res_musiconhold: Add new 'playlist' mode

Allow the list of files to be played to be provided explicitly in the
music class's configuration. The primary driver for this change is to
allow URLs to be used for MoH.

Change-Id: I9f43b80b43880980b18b2bee26ec09429d0b92fa

contrib/ast-db-manage/config/versions/fbb7766f17bc_add_playlist_to_moh.py

@@ -0,0 +1,54 @@
+"""add playlist to moh
+
+Revision ID: fbb7766f17bc
+Revises: 3a094a18e75b
+Create Date: 2019-09-18 10:24:18.731798
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = 'fbb7766f17bc'
+down_revision = '3a094a18e75b'
+
+from alembic import op
+import sqlalchemy as sa
+
+
+def enum_update(table_name, column_name, enum_name, enum_values):
+    if op.get_context().bind.dialect.name != 'postgresql':
+        if op.get_context().bind.dialect.name == 'mssql':
+            op.drop_constraint('ck_musiconhold_mode_moh_mode_values', 'musiconhold')
+        op.alter_column(table_name, column_name,
+                        type_=sa.Enum(*enum_values, name=enum_name))
+        return
+
+    # Postgres requires a few more steps
+    tmp = enum_name + '_tmp'
+
+    op.execute('ALTER TYPE ' + enum_name + ' RENAME TO ' + tmp)
+
+    updated = sa.Enum(*enum_values, name=enum_name)
+    updated.create(op.get_bind(), checkfirst=False)
+
+    op.execute('ALTER TABLE ' + table_name + ' ALTER COLUMN ' + column_name +
+               ' TYPE ' + enum_name + ' USING mode::text::' + enum_name)
+
+    op.execute('DROP TYPE ' + tmp)
+
+
+def upgrade():
+    op.create_table(
+        'musiconhold_entry',
+        sa.Column('name', sa.String(80), primary_key=True, nullable=False),
+        sa.Column('position', sa.Integer, primary_key=True, nullable=False),
+        sa.Column('entry', sa.String(1024), nullable=False)
+    )
+    op.create_foreign_key('fk_musiconhold_entry_name_musiconhold', 'musiconhold_entry', 'musiconhold', ['name'], ['name'])
+    enum_update('musiconhold', 'mode', 'moh_mode_values',
+                ['custom', 'files', 'mp3nb', 'quietmp3nb', 'quietmp3', 'playlist'])
+
+
+def downgrade():
+    enum_update('musiconhold', 'mode', 'moh_mode_values',
+                ['custom', 'files', 'mp3nb', 'quietmp3nb', 'quietmp3'])
+    op.drop_table('musiconhold_entry')