#!/usr/bin/env bash

# Minimal throttle runner: queues a command once within a delay window.

set -o pipefail

name="throt"
config_file="${HOME}/.throt"

[[ -r "$config_file" ]] && . "$config_file"

lock_dir="${THROT_LOCK_DIR:-$HOME/tmp/throt-locks}"
log_file="${THROT_LOG_FILE:-$HOME/tmp/throt.log}"

usage() {
  cat <<EOF
Usage: $name --delay <seconds> <cmd ...>
EOF
  exit 1
}

log() {
  local ts
  ts=$(date -Iseconds)
  printf '%s %s\n' "$ts" "$*" >>"$log_file"
}

ensure_dirs() {
  mkdir -p "$lock_dir"
  mkdir -p "$(dirname "$log_file")"
}

file_age() {
  local path="$1" now="$2" ts
  if read -r ts <"$path" 2>/dev/null && [[ "$ts" =~ ^[0-9]+$ ]]; then
    echo $((now - ts))
    return
  fi

  ts=$(stat -f %m "$path" 2>/dev/null || stat -c %Y "$path" 2>/dev/null || echo "$now")
  echo $((now - ts))
}

parse_args() {
  delay=""
  detached=0
  while [[ $# -gt 0 ]]; do
    case "$1" in
      --delay)
        delay="${2:-}"
        shift 2 || usage
        ;;
      --detached)
        detached=1
        shift
        ;;
      --)
        shift
        break
        ;;
      -*)
        usage
        ;;
      *)
        break
        ;;
    esac
  done

  [[ -n "$delay" && "$delay" =~ ^[0-9]+$ && "$delay" -gt 0 ]] || usage
  cmd=("$@")
  [[ ${#cmd[@]} -gt 0 ]] || usage
}

start_detached() {
  local delay="$1" lock_file="$2"
  shift 2
  nohup "$0" --detached --delay "$delay" -- "$@" >/dev/null 2>&1 &
  log "[main] queued delay=$delay lock=$lock_file cmd=${*}"
}

main_run() {
  parse_args "$@"
  ensure_dirs

  local cmd_str="${cmd[*]}"
  local hash
  hash=$(printf '%s' "$cmd_str" | shasum -a 256 | awk '{print $1}')
  local lock_file="${lock_dir}/${hash}.lock"
  local now
  now=$(date +%s)
  local window=$((delay * 5))

  if [[ -f "$lock_file" ]]; then
    local age
    age=$(file_age "$lock_file" "$now")
    if (( age < window )); then
      log "[main] skip existing age=${age}s delay=$delay lock=$lock_file cmd=${cmd_str}"
      exit 0
    fi
    rm -f "$lock_file"
    log "[main] removed stale age=${age}s delay=$delay lock=$lock_file"
  fi

  if ( set -o noclobber; : >"$lock_file" ) 2>/dev/null; then
    printf '%s\n' "$now" >"$lock_file"
    start_detached "$delay" "$lock_file" "${cmd[@]}"
  else
    log "[main] skip lock-race lock=$lock_file cmd=${cmd_str}"
  fi
}

worker_run() {
  parse_args "$@"
  ensure_dirs

  local cmd_str="${cmd[*]}"
  local hash
  hash=$(printf '%s' "$cmd_str" | shasum -a 256 | awk '{print $1}')
  local lock_file="${lock_dir}/${hash}.lock"
  trap 'rm -f "$lock_file"' EXIT

  sleep "$delay"
  log "[worker] start delay=$delay lock=$lock_file cmd=${cmd_str}"
  "${cmd[@]}"
  local status=$?
  log "[worker] done status=$status cmd=${cmd_str}"
  exit "$status"
}

if [[ "${1:-}" == "--detached" ]]; then
  worker_run "$@"
else
  main_run "$@"
fi