rea/src/domain/javascript/javascriptRouteResultBudget.ts

import { jsonValueByteLength } from "../jsonValueByteLength.js";
import type { JsonValue } from "../jsonValue.js";
import type { JavaScriptRouteSourceFacts } from "./javascriptRouteFacts.js";

/**
 * Admit this optional facet inside the enclosing result's actual remaining
 * serialized bytes. The serialization owner supplies the space after all
 * existing facts and this member's key/colon/comma; no worker protocol lives here.
 * Omission means even a capacity envelope cannot fit, never an empty measurement.
 */
export const fitJavaScriptRouteSourceFacts = (
  facts: JavaScriptRouteSourceFacts,
  availableBytes: number,
): JavaScriptRouteSourceFacts | undefined => {
  if (availableBytes <= 0) return undefined;
  if (jsonValueByteLength(facts, availableBytes) <= availableBytes)
    return facts;
  const result: JavaScriptRouteSourceFacts = {
    candidates: [],
    unresolved: [],
    capacity: {
      kind: "result-bytes",
      limit_bytes: availableBytes,
      preceding_work_capacity:
        facts.capacity === null
          ? null
          : facts.capacity.kind === "route-work-or-facts"
            ? facts.capacity
            : facts.capacity.preceding_work_capacity,
    },
  };
  let bytes = jsonValueByteLength(result, availableBytes);
  if (bytes > availableBytes) return undefined;
  const append = <T extends JsonValue>(
    source: readonly T[],
    output: T[],
  ): void => {
    for (const fact of source) {
      const added =
        jsonValueByteLength(fact, availableBytes - bytes) +
        (output.length === 0 ? 0 : 1);
      if (bytes + added > availableBytes) break;
      output.push(fact);
      bytes += added;
    }
  };
  // Preserve uncertainty before route candidates when a prefix must be returned.
  append(facts.unresolved, result.unresolved);
  append(facts.candidates, result.candidates);
  return result;
};