import { promises as fs } from "fs";
import { fsError, looksBinary, MAX_FILE_BYTES } from "../fsutil";
import { resolveInScope } from "../paths";

const DEFAULT_LINES = 100;
const MAX_LINES = 1000;
const TOKEN_BUDGET = 1000;
const TOKENS_PER_WORD = 1.3;

function splitLines(text: string): string[] {
  if (text === "") return [];
  const lines = text.split(/\r\n|\n|\r/);
  if (/(\r\n|\n|\r)$/.test(text)) lines.pop();
  return lines;
}

const wordCount = (s: string) => s.split(/\s+/).filter(Boolean).length;

/** How many of `lines` fit the token budget (always at least 1). */
function fitCount(lines: string[]): number {
  let words = 0;
  let n = 0;
  for (const line of lines) {
    words += wordCount(line);
    if (n > 0 && Math.round(words * TOKENS_PER_WORD) > TOKEN_BUDGET) break;
    n++;
  }
  return n;
}

export async function runRead(
  root: string,
  args: { path: string; offset?: number; limit?: number },
): Promise<string> {
  const r = await resolveInScope(root, args.path);
  if (!r.ok) return r.error;

  let buf: Buffer;
  try {
    const st = await fs.stat(r.abs);
    if (st.isDirectory()) return `Error: is a directory, not a file: ${args.path}`;
    if (!st.isFile()) return `Error: not a regular file: ${args.path}`;
    if (st.size > MAX_FILE_BYTES) {
      return `Error: file is too large to read (${st.size} bytes, limit ${MAX_FILE_BYTES})`;
    }
    buf = await fs.readFile(r.abs);
  } catch (e) {
    return fsError(e, args.path);
  }
  if (looksBinary(buf.subarray(0, 8192))) {
    return `Error: binary file, cannot read as text: ${args.path}`;
  }

  const lines = splitLines(buf.toString("utf8"));
  const total = lines.length;
  if (total === 0) return "(empty file)";

  const offset = Math.max(1, Math.trunc(args.offset ?? 1));
  const limit = Math.min(MAX_LINES, Math.max(1, Math.trunc(args.limit ?? DEFAULT_LINES)));
  const start = offset - 1;
  if (start >= total) return `Error: offset ${offset} past end of file (${total} lines)`;

  const window = lines.slice(start, Math.min(start + limit, total));
  const shown = fitCount(window);
  const truncated = shown < window.length;
  const end = start + shown;
  const width = String(end).length;
  const body = window
    .slice(0, shown)
    .map((line, i) => `${String(start + i + 1).padStart(width)}  ${line}`)
    .join("\n");

  let footer = `--- lines ${offset}-${end} of ${total}`;
  if (truncated) footer += ` | truncated at ~${TOKEN_BUDGET} tokens`;
  if (end < total) footer += ` | continue: offset=${end + 1}`;
  return `${body}\n${footer}`;
}

import { promises as fs } from "fs";
import { fsError, looksBinary, MAX_FILE_BYTES } from "../fsutil";
import { resolveInScope } from "../paths";

const DEFAULT_LINES = 100;
const MAX_LINES = 1000;
const TOKEN_BUDGET = 1000;
const TOKENS_PER_WORD = 1.3;

function splitLines(text: string): string[] {
  if (text === "") return [];
  const lines = text.split(/\r\n|\n|\r/);
  if (/(\r\n|\n|\r)$/.test(text)) lines.pop();
  return lines;
}

const wordCount = (s: string) => s.split(/\s+/).filter(Boolean).length;

/** How many of `lines` fit the token budget (always at least 1). */
function fitCount(lines: string[]): number {
  let words = 0;
  let n = 0;
  for (const line of lines) {
    words += wordCount(line);
    if (n > 0 && Math.round(words * TOKENS_PER_WORD) > TOKEN_BUDGET) break;
    n++;
  }
  return n;
}

export async function runRead(
  root: string,
  args: { path: string; offset?: number; limit?: number },
): Promise<string> {
  const r = await resolveInScope(root, args.path);
  if (!r.ok) return r.error;

  let buf: Buffer;
  try {
    const st = await fs.stat(r.abs);
    if (st.isDirectory()) return `Error: is a directory, not a file: ${args.path}`;
    if (!st.isFile()) return `Error: not a regular file: ${args.path}`;
    if (st.size > MAX_FILE_BYTES) {
      return `Error: file is too large to read (${st.size} bytes, limit ${MAX_FILE_BYTES})`;
    }
    buf = await fs.readFile(r.abs);
  } catch (e) {
    return fsError(e, args.path);
  }
  if (looksBinary(buf.subarray(0, 8192))) {
    return `Error: binary file, cannot read as text: ${args.path}`;
  }

  const lines = splitLines(buf.toString("utf8"));
  const total = lines.length;
  if (total === 0) return "(empty file)";

  const offset = Math.max(1, Math.trunc(args.offset ?? 1));
  const limit = Math.min(MAX_LINES, Math.max(1, Math.trunc(args.limit ?? DEFAULT_LINES)));
  const start = offset - 1;
  if (start >= total) return `Error: offset ${offset} past end of file (${total} lines)`;

  const window = lines.slice(start, Math.min(start + limit, total));
  const shown = fitCount(window);
  const truncated = shown < window.length;
  const end = start + shown;
  const width = String(end).length;
  const body = window
    .slice(0, shown)
    .map((line, i) => `${String(start + i + 1).padStart(width)}  ${line}`)
    .join("\n");

  let footer = `--- lines ${offset}-${end} of ${total}`;
  if (truncated) footer += ` | truncated at ~${TOKEN_BUDGET} tokens`;
  if (end < total) footer += ` | continue: offset=${end + 1}`;
  return `${body}\n${footer}`;
}