#!/usr/bin/python3

import argparse
import datetime
import logging
import os
import psycopg2
from   psycopg2.extras import NamedTupleCursor
from   psycopg2.extensions import quote_ident
import sys
import hashlib

parser = argparse.ArgumentParser(description='Record changes in tables')
parser.add_argument('--dbhost')
parser.add_argument('--dbname')
parser.add_argument('--dbuser')
parser.add_argument('--schema', default='public')

a = parser.parse_args()

conn = ""
if a.dbhost:
    conn += "host='%s' " % a.dbhost
if a.dbname:
    conn += "dbname='%s' " % a.dbname
if a.dbuser:
    conn += "user='%s' " % a.dbuser
db = psycopg2.connect(conn)
csr = db.cursor(cursor_factory=NamedTupleCursor)

# Create table if necessary
audit_table = quote_ident(a.schema, csr) + ".changed_tables"
try:
    csr.execute("select * from " + audit_table)
    csr.fetchone()
except Exception as e:
    db.rollback()
    csr.execute("create table " + audit_table +
                """
                (
                    id serial,
                    table_schema text,
                    table_name text,
                    ts timestamptz,
                    last_seen timestamptz,
                    sha256 text
                )
                """
        )
    db.commit()
try:
    csr.execute("select last_seen from " + audit_table)
    csr.fetchone()
except Exception as e:
    db.rollback()
    csr.execute("alter table " + audit_table + " add column last_seen timestamptz")
    db.commit()


csr.execute("select * from information_schema.tables where table_schema = %s", (a.schema,))

for table in csr.fetchall():
    print(table.table_schema, table.table_name, end="", flush=True)
    q = "select * from " + quote_ident(table.table_schema, csr) + "." + quote_ident(table.table_name, csr)
    hash = hashlib.sha256()
    csr = db.cursor()
    csr.execute(q)
    for r in csr:
        r_bytes = ("\N{US}".join(map(lambda x: str(x), r)) + "\N{RS}").encode()
        hash.update(r_bytes)
    digest = hash.hexdigest()
    csr = db.cursor(cursor_factory=NamedTupleCursor)
    q = """
        with m as (
            select table_schema, table_name, max(ts) as ts
            from {audit_table}
            where table_schema=%(table_schema)s and table_name=%(table_name)s
            group by table_schema, table_name
        )
        select * from {audit_table} natural join m
        """.format(audit_table=audit_table)
    csr.execute(q, {"table_schema": table.table_schema, "table_name": table.table_name})
    old = csr.fetchone()
    if not old or old.sha256 != digest:
        print(" changed", digest, end="")
        q = "insert into {audit_table}(table_schema, table_name, ts, last_seen, sha256) values(%s, %s, now(), now(), %s)".format(audit_table=audit_table)
        csr.execute(q, (table.table_schema, table.table_name, digest))
        db.commit()
    else:
        print(" unchanged", digest, end="")
        q = "update {audit_table} set last_seen=now() where id = %s".format(audit_table=audit_table)
        csr.execute(q, (old.id,))
        db.commit()
    db.rollback() # to close transaction
    print(flush=True)

# vim: tw=99