"""Unified Task System (F.14).

Adds polymorphic assignment/entity/creator fields, subtasks, dependencies,
goals/milestones and agent-subtask support to the tasks table. Migrates
legacy ``contact_id``/``assigned_to`` values into the polymorphic fields and
migrates existing ``agent_subtasks`` rows into tasks with
``task_type='agent_subtask'``.

Revision ID: 0124
Revises: 0123
"""

from alembic import op
import sqlalchemy as sa
from sqlalchemy.dialects.postgresql import JSONB, UUID as PGUUID

revision = "0124"
down_revision = "0123"
branch_labels = None
depends_on = None


def _table_exists(conn, table_name: str) -> bool:
    """True when the table exists (dual-path convergence, Gate B).

    On a fresh install the tasks plugin SQL migration has not run yet when
    Alembic reaches this revision — skip instead of failing. The plugin-side
    convergence migration adds the same columns/indexes. The legacy-data
    backfills below only matter for pre-existing rows and are correctly
    empty on a fresh install.
    """
    row = conn.execute(
        sa.text("SELECT to_regclass(:tname) IS NOT NULL"),
        {"tname": f"public.{table_name}"},
    ).scalar()
    return bool(row)


def upgrade() -> None:
    conn = op.get_bind()
    if not _table_exists(conn, "tasks"):
        return

    # ── Add new columns to tasks ────────────────────────────────────────────
    op.add_column("tasks", sa.Column("assignee_type", sa.String(20), nullable=False, server_default="user"))
    op.add_column("tasks", sa.Column("assignee_id", PGUUID(as_uuid=True), nullable=True))
    op.add_column("tasks", sa.Column("entity_type", sa.String(80), nullable=True))
    op.add_column("tasks", sa.Column("entity_id", PGUUID(as_uuid=True), nullable=True))
    op.add_column("tasks", sa.Column("creator_type", sa.String(20), nullable=False, server_default="user"))
    op.add_column("tasks", sa.Column("creator_id", PGUUID(as_uuid=True), nullable=True))
    op.add_column("tasks", sa.Column("parent_task_id", PGUUID(as_uuid=True), nullable=True))
    op.add_column("tasks", sa.Column("depends_on", JSONB, nullable=False, server_default=sa.text("'[]'::jsonb")))
    op.add_column("tasks", sa.Column("task_type", sa.String(30), nullable=False, server_default="todo"))
    op.add_column("tasks", sa.Column("success_criteria", JSONB, nullable=True))
    op.add_column("tasks", sa.Column("target_date", sa.DateTime(timezone=True), nullable=True))
    op.add_column("tasks", sa.Column("progress", sa.Integer(), nullable=False, server_default="0"))

    # ── Migrate legacy data into polymorphic fields ─────────────────────────
    # contact_id → entity_type='contact' + entity_id
    op.execute(
        """
        UPDATE tasks
        SET entity_type = 'contact', entity_id = contact_id
        WHERE contact_id IS NOT NULL AND entity_type IS NULL
        """
    )
    # assigned_to → assignee_type='user' + assignee_id
    op.execute(
        """
        UPDATE tasks
        SET assignee_type = 'user', assignee_id = assigned_to
        WHERE assigned_to IS NOT NULL AND assignee_id IS NULL
        """
    )
    # created_by → creator_type='user' + creator_id
    op.execute(
        """
        UPDATE tasks
        SET creator_type = 'user', creator_id = created_by
        WHERE created_by IS NOT NULL AND creator_id IS NULL
        """
    )

    # ── Migrate AgentSubtask rows into tasks ────────────────────────────────
    op.execute(
        """
        INSERT INTO tasks (
            id, tenant_id, title, description, status, priority,
            assignee_type, assignee_id, entity_type, entity_id,
            creator_type, creator_id, task_type, depends_on, progress,
            created_at, updated_at
        )
        SELECT
            asub.id, asub.tenant_id,
            asub.task_description, asub.task_description, asub.status, 'medium',
            'agent', asub.child_agent_id, 'agent', asub.parent_agent_id,
            'agent', asub.parent_agent_id, 'agent_subtask', '[]'::jsonb, 0,
            asub.created_at, asub.updated_at
        FROM agent_subtasks asub
        WHERE NOT EXISTS (
            SELECT 1 FROM tasks t WHERE t.id = asub.id
        )
        """
    )

    # ── Indexes ─────────────────────────────────────────────────────────────
    op.create_index("ix_tasks_tenant_entity", "tasks", ["tenant_id", "entity_type", "entity_id"])
    op.create_index("ix_tasks_tenant_assignee", "tasks", ["tenant_id", "assignee_type", "assignee_id"])
    op.create_index("ix_tasks_tenant_parent", "tasks", ["tenant_id", "parent_task_id"])
    op.create_index("ix_tasks_tenant_type", "tasks", ["tenant_id", "task_type"])
    op.create_foreign_key(
        "fk_tasks_parent_task_id", "tasks", "tasks", ["parent_task_id"], ["id"],
        ondelete="CASCADE",
    )


def downgrade() -> None:
    op.drop_constraint("fk_tasks_parent_task_id", "tasks", type_="foreignkey")
    op.drop_index("ix_tasks_tenant_type", table_name="tasks")
    op.drop_index("ix_tasks_tenant_parent", table_name="tasks")
    op.drop_index("ix_tasks_tenant_assignee", table_name="tasks")
    op.drop_index("ix_tasks_tenant_entity", table_name="tasks")
    op.drop_column("tasks", "progress")
    op.drop_column("tasks", "target_date")
    op.drop_column("tasks", "success_criteria")
    op.drop_column("tasks", "task_type")
    op.drop_column("tasks", "depends_on")
    op.drop_column("tasks", "parent_task_id")
    op.drop_column("tasks", "creator_id")
    op.drop_column("tasks", "creator_type")
    op.drop_column("tasks", "entity_id")
    op.drop_column("tasks", "entity_type")
    op.drop_column("tasks", "assignee_id")
    op.drop_column("tasks", "assignee_type")