"""合成FCFF DCF；年度末折现，金额/股本均以百万计。"""
import json
from decimal import Decimal as D

drivers = [("100", "5", "8", "2"), ("110", "5", "9", "3"), ("120", "6", "10", "3")]

def dcf(wacc=D("0.10"), growth=D("0.02"), currency="CNY", debt_currency="CNY", shares=D("100")):
    if currency != debt_currency:
        raise ValueError("mixed_currency")
    if not wacc > growth or shares <= 0:
        raise ValueError("invalid_terminal_or_shares")
    flows = [D(ebit) * (1-D("0.25")) + D(da) - D(capex) - D(wc)
             for ebit, da, capex, wc in drivers]
    pv = [fcff / (1+wacc)**t for t, fcff in enumerate(flows, 1)]
    terminal = flows[-1] * (1+growth) / (wacc-growth)
    terminal_pv = terminal / (1+wacc)**len(flows)
    enterprise = sum(pv) + terminal_pv
    equity = enterprise - D("150") + D("30")
    return {"fcff": flows, "pv": pv, "terminal": terminal, "terminal_pv": terminal_pv,
            "enterprise": enterprise, "equity": equity, "per_share": equity/shares}

base = dcf()
assert base["fcff"] == [D("70.00"), D("75.50"), D("83.00")]
assert abs(base["enterprise"] - (sum(base["pv"]) + base["terminal_pv"])) < D("0.000001")
assert dcf(wacc=D("0.11"))["per_share"] < base["per_share"]
sensitivity = {str(w): str(dcf(wacc=w)["per_share"].quantize(D("0.01")))
               for w in [D("0.09"), D("0.10"), D("0.11")]}
assert sensitivity == {"0.09": "10.06", "0.10": "8.63", "0.11": "7.53"}
blocked = []
for kwargs in [{"growth": D("0.10")}, {"debt_currency": "USD"}, {"shares": D("0")}]:
    try:
        dcf(**kwargs)
    except ValueError as exc:
        blocked.append(str(exc))
assert len(blocked) == 3
print(json.dumps({"fcff": [str(x) for x in base["fcff"]],
                  "enterprise": str(base["enterprise"].quantize(D("0.01"))),
                  "equity": str(base["equity"].quantize(D("0.01"))),
                  "per_share": str(base["per_share"].quantize(D("0.01"))),
                  "terminal_share": str((base["terminal_pv"]/base["enterprise"]).quantize(D("0.0001"))),
                  "sensitivity": sensitivity,
                  "blocked": blocked}, sort_keys=True))