from datetime import date
from decimal import Decimal
from typing import Literal

from fastapi import APIRouter, Depends, HTTPException
from pydantic import BaseModel, ConfigDict, Field
from sqlalchemy import delete, select
from sqlalchemy.orm import Session

from app.auth import require_auth
from app.db import get_session
from app.engine.loans import loan_schedule
from app.models.tables import (Category, Loan, PlannedItem, RecurringItem,
                               ScenarioLoan)
from app.services.suggestions import suggest_recurring

router = APIRouter(prefix="/api", tags=["planning"],
                   dependencies=[Depends(require_auth)])


# ---------------------------------------------------------------- Recurring
class RecurringIn(BaseModel):
    name: str
    amount: Decimal
    rhythm: Literal["monthly", "quarterly", "yearly"]
    due_day: int = Field(ge=1, le=31)
    start_date: date | None = None
    end_date: date | None = None
    category_id: int | None = None


class RecurringOut(RecurringIn):
    model_config = ConfigDict(from_attributes=True)
    id: int


class RecurringPatch(BaseModel):
    name: str | None = None
    amount: Decimal | None = None
    rhythm: Literal["monthly", "quarterly", "yearly"] | None = None
    due_day: int | None = Field(default=None, ge=1, le=31)
    start_date: date | None = None
    end_date: date | None = None
    category_id: int | None = None


class SuggestionOut(BaseModel):
    name: str
    amount: Decimal
    rhythm: str
    due_day: int
    category_id: int | None = None


def _check_category(session: Session, category_id: int | None) -> None:
    if category_id is not None and session.get(Category, category_id) is None:
        raise HTTPException(404, "Kategorie nicht gefunden")


@router.get("/recurring", response_model=list[RecurringOut])
def list_recurring(session: Session = Depends(get_session)):
    return [RecurringOut.model_validate(r)
            for r in session.execute(select(RecurringItem)).scalars()]


@router.post("/recurring", response_model=RecurringOut, status_code=201)
def create_recurring(data: RecurringIn, session: Session = Depends(get_session)):
    _check_category(session, data.category_id)
    item = RecurringItem(**data.model_dump())
    session.add(item)
    session.commit()
    session.refresh(item)
    return RecurringOut.model_validate(item)


# Muss vor /recurring/{item_id} stehen, sonst faengt die {id}-Route den Pfad ab.
@router.get("/recurring/suggestions", response_model=list[SuggestionOut])
def recurring_suggestions(session: Session = Depends(get_session)):
    return suggest_recurring(session)


@router.patch("/recurring/{item_id}", response_model=RecurringOut)
def patch_recurring(item_id: int, data: RecurringPatch,
                    session: Session = Depends(get_session)):
    item = session.get(RecurringItem, item_id)
    if item is None:
        raise HTTPException(404, "Fixposten nicht gefunden")
    fields = data.model_dump(exclude_unset=True)
    if "category_id" in fields:
        _check_category(session, fields["category_id"])
    for key, value in fields.items():
        setattr(item, key, value)
    session.commit()
    session.refresh(item)
    return RecurringOut.model_validate(item)


@router.delete("/recurring/{item_id}", status_code=204)
def delete_recurring(item_id: int, session: Session = Depends(get_session)):
    item = session.get(RecurringItem, item_id)
    if item is None:
        raise HTTPException(404, "Fixposten nicht gefunden")
    session.delete(item)
    session.commit()


# ------------------------------------------------------------------ Planned
class PlannedIn(BaseModel):
    name: str
    amount: Decimal
    due: date
    category_id: int | None = None


class PlannedOut(PlannedIn):
    model_config = ConfigDict(from_attributes=True)
    id: int


class PlannedPatch(BaseModel):
    name: str | None = None
    amount: Decimal | None = None
    due: date | None = None
    category_id: int | None = None


@router.get("/planned", response_model=list[PlannedOut])
def list_planned(session: Session = Depends(get_session)):
    return [PlannedOut.model_validate(p)
            for p in session.execute(select(PlannedItem)).scalars()]


@router.post("/planned", response_model=PlannedOut, status_code=201)
def create_planned(data: PlannedIn, session: Session = Depends(get_session)):
    _check_category(session, data.category_id)
    item = PlannedItem(**data.model_dump())
    session.add(item)
    session.commit()
    session.refresh(item)
    return PlannedOut.model_validate(item)


@router.patch("/planned/{item_id}", response_model=PlannedOut)
def patch_planned(item_id: int, data: PlannedPatch,
                  session: Session = Depends(get_session)):
    item = session.get(PlannedItem, item_id)
    if item is None:
        raise HTTPException(404, "Einmalposten nicht gefunden")
    fields = data.model_dump(exclude_unset=True)
    if "category_id" in fields:
        _check_category(session, fields["category_id"])
    for key, value in fields.items():
        setattr(item, key, value)
    session.commit()
    session.refresh(item)
    return PlannedOut.model_validate(item)


@router.delete("/planned/{item_id}", status_code=204)
def delete_planned(item_id: int, session: Session = Depends(get_session)):
    item = session.get(PlannedItem, item_id)
    if item is None:
        raise HTTPException(404, "Einmalposten nicht gefunden")
    session.delete(item)
    session.commit()


# --------------------------------------------------------------------- Loans
class LoanIn(BaseModel):
    name: str
    principal: Decimal
    annual_rate_pct: Decimal
    term_months: int
    payout_date: date
    repayment_type: Literal["annuity", "bullet"] = "annuity"


class LoanOut(LoanIn):
    model_config = ConfigDict(from_attributes=True)
    id: int


class LoanPatch(BaseModel):
    name: str | None = None
    principal: Decimal | None = None
    annual_rate_pct: Decimal | None = None
    term_months: int | None = None
    payout_date: date | None = None
    repayment_type: Literal["annuity", "bullet"] | None = None


class InstallmentOut(BaseModel):
    due: date
    payment: Decimal
    interest: Decimal
    principal: Decimal
    remaining: Decimal


@router.get("/loans", response_model=list[LoanOut])
def list_loans(session: Session = Depends(get_session)):
    return [LoanOut.model_validate(l)
            for l in session.execute(select(Loan)).scalars()]


@router.post("/loans", response_model=LoanOut, status_code=201)
def create_loan(data: LoanIn, session: Session = Depends(get_session)):
    loan = Loan(**data.model_dump())
    session.add(loan)
    session.commit()
    session.refresh(loan)
    return LoanOut.model_validate(loan)


@router.patch("/loans/{loan_id}", response_model=LoanOut)
def patch_loan(loan_id: int, data: LoanPatch, session: Session = Depends(get_session)):
    loan = session.get(Loan, loan_id)
    if loan is None:
        raise HTTPException(404, "Kredit nicht gefunden")
    for key, value in data.model_dump(exclude_unset=True).items():
        setattr(loan, key, value)
    session.commit()
    session.refresh(loan)
    return LoanOut.model_validate(loan)


@router.delete("/loans/{loan_id}", status_code=204)
def delete_loan(loan_id: int, session: Session = Depends(get_session)):
    loan = session.get(Loan, loan_id)
    if loan is None:
        raise HTTPException(404, "Kredit nicht gefunden")
    # Remove scenario assignments first: no DB-level cascade exists, so a
    # dangling ScenarioLoan row would raise a foreign-key violation (500 on
    # Postgres).
    session.execute(delete(ScenarioLoan).where(ScenarioLoan.loan_id == loan_id))
    session.delete(loan)
    session.commit()


@router.get("/loans/{loan_id}/schedule", response_model=list[InstallmentOut])
def get_loan_schedule(loan_id: int, session: Session = Depends(get_session)):
    loan = session.get(Loan, loan_id)
    if loan is None:
        raise HTTPException(404, "Kredit nicht gefunden")
    plan = loan_schedule(Decimal(loan.principal), Decimal(loan.annual_rate_pct),
                         loan.term_months, loan.payout_date, loan.repayment_type)
    return [InstallmentOut(due=i.due, payment=i.payment, interest=i.interest,
                           principal=i.principal, remaining=i.remaining)
           for i in plan]