import heapq
from itertools import chain, product
from typing import Iterable, Iterator
from functools import cached_property
from .common import Resolver, ResolverRequest, ResultPriority
from ..dataset import DatasetCollection, Dataset
from ..common import Circuit, DeviceKind, JointKind, LcrConnException


class LutItem:
    """
    An item in the lookup table.
    """

    __circuit: Circuit
    """The circuit represented by this item."""
    __device_kind: DeviceKind
    """The device kind applied for this circuit."""

    def __init__(self, circuit: Circuit, device_kind: DeviceKind):
        self.__circuit = circuit
        self.__device_kind = device_kind

    @property
    def circuit(self) -> Circuit:
        return self.__circuit

    @cached_property
    def value(self) -> float:
        """
        The computed value of the circuit.

        :return: The computed value.
        """
        return self.__circuit.compute(self.__device_kind)


class ResultBucket(Iterable[LutItem]):
    """
    A bounded bucket that keeps up to `N` LutItem entries with the smallest floats.

    When the bucket is full, inserting a new item only succeeds if its float
    is less than the current maximum; the maximum is then evicted.
    """

    class ResultBucketItem:
        """
        An item stored in a :class:`ResultBucket`.
        """

        __score: float
        """The score associated with this item."""
        __item: LutItem
        """The underlying LutItem."""
        __seq: int
        """
        Monotonic counter used as a tiebreaker when scores are equal,
        ensuring that heapq never compares :class:`LutItem` directly.
        """

        def __init__(self, score: float, item: LutItem, seq: int):
            self.__score = score
            self.__item = item
            self.__seq = seq

        @property
        def score(self) -> float:
            """The score associated with this item."""
            return self.__score
        
        @property
        def item(self) -> LutItem:
            """The underlying LutItem."""
            return self.__item

        def __lt__(self, other: 'ResultBucket.ResultBucketItem') -> bool:
            # heapq is a min-heap: it always pops the smallest element.
            # We invert the comparison so that an item with a larger score
            # is considered "smaller", effectively turning the min-heap
            # into a max-heap (largest-score item at the top).
            if self.__score != other.__score:
                return self.__score > other.__score
            # Counter tiebreaker: when scores are equal the later-inserted
            # item (higher seq) is considered "smaller" and gets evicted first.
            return self.__seq > other.__seq

    __n: int
    """Maximum number of items the bucket can hold."""
    __heap: list[ResultBucketItem]
    """
    Min-heap of :class:`ResultBucketItem`.  The heap invariant is inverted
    via :meth:`ResultBucketItem.__lt__` so the entry with the largest score
    sits at index 0.
    """
    __counter: int
    """
    Monotonic counter fed to each :class:`ResultBucketItem` as a tiebreaker,
    preventing heapq from comparing :class:`LutItem` on score collisions.
    """

    def __init__(self, n: int):
        self.__n = n
        self.__heap = []
        self.__counter = 0

    def __len__(self) -> int:
        return len(self.__heap)

    def __iter__(self) -> Iterator[LutItem]:
        for entry in self.__heap:
            yield entry.item

    def insert(self, item: LutItem, score: float) -> bool:
        """
        Insert a :class:`LutItem` with the given score.

        If the bucket is not yet full the item is always inserted.
        Otherwise the item is only inserted when *score* is smaller
        than the largest score currently in the bucket; the entry
        with the largest score is then evicted.

        :param item: The LutItem to insert.
        :param score: The score associated with the item.
        :return: ``True`` if the item was inserted, ``False`` otherwise.
        """
        entry = ResultBucket.ResultBucketItem(score, item, self.__counter)
        if len(self.__heap) < self.__n:
            heapq.heappush(self.__heap, entry)
            self.__counter += 1
            return True
        if score >= self.__heap[0].score:
            return False
        heapq.heapreplace(self.__heap, entry)
        self.__counter += 1
        return True


class LutResolver(Resolver):
    """
    A resolver that uses a lookup table to find the best matching circuit.
    """

    __resistor_lut: list[LutItem]
    """The lookup table for resistors."""
    __capacitor_lut: list[LutItem]
    """The lookup table for capacitors."""
    __inductor_lut: list[LutItem]
    """The lookup table for inductors."""

    def __init__(self, datasets: DatasetCollection):
        self.__resistor_lut = LutResolver.__build_lut(
            datasets.resistor_values, DeviceKind.RESISTOR
        )
        self.__capacitor_lut = LutResolver.__build_lut(
            datasets.capacitor_values, DeviceKind.CAPACITOR
        )
        self.__inductor_lut = LutResolver.__build_lut(
            datasets.inductor_values, DeviceKind.INDUCTOR
        )

    @staticmethod
    def __build_lut(dataset: Dataset, device_kind: DeviceKind) -> list[LutItem]:
        values = dataset.values
        joints = tuple(JointKind)
        return [
            LutItem(circuit, device_kind)
            for circuit in chain(
                (Circuit.from_one_device(v1) for v1 in values),
                (
                    Circuit.from_two_devices(v1, v2, j2)
                    for v1, v2, j2 in product(values, values, joints)
                ),
                (
                    Circuit.from_three_devices(v1, v2, j2, v3, j3)
                    for v1, v2, j2, v3, j3 in product(
                        values, values, joints, values, joints
                    )
                ),
            )
        ]

    def resolve(self, request: ResolverRequest) -> Iterator[Circuit]:
        # Fetch LUT by device kind
        lut: list[LutItem]
        match request.device_kind:
            case DeviceKind.RESISTOR:
                lut = self.__resistor_lut
            case DeviceKind.CAPACITOR:
                lut = self.__capacitor_lut
            case DeviceKind.INDUCTOR:
                lut = self.__inductor_lut

        # Check LUT item one by one
        bucket = ResultBucket(min(request.count_limit, 100))
        for item in lut:
            # compute absolute difference
            difference = abs(request.target_value - item.value)
            # If it is out of tolerance, skip it directly.
            if difference > request.tolerance:
                continue
            # put it into bucket
            bucket.insert(item, difference)

        # Return result
        return map(lambda item: item.circuit, bucket)