import re
import time

from flask import Blueprint, request, jsonify, g, session
from app import db, limiter
from app.models.user import User
from app.models.audit_log import AuditLog
from app.services.auth_service import (
    hash_auth_token,
    verify_auth_token,
    generate_tokens,
    generate_mfa_token,
    decode_token,
    blacklist_token,
    require_jwt,
    encrypt_totp_secret,
    decrypt_totp_secret,
    generate_recovery_nonce,
    verify_recovery_proof,
    generate_backup_codes,
    verify_and_consume_backup_code,
)

auth_bp = Blueprint('auth', __name__)

EMAIL_RE = re.compile(r'^[^@\s]+@[^@\s]+\.[^@\s]+$')


def _client_ip():
    """Return the best-effort client IP from the request context."""
    return request.headers.get('X-Forwarded-For', request.remote_addr or '').split(',')[0].strip()


@auth_bp.route('/register', methods=['POST'])
@limiter.limit('10 per minute')
def register():
    data = request.get_json(silent=True) or {}
    email = (data.get('email') or '').strip().lower()
    auth_hash = data.get('auth_hash', '')
    enc_key_salt = data.get('enc_key_salt', '')

    if not email or not EMAIL_RE.match(email):
        return jsonify({'error': 'Invalid email address'}), 400
    if not auth_hash:
        return jsonify({'error': 'auth_hash is required'}), 400
    if not enc_key_salt:
        return jsonify({'error': 'enc_key_salt is required'}), 400

    if User.query.filter_by(email=email).first():
        return jsonify({'error': 'Email already registered'}), 409

    master_hash = hash_auth_token(auth_hash)
    user = User(email=email, master_hash=master_hash, enc_key_salt=enc_key_salt)
    db.session.add(user)
    db.session.flush()  # populate user.id before logging

    AuditLog.log(
        user_id=user.id,
        action='auth.register',
        resource_type='user',
        resource_id=user.id,
        detail=f'New account registered: {email}',
        ip_address=_client_ip(),
    )
    db.session.commit()

    return jsonify({'message': 'Account created successfully'}), 201


@auth_bp.route('/login', methods=['POST'])
@limiter.limit('10 per minute')
def login():
    from datetime import datetime, timezone, timedelta
    from sqlalchemy.exc import OperationalError

    # Number of consecutive failures before a temporary lockout is applied.
    MAX_FAILED_LOGINS = 5
    LOCKOUT_MINUTES = 15

    data = request.get_json(silent=True) or {}
    email = (data.get('email') or '').strip().lower()
    auth_hash = data.get('auth_hash', '')

    time.sleep(0.1)  # mitigate timing-based user enumeration

    if not email or not auth_hash:
        return jsonify({'error': 'Email and auth_hash are required'}), 400

    user = User.query.filter_by(email=email).first()

    # Per-account lockout check.
    # Guarded with try/except so that a deployment where the migration has not
    # yet been run (columns missing) degrades gracefully instead of returning
    # an HTML 500 page that breaks JSON parsing in the extension.
    try:
        if user and user.locked_until:
            now = datetime.now(timezone.utc).replace(tzinfo=None)
            if user.locked_until > now:
                remaining = int((user.locked_until - now).total_seconds() // 60) + 1
                AuditLog.log(
                    user_id=user.id,
                    action='auth.login_blocked',
                    resource_type='user',
                    resource_id=user.id,
                    detail=f'Login blocked — account locked for {remaining} more minute(s)',
                    ip_address=_client_ip(),
                )
                db.session.commit()
                return jsonify({
                    'error': f'Account temporarily locked. Try again in {remaining} minute(s).'
                }), 429
            else:
                # Lockout has expired — reset the counter.
                user.failed_login_count = 0
                user.locked_until = None
    except OperationalError:
        # Columns do not exist yet — migration pending. Skip lockout check.
        db.session.rollback()

    if not user or not verify_auth_token(auth_hash, user.master_hash):
        if user:
            try:
                user.failed_login_count = (user.failed_login_count or 0) + 1
                if user.failed_login_count >= MAX_FAILED_LOGINS:
                    user.locked_until = datetime.now(timezone.utc).replace(tzinfo=None) + timedelta(minutes=LOCKOUT_MINUTES)
                    AuditLog.log(
                        user_id=user.id,
                        action='auth.account_locked',
                        resource_type='user',
                        resource_id=user.id,
                        detail=f'Account locked for {LOCKOUT_MINUTES} minutes after {user.failed_login_count} failed attempts',
                        ip_address=_client_ip(),
                    )
                else:
                    AuditLog.log(
                        user_id=user.id,
                        action='auth.login_failed',
                        resource_type='user',
                        resource_id=user.id,
                        detail=f'Failed login attempt — invalid password ({user.failed_login_count}/{MAX_FAILED_LOGINS})',
                        ip_address=_client_ip(),
                    )
                db.session.commit()
            except OperationalError:
                db.session.rollback()
                AuditLog.log(
                    user_id=user.id,
                    action='auth.login_failed',
                    resource_type='user',
                    resource_id=user.id,
                    detail='Failed login attempt — invalid password',
                    ip_address=_client_ip(),
                )
                db.session.commit()
        return jsonify({'error': 'Invalid email or password'}), 401

    # Successful authentication — reset lockout state.
    try:
        user.failed_login_count = 0
        user.locked_until = None
    except OperationalError:
        db.session.rollback()

    user.last_login = datetime.now(timezone.utc).replace(tzinfo=None)

    AuditLog.log(
        user_id=user.id,
        action='auth.login',
        resource_type='user',
        resource_id=user.id,
        detail=f'Successful login{" (MFA pending)" if user.totp_enabled else ""}',
        ip_address=_client_ip(),
    )
    db.session.commit()

    # MFA gate: if enabled, issue a short-lived mfa_token instead of full tokens
    if user.totp_enabled:
        mfa_token = generate_mfa_token(user.id)
        return jsonify({
            'mfa_required': True,
            'mfa_token': mfa_token,
            'enc_key_salt': user.enc_key_salt,
        }), 200

    tokens = generate_tokens(user.id)
    return jsonify({
        'access_token': tokens['access_token'],
        'refresh_token': tokens['refresh_token'],
        'enc_key_salt': user.enc_key_salt,
    }), 200


@auth_bp.route('/logout', methods=['POST'])
@limiter.limit('60 per minute')
def logout():
    """Blacklist both the access token (from header) and refresh token (from body)."""
    auth_header = request.headers.get('Authorization', '')
    if auth_header.startswith('Bearer '):
        blacklist_token(auth_header[7:], 'access')

    data = request.get_json(silent=True) or {}
    refresh_token = data.get('refresh_token', '')
    if refresh_token:
        blacklist_token(refresh_token, 'refresh')

    return jsonify({'message': 'Logged out'}), 200


@auth_bp.route('/refresh', methods=['POST'])
@limiter.limit('30 per minute')
def refresh():
    data = request.get_json(silent=True) or {}
    refresh_token = data.get('refresh_token', '')
    if not refresh_token:
        return jsonify({'error': 'refresh_token is required'}), 400

    try:
        payload = decode_token(refresh_token, expected_type='refresh')
    except Exception:
        return jsonify({'error': 'Invalid or expired refresh token'}), 401

    # Rotate: blacklist old refresh token and issue fresh pair
    blacklist_token(refresh_token, 'refresh')
    tokens = generate_tokens(int(payload['sub']))
    return jsonify({
        'access_token': tokens['access_token'],
        'refresh_token': tokens['refresh_token'],
    }), 200


# ── MFA / TOTP endpoints ─────────────────────────────────────────────────────

@auth_bp.route('/mfa/setup', methods=['GET'])
@limiter.limit('10 per minute')
@require_jwt
def mfa_setup():
    """Generate a new TOTP secret and return QR code (as base64 PNG data URI)."""
    user = db.session.get(User, g.current_user_id)
    if user.totp_enabled:
        return jsonify({'error': 'MFA is already enabled'}), 400

    import pyotp
    import qrcode
    import io
    import base64

    secret = pyotp.random_base32()
    uri = pyotp.TOTP(secret).provisioning_uri(
        name=user.email,
        issuer_name='PassKeeper',
    )

    img = qrcode.make(uri)
    buf = io.BytesIO()
    img.save(buf, format='PNG')
    qr_b64 = base64.b64encode(buf.getvalue()).decode()

    return jsonify({
        'secret': secret,
        'qr_code': f'data:image/png;base64,{qr_b64}',
        'uri': uri,
    }), 200


@auth_bp.route('/mfa/enable', methods=['POST'])
@limiter.limit('10 per minute')
@require_jwt
def mfa_enable():
    """Enable MFA after verifying the first TOTP code. Returns one-time backup codes."""
    import json
    user = db.session.get(User, g.current_user_id)
    if user.totp_enabled:
        return jsonify({'error': 'MFA is already enabled'}), 400

    data = request.get_json(silent=True) or {}
    secret = (data.get('secret') or '').strip()
    totp_code = (data.get('totp_code') or '').strip()

    if not secret or not totp_code:
        return jsonify({'error': 'secret and totp_code are required'}), 400

    import pyotp
    if not pyotp.TOTP(secret).verify(totp_code, valid_window=1):
        return jsonify({'error': 'Invalid verification code'}), 400

    totp_secret_enc, totp_iv = encrypt_totp_secret(secret)
    user.totp_secret = totp_secret_enc
    user.totp_iv = totp_iv
    user.totp_enabled = True

    # Generate one-time backup codes — plaintext shown once, only hashes stored.
    plaintext_codes, hashed_codes = generate_backup_codes()
    user.mfa_backup_codes = json.dumps(hashed_codes)

    AuditLog.log(
        user_id=user.id,
        action='auth.mfa_enable',
        resource_type='user',
        resource_id=user.id,
        detail='TOTP two-factor authentication enabled; backup codes generated',
        ip_address=_client_ip(),
    )
    db.session.commit()

    return jsonify({
        'message': 'MFA enabled successfully',
        'backup_codes': plaintext_codes,
    }), 200


@auth_bp.route('/mfa/disable', methods=['POST'])
@limiter.limit('10 per minute')
@require_jwt
def mfa_disable():
    """Disable MFA after verifying the current TOTP code or a backup code."""
    import json
    user = db.session.get(User, g.current_user_id)
    if not user.totp_enabled:
        return jsonify({'error': 'MFA is not enabled'}), 400

    data = request.get_json(silent=True) or {}
    totp_code = (data.get('totp_code') or '').strip()
    backup_code = (data.get('backup_code') or '').strip().lower().replace('-', '').replace(' ', '')

    import pyotp
    plaintext_secret = decrypt_totp_secret(user.totp_secret, user.totp_iv)
    verified = False

    if totp_code:
        verified = pyotp.TOTP(plaintext_secret).verify(totp_code, valid_window=1)
    elif backup_code:
        stored = json.loads(user.mfa_backup_codes or '[]')
        matched, remaining = verify_and_consume_backup_code(stored, backup_code)
        if matched:
            user.mfa_backup_codes = json.dumps(remaining)
            verified = True

    if not verified:
        return jsonify({'error': 'Invalid verification code'}), 400

    user.totp_secret = None
    user.totp_iv = None
    user.totp_enabled = False
    user.mfa_backup_codes = None

    AuditLog.log(
        user_id=user.id,
        action='auth.mfa_disable',
        resource_type='user',
        resource_id=user.id,
        detail='TOTP two-factor authentication disabled; backup codes cleared',
        ip_address=_client_ip(),
    )
    db.session.commit()

    return jsonify({'message': 'MFA disabled'}), 200


@auth_bp.route('/mfa/verify', methods=['POST'])
@limiter.limit('10 per minute')
def mfa_verify():
    """Complete MFA login: verify TOTP code (or backup code) and exchange mfa_token for real tokens."""
    import json
    data = request.get_json(silent=True) or {}
    mfa_token = data.get('mfa_token', '')
    totp_code = (data.get('totp_code') or '').strip()
    backup_code = (data.get('backup_code') or '').strip().lower().replace('-', '').replace(' ', '')

    if not mfa_token or (not totp_code and not backup_code):
        return jsonify({'error': 'mfa_token and either totp_code or backup_code are required'}), 400

    try:
        payload = decode_token(mfa_token, expected_type='mfa', check_blacklist=True)
    except Exception:
        return jsonify({'error': 'Invalid or expired MFA token'}), 401

    user = db.session.get(User, int(payload['sub']))
    if not user or not user.totp_enabled:
        return jsonify({'error': 'MFA not configured for this account'}), 400

    import pyotp
    plaintext_secret = decrypt_totp_secret(user.totp_secret, user.totp_iv)
    verified = False

    if totp_code:
        verified = pyotp.TOTP(plaintext_secret).verify(totp_code, valid_window=1)

    if not verified and backup_code:
        stored = json.loads(user.mfa_backup_codes or '[]')
        matched, remaining = verify_and_consume_backup_code(stored, backup_code)
        if matched:
            user.mfa_backup_codes = json.dumps(remaining)
            verified = True
            AuditLog.log(
                user_id=user.id,
                action='auth.mfa_backup_code_used',
                resource_type='user',
                resource_id=user.id,
                detail=f'MFA backup code used; {len(remaining)} code(s) remaining',
                ip_address=_client_ip(),
            )

    if not verified:
        return jsonify({'error': 'Invalid verification code'}), 400

    # One-time use: blacklist the mfa_token
    blacklist_token(mfa_token, 'mfa')

    AuditLog.log(
        user_id=user.id,
        action='auth.mfa_verify',
        resource_type='user',
        resource_id=user.id,
        detail='MFA verification successful — session tokens issued',
        ip_address=_client_ip(),
    )
    db.session.commit()

    tokens = generate_tokens(user.id)
    return jsonify({
        'access_token': tokens['access_token'],
        'refresh_token': tokens['refresh_token'],
    }), 200


@auth_bp.route('/mfa/status', methods=['GET'])
@limiter.limit('60 per minute')
@require_jwt
def mfa_status():
    user = db.session.get(User, g.current_user_id)
    import json
    stored = json.loads(user.mfa_backup_codes or '[]')
    return jsonify({
        'totp_enabled': user.totp_enabled,
        'backup_codes_remaining': len(stored),
    }), 200


@auth_bp.route('/mfa/backup-codes/regenerate', methods=['POST'])
@limiter.limit('5 per minute')
@require_jwt
def mfa_backup_codes_regenerate():
    """
    Regenerate MFA backup codes. Requires a valid TOTP code to authorise.
    All existing backup codes are invalidated and replaced.
    Returns the new plaintext codes — shown once, never stored.
    """
    import json
    user = db.session.get(User, g.current_user_id)
    if not user.totp_enabled:
        return jsonify({'error': 'MFA is not enabled'}), 400

    data = request.get_json(silent=True) or {}
    totp_code = (data.get('totp_code') or '').strip()
    if not totp_code:
        return jsonify({'error': 'totp_code is required'}), 400

    import pyotp
    plaintext_secret = decrypt_totp_secret(user.totp_secret, user.totp_iv)
    if not pyotp.TOTP(plaintext_secret).verify(totp_code, valid_window=1):
        return jsonify({'error': 'Invalid verification code'}), 400

    plaintext_codes, hashed_codes = generate_backup_codes()
    user.mfa_backup_codes = json.dumps(hashed_codes)

    AuditLog.log(
        user_id=user.id,
        action='auth.mfa_backup_codes_regenerated',
        resource_type='user',
        resource_id=user.id,
        detail='MFA backup codes regenerated — previous codes invalidated',
        ip_address=_client_ip(),
    )
    db.session.commit()

    return jsonify({
        'message': 'Backup codes regenerated. Save these — they will not be shown again.',
        'backup_codes': plaintext_codes,
    }), 200


@auth_bp.route('/me', methods=['GET'])
@limiter.limit('60 per minute')
@require_jwt
def me():
    """Return basic profile info for the authenticated user."""
    import json
    user = db.session.get(User, g.current_user_id)
    stored_codes = json.loads(user.mfa_backup_codes or '[]')
    return jsonify({
        'id': user.id,
        'email': user.email,
        'created_at': user.created_at.isoformat() if user.created_at else None,
        'last_login': user.last_login.isoformat() if user.last_login else None,
        'totp_enabled': user.totp_enabled,
        'backup_codes_remaining': len(stored_codes),
        'recovery_configured': bool(user.recovery_enc_salt),
    }), 200


@auth_bp.route('/audit-log', methods=['GET'])
@require_jwt
@limiter.limit('30 per minute')
def audit_log():
    """
    Return the authenticated user's recent audit log entries.

    Query params:
      limit  — max entries to return (default 50, max 200)
      offset — pagination offset (default 0)

    Sensitive field values are never logged — entries contain only action
    types, resource IDs, timestamps, and IP addresses.
    """
    try:
        limit = min(int(request.args.get('limit', 50)), 200)
        offset = max(int(request.args.get('offset', 0)), 0)
    except (ValueError, TypeError):
        return jsonify({'error': 'limit and offset must be integers'}), 400

    entries = (
        AuditLog.query
        .filter_by(user_id=g.current_user_id)
        .order_by(AuditLog.created_at.desc())
        .limit(limit)
        .offset(offset)
        .all()
    )
    total = AuditLog.query.filter_by(user_id=g.current_user_id).count()

    return jsonify({
        'total': total,
        'limit': limit,
        'offset': offset,
        'entries': [e.to_dict() for e in entries],
    }), 200


# ── Account management ────────────────────────────────────────────────────────

@auth_bp.route('/change-password', methods=['POST'])
@limiter.limit('5 per minute')
@require_jwt
def change_password():
    """
    Change master password — zero-knowledge atomic re-encryption.

    The client must:
      1. Derive current auth_hash and verify it locally against what it knows.
      2. Re-encrypt every vault item with the new vault key client-side.
      3. POST the new credentials + all re-encrypted item blobs in one request.

    The server verifies the current password, updates master_hash + enc_key_salt,
    and bulk-replaces all vault item ciphertexts atomically. If any step fails,
    the entire transaction is rolled back — the vault is never left in a split state.
    """
    data = request.get_json(silent=True) or {}
    current_auth_hash = data.get('current_auth_hash', '')
    new_auth_hash = data.get('new_auth_hash', '')
    new_enc_key_salt = data.get('new_enc_key_salt', '')
    items = data.get('items', [])  # [{id, enc_data, iv}, ...]

    if not current_auth_hash or not new_auth_hash or not new_enc_key_salt:
        return jsonify({'error': 'current_auth_hash, new_auth_hash, and new_enc_key_salt are required'}), 400

    user = db.session.get(User, g.current_user_id)

    if not verify_auth_token(current_auth_hash, user.master_hash):
        AuditLog.log(
            user_id=user.id,
            action='auth.change_password_failed',
            resource_type='user',
            resource_id=user.id,
            detail='Password change rejected — current password incorrect',
            ip_address=_client_ip(),
        )
        db.session.commit()
        return jsonify({'error': 'Current password is incorrect'}), 401

    try:
        from app.models.vault_item import VaultItem

        # Bulk-update all vault item ciphertexts with new vault key encryption
        item_ids = [i.get('id') for i in items if i.get('id')]
        existing = {
            v.id: v
            for v in VaultItem.query.filter(
                VaultItem.user_id == user.id,
                VaultItem.id.in_(item_ids),
            ).all()
        } if item_ids else {}

        for item_data in items:
            item_id = item_data.get('id')
            enc_data = item_data.get('enc_data', '')
            iv = item_data.get('iv', '')
            if not item_id or not enc_data or not iv:
                continue
            vault_item = existing.get(item_id)
            if vault_item:
                vault_item.enc_data = enc_data
                vault_item.iv = iv
                # Re-encrypt the name ciphertext if the client sent updated enc_name/iv_name.
                if item_data.get('enc_name'):
                    vault_item.enc_name = item_data['enc_name']
                if item_data.get('iv_name'):
                    vault_item.iv_name = item_data['iv_name']

        # Update credentials
        user.master_hash = hash_auth_token(new_auth_hash)
        user.enc_key_salt = new_enc_key_salt
        # Clear recovery data — it was encrypted with the old vault key and is now invalid
        user.recovery_enc_salt = None
        user.recovery_iv = None

        AuditLog.log(
            user_id=user.id,
            action='auth.change_password',
            resource_type='user',
            resource_id=user.id,
            detail=f'Master password changed; {len(existing)} vault item(s) re-encrypted; recovery code cleared',
            ip_address=_client_ip(),
        )
        db.session.commit()
    except Exception as e:
        db.session.rollback()
        return jsonify({'error': f'Password change failed: {str(e)}'}), 500

    return jsonify({'message': 'Password changed successfully. Please log in again.'}), 200


@auth_bp.route('/account', methods=['DELETE'])
@limiter.limit('3 per minute')
@require_jwt
def delete_account():
    """
    Permanently delete the authenticated user's account and all associated data.
    Requires the current auth_hash for confirmation.
    Cascading deletes handle vault_items, folders, shared_items, emergency_access.
    """
    data = request.get_json(silent=True) or {}
    auth_hash = data.get('auth_hash', '')

    if not auth_hash:
        return jsonify({'error': 'auth_hash is required for account deletion'}), 400

    user = db.session.get(User, g.current_user_id)

    if not verify_auth_token(auth_hash, user.master_hash):
        AuditLog.log(
            user_id=user.id,
            action='auth.delete_account_failed',
            resource_type='user',
            resource_id=user.id,
            detail='Account deletion rejected — password incorrect',
            ip_address=_client_ip(),
        )
        db.session.commit()
        return jsonify({'error': 'Incorrect password'}), 401

    user_id = user.id
    user_email = user.email
    try:
        # Log before delete (user row will be gone after commit)
        AuditLog.log(
            user_id=user_id,
            action='auth.delete_account',
            resource_type='user',
            resource_id=user_id,
            detail=f'Account permanently deleted: {user_email}',
            ip_address=_client_ip(),
        )
        db.session.delete(user)
        db.session.commit()
    except Exception as e:
        db.session.rollback()
        return jsonify({'error': f'Account deletion failed: {str(e)}'}), 500

    return jsonify({'message': 'Account deleted'}), 200


# ── Account Recovery ──────────────────────────────────────────────────────────

@auth_bp.route('/recovery/setup', methods=['POST'])
@limiter.limit('10 per minute')
@require_jwt
def recovery_setup():
    """
    Store a recovery-key-encrypted copy of enc_key_salt.

    The client generates a random 128-bit recovery code, derives a recovery key
    from it (PBKDF2), encrypts enc_key_salt with that key (AES-256-GCM), and
    sends the ciphertext + iv. The server stores these blobs — it never sees the
    recovery code or enc_key_salt plaintext.

    The recovery code is displayed to the user once and never stored server-side.
    """
    data = request.get_json(silent=True) or {}
    recovery_enc_salt = data.get('recovery_enc_salt', '').strip()
    recovery_iv = data.get('recovery_iv', '').strip()

    if not recovery_enc_salt or not recovery_iv:
        return jsonify({'error': 'recovery_enc_salt and recovery_iv are required'}), 400

    user = db.session.get(User, g.current_user_id)
    user.recovery_enc_salt = recovery_enc_salt
    user.recovery_iv = recovery_iv

    AuditLog.log(
        user_id=user.id,
        action='auth.recovery_setup',
        resource_type='user',
        resource_id=user.id,
        detail='Account recovery code configured',
        ip_address=_client_ip(),
    )
    db.session.commit()

    return jsonify({'message': 'Recovery code saved'}), 200


@auth_bp.route('/recovery/status', methods=['GET'])
@limiter.limit('60 per minute')
@require_jwt
def recovery_status():
    """Return whether the user has a recovery code configured."""
    user = db.session.get(User, g.current_user_id)
    return jsonify({'recovery_configured': bool(user.recovery_enc_salt)}), 200


@auth_bp.route('/recover', methods=['POST'])
@limiter.limit('5 per minute')
def recover_account():
    """
    Recover account access using a recovery code.

    Flow:
      1. Client calls /recovery/data → receives enc_key_salt, recovery blobs, nonce.
      2. Client decrypts recovery_enc_salt using the recovery key → gets enc_key_salt.
      3. Client computes: recovery_proof = HMAC-SHA256(enc_key_salt_bytes, nonce).
      4. Client derives new credentials and re-encrypts all vault items.
      5. Client POSTs everything here in one atomic payload.

    The server validates recovery_proof against the value precomputed during
    /recovery/data — enc_key_salt is never sent in plaintext.
    The nonce is consumed on first use to prevent replay.
    """
    data = request.get_json(silent=True) or {}
    email = (data.get('email') or '').strip().lower()
    new_auth_hash = data.get('new_auth_hash', '')
    new_enc_key_salt = data.get('new_enc_key_salt', '')
    client_proof = data.get('recovery_proof', '')
    items = data.get('items', [])

    if not all([email, new_auth_hash, new_enc_key_salt, client_proof]):
        return jsonify({'error': 'email, new_auth_hash, new_enc_key_salt, and recovery_proof are required'}), 400

    time.sleep(0.1)  # timing mitigation

    # Validate session binding.
    expected_proof = session.get('recovery_expected_proof', '')
    session_user_id = session.get('recovery_user_id')

    if not expected_proof or not session_user_id:
        return jsonify({'error': 'No active recovery challenge. Call /recovery/data first.'}), 400

    user = User.query.filter_by(email=email).first()
    if not user or not user.recovery_enc_salt or user.id != session_user_id:
        return jsonify({'error': 'No recovery code found for this account'}), 404

    if not verify_recovery_proof(expected_proof, client_proof):
        AuditLog.log(
            user_id=user.id,
            action='auth.recovery_failed',
            resource_type='user',
            resource_id=user.id,
            detail='Recovery attempt failed — incorrect recovery proof',
            ip_address=_client_ip(),
        )
        db.session.commit()
        return jsonify({'error': 'Invalid recovery code'}), 401

    # Consume the nonce — one-time use only.
    session.pop('recovery_nonce', None)
    session.pop('recovery_expected_proof', None)
    session.pop('recovery_user_id', None)

    try:
        from app.models.vault_item import VaultItem

        item_ids = [i.get('id') for i in items if i.get('id')]
        existing = {
            v.id: v
            for v in VaultItem.query.filter(
                VaultItem.user_id == user.id,
                VaultItem.id.in_(item_ids),
            ).all()
        } if item_ids else {}

        for item_data in items:
            item_id = item_data.get('id')
            enc_data = item_data.get('enc_data', '')
            iv = item_data.get('iv', '')
            if not item_id or not enc_data or not iv:
                continue
            vault_item = existing.get(item_id)
            if vault_item:
                vault_item.enc_data = enc_data
                vault_item.iv = iv
                if item_data.get('enc_name'):
                    vault_item.enc_name = item_data['enc_name']
                if item_data.get('iv_name'):
                    vault_item.iv_name = item_data['iv_name']

        user.master_hash = hash_auth_token(new_auth_hash)
        user.enc_key_salt = new_enc_key_salt
        # Recovery code is consumed — clear it so it cannot be reused.
        user.recovery_enc_salt = None
        user.recovery_iv = None

        AuditLog.log(
            user_id=user.id,
            action='auth.recovery_success',
            resource_type='user',
            resource_id=user.id,
            detail=f'Account recovered; {len(existing)} vault item(s) re-encrypted; recovery code consumed',
            ip_address=_client_ip(),
        )
        db.session.commit()
    except Exception as e:
        db.session.rollback()
        return jsonify({'error': f'Recovery failed: {str(e)}'}), 500

    tokens = generate_tokens(user.id)
    return jsonify({
        'message': 'Account recovered successfully',
        'access_token': tokens['access_token'],
        'refresh_token': tokens['refresh_token'],
        'enc_key_salt': user.enc_key_salt,
    }), 200


@auth_bp.route('/recovery/data', methods=['GET'])
@limiter.limit('10 per minute')
def recovery_data():
    """
    Return the data the client needs to attempt recovery (unauthenticated).
    Exposes: enc_key_salt, recovery_enc_salt, recovery_iv, and a one-time nonce.

    The nonce is used for the HMAC-SHA256 challenge-response proof:
      - Client decrypts recovery_enc_salt → gets enc_key_salt bytes.
      - Client computes: proof = HMAC-SHA256(key=enc_key_salt_bytes, msg=nonce)
      - Server stores expected proof in server-side session at challenge time,
        verifying it on /recover and /recovery/items without ever receiving
        enc_key_salt in plaintext.

    Returns 404 if no recovery code is configured (prevents user enumeration).
    """
    email = (request.args.get('email') or '').strip().lower()
    if not email:
        return jsonify({'error': 'email is required'}), 400

    user = User.query.filter_by(email=email).first()
    if not user or not user.recovery_enc_salt:
        return jsonify({'error': 'No recovery data found'}), 404

    # Generate a fresh nonce and precompute the expected HMAC using the stored
    # enc_key_salt.  The client must return HMAC-SHA256(enc_key_salt, nonce).
    # This proves it decrypted the recovery blob correctly without sending
    # enc_key_salt in plaintext.
    import hashlib, hmac as _hmac
    nonce = generate_recovery_nonce()
    expected_proof = _hmac.new(
        user.enc_key_salt.encode(),
        nonce.encode(),
        hashlib.sha256,
    ).hexdigest()

    # Store expected proof and bind it to the user — consumed on first use.
    session['recovery_nonce'] = nonce
    session['recovery_expected_proof'] = expected_proof
    session['recovery_user_id'] = user.id

    return jsonify({
        'enc_key_salt': user.enc_key_salt,
        'recovery_enc_salt': user.recovery_enc_salt,
        'recovery_iv': user.recovery_iv,
        'nonce': nonce,
    }), 200


@auth_bp.route('/recovery/items', methods=['GET'])
@limiter.limit('10 per minute')
def recovery_items():
    """
    Return encrypted vault items for recovery re-encryption (unauthenticated).

    Requires X-Recovery-Proof header containing the HMAC-SHA256 proof:
        proof = HMAC-SHA256(key=enc_key_salt_bytes, msg=nonce_from_recovery_data)

    The server validates the proof against the value precomputed and stored in
    flask.session during /recovery/data — enc_key_salt is never sent in plaintext.
    Items are returned as encrypted ciphertext blobs only.
    """
    email = (request.args.get('email') or '').strip().lower()
    client_proof = request.headers.get('X-Recovery-Proof', '').strip()

    if not email or not client_proof:
        return jsonify({'error': 'email and X-Recovery-Proof header are required'}), 400

    # Validate session binding: proof must match what was issued to this session.
    expected_proof = session.get('recovery_expected_proof', '')
    session_user_id = session.get('recovery_user_id')

    if not expected_proof or not session_user_id:
        return jsonify({'error': 'No active recovery challenge. Call /recovery/data first.'}), 400

    user = User.query.filter_by(email=email).first()
    if not user or not user.recovery_enc_salt or user.id != session_user_id:
        return jsonify({'error': 'No recovery data found'}), 404

    if not verify_recovery_proof(expected_proof, client_proof):
        AuditLog.log(
            user_id=user.id,
            action='auth.recovery_items_denied',
            resource_type='user',
            resource_id=user.id,
            detail='Recovery items request denied — incorrect recovery proof',
            ip_address=_client_ip(),
        )
        db.session.commit()
        return jsonify({'error': 'Invalid recovery proof'}), 401

    from app.models.vault_item import VaultItem
    items = VaultItem.query.filter_by(user_id=user.id).all()
    return jsonify({
        'items': [
            {'id': item.id, 'enc_data': item.enc_data, 'iv': item.iv}
            for item in items
        ]
    }), 200