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
"""


# Per-account earliest day the daily series needs to start at: the earlier of
# the account's first confirmed booking and its anchor_date (an anchor can
# predate the first booking, e.g. an anchor set before any import). Accounts
# with neither an anchor nor any confirmed booking have no meaningful start
# and are excluded (nothing to plot).
_ACCOUNT_START = """
    SELECT a.id AS account_id, a.name AS account,
           LEAST(
               COALESCE(a.anchor_date, ft.first_date),
               COALESCE(ft.first_date, a.anchor_date)
           ) AS start_date
    FROM accounts a
    LEFT JOIN (
        SELECT account_id, MIN(booking_date) AS first_date
        FROM transactions WHERE status = 'confirmed'
        GROUP BY account_id
    ) ft ON ft.account_id = a.id
    WHERE a.anchor_date IS NOT NULL OR ft.first_date IS NOT NULL
"""

VIEWS: dict[str, str] = {
    # Daily (gap-free) balance per account: one row per calendar day from the
    # account's start date (see _ACCOUNT_START) through CURRENT_DATE. The
    # cumulative SUM ... OVER (... ROWS UNBOUNDED PRECEDING) carries the
    # previous day's balance forward on days without any confirmed booking,
    # matching services.balances.account_balance's per-Tagesende semantics
    # (base + cumulated amounts up to and including that day).
    "v_balance_history": f"""
        WITH offsets AS ({_ACCOUNT_OFFSET}),
        bounds AS ({_ACCOUNT_START}),
        days AS (
            SELECT b.account_id, b.account, gs.day::date AS day
            FROM bounds b
            CROSS JOIN LATERAL generate_series(
                b.start_date, CURRENT_DATE, interval '1 day') AS gs(day)
        ),
        daily_tx AS (
            SELECT account_id, booking_date AS day, SUM(amount) AS day_amount
            FROM transactions WHERE status = 'confirmed'
            GROUP BY account_id, booking_date
        )
        SELECT d.day, d.account,
               COALESCE(o.base, 0)
                 + SUM(COALESCE(dt.day_amount, 0)) OVER (
                       PARTITION BY d.account_id ORDER BY d.day
                       ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS balance
        FROM days d
        LEFT JOIN daily_tx dt ON dt.account_id = d.account_id AND dt.day = d.day
        LEFT JOIN offsets o ON o.account_id = d.account_id""",
    # Daily (gap-free) total balance across all accounts: same carry-forward
    # logic as v_balance_history, but summed globally (equivalent to summing
    # each account's own base + cumulated amounts, since a cumulative sum of
    # a union of per-day amounts equals the sum of per-account cumulative
    # sums). The day series spans from the earliest account start date
    # through CURRENT_DATE.
    "v_balance_total": f"""
        WITH offsets AS ({_ACCOUNT_OFFSET}),
        bounds AS ({_ACCOUNT_START}),
        days AS (
            SELECT gs.day::date AS day
            FROM (SELECT MIN(start_date) AS start_date FROM bounds) b
            CROSS JOIN LATERAL generate_series(
                b.start_date, CURRENT_DATE, interval '1 day') AS gs(day)
        ),
        daily_tx AS (
            SELECT booking_date AS day, SUM(amount) AS day_amount
            FROM transactions WHERE status = 'confirmed'
            GROUP BY booking_date
        )
        SELECT d.day,
               (SELECT COALESCE(SUM(base), 0) FROM offsets)
                 + SUM(COALESCE(dt.day_amount, 0)) OVER (
                       ORDER BY d.day
                       ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS balance
        FROM days d
        LEFT JOIN daily_tx dt ON dt.day = d.day""",
    "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}"))