#!/usr/bin/env node
/**
 * Mosaic development configuration: bootstrap, validate, resolve.
 *
 * Operations:
 *   bootstrap  Create the default config ONLY if absent; otherwise validate
 *              the existing file without writing (idempotent).
 *   validate   Load and strictly validate; print resolved config on stdout.
 *   env        Print shell-safe exports for launcher scripts:
 *              MOSAIC_DATA_ROOT, MOSAIC_PROVIDER, MOSAIC_MODEL.
 *
 * Config location: $MOSAIC_CONFIG or ~/.config/mosaic-dev/config.json
 *
 * Exit codes:
 *   0 success
 *   2 configuration exists but is invalid (never modified by this tool)
 *   3 configuration is missing for a read operation (validate/env)
 *
 * Invariants (docs/plans/2026-09-02_atomic-mosaic-foundation.md):
 *   - Existing configuration is never overwritten.
 *   - Validation failure modifies nothing.
 *   - Secrets are never stored in configuration.
 */

import fs from "node:fs";
import os from "node:os";
import path from "node:path";
import process from "node:process";

const SUPPORTED_CONFIG_VERSION = 1;
const SUPPORTED_ENVIRONMENTS = new Set(["development", "production"]);
const SUPPORTED_BACKENDS = new Set(["docker"]);
const SUPPORTED_ADAPTERS = new Set(["pi", "mock"]); // mock: test-only, see adapters/README.md
const NAME_PATTERN = /^[A-Za-z0-9][A-Za-z0-9._:/-]{0,199}$/;

function fail(exitCode, message) {
  process.stderr.write(`mosaic-config: ${message}\n`);
  process.exit(exitCode);
}

function configPath() {
  return process.env.MOSAIC_CONFIG
    ? path.resolve(process.env.MOSAIC_CONFIG)
    : path.join(os.homedir(), ".config", "mosaic-dev", "config.json");
}

function readRaw(file) {
  let stat;
  try {
    stat = fs.lstatSync(file);
  } catch {
    return null; // missing
  }
  if (!stat.isFile() || stat.isSymbolicLink()) {
    fail(2, `configuration path must be a regular, non-symbolic-link file: ${file}`);
  }
  try {
    return fs.readFileSync(file, "utf8");
  } catch {
    fail(2, `configuration file is not readable: ${file}`);
  }
}

function rejectUnknownKeys(object, allowed, where) {
  for (const key of Object.keys(object)) {
    if (!allowed.includes(key)) {
      fail(2, `unsupported ${where} key: "${key}"`);
    }
  }
}

function isPlainObject(value) {
  return typeof value === "object" && value !== null && !Array.isArray(value);
}

function validateDataRoot(value, file) {
  if (typeof value !== "string" || value.length === 0) {
    fail(2, 'execution "dataRoot" must be a non-empty string');
  }
  if (value.includes("\0")) {
    fail(2, 'execution "dataRoot" contains a NUL byte');
  }
  if (!path.isAbsolute(value)) {
    fail(2, `execution "dataRoot" must be an absolute path (got "${value}")`);
  }
  const resolved = path.resolve(value);
  if (resolved !== value) {
    fail(2, `execution "dataRoot" must be canonical without ".", "..", trailing slashes, or redundant separators (got "${value}")`);
  }
  if (resolved === path.parse(resolved).root) {
    fail(2, 'execution "dataRoot" must not be the filesystem root');
  }
  const home = path.resolve(os.homedir());
  if (resolved === home || isAncestorOf(resolved, home)) {
    fail(2, `execution "dataRoot" must not be or contain the home directory (${home})`);
  }
  const configDir = path.dirname(path.resolve(file));
  if (resolved === configDir || isAncestorOf(resolved, configDir)) {
    fail(2, `execution "dataRoot" must not be or contain the configuration directory (${configDir})`);
  }
  return resolved;
}

function isAncestorOf(ancestor, candidate) {
  const rel = path.relative(ancestor, candidate);
  return rel !== "" && !rel.startsWith("..") && !path.isAbsolute(rel);
}

function validate(document, file) {
  if (!isPlainObject(document)) {
    fail(2, "configuration must be a JSON object");
  }
  rejectUnknownKeys(
    document,
    ["configVersion", "environment", "dataRoot", "execution"],
    "configuration",
  );

  if (document.configVersion !== SUPPORTED_CONFIG_VERSION) {
    fail(2, `unsupported configVersion: ${JSON.stringify(document.configVersion)} (supported: ${SUPPORTED_CONFIG_VERSION})`);
  }
  if (!SUPPORTED_ENVIRONMENTS.has(document.environment)) {
    fail(2, `unsupported environment: ${JSON.stringify(document.environment)} (supported: ${[...SUPPORTED_ENVIRONMENTS].join(", ")})`);
  }

  const dataRoot = validateDataRoot(document.dataRoot, file);

  if (!isPlainObject(document.execution)) {
    fail(2, '"execution" must be a JSON object');
  }
  rejectUnknownKeys(document.execution, ["backend", "provider", "model", "adapter"], '"execution"');
  if (!SUPPORTED_BACKENDS.has(document.execution.backend)) {
    fail(2, `unsupported execution.backend: ${JSON.stringify(document.execution.backend)} (supported: ${[...SUPPORTED_BACKENDS].join(", ")})`);
  }
  for (const key of ["provider", "model"]) {
    const value = document.execution[key];
    if (typeof value !== "string" || !NAME_PATTERN.test(value)) {
      fail(2, `execution.${key} must match ${NAME_PATTERN} (got ${JSON.stringify(value)})`);
    }
  }

  const adapter = document.execution.adapter === undefined || document.execution.adapter === null
    ? "pi"
    : document.execution.adapter;
  if (typeof adapter !== "string" || !SUPPORTED_ADAPTERS.has(adapter)) {
    fail(2, `unsupported execution.adapter: ${JSON.stringify(adapter)} (supported: ${[...SUPPORTED_ADAPTERS].join(", ")})`);
  }

  return {
    configVersion: document.configVersion,
    environment: document.environment,
    dataRoot,
    execution: {
      backend: document.execution.backend,
      provider: document.execution.provider,
      model: document.execution.model,
      adapter,
    },
  };
}

function load(file) {
  const raw = readRaw(file);
  if (raw === null) {
    fail(3, `configuration not found: ${file} (run scripts/bootstrap.sh to create it)`);
  }
  let document;
  try {
    document = JSON.parse(raw);
  } catch (error) {
    fail(2, `configuration is not valid JSON (${file}): ${error.message}`);
  }
  return validate(document, file);
}

function shellQuote(value) {
  return `'${String(value).replaceAll("'", `'\\''`)}'`;
}

const DEFAULT_CONFIG = {
  configVersion: 1,
  environment: "development",
  dataRoot: path.join(os.homedir(), ".mosaic-dev"),
  execution: {
    backend: "docker",
    provider: "zai",
    model: "glm-5.3-flash",
  },
};

const operation = process.argv[2];
const file = configPath();

switch (operation) {
  case "bootstrap": {
    if (fs.existsSync(file)) {
      load(file); // validate only; never rewrite
      process.stderr.write(`mosaic-config: configuration already present, validated without changes: ${file}\n`);
      process.exit(0);
    }
    fs.mkdirSync(path.dirname(file), { recursive: true });
    let fd;
    try {
      // 'wx': creation is exclusive; an existing file is never overwritten.
      fd = fs.openSync(file, "wx", 0o644);
      fs.writeFileSync(fd, `${JSON.stringify(DEFAULT_CONFIG, null, 2)}\n`);
    } catch (error) {
      if (error.code === "EEXIST") {
        load(file);
        process.exit(0);
      }
      fail(1, `unable to create configuration: ${error.message}`);
    } finally {
      if (fd !== undefined) fs.closeSync(fd);
    }
    load(file);
    process.stderr.write(`mosaic-config: created default configuration: ${file}\n`);
    process.exit(0);
  }

  case "validate": {
    const resolved = load(file);
    process.stdout.write(`${JSON.stringify(resolved, null, 2)}\n`);
    process.exit(0);
  }

  case "env": {
    const resolved = load(file);
    process.stdout.write(
      [
        `MOSAIC_DATA_ROOT=${shellQuote(resolved.dataRoot)}`,
        `MOSAIC_PROVIDER=${shellQuote(resolved.execution.provider)}`,
        `MOSAIC_MODEL=${shellQuote(resolved.execution.model)}`,
        `MOSAIC_ADAPTER=${shellQuote(resolved.execution.adapter)}`,
        "",
      ].join("\n"),
    );
    process.exit(0);
  }

  default:
    fail(1, `unknown operation: ${JSON.stringify(operation ?? "")} (expected bootstrap | validate | env)`);
}