import { existsSync } from "fs";
import { readFile } from "fs/promises";
import { extname } from "path";
import { runCommand } from "./shell";
import type { Workspace } from "./workspace";

/**
 * Cheap syntax validation run automatically after a write. A small model will
 * happily emit code with an unclosed brace and only discover it much later, so
 * every write reports its own damage immediately.
 *
 * Conservative by design: it only speaks up when it is confident something is
 * wrong. An unknown file type, a missing interpreter, or a checker that cannot
 * run all return "no complaint" rather than a false alarm.
 */

const CHECK_TIMEOUT_MS = 8000;
const MAX_CHECKED_BYTES = 512 * 1024;

/** Returns a warning line to append to the tool result, or "" if it looks fine. */
export async function validateSyntax(ws: Workspace, absPath: string): Promise<string> {
  try {
    if (!existsSync(absPath)) return "";
    const ext = extname(absPath).toLowerCase();
    const display = ws.rel(absPath);

    if (ext === ".json") return await checkJson(absPath, display);
    if ([".js", ".mjs", ".cjs"].includes(ext)) return await checkWithCommand(ws, absPath, display, "node --check");
    if (ext === ".py") return await checkWithCommand(ws, absPath, display, "python -m py_compile");
    return "";
  } catch {
    // Validation is a courtesy; never let it interfere with the write itself.
    return "";
  }
}

async function checkJson(absPath: string, display: string): Promise<string> {
  const body = await readFile(absPath, "utf-8");
  if (body.trim() === "") return "";
  try {
    JSON.parse(body);
    return "";
  } catch (error) {
    const message = (error as Error).message;
    const line = locateJsonError(body, message);
    return warn(display, line === undefined ? message : `${message} (near line ${line})`);
  }
}

/** JSON.parse reports a character offset; turn it into something actionable. */
function locateJsonError(body: string, message: string): number | undefined {
  const match = /position (\d+)/.exec(message);
  if (match === null) return undefined;
  const offset = Number(match[1]);
  if (!Number.isFinite(offset)) return undefined;
  return body.slice(0, offset).split(/\r?\n/).length;
}

async function checkWithCommand(
  ws: Workspace,
  absPath: string,
  display: string,
  command: string,
): Promise<string> {
  const { statSync } = await import("fs");
  if (statSync(absPath).size > MAX_CHECKED_BYTES) return "";

  const result = await runCommand(`${command} "${absPath}"`, {
    cwd: ws.root,
    timeoutMs: CHECK_TIMEOUT_MS,
    maxBuffer: 256 * 1024,
  });
  if (result.ok) return "";

  const output = `${result.stderr}\n${result.stdout}`.trim();
  // The checker itself being absent is not a syntax problem.
  if (output === "" || /not recognized|command not found|ENOENT|No such file/i.test(output)) return "";

  return warn(display, firstUsefulLine(output, absPath));
}

/** Build output repeats the absolute path on every line; the model needs the reason. */
function firstUsefulLine(output: string, absPath: string): string {
  const lines = output
    .split(/\r?\n/)
    .map((line) => line.replace(absPath, "").trim())
    .filter((line) => line !== "" && !line.startsWith("^"));
  const pointed = lines.find((line) => /error|Error|SyntaxError|line \d+/.test(line));
  return (pointed ?? lines[0] ?? "syntax error").slice(0, 300);
}

function warn(display: string, detail: string): string {
  return (
    `\n\nWARNING: ${display} does not parse -- ${detail}\n` +
    `The file was still written. Read it back and fix the syntax before moving on.`
  );
}

import { existsSync } from "fs";
import { readFile } from "fs/promises";
import { extname } from "path";
import { runCommand } from "./shell";
import type { Workspace } from "./workspace";

/**
 * Cheap syntax validation run automatically after a write. A small model will
 * happily emit code with an unclosed brace and only discover it much later, so
 * every write reports its own damage immediately.
 *
 * Conservative by design: it only speaks up when it is confident something is
 * wrong. An unknown file type, a missing interpreter, or a checker that cannot
 * run all return "no complaint" rather than a false alarm.
 */

const CHECK_TIMEOUT_MS = 8000;
const MAX_CHECKED_BYTES = 512 * 1024;

/** Returns a warning line to append to the tool result, or "" if it looks fine. */
export async function validateSyntax(ws: Workspace, absPath: string): Promise<string> {
  try {
    if (!existsSync(absPath)) return "";
    const ext = extname(absPath).toLowerCase();
    const display = ws.rel(absPath);

    if (ext === ".json") return await checkJson(absPath, display);
    if ([".js", ".mjs", ".cjs"].includes(ext)) return await checkWithCommand(ws, absPath, display, "node --check");
    if (ext === ".py") return await checkWithCommand(ws, absPath, display, "python -m py_compile");
    return "";
  } catch {
    // Validation is a courtesy; never let it interfere with the write itself.
    return "";
  }
}

async function checkJson(absPath: string, display: string): Promise<string> {
  const body = await readFile(absPath, "utf-8");
  if (body.trim() === "") return "";
  try {
    JSON.parse(body);
    return "";
  } catch (error) {
    const message = (error as Error).message;
    const line = locateJsonError(body, message);
    return warn(display, line === undefined ? message : `${message} (near line ${line})`);
  }
}

/** JSON.parse reports a character offset; turn it into something actionable. */
function locateJsonError(body: string, message: string): number | undefined {
  const match = /position (\d+)/.exec(message);
  if (match === null) return undefined;
  const offset = Number(match[1]);
  if (!Number.isFinite(offset)) return undefined;
  return body.slice(0, offset).split(/\r?\n/).length;
}

async function checkWithCommand(
  ws: Workspace,
  absPath: string,
  display: string,
  command: string,
): Promise<string> {
  const { statSync } = await import("fs");
  if (statSync(absPath).size > MAX_CHECKED_BYTES) return "";

  const result = await runCommand(`${command} "${absPath}"`, {
    cwd: ws.root,
    timeoutMs: CHECK_TIMEOUT_MS,
    maxBuffer: 256 * 1024,
  });
  if (result.ok) return "";

  const output = `${result.stderr}\n${result.stdout}`.trim();
  // The checker itself being absent is not a syntax problem.
  if (output === "" || /not recognized|command not found|ENOENT|No such file/i.test(output)) return "";

  return warn(display, firstUsefulLine(output, absPath));
}

/** Build output repeats the absolute path on every line; the model needs the reason. */
function firstUsefulLine(output: string, absPath: string): string {
  const lines = output
    .split(/\r?\n/)
    .map((line) => line.replace(absPath, "").trim())
    .filter((line) => line !== "" && !line.startsWith("^"));
  const pointed = lines.find((line) => /error|Error|SyntaxError|line \d+/.test(line));
  return (pointed ?? lines[0] ?? "syntax error").slice(0, 300);
}

function warn(display: string, detail: string): string {
  return (
    `\n\nWARNING: ${display} does not parse -- ${detail}\n` +
    `The file was still written. Read it back and fix the syntax before moving on.`
  );
}