import assert from 'node:assert/strict';
import { spawnSync } from 'node:child_process';
import fs from 'node:fs';
import os from 'node:os';
import path from 'node:path';
import test from 'node:test';
import { fileURLToPath } from 'node:url';

const scriptDir = path.dirname(fileURLToPath(import.meta.url));
const repoRoot = path.resolve(scriptDir, '..');
const mergeScript = path.join(scriptDir, 'merge-vscode-settings.mjs');
const templateFile = path.join(repoRoot, 'config', 'vscode', 'settings.template.jsonc');

function stripJsonComments(input) {
  let output = '';
  let inString = false;
  let escaping = false;
  let inLineComment = false;
  let inBlockComment = false;

  for (let index = 0; index < input.length; index += 1) {
    const char = input[index];
    const next = input[index + 1];

    if (inLineComment) {
      if (char === '\n') {
        inLineComment = false;
        output += char;
      }
      continue;
    }

    if (inBlockComment) {
      if (char === '*' && next === '/') {
        inBlockComment = false;
        index += 1;
      } else if (char === '\n' || char === '\r') {
        output += char;
      }
      continue;
    }

    if (inString) {
      output += char;
      if (escaping) {
        escaping = false;
      } else if (char === '\\') {
        escaping = true;
      } else if (char === '"') {
        inString = false;
      }
      continue;
    }

    if (char === '"') {
      inString = true;
      output += char;
      continue;
    }

    if (char === '/' && next === '/') {
      inLineComment = true;
      index += 1;
      continue;
    }

    if (char === '/' && next === '*') {
      inBlockComment = true;
      index += 1;
      continue;
    }

    output += char;
  }

  return output;
}

function stripTrailingCommas(input) {
  let output = '';
  let inString = false;
  let escaping = false;

  for (let index = 0; index < input.length; index += 1) {
    const char = input[index];

    if (inString) {
      output += char;
      if (escaping) {
        escaping = false;
      } else if (char === '\\') {
        escaping = true;
      } else if (char === '"') {
        inString = false;
      }
      continue;
    }

    if (char === '"') {
      inString = true;
      output += char;
      continue;
    }

    if (char === ',') {
      let lookahead = index + 1;
      while (lookahead < input.length && /\s/.test(input[lookahead])) {
        lookahead += 1;
      }
      if (input[lookahead] === '}' || input[lookahead] === ']') {
        continue;
      }
    }

    output += char;
  }

  return output;
}

function parseJsonc(input) {
  return JSON.parse(stripTrailingCommas(stripJsonComments(input)));
}

function runMerge(targetFile) {
  return spawnSync(
    process.execPath,
    [
      mergeScript,
      '--target',
      targetFile,
      '--template',
      templateFile,
      '--set',
      'COPILOT_RESOURCES_HOME=/repo/home',
    ],
    {
      cwd: repoRoot,
      encoding: 'utf8',
    }
  );
}

test('preserves comments and custom nested entries while inserting managed settings', () => {
  const tempDir = fs.mkdtempSync(path.join(os.tmpdir(), 'copilot-settings-'));
  const targetFile = path.join(tempDir, 'settings.json');

  fs.writeFileSync(
    targetFile,
    `{
  // keep this comment
  "workbench.colorTheme": "GitHub Dark Mode",

  // preserve nested comments
  "chat.agentFilesLocations": {
    // custom agents stay
    "/custom/agents": true
  },

  "chat.instructionsFilesLocations": {
    "/old/instructions": true,
    "~/.claude/rules": false,
  }
}
`,
    'utf8'
  );

  const result = runMerge(targetFile);
  assert.equal(result.status, 0, result.stderr);

  const output = fs.readFileSync(targetFile, 'utf8');
  assert.match(output, /\/\/ keep this comment/);
  assert.match(output, /\/\/ preserve nested comments/);
  assert.match(output, /\/\/ custom agents stay/);
  assert.match(output, /"\/custom\/agents": true/);
  assert.match(output, /"\/repo\/home\/resources\/agents": true/);

  const parsed = parseJsonc(output);
  assert.equal(parsed['workbench.colorTheme'], 'GitHub Dark Mode');
  assert.equal(parsed['chat.agentFilesLocations']['/custom/agents'], true);
  assert.equal(parsed['chat.agentFilesLocations']['/repo/home/resources/agents'], true);
  assert.equal(parsed['chat.agentFilesLocations']['~/.copilot/agents'], true);
  assert.equal(parsed['chat.instructionsFilesLocations']['/old/instructions'], true);
  assert.equal(parsed['chat.instructionsFilesLocations']['/repo/home/resources/instructions'], true);
  assert.equal(parsed['chat.instructionsFilesLocations']['~/.claude/rules'], true);
});

test('second run is idempotent and keeps the file text unchanged', () => {
  const tempDir = fs.mkdtempSync(path.join(os.tmpdir(), 'copilot-settings-'));
  const targetFile = path.join(tempDir, 'settings.json');

  fs.writeFileSync(
    targetFile,
    `{
  // user comment
  "chat.promptFilesLocations": {
    "/custom/prompts": true
  }
}
`,
    'utf8'
  );

  const firstRun = runMerge(targetFile);
  assert.equal(firstRun.status, 0, firstRun.stderr);
  const firstOutput = fs.readFileSync(targetFile, 'utf8');

  const secondRun = runMerge(targetFile);
  assert.equal(secondRun.status, 0, secondRun.stderr);
  assert.match(secondRun.stdout, /already up to date/);

  const secondOutput = fs.readFileSync(targetFile, 'utf8');
  assert.equal(secondOutput, firstOutput);
  assert.match(secondOutput, /\/\/ user comment/);
});