"""
Shared openpyxl helpers for rendering a day x time-slot timetable grid.
Used by every templates/*-wise/*_template.py module so styling stays
consistent across views.
"""

import os

from openpyxl import Workbook
from openpyxl.styles import Alignment, Border, Font, PatternFill, Side
from openpyxl.utils import get_column_letter

DAYS = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"]

HEADER_FILL = PatternFill(start_color="1F4E78", end_color="1F4E78", fill_type="solid")
HEADER_FONT = Font(color="FFFFFF", bold=True)
LUNCH_FILL = PatternFill(start_color="D9D9D9", end_color="D9D9D9", fill_type="solid")
GENERAL_FILL = PatternFill(start_color="FFF2CC", end_color="FFF2CC", fill_type="solid")
LAB_FILL = PatternFill(start_color="D9EAD3", end_color="D9EAD3", fill_type="solid")
THEORY_FILL = PatternFill(start_color="DDEBF7", end_color="DDEBF7", fill_type="solid")
THIN_BORDER = Border(
    left=Side(style="thin"), right=Side(style="thin"),
    top=Side(style="thin"), bottom=Side(style="thin"),
)
CENTER = Alignment(horizontal="center", vertical="center", wrap_text=True)


def cell_fill_for(session):
    if session is None:
        return None
    if session.get("is_general"):
        return GENERAL_FILL
    if session.get("course_type") == "lab":
        return LAB_FILL
    return THEORY_FILL


def build_grid_sheet(ws, title, subtitle, time_slots, sessions_by_day_slot, cell_text_fn):
    """
    Renders one timetable grid onto worksheet `ws`.

    time_slots: ordered list of dicts: {"label": str, "start": str, "end": str,
                "is_lunch": bool}
    sessions_by_day_slot: dict[(day, slot_index)] -> session dict (or list of
                session dicts for slots spanning a double/lab period), used
                only to decide fill color via cell_fill_for().
    cell_text_fn: function(day, slot_index) -> str to render into the cell.
    """
    invalid_chars = ':\\/?*[]'
    sheet_name = "".join(c for c in title if c not in invalid_chars)
    ws.title = sheet_name[:31]  # Excel sheet name limit

    ws.merge_cells("A1:F1")
    ws["A1"] = title
    ws["A1"].font = Font(bold=True, size=14)
    ws["A1"].alignment = CENTER

    if subtitle:
        ws.merge_cells("A2:F2")
        ws["A2"] = subtitle
        ws["A2"].font = Font(italic=True, size=10, color="555555")
        ws["A2"].alignment = CENTER

    header_row = 4
    ws.cell(row=header_row, column=1, value="Time").font = HEADER_FONT
    ws.cell(row=header_row, column=1).fill = HEADER_FILL
    ws.cell(row=header_row, column=1).alignment = CENTER
    ws.cell(row=header_row, column=1).border = THIN_BORDER

    for col, day in enumerate(DAYS, start=2):
        c = ws.cell(row=header_row, column=col, value=day)
        c.font = HEADER_FONT
        c.fill = HEADER_FILL
        c.alignment = CENTER
        c.border = THIN_BORDER

    for row_offset, slot in enumerate(time_slots):
        row = header_row + 1 + row_offset
        time_cell = ws.cell(row=row, column=1, value=f'{slot["start"]} - {slot["end"]}')
        time_cell.font = Font(bold=True, size=9)
        time_cell.alignment = CENTER
        time_cell.border = THIN_BORDER
        if slot.get("is_lunch"):
            time_cell.fill = LUNCH_FILL

        for col, day in enumerate(DAYS, start=2):
            cell = ws.cell(row=row, column=col)
            cell.border = THIN_BORDER
            cell.alignment = CENTER
            cell.font = Font(size=9)

            if slot.get("is_lunch"):
                cell.fill = LUNCH_FILL
                cell.value = "LUNCH BREAK"
                continue

            text = cell_text_fn(day, row_offset)
            cell.value = text if text else ""

            session = sessions_by_day_slot.get((day, row_offset))
            fill = cell_fill_for(session)
            if fill:
                cell.fill = fill

    ws.column_dimensions["A"].width = 16
    for col in range(2, 2 + len(DAYS)):
        ws.column_dimensions[get_column_letter(col)].width = 26

    for row_offset in range(len(time_slots)):
        ws.row_dimensions[header_row + 1 + row_offset].height = 42


def save_workbook(wb, output_dir, filename):
    os.makedirs(output_dir, exist_ok=True)
    path = os.path.join(output_dir, filename)
    wb.save(path)
    return path


def new_workbook():
    wb = Workbook()
    return wb