compute_layout.py

"""
Pre-compute force-directed layout for Steam co-review network.

Uses networkx spring_layout (Fruchterman-Reingold) with scipy acceleration.
26K nodes, filtered edges. Outputs steam_force_layout.json.

Usage:
    python3 compute_layout.py
"""

import json
import time
import sys
from pathlib import Path

try:
    import networkx as nx
except ImportError:
    print("ERROR: networkx required. pip install networkx")
    sys.exit(1)

# ── Config ──────────────────────────────────────────────────────────
HERE = Path(__file__).parent
NETWORK_JSON = HERE / 'steam_network.json'
OUTPUT = HERE / 'steam_force_layout.json'

# Edge weight threshold — only include edges with weight >= this
# Higher = fewer edges = faster layout. 100 gives ~9K nodes, ~219K edges.
MIN_WEIGHT = 100
# Layout iterations (more = better convergence, slower)
ITERATIONS = 80
# Spring constant (lower = more spread out)
K_SPRING = None  # None = auto (1/sqrt(n))
# Seed for reproducibility
SEED = 42

def main():
    t0 = time.time()
    print("=" * 60)
    print("Steam Network Force Layout Generator")
    print("=" * 60)

    # 1. Load network data
    print("\n[1/4] Loading network data...")
    with open(NETWORK_JSON) as f:
        data = json.load(f)

    nodes = data['nodes']
    links = data['links']
    print(f"  {len(nodes):,} nodes, {len(links):,} links")

    # 2. Build graph with filtered edges
    print(f"\n[2/4] Building graph (min weight={MIN_WEIGHT})...")
    G = nx.Graph()

    # Add all nodes with metadata
    for i, node in enumerate(nodes):
        G.add_node(i, title=node['title'], reviews=node.get('reviews', 0))

    # Add edges above threshold
    added = 0
    skipped = 0
    for link in links:
        if link['weight'] >= MIN_WEIGHT:
            G.add_edge(link['source'], link['target'], weight=link['weight'])
            added += 1
        else:
            skipped += 1

    # Remove isolated nodes (no edges after filtering)
    isolates = list(nx.isolates(G))
    G.remove_nodes_from(isolates)

    print(f"  {G.number_of_nodes():,} nodes, {G.number_of_edges():,} edges")
    print(f"  ({len(isolates):,} isolated nodes removed, {skipped:,} edges below threshold)")

    # 3. Compute layout
    print(f"\n[3/4] Computing spring layout ({ITERATIONS} iterations)...")
    print(f"  This may take a few minutes for {G.number_of_nodes():,} nodes...")

    t1 = time.time()

    # Use weight for layout — higher weight = stronger attraction
    pos = nx.spring_layout(
        G,
        k=K_SPRING,
        iterations=ITERATIONS,
        seed=SEED,
        weight='weight',
    )

    layout_time = time.time() - t1
    print(f"  Layout computed in {layout_time:.1f}s")

    # 4. Build output — map node index back to node ID
    print("\n[4/4] Writing output...")
    output = {
        'positions': {},
        'meta': {
            'node_count': G.number_of_nodes(),
            'edge_count': G.number_of_edges(),
            'min_weight': MIN_WEIGHT,
            'iterations': ITERATIONS,
            'layout_time_seconds': round(layout_time, 1),
        }
    }

    # Normalize positions to [0, 1] using percentile-based scaling.
    # Min/max normalization is ruined by outlier nodes — a few extreme
    # positions compress the main cluster into a tiny area. Percentile
    # scaling maps the 1st-99th percentile range to [0.02, 0.98] and
    # clamps outliers to the edges.
    all_x = sorted(float(xy[0]) for xy in pos.values())
    all_y = sorted(float(xy[1]) for xy in pos.values())
    n = len(all_x)
    p_lo, p_hi = 0.01, 0.99
    x_lo = all_x[int(n * p_lo)]
    x_hi = all_x[int(n * p_hi)]
    y_lo = all_y[int(n * p_lo)]
    y_hi = all_y[int(n * p_hi)]
    x_range = x_hi - x_lo or 1
    y_range = y_hi - y_lo or 1
    margin = 0.02

    for node_idx, (x, y) in pos.items():
        node_id = nodes[node_idx]['id']
        nx = (float(x) - x_lo) / x_range * (1 - 2 * margin) + margin
        ny = (float(y) - y_lo) / y_range * (1 - 2 * margin) + margin
        nx = max(0.0, min(1.0, nx))
        ny = max(0.0, min(1.0, ny))
        output['positions'][node_id] = [round(nx, 6), round(ny, 6)]

    with open(OUTPUT, 'w') as f:
        json.dump(output, f, separators=(',', ':'))

    size_mb = OUTPUT.stat().st_size / (1024 * 1024)
    elapsed = time.time() - t0

    print(f"\n{'=' * 60}")
    print(f"Saved: {OUTPUT}")
    print(f"  {output['meta']['node_count']:,} nodes with positions")
    print(f"  {output['meta']['edge_count']:,} edges used for layout")
    print(f"  Size: {size_mb:.1f} MB")
    print(f"  Total time: {elapsed:.0f}s ({elapsed/60:.1f} min)")
    print("=" * 60)


if __name__ == '__main__':
    main()