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164 | def build_main_tab(
app: RefinanceCalculatorApp,
parent: ttk.Frame,
) -> None:
"""Build the calculator tab inputs and result panels.
Args:
app: Application instance that owns the tab data.
parent: Frame that hosts the calculator elements.
"""
input_frame = ttk.Frame(parent)
input_frame.pack(fill=tk.X, pady=(0, 10))
current_frame = ttk.LabelFrame(input_frame, text="Current Loan", padding=10)
current_frame.pack(side=tk.LEFT, fill=tk.BOTH, expand=True, padx=(0, 5))
add_input(current_frame, "Balance ($):", app.current_balance, 0, app._calculate)
add_input(current_frame, "Rate (%):", app.current_rate, 1, app._calculate)
add_input(current_frame, "Years Remaining:", app.current_remaining, 2, app._calculate)
new_frame = ttk.LabelFrame(input_frame, text="New Loan", padding=10)
new_frame.pack(side=tk.LEFT, fill=tk.BOTH, expand=True, padx=(5, 0))
add_input(new_frame, "Rate (%):", app.new_rate, 0, app._calculate)
add_input(new_frame, "Term (years):", app.new_term, 1, app._calculate)
add_input(new_frame, "Closing Costs ($):", app.closing_costs, 2, app._calculate)
add_input(new_frame, "Cash Out ($):", app.cash_out, 3, app._calculate)
add_input(new_frame, "Opportunity Rate (%):", app.opportunity_rate, 4, app._calculate)
add_input(new_frame, "Marginal Tax Rate (%):", app.marginal_tax_rate, 5, app._calculate)
maintain_frame = ttk.Frame(new_frame)
maintain_frame.grid(row=6, column=0, columnspan=2, sticky=tk.W, pady=(8, 0))
ttk.Checkbutton(
maintain_frame,
text="Maintain current payment (extra → principal)",
variable=app.maintain_payment,
command=app._calculate,
).pack(anchor=tk.W)
btn_frame = ttk.Frame(parent)
btn_frame.pack(pady=8)
ttk.Button(btn_frame, text="Calculate", command=app._calculate).pack(side=tk.LEFT, padx=5)
ttk.Button(btn_frame, text="Export CSV", command=app._export_csv).pack(
side=tk.LEFT,
padx=5,
)
results_frame = ttk.LabelFrame(parent, text="Analysis Results", padding=12)
results_frame.pack(fill=tk.BOTH, expand=True)
style = ttk.Style()
style.configure("Header.TLabel", font=("Segoe UI", 9, "bold"))
style.configure("Result.TLabel", font=("Segoe UI", 10))
style.configure("Big.TLabel", font=("Segoe UI", 13, "bold"))
app.pay_frame = ttk.Frame(results_frame)
app.pay_frame.pack(fill=tk.X, pady=(0, 8))
app.current_pmt_label = result_block(app.pay_frame, "Current Payment", 0)
app.new_pmt_label = result_block(app.pay_frame, "New Payment", 1)
app.savings_label = result_block(app.pay_frame, "Monthly Δ", 2)
app.balance_frame = ttk.Frame(results_frame)
app.balance_frame.pack(fill=tk.X, pady=(0, 8))
app.new_balance_label = result_block(app.balance_frame, "New Loan Balance", 0)
app.cash_out_label = result_block(app.balance_frame, "Cash Out", 1)
result_block(app.balance_frame, "", 2)
app.balance_frame.pack_forget()
ttk.Separator(results_frame, orient=tk.HORIZONTAL).pack(fill=tk.X, pady=6)
be_frame = ttk.Frame(results_frame)
be_frame.pack(fill=tk.X, pady=(0, 8))
app.simple_be_label = result_block(be_frame, "Simple Breakeven", 0)
app.npv_be_label = result_block(be_frame, "NPV Breakeven", 1)
ttk.Separator(results_frame, orient=tk.HORIZONTAL).pack(fill=tk.X, pady=6)
int_frame = ttk.Frame(results_frame)
int_frame.pack(fill=tk.X, pady=(0, 8))
app.curr_int_label = result_block(int_frame, "Current Total Interest", 0)
app.new_int_label = result_block(int_frame, "New Total Interest", 1)
app.int_delta_label = result_block(int_frame, "Interest Δ", 2)
ttk.Separator(results_frame, orient=tk.HORIZONTAL).pack(fill=tk.X, pady=6)
app.tax_section_label = ttk.Label(
results_frame,
text="After-Tax Analysis (0% marginal rate)",
style="Header.TLabel",
)
app.tax_section_label.pack(anchor=tk.W, pady=(0, 6))
tax_pay_frame = ttk.Frame(results_frame)
tax_pay_frame.pack(fill=tk.X, pady=(0, 8))
app.at_current_pmt_label = result_block(tax_pay_frame, "Current (After-Tax)", 0)
app.at_new_pmt_label = result_block(tax_pay_frame, "New (After-Tax)", 1)
app.at_savings_label = result_block(tax_pay_frame, "Monthly Δ (A-T)", 2)
tax_be_frame = ttk.Frame(results_frame)
tax_be_frame.pack(fill=tk.X, pady=(0, 8))
app.at_simple_be_label = result_block(tax_be_frame, "Simple BE (A-T)", 0)
app.at_npv_be_label = result_block(tax_be_frame, "NPV BE (A-T)", 1)
app.at_int_delta_label = result_block(tax_be_frame, "Interest Δ (A-T)", 2)
ttk.Separator(results_frame, orient=tk.HORIZONTAL).pack(fill=tk.X, pady=6)
app.accel_section_frame = ttk.Frame(results_frame)
app.accel_section_label = ttk.Label(
app.accel_section_frame,
text="Accelerated Payoff (Maintain Payment)",
style="Header.TLabel",
)
app.accel_section_label.pack(anchor=tk.W, pady=(0, 6))
accel_row1 = ttk.Frame(app.accel_section_frame)
accel_row1.pack(fill=tk.X, pady=(0, 8))
app.accel_months_label = result_block(accel_row1, "Payoff Time", 0)
app.accel_time_saved_label = result_block(accel_row1, "Time Saved", 1)
app.accel_interest_saved_label = result_block(accel_row1, "Interest Saved", 2)
ttk.Separator(app.accel_section_frame, orient=tk.HORIZONTAL).pack(fill=tk.X, pady=6)
npv_cost_frame = ttk.Frame(results_frame)
npv_cost_frame.pack(fill=tk.X, pady=(0, 8))
ttk.Label(results_frame, text="Total Cost NPV Analysis", style="Header.TLabel").pack(
anchor=tk.W,
pady=(0, 6),
)
npv_cost_row = ttk.Frame(results_frame)
npv_cost_row.pack(fill=tk.X, pady=(0, 8))
app.current_cost_npv_label = result_block(npv_cost_row, "Current Loan NPV", 0)
app.new_cost_npv_label = result_block(npv_cost_row, "New Loan NPV", 1)
app.cost_npv_advantage_label = result_block(npv_cost_row, "NPV Advantage", 2)
ttk.Separator(results_frame, orient=tk.HORIZONTAL).pack(fill=tk.X, pady=6)
npv_frame = ttk.Frame(results_frame)
npv_frame.pack(fill=tk.X)
app.npv_title_label = ttk.Label(
npv_frame,
text="5-Year NPV of Refinancing",
style="Header.TLabel",
)
app.npv_title_label.pack()
app.five_yr_npv_label = ttk.Label(npv_frame, text="$0", style="Big.TLabel")
app.five_yr_npv_label.pack(pady=3)
|