"""Intern attendance: make ``work_days`` duration-weighted (Integer→Float).

出勤天数 for interns is now counted by clocked duration, not whole days: a
day on the clock accrues ``min(1.0, span/9h)`` (满勤标准 = 每日打卡总时长满
9 小时含午休), rounded to 0.1 天. A short day like 15:15→18:38 (~3.4h) now
counts as 0.4 天 instead of a full day. The denormalised
``attendance_reports.work_days`` column must therefore hold a fractional
value.

Idempotent + safe: existing integer values (historical, already-confirmed
reports) survive the widening unchanged — 19 stays 19.0. Only cycles
re-generated after this ships recompute with the fractional logic (which
is correct: a confirmed historical report should not silently change).
"""
import sqlalchemy as sa

from alembic import op

revision = "403"
down_revision = "402"
branch_labels = None
depends_on = None


def _column_type(bind, table: str, column: str) -> str | None:
    return bind.execute(
        sa.text(
            "SELECT DATA_TYPE FROM information_schema.COLUMNS "
            "WHERE TABLE_SCHEMA = DATABASE() AND TABLE_NAME = :t "
            "AND COLUMN_NAME = :c"
        ),
        {"t": table, "c": column},
    ).scalar()


def upgrade() -> None:
    bind = op.get_bind()
    dtype = (_column_type(bind, "attendance_reports", "work_days") or "").lower()
    # Only alter if it isn't already a floating type (re-run safe).
    if dtype in ("float", "double", "decimal", "newdecimal"):
        return
    op.alter_column(
        "attendance_reports",
        "work_days",
        existing_type=sa.Integer(),
        type_=sa.Float(),
        existing_nullable=False,
        existing_server_default=None,
    )


def downgrade() -> None:
    bind = op.get_bind()
    dtype = (_column_type(bind, "attendance_reports", "work_days") or "").lower()
    if dtype == "int":
        return
    # Fractional values round to nearest whole day on the way down.
    op.execute(sa.text("UPDATE attendance_reports SET work_days = ROUND(work_days)"))
    op.alter_column(
        "attendance_reports",
        "work_days",
        existing_type=sa.Float(),
        type_=sa.Integer(),
        existing_nullable=False,
    )