"""Realized cost-optimization savings ledger.

Revision ID: 423
Revises: 422
Create Date: 2026-07-20

Why this exists
---------------
The cloud efficiency feature reported only ESTIMATED savings ("if you
acted, you'd save $X"). Leadership asked the obvious question — did we
ACTUALLY save money, how much, and how. This ledger closes the loop: an
audit post-log hook (``cmdb.savings_tracker``) records a row here when a
server that was flagged idle/oversized is actually destroyed or stopped,
snapshotting the pre-action monthly cost baseline. The realized amount is
derived at read time (``savings_service``) as baseline − actual
post-action cost from ``cmdb_cost_facts`` — so a destroy shows the full
drop and a restarted box self-corrects to ~0 (no overcount, no cron).

``server_id`` is a plain string (NOT an FK): the server is typically
soft-deleted / terminated right after the action, and the outcome must
survive that. One row per server (``uq_savings_event_server``).

Idempotency: ``CREATE TABLE IF NOT EXISTS`` via ``_table_exists``.
"""
from __future__ import annotations

import sqlalchemy as sa

from alembic import op
from app.core.migration_helpers import id_type_for, table_kw_for

revision = "423"
down_revision = "422"
branch_labels = None
depends_on = None


TABLE = "cmdb_efficiency_savings_events"


def _table_exists(bind, name: str) -> bool:
    return bind.execute(
        sa.text(
            "SELECT 1 FROM information_schema.TABLES "
            "WHERE TABLE_SCHEMA = DATABASE() AND TABLE_NAME = :n"
        ),
        {"n": name},
    ).scalar() is not None


def upgrade() -> None:
    bind = op.get_bind()
    id_t = id_type_for("cmdb_servers")
    kw = table_kw_for("cmdb_servers")

    if _table_exists(bind, TABLE):
        return

    op.create_table(
        TABLE,
        sa.Column("id", id_t, primary_key=True),
        sa.Column("server_id", sa.String(36), nullable=False),
        sa.Column("instance_id", sa.String(512), nullable=True),
        sa.Column("integration_id", sa.String(36), nullable=True),
        sa.Column("scope_id", sa.String(36), nullable=True),
        sa.Column("method", sa.String(16), nullable=False),
        sa.Column("verdict_at_action", sa.String(32), nullable=True),
        sa.Column("monthly_cost_baseline_usd", sa.Numeric(14, 2), nullable=True),
        sa.Column("cost_currency", sa.String(8), nullable=True),
        sa.Column("owner_person_id", sa.String(36), nullable=True),
        sa.Column("owner_department", sa.String(256), nullable=True),
        sa.Column("acted_by_person_id", sa.String(36), nullable=True),
        sa.Column(
            "acted_at", sa.DateTime(timezone=True), nullable=False,
            server_default=sa.func.now(),
        ),
        sa.Column(
            "created_at", sa.DateTime(timezone=True), nullable=False,
            server_default=sa.func.now(),
        ),
        sa.Column(
            "updated_at", sa.DateTime(timezone=True), nullable=False,
            server_default=sa.func.now(),
        ),
        sa.UniqueConstraint("server_id", name="uq_savings_event_server"),
        **kw,
    )
    op.create_index("ix_savings_event_acted", TABLE, ["acted_at"])
    op.create_index("ix_savings_event_integration", TABLE, ["integration_id"])


def downgrade() -> None:
    bind = op.get_bind()
    if _table_exists(bind, TABLE):
        op.drop_table(TABLE)