"""Renders one timetable grid per department, aggregating all its batches."""

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 generate_department_wise_templates(sessions, data, output_dir):
    departments = sorted({b["department"] for b in data["batches"]})
    written = []

    for department in departments:
        dept_batch_codes = {b["batch_code"] for b in data["batches"] if b["department"] == department}
        dept_sessions = [s for s in sessions if any(bc in dept_batch_codes for bc in s["batch_codes"])]

        by_day_slot = {}
        for s in dept_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 "")
                batches = "+".join(s["batch_codes"])
                lines.append(f'{s["course_name"]}{tag} [{batches}]\n{s["instructor_name"]} @ {s["room_id"]}')
            return "\n---\n".join(lines)

        # for fill-color purposes just use the first session in each cell
        first_by_day_slot = {k: v[0] for k, v in by_day_slot.items()}

        wb = new_workbook()
        ws = wb.active
        build_grid_sheet(
            ws,
            title=f"Department: {department}",
            subtitle="All batches / programs",
            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"{department}.xlsx")
        written.append(path)

    return written