import { useMemo } from "react";
import type { Human, Particle } from "@/api/types";

export interface HumanPresence {
  humanId: string;
  email: string;
  emailPrefix: string;
}

/**
 * Maps playback markers to segment indices, returning which users are present at each particle.
 */
export function usePresencePositions(
  playbackMarkers: Record<string, Date> | undefined,
  children: Particle[],
  networkHumans: Human[] | undefined,
  currentUserId: string | undefined,
): Map<number, HumanPresence[]> {
  return useMemo(() => {
    const result = new Map<number, HumanPresence[]>();
    if (!playbackMarkers || !networkHumans || children.length === 0) return result;

    for (const [userId, markerTimestamp] of Object.entries(playbackMarkers)) {
      if (userId === currentUserId) continue;

      const human = networkHumans.find((h) => h.id === userId);
      if (!human) continue;

      // Find the last particle whose created_at <= marker timestamp
      let segmentIndex = -1;
      for (let i = children.length - 1; i >= 0; i--) {
        if (children[i].created_at.getTime() <= markerTimestamp.getTime()) {
          segmentIndex = i;
          break;
        }
      }
      if (segmentIndex === -1) continue;

      const existing = result.get(segmentIndex);
      const presence: HumanPresence = { humanId: human.id, email: human.email, emailPrefix: human.email_prefix };
      if (existing) {
        existing.push(presence);
      } else {
        result.set(segmentIndex, [presence]);
      }
    }

    // Sort each segment's presence list by humanId for stable render order
    for (const presenceList of result.values()) {
      presenceList.sort((a, b) => a.humanId.localeCompare(b.humanId));
    }

    return result;
  }, [playbackMarkers, children, networkHumans, currentUserId]);
}