// Headless guard for the trace-chart viewer (chart-viewer.js) gap-handling.
// Property protected: when taps fire at DIFFERENT cadences, the CLI's union-spine
// alignment (spec 0056 §6) null-fills the timestamps a tap did NOT fire at, and
// buildCharts must hand those nulls to uPlot VERBATIM as the data array — a null is
// a rendered gap, never dropped, never coerced to 0. This is the observable end of
// the "no tap's points dropped, no privileged spine" contract: a positional shift or
// a `null -> 0` coercion would silently misalign every series past the first gap.
//
// It loads the real viewer module (a regression there is observed here) and drives
// the exported pure `buildCharts` over a fixture whose two series have nulls at
// DIFFERENT positions; uPlot itself (which needs `document`) is never instantiated.

import { createRequire } from "node:module";
import { readFileSync } from "node:fs";
import { fileURLToPath } from "node:url";
import { dirname, join } from "node:path";

const require = createRequire(import.meta.url);
const here = dirname(fileURLToPath(import.meta.url));
const traces = JSON.parse(readFileSync(join(here, "fixtures", "sparse-traces.json"), "utf8"));

const fail = (msg) => { console.error("FAIL: " + msg); process.exit(1); };
const sameArr = (a, b, msg) => {
  // strict identity per slot, so a null that became 0 (or a shifted point) fails.
  if (!Array.isArray(a) || !Array.isArray(b) || a.length !== b.length || a.some((v, i) => v !== b[i])) fail(msg);
};

// No `document` global -> the browser mount is skipped; we get only the pure export.
global.window = { AURA_TRACES: traces };
const { buildCharts } = require(join(here, "..", "assets", "chart-viewer.js"));

const eqPoints = traces.series[0].points;   // [0.0, 0.001, null, 0.004]
const exPoints = traces.series[1].points;   // [1.0, null, null, -1.0]
const idx = Array.from({ length: traces.xs.length }, (_, i) => i);

// overlay: the data array is [ordinal spine, ...each series' points], nulls preserved.
const overlay = buildCharts(traces, "overlay")[0];
sameArr(overlay.data[0], idx, "overlay x is the ordinal index spine (gaps collapsed)");
sameArr(overlay.data[1], eqPoints, "overlay equity points carry their null gap verbatim");
sameArr(overlay.data[2], exPoints, "overlay exposure points carry their null gaps verbatim");

// panels: each panel is [ordinal spine, its own series' points] — same nulls.
const panels = buildCharts(traces, "panels");
sameArr(panels[0].data[0], idx, "panel 0 shares the ordinal index spine");
sameArr(panels[0].data[1], eqPoints, "panel 0 carries equity's null gap verbatim");
sameArr(panels[1].data[1], exPoints, "panel 1 carries exposure's null gaps verbatim");

console.log("OK — null gaps preserved verbatim across overlay + panels, shared union xs.");
process.exit(0);
