"""
Phase 1: general courses (shared across every batch of a session).

Simple strategy — small offering count, Mon/Wed preferred first. After
placing everything, self-repair: any batch left with two general-course
sessions in the same slot has the losing session unmarked and re-placed
(scanning every day) until this phase's own sessions are clash-free.
"""

from . import grid


def run(board, data, preferred_days=("Monday", "Wednesday"), max_repair_attempts=20):
    """Places every general-course offering's weekly lectures. Returns this phase's sessions."""
    general = [o for o in data["offerings"] if o["course"]["is_general"]]
    preferred_order = list(preferred_days) + [d for d in grid.DAYS if d not in preferred_days]
    phase_start = len(board.sessions)

    for offering in general:
        course = offering["course"]
        room_candidates = board.room_candidates(course["lecture_room_id"], board.classrooms)
        for _ in range(course["lectures_per_week"]):
            session = board.place_lecture(offering, room_candidates, preferred_order)
            if session is None:
                print(f"WARNING: could not place a lecture for general course {offering['course_id']} section {offering['section_id']}")

    phase_sessions = board.sessions[phase_start:]
    _repair_general_conflicts(board, data, phase_sessions, max_repair_attempts)
    return phase_sessions


def _repair_general_conflicts(board, data, phase_sessions, max_attempts):
    """Moves general-course sessions that clash for a batch to a free slot on any day."""
    from conflict_checker.student_conflict_checker import check_student_conflicts

    any_day_order = list(grid.DAYS)
    for _ in range(max_attempts):
        conflicts = check_student_conflicts(phase_sessions)
        if not conflicts:
            return

        # Re-place the last session involved in the first conflict; the
        # other session(s) in that cell stay put.
        losing_session = conflicts[0]["sessions"][-1]
        offering = next(
            o for o in data["offerings"]
            if o["course_id"] == losing_session["course_id"] and o["section_id"] == losing_session["section_id"]
        )
        board.remove_session(losing_session)
        phase_sessions.remove(losing_session)

        room_candidates = board.room_candidates(offering["course"]["lecture_room_id"], board.classrooms)
        new_session = board.place_lecture(offering, room_candidates, any_day_order)
        if new_session is None:
            print(f"WARNING: could not repair general-course conflict for {offering['course_id']} section {offering['section_id']}")
            return
        phase_sessions.append(new_session)

    print("WARNING: general-course conflicts remained unresolved after max repair attempts")