from io import BytesIO
from openpyxl import Workbook
from openpyxl.styles import Alignment, Font
from openpyxl.utils import get_column_letter

def build_overview_xlsx(period_name: str, rows: list):
    """
    Build an Excel workbook for the time period overview.

    period_name: e.g. "Dec 1..Dec 15, 2025" (or your custom name)
    rows: list of dicts per employee:
      {
        "employee_name": str,
        "regular": float,
        "overtime": float,
        "pto": float,
        "holiday": float,
        "paid_total": float,
        "reimbursement": float,
        "additional_payroll": float,
        "notes": str,
      }
    """
    wb = Workbook()
    ws = wb.active
    ws.title = "Overview"

    # Title row
    ws["A1"] = period_name
    ws["A1"].font = Font(bold=True, size=14)

    headers = [
        "Employee",
        "Regular Hours",
        "Overtime Hours",
        "PTO Hours",
        "Holiday",
        "Reimbursement",
        "Additional Payroll Changes",
        "Total hours for pay period",
        "Notes",
    ]
    # Header row at row 2 (keep space for title row)
    for col, text in enumerate(headers, start=1):
        cell = ws.cell(row=2, column=col, value=text)
        cell.font = Font(bold=True)

    # Freeze the header row (row 2)
    ws.freeze_panes = "A3"

    # Data
    row_idx = 3
    for r in rows:
        ws.cell(row=row_idx, column=1, value=r.get("employee_name", ""))
        ws.cell(row=row_idx, column=2, value=r.get("regular", 0.0))
        ws.cell(row=row_idx, column=3, value=r.get("overtime", 0.0))
        ws.cell(row=row_idx, column=4, value=r.get("pto", 0.0))
        ws.cell(row=row_idx, column=5, value=r.get("holiday", 0.0))
        ws.cell(row=row_idx, column=6, value=r.get("reimbursement", 0.0) or 0.0)
        ws.cell(row=row_idx, column=7, value=r.get("additional_payroll", 0.0) or 0.0)
        ws.cell(row=row_idx, column=8, value=r.get("paid_total", 0.0))
        ws.cell(row=row_idx, column=9, value=r.get("notes", "") or "")
        row_idx += 1

    # Number formats and alignment
    num_cols = [2, 3, 4, 5, 8]  # hour columns and total hours
    currency_cols = [6, 7]      # reimbursement, additional payroll
    wrap_cols = [9]             # notes

    max_row = ws.max_row
    for r in range(3, max_row + 1):
        for c in num_cols:
            cell = ws.cell(row=r, column=c)
            cell.number_format = "0.00"
            cell.alignment = Alignment(horizontal="right")
        for c in currency_cols:
            cell = ws.cell(row=r, column=c)
            cell.number_format = "$#,##0.00"
            cell.alignment = Alignment(horizontal="right")
        for c in wrap_cols:
            cell = ws.cell(row=r, column=c)
            cell.alignment = Alignment(wrap_text=True)

    # Autosize columns (basic heuristic)
    for col in range(1, len(headers) + 1):
        letter = get_column_letter(col)
        max_len = len(headers[col - 1])
        for cell in ws[letter]:
            val = "" if cell.value is None else str(cell.value)
            max_len = max(max_len, len(val))
        ws.column_dimensions[letter].width = min(max_len + 2, 40)

    buf = BytesIO()
    wb.save(buf)
    buf.seek(0)
    return buf.getvalue()