"""Add start_date to tasks and create task dependencies table for Gantt view

Revision ID: 013
Revises: 012
Create Date: 2026-01-05

FEAT-003: Add Gantt view support with task dependencies and start dates.
"""
from typing import Sequence, Union
from alembic import op
import sqlalchemy as sa

revision: str = '013'
down_revision: Union[str, None] = '012'
branch_labels: Union[str, Sequence[str], None] = None
depends_on: Union[str, Sequence[str], None] = None


def upgrade() -> None:
    # Add start_date column to pjctrl_tasks
    op.add_column(
        'pjctrl_tasks',
        sa.Column('start_date', sa.DateTime, nullable=True)
    )

    # Create dependency_type_enum
    dependency_type_enum = sa.Enum(
        'FS', 'SS', 'FF', 'SF',
        name='dependency_type_enum'
    )
    dependency_type_enum.create(op.get_bind(), checkfirst=True)

    # Create pjctrl_task_dependencies table
    op.create_table(
        'pjctrl_task_dependencies',
        sa.Column('id', sa.String(36), primary_key=True),
        sa.Column(
            'predecessor_id',
            sa.String(36),
            sa.ForeignKey('pjctrl_tasks.id', ondelete='CASCADE'),
            nullable=False
        ),
        sa.Column(
            'successor_id',
            sa.String(36),
            sa.ForeignKey('pjctrl_tasks.id', ondelete='CASCADE'),
            nullable=False
        ),
        sa.Column(
            'dependency_type',
            dependency_type_enum,
            default='FS',
            nullable=False
        ),
        sa.Column('lag_days', sa.Integer, default=0, nullable=False),
        sa.Column('created_at', sa.DateTime, server_default=sa.func.now(), nullable=False),
        # Unique constraint to prevent duplicate dependencies
        sa.UniqueConstraint('predecessor_id', 'successor_id', name='uq_predecessor_successor'),
    )

    # Create indexes for efficient dependency lookups
    op.create_index(
        'ix_pjctrl_task_dependencies_predecessor_id',
        'pjctrl_task_dependencies',
        ['predecessor_id']
    )
    op.create_index(
        'ix_pjctrl_task_dependencies_successor_id',
        'pjctrl_task_dependencies',
        ['successor_id']
    )


def downgrade() -> None:
    # Drop indexes
    op.drop_index(
        'ix_pjctrl_task_dependencies_successor_id',
        table_name='pjctrl_task_dependencies'
    )
    op.drop_index(
        'ix_pjctrl_task_dependencies_predecessor_id',
        table_name='pjctrl_task_dependencies'
    )

    # Drop the table
    op.drop_table('pjctrl_task_dependencies')

    # Drop the enum type
    sa.Enum(name='dependency_type_enum').drop(op.get_bind(), checkfirst=True)

    # Remove start_date column from tasks
    op.drop_column('pjctrl_tasks', 'start_date')