import type { UIMessage } from 'ai';

type HistoryMessage = Pick<UIMessage, 'id' | 'role' | 'parts'>;

/** 去掉 system / data-system / part.role=system 等权限污染，保留可继续对话的 user/assistant 内容。 */
export function scrubClientPrivilegeMessages(messages: unknown[]): unknown[] {
  const scrubbed: unknown[] = [];
  for (const rawMessage of messages) {
    if (!isRecord(rawMessage)) {
      continue;
    }
    if (rawMessage.role !== 'user' && rawMessage.role !== 'assistant') {
      continue;
    }
    if (!Array.isArray(rawMessage.parts)) {
      continue;
    }
    const parts: unknown[] = [];
    for (const rawPart of rawMessage.parts) {
      const part = scrubClientPrivilegePart(rawPart, rawMessage.role);
      if (part) {
        parts.push(part);
      }
    }
    if (parts.length === 0) {
      continue;
    }
    scrubbed.push({
      ...rawMessage,
      parts,
    });
  }
  return scrubbed;
}

/**
 * 仅保留 user/assistant 的纯文本 parts，供客户端上报与本地持久化。
 * 与服务端模型上下文对齐，避免 tool/system 等 UI 结构触发 4513。
 */
export function toPlainTextHistory<T extends HistoryMessage>(messages: T[]): Array<{
  id: string;
  role: 'user' | 'assistant';
  parts: Array<{ type: 'text'; text: string }>;
}> {
  return messages
    .filter((message): message is T & { role: 'user' | 'assistant' } => (
      message.role === 'user' || message.role === 'assistant'
    ))
    .map((message) => ({
      id: message.id,
      role: message.role,
      parts: message.parts.flatMap((part) => (
        isTextPart(part) ? [{ type: 'text' as const, text: part.text }] : []
      )),
    }))
    .filter((message) => message.parts.length > 0);
}

function scrubClientPrivilegePart(
  rawPart: unknown,
  messageRole: 'user' | 'assistant',
): Record<string, unknown> | null {
  if (!isRecord(rawPart) || typeof rawPart.type !== 'string') {
    return null;
  }
  if (rawPart.type === 'system' || rawPart.type === 'data-system') {
    return null;
  }
  if (messageRole === 'user') {
    if (rawPart.type !== 'text' || typeof rawPart.text !== 'string') {
      return null;
    }
    return { type: 'text', text: rawPart.text };
  }
  if ('role' in rawPart && rawPart.role === 'system') {
    // 历史里偶发把 role 写进 text part；保留文本、去掉权限标记，避免整会话被拒。
    if (rawPart.type === 'text' && typeof rawPart.text === 'string') {
      return { type: 'text', text: rawPart.text };
    }
    return null;
  }
  return rawPart;
}

function isTextPart(part: unknown): part is { type: 'text'; text: string } {
  return isRecord(part) && part.type === 'text' && typeof part.text === 'string';
}

function isRecord(value: unknown): value is Record<string, unknown> {
  return Boolean(value) && typeof value === 'object' && !Array.isArray(value);
}