import numpy as np
import holoviews as hv
from holoviews import opts
hv.extension('bokeh')

opts.defaults(opts.Graph(width=400, height=400))

# Declare abstract edges
N = 8
node_indices = np.arange(N)
source = np.zeros(N)
target = node_indices

simple_graph = hv.Graph(((source, target),))
simple_graph

simple_graph.opts(directed=True, arrowhead_length=0.05)

simple_graph.nodes + simple_graph.edgepaths

# Node info
np.random.seed(7)
x, y = simple_graph.nodes.array([0, 1]).T
node_labels = ['Output']+['Input']*(N-1)
edge_weights = np.random.rand(8)

# Compute edge paths
def bezier(start, end, control, steps=np.linspace(0, 1, 100)):
    return (1-steps)**2*start + 2*(1-steps)*steps*control+steps**2*end

paths = []
for node_index in node_indices:
    ex, ey = x[node_index], y[node_index]
    paths.append(np.column_stack([bezier(x[0], ex, 0), bezier(y[0], ey, 0)]))

# Declare Graph
nodes = hv.Nodes((x, y, node_indices, node_labels), vdims='Type')
graph = hv.Graph(((source, target, edge_weights), nodes, paths), vdims='Weight')

graph.opts(node_color='Type', edge_color='Weight', cmap=['blue', 'red'], edge_cmap='viridis')