"""Add musehub_commit_graph — precomputed reachability for O(frontier) DAG walks.

Issue #63 Phase 2: commit graph enables _walk_commit_delta to query in bulk
per BFS frontier instead of one DB call per commit.
"""

from __future__ import annotations

import sqlalchemy as sa
from alembic import op

revision = "0060"
down_revision = "0059"
branch_labels = None
depends_on = None


def upgrade() -> None:
    op.create_table(
        "musehub_commit_graph",
        sa.Column("repo_id", sa.String(128), nullable=False),
        sa.Column("commit_id", sa.String(128), nullable=False),
        sa.Column(
            "parent_ids",
            sa.ARRAY(sa.Text),
            nullable=False,
            server_default="{}",
        ),
        sa.Column("generation", sa.BigInteger, nullable=False, server_default="0"),
        sa.Column("snapshot_id", sa.String(128), nullable=True),
        sa.Column(
            "created_at",
            sa.DateTime(timezone=True),
            nullable=False,
            server_default=sa.text("now()"),
        ),
        sa.ForeignKeyConstraint(
            ["repo_id"],
            ["musehub_repos.repo_id"],
            ondelete="CASCADE",
        ),
        sa.PrimaryKeyConstraint("repo_id", "commit_id"),
    )
    op.create_index(
        "ix_musehub_commit_graph_repo_generation",
        "musehub_commit_graph",
        ["repo_id", "generation"],
    )


def downgrade() -> None:
    op.drop_index("ix_musehub_commit_graph_repo_generation", table_name="musehub_commit_graph")
    op.drop_table("musehub_commit_graph")