tmp="$(dateas +%Y%j)"	# %j is padded to 3 digits, so Feb 1 = 032
    year="${tmp%?????}${year#\'}"	# use current century for given year
    if [ $((tmp + 50183)) -le ${year}000 ]; then  # if (now + 50.5y <= $year)
      year=$((year - 100))
    elif [ $(( ${year}000 + 50000 )) -lt $tmp ]; then
      year=$((year + 100))
    fi
    ;;
esac

# Relative month
if [ "$month" != "${month#[+-]}" ]; then	# month by offset
  # The leading 1 adds 100 to guard against octal interpretation. We then add
  # the offset and subtract that 100 and one to zero-index, so Jan=0, Dec=11.
  month=$(( 1$(dateas +%m) + ${month#+} - 101 ))
  if [ $month -gt 11 ]; then
    year=$((year + (month + 12)/12))
  elif [ $month -lt 0 ]; then
    year=$((year + (month - 12)/12))
  fi
  # -1 % 12 = -1  so we pad with +10,000y of months:  (120000 + -1) % 12 = 11
  month=$(( (120000 + month) % 12 + 1 ))  # pad, modulo, convert to one-index
fi

if [ -z "$year" ] && [ -n "$month" ]; then  # no year: use the closest to $month
  now="$(dateas +%Y%m)"
  year="${now%%??}"		# current year
  now_month="${now#????}"	# current month
  now_month="${now_month#0}"	# remove zero-padding (no octal!)
  if [ $((month + 6)) -lt $now_month ]; then
    year=$((year + 1))
  elif [ $((now_month + 6)) -lt $month ]; then
    year=$((year - 1))
  fi
fi

run