import { readFile as fsReadFile, stat as fsStat } from "node:fs/promises";
import path from "node:path";
import { z } from "zod";
import { truncate } from "../utils/truncate.js";
import { imageMimeType, MAX_IMAGE_BYTES } from "../utils/image.js";
import type { ToolDef } from "./types.js";

const schema = z.object({
  path: z.string().describe("File path to read, relative to the working directory or absolute."),
  offset: z.number().int().min(1).optional().describe("1-indexed line number to start reading from (text files only)."),
  limit: z.number().int().min(1).max(2000).optional().describe("Maximum number of lines to read (text files only)."),
});

export const readFileTool: ToolDef<z.infer<typeof schema>> = {
  name: "read_file",
  description:
    "Read a file from the local filesystem. Text files return content with 1-indexed line numbers, optionally a specific " +
    "line range. Image files (png, jpg, jpeg, gif, webp, bmp) are returned as image content for the model to see directly " +
    "— this requires a vision-capable model/backend; others may error on the request.",
  schema,
  mutating: false,
  handler: async ({ path: filePath, offset, limit }, ctx) => {
    const resolved = path.resolve(ctx.cwd, filePath);

    const mimeType = imageMimeType(resolved);
    if (mimeType) {
      const stats = await fsStat(resolved);
      if (stats.size > MAX_IMAGE_BYTES) {
        throw new Error(
          `${filePath} is ${(stats.size / 1_048_576).toFixed(1)}MB, over the ${MAX_IMAGE_BYTES / 1_048_576}MB limit for image reads.`,
        );
      }
      const buffer = await fsReadFile(resolved);
      return { path: resolved, image: true, mimeType, bytes: buffer.byteLength, base64: buffer.toString("base64") };
    }

    const content = await fsReadFile(resolved, "utf-8");
    const lines = content.split("\n");
    const start = offset ? offset - 1 : 0;
    const end = limit ? start + limit : lines.length;
    const slice = lines.slice(start, end);
    const numbered = slice.map((line, i) => `${start + i + 1}\t${line}`).join("\n");
    return { path: resolved, totalLines: lines.length, content: truncate(numbered) };
  },
};