"""
Python module wrapper for _functools C module
to allow utilities written in Python to be added
to the functools module.
Written by Nick Coghlan <ncoghlan at gmail.com>,
Raymond Hettinger <python at rcn.com>,
and Łukasz Langa <lukasz at langa.pl>.
  Copyright (C) 2006-2013 Python Software Foundation.
See C source code for _functools credits/copyright
Modified from
https://github.com/python/cpython/blob/3.12/Lib/functools.py
"""

from typing import Callable, Generic, TypeVar

K = TypeVar("K")
T = TypeVar("T")
PREV, NEXT, KEY, RESULT = 0, 1, 2, 3  # names for the link fields


class Cache(Generic[K, T]):
    """
    A generic caching mechanism that stores the results of a function call and
    retrieves them to avoid repeated calculations.

    This class implements a dictionary-based cache with a circular doubly linked
    list to manage the cache entries efficiently. It is designed to be generic,
    allowing for caching of any callable function.

    Parameters
    ----------
    func : Callable[[K], T]
        The function to be cached. This function takes an argument of type K and
        returns a value of type T.
    """

    def __init__(self, func: Callable[[K], T]):
        self.func = func
        self.has_init = False

        self.cache = False
        self.cache_dict = {}
        self.key_func = None
        self.max_size = 0

        self.hits, self.misses = 0, 0
        self.full = False
        self.root = []  # root of the circular doubly linked list
        self.root[:] = [self.root, self.root, None, None]

    def __getitem__(self, obj, *args) -> T:
        return self.get_from_dict(obj, *args)

    def clear_cache(self):
        """
        Invalidate the entire cache.
        """
        self.cache_dict.clear()

    def init_cache(self, obj):
        """
        Initialize the cache settings.

        Parameters
        ----------
        obj : Any
            The object containing settings for cache initialization.
        """
        if self.has_init:
            return

        self.cache = True
        self.cache_dict = {}
        self.key_func = obj.key_func
        self.max_size = obj.cache_size

        self.hits, self.misses = 0, 0
        self.full = False
        self.root = []  # root of the circular doubly linked list
        self.root[:] = [self.root, self.root, None, None]

        self.has_init = True

    def get_from_dict(self, obj, *args) -> T:
        """
        Retrieve a value from the cache or compute it using ``self.func``.

        Parameters
        ----------
        obj : Any
            The object to which the cached method/function belongs.
        *args : Any
            Arguments used in key generation for cache retrieval or function computation.

        Returns
        -------
        T
            The value from the cache or computed by the function.
        """
        # x is not used in cache key
        pred_pseudo_label, y, _x, *res_args = args
        cache_key = (self.key_func(pred_pseudo_label), self.key_func(y), *res_args)
        link = self.cache_dict.get(cache_key)
        if link is not None:
            # Move the link to the front of the circular queue
            link_prev, link_next, _key, result = link
            link_prev[NEXT] = link_next
            link_next[PREV] = link_prev
            last = self.root[PREV]
            last[NEXT] = self.root[PREV] = link
            link[PREV] = last
            link[NEXT] = self.root
            self.hits += 1
            return result
        self.misses += 1

        result = self.func(obj, *args)

        if self.full:
            # Use the old root to store the new key and result.
            oldroot = self.root
            oldroot[KEY] = cache_key
            oldroot[RESULT] = result
            # Empty the oldest link and make it the new root.
            self.root = oldroot[NEXT]
            oldkey = self.root[KEY]
            self.root[KEY] = self.root[RESULT] = None
            # Now update the cache dictionary.
            del self.cache_dict[oldkey]
            self.cache_dict[cache_key] = oldroot
        else:
            # Put result in a new link at the front of the queue.
            last = self.root[PREV]
            link = [last, self.root, cache_key, result]
            last[NEXT] = self.root[PREV] = self.cache_dict[cache_key] = link
            if isinstance(self.max_size, int):
                self.full = len(self.cache_dict) >= self.max_size
        return result


def abl_cache():
    """
    Decorator to enable caching for a function.

    Returns
    -------
    Callable
        The wrapped function with caching capability.
    """

    def decorator(func):
        cache_instance = Cache(func)

        def wrapper(obj, *args):
            if obj.use_cache:
                cache_instance.init_cache(obj)
                return cache_instance.get_from_dict(obj, *args)
            return func(obj, *args)

        return wrapper

    return decorator