#!/usr/bin/env bash
# 013-install-pgbouncer - Connection pooling for serverless clients.
#
# Workload: a handful of TPS, but many (serverless) clients -> many short
# connections. PgBouncer fronts PostgreSQL in transaction mode; PostgreSQL
# itself keeps max_connections=30 (010). Server connections go over TCP
# 127.0.0.1:5432 so the existing pg_hba `host ... scram-sha-256` line applies
# unchanged (PgBouncer re-uses the client's SCRAM verifier from userlist.txt).
#
# Listens on 127.0.0.1:6432 ONLY - remote access is a later migration
# (roadmap): flip listen_addr, populate userlist.txt with an app role, open
# the firewall. Until then nothing can connect through it; that is expected.
#
# Populating userlist.txt when the app role exists (SCRAM pass-through):
#   runuser -u postgres -- psql -tAc \
#     "SELECT '\"'||rolname||'\" \"'||rolpassword||'\"' \
#        FROM pg_authid WHERE rolname='APP' AND rolpassword LIKE 'SCRAM%'" \
#     | sudo tee -a /etc/pgbouncer/userlist.txt && sudo systemctl reload pgbouncer
#
# up:    install package (PGDG/Debian repo), write ini + empty userlist,
#        enable + restart service, verify it accepts connections
# down:  stop + disable service, purge package, remove config
set -euo pipefail

INI=/etc/pgbouncer/pgbouncer.ini
USERLIST=/etc/pgbouncer/userlist.txt
LOG=/var/log/postgresql/pgbouncer.log

write_ini() {
  install -d -o postgres -g postgres -m 750 /etc/pgbouncer
  cat > "$INI" <<'EOF'
;; managed by sysmig 013-install-pgbouncer - serverless connection pooler
[databases]
;; server side: TCP + scram against stock pg_hba (127.0.0.1/32 line)
iwanhae = host=127.0.0.1 port=5432 dbname=iwanhae

[pgbouncer]
;; --- client side: localhost only until the remote-access migration ---
listen_addr = 127.0.0.1
listen_port = 6432
unix_socket_dir = /var/run/postgresql

auth_type = scram-sha-256
auth_file = /etc/pgbouncer/userlist.txt
admin_users = iwanhae

;; --- pooling: many short serverless clients, few real workers ---
pool_mode = transaction
max_client_conn = 300
default_pool_size = 20
reserve_pool_size = 5
reserve_pool_timeout = 3

;; named prepared statements in transaction mode (ORMs need this, >=1.22)
max_prepared_statements = 200
ignore_startup_parameters = extra_float_digits

;; --- server connection lifecycle ---
server_reset_query = DISCARD ALL
server_idle_timeout = 60

;; --- process ---
logfile = /var/log/postgresql/pgbouncer.log
pidfile = /var/run/postgresql/pgbouncer.pid
user = postgres
EOF
  chown postgres:postgres "$INI"
  chmod 640 "$INI"
}

case "${1:-}" in
  up)
    if ! dpkg -s pgbouncer >/dev/null 2>&1; then
      export DEBIAN_FRONTEND=noninteractive
      apt-get update -qq
      apt-get install -y pgbouncer >/dev/null
      echo "    pgbouncer installed"
    else
      echo "    pgbouncer already installed"
    fi
    write_ini
    # empty placeholder; populated by the future remote-access migration
    touch "$USERLIST"
    chown postgres:postgres "$USERLIST"
    chmod 640 "$USERLIST"
    systemctl enable pgbouncer >/dev/null
    systemctl restart pgbouncer
    ok=0
    for _ in $(seq 1 10); do
      if pg_isready -h 127.0.0.1 -p 6432 -q 2>/dev/null; then ok=1; break; fi
      sleep 1
    done
    [[ $ok -eq 1 ]] || { echo "FATAL: pgbouncer not accepting on 127.0.0.1:6432 - check $LOG" >&2; exit 1; }
    echo "    listening on 127.0.0.1:6432 (transaction pool, ready for userlist entries)"
    ;;
  status)
    [[ -f $INI ]] || { echo "DRIFT $INI missing"; exit 1; }
    systemctl is-active --quiet pgbouncer || { echo "DRIFT pgbouncer service not active"; exit 1; }
    pg_isready -h 127.0.0.1 -p 6432 -q 2>/dev/null \
      || { echo "DRIFT nothing accepting on 127.0.0.1:6432"; exit 1; }
    grep -q '^pool_mode = transaction' "$INI" || { echo "DRIFT pool_mode not transaction"; exit 1; }
    grep -q '^listen_addr = 127.0.0.1' "$INI" || { echo "DRIFT listen_addr changed (remote access migration?)"; exit 1; }
    echo "OK pgbouncer on 127.0.0.1:6432, transaction mode"
    ;;
  down)
    systemctl disable --now pgbouncer 2>/dev/null || true
    export DEBIAN_FRONTEND=noninteractive
    apt-get purge -y pgbouncer >/dev/null
    rm -rf /etc/pgbouncer "$LOG"
    echo "    pgbouncer stopped, purged, config removed"
    ;;
esac