import { sortObservations } from "./render.ts";
import type { Observation } from "./types.ts";

export function poolTokens(observations: Observation[]): number {
  let total = 0;
  for (const observation of observations) total += observation.tokenCount;
  return total;
}

export type PromotionOverflow = {
  /** Oldest observations to hand to the consolidator (chronological order). */
  promote: Observation[];
  /** Token total of the observations kept in the buffer. */
  keptTokens: number;
  /** Token total of the whole active pool. */
  totalTokens: number;
};

/**
 * Select the promotion overflow: keep the newest observations whose cumulative tokens stay
 * within `poolTargetTokens`, promote everything older. Always keeps at least the single
 * newest observation, even if it alone exceeds the target.
 */
export function selectPromotionOverflow(active: Observation[], poolTargetTokens: number): PromotionOverflow {
  const sorted = sortObservations(active);
  const totalTokens = poolTokens(sorted);

  let keptTokens = 0;
  let firstKeptIdx = sorted.length;
  for (let i = sorted.length - 1; i >= 0; i--) {
    const t = sorted[i].tokenCount;
    if (firstKeptIdx !== sorted.length && keptTokens + t > poolTargetTokens) break;
    keptTokens += t;
    firstKeptIdx = i;
  }

  return { promote: sorted.slice(0, firstKeptIdx), keptTokens, totalTokens };
}