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backend/graph_utils.py
NetworkX graph construction + Matplotlib diff visualisation + JSON export.
"""
import io, base64
import networkx as nx
import matplotlib
matplotlib.use('Agg')
import matplotlib.pyplot as plt
import matplotlib.patches as mpatches
from matplotlib.colors import to_rgba
# ── Palette ──────────────────────────────────────────────────────────────────
ADD_NODE = '#1D9E75'
ADD_EDGE = '#1D9E75'
REM_NODE = '#D85A30'
REM_EDGE = '#D85A30'
NEU_NODE = '#5a7fa8'
NEU_EDGE = '#9aa8b8'
BG = '#0f1117'
TEXT_COL = '#e8e6e0'
def build_graph(extracted_data: dict) -> nx.DiGraph:
"""Build a directed NetworkX graph from extraction output."""
G = nx.DiGraph()
for entity in extracted_data.get('entities', []):
G.add_node(entity)
for rel in extracted_data.get('relations', []):
if len(rel) == 3:
subj, pred, obj = rel
G.add_edge(subj, obj, label=pred)
return G
def visualise_diff(old_graph: nx.DiGraph,
new_graph: nx.DiGraph,
diff: dict) -> str:
"""
Render a side-by-side diff visualisation.
Returns a base64-encoded PNG string.
"""
added_ents = set(diff.get('added_entities', []))
removed_ents = set(diff.get('removed_entities', []))
added_rels = {tuple(r) for r in diff.get('added_relations', [])}
removed_rels = {tuple(r) for r in diff.get('removed_relations', [])}
fig, axes = plt.subplots(1, 2, figsize=(18, 8), facecolor=BG)
fig.suptitle('Knowledge Graph Diff', fontsize=15, fontweight='bold',
color=TEXT_COL, y=0.98)
pairs = [(axes[0], old_graph, 'Baseline (v1)'),
(axes[1], new_graph, 'Updated (v2)')]
for ax, G, title in pairs:
ax.set_facecolor(BG)
ax.set_title(title, fontsize=12, color=TEXT_COL, pad=10)
ax.axis('off')
if len(G.nodes) == 0:
ax.text(0.5, 0.5, 'No entities extracted',
ha='center', va='center', transform=ax.transAxes,
fontsize=11, color=TEXT_COL, alpha=0.5)
continue
pos = nx.spring_layout(G, seed=42, k=1.6)
# Node colours
node_colours = []
node_sizes = []
for node in G.nodes:
if node in added_ents:
node_colours.append(ADD_NODE)
node_sizes.append(2400)
elif node in removed_ents:
node_colours.append(REM_NODE)
node_sizes.append(2400)
else:
node_colours.append(NEU_NODE)
node_sizes.append(2000)
# Edge colours
edge_colours = []
edge_widths = []
for u, v in G.edges:
label = G[u][v].get('label', '')
triple = (u, label, v)
if triple in added_rels:
edge_colours.append(ADD_EDGE)
edge_widths.append(2.5)
elif triple in removed_rels:
edge_colours.append(REM_EDGE)
edge_widths.append(2.5)
else:
edge_colours.append(NEU_EDGE)
edge_widths.append(1.2)
nx.draw_networkx_nodes(G, pos, ax=ax,
node_color=node_colours,
node_size=node_sizes, alpha=0.92)
nx.draw_networkx_labels(G, pos, ax=ax,
font_size=7.5, font_color='white',
font_weight='bold')
nx.draw_networkx_edges(G, pos, ax=ax,
edge_color=edge_colours,
width=edge_widths,
arrows=True, arrowsize=18,
connectionstyle='arc3,rad=0.12',
min_source_margin=18, min_target_margin=18)
edge_labels = {(u, v): G[u][v].get('label', '') for u, v in G.edges}
nx.draw_networkx_edge_labels(G, pos, edge_labels=edge_labels, ax=ax,
font_size=6.5, font_color=TEXT_COL,
label_pos=0.35, alpha=0.85)
# Legend
legend_handles = [
mpatches.Patch(color=NEU_NODE, label='Unchanged node'),
mpatches.Patch(color=ADD_NODE, label='Added node'),
mpatches.Patch(color=REM_NODE, label='Removed node'),
mpatches.Patch(color=NEU_EDGE, label='Unchanged edge'),
mpatches.Patch(color=ADD_EDGE, label='Added edge'),
mpatches.Patch(color=REM_EDGE, label='Removed edge'),
]
fig.legend(handles=legend_handles, loc='lower center', ncol=6,
fontsize=9, framealpha=0.25, facecolor=BG,
labelcolor=TEXT_COL, edgecolor='none')
plt.tight_layout(rect=[0, 0.06, 1, 0.97])
buf = io.BytesIO()
plt.savefig(buf, format='png', dpi=130, bbox_inches='tight',
facecolor=BG)
plt.close(fig)
buf.seek(0)
return base64.b64encode(buf.read()).decode('utf-8')
def graph_to_json(G: nx.DiGraph) -> dict:
"""Export graph as a node/edge list for D3 rendering in the frontend."""
nodes = [{'id': n} for n in G.nodes]
links = [{'source': u, 'target': v, 'label': G[u][v].get('label', '')}
for u, v in G.edges]
return {'nodes': nodes, 'links': links}
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