MIL-003: Step 2 - New flash cards

Review record RC-025 (Go, autonomous mode, not independent).

Task: MIL-003#1
Task: MIL-003#2
Task: MIL-003#3
Task: MIL-003#4
Task: MIL-003#5

src/flash_card/application/use_cases/study_session.py

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+"""One study session.
+
+@file study_session.py
+@brief The StudySession use case: draws the cards the user studies.
+"""
+
+from collections.abc import Callable, Sequence
+
+from flash_card.application.dto.card_dto import CardDto
+from flash_card.domain.entities.card import Card
+from flash_card.domain.entities.deck import Deck
+
+
+class StudySession:
+    """Draws cards from a deck, one after another."""
+
+    def __init__(self, deck: Deck, choose: Callable[[Sequence[Card]], Card]) -> None:
+        """Create a session.
+
+        @param deck The cards still to learn.
+        @param choose Picks one card from a non-empty sequence.
+        """
+        ## @brief The cards still to learn.
+        self._deck = deck
+        ## @brief Picks one card from a non-empty sequence.
+        self._choose = choose
+        ## @brief The card shown now, or None.
+        self._current: Card | None = None
+
+    @property
+    def current_card(self) -> CardDto | None:
+        """Return the card shown now.
+
+        @return The card, or None before the first draw or when none is left.
+        """
+        return self._to_dto(self._current)
+
+    @property
+    def remaining(self) -> int:
+        """Return the number of cards still to learn.
+
+        @return The card count.
+        """
+        return len(self._deck)
+
+    def next_card(self) -> CardDto | None:
+        """Draw the next card, different from the current one when possible.
+
+        @return The new card, or None when the deck is empty.
+        """
+        if self._deck.is_empty:
+            self._current = None
+            return None
+        self._current = self._deck.draw(self._choose, exclude=self._current)
+        return self._to_dto(self._current)
+
+    def _to_dto(self, card: Card | None) -> CardDto | None:
+        """Map a card to its DTO.
+
+        @param card The card, or None.
+        @return The DTO, or None when there is no card.
+        """
+        if card is None:
+            return None
+        pair = self._deck.language_pair
+        return CardDto(card.front, card.back, pair.front_code, pair.back_code)