#!/usr/bin/python
import argparse
from contextlib import contextmanager
from datetime import datetime
import ldb
import os
from samba import Ldb
from samba.auth import system_session
from samba.param import LoadParm
import shutil
import subprocess
import sys
import tdb
import time


def install_python_lmdb():
    from univention.config_registry import ConfigRegistry, handler_set
    ucr = ConfigRegistry()
    ucr.load()
    if not ucr.is_true("repository/online/unmaintained"):
        handler_set(["repository/online/unmaintained=yes"])
        subprocess.call(("univention-install", "python-lmdb"))


try:
    import lmdb
except ImportError:
    install_python_lmdb()
    import lmdb

# Default the mdb file size for the individual partitions to 8GB
DEFAULT_BACKEND_SIZE = 8 * 1024**3

def migrate_sam_ldb_backends_from_tdb_to_mdb(ldb_tdb_backend_dir, ldb_mdb_backend_dir):
    print("PROCESS: Migrating sam.ldb.d backend files from TDB to MDB")
    ldb_tdb_backend_files = [fn for fn in os.listdir(ldb_tdb_backend_dir) if fn.endswith(".ldb")]
    for fn in ldb_tdb_backend_files:
        t = tdb.Tdb(os.path.join(ldb_tdb_backend_dir, fn))
        mdb_env = lmdb.open(os.path.join(ldb_mdb_backend_dir, fn), map_size=DEFAULT_BACKEND_SIZE, subdir=False)
        os.chmod(mdb_env.path(), 0o600)

        with mdb_env.begin(write=True) as txn:
            for i in t:
                txn.put(i, t[i])
    print("PROCESS: Migration of sam.ldb.d backend files done")


@contextmanager
def sam_ldb_backends_from_tdb_to_mdb(lp):
    print("PROCESS: Creating new sam.ldb.d directory for Migration")
    sam_backend_dir = lp.private_path("sam.ldb.d")
    sam_tdb_backend_dir = lp.private_path("sam.ldb.tdb.d")
    sam_ldb = lp.private_path("sam.ldb")
    sam_ldb_bak = lp.private_path("sam.ldb.tdb")

    try:
        os.rename(sam_backend_dir, sam_tdb_backend_dir)
    except OSError:
        print("ERROR: An exception occurred, aborting migration")
        raise

    os.mkdir(sam_backend_dir)
    os.chmod(sam_backend_dir, 0o700)

    shutil.copy(sam_ldb, sam_ldb_bak)
    os.chmod(sam_ldb_bak, 0o600)

    migrate_sam_ldb_backends_from_tdb_to_mdb(sam_tdb_backend_dir, sam_backend_dir)

    try:
        yield
    except Exception:
        print("ERROR: An exception occurred, reverting sam.ldb.d to original state")
        shutil.rmtree(sam_backend_dir)
        os.rename(sam_tdb_backend_dir, sam_backend_dir)
        os.unlink(sam_ldb)
        os.rename(sam_ldb_bak, sam_ldb)
        raise

    print("PROCESS: Moving metadata file to new sam.ldb.d directory")
    os.rename(os.path.join(sam_tdb_backend_dir, "metadata.tdb"), os.path.join(sam_backend_dir, "metadata.tdb"))


def open_samdb_raw(lp):
    # Use options=["modules:"] to keep the attached LDB modules from loading
    samdb_path = lp.private_path("sam.ldb")
    return Ldb(url=samdb_path, session_info=system_session(),
                            lp=lp, options=["modules:"])


def activate_mdb(lp):
    print("PROCESS: Switching sam.ldb from TDB to MDB")
    samdb = open_samdb_raw(lp)

    samdb.transaction_start()
    try:
        delta = ldb.Message()
        delta.dn = ldb.Dn(samdb, "@PARTITION")
        delta["backendStore"] = \
           ldb.MessageElement("mdb",
                           ldb.FLAG_MOD_REPLACE,
                           "backendStore")
        samdb.modify(delta)

        delta = ldb.Message()
        delta.dn = ldb.Dn(samdb, "@SAMBA_DSDB")
        delta["requiredFeatures"] = \
           ldb.MessageElement("lmdbLevelOne",
                           ldb.FLAG_MOD_ADD,
                           "requiredFeatures")
        samdb.modify(delta)
    except ldb.LdbError:
        samdb.transaction_cancel()
        print("PROCESS: Switching sam.ldb from TDB to MDB failed")
        raise
    else:
        samdb.transaction_commit()
        print("PROCESS: Switching sam.ldb from TDB to MDB successful")


@contextmanager
def stopped_samba_and_s4c():
    print("PROCESS: Stopping Samba and S4-Connector")
    subprocess.call(("systemctl", "stop", "univention-s4-connector"))
    subprocess.call(("/etc/init.d/samba", "stop"))

    try:
        yield
    except Exception:
        raise

    print("PROCESS: Starting Samba and S4-Connector again")
    subprocess.call(("/etc/init.d/samba", "start"))
    time.sleep(5)
    subprocess.call(("systemctl", "start", "univention-s4-connector"))


def sam_ldb_is_using_mdb(lp):
    samdb = open_samdb_raw(lp)
    res = samdb.search(base="@PARTITION", scope=ldb.SCOPE_BASE, attrs=["backendStore"])
    return (res and "backendStore" in res[0] and str(res[0]["backendStore"]) == "mdb")


if __name__ == "__main__":
    parser = argparse.ArgumentParser(description="Migrate sam.ldb from TDB to MDB")
    parser.add_argument("--skip-dbcheck", action='store_true')
    args = parser.parse_args()

    lp = LoadParm()

    if sam_ldb_is_using_mdb(lp):
        print("INFO: Nothing to do, sam.ldb is already using MDB")
        sys.exit(0)

    with stopped_samba_and_s4c():
        if not args.skip_dbcheck:
            print("PROCESS: Running pre-migration check of sam.ldb database")
            if subprocess.call(("samba-tool", "dbcheck", "--cross-ncs")):
                sys.exit(1)

        t0 = datetime.now()

        with sam_ldb_backends_from_tdb_to_mdb(lp):
            activate_mdb(lp)

        duration = str(datetime.now() - t0).split('.')[:-1][0]
        print("INFO: Duration: %s" % duration)

        if not args.skip_dbcheck:
            print("PROCESS: Running post-migration check of sam.ldb database")
            if subprocess.call(("samba-tool", "dbcheck", "--cross-ncs")):
                sys.exit(1)