tz

#!/usr/bin/env bash
# tz — quick timezone display and converter
# Usage: tz              Show current time in common zones
#        tz <HH:MM> <FROM> <TO>  Convert time between zones
# Zones: utc, est, pst, cet, ist, jst, gmt, ct (or full TZ names)
set -euo pipefail

# Zone aliases
resolve_zone() {
  case "${1,,}" in
    utc|gmt)  echo "UTC" ;;
    est|et)   echo "America/New_York" ;;
    cst|ct)   echo "America/Chicago" ;;
    mst|mt)   echo "America/Denver" ;;
    pst|pt)   echo "America/Los_Angeles" ;;
    cet)      echo "Europe/Berlin" ;;
    gmt+0|uk) echo "Europe/London" ;;
    ist)      echo "Asia/Kolkata" ;;
    jst)      echo "Asia/Tokyo" ;;
    kst)      echo "Asia/Seoul" ;;
    cst-asia) echo "Asia/Shanghai" ;;
    aest)     echo "Australia/Sydney" ;;
    *)        echo "$1" ;;  # pass through full TZ names
  esac
}

if [[ $# -eq 0 ]]; then
  # Show current time in common zones
  echo -e "\033[1m🕐 Current time\033[0m"
  echo ""
  for z in "UTC" "America/New_York:EST" "America/Chicago:CST" "America/Los_Angeles:PST" "Europe/London:GMT" "Europe/Berlin:CET" "Asia/Kolkata:IST" "Asia/Tokyo:JST"; do
    tz_full="${z%%:*}"
    label="${z##*:}"
    time=$(TZ="$tz_full" date +"%H:%M %a %b %d")
    printf "  \033[33m%-4s\033[0m %s\n" "$label" "$time"
  done

elif [[ $# -ge 3 ]]; then
  # Convert: tz 14:30 est pst
  TIME="$1"
  FROM=$(resolve_zone "$2")
  TO=$(resolve_zone "$3")
  
  # Parse time
  HOUR="${TIME%%:*}"
  MIN="${TIME##*:}"
  
  # Convert using date
  RESULT=$(TZ="$TO" date -d "TZ=\"$FROM\" ${HOUR}:${MIN}" +"%H:%M %Z" 2>/dev/null) || {
    # Fallback for systems without GNU date
    echo "ERROR: conversion failed. Need GNU date." >&2
    exit 1
  }
  
  FROM_LABEL=$(TZ="$FROM" date +"%Z")
  TO_LABEL=$(TZ="$TO" date +"%Z")
  
  echo -e "\033[33m${TIME}\033[0m ${FROM_LABEL} → \033[1m${RESULT}\033[0m"

elif [[ $# -eq 1 ]]; then
  # Show time in a specific zone
  ZONE=$(resolve_zone "$1")
  time=$(TZ="$ZONE" date +"%H:%M %Z %a %b %d")
  echo -e "\033[33m${1}\033[0m → \033[1m${time}\033[0m"

else
  cat <<EOF
tz — quick timezone display and converter

Usage:
  tz                    Show current time in common zones
  tz <zone>             Show current time in a specific zone
  tz <HH:MM> <from> <to>  Convert time between zones

Zones: utc, est, cst, pst, cet, ist, jst, gmt, uk, kst, aest
       (or full TZ names like America/New_York)

Examples:
  tz                    # show all zones
  tz est                # show EST time
  tz 14:30 utc est      # convert 14:30 UTC to EST
  tz 9:00 pst jst       # convert 9:00 PST to JST
EOF
fi