import type { StepTechStepView } from "@batch-cooking/shared";

/**
 * One run of a step's `description` — either plain text, or the exact
 * words that triggered a technique match (`techStep` set). What
 * `StepDescription.tsx` renders: plain segments as-is, technique segments
 * wrapped in a highlighted, tooltip-bearing `<mark>`.
 */
export interface DescriptionSegment {
  text: string;
  techStep: StepTechStepView["techStep"] | null;
}

/**
 * Splits `description` into an ordered sequence of plain/technique
 * {@link DescriptionSegment}s using each `techSteps` entry's `start`/`end`
 * (see `StepTechStepView`, resolved server-side by
 * `tech-step-matcher.ts`'s `matchTechStepSpans`).
 *
 * `techSteps` is expected already sorted by `start` (the API returns it in
 * `StepTechStep.order`, which *is* reading order — see that model's schema
 * doc comment) but this re-sorts defensively rather than assuming it, and
 * silently drops any entry whose bounds don't make sense against
 * `description` (`start < 0`, `end > description.length`, `start >= end`,
 * or overlapping a previously-accepted entry) — a malformed/out-of-date
 * span degrades to "just don't highlight that one" rather than a garbled
 * slice or a crash.
 */
export function splitDescriptionByTechSteps(
  description: string,
  techSteps: StepTechStepView[],
): DescriptionSegment[] {
  const sorted = [...techSteps].sort((a, b) => a.start - b.start);

  const segments: DescriptionSegment[] = [];
  let cursor = 0;
  for (const { techStep, start, end } of sorted) {
    if (start < 0 || end > description.length || start >= end || start < cursor) continue;
    if (start > cursor) segments.push({ text: description.slice(cursor, start), techStep: null });
    segments.push({ text: description.slice(start, end), techStep });
    cursor = end;
  }
  if (cursor < description.length) {
    segments.push({ text: description.slice(cursor), techStep: null });
  }
  return segments;
}