"""Renders one timetable grid per batch."""

import sys
import os

_ROOT = os.path.join(os.path.dirname(os.path.abspath(__file__)), "..", "..")
sys.path.insert(0, os.path.join(_ROOT, "app"))
sys.path.insert(0, os.path.join(_ROOT, "controller"))

from xlsx_grid_helper import build_grid_sheet, new_workbook, save_workbook  # noqa: E402
from template_controller import TIME_SLOTS as GRID_TIME_SLOTS  # noqa: E402


def _sessions_for_batch(sessions, batch_code):
    return [s for s in sessions if batch_code in s["batch_codes"]]


def generate_batch_wise_templates(sessions, data, output_dir):
    written = []
    for batch in data["batches"]:
        batch_code = batch["batch_code"]
        batch_sessions = _sessions_for_batch(sessions, batch_code)

        # A batch-wise view can legitimately show more than one lecture in
        # the same slot (e.g. sections of the batch split across rooms), so
        # every session landing on a cell is kept and rendered — none are
        # dropped or overwritten.
        by_day_slot = {}
        for s in batch_sessions:
            for slot_index in s["slot_indices"]:
                by_day_slot.setdefault((s["day"], slot_index), []).append(s)

        def cell_text(day, slot_index, by_day_slot=by_day_slot):
            entries = by_day_slot.get((day, slot_index))
            if not entries:
                return ""
            lines = []
            for s in entries:
                tag = " (Lab)" if s["course_type"] == "lab" else (" (General)" if s["is_general"] else "")
                lines.append(f'{s["course_name"]}{tag} [Sec {s["section_id"]}]\n{s["instructor_name"]}\n{s["room_id"]}')
            return "\n---\n".join(lines)

        first_by_day_slot = {k: v[0] for k, v in by_day_slot.items()}

        wb = new_workbook()
        ws = wb.active
        subtitle = f'{batch["department"]} - {batch["program"]} - Session {batch["session"]}'
        build_grid_sheet(
            ws,
            title=f"Batch {batch_code}",
            subtitle=subtitle,
            time_slots=GRID_TIME_SLOTS,
            sessions_by_day_slot=first_by_day_slot,
            cell_text_fn=cell_text,
        )
        path = save_workbook(wb, output_dir, f"{batch_code}.xlsx")
        written.append(path)
    return written