# management.py:

from django.dispatch import dispatcher
from django.db.models import signals, get_apps, get_models
from django.db import backend, connection, transaction
from sphene.community.models import ApplicationChangelog
from datetime import datetime

def do_changelog(app, created_models, verbosity, **kwargs):
    app_models = get_models( app )
    if app_models == None: return

    sql = ()
    for clazz in app_models:
        changelog = getattr(clazz, 'changelog', None)
        if not changelog: continue
        #changelog = get_changelog(None)

        version = None
        currentversion = changelog[-1][0]
        currentcl = ApplicationChangelog( app_label = clazz._meta.app_label,
                                          model = clazz._meta.object_name.lower(),
                                          version = currentversion,
                                          applied = datetime.today(), )
        try:
            appcl = ApplicationChangelog.objects.filter( app_label = clazz._meta.app_label,
                                                         model = clazz._meta.object_name.lower(), ).latest()
            version = appcl.version
            if currentversion == version:
                continue
        except ApplicationChangelog.DoesNotExist:
            # See if model was just created...
            if clazz in created_models:
                # Store latest version in changelog ...
                currentcl.save()
                continue # No need to do anything ...
            else:
                # We need to do the whole changelog ...
                version = None


        for change in changelog:
            date, changetype, stmt = change
            if version != None and version >= date:
                # This change was already applied ...
                continue

            if changetype == 'alter':
                sqlstmt = 'ALTER TABLE %s %s' % (backend.quote_name(clazz._meta.db_table), stmt)
                sql += (sqlstmt,)
                print "%s: SQL Statement: %s" % (date, sqlstmt)
            elif changetype == 'update':
                sqlstmt = 'UPDATE %s %s' % (backend.quote_name(clazz._meta.db_table), stmt)
                sql += (sqlstmt,)
                print "%s: SQL Statement: %s" % (date, sqlstmt)
            else:
                print "Unknown changetype: %s - %s" % (changetype, str(change))

        # Store new version ...
        currentcl.save()

    if len(sql) > 0:
        confirm = 'x'
        while confirm not in ('yes', 'no'):
            confirm = raw_input("Detected changes - Do you want to execute SQL Statements ? (yes,no): ")
        if confirm == 'yes':
            curs = connection.cursor()
            for sqlstmt in sql:
                curs.execute( sqlstmt )
            transaction.commit_unless_managed()
        else:
            print "Not updating database. You have to do this by hand !"


dispatcher.connect(do_changelog, signal=signals.post_syncdb)




# models.py

class ApplicationChangelog(models.Model):
        app_label = models.CharField(maxlength = 250)
        model = models.CharField(maxlength = 250)
        version = models.CharField(maxlength = 250)
        applied = models.DateTimeField()

        class Meta:
                get_latest_by = 'applied'



# Example changelog entries:
class Post(models.Model):
    # your model fields & co come here
    # ....

    # the changelog entry define the schema evolution over time
    # The list arguments are:
    #   1. A unique and incrementing ID of the changelog entry
    #   2. The type of statement ('alter' and 'update' supported)
    #   3. The SQL statement from AFTER the table name. the 'ALTER TABLE xxxx' or 'UPDATE xxxx' is autogenerated.
    # i usually use '<date> <incrementing number>' to identify each changelog entry
    # but since it uses simple string comparsion anything which simply counts whould be
    # sufficient.
    
    changelog = ( ( '2007-04-07 00', 'alter', 'ALTER author_id DROP NOT NULL', ),
                  ( '2007-06-16 00', 'alter', 'ADD markup varchar(250) NULL', ),
                  )