"""Cards remember when they were last answered

"Known" and "to review" were React state: they vanished on reload, so a deck of
two hundred was two hundred cards every time and the only spacing was whichever
cards a learner remembered to skip. This is the log the scheduler reads.

A log rather than a row per card, because what the scheduler needs is the
latest verdict and its age — and keeping the history means a card missed three
times running can later be treated differently from one missed once, without a
migration to add the column that would have recorded it.

Revision ID: m3d4e5f6a7b8
Revises: l2c3d4e5f6a7
"""
import sqlalchemy as sa
from alembic import op

revision = "m3d4e5f6a7b8"
down_revision = "l2c3d4e5f6a7"
branch_labels = None
depends_on = None


def upgrade() -> None:
    if "flashcard_reviews" in sa.inspect(op.get_bind()).get_table_names():
        return
    op.create_table(
        "flashcard_reviews",
        sa.Column("id", sa.Integer(), primary_key=True),
        sa.Column("user_id", sa.Integer(),
                  sa.ForeignKey("users.id", ondelete="CASCADE"), nullable=False),
        sa.Column("flashcard_id", sa.Integer(),
                  sa.ForeignKey("flashcards.id", ondelete="CASCADE"), nullable=False),
        sa.Column("outcome", sa.String(length=10), nullable=False),
        sa.Column("created_at", sa.DateTime(), nullable=True),
    )
    op.create_index("ix_flashcard_reviews_user_id", "flashcard_reviews", ["user_id"])
    op.create_index("ix_flashcard_reviews_flashcard_id", "flashcard_reviews", ["flashcard_id"])
    # The scheduler asks "this learner's latest verdict per card", which is this
    # index read backwards.
    op.create_index("ix_flashcard_reviews_recent", "flashcard_reviews",
                    ["user_id", "flashcard_id", "created_at"])


def downgrade() -> None:
    op.drop_table("flashcard_reviews")