"""Single administrator credentials, independent API token and atomic persistence."""
import hashlib
import hmac
import json
import os
from pathlib import Path
import re
import secrets
import threading
import time

ITERATIONS = 600000


def password_hash(password):
    if not isinstance(password, str) or not 16 <= len(password) <= 256:
        raise ValueError('Das Kennwort muss 16 bis 256 Zeichen lang sein.')
    salt = secrets.token_bytes(16)
    return dict(salt=salt.hex(), hash=hashlib.pbkdf2_hmac('sha256', password.encode(), salt, ITERATIONS).hex())


def verify_password(password, record):
    if not isinstance(password, str) or len(password) > 256 or not record:
        return False
    actual = hashlib.pbkdf2_hmac('sha256', password.encode(), bytes.fromhex(record['salt']), ITERATIONS).hex()
    return hmac.compare_digest(actual, record['hash'])


def token_hash(token):
    if not isinstance(token, str) or not re.fullmatch(r'[A-Za-z0-9_-]{32,256}', token):
        raise ValueError('Der API-Token muss 32 bis 256 Zeichen enthalten: Buchstaben, Ziffern, - oder _.')
    return hashlib.sha256(token.encode()).hexdigest()


def normalize(record):
    # Existing 0.2 installs keep their password; API access stays disabled until a token is set.
    if record and set(record) == {'salt', 'hash'}:
        return dict(version=1, password=record, revision=record['hash'], api_token_hash=None,
                    password_changed_at=None, token_changed_at=None)
    return record


def validate_record(record):
    if not isinstance(record, dict) or set(record) != {'version','password','revision','api_token_hash','password_changed_at','token_changed_at'}:
        raise ValueError('Ungültiger Zugangsdatenstand.')
    p = record['password']
    if record['version'] != 1 or not isinstance(p, dict) or set(p) != {'salt','hash'}:
        raise ValueError('Ungültiger Zugangsdatenstand.')
    if not re.fullmatch('[a-f0-9]{32}', str(p['salt'])) or not re.fullmatch('[a-f0-9]{64}', str(p['hash'])):
        raise ValueError('Ungültiger Zugangsdatenstand.')
    if not re.fullmatch('[a-f0-9]{32,64}', str(record['revision'])):
        raise ValueError('Ungültiger Zugangsdatenstand.')
    if record['api_token_hash'] is not None and not re.fullmatch('[a-f0-9]{64}', str(record['api_token_hash'])):
        raise ValueError('Ungültiger Zugangsdatenstand.')
    for field in ('password_changed_at','token_changed_at'):
        if record[field] is not None and (not isinstance(record[field], (float,int)) or not 0 < record[field] < 1e12):
            raise ValueError('Ungültiger Zugangsdatenstand.')
    return record


def initial_record(password, token):
    if password == token:
        raise ValueError('Oberflächenkennwort und API-Token müssen verschieden sein.')
    now = time.time()
    return dict(version=1, password=password_hash(password), revision=secrets.token_hex(16),
                api_token_hash=token_hash(token), password_changed_at=now, token_changed_at=now)


def atomic_write(path, record):
    path = Path(path)
    path.parent.mkdir(mode=0o700, parents=True, exist_ok=True)
    temporary = path.with_name(path.name+'.'+secrets.token_hex(8)+'.tmp')
    fd = os.open(temporary, os.O_WRONLY | os.O_CREAT | os.O_EXCL, 0o600)
    try:
        with os.fdopen(fd,'w') as stream:
            json.dump(record,stream)
            stream.flush()
            os.fsync(stream.fileno())
        os.replace(temporary,path)
    finally:
        temporary.unlink(missing_ok=True)

class CredentialStore:
    def __init__(self, path=None, rpc=None):
        self.path = Path(path) if path else None
        self.rpc = rpc
        self.lock = threading.RLock()

    def read(self):
        with self.lock:
            if self.rpc:
                record = self.rpc({'action':'credentials-read'})['credentials']
            else:
                try:
                    record = json.loads(self.path.read_text())
                except FileNotFoundError:
                    return None
            return validate_record(normalize(record)) if record else None

    def write(self, record, expected):
        validate_record(record)
        if self.rpc:
            self.rpc({'action':'credentials-write','expected_revision':expected,'credentials':record})
        else:
            current = self.read()
            if (current['revision'] if current else None) != expected:
                raise ValueError('Zugangsdaten wurden inzwischen geändert. Bitte erneut anmelden.')
            atomic_write(self.path, record)

    def setup(self, password, token):
        with self.lock:
            if self.read() is not None:
                raise ValueError('Die Ersteinrichtung ist bereits abgeschlossen.')
            record = initial_record(password,token)
            self.write(record,None)
            return record

    def change(self, kind, current_password, value):
        with self.lock:
            record = self.read()
            if not record or not verify_password(current_password,record['password']):
                raise ValueError('Das aktuelle Kennwort ist nicht korrekt.')
            expected = record['revision']
            if kind == 'password':
                if verify_password(value,record['password']):
                    raise ValueError('Bitte ein anderes neues Kennwort wählen.')
                if record['api_token_hash'] and isinstance(value,str) and hmac.compare_digest(hashlib.sha256(value.encode()).hexdigest(),record['api_token_hash']):
                    raise ValueError('Oberflächenkennwort und API-Token müssen verschieden sein.')
                record.update(password=password_hash(value), password_changed_at=time.time(), revision=secrets.token_hex(16))
            elif kind == 'token':
                digest = token_hash(value)
                if verify_password(value,record['password']):
                    raise ValueError('Oberflächenkennwort und API-Token müssen verschieden sein.')
                if record['api_token_hash'] and hmac.compare_digest(digest,record['api_token_hash']):
                    raise ValueError('Bitte einen anderen neuen API-Token wählen.')
                record.update(api_token_hash=digest,token_changed_at=time.time(),revision=secrets.token_hex(16))
            else:
                raise ValueError('Unbekannte Zugangsdatenaktion.')
            self.write(record,expected)
            return record