import { readFileSync } from "node:fs";
import { type } from "arktype";
import type { ToolContext } from "./server.ts";
import { execute, tool } from "./shared.ts";

export const ReadFileParams = type({
  path: type.string.describe("absolute path to the file to read"),
  "start_line?": type.number.describe("start line, 1-based inclusive (default: 1)"),
  "end_line?": type.number.describe("end line, 1-based inclusive (default: end of file)"),
});

export function ReadFileTool(_ctx: ToolContext) {
  return tool({
    name: "read_file",
    description:
      "Read lines from a file. Use this to read sections of the PR diff returned by checkout_pr. " +
      "Example: `read_file({ path: diffPath, start_line: 5, end_line: 42 })`.",
    parameters: ReadFileParams,
    execute: execute(async ({ path, start_line, end_line }) => {
      let content: string;
      try {
        content = readFileSync(path, "utf-8");
      } catch (err) {
        const msg = err instanceof Error ? err.message : String(err);
        throw new Error(`failed to read ${path}: ${msg}`);
      }

      if (start_line === undefined && end_line === undefined) {
        return { content };
      }

      const lines = content.split("\n");
      const start = Math.max(0, (start_line ?? 1) - 1);
      const end = Math.min(lines.length, end_line ?? lines.length);
      return { content: lines.slice(start, end).join("\n") };
    }),
  });
}