import crypto from "node:crypto";

export type SessionBinding = {
  clientSessionId: string;
  sessionId: string;
  lastUsedAt: number;
};

export type SessionContext = {
  clientSessionId: string;
  accessToken?: string;
  projectId?: string;
  userId?: string;
};

export class SessionRegistry {
  private readonly ttlMs: number;
  private readonly bindings = new Map<string, SessionBinding>();

  constructor(ttlSeconds: number) {
    this.ttlMs = ttlSeconds * 1000;
  }

  upsert(context: SessionContext, sessionId: string): SessionBinding {
    const binding: SessionBinding = {
      clientSessionId: context.clientSessionId,
      sessionId,
      lastUsedAt: Date.now(),
    };
    this.bindings.set(this.makeKey(context), binding);
    return binding;
  }

  get(context: SessionContext): SessionBinding | null {
    const key = this.makeKey(context);
    const binding = this.bindings.get(key);
    if (!binding) {
      return null;
    }
    if (Date.now() - binding.lastUsedAt > this.ttlMs) {
      this.bindings.delete(key);
      return null;
    }
    binding.lastUsedAt = Date.now();
    return binding;
  }

  count(): number {
    this.evictExpired();
    return this.bindings.size;
  }

  evictExpired(): string[] {
    const expired: string[] = [];
    const now = Date.now();
    for (const [key, binding] of this.bindings.entries()) {
      if (now - binding.lastUsedAt > this.ttlMs) {
        expired.push(binding.sessionId);
        this.bindings.delete(key);
      }
    }
    return expired;
  }

  private makeKey(context: SessionContext): string {
    // 会话隔离不能只看前端 session_id；同一浏览器会话切换用户或项目时必须映射到不同 opencode session。
    const digest = crypto
      .createHash("sha256")
      .update(
        [
          context.clientSessionId,
          context.userId?.trim() ?? "",
          context.projectId ?? "",
        ].join("|"),
      )
      .digest("hex");

    return digest;
  }
}