from pathlib import Path
import string
import random
import logging
import json
import uuid
from subprocess import Popen, CalledProcessError, check_output
from typing import Optional
import hashlib
import base64

import redis
from fastapi import FastAPI, APIRouter, HTTPException, Cookie, Request
from fastapi.responses import Response, RedirectResponse
from fastapi.staticfiles import StaticFiles
from pydantic import BaseModel, BaseSettings


code_dir = Path(".")


class Settings(BaseSettings):
    app_name: str = "tResetter"
    validate_login_exe: str
    change_password_exe: str
    generate_password: Optional[str]
    redis_host: str = "localhost"
    expire_time: int = 60 * 20
    root_path: Optional[str]
    root_prefix: str = "/tresetter"

    class Config:
        pass

    @property
    def redis_params(self):
        return {"host": self.redis_host}


settings = Settings()
kwargs = {}
if settings.root_path:
    kwargs["root_path"] = settings.root_path
app = FastAPI(**kwargs)

router = APIRouter(prefix=settings.root_prefix)

app.mount(
    settings.root_prefix + "/s",
    StaticFiles(directory=str(code_dir / "static")),
    name="static",
)

logger = logging.getLogger("server")


# Session {{{


class SessionNotFoundException(HTTPException):
    def __init__(self):
        super().__init__(status_code=401)


def create_session(content) -> str:
    session_id = str(uuid.uuid4())
    set_session(session_id, content)
    return session_id


def set_session(session_id: str, content) -> bool:
    r = redis.Redis(**settings.redis_params)
    serialized = json.dumps(content)
    ret = r.set(session_id, serialized)
    r.expire(session_id, settings.expire_time)


def get_session(session_id: str, renew=True):
    if session_id is None:
        raise SessionNotFoundException()
    r = redis.Redis(**settings.redis_params)
    serialized = r.get(session_id)
    logger.error("%s", repr(serialized))
    if serialized is None:
        raise SessionNotFoundException()
    if renew:
        r.expire(session_id, settings.expire_time)
    return json.loads(serialized)


def delete_session(session_id: str):
    r = redis.Redis(**settings.redis_params)
    r.delete(session_id)


# end session }}}

# Models {{{


class UserData(BaseModel):
    username: str


class ChangeData(BaseModel):
    password: str


class LoginData(UserData, ChangeData):
    pass


class SuccessData(BaseModel):
    success: bool = True


# end Models }}}


# external commands {{{
def validate(username, password):
    p = Popen(
        [settings.validate_login_exe],
        env={"VERIRY_USERNAME": username, "VERIFY_PASSWORD": password},
    )
    try:
        p.communicate()
    except CalledProcessError:
        return False

    return p.returncode == 0


def password_generate() -> str:
    if settings.generate_password:
        s = check_output([settings.generate_password], encoding='utf8')
        assert type(s) is str
        return s.strip()

    else:
        symbols = list(string.ascii_lowercase) + list(string.digits)
        return "".join(random.choices(symbols, k=10))


def change_password(username: str, new_password: str) -> bool:
    p = Popen(
        [settings.change_password_exe],
        env={"CHANGE_USERNAME": username, "CHANGE_PASSWORD": new_password},
    )

    try:
        p.communicate()
    except CalledProcessError:
        return False

    if p.returncode != 0:
        return False
    return True


# end external commands }}}


@router.get("/")
async def home(request: Request, session_id: str = Cookie(None)):
    """redirects to the user to the home"""
    try:
        get_session(session_id)
    except SessionNotFoundException:
        return RedirectResponse(app.url_path_for("static", path="login.html"))
    return RedirectResponse(app.url_path_for("static", path="change.html"))


@router.post("/login", tags=["session"])
async def login(req: LoginData):
    """
    performs login
    """

    ok = validate(req.username, req.password)
    if not ok:
        raise HTTPException(status_code=401, detail="Authentication error")
    session_id = create_session(
        {
            "username": req.username,
        }
    )
    response = Response()
    response.set_cookie(key="session_id", value=session_id)
    return response


@router.get("/whoami", tags=["session"])
async def whoami(session_id: str = Cookie(None)):
    """Confirm login information"""
    session = get_session(session_id)
    return UserData(username=session["username"])


@router.post("/logout", tags=["session"])
async def logout(session_id: str = Cookie(None)) -> BaseModel:
    get_session(session_id)
    delete_session(session_id)
    return BaseModel()

KDF_SALT_SIZE = 16


def kdf_gen(password, salt=None) -> str:
    if salt is None:
        salt = random.randbytes(KDF_SALT_SIZE)
    if hasattr(password, 'encode'):
        password = password.encode('utf8')
    raw = hashlib.scrypt(password, n=2, r=1, p=1, salt=salt)
    with_salt = salt + raw
    return base64.b64encode(with_salt).decode('ascii')

def kdf_get_salt(hashed: str):
    hashed_str = hashed.decode('ascii') if hasattr(hashed, 'decode') else hashed
    with_salt = base64.b64decode(hashed_str)
    salt = with_salt[:KDF_SALT_SIZE]
    return salt

def kdf_verify(hashed: str, password: str) -> bool:
    salt = kdf_get_salt(hashed)
    hashed2 = kdf_gen(password, salt=salt)
    return hashed == hashed2


@router.post("/generate", tags=["password"])
async def generate(session_id: str = Cookie(None)):
    session = get_session(session_id)
    proposed_password = password_generate()
    session["proposed_password_hash"] = kdf_gen(proposed_password)
    set_session(session_id, session)

    return ChangeData(password=proposed_password)


@router.post("/change", tags=["password"])
async def change(req: ChangeData, session_id: str = Cookie(None)) -> SuccessData:
    session = get_session(session_id)
    if "proposed_password_hash" not in session:
        raise HTTPException(status_code=400, detail="You must generate it first")
    hashed = session["proposed_password_hash"]
    if not kdf_verify(hashed, req.password):
        raise HTTPException(status_code=409)
    delete_session(session_id)

    success = change_password(session["username"], req.password)
    return SuccessData(success=success)


app.include_router(router)


# vim: set fdm=marker: