zigzag-engine/examples/trace_scaffold.rs

//! Trace scaffold nodes for visible wires through all time heights
//!
//! Run with: cargo run --example trace_scaffold

use std::fs;
use zigzag_engine::diagram::Diagram;
use zigzag_engine::import::load_homotopy_diagram_n;

fn main() {
    let json = fs::read_to_string("fixtures/half_braid.json")
        .expect("Failed to read half_braid.json");
    let half_braid = load_homotopy_diagram_n(&json)
        .expect("Failed to parse");

    println!("=== SCAFFOLD NODE TRACING ===\n");

    // Time structure of the 3-diagram
    println!("TIME STRUCTURE (coord[2]):");
    println!("  The half_braid has {} cospan(s)", half_braid.cospans.len());
    println!("  Time heights: r0 (source), s0 (merge), r1 (target)");
    println!();

    // Source 2-diagram heights
    if let Diagram::DiagramN(src) = half_braid.source() {
        println!("SOURCE 2-DIAGRAM (at time r0):");
        println!("  {} cospans → heights: r0, s0, r1, s1, r2", src.cospans.len());
        println!("  Y-mapping: r0→-1, s0→0, r1→0, s1→1, r2→+1");
        println!();
    }

    // Target 2-diagram heights
    let target = half_braid.target();
    if let Diagram::DiagramN(tgt) = &target {
        println!("TARGET 2-DIAGRAM (at time r1):");
        println!("  {} cospan(s) → heights: r0, s0, r1", tgt.cospans.len());
        println!("  Y-mapping: r0→-1, s0→0, r1→0");
        println!();
    }

    println!("=== HEIGHT MAPPING THROUGH MERGE ===");
    println!();
    println!("The merge contracts source heights to target heights:");
    println!("  Source r0 → Target r0  (preserved, y stays at -1)");
    println!("  Source s0 → Target s0  (merges, y=0 → y=0)");
    println!("  Source r1 → Target s0  (absorbed into merge, y=0 → y=0)");
    println!("  Source s1 → Target s0  (merges, y=1 → y=0)");
    println!("  Source r2 → Target r1  (contracts down, y=+1 → y=0)");
    println!();

    println!("=== SCAFFOLD NODE POSITIONS FOR EACH WIRE ===");
    println!();
    println!("Time positions: r0 at x=-1, s0 at x=0, r1 at x=+1");
    println!("Depth positions: r0→z=-1, r1→z=0, r2→z=+1");
    println!();

    // Wire r0
    println!("WIRE r0 (coord[0]=r0, depth z=-1):");
    println!("  At time r0 (source): coord=(r0, r0, r0)");
    println!("    → coord[1]=r0=Regular(0) → y = -1");
    println!("    → position: (-1, -1, -1)");
    println!();
    println!("  At time s0 (merge): coord=(r0, s0, s0)");
    println!("    → coord[1]=s0=Singular(0) → y = 0");
    println!("    → position: (0, 0, -1)");
    println!();
    println!("  At time r1 (target): coord=(r0, r0, r1)");
    println!("    → coord[1]=r0=Regular(0) → y = -1");
    println!("    → position: (+1, -1, -1)");
    println!();
    println!("  Wire r0 polyline: [(-1,-1,-1), (0,0,-1), (+1,-1,-1)]");
    println!("  Shape: DIPS to merge, returns to original height");
    println!();

    // Wire r1
    println!("WIRE r1 (coord[0]=r1, depth z=0):");
    println!("  At time r0 (source): coord=(r1, r1, r0)");
    println!("    → coord[1]=r1=Regular(1) → y = 0");
    println!("    → position: (-1, 0, 0)");
    println!();
    println!("  At time s0 (merge): coord=(r1, s0, s0)");
    println!("    → coord[1]=s0=Singular(0) → y = 0");
    println!("    → position: (0, 0, 0)");
    println!();
    println!("  At time r1 (target): coord=(r1, s0, r1)");
    println!("    → coord[1]=s0=Singular(0) → y = 0  (r1 absorbed into s0)");
    println!("    → position: (+1, 0, 0)");
    println!();
    println!("  Wire r1 polyline: [(-1,0,0), (0,0,0), (+1,0,0)]");
    println!("  Shape: FLAT at y=0 throughout - this is the STEM");
    println!();

    // Wire r2
    println!("WIRE r2 (coord[0]=r2, depth z=+1):");
    println!("  At time r0 (source): coord=(r2, r2, r0)");
    println!("    → coord[1]=r2=Regular(2) → y = +1");
    println!("    → position: (-1, +1, +1)");
    println!();
    println!("  At time s0 (merge): coord=(r2, s0, s0)");
    println!("    → coord[1]=s0=Singular(0) → y = 0");
    println!("    → position: (0, 0, +1)");
    println!();
    println!("  At time r1 (target): coord=(r2, r1, r1)");
    println!("    → coord[1]=r1=Regular(1) → y = 0  (r2 contracted to r1)");
    println!("    → position: (+1, 0, +1)");
    println!();
    println!("  Wire r2 polyline: [(-1,+1,+1), (0,0,+1), (+1,0,+1)]");
    println!("  Shape: DROPS from y=+1 to y=0, stays at y=0");
    println!();

    println!("=== SUMMARY ===");
    println!();
    println!("Wire r0: [(-1,-1,-1), (0,0,-1), (1,-1,-1)]  // dips and returns");
    println!("Wire r1: [(-1, 0, 0), (0,0, 0), (1, 0, 0)]  // flat stem");
    println!("Wire r2: [(-1,+1,+1), (0,0,+1), (1, 0,+1)]  // drops and stays");
}