// Per-session resource buffers for large stdout/stderr from bash_exec.
// Implements ring buffer over last N execs, byte caps per session and global.

export interface ResourceBuffer {
  sessionId: string;
  execId: string;
  stream: "stdout" | "stderr";
  bytes: Buffer;
  complete: boolean; // true when not truncated below capturedOutputBytesExec cap
  createdAt: number;
  expiresAt: number;
}

export class ResourceStore {
  private byKey = new Map<string, ResourceBuffer>(); // key: sessionId/execId/stream
  private bySession = new Map<string, string[]>(); // sessionId -> [execId in insertion order]
  private totalBytes = 0;
  constructor(
    private readonly maxExecsRetainedSession: number,
    private readonly maxResourceBytesSession: number,
    private readonly maxResourceBytesGlobal: number,
  ) {}

  private key(sessionId: string, execId: string, stream: "stdout" | "stderr") {
    return `${sessionId}::${execId}::${stream}`;
  }

  store(
    sessionId: string,
    execId: string,
    stream: "stdout" | "stderr",
    text: string,
    complete: boolean,
    ttlMs: number,
  ): boolean {
    const bytes = Buffer.from(text, "utf8");
    if (bytes.length === 0) return false;
    if (bytes.length > this.maxResourceBytesGlobal) return false;
    this.evictForCapacity(sessionId, bytes.length);
    const buf: ResourceBuffer = {
      sessionId,
      execId,
      stream,
      bytes,
      complete,
      createdAt: Date.now(),
      expiresAt: Date.now() + ttlMs,
    };
    this.byKey.set(this.key(sessionId, execId, stream), buf);
    const list = this.bySession.get(sessionId) ?? [];
    if (!list.includes(execId)) list.push(execId);
    this.bySession.set(sessionId, list);
    this.totalBytes += bytes.length;
    return true;
  }

  get(
    sessionId: string,
    execId: string,
    stream: "stdout" | "stderr",
  ): ResourceBuffer | null {
    const b = this.byKey.get(this.key(sessionId, execId, stream));
    if (!b) return null;
    if (b.expiresAt < Date.now()) {
      this.delete(sessionId, execId, stream);
      return null;
    }
    return b;
  }

  delete(sessionId: string, execId: string, stream: "stdout" | "stderr") {
    const k = this.key(sessionId, execId, stream);
    const b = this.byKey.get(k);
    if (b) {
      this.totalBytes -= b.bytes.length;
      this.byKey.delete(k);
    }
  }

  deleteSession(sessionId: string) {
    const execs = this.bySession.get(sessionId) ?? [];
    for (const eid of execs) {
      for (const s of ["stdout", "stderr"] as const) {
        this.delete(sessionId, eid, s);
      }
    }
    this.bySession.delete(sessionId);
  }

  totalBytesUsed() {
    return this.totalBytes;
  }

  sessionBytesUsed(sessionId: string): number {
    let total = 0;
    const execs = this.bySession.get(sessionId) ?? [];
    for (const eid of execs) {
      for (const s of ["stdout", "stderr"] as const) {
        const b = this.byKey.get(this.key(sessionId, eid, s));
        if (b) total += b.bytes.length;
      }
    }
    return total;
  }

  // Evict oldest exec resources for session until we fit incoming bytes within caps.
  private evictForCapacity(sessionId: string, incomingBytes: number) {
    // Per-session: if exec count limit would be exceeded, drop oldest. (Counts exec ids.)
    const execs = this.bySession.get(sessionId) ?? [];
    while (execs.length >= this.maxExecsRetainedSession) {
      const oldest = execs.shift();
      if (!oldest) break;
      for (const s of ["stdout", "stderr"] as const) {
        this.delete(sessionId, oldest, s);
      }
    }
    // Per-session byte cap
    while (this.sessionBytesUsed(sessionId) + incomingBytes > this.maxResourceBytesSession) {
      const oldest = execs.shift();
      if (!oldest) break;
      for (const s of ["stdout", "stderr"] as const) {
        this.delete(sessionId, oldest, s);
      }
    }
    // Global byte cap: drop oldest entries across all sessions.
    while (this.totalBytes + incomingBytes > this.maxResourceBytesGlobal) {
      const allKeys = Array.from(this.byKey.values()).sort(
        (a, b) => a.createdAt - b.createdAt,
      );
      const oldest = allKeys[0];
      if (!oldest) break;
      this.delete(oldest.sessionId, oldest.execId, oldest.stream);
      // also prune from per-session list
      const list = this.bySession.get(oldest.sessionId);
      if (list) {
        const idx = list.indexOf(oldest.execId);
        const stillHas =
          this.byKey.has(this.key(oldest.sessionId, oldest.execId, "stdout")) ||
          this.byKey.has(this.key(oldest.sessionId, oldest.execId, "stderr"));
        if (!stillHas && idx >= 0) list.splice(idx, 1);
      }
    }
    this.bySession.set(sessionId, execs);
  }

  sweepExpired() {
    const now = Date.now();
    for (const [, b] of this.byKey) {
      if (b.expiresAt < now) {
        this.delete(b.sessionId, b.execId, b.stream);
      }
    }
  }
}