graph TD
    A[Trigger: Manual / Schedule / Webhook] --> B[Node 1: Input Parser]
    B --> C{Conditional Router}
    C -->|Type A| D[Node 2a: LLM Analysis]
    C -->|Type B| E[Node 2b: Database Query via MCP]
    D --> F[Node 3: Parallel Execution]
    E --> F
    F --> G[Node 3a: Image Generation]
    F --> H[Node 3b: Content Formatting]
    G --> I[Node 4: Human Review Checkpoint]
    H --> I
    I -->|Approved| J[Node 5: Publish via MCP]
    I -->|Rejected| K[Node 5: Return to Step 2]
    J --> L[Node 6: Log + Notify]

interface WorkflowNode {
  id: string;
  type: "llm" | "mcp" | "transform" | "condition" | "human_review" | "parallel";
  config: Record<string, unknown>;
  next: string | string[] | ConditionalNext[];
  retries?: number;
  timeout_ms?: number;
}

interface ConditionalNext {
  condition: string;
  target: string;
}

interface Workflow {
  id: string;
  name: string;
  trigger: { type: "manual" | "schedule" | "webhook"; config: Record<string, unknown> };
  nodes: WorkflowNode[];
}

class WorkflowEngine {
  private state = new Map<string, unknown>();

  async execute(workflow: Workflow, input: unknown): Promise<unknown> {
    this.state.set("input", input);
    let currentNode = workflow.nodes[0];

    while (currentNode) {
      const result = await this.executeNode(currentNode);
      this.state.set(currentNode.id, result);

      const nextId = this.resolveNext(currentNode, result);
      currentNode = nextId ? workflow.nodes.find(n => n.id === nextId)! : undefined!;
    }

    return Object.fromEntries(this.state);
  }

  private async executeNode(node: WorkflowNode): Promise<unknown> {
    for (let attempt = 0; attempt <= (node.retries ?? 0); attempt++) {
      try {
        switch (node.type) {
          case "llm": return await this.executeLLM(node.config);
          case "mcp": return await this.executeMCP(node.config);
          case "transform": return this.executeTransform(node.config);
          case "parallel": return await this.executeParallel(node.config);
          case "human_review": return await this.waitForHumanReview(node.config);
          default: throw new Error(`Unknown node type: ${node.type}`);
        }
      } catch (error) {
        if (attempt === (node.retries ?? 0)) throw error;
        await this.delay(1000 * Math.pow(2, attempt));
      }
    }
  }

  private async executeMCP(config: Record<string, unknown>): Promise<unknown> {
    const { server, tool, arguments: args } = config as {
      server: string; tool: string; arguments: Record<string, unknown>;
    };
    return callMcpTool(server, tool, this.interpolate(args));
  }

  private async executeParallel(config: Record<string, unknown>): Promise<unknown[]> {
    const { nodeIds } = config as { nodeIds: string[] };
    const nodes = nodeIds.map(id => this.findNode(id));
    return Promise.all(nodes.map(n => this.executeNode(n)));
  }

  private interpolate(obj: Record<string, unknown>): Record<string, unknown> {
    return JSON.parse(
      JSON.stringify(obj).replace(/\{\{(\w+)\.(\w+)\}\}/g, (_, nodeId, key) => {
        const nodeResult = this.state.get(nodeId) as Record<string, unknown>;
        return String(nodeResult?.[key] ?? "");
      })
    );
  }
}