import sys
import time

from django.conf import settings
from django.core.management import call_command

# The prefix to put on the default database name when creating
# the test database.
TEST_DATABASE_PREFIX = 'test_'

class BaseDatabaseCreation(object):
    """
    This class encapsulates all backend-specific differences that pertain to
    database *creation*, such as the column types to use for particular Django
    Fields, the SQL used to create and destroy tables, and the creation and
    destruction of test databases.
    """
    data_types = {}

    def __init__(self, connection):
        self.connection = connection

    def _digest(self, *args):
        """
        Generates a 32-bit digest of a set of arguments that can be used to
        shorten identifying names.
        """
        return '%x' % (abs(hash(args)) % 4294967296L)  # 2**32

    def sql_create_model(self, model, style, known_models=set()):
        """
        Returns the SQL required to create a single model, as a tuple of:
            (list_of_sql, pending_references_dict)
        """
        from django.db import models

        opts = model._meta
        if not opts.managed or opts.proxy:
            return [], {}
        final_output = []
        table_output = []
        pending_references = {}
        qn = self.connection.ops.quote_name
        for f in opts.local_fields:
            col_type = f.db_type(connection=self.connection)
            tablespace = f.db_tablespace or opts.db_tablespace
            if col_type is None:
                # Skip ManyToManyFields, because they're not represented as
                # database columns in this table.
                continue
            # Make the definition (e.g. 'foo VARCHAR(30)') for this field.
            field_output = [style.SQL_FIELD(qn(f.column)),
                style.SQL_COLTYPE(col_type)]
            if not f.null:
                field_output.append(style.SQL_KEYWORD('NOT NULL'))
            if f.primary_key:
                field_output.append(style.SQL_KEYWORD('PRIMARY KEY'))
            elif f.unique:
                field_output.append(style.SQL_KEYWORD('UNIQUE'))
            if tablespace and f.unique:
                # We must specify the index tablespace inline, because we
                # won't be generating a CREATE INDEX statement for this field.
                field_output.append(self.connection.ops.tablespace_sql(tablespace, inline=True))
            if f.rel:
                ref_output, pending = self.sql_for_inline_foreign_key_references(f, known_models, style)
                if pending:
                    pr = pending_references.setdefault(f.rel.to, []).append((model, f))
                else:
                    field_output.extend(ref_output)
            table_output.append(' '.join(field_output))
        for field_constraints in opts.unique_together:
            table_output.append(style.SQL_KEYWORD('UNIQUE') + ' (%s)' % \
                ", ".join([style.SQL_FIELD(qn(opts.get_field(f).column)) for f in field_constraints]))

        full_statement = [style.SQL_KEYWORD('CREATE TABLE') + ' ' + style.SQL_TABLE(qn(opts.db_table)) + ' (']
        for i, line in enumerate(table_output): # Combine and add commas.
            full_statement.append('    %s%s' % (line, i < len(table_output)-1 and ',' or ''))
        full_statement.append(')')
        if opts.db_tablespace:
            full_statement.append(self.connection.ops.tablespace_sql(opts.db_tablespace))
        full_statement.append(';')
        final_output.append('\n'.join(full_statement))

        if opts.has_auto_field:
            # Add any extra SQL needed to support auto-incrementing primary keys.
            auto_column = opts.auto_field.db_column or opts.auto_field.name
            autoinc_sql = self.connection.ops.autoinc_sql(opts.db_table, auto_column)
            if autoinc_sql:
                for stmt in autoinc_sql:
                    final_output.append(stmt)

        return final_output, pending_references

    def sql_for_inline_foreign_key_references(self, field, known_models, style):
        "Return the SQL snippet defining the foreign key reference for a field"
        qn = self.connection.ops.quote_name
        if field.rel.to in known_models:
            output = [style.SQL_KEYWORD('REFERENCES') + ' ' + \
                style.SQL_TABLE(qn(field.rel.to._meta.db_table)) + ' (' + \
                style.SQL_FIELD(qn(field.rel.to._meta.get_field(field.rel.field_name).column)) + ')' +
                self.connection.ops.deferrable_sql()
            ]
            pending = False
        else:
            # We haven't yet created the table to which this field
            # is related, so save it for later.
            output = []
            pending = True

        return output, pending

    def sql_for_pending_references(self, model, style, pending_references):
        "Returns any ALTER TABLE statements to add constraints after the fact."
        from django.db.backends.util import truncate_name

        if not model._meta.managed or model._meta.proxy:
            return []
        qn = self.connection.ops.quote_name
        final_output = []
        opts = model._meta
        if model in pending_references:
            for rel_class, f in pending_references[model]:
                rel_opts = rel_class._meta
                r_table = rel_opts.db_table
                r_col = f.column
                table = opts.db_table
                col = opts.get_field(f.rel.field_name).column
                # For MySQL, r_name must be unique in the first 64 characters.
                # So we are careful with character usage here.
                r_name = '%s_refs_%s_%s' % (r_col, col, self._digest(r_table, table))
                final_output.append(style.SQL_KEYWORD('ALTER TABLE') + ' %s ADD CONSTRAINT %s FOREIGN KEY (%s) REFERENCES %s (%s)%s;' % \
                    (qn(r_table), qn(truncate_name(r_name, self.connection.ops.max_name_length())),
                    qn(r_col), qn(table), qn(col),
                    self.connection.ops.deferrable_sql()))
            del pending_references[model]
        return final_output

    def sql_for_many_to_many(self, model, style):
        "Return the CREATE TABLE statments for all the many-to-many tables defined on a model"
        import warnings
        warnings.warn(
            'Database creation API for m2m tables has been deprecated. M2M models are now automatically generated',
            PendingDeprecationWarning
        )

        output = []
        for f in model._meta.local_many_to_many:
            if model._meta.managed or f.rel.to._meta.managed:
                output.extend(self.sql_for_many_to_many_field(model, f, style))
        return output

    def sql_for_many_to_many_field(self, model, f, style):
        "Return the CREATE TABLE statements for a single m2m field"
        import warnings
        warnings.warn(
            'Database creation API for m2m tables has been deprecated. M2M models are now automatically generated',
            PendingDeprecationWarning
        )

        from django.db import models
        from django.db.backends.util import truncate_name

        output = []
        if f.auto_created:
            opts = model._meta
            qn = self.connection.ops.quote_name
            tablespace = f.db_tablespace or opts.db_tablespace
            if tablespace:
                sql = self.connection.ops.tablespace_sql(tablespace, inline=True)
                if sql:
                    tablespace_sql = ' ' + sql
                else:
                    tablespace_sql = ''
            else:
                tablespace_sql = ''
            table_output = [style.SQL_KEYWORD('CREATE TABLE') + ' ' + \
                style.SQL_TABLE(qn(f.m2m_db_table())) + ' (']
            table_output.append('    %s %s %s%s,' %
                (style.SQL_FIELD(qn('id')),
                style.SQL_COLTYPE(models.AutoField(primary_key=True).db_type(connection=self.connection)),
                style.SQL_KEYWORD('NOT NULL PRIMARY KEY'),
                tablespace_sql))

            deferred = []
            inline_output, deferred = self.sql_for_inline_many_to_many_references(model, f, style)
            table_output.extend(inline_output)

            table_output.append('    %s (%s, %s)%s' %
                (style.SQL_KEYWORD('UNIQUE'),
                style.SQL_FIELD(qn(f.m2m_column_name())),
                style.SQL_FIELD(qn(f.m2m_reverse_name())),
                tablespace_sql))
            table_output.append(')')
            if opts.db_tablespace:
                # f.db_tablespace is only for indices, so ignore its value here.
                table_output.append(self.connection.ops.tablespace_sql(opts.db_tablespace))
            table_output.append(';')
            output.append('\n'.join(table_output))

            for r_table, r_col, table, col in deferred:
                r_name = '%s_refs_%s_%s' % (r_col, col, self._digest(r_table, table))
                output.append(style.SQL_KEYWORD('ALTER TABLE') + ' %s ADD CONSTRAINT %s FOREIGN KEY (%s) REFERENCES %s (%s)%s;' %
                (qn(r_table),
                qn(truncate_name(r_name, self.connection.ops.max_name_length())),
                qn(r_col), qn(table), qn(col),
                self.connection.ops.deferrable_sql()))

            # Add any extra SQL needed to support auto-incrementing PKs
            autoinc_sql = self.connection.ops.autoinc_sql(f.m2m_db_table(), 'id')
            if autoinc_sql:
                for stmt in autoinc_sql:
                    output.append(stmt)
        return output

    def sql_for_inline_many_to_many_references(self, model, field, style):
        "Create the references to other tables required by a many-to-many table"
        import warnings
        warnings.warn(
            'Database creation API for m2m tables has been deprecated. M2M models are now automatically generated',
            PendingDeprecationWarning
        )

        from django.db import models
        opts = model._meta
        qn = self.connection.ops.quote_name

        table_output = [
            '    %s %s %s %s (%s)%s,' %
                (style.SQL_FIELD(qn(field.m2m_column_name())),
                style.SQL_COLTYPE(models.ForeignKey(model).db_type(connection=self.connection)),
                style.SQL_KEYWORD('NOT NULL REFERENCES'),
                style.SQL_TABLE(qn(opts.db_table)),
                style.SQL_FIELD(qn(opts.pk.column)),
                self.connection.ops.deferrable_sql()),
            '    %s %s %s %s (%s)%s,' %
                (style.SQL_FIELD(qn(field.m2m_reverse_name())),
                style.SQL_COLTYPE(models.ForeignKey(field.rel.to).db_type(connection=self.connection)),
                style.SQL_KEYWORD('NOT NULL REFERENCES'),
                style.SQL_TABLE(qn(field.rel.to._meta.db_table)),
                style.SQL_FIELD(qn(field.rel.to._meta.pk.column)),
                self.connection.ops.deferrable_sql())
        ]
        deferred = []

        return table_output, deferred

    def sql_indexes_for_model(self, model, style):
        "Returns the CREATE INDEX SQL statements for a single model"
        if not model._meta.managed or model._meta.proxy:
            return []
        output = []
        for f in model._meta.local_fields:
            output.extend(self.sql_indexes_for_field(model, f, style))
        return output

    def sql_indexes_for_field(self, model, f, style):
        "Return the CREATE INDEX SQL statements for a single model field"
        from django.db.backends.util import truncate_name

        if f.db_index and not f.unique:
            qn = self.connection.ops.quote_name
            tablespace = f.db_tablespace or model._meta.db_tablespace
            if tablespace:
                sql = self.connection.ops.tablespace_sql(tablespace)
                if sql:
                    tablespace_sql = ' ' + sql
                else:
                    tablespace_sql = ''
            else:
                tablespace_sql = ''
            i_name = '%s_%s' % (model._meta.db_table, self._digest(f.column))
            output = [style.SQL_KEYWORD('CREATE INDEX') + ' ' +
                style.SQL_TABLE(qn(truncate_name(i_name, self.connection.ops.max_name_length()))) + ' ' +
                style.SQL_KEYWORD('ON') + ' ' +
                style.SQL_TABLE(qn(model._meta.db_table)) + ' ' +
                "(%s)" % style.SQL_FIELD(qn(f.column)) +
                "%s;" % tablespace_sql]
        else:
            output = []
        return output

    def sql_destroy_model(self, model, references_to_delete, style):
        "Return the DROP TABLE and restraint dropping statements for a single model"
        if not model._meta.managed or model._meta.proxy:
            return []
        # Drop the table now
        qn = self.connection.ops.quote_name
        output = ['%s %s;' % (style.SQL_KEYWORD('DROP TABLE'),
                              style.SQL_TABLE(qn(model._meta.db_table)))]
        if model in references_to_delete:
            output.extend(self.sql_remove_table_constraints(model, references_to_delete, style))

        if model._meta.has_auto_field:
            ds = self.connection.ops.drop_sequence_sql(model._meta.db_table)
            if ds:
                output.append(ds)
        return output

    def sql_remove_table_constraints(self, model, references_to_delete, style):
        from django.db.backends.util import truncate_name

        if not model._meta.managed or model._meta.proxy:
            return []
        output = []
        qn = self.connection.ops.quote_name
        for rel_class, f in references_to_delete[model]:
            table = rel_class._meta.db_table
            col = f.column
            r_table = model._meta.db_table
            r_col = model._meta.get_field(f.rel.field_name).column
            r_name = '%s_refs_%s_%s' % (col, r_col, self._digest(table, r_table))
            output.append('%s %s %s %s;' % \
                (style.SQL_KEYWORD('ALTER TABLE'),
                style.SQL_TABLE(qn(table)),
                style.SQL_KEYWORD(self.connection.ops.drop_foreignkey_sql()),
                style.SQL_FIELD(qn(truncate_name(r_name, self.connection.ops.max_name_length())))))
        del references_to_delete[model]
        return output

    def sql_destroy_many_to_many(self, model, f, style):
        "Returns the DROP TABLE statements for a single m2m field"
        import warnings
        warnings.warn(
            'Database creation API for m2m tables has been deprecated. M2M models are now automatically generated',
            PendingDeprecationWarning
        )

        qn = self.connection.ops.quote_name
        output = []
        if f.auto_created:
            output.append("%s %s;" % (style.SQL_KEYWORD('DROP TABLE'),
                style.SQL_TABLE(qn(f.m2m_db_table()))))
            ds = self.connection.ops.drop_sequence_sql("%s_%s" % (model._meta.db_table, f.column))
            if ds:
                output.append(ds)
        return output

    def create_test_db(self, verbosity=1, autoclobber=False):
        """
        Creates a test database, prompting the user for confirmation if the
        database already exists. Returns the name of the test database created.
        """
        if verbosity >= 1:
            print "Creating test database '%s'..." % self.connection.alias

        test_database_name = self._create_test_db(verbosity, autoclobber)

        self.connection.close()
        self.connection.settings_dict["NAME"] = test_database_name
        can_rollback = self._rollback_works()
        self.connection.settings_dict["SUPPORTS_TRANSACTIONS"] = can_rollback

        call_command('syncdb', verbosity=verbosity, interactive=False, database=self.connection.alias)

        if settings.CACHE_BACKEND.startswith('db://'):
            from django.core.cache import parse_backend_uri
            _, cache_name, _ = parse_backend_uri(settings.CACHE_BACKEND)
            call_command('createcachetable', cache_name)

        # Get a cursor (even though we don't need one yet). This has
        # the side effect of initializing the test database.
        cursor = self.connection.cursor()

        return test_database_name

    def _create_test_db(self, verbosity, autoclobber):
        "Internal implementation - creates the test db tables."
        suffix = self.sql_table_creation_suffix()

        if self.connection.settings_dict['TEST_NAME']:
            test_database_name = self.connection.settings_dict['TEST_NAME']
        else:
            test_database_name = TEST_DATABASE_PREFIX + self.connection.settings_dict['NAME']

        qn = self.connection.ops.quote_name

        # Create the test database and connect to it. We need to autocommit
        # if the database supports it because PostgreSQL doesn't allow
        # CREATE/DROP DATABASE statements within transactions.
        cursor = self.connection.cursor()
        self.set_autocommit()
        try:
            cursor.execute("CREATE DATABASE %s %s" % (qn(test_database_name), suffix))
        except Exception, e:
            sys.stderr.write("Got an error creating the test database: %s\n" % e)
            if not autoclobber:
                confirm = raw_input("Type 'yes' if you would like to try deleting the test database '%s', or 'no' to cancel: " % test_database_name)
            if autoclobber or confirm == 'yes':
                try:
                    if verbosity >= 1:
                        print "Destroying old test database..."
                    cursor.execute("DROP DATABASE %s" % qn(test_database_name))
                    if verbosity >= 1:
                        print "Creating test database..."
                    cursor.execute("CREATE DATABASE %s %s" % (qn(test_database_name), suffix))
                except Exception, e:
                    sys.stderr.write("Got an error recreating the test database: %s\n" % e)
                    sys.exit(2)
            else:
                print "Tests cancelled."
                sys.exit(1)

        return test_database_name

    def _rollback_works(self):
        cursor = self.connection.cursor()
        cursor.execute('CREATE TABLE ROLLBACK_TEST (X INT)')
        self.connection._commit()
        cursor.execute('INSERT INTO ROLLBACK_TEST (X) VALUES (8)')
        self.connection._rollback()
        cursor.execute('SELECT COUNT(X) FROM ROLLBACK_TEST')
        count, = cursor.fetchone()
        cursor.execute('DROP TABLE ROLLBACK_TEST')
        self.connection._commit()
        return count == 0

    def destroy_test_db(self, old_database_name, verbosity=1):
        """
        Destroy a test database, prompting the user for confirmation if the
        database already exists. Returns the name of the test database created.
        """
        if verbosity >= 1:
            print "Destroying test database '%s'..." % self.connection.alias
        self.connection.close()
        test_database_name = self.connection.settings_dict['NAME']
        self.connection.settings_dict['NAME'] = old_database_name

        self._destroy_test_db(test_database_name, verbosity)

    def _destroy_test_db(self, test_database_name, verbosity):
        "Internal implementation - remove the test db tables."
        # Remove the test database to clean up after
        # ourselves. Connect to the previous database (not the test database)
        # to do so, because it's not allowed to delete a database while being
        # connected to it.
        cursor = self.connection.cursor()
        self.set_autocommit()
        time.sleep(1) # To avoid "database is being accessed by other users" errors.
        cursor.execute("DROP DATABASE %s" % self.connection.ops.quote_name(test_database_name))
        self.connection.close()

    def set_autocommit(self):
        "Make sure a connection is in autocommit mode."
        if hasattr(self.connection.connection, "autocommit"):
            if callable(self.connection.connection.autocommit):
                self.connection.connection.autocommit(True)
            else:
                self.connection.connection.autocommit = True
        elif hasattr(self.connection.connection, "set_isolation_level"):
            self.connection.connection.set_isolation_level(0)

    def sql_table_creation_suffix(self):
        "SQL to append to the end of the test table creation statements"
        return ''
