#!/usr/bin/env python3
"""Price and roll forward Cedar Trail's fictional bond issue.

Run with ``uv run python`` and this file's path. This dependency-free script
recomputes supplied facts; it does not choose a yield, qualify issuance costs,
interpret an indenture, or approve accounting and disclosure conclusions.
"""


def money(amount: float) -> str:
    """Format a number as accounting-style US dollars."""
    return f"${amount:,.2f}" if amount >= 0 else f"(${abs(amount):,.2f})"


def percent(rate: float) -> str:
    """Format a decimal rate as a percentage without hiding useful precision."""
    return f"{rate:.10%}"


def heading(title: str) -> None:
    print(f"\n{title}\n{'-' * len(title)}")


def present_value(rate: float, coupon: float, face: float, periods: int) -> float:
    """Present value of equal coupons and principal paid at period-end."""
    annuity_factor = (1 - (1 + rate) ** -periods) / rate
    return coupon * annuity_factor + face * (1 + rate) ** -periods


def solve_yield(proceeds: float, coupon: float, face: float, periods: int) -> float:
    """Solve the positive periodic yield for conventional debt cash flows."""
    low, high = 0.0, 1.0
    for _ in range(200):
        midpoint = (low + high) / 2
        if present_value(midpoint, coupon, face, periods) > proceeds:
            low = midpoint
        else:
            high = midpoint
    return (low + high) / 2


face_amount = 2_000_000.00
stated_annual_rate = 0.06
market_annual_rate = 0.08
payments_per_year = 2
periods = 8
issuance_costs = 25_000.00

stated_periodic_rate = stated_annual_rate / payments_per_year
market_periodic_rate = market_annual_rate / payments_per_year
cash_interest = face_amount * stated_periodic_rate

heading("1. Contract cash flows")
print(f"{'Face amount':<38} {money(face_amount):>20}")
print(f"{'Stated rate each half-year':<38} {percent(stated_periodic_rate):>20}")
print(f"{'Coupon cash each half-year':<38} {money(cash_interest):>20}")
print(f"{'Coupon periods':<38} {periods:>20,}")

heading("2. Issue price at the supplied market yield")
coupon_present_value = cash_interest * (
    1 - (1 + market_periodic_rate) ** -periods
) / market_periodic_rate
principal_present_value = face_amount * (1 + market_periodic_rate) ** -periods
issue_price = coupon_present_value + principal_present_value
discount = face_amount - issue_price
print(f"{'Coupon present value':<38} {money(coupon_present_value):>20}")
print(f"{'Principal present value':<38} {money(principal_present_value):>20}")
print(f"{'Issue price':<38} {money(issue_price):>20}")
print(f"{'Gross discount':<38} {money(discount):>20}")

heading("3. Opening net carrying amount and effective yield")
opening_carrying_amount = issue_price - issuance_costs
effective_periodic_yield = solve_yield(
    opening_carrying_amount, cash_interest, face_amount, periods
)
print(f"{'Issue price':<38} {money(issue_price):>20}")
print(f"{'Qualifying issuance costs':<38} {money(-issuance_costs):>20}")
print(f"{'Opening net carrying amount':<38} {money(opening_carrying_amount):>20}")
print(f"{'Solved effective half-year yield':<38} {percent(effective_periodic_yield):>20}")

heading("4. Full-precision effective-interest schedule")
print(
    f"{'Per.':>4} {'Opening':>18} {'Cash':>14} {'Expense':>16} "
    f"{'Increase':>16} {'Ending':>18}"
)
carrying_amount = opening_carrying_amount
total_interest_expense = 0.0
for period in range(1, periods + 1):
    opening = carrying_amount
    interest_expense = opening * effective_periodic_yield
    carrying_increase = interest_expense - cash_interest
    carrying_amount = opening + carrying_increase
    total_interest_expense += interest_expense
    print(
        f"{period:>4} {money(opening):>18} {money(cash_interest):>14} "
        f"{money(interest_expense):>16} {money(carrying_increase):>16} "
        f"{money(carrying_amount):>18}"
    )

heading("5. Reconciliations")
total_cash_interest = cash_interest * periods
total_carrying_increase = carrying_amount - opening_carrying_amount
print(f"{'Total cash interest':<38} {money(total_cash_interest):>20}")
print(f"{'Total interest expense':<38} {money(total_interest_expense):>20}")
print(f"{'Total carrying increase':<38} {money(total_carrying_increase):>20}")
print(f"{'Ending carrying amount':<38} {money(carrying_amount):>20}")

if abs(issue_price - 1_865_345.102500992) > 0.000001:
    raise SystemExit("FAIL: issue price does not match the controlled value")
if abs(carrying_amount - face_amount) > 0.000001:
    raise SystemExit("FAIL: calculated schedule does not reach face amount")
if abs(total_interest_expense - total_cash_interest - total_carrying_increase) > 0.000001:
    raise SystemExit("FAIL: interest, cash, and carrying amount do not reconcile")

print("\nPASS: price, basis, effective interest, and maturity reconcile without a plug.")
print("Boundary: PASS verifies arithmetic only; contract, yield, scope, and reporting need review.")