/**
 * Node.js secure memory implementation.
 *
 * When the optional native addon (nomyo-native) is installed and built,
 * this implementation provides true OS-level memory locking (mlock) and
 * secure zeroing via explicit_bzero / SecureZeroMemory.
 *
 * Without the native addon it falls back to pure-JS zeroing only.
 *
 * To build the native addon:
 *   cd native && npm install && npm run build
 */

import { SecureMemory } from './secure';
import { ProtectionInfo } from '../../types/crypto';

interface NativeAddon {
    mlockBuffer(buf: Buffer): boolean;
    munlockBuffer(buf: Buffer): boolean;
    secureZeroBuffer(buf: Buffer): void;
    getPageSize(): number;
}

// Try to load the optional native addon once at module init time.
let nativeAddon: NativeAddon | null = null;
try {
    // eslint-disable-next-line @typescript-eslint/no-var-requires
    const loaded = require('nomyo-native') as NativeAddon | null;
    if (loaded && typeof loaded.mlockBuffer === 'function') {
        nativeAddon = loaded;
    }
} catch (_e) {
    // Native addon not installed — degrade gracefully
}

/**
 * Whether mlock actually succeeds in this process, determined once by trying it.
 *
 * Having the addon loaded is not the same as being allowed to lock: mlock is
 * routinely refused by RLIMIT_MEMLOCK (often only a few MB, and 0 in some
 * containers) without any elevated privileges. Reporting the capability rather
 * than the reality would overstate the protection actually in force.
 */
let lockProbeResult: boolean | null = null;

function canActuallyLock(): boolean {
    if (lockProbeResult !== null) return lockProbeResult;
    if (nativeAddon === null) {
        lockProbeResult = false;
        return false;
    }
    try {
        const probe = Buffer.alloc(nativeAddon.getPageSize());
        const locked = nativeAddon.mlockBuffer(probe);
        if (locked) {
            nativeAddon.munlockBuffer(probe);
        }
        lockProbeResult = locked;
    } catch (_e) {
        lockProbeResult = false;
    }
    return lockProbeResult;
}

export class NodeSecureMemory implements SecureMemory {
    private readonly hasNative: boolean;

    constructor() {
        // Deliberately silent: a library must not write to stdout on construction.
        // Callers surface this via getProtectionInfo() under their own debug flag.
        this.hasNative = nativeAddon !== null;
    }

    /**
     * Zero memory.
     * With native addon: uses explicit_bzero / SecureZeroMemory (not optimized away).
     * Without native addon: fills ArrayBuffer with zeros via Uint8Array (best effort).
     */
    zeroMemory(data: ArrayBuffer): void {
        if (this.hasNative && nativeAddon) {
            // Buffer.from(arrayBuffer) shares the underlying memory (no copy)
            const buf = Buffer.from(data);
            nativeAddon.secureZeroBuffer(buf);
        }
        // Always also zero via JS for defence-in-depth
        const view = new Uint8Array(data);
        view.fill(0);
    }

    /**
     * Attempt to lock an ArrayBuffer in physical memory (prevent swapping).
     * Best-effort: fails gracefully without CAP_IPC_LOCK / elevated privileges.
     */
    lockMemory(data: ArrayBuffer): boolean {
        if (!this.hasNative || !nativeAddon) return false;
        const buf = Buffer.from(data);
        return nativeAddon.mlockBuffer(buf);
    }

    /**
     * Unlock previously locked memory.
     */
    unlockMemory(data: ArrayBuffer): boolean {
        if (!this.hasNative || !nativeAddon) return false;
        const buf = Buffer.from(data);
        return nativeAddon.munlockBuffer(buf);
    }

    /**
     * Get memory protection information.
     *
     * Reports what is actually in force, not what is theoretically supported —
     * `canLock` reflects a real mlock attempt.
     */
    getProtectionInfo(): ProtectionInfo {
        if (!this.hasNative) {
            return {
                canLock: false,
                isPlatformSecure: false,
                method: 'zero-only',
                platform: process.platform,
                hasSecureZeroing: false,
                details:
                    'Node.js (pure JS): memory locking not available without the native addon. ' +
                    'Using best-effort zeroing only. ' +
                    'Build the optional addon for mlock support: cd native && npm install && npm run build',
            };
        }

        if (!canActuallyLock()) {
            return {
                canLock: false,
                isPlatformSecure: false,
                method: 'zero-only',
                platform: process.platform,
                hasSecureZeroing: true,
                pageSize: nativeAddon!.getPageSize(),
                details:
                    'Node.js with nomyo-native addon: secure zeroing available, but mlock was ' +
                    'refused by the OS (typically RLIMIT_MEMLOCK). Sensitive buffers may still ' +
                    'be swapped to disk. Raise the memlock limit or grant CAP_IPC_LOCK to enable locking.',
            };
        }

        return {
            canLock: true,
            isPlatformSecure: true,
            method: 'mlock',
            platform: process.platform,
            hasSecureZeroing: true,
            pageSize: nativeAddon!.getPageSize(),
            details:
                'Node.js with nomyo-native addon: mlock + explicit_bzero/SecureZeroMemory active.',
        };
    }
}