import { Type } from "@sinclair/typebox";

// Keep this policy in sync with packages/vera-session-tools/extensions/read-cap/policy.ts.
export const MAX_READ_LINES = 200;

const READ_CAP_DESCRIPTION =
  "Read a slice of a text file. Both `offset` (1-indexed start line) and `limit` (max 200) are REQUIRED. Reading whole files is forbidden — supply a tight range. If the file is larger than expected, call read again with a new offset.";
const READ_CAP_PROMPT_SNIPPET = "read <path> with required offset+limit (limit ≤ 200).";

const readCapParameters = Type.Object({
  path: Type.String({ description: "Path to the file to read (relative or absolute)" }),
  offset: Type.Number({ minimum: 1, description: "Line number to start reading from (1-indexed)" }),
  limit: Type.Number({ minimum: 1, maximum: MAX_READ_LINES, description: "Maximum number of lines to read" }),
});

function rejected(reason: string) {
  return {
    isError: true,
    content: [{ type: "text", text: `read rejected: ${reason}` }],
  };
}

function validateReadCapParams(params: any): string | null {
  if (typeof params?.offset !== "number") return "missing required `offset` (1-indexed start line)";
  if (typeof params?.limit !== "number") return "missing required `limit` (max 200 lines)";
  if (params.offset < 1) return "`offset` must be >= 1";
  if (params.limit < 1) return "`limit` must be >= 1";
  if (params.limit > MAX_READ_LINES) {
    return `\`limit\` ${params.limit} exceeds cap ${MAX_READ_LINES} — call read multiple times with adjacent offsets to read more`;
  }
  return null;
}

export function wrapReadWithLineCap(builtinRead: any) {
  return {
    ...builtinRead,
    description: READ_CAP_DESCRIPTION,
    promptSnippet: READ_CAP_PROMPT_SNIPPET,
    parameters: readCapParameters,
    async execute(toolCallId: any, params: any, signal: any, onUpdate: any, ctx: any) {
      const rejectionReason = validateReadCapParams(params);
      if (rejectionReason) return rejected(rejectionReason);
      return builtinRead.execute(toolCallId, params, signal, onUpdate, ctx);
    },
  };
}