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#!/usr/bin/python
#
# Copyright (C) 2014  Codethink Limited
#
# 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; version 2 of the License.
#
# 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.


import argparse
import subprocess
import tempfile
import os
import sys


class AppException(Exception):
    pass

class SystemNotCompatibleError(Exception):
    pass

class SystemVersionManager(object):
    def __init__(self):
        self.device, self.current_system = self._get_mount_info()
        self.mount_dir = tempfile.mkdtemp()

    def status(self, msg, *args):
        print msg % args

    def _check_system_exists(self, system_name):
        systems_list = self._get_systems()

        if system_name not in systems_list:
            print "ERROR: the system " + system_name + " doesn't exist"
            sys.exit(1)

    # To get the systems the script lists the systems under the 'systems'
    # folder which are directories and are not symlinks
    def _get_systems(self):
        systems = os.path.join(self.mount_dir, 'systems')
        return [filename for filename in os.listdir(systems)
            if os.path.isdir(os.path.join(systems, filename))
            and not os.path.islink(os.path.join(systems, filename))]

    # To check which system is the default one, it checks the 'ontimeout'
    # value in the extlinux.conf file. If it's not present, then pick
    # the first of the present systems.
    def _get_default(self):
        extlinux = os.path.join(self.mount_dir, 'extlinux.conf')
        for line in open(extlinux,'r'):
            line = line.rstrip('\n')
            key, value= line.split(' ', 1)
            if key == "ontimeout":
                return value
            if key == "label":
                break

        return self.current_system

    def _rewrite_boot_menu(self, device, default, systems):
        temp_config = os.path.join(self.mount_dir, 'extlinux.tmp')
        config = os.path.join(self.mount_dir, 'extlinux.conf')
        with open(temp_config, 'w') as f:
            f.write('default menu.c32\n')
            f.write('timeout 50\n')
            f.write('prompt 0\n')
            f.write('ontimeout ' + default +'\n')
            for system in systems:
                f.write('label ' + system +'\n')
                f.write('kernel /systems/'+ system +'/kernel\n')
                f.write('append root='+ device +' '
                        'rootflags=subvol=systems/'+ system +'/run '
                        'init=/sbin/init rw\n')
        os.rename(temp_config, config)

        default_path = os.path.join(self.mount_dir, 'systems', 'default')
        if os.path.islink(default_path):
            try:
                os.unlink(default_path)
            finally:
                os.symlink(default, default_path)

    def cmd_list (self):
        for system in self._get_systems():
            print system

    def cmd_get_default(self):
        print self._get_default()

    def cmd_get_running(self):
        print self.current_system

    def _parse_deploy_location(self, location):
        label, snapshot = os.path.split(location)
        root, label = os.path.split(label)
        if root != '/systems' or snapshot != 'orig':
            raise AppException(
                    "Invalid deploy location %s. Upgrades should be deployed "
                    "from a Btrfs snapshot following the pattern: "
                    "/systems/$LABEL/orig" % location)
        return label

    def cmd_deploy(self, location):
        '''Client-side deployment of a new base OS version.

        This code assumes that the 'orig' subvolume has been correctly created
        already. In future it could be extended to receive a delta of the
        upgraded version over network somehow.
        '''
        label = self._parse_deploy_location(location)
        version_root = os.path.join(self.mount_dir, 'systems', label)

        orig_dir = os.path.join(version_root, 'orig')
        run_dir = os.path.join(version_root, 'run')
        try:
            self.status(msg="Creating 'run' subvolume")
            subprocess.check_call(
                    ['btrfs', 'subvolume', 'snapshot', orig_dir, run_dir])

            self.status(msg='Updating system configuration')
            log = os.path.join('/var', 'log', 'baserock-system-config-sync.log')

            baserock_system_config_sync = os.environ.get(
                    'BASEROCK_SYSTEM_CONFIG_SYNC',
                    'baserock-system-config-sync')

            with open(log, 'w') as f:
                subprocess.check_call(
                        [baserock-system-config-sync, 'merge',
                         self.current_system, label], stdout=f)

            self.status(msg="Installing the kernel")
            self._install_kernel(version_root)

        except Exception as e:
            subprocess.call(['btrfs', 'subvolume', 'delete', run_dir])
            raise

        self._rewrite_boot_menu(self.device, self._get_default(), self._get_systems())

    def _install_kernel(self, version_root):
        '''Install the kernel outside of 'orig' or 'run' subvolumes

        This code is kind of duplicated in morphlib/writeexts.py.

        '''
        image_names = ['vmlinuz', 'zImage', 'uImage']
        kernel_dest = os.path.join(version_root, 'kernel')
        for name in image_names:
            try_path = os.path.join(version_root, 'run', 'boot', name)
            if os.path.exists(try_path):
                subprocess.check_call(['cp', '-a', try_path, kernel_dest])
                break

    def _get_mount_info(self):
        mountpoint = subprocess.check_output(['findmnt', '/', '-l', '-n',
            '-o', 'SOURCE'])
        device, subvolume = mountpoint.split('[', 1)
        subvolume = subvolume.split('/run',1)[0]
        current_system = os.path.basename(subvolume)

        # Following the symlink of the device.
        device = os.path.realpath(device)
        return device, current_system

    def cmd_remove (self, system_name):
        self._check_system_exists(system_name)

        default_system = self._get_default()

        if system_name == default_system:
            print "ERROR: you can't remove the default system"
            sys.exit(1)
        if system_name == self.current_system:
            print "ERROR: you can't remove the running system"
            sys.exit(1)

        system_root = os.path.join(self.mount_dir, 'systems', system_name)

        subprocess.call(['btrfs', 'subvolume', 'delete',
            os.path.join(system_root, 'run')])
        subprocess.call(['btrfs', 'subvolume', 'delete',
            os.path.join(system_root, 'orig')])
        os.rmdir(system_root)

        self._rewrite_boot_menu(self.device, default_system, self._get_systems())

    def cmd_set_default (self, system_name):
        self._check_system_exists(system_name)
        self._rewrite_boot_menu(self.device, system_name, self._get_systems())

    def mount_fs(self):
        subprocess.check_call(['mount', self.device, self.mount_dir])

    def umount_fs(self):
        subprocess.call(['umount', self.mount_dir])

    def _check_system_compatibility(self):
        menu_file = os.path.join(self.mount_dir, 'menu.c32')
        if not os.path.isfile(menu_file):
            raise SystemNotCompatibleError("menu.c32 not found")

    def main(self, args):

        # create the top-level parser
        parser = argparse.ArgumentParser(prog='system-version-manager')
        subparsers = parser.add_subparsers(help='sub-command help')

        # create the parser for the "list" command
        parser_list = subparsers.add_parser('list',
            help='list show you a list of systems')
        parser_list.set_defaults(action = 'list')

        # create the parser for the "deploy" command
        parser_deploy= subparsers.add_parser('deploy',
            help='deploy an updated base OS version to the running Baserock system')
        parser_deploy.set_defaults(action = 'deploy')
        parser_deploy.add_argument('location')

        # create the parser for the "get-default" command
        parser_get_default = subparsers.add_parser('get-default',
            help='prints the default system')
        parser_get_default.set_defaults(action = 'get-default')

        # create the parser for the "get-running" command
        parser_get_running = subparsers.add_parser('get-running',
            help='prints the running system')
        parser_get_running.set_defaults(action = 'get-running')

        # create the parser for the "remove" command
        parser_remove = subparsers.add_parser('remove', help='remove a system')
        parser_remove.add_argument('system_name', help='name of the system to remove')
        parser_remove.set_defaults(action = 'remove')

        # create the parser for the "set-default" command
        parser_set_default = subparsers.add_parser('set-default',
            help='set a system as default')
        parser_set_default.add_argument('system_name', help='name of the system to set')
        parser_set_default.set_defaults(action = 'set-default')

        args = parser.parse_args(args)
        action = args.action

        self.mount_fs()
        try:
            self._check_system_compatibility()

            if action == "list":
                self.cmd_list()
            elif action == "deploy":
                self.cmd_deploy(args.location)
            elif action == "remove":
                self.cmd_remove(args.system_name)
            elif action == "set-default":
                self.cmd_set_default(args.system_name)
            elif action == "get-default":
                self.cmd_get_default()
            elif action == "get-running":
                self.cmd_get_running()
            else:
                raise NotImplementedError("Unknown command %s" % action)
        except SystemNotCompatibleError, e:
            print "ERROR, system not compatible: %s" % e.args[0]
            raise
        finally:
            self.umount_fs()


if __name__ == "__main__":

    sys_mgr = SystemVersionManager()
    sys_mgr.main(sys.argv[1:])