add broadcast_message to database

new broadcast_message table. contains a whole bunch of timestamps, a
couple of user ids for who created and who approved, some
personalisation and a template id/version. areas is a jsonb field - it
is expected that this will be an array, for example `["england",
"wales"]`

intended valid state transitions are as follows, from an initial status
of draft

* draft -> pending-approval, rejected
* pending-approval -> broadcasting, rejected, (draft maybe)
* broadcasting -> completed, cancelled

rejected, completed, cancelled and technical-failure are terminating
states.

also copy across the enum switching code from migration 0060 (adding
letter type).

migrations/versions/0323_broadcast_message.py

@@ -0,0 +1,98 @@
+"""
+
+Revision ID: 0323_broadcast_message
+Revises: 0322_broadcast_service_perm
+Create Date: 2020-07-02 11:59:38.734650
+
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.sql import column, func
+from sqlalchemy.dialects import postgresql
+
+from app.models import BroadcastMessage
+
+revision = '0323_broadcast_message'
+down_revision = '0322_broadcast_service_perm'
+
+
+name = 'template_type'
+tmp_name = 'tmp_' + name
+
+old_options = ('sms', 'email', 'letter')
+new_options = old_options + ('broadcast',)
+
+new_type = sa.Enum(*new_options, name=name)
+old_type = sa.Enum(*old_options, name=name)
+
+
+STATUSES = [
+    'draft',
+    'pending-approval',
+    'rejected',
+    'broadcasting',
+    'completed',
+    'cancelled',
+    'technical-failure',
+]
+
+
+def upgrade():
+    op.execute(f'ALTER TYPE {name} RENAME TO {tmp_name}')
+    new_type.create(op.get_bind())
+
+    for table in ['templates', 'templates_history', 'service_contact_list']:
+        op.execute(f'ALTER TABLE {table} ALTER COLUMN template_type TYPE {name} USING template_type::text::{name}')
+
+    op.execute(f'DROP TYPE {tmp_name}')
+
+    broadcast_status_type = op.create_table(
+        'broadcast_status_type',
+        sa.Column('name', sa.String(), nullable=False),
+        sa.PrimaryKeyConstraint('name')
+    )
+    op.bulk_insert(broadcast_status_type, [{'name': state} for state in STATUSES])
+
+    op.create_table(
+        'broadcast_message',
+        sa.Column('id', postgresql.UUID(as_uuid=True), nullable=False),
+        sa.Column('service_id', postgresql.UUID(as_uuid=True)),
+        sa.Column('template_id', postgresql.UUID(as_uuid=True), nullable=False),
+        sa.Column('template_version', sa.Integer(), nullable=False),
+        sa.Column('_personalisation', sa.String()),
+        sa.Column('areas', postgresql.JSONB(none_as_null=True, astext_type=sa.Text())),
+        sa.Column('status', sa.String()),
+        sa.Column('starts_at', sa.DateTime()),
+        sa.Column('finishes_at', sa.DateTime()),
+        sa.Column('created_at', sa.DateTime(), nullable=False),
+        sa.Column('approved_at', sa.DateTime()),
+        sa.Column('cancelled_at', sa.DateTime()),
+        sa.Column('updated_at', sa.DateTime()),
+        sa.Column('created_by_id', postgresql.UUID(as_uuid=True), nullable=False),
+        sa.Column('approved_by_id', postgresql.UUID(as_uuid=True)),
+        sa.Column('cancelled_by_id', postgresql.UUID(as_uuid=True)),
+
+        sa.ForeignKeyConstraint(['approved_by_id'], ['users.id'], ),
+        sa.ForeignKeyConstraint(['cancelled_by_id'], ['users.id'], ),
+        sa.ForeignKeyConstraint(['created_by_id'], ['users.id'], ),
+        sa.ForeignKeyConstraint(['service_id'], ['services.id'], ),
+        sa.ForeignKeyConstraint(['template_id', 'template_version'], ['templates_history.id', 'templates_history.version'], ),
+        sa.PrimaryKeyConstraint('id')
+    )
+
+    op.add_column('templates', sa.Column('broadcast_data', postgresql.JSONB(none_as_null=True, astext_type=sa.Text())))
+    op.add_column('templates_history', sa.Column('broadcast_data', postgresql.JSONB(none_as_null=True, astext_type=sa.Text())))
+
+
+def downgrade():
+    op.execute(f'ALTER TYPE {name} RENAME TO {tmp_name}')
+    old_type.create(op.get_bind())
+
+    for table in ['templates', 'templates_history', 'service_contact_list']:
+        op.execute(f'ALTER TABLE {table} ALTER COLUMN template_type TYPE {name} USING template_type::text::{name}')
+    op.execute(f'DROP TYPE {tmp_name}')
+
+    op.drop_column('templates_history', 'broadcast_data')
+    op.drop_column('templates', 'broadcast_data')
+    op.drop_table('broadcast_message')
+    op.drop_table('broadcast_status_type')