#!/usr/bin/env python3
# -*- coding: utf-8 -*-

# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# IMPORTS
# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

from __future__ import annotations;

from src.local.typing import *;

# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# EXPORTS
# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

__all__ = [
    'Graph',
];

# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# CLASS Graph
# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

class Graph(object):
    '''
    a data structure for graphs
    '''
    nodes: list[Any];
    edges: list[tuple[Any,Any]]

    def __init__(self, nodes: list[Any], edges: list[tuple[Any,Any]]):
        self.nodes = nodes;
        self.edges = edges;
        return;

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

    def subgraph(self, nodes: list[Any]) -> Graph:
        '''
        @returns graph induced by subset of nodes
        '''
        return Graph(
            nodes = [ u for u in self.nodes if u in nodes ],
            edges = [ (u, v) for u, v in self.edges if u in nodes and v in nodes ],
        );

    def successors(self, u: str):
        '''
        @returns
        list of successor nodes
        '''
        return [ v for (u_, v) in self.edges if u == u_ ];

    def predecessors(self, v: str):
        '''
        @returns
        list of predecessor nodes
        '''
        return [ u for (u, v_) in self.edges if v == v_ ];