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/);
});

test("creates a valid settings file from an empty target", () => {
  const tempDir = fs.mkdtempSync(path.join(os.tmpdir(), "copilot-settings-"));
  const targetFile = path.join(tempDir, "settings.json");

  fs.writeFileSync(targetFile, "{}\n", "utf8");

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

  const parsed = parseJsonc(fs.readFileSync(targetFile, "utf8"));
  assert.equal(
    parsed["chat.agentFilesLocations"]["/repo/home/resources/agents"],
    true,
  );
  assert.equal(
    parsed["chat.instructionsFilesLocations"][
      "/repo/home/resources/instructions"
    ],
    true,
  );
});