// Extract ONE clip [tStart,tEnd] (seconds) from a GLB's baked Take, rebased to start at 0,
// and report the root joint's net translation over the clip (so we know if a swim cycle
// drifts the fish through space vs. swims in place). Usage:
//   node trim-clip.mjs in.glb out.glb 3.667 6.167
import { NodeIO } from '@gltf-transform/core';
import { ALL_EXTENSIONS } from '@gltf-transform/extensions';
import { prune } from '@gltf-transform/functions';

const [, , inPath, outPath, s0, s1] = process.argv;
const tStart = parseFloat(s0), tEnd = parseFloat(s1), EPS = 1e-4;
const io = new NodeIO().registerExtensions(ALL_EXTENSIONS);
const doc = await io.read(inPath);
const root = doc.getRoot();

// Pass 1: per unique input, find the kept index window + rebase times to 0.
const win = new Map();  // input -> {a,b}
for (const anim of root.listAnimations())
  for (const sm of anim.listSamplers()) {
    const input = sm.getInput();
    if (win.has(input)) continue;
    const t = input.getArray();
    let a = 0; while (a < t.length - 1 && t[a] < tStart - EPS) a++;
    let b = t.length - 1; while (b > a && t[b] > tEnd + EPS) b--;
    win.set(input, { a, b });
    const base = t[a];
    input.setArray(t.slice(a, b + 1).map((x) => x - base));
  }
// Pass 2: slice each output to its input's window.
for (const anim of root.listAnimations())
  for (const sm of anim.listSamplers()) {
    const { a, b } = win.get(sm.getInput());
    const out = sm.getOutput();
    const c = out.getElementSize();
    out.setArray(out.getArray().slice(a * c, (b + 1) * c));
  }

// Report root-joint translation drift over the clip (first joint's translation track).
const skin = root.listSkins()[0];
const rootJoint = skin?.listJoints()[0];
let drift = 'n/a';
if (rootJoint) {
  for (const anim of root.listAnimations())
    for (const ch of anim.listChannels()) {
      if (ch.getTargetNode() === rootJoint && ch.getTargetPath() === 'translation') {
        const o = ch.getSampler().getOutput().getArray();
        const n = o.length / 3;
        const dx = o[(n - 1) * 3] - o[0], dy = o[(n - 1) * 3 + 1] - o[1], dz = o[(n - 1) * 3 + 2] - o[2];
        drift = `Δ[${dx.toFixed(4)}, ${dy.toFixed(4)}, ${dz.toFixed(4)}] (model units)`;
      }
    }
}
await doc.transform(prune());
await io.write(outPath, doc);
const a = root.listAnimations()[0];
let tmax = 0; for (const ch of a.listChannels()) { const arr = ch.getSampler().getInput().getArray(); tmax = Math.max(tmax, arr[arr.length - 1]); }
console.log(`wrote ${outPath}  | clip duration ${tmax.toFixed(2)}s  | root drift ${drift}`);