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* EI-3152 — Calculus Visualization: export helpers (SVG / PNG) + format gating.
*
* function-plot renders a d3 <svg>. Export = serialize the SVG (lossless) or
* rasterize it to a PNG data URL via a canvas. `canExport(format)` gates the
* Export button: it is false until a KNOWN format is selected (EI-TC-2654).
*/
export const EXPORT_FORMATS = Object.freeze([
{ value: "svg", label: "SVG" },
{ value: "png", label: "PNG" },
]);
/** The selectable export formats (for the format <Select>). */
export function getAvailableExportFormats() {
return EXPORT_FORMATS;
}
/**
* Whether an export is allowed for the currently-selected format.
* Returns false for empty / null / unknown formats → the Export button stays
* disabled until the user picks SVG or PNG. (Drives EI-TC-2654.)
*/
export function canExport(format) {
return EXPORT_FORMATS.some((f) => f.value === format);
}
/** A stable download filename, e.g. "calculus-derivative.svg". */
export function buildExportFilename(mode, format) {
const safeMode = mode === "integral" || mode === "derivative" ? mode : "graph";
const safeExt = canExport(format) ? format : "svg";
return `calculus-${safeMode}.${safeExt}`;
}
const SVG_NS = "http://www.w3.org/2000/svg";
/**
* Serialize an <svg> element to a standalone SVG string.
*
* Modified by Allan Ninal — every exported SVG was malformed. `getAttribute("xmlns")`
* is null for a NAMESPACED element (a namespace is not an attribute), and d3 /
* function-plot produce exactly that, so the old guard always added a literal xmlns
* on top of the one XMLSerializer emits itself:
*
* <svg xmlns="http://www.w3.org/2000/svg" xmlns="http://www.w3.org/2000/svg"/>
*
* A duplicate attribute is invalid XML, so the downloaded file is rejected outright
* by strict parsers — which is most things that open an .svg other than a browser.
*/
export function serializeSvg(svgEl) {
if (!svgEl) return "";
const clone = svgEl.cloneNode(true);
if (clone.namespaceURI === SVG_NS) {
// The serializer writes xmlns for us; anything literal here is a duplicate.
clone.removeAttribute("xmlns");
} else Eif (!clone.getAttribute("xmlns")) {
clone.setAttribute("xmlns", SVG_NS);
}
return new XMLSerializer().serializeToString(clone);
}
/**
* Rasterize an <svg> element to a PNG data URL via a canvas.
* Returns a Promise<string> (the data: URL). Rejects if the format is not PNG
* or the SVG can't be loaded.
*/
export function svgToPngDataUrl(svgEl, width, height) {
return new Promise((resolve, reject) => {
if (!svgEl) {
reject(new Error("No SVG to export"));
return;
}
const svgString = serializeSvg(svgEl);
const blob = new Blob([svgString], { type: "image/svg+xml;charset=utf-8" });
const url = URL.createObjectURL(blob);
const img = new Image();
img.onload = () => {
try {
const canvas = document.createElement("canvas");
canvas.width = width || svgEl.clientWidth || 600;
canvas.height = height || svgEl.clientHeight || 400;
const ctx = canvas.getContext("2d");
ctx.fillStyle = "#ffffff";
ctx.fillRect(0, 0, canvas.width, canvas.height);
ctx.drawImage(img, 0, 0, canvas.width, canvas.height);
URL.revokeObjectURL(url);
resolve(canvas.toDataURL("image/png"));
} catch (e) {
URL.revokeObjectURL(url);
reject(e);
}
};
img.onerror = (e) => {
URL.revokeObjectURL(url);
reject(e instanceof Error ? e : new Error("Failed to rasterize SVG"));
};
img.src = url;
});
}
/**
* Produce the export payload for the chosen format. Throws if no valid format is
* selected (mirrors the disabled Export button — EI-TC-2654 defense in depth).
*/
export async function exportCalculusGraph(svgEl, format, { width, height } = {}) {
if (!canExport(format)) {
throw new Error("Select an export format first.");
}
// Modified by Allan Ninal — the two formats disagreed about a missing graph. The
// PNG path rejected with this same message, while the SVG path serialised nothing
// into "" and SUCCEEDED, handing the teacher a zero-byte .svg download. An empty
// file looks like something they did wrong; a refusal does not.
if (!svgEl) {
throw new Error("No SVG to export");
}
if (format === "svg") {
return { format, data: serializeSvg(svgEl), mime: "image/svg+xml" };
}
const dataUrl = await svgToPngDataUrl(svgEl, width, height);
return { format, data: dataUrl, mime: "image/png" };
}
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