from sqlalchemy import text
from sqlalchemy.engine import Engine

# Per-account offset for the Konto-Saldo-Anker (Ausbaustufe 3 Task 1): the
# same math as app.services.balances.account_balance, expressed as a single
# constant "base" per account so it can be added to a plain (anchor-agnostic)
# running sum of transaction amounts:
#
#   balance(day) = anchor_balance + Sum(tx: anchor_date < booking_date <= day)
#                                  - Sum(tx: day < booking_date <= anchor_date)
#                = anchor_balance - cumsum(<=anchor_date) + cumsum(<=day)
#                = base + cumsum(<=day)
#
# ... which holds for `day` both before and after anchor_date, since the
# subtracted/added transaction windows collapse into the same telescoping
# sum. Accounts without an anchor get base=0 (via COALESCE below), matching
# account_balance's "Ohne Anker: Summe ab 0" fallback.
_ACCOUNT_OFFSET = """
    SELECT a.id AS account_id,
           a.anchor_balance - COALESCE((
               SELECT SUM(t2.amount) FROM transactions t2
               WHERE t2.account_id = a.id AND t2.status = 'confirmed'
                 AND t2.booking_date <= a.anchor_date
           ), 0) AS base
    FROM accounts a
    WHERE a.anchor_date IS NOT NULL AND a.anchor_balance IS NOT NULL
"""

VIEWS: dict[str, str] = {
    "v_balance_history": f"""
        SELECT t.booking_date AS day, a.name AS account,
               COALESCE(b.base, 0)
                 + SUM(SUM(t.amount)) OVER (PARTITION BY a.id
                                            ORDER BY t.booking_date) AS balance
        FROM transactions t JOIN accounts a ON a.id = t.account_id
        LEFT JOIN ({_ACCOUNT_OFFSET}) b ON b.account_id = a.id
        WHERE t.status = 'confirmed'
        GROUP BY a.id, a.name, t.booking_date, b.base""",
    "v_balance_total": f"""
        SELECT booking_date AS day,
               (SELECT COALESCE(SUM(base), 0)
                FROM ({_ACCOUNT_OFFSET}) s)
                 + SUM(SUM(amount)) OVER (ORDER BY booking_date) AS balance
        FROM transactions WHERE status = 'confirmed' GROUP BY booking_date""",
    "v_monthly_by_category": """
        SELECT date_trunc('month', t.booking_date) AS month,
               COALESCE(c.name, 'unkategorisiert') AS category,
               SUM(t.amount) AS total
        FROM transactions t LEFT JOIN categories c ON c.id = t.category_id
        WHERE t.status = 'confirmed' GROUP BY 1, 2""",
    "v_projection": """
        SELECT s.name AS scenario, p.day, p.balance
        FROM projection_points p JOIN scenarios s ON s.id = p.scenario_id""",
}


def create_views(engine: Engine) -> None:
    if engine.dialect.name != "postgresql":
        return
    with engine.begin() as conn:
        for name, body in VIEWS.items():
            # CREATE OR REPLACE VIEW fails if the output column set changed
            # (name/type/order). Fall back to DROP + CREATE in that case so a
            # redeploy always applies the current definition.
            try:
                with conn.begin_nested():
                    conn.execute(
                        text(f"CREATE OR REPLACE VIEW {name} AS {body}"))
            except Exception:
                conn.execute(text(f"DROP VIEW IF EXISTS {name} CASCADE"))
                conn.execute(text(f"CREATE VIEW {name} AS {body}"))