"""
Created on Sat Oct 25 21:59:15 2025

@author: boranozdemir
"""

import numpy as np
import numpy_financial as npf
from datetime import datetime


def create_cash_flow(face_value,coupon_rate, bond_length, freq=1):
    coupon_payment = face_value * coupon_rate / freq
    cash_flows = [coupon_payment] * (bond_length - 1) + [coupon_payment + face_value]
    cash_flows.insert(0, 0)
    return cash_flows

def calculate_macualy_duration(yield_, face_value, coupon_rate, bond_length, freq=1):
    # i should start from 1 
    dur = 0
    cf = create_cash_flow(face_value, coupon_rate, bond_length)
    npv = npf.npv(yield_, cf)
    coupon_value = coupon_rate * face_value
    for i in range(1, bond_length+1):
        if i == bond_length:
            dur += ((coupon_value + face_value)*i)/((1+yield_)**i)
            continue 
        dur += ((coupon_value*i)/((1+yield_)**i))
    dur = (1/(1+yield_))*(dur/npv)
    return dur

def calculate_modified_duration(macaulay_duration, yield_):
    mod_duration = macaulay_duration / (1 + yield_)
    return mod_duration

def calculate_convexity(yield_, face_value, coupon_rate, bond_length, freq=1):
    conv = 0
    cf = create_cash_flow(face_value, coupon_rate, bond_length)
    npv = npf.npv(yield_, cf)
    coupon_value = coupon_rate * face_value
    for i in range(1, bond_length+1):
        if i == bond_length:
            conv += ((coupon_value + face_value)*i*(i+1))/((1+yield_/freq)**i)
            continue 
        conv += ((coupon_value*i*(i+1))/((1+yield_/freq)**i))
    conv = (1/(1+yield_)**2)*(conv/npv)
    return conv

def calculate_periodic_duration(macualy_duration, freq):
    periodic_duration = macualy_duration * freq
    return periodic_duration

def calculate_time_to_maturity(settle_date_str, maturity_date_str, freq=1):
    settle = datetime.strptime(settle_date_str, '%d-%m-%Y') 
    maturity = datetime.strptime(maturity_date_str, '%d-%m-%Y')
    time_delta = maturity - settle
    T = time_delta.days / 365.25
    periods = int(np.ceil(T * freq)) 
    return T, periods