#!/bin/bash

readonly Prime=foo1.example.com
readonly Replica=foo2.example.com

wal_location_to_64bits()
{
    local id="${1%%/*}"
    local offset="${1##*/}"
    echo $((0xFF000000 * 0x$id + 0x$offset))
}

declare Prime_SSE Prime_LSN
declare Second_SSE Second_Recv_LSN Second_Repl_LSN

IFS=$'\t' read -r Prime_LSN \
        <<<$(psql --host=$Prime -XAt -F$'\t' \
                -c "select pg_current_wal_lsn();")
IFS=$'\t' read -r Second_Timestamp Second_Recv_LSN Second_Repl_LSN \
        <<<$(psql --host=$Replica -XAt -F$'\t' \
                -c "select pg_last_wal_receive_lsn()
                        , pg_last_wal_replay_lsn();")

Prime_SSE=$(date +"%s.%N" -d "$Prime_Timestamp")
Second_SSE=$(date +"%s.%N" -d "$Second_Timestamp")
declare Query_Lag=$(echo "$Second_SSE - $Prime_SSE" | bc -l)

printf "Query Lag: %f\n" $Query_Lag

echo "LSN:"
printf "  Prime:            = %s\n" $Prime_LSN
printf "  Replica Received: = %s\n" $Second_Recv_LSN
printf "  Replica Replayed: = %s\n" $Second_Repl_LSN

declare -i Prime_Bytes=$(wal_location_to_64bits $Prime_LSN)
declare -i Second_Recv_Bytes=$(wal_location_to_64bits $Second_Recv_LSN)
declare -i Second_Repl_Bytes=$(wal_location_to_64bits $Second_Repl_LSN)

echo "Backlog Bytes:"
printf "  Received = %'18d\n" $(echo "($Prime_Bytes - $Second_Recv_Bytes)" | bc -l)
printf "  Replayed = %'18d\n" $(echo "($Prime_Bytes - $Second_Repl_Bytes)" | bc -l)