#!/usr/bin/env bash
# source: /home/_crossfeed/tooling/agent-stack @ HEAD
# semaphore.sh — org-wide agent-turn concurrency gate (z.ai plan: 3
# simultaneous API calls; we approximate by limiting concurrent ACTIVE
# agent processes: headless work-turns + freshly-dispatched turns).
#
# Usage:
#   semaphore.sh status            -> print active count / max
#   semaphore.sh try <tag> <secs>  -> exit 0 + hold slot if free, else exit 1
#   semaphore.sh release <tag>     -> release slot held by <tag>
#   semaphore.sh clean             -> drop stale holds (>MaxAge, default 30m)
#
# Slot dir: /home/_crossfeed/metrics/active/ (one file per active turn,
# filename = <tag>.pid; content = ISO start). Not a hard API-call gate —
# it bounds AGENT TURN concurrency, the controllable unit.
set -uo pipefail

METRICS=${METRICS:-/home/_crossfeed/metrics}
ACTIVE="$METRICS/active"
MAX=${MAX_CONCURRENT:-2}   # headroom of 1 below z.ai cap for interactive PMO use
STALE_SECS=${STALE_SECS:-1800}

mkdir -p "$ACTIVE" 2>/dev/null || true
# graceful degrade: no writable metrics dir -> gate unavailable (exit 99)
[ -w "$ACTIVE" ] || { [ "${1:-}" = status ] && echo "gate=unavailable"; exit 99; }

active_count() {
  local n=0 f
  for f in "$ACTIVE"/*; do
    [ -f "$f" ] || continue
    if [ "$STALE_SECS" -gt 0 ]; then
      local age=$(( $(date +%s) - $(stat -c %Y "$f") ))
      [ "$age" -gt "$STALE_SECS" ] && continue
    fi
    n=$((n+1))
  done
  echo "$n"
}

cmd=${1:-status}
case "$cmd" in
  status)
    echo "active=$(active_count)/$MAX"
    [ "$(active_count)" -lt "$MAX" ] && exit 0 || exit 1
    ;;
  try)
    tag=${2:?tag}; [ "$#" -ge 3 ] || { echo "usage: try <tag> <max-wait-secs>" >&2; exit 2; }
    wait_secs=$3; waited=0
    while true; do
      if [ "$(active_count)" -lt "$MAX" ]; then
        date -Is > "$ACTIVE/$tag.pid" 2>/dev/null && { echo "acquired: $tag"; exit 0; }
        echo "ERROR: cannot write $ACTIVE (perms?)" >&2; exit 2
      fi
      [ "$waited" -ge "$wait_secs" ] && { echo "timeout: no slot after ${wait_secs}s (active=$(active_count)/$MAX)" >&2; exit 1; }
      sleep 10; waited=$((waited+10))
    done
    ;;
  release)
    tag=${2:?tag}
    rm -f "$ACTIVE/$tag.pid" && echo "released: $tag"
    ;;
  clean)
    for f in "$ACTIVE"/*; do
      [ -f "$f" ] || continue
      age=$(( $(date +%s) - $(stat -c %Y "$f") ))
      [ "$age" -gt "$STALE_SECS" ] && { rm -f "$f"; echo "dropped stale: $(basename "$f")"; }
    done
    ;;
  *)
    echo "usage: semaphore.sh {status|try <tag> <secs>|release <tag>|clean}" >&2; exit 2
    ;;
esac