langchain/libs/core/langchain_core/runnables/graph.py

from __future__ import annotations

from dataclasses import dataclass, field
from typing import TYPE_CHECKING, Dict, List, NamedTuple, Optional, Type, Union
from uuid import uuid4

from langchain_core.pydantic_v1 import BaseModel
from langchain_core.runnables.graph_draw import draw

if TYPE_CHECKING:
    from langchain_core.runnables.base import Runnable as RunnableType


class Edge(NamedTuple):
    source: str
    target: str


class Node(NamedTuple):
    id: str
    data: Union[Type[BaseModel], RunnableType]


@dataclass
class Graph:
    nodes: Dict[str, Node] = field(default_factory=dict)
    edges: List[Edge] = field(default_factory=list)

    def __bool__(self) -> bool:
        return bool(self.nodes)

    def next_id(self) -> str:
        return uuid4().hex

    def add_node(self, data: Union[Type[BaseModel], RunnableType]) -> Node:
        """Add a node to the graph and return it."""
        node = Node(id=self.next_id(), data=data)
        self.nodes[node.id] = node
        return node

    def remove_node(self, node: Node) -> None:
        """Remove a node from the graphm and all edges connected to it."""
        self.nodes.pop(node.id)
        self.edges = [
            edge
            for edge in self.edges
            if edge.source != node.id and edge.target != node.id
        ]

    def add_edge(self, source: Node, target: Node) -> Edge:
        """Add an edge to the graph and return it."""
        if source.id not in self.nodes:
            raise ValueError(f"Source node {source.id} not in graph")
        if target.id not in self.nodes:
            raise ValueError(f"Target node {target.id} not in graph")
        edge = Edge(source=source.id, target=target.id)
        self.edges.append(edge)
        return edge

    def extend(self, graph: Graph) -> None:
        """Add all nodes and edges from another graph.
        Note this doesn't check for duplicates, nor does it connect the graphs."""
        self.nodes.update(graph.nodes)
        self.edges.extend(graph.edges)

    def first_node(self) -> Optional[Node]:
        """Find the single node that is not a target of any edge.
        If there is no such node, or there are multiple, return None.
        When drawing the graph this node would be the origin."""
        targets = {edge.target for edge in self.edges}
        found: List[Node] = []
        for node in self.nodes.values():
            if node.id not in targets:
                found.append(node)
        return found[0] if len(found) == 1 else None

    def last_node(self) -> Optional[Node]:
        """Find the single node that is not a source of any edge.
        If there is no such node, or there are multiple, return None.
        When drawing the graph this node would be the destination.
        """
        sources = {edge.source for edge in self.edges}
        found: List[Node] = []
        for node in self.nodes.values():
            if node.id not in sources:
                found.append(node)
        return found[0] if len(found) == 1 else None

    def trim_first_node(self) -> None:
        """Remove the first node if it exists and has a single outgoing edge,
        ie. if removing it would not leave the graph without a "first" node."""
        first_node = self.first_node()
        if first_node:
            if (
                len(self.nodes) == 1
                or len([edge for edge in self.edges if edge.source == first_node.id])
                == 1
            ):
                self.remove_node(first_node)

    def trim_last_node(self) -> None:
        """Remove the last node if it exists and has a single incoming edge,
        ie. if removing it would not leave the graph without a "last" node."""
        last_node = self.last_node()
        if last_node:
            if (
                len(self.nodes) == 1
                or len([edge for edge in self.edges if edge.target == last_node.id])
                == 1
            ):
                self.remove_node(last_node)

    def draw_ascii(self) -> str:
        from langchain_core.runnables.base import Runnable

        def node_data(node: Node) -> str:
            if isinstance(node.data, Runnable):
                try:
                    data = str(node.data)
                    if (
                        data.startswith("<")
                        or data[0] != data[0].upper()
                        or len(data.splitlines()) > 1
                    ):
                        data = node.data.__class__.__name__
                    elif len(data) > 42:
                        data = data[:42] + "..."
                except Exception:
                    data = node.data.__class__.__name__
            else:
                data = node.data.__name__
            return data if not data.startswith("Runnable") else data[8:]

        return draw(
            {node.id: node_data(node) for node in self.nodes.values()},
            [(edge.source, edge.target) for edge in self.edges],
        )

    def print_ascii(self) -> None:
        print(self.draw_ascii())