/**
 * Boot-time configuration checks.
 *
 * The backend reads environment variables in a couple of dozen places, and a
 * missing or misspelled one used to be `undefined` until the first line of code
 * that happened to need it — which could be a very long time after the
 * container reported healthy. Several of those failures are silent and
 * customer-visible: mail containing `undefined` in a link, or a shop that
 * quietly stops charging anyone.
 *
 * The container already refuses to start on a failed migration rather than
 * serving against a schema it does not match. This is the same argument applied
 * to configuration.
 *
 * Kept a pure function of the environment it is handed, rather than reading
 * `process.env` itself, so it can be tested exhaustively without booting a
 * server or mutating global state. `server.ts` calls it; `app.ts` deliberately
 * does not, because the integration suite imports `app` directly and would
 * otherwise become a configuration exercise.
 */

export interface EnvValidation {
  /** Configuration that must be fixed. The process should not start. */
  errors: string[];
  /** Working, but worth saying out loud — usually a capability that is off. */
  warnings: string[];
}

// Without these the process cannot do its job at all.
//
// Exported so tests/unit/composeEnvironment.test.ts can assert the deploying
// environment actually sets them. #107 happened because this list grew and
// docker-compose.qa.yml did not: the check has to read this list rather than a
// copy of it, or the next variable added here goes unguarded in exactly the
// same way.
export const ALWAYS_REQUIRED = [
  'PGHOST',
  'PGPORT',
  'PGUSER',
  'PGPASSWORD',
  'PGDATABASE',
  // No reprieve for this one despite having a fallback: '/app/uploads' is
  // correct inside the container and wrong everywhere else, so inheriting it
  // silently writes uploads somewhere nobody is looking.
  'UPLOADS_DIR'
] as const;

// Only meaningful once real payments are switched on. QA runs with none of
// these on purpose, which is why the requirement is conditional rather than
// absolute.
const PAYPAL_REQUIRED = [
  'PAYPAL_CLIENT_ID',
  'PAYPAL_CLIENT_SECRET',
  'PAYPAL_WEBHOOK_ID',
  'PAYPAL_ENV'
] as const;

// A variable set to spaces is a configuration mistake, not a value.
function isPresent(env: NodeJS.ProcessEnv, name: string): boolean {
  const value = env[name];
  return typeof value === 'string' && value.trim() !== '';
}

// One function per rule, at module level rather than nested. Each is small
// enough to read on its own, and cognitive complexity counts everything
// declared inside a function — so keeping these out of validateEnv is what
// keeps the composition below flat.

function checkAlwaysRequired(env: NodeJS.ProcessEnv): string[] {
  return ALWAYS_REQUIRED.filter((name) => !isPresent(env, name)).map(
    (name) => `${name} is required and is not set.`
  );
}

// Strict rather than truthy. This used to be read as "demo unless the value is
// exactly 'false'", so DEMO_MODE=False, 0, or any typo meant demo mode was on —
// a configuration slip that stopped the shop taking money and said nothing.
function checkDemoMode(env: NodeJS.ProcessEnv): string[] {
  const demoMode = env.DEMO_MODE;

  if (demoMode === undefined || demoMode.trim() === '') {
    return [
      "DEMO_MODE is required and must be exactly 'true' or 'false'. It decides whether real " +
        'payments are taken, so it has to be stated rather than inherited.'
    ];
  }

  if (demoMode !== 'true' && demoMode !== 'false') {
    return [
      `DEMO_MODE must be exactly 'true' or 'false', but is '${demoMode}'. Anything else used to ` +
        'be read as demo mode, which meant a typo here quietly stopped the shop charging anyone.'
    ];
  }

  return [];
}

// Conditional rather than absolute: QA runs with no PayPal credentials on
// purpose, so requiring them unconditionally would be wrong.
function checkPayPal(env: NodeJS.ProcessEnv): string[] {
  if (env.DEMO_MODE !== 'false') {
    return [];
  }
  return PAYPAL_REQUIRED.filter((name) => !isPresent(env, name)).map(
    (name) => `${name} is required when DEMO_MODE=false, because real payments are enabled.`
  );
}

// SMTP is all or nothing, and two other variables hang off whether it is set.
function checkMail(env: NodeJS.ProcessEnv): EnvValidation {
  const errors: string[] = [];
  const warnings: string[] = [];

  const hasUser = isPresent(env, 'SMTP_USER');
  const hasPassword = isPresent(env, 'SMTP_PASSWORD');

  // Half-configured is worse than absent: the mailer only skips when both are
  // missing, so setting one produces a connection that fails at send time
  // instead of a clean "mail is off".
  if (hasUser && !hasPassword) {
    errors.push('SMTP_PASSWORD is required when SMTP_USER is set — set both or neither.');
  }
  if (hasPassword && !hasUser) {
    errors.push('SMTP_USER is required when SMTP_PASSWORD is set — set both or neither.');
  }

  if (!hasUser || !hasPassword) {
    warnings.push(
      'SMTP is not configured — no email will be sent. Verification, password reset, favorite ' +
        'alerts and cart reminders will all be skipped with a warning.'
    );
    return { errors, warnings };
  }

  // Demanded only alongside SMTP. Its sole job is building links in email, so a
  // local environment that cannot send mail does not need it, and requiring it
  // there would break every existing local setup to prevent nothing.
  if (!isPresent(env, 'PUBLIC_URL')) {
    errors.push(
      'PUBLIC_URL is required when SMTP is configured, or every link in a verification, ' +
        'password-reset, favorite-alert or cart-reminder email reads "undefined".'
    );
  }

  if (!isPresent(env, 'MAIL_ALLOWLIST')) {
    warnings.push(
      'MAIL_ALLOWLIST is not set while SMTP is configured — this environment can email real ' +
        'customers. That is correct for production and a hazard anywhere else.'
    );
  }

  return { errors, warnings };
}

function checkAdminGate(env: NodeJS.ProcessEnv): string[] {
  if (isPresent(env, 'ADMIN_GATE_SECRET')) {
    return [];
  }
  return [
    'ADMIN_GATE_SECRET is not set — /api/admin is protected only by the reverse proxy. ' +
      'Anything able to reach this container directly can administer the store.'
  ];
}

// Optional on purpose, and unlike the two above, unset costs nothing in
// safety. A submission still arrives, keeps its photos and waits in the queue
// undrafted (#223). It is a warning rather than an error because the photos are
// often the only copy of an item no longer in the sender's hands, so losing a
// consignment to an expired key would be far worse than an item arriving
// without its description written. Silence would be the wrong answer too: an
// operator who believes drafting is on and finds every item undrafted has
// nothing to tell them why.
// Optional, like the drafting key below. Absent, the notification still sends
// with its review link and simply carries no shortcuts — being told an item
// arrived matters far more than being able to discard it in one click.
function checkIntakeActionSecret(env: NodeJS.ProcessEnv): string[] {
  if (isPresent(env, 'INTAKE_ACTION_SECRET')) {
    return [];
  }
  return [
    'INTAKE_ACTION_SECRET is not set — intake notifications will link to the review queue ' +
      'but carry no regenerate or discard shortcuts.'
  ];
}

function checkDraftingKey(env: NodeJS.ProcessEnv): string[] {
  if (isPresent(env, 'ANTHROPIC_API_KEY')) {
    return [];
  }
  return [
    'ANTHROPIC_API_KEY is not set — submitted items will arrive undrafted and wait in the ' +
      'review queue for someone to write them up by hand.'
  ];
}

// Optional, and the same shape as the admin gate above: unset is a working
// configuration with one defence switched off, which is worth saying out loud
// rather than leaving to be discovered. Set, it has to be an absolute origin —
// a value missing its scheme joins into a relative path and silently breaks
// every image on the site, which is a worse outcome than either extreme.
function checkUploadsOrigin(env: NodeJS.ProcessEnv): EnvValidation {
  if (!isPresent(env, 'UPLOADS_BASE_URL')) {
    return {
      errors: [],
      warnings: [
        'UPLOADS_BASE_URL is not set — uploaded files are served from this application on its ' +
          'own origin, so anything reaching the uploads directory shares an origin with the site.'
      ]
    };
  }

  const value = (env.UPLOADS_BASE_URL ?? '').trim();
  if (!value.startsWith('https://') && !value.startsWith('http://')) {
    return {
      errors: [
        'UPLOADS_BASE_URL must be an absolute origin including the scheme, such as ' +
          'https://uploads.example.com. Without one it joins into a relative path and every ' +
          'image on the site breaks.'
      ],
      warnings: []
    };
  }

  return { errors: [], warnings: [] };
}

export function validateEnv(env: NodeJS.ProcessEnv): EnvValidation {
  const mail = checkMail(env);
  const uploads = checkUploadsOrigin(env);

  return {
    errors: [
      ...checkAlwaysRequired(env),
      ...checkDemoMode(env),
      ...checkPayPal(env),
      ...mail.errors,
      ...uploads.errors
    ],
    warnings: [...mail.warnings, ...checkAdminGate(env), ...uploads.warnings, ...checkDraftingKey(env), ...checkIntakeActionSecret(env)]
  };
}