// preview.jsx — right-hand HTML / Inbox / Preview pane (step 4).
//
// Purely derived from the live `blocks` array and `subject` — nothing here
// keeps its own copy of the email, so it is regenerated on every render, the
// same way the canvas itself already is. window.buildEmailHtmlRanges
// (email-export.js) is the SAME renderer that builds the real send/export
// HTML — this pane can never drift from what Send/Export would actually
// produce, because it calls the one function that builds both.
// Splits on '\n' the same way the HTML was joined, so line N here is line N
// of what a "View source" on the real email would show.
function previewSplitLines(html) {
return html.split('\n');
}
// Which 0-based line indexes a [start, end) character range (as reported by
// buildEmailHtmlRanges) touches, walking the lines once rather than
// re-scanning the whole string per line.
function previewLinesTouchedBy(lines, start, end) {
const touched = new Set();
let pos = 0;
for (let i = 0; i < lines.length; i++) {
const lineStart = pos;
const lineEnd = lineStart + lines[i].length; // excludes the '\n' split() ate
if (lineEnd >= start && lineStart < end) touched.add(i);
pos = lineEnd + 1;
if (lineStart >= end) break;
}
return touched;
}
// Reduces the FULL document (head, Outlook conditional comments, the one
//