#!/usr/bin/python
#

# Copyright (C) 2008 Google Inc.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
# 02110-1301, USA.

"""Simple first-fit allocator for ganeti instance allocation framework.

This allocator just iterates over the nodes and selects the first one
that fits in both memory and disk space, without any consideration for
equal spread or VCPU oversubscription.

"""

import simplejson
import sys


def SelectNode(nodes, request, to_skip):
  """Select a node for the given instance

  """
  disk_size = request["disk_space_total"]
  selected = None
  for nname, ninfo in nodes.iteritems():
    if nname in to_skip:
      continue
    if request["memory"] > ninfo["free_memory"]:
      continue
    if disk_size > ninfo["free_disk"]:
      continue
    selected = nname
    break
  return selected


def OutputError(text, exit_code=1):
  """Builds an error response with a given info message.

  """
  error = {
    "success": False,
    "info": text,
    "nodes": [],
    }
  print simplejson.dumps(error, indent=2)
  return exit_code


def main():
  """Main function.

  """
  if len(sys.argv) < 2:
    print >> sys.stderr, "Usage: %s cluster.json" % (sys.argv[0])
    return 1

  data = simplejson.load(open(sys.argv[1]))

  nodes =  data["nodes"]
  request = data["request"]
  req_type = request["type"]
  offline_nodes = [name for name in nodes if nodes[name]["offline"]]
  if req_type == "allocate":
    forbidden_nodes = offline_nodes
    inst_data = request
  elif req_type == "relocate":
    idict = data["instances"][request["name"]]
    forbidden_nodes = idict["nodes"] + offline_nodes
    inst_data = idict
    inst_data["disk_space_total"] = request["disk_space_total"]
  else:
    return OutputError("Unsupported allocator mode '%s'" % req_type)

  result_nodes = []
  while len(result_nodes) < request["required_nodes"]:
    new_selection = SelectNode(nodes, inst_data, result_nodes+forbidden_nodes)
    if new_selection is None:
      return OutputError("Can't find a suitable node for position %s"
                         " (already selected: %s)" %
                         (len(result_nodes) + 1, ", ".join(result_nodes)),
                         exit_code=0)
    result_nodes.append(new_selection)

  result = {
    "success": True,
    "info": "Allocation successful",
    "nodes": result_nodes,
    }
  print simplejson.dumps(result, indent=2)
  return 0


if __name__ == "__main__":
    sys.exit(main())