Feature: LangGraph Core Functionality
  As a developer
  I want to use LangGraph for complex graph-based agent workflows
  So that I can build reactive agent systems with proper state management

  Background:
    Given I have imported the necessary modules
    And I have a clean graph test environment

  Scenario: Initialize basic LangGraph with minimal configuration
    Given I have a GraphConfig with name "test_graph"
    When I create a LangGraph instance
    Then the graph should be initialized successfully
    And the graph should have "start" and "end" nodes
    And the state manager should be initialized

  Scenario: Initialize LangGraph with custom state class
    Given I have a custom state class
    And I have a GraphConfig with custom state class
    When I create a LangGraph instance with the custom state
    Then the state manager should use the custom state class

  Scenario: Initialize LangGraph with checkpointing enabled
    Given I have a temporary checkpoint directory
    And I have a GraphConfig with checkpointing enabled
    When I create a LangGraph instance
    Then the state manager should have checkpointing enabled

  Scenario: Initialize LangGraph with provided scheduler
    Given I have an AsyncIO scheduler for graph
    And I have a GraphConfig with name "scheduled_graph"
    When I create a LangGraph instance with the scheduler
    Then the graph should use the provided scheduler

  Scenario: Initialize LangGraph with existing stream router
    Given I have a ReactiveStreamRouter instance
    And I have a GraphConfig with name "routed_graph"
    When I create a LangGraph instance with the router
    Then the graph should use the provided router

  Scenario: Validate graph with invalid entry point
    Given I have a GraphConfig with invalid entry point "nonexistent"
    When I try to create a LangGraph instance
    Then it should raise a ValueError with message "Entry point 'nonexistent' not found"

  Scenario: Validate graph with invalid edge source
    Given I have a GraphConfig with name "invalid_edge_graph"
    And I add an edge from "nonexistent" to "end"
    When I try to create a LangGraph instance
    Then it should raise a ValueError with message "Edge source 'nonexistent' not found"

  Scenario: Validate graph with invalid edge target
    Given I have a GraphConfig with name "invalid_target_graph"
    And I add an edge from "start" to "nonexistent"
    When I try to create a LangGraph instance
    Then it should raise a ValueError with message "Edge target 'nonexistent' not found"

  Scenario: Detect cycles in graph
    Given I have a GraphConfig with cyclic edges
    When I create a LangGraph instance
    Then the graph should detect cycles

  Scenario: Find parallel execution groups
    Given I have a GraphConfig with parallel execution enabled
    And I have nodes that can execute in parallel
    When I create a LangGraph instance
    Then the graph should identify parallel groups

  Scenario: Find reachable nodes from entry point
    Given I have a GraphConfig with disconnected nodes
    When I create a LangGraph instance
    Then the graph should warn about unreachable nodes

  Scenario: Execute graph with message input
    Given I have a GraphConfig with agent nodes
    And I have created a LangGraph instance
    When I execute the graph with message input
    Then the state should be updated with messages

  Scenario: Execute graph while already running
    Given I have a GraphConfig with name "busy_graph"
    And I have created a LangGraph instance
    And the graph is already running
    When I try to execute the graph again
    Then it should raise a RuntimeError with message "Graph is already running"

  Scenario: Add node to existing graph
    Given I have a GraphConfig with basic nodes
    And I have created a LangGraph instance
    When I add a new node "processor"
    Then the node should be added successfully
    And the graph should be re-analyzed

  Scenario: Add duplicate node to graph
    Given I have a GraphConfig with a node "processor"
    And I have created a LangGraph instance
    When I try to add a duplicate node "processor"
    Then it should raise a ValueError with message "Node 'processor' already exists"

  Scenario: Add edge to existing graph
    Given I have a GraphConfig with nodes "start", "middle", "end"
    And I have created a LangGraph instance
    When I add an edge from "middle" to "end"
    Then the edge should be added successfully
    And the graph should be re-analyzed

  Scenario: Add edge with invalid source
    Given I have a GraphConfig with basic nodes
    And I have created a LangGraph instance
    When I try to add an edge from "invalid" to "end"
    Then it should raise a ValueError with message "Source node 'invalid' not found"

  Scenario: Add edge with invalid target
    Given I have a GraphConfig with basic nodes
    And I have created a LangGraph instance
    When I try to add an edge from "start" to "invalid"
    Then it should raise a ValueError with message "Target node 'invalid' not found"

  Scenario: Get current graph state
    Given I have a GraphConfig with state management
    And I have created a LangGraph instance
    When I get the current state
    Then I should receive the current GraphState

  Scenario: Get execution history
    Given I have a GraphConfig with tracking enabled
    And I have created a LangGraph instance
    And I have executed some nodes
    When I get the execution history
    Then I should receive a copy of the execution history

  Scenario: Visualize graph in mermaid format
    Given I have a GraphConfig with various node types
    And I have created a LangGraph instance
    When I visualize the graph in "mermaid" format
    Then I should receive valid mermaid diagram syntax

  Scenario: Visualize graph in unsupported format
    Given I have a GraphConfig with basic nodes
    And I have created a LangGraph instance
    When I visualize the graph in "invalid" format
    Then I should receive "Format invalid not supported"

  Scenario: Register node executor function
    Given I have a GraphConfig with a node "worker"
    And I have created a LangGraph instance
    When the node executor is registered
    Then the executor function should be stored in the router

  Scenario: Execute node with state updates
    Given I have a GraphConfig with an agent node
    And I have created a LangGraph instance
    When I execute a node that returns updates
    Then the state should be updated accordingly
    And the execution history should be recorded

  Scenario: Analyze graph with topological levels
    Given I have a GraphConfig with hierarchical structure
    When I create a LangGraph instance
    Then the topological levels should be computed correctly

  Scenario: Check node execution prerequisites
    Given I have a GraphConfig with dependencies
    And I have created a LangGraph instance
    When I check if a node can execute
    Then it should verify all predecessors are executed

  Scenario: Get next nodes with conditional edges
    Given I have a GraphConfig with conditional routing
    And I have created a LangGraph instance
    When I get next nodes for execution
    Then it should evaluate edge conditions

  Scenario: Create control streams for graph
    Given I have a GraphConfig with stream control
    And I have created a LangGraph instance
    When I check control and state streams
    Then control and state streams should be created

  Scenario: Execute nodes in parallel mode
    Given I have a GraphConfig with parallel execution
    And I have created a LangGraph instance
    When I execute multiple nodes in parallel
    Then they should run concurrently

  Scenario: Execute graph from specific node
    Given I have a GraphConfig with multiple paths
    And I have created a LangGraph instance
    When I execute from a specific node
    Then execution should follow the correct path

  Scenario: Handle node shape mapping for visualization
    Given I have a GraphConfig with all node types
    And I have created a LangGraph instance
    When I get node shapes for visualization
    Then each node type should have the correct shape