"""
Edge processing logic for graph traversal.
"""

from collections.abc import Sequence
from typing import TYPE_CHECKING, final

from graphon.enums import NodeExecutionType
from graphon.graph import Edge, Graph
from graphon.graph_events import NodeRunStreamChunkEvent

from ..graph_state_manager import GraphStateManager
from ..response_coordinator import ResponseStreamCoordinator

if TYPE_CHECKING:
    from .skip_propagator import SkipPropagator


@final
class EdgeProcessor:
    """
    Processes edges during graph execution.

    This handles marking edges as taken or skipped, notifying
    the response coordinator, triggering downstream node execution,
    and managing branch node logic.
    """

    def __init__(
        self,
        graph: Graph,
        state_manager: GraphStateManager,
        response_coordinator: ResponseStreamCoordinator,
        skip_propagator: "SkipPropagator",
    ) -> None:
        """
        Initialize the edge processor.

        Args:
            graph: The workflow graph
            state_manager: Unified state manager
            response_coordinator: Response stream coordinator
            skip_propagator: Propagator for skip states
        """
        self._graph = graph
        self._state_manager = state_manager
        self._response_coordinator = response_coordinator
        self._skip_propagator = skip_propagator

    def process_node_success(
        self, node_id: str, selected_handle: str | None = None
    ) -> tuple[Sequence[str], Sequence[NodeRunStreamChunkEvent]]:
        """
        Process edges after a node succeeds.

        Args:
            node_id: The ID of the succeeded node
            selected_handle: For branch nodes, the selected edge handle

        Returns:
            Tuple of (list of downstream node IDs that are now ready, list of streaming events)
        """
        node = self._graph.nodes[node_id]

        if node.execution_type == NodeExecutionType.BRANCH:
            return self._process_branch_node_edges(node_id, selected_handle)
        else:
            return self._process_non_branch_node_edges(node_id)

    def _process_non_branch_node_edges(self, node_id: str) -> tuple[Sequence[str], Sequence[NodeRunStreamChunkEvent]]:
        """
        Process edges for non-branch nodes (mark all as TAKEN).

        Args:
            node_id: The ID of the succeeded node

        Returns:
            Tuple of (list of downstream nodes ready for execution, list of streaming events)
        """
        ready_nodes: list[str] = []
        all_streaming_events: list[NodeRunStreamChunkEvent] = []
        outgoing_edges = self._graph.get_outgoing_edges(node_id)

        for edge in outgoing_edges:
            nodes, events = self._process_taken_edge(edge)
            ready_nodes.extend(nodes)
            all_streaming_events.extend(events)

        return ready_nodes, all_streaming_events

    def _process_branch_node_edges(
        self, node_id: str, selected_handle: str | None
    ) -> tuple[Sequence[str], Sequence[NodeRunStreamChunkEvent]]:
        """
        Process edges for branch nodes.

        Args:
            node_id: The ID of the branch node
            selected_handle: The handle of the selected edge

        Returns:
            Tuple of (list of downstream nodes ready for execution, list of streaming events)

        Raises:
            ValueError: If no edge was selected
        """
        if not selected_handle:
            raise ValueError(f"Branch node {node_id} did not select any edge")

        ready_nodes: list[str] = []
        all_streaming_events: list[NodeRunStreamChunkEvent] = []

        # Categorize edges
        selected_edges, unselected_edges = self._state_manager.categorize_branch_edges(node_id, selected_handle)

        # Process unselected edges first (mark as skipped)
        for edge in unselected_edges:
            self._process_skipped_edge(edge)

        # Process selected edges
        for edge in selected_edges:
            nodes, events = self._process_taken_edge(edge)
            ready_nodes.extend(nodes)
            all_streaming_events.extend(events)

        return ready_nodes, all_streaming_events

    def _process_taken_edge(self, edge: Edge) -> tuple[Sequence[str], Sequence[NodeRunStreamChunkEvent]]:
        """
        Mark edge as taken and check downstream node.

        Args:
            edge: The edge to process

        Returns:
            Tuple of (list containing downstream node ID if it's ready, list of streaming events)
        """
        # Mark edge as taken
        self._state_manager.mark_edge_taken(edge.id)

        # Notify response coordinator and get streaming events
        streaming_events = self._response_coordinator.on_edge_taken(edge.id)

        # Check if downstream node is ready
        ready_nodes: list[str] = []
        if self._state_manager.is_node_ready(edge.head):
            ready_nodes.append(edge.head)

        return ready_nodes, streaming_events

    def _process_skipped_edge(self, edge: Edge) -> None:
        """
        Mark edge as skipped.

        Args:
            edge: The edge to skip
        """
        self._state_manager.mark_edge_skipped(edge.id)

    def handle_branch_completion(
        self, node_id: str, selected_handle: str | None
    ) -> tuple[Sequence[str], Sequence[NodeRunStreamChunkEvent]]:
        """
        Handle completion of a branch node.

        Args:
            node_id: The ID of the branch node
            selected_handle: The handle of the selected branch

        Returns:
            Tuple of (list of downstream nodes ready for execution, list of streaming events)

        Raises:
            ValueError: If no branch was selected
        """
        if not selected_handle:
            raise ValueError(f"Branch node {node_id} completed without selecting a branch")

        # Categorize edges into selected and unselected
        _, unselected_edges = self._state_manager.categorize_branch_edges(node_id, selected_handle)

        # Skip all unselected paths
        self._skip_propagator.skip_branch_paths(unselected_edges)

        # Process selected edges and get ready nodes and streaming events
        return self.process_node_success(node_id, selected_handle)

    def validate_branch_selection(self, node_id: str, selected_handle: str) -> bool:
        """
        Validate that a branch selection is valid.

        Args:
            node_id: The ID of the branch node
            selected_handle: The handle to validate

        Returns:
            True if the selection is valid
        """
        outgoing_edges = self._graph.get_outgoing_edges(node_id)
        valid_handles = {edge.source_handle for edge in outgoing_edges}
        return selected_handle in valid_handles