/**
 * `useLogTail` — tail a managed process's stdout/stderr over SSE.
 *
 * Watches a process-id ref; (re)opens `/__nwire/run/logs/:id/stream` whenever it
 * changes, parses each `LogLine`, and keeps a bounded buffer. The scoped
 * `EventSource` (patched in main.ts) carries `?project=`; SSE reconnects on
 * drop natively. Shared by the Run + Commands panels so the streaming logic
 * lives in one place.
 */
import { ref, watch, onUnmounted, toValue, type MaybeRefOrGetter } from "vue";
import type { LogLine } from "@/lib/operate";

const MAX_LINES = 5000;

export function useLogTail(id: MaybeRefOrGetter<string | null | undefined>) {
  const logs = ref<LogLine[]>([]);
  let es: EventSource | null = null;

  function close(): void {
    es?.close();
    es = null;
  }

  function clear(): void {
    logs.value = [];
  }

  function connect(target: string | null | undefined): void {
    close();
    clear();
    if (!target) return;
    es = new EventSource(`/__nwire/run/logs/${encodeURIComponent(target)}/stream`);
    es.onmessage = (msg) => {
      try {
        const line = JSON.parse(msg.data) as LogLine;
        const next =
          logs.value.length >= MAX_LINES ? logs.value.slice(-(MAX_LINES - 1)) : logs.value.slice();
        next.push(line);
        logs.value = next;
      } catch {
        /* keepalive comment / non-JSON frame — ignore */
      }
    };
    // EventSource auto-reconnects on error; nothing to do.
  }

  watch(() => toValue(id), connect, { immediate: true });
  onUnmounted(close);

  return { logs, clear };
}