vector-core 0.3.0

pub mod guarded_key;
pub use guarded_key::GuardedKey;

mod signer;
pub use signer::GuardedSigner;

use argon2::Argon2;
use chacha20poly1305::{aead::Aead, ChaCha20Poly1305, KeyInit};
use zeroize::Zeroize;

/// Derive a 32-byte key from a password using Argon2id.
/// Parameters: 150MB memory, 10 iterations (matches src-tauri).
pub async fn hash_pass(password: &str) -> [u8; 32] {
    let password = password.to_string();
    tokio::task::spawn_blocking(move || {
        let salt = b"vectorvectovectvecvev";
        let mut output = [0u8; 32];

        let params = argon2::Params::new(
            150_000, // 150 MB
            10,      // iterations
            1,       // parallelism
            Some(32),
        ).unwrap();

        let argon2 = Argon2::new(argon2::Algorithm::Argon2id, argon2::Version::V0x13, params);
        argon2.hash_password_into(password.as_bytes(), salt, &mut output).unwrap();

        output
    }).await.unwrap()
}

/// Encrypt a string with the global ENCRYPTION_KEY (ChaCha20-Poly1305).
pub fn encrypt_with_key(plaintext: &str, key: &[u8; 32]) -> Result<String, String> {
    use chacha20poly1305::aead::OsRng;
    use chacha20poly1305::AeadCore;

    let cipher = ChaCha20Poly1305::new(key.into());
    let nonce = ChaCha20Poly1305::generate_nonce(&mut OsRng);

    let ciphertext = cipher.encrypt(&nonce, plaintext.as_bytes())
        .map_err(|e| format!("Encryption failed: {}", e))?;

    // Encode as hex: nonce + ciphertext
    let mut result = hex::encode(&nonce[..]);
    result.push_str(&hex::encode(&ciphertext));
    Ok(result)
}

/// Decrypt a hex-encoded ciphertext with a key.
pub fn decrypt_with_key(hex_data: &str, key: &[u8; 32]) -> Result<String, String> {
    if hex_data.len() < 24 {
        return Err("Ciphertext too short".to_string());
    }

    let nonce_hex = &hex_data[..24]; // 12 bytes = 24 hex chars
    let ciphertext_hex = &hex_data[24..];

    let nonce_bytes = hex::decode(nonce_hex)
        .map_err(|e| format!("Invalid nonce hex: {}", e))?;
    let ciphertext = hex::decode(ciphertext_hex)
        .map_err(|e| format!("Invalid ciphertext hex: {}", e))?;

    let nonce_arr: [u8; 12] = nonce_bytes.try_into()
        .map_err(|_| "Invalid nonce length".to_string())?;
    let nonce = chacha20poly1305::Nonce::from(nonce_arr);
    let cipher = ChaCha20Poly1305::new(key.into());

    let mut plaintext = cipher.decrypt(&nonce, ciphertext.as_ref())
        .map_err(|_| "Decryption failed (wrong key or corrupted data)".to_string())?;

    let result = String::from_utf8(plaintext.clone())
        .map_err(|_| "Decrypted data is not valid UTF-8".to_string())?;

    plaintext.zeroize();
    Ok(result)
}

/// Check if encryption is enabled in the database.
///
/// Delegates to `state::resolve_encryption_enabled_from_db` — the single
/// source of truth that handles the missing-row case consistently. The
/// previous implementation defaulted to `false` on missing rows, which
/// silently disagreed with `init_encryption_enabled` (defaulted to `true`)
/// and silently mis-routed login flows after an account swap.
pub fn is_encryption_enabled() -> bool {
    crate::state::resolve_encryption_enabled_from_db()
}

/// Simple hex encode/decode (for crypto module internal use).
mod hex {
    pub fn encode(bytes: &[u8]) -> String {
        // SIMD hex encode (NEON/SSE2, fast-pathing 32/16-byte). Identical lowercase output to the
        // old per-byte format! loop, but it runs on every encrypt (ciphertext + nonce).
        crate::simd::hex::bytes_to_hex_string(bytes)
    }

    pub fn decode(hex: &str) -> Result<Vec<u8>, String> {
        if hex.len() % 2 != 0 {
            return Err("Odd-length hex string".to_string());
        }
        // SIMD-validated decode (NEON/SSE2 in-register hex validation). Runs on every message read
        // (decrypt), so the recurring path stays fast; rejects non-hex like the old scalar loop.
        crate::simd::hex::hex_string_to_bytes_checked(hex)
            .ok_or_else(|| "Invalid hex character".to_string())
    }
}

// ============================================================================
// AES-256-GCM File Encryption (for NIP-96/Blossom attachments)
// ============================================================================

/// Parameters for AES-256-GCM file encryption (hex-encoded key + nonce).
#[derive(Debug)]
pub struct EncryptionParams {
    pub key: String,   // 32-byte key as hex
    pub nonce: String, // 16-byte nonce as hex (0xChat-compatible)
}

/// Generate random AES-256-GCM encryption parameters.
pub fn generate_encryption_params() -> EncryptionParams {
    use rand::Rng;
    let mut rng = rand::thread_rng();
    let mut key: [u8; 32] = rng.gen();
    let nonce: [u8; 16] = rng.gen();
    let params = EncryptionParams {
        key: hex::encode(&key),
        nonce: hex::encode(&nonce),
    };
    key.iter_mut().for_each(|b| *b = 0); // zeroize
    params
}

/// Encrypt data with AES-256-GCM using a 16-byte nonce (0xChat-compatible).
pub fn encrypt_data(data: &[u8], params: &EncryptionParams) -> Result<Vec<u8>, String> {
    use aes::Aes256;
    use aes::cipher::typenum::U16;
    use aes_gcm::{AesGcm, AeadInPlace, KeyInit as AesKeyInit};

    let key_bytes = hex::decode(&params.key).map_err(|e| format!("Invalid key: {}", e))?;
    let nonce_bytes = hex::decode(&params.nonce).map_err(|e| format!("Invalid nonce: {}", e))?;

    let cipher = AesGcm::<Aes256, U16>::new_from_slice(&key_bytes)
        .map_err(|_| "Invalid encryption key".to_string())?;

    let nonce_arr: [u8; 16] = nonce_bytes.try_into()
        .map_err(|_| "Invalid nonce length".to_string())?;
    let nonce = aes_gcm::Nonce::<U16>::from(nonce_arr);

    let mut buffer = data.to_vec();
    let tag = cipher.encrypt_in_place_detached(&nonce, &[], &mut buffer)
        .map_err(|_| "Encryption failed".to_string())?;

    buffer.extend_from_slice(&tag);
    Ok(buffer)
}

/// Decrypt data with AES-256-GCM using a 16-byte nonce (0xChat-compatible).
/// Input format: ciphertext || 16-byte auth tag.
pub fn decrypt_data(encrypted_data: &[u8], key_hex: &str, nonce_hex: &str) -> Result<Vec<u8>, String> {
    use aes::Aes256;
    use aes::cipher::typenum::U16;
    use aes_gcm::{AesGcm, AeadInPlace, KeyInit as AesKeyInit};

    if encrypted_data.len() < 16 {
        return Err(format!("Invalid Input: encrypted data too small ({} bytes, minimum 16 bytes required for authentication tag)", encrypted_data.len()));
    }

    let key_bytes = hex::decode(key_hex).map_err(|e| format!("Invalid key: {}", e))?;
    let nonce_bytes = hex::decode(nonce_hex).map_err(|e| format!("Invalid nonce: {}", e))?;

    let (ciphertext, tag_bytes) = encrypted_data.split_at(encrypted_data.len() - 16);

    let cipher = AesGcm::<Aes256, U16>::new_from_slice(&key_bytes)
        .map_err(|_| "Invalid decryption key".to_string())?;

    let nonce_arr: [u8; 16] = nonce_bytes.try_into()
        .map_err(|_| "Invalid nonce length".to_string())?;
    let nonce = aes_gcm::Nonce::<U16>::from(nonce_arr);
    let tag_arr: [u8; 16] = tag_bytes.try_into()
        .map_err(|_| "Invalid tag length".to_string())?;
    let tag = aes_gcm::Tag::<U16>::from(tag_arr);

    let mut buffer = ciphertext.to_vec();
    cipher.decrypt_in_place_detached(&nonce, &[], &mut buffer, &tag)
        .map_err(|e| e.to_string())?;

    Ok(buffer)
}

/// Calculate SHA-256 hash of data, returned as hex string.
pub fn sha256_hex(data: &[u8]) -> String {
    use sha2::{Sha256, Digest};
    let mut hasher = Sha256::new();
    hasher.update(data);
    hex::encode(&hasher.finalize())
}

/// Identity basis for a RECEIVED attachment: the sender's `ox` (plaintext
/// hash) when provided — it's what enables honest cross-message dedup — else
/// a digest of nonce+url. Never the raw nonce: senders can and do reuse
/// nonces, which cross-bound DIFFERENT files to one identity (the "new image
/// renders as an old one" class). The upload URL is unique per ciphertext,
/// so the digest is collision-resistant even against nonce reuse. Nothing
/// honest ever writes a file under the digest name, so existence of one is
/// never proof of download — reuse decisions stay with the content-verified
/// download path.
pub fn attachment_identity_basis(ox: Option<&str>, nonce: &str, url: &str) -> String {
    match ox.filter(|h| !h.is_empty()) {
        Some(h) => h.to_string(),
        None => {
            let mut buf = Vec::with_capacity(nonce.len() + 1 + url.len());
            buf.extend_from_slice(nonce.as_bytes());
            buf.push(0);
            buf.extend_from_slice(url.as_bytes());
            sha256_hex(&buf)
        }
    }
}

/// Get MIME type from file extension.
pub fn mime_from_extension(ext: &str) -> &'static str {
    match ext.to_lowercase().as_str() {
        "png" => "image/png",
        "jpg" | "jpeg" => "image/jpeg",
        "gif" => "image/gif",
        "webp" => "image/webp",
        "svg" => "image/svg+xml",
        "bmp" => "image/bmp",
        "ico" => "image/x-icon",
        "tiff" | "tif" => "image/tiff",
        "dng" => "image/x-adobe-dng",
        "cr2" => "image/x-canon-cr2",
        "nef" => "image/x-nikon-nef",
        "arw" => "image/x-sony-arw",
        "mp4" => "video/mp4",
        "webm" => "video/webm",
        "mov" => "video/quicktime",
        "avi" => "video/x-msvideo",
        "mkv" => "video/x-matroska",
        "flv" => "video/x-flv",
        "wmv" => "video/x-ms-wmv",
        "mpg" | "mpeg" => "video/mpeg",
        "3gp" => "video/3gpp",
        "ogv" => "video/ogg",
        "ts" => "video/mp2t",
        "mp3" => "audio/mpeg",
        "ogg" => "audio/ogg",
        "wav" => "audio/wav",
        "flac" => "audio/flac",
        "m4a" => "audio/mp4",
        "aac" => "audio/aac",
        "wma" => "audio/x-ms-wma",
        "opus" => "audio/opus",
        "pdf" => "application/pdf",
        "doc" => "application/msword",
        "docx" => "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
        "xls" => "application/vnd.ms-excel",
        "xlsx" => "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
        "ppt" => "application/vnd.ms-powerpoint",
        "pptx" => "application/vnd.openxmlformats-officedocument.presentationml.presentation",
        "odt" => "application/vnd.oasis.opendocument.text",
        "ods" => "application/vnd.oasis.opendocument.spreadsheet",
        "odp" => "application/vnd.oasis.opendocument.presentation",
        "rtf" => "application/rtf",
        "txt" => "text/plain",
        "md" => "text/markdown",
        "csv" => "text/csv",
        "json" => "application/json",
        "xml" => "application/xml",
        "yaml" | "yml" => "application/x-yaml",
        "toml" => "application/toml",
        "sql" => "application/sql",
        "zip" => "application/zip",
        "rar" => "application/vnd.rar",
        "7z" => "application/x-7z-compressed",
        "tar" => "application/x-tar",
        "gz" => "application/gzip",
        "bz2" => "application/x-bzip2",
        "xz" => "application/x-xz",
        "iso" => "application/x-iso9660-image",
        "dmg" => "application/x-apple-diskimage",
        "apk" => "application/vnd.android.package-archive",
        "jar" => "application/java-archive",
        "xdc" => "application/vnd.webxdc+zip",
        "obj" => "model/obj",
        "gltf" => "model/gltf+json",
        "glb" => "model/gltf-binary",
        "stl" => "model/stl",
        "dae" => "model/vnd.collada+xml",
        "js" => "text/javascript",
        "py" => "text/x-python",
        "rs" => "text/x-rust",
        "go" => "text/x-go",
        "java" => "text/x-java",
        "c" => "text/x-c",
        "cpp" => "text/x-c++",
        "cs" => "text/x-csharp",
        "rb" => "text/x-ruby",
        "php" => "text/x-php",
        "swift" => "text/x-swift",
        "html" | "htm" => "text/html",
        "css" => "text/css",
        "exe" => "application/x-msdownload",
        "msi" => "application/x-msi",
        "ttf" => "font/ttf",
        "otf" => "font/otf",
        "woff" => "font/woff",
        "woff2" => "font/woff2",
        _ => "application/octet-stream",
    }
}

/// Convert a MIME type to a file extension.
/// Falls back to using the MIME subtype when unknown.
pub fn extension_from_mime(mime: &str) -> String {
    match mime.trim().to_lowercase().as_str() {
        // Images
        "image/png" => "png",
        "image/jpeg" | "image/jpg" => "jpg",
        "image/gif" => "gif",
        "image/webp" => "webp",
        "image/svg+xml" => "svg",
        "image/bmp" | "image/x-ms-bmp" => "bmp",
        "image/x-icon" | "image/vnd.microsoft.icon" => "ico",
        "image/tiff" => "tiff",
        "image/x-adobe-dng" => "dng",
        "image/x-canon-cr2" => "cr2",
        "image/x-nikon-nef" => "nef",
        "image/x-sony-arw" => "arw",
        // Audio
        "audio/wav" | "audio/x-wav" | "audio/wave" => "wav",
        "audio/mp3" | "audio/mpeg" => "mp3",
        "audio/flac" => "flac",
        "audio/ogg" => "ogg",
        "audio/mp4" => "m4a",
        "audio/aac" | "audio/x-aac" => "aac",
        "audio/x-ms-wma" => "wma",
        "audio/opus" => "opus",
        // Video
        "video/mp4" => "mp4",
        "video/webm" => "webm",
        "video/quicktime" => "mov",
        "video/x-msvideo" => "avi",
        "video/x-matroska" => "mkv",
        "video/x-flv" => "flv",
        "video/x-ms-wmv" => "wmv",
        "video/mpeg" => "mpg",
        "video/3gpp" => "3gp",
        "video/ogg" => "ogv",
        "video/mp2t" => "ts",
        // Documents
        "application/pdf" => "pdf",
        "application/msword" => "doc",
        "application/vnd.openxmlformats-officedocument.wordprocessingml.document" => "docx",
        "application/vnd.ms-excel" => "xls",
        "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet" => "xlsx",
        "application/vnd.ms-powerpoint" => "ppt",
        "application/vnd.openxmlformats-officedocument.presentationml.presentation" => "pptx",
        "application/vnd.oasis.opendocument.text" => "odt",
        "application/vnd.oasis.opendocument.spreadsheet" => "ods",
        "application/vnd.oasis.opendocument.presentation" => "odp",
        "application/rtf" => "rtf",
        // Text/Data
        "text/plain" => "txt",
        "text/markdown" => "md",
        "text/csv" => "csv",
        "application/json" => "json",
        "application/xml" | "text/xml" => "xml",
        "application/x-yaml" | "text/yaml" => "yaml",
        "application/toml" => "toml",
        "application/sql" => "sql",
        // Archives
        "application/zip" => "zip",
        "application/x-rar-compressed" | "application/vnd.rar" => "rar",
        "application/x-7z-compressed" => "7z",
        "application/x-tar" => "tar",
        "application/gzip" => "gz",
        "application/x-bzip2" => "bz2",
        "application/x-xz" => "xz",
        "application/x-iso9660-image" => "iso",
        "application/x-apple-diskimage" => "dmg",
        "application/vnd.android.package-archive" => "apk",
        "application/java-archive" => "jar",
        "application/vnd.webxdc+zip" => "xdc",
        // 3D
        "model/obj" => "obj",
        "model/gltf+json" => "gltf",
        "model/gltf-binary" => "glb",
        "model/stl" | "application/sla" => "stl",
        "model/vnd.collada+xml" => "dae",
        // Code
        "text/javascript" | "application/javascript" => "js",
        "text/typescript" | "application/typescript" => "ts",
        "text/x-python" | "application/x-python" => "py",
        "text/x-rust" => "rs",
        "text/x-go" => "go",
        "text/x-java" => "java",
        "text/x-c" => "c",
        "text/x-c++" => "cpp",
        "text/x-csharp" => "cs",
        "text/x-ruby" => "rb",
        "text/x-php" => "php",
        "text/x-swift" => "swift",
        // Web
        "text/html" => "html",
        "text/css" => "css",
        // Other
        "application/x-msdownload" | "application/x-dosexec" => "exe",
        "application/x-msi" => "msi",
        "application/x-font-ttf" | "font/ttf" => "ttf",
        "application/x-font-otf" | "font/otf" => "otf",
        "font/woff" => "woff",
        "font/woff2" => "woff2",
        // Fallback: extract subtype
        _ => {
            let lower = mime.trim().to_lowercase();
            return lower.split('/').nth(1).unwrap_or("bin").to_string();
        }
    }.to_string()
}

/// Sanitize a filename for safe filesystem use.
/// Strips path traversal, dangerous characters, and truncates to 64-char stem.
pub fn sanitize_filename(name: &str) -> String {
    let base = name.rsplit('/').next().unwrap_or(name);
    let base = base.rsplit('\\').next().unwrap_or(base);

    let sanitized: String = base.chars().filter(|c| {
        !matches!(c, '/' | '\\' | ':' | '*' | '?' | '"' | '<' | '>' | '|' | '\0')
    }).collect();

    let sanitized = sanitized.trim_matches(|c: char| c == '.' || c == ' ');

    if sanitized.is_empty() {
        return String::new();
    }

    if let Some(dot_pos) = sanitized.rfind('.') {
        let stem = &sanitized[..dot_pos];
        let ext = &sanitized[dot_pos..];
        if stem.len() > 64 {
            let truncated = &stem[..stem.floor_char_boundary(64)];
            return format!("{}{}", truncated, ext);
        }
    } else if sanitized.len() > 64 {
        let truncated = &sanitized[..sanitized.floor_char_boundary(64)];
        return truncated.to_string();
    }

    sanitized.to_string()
}

/// Resolve a unique filename in `dir`, appending `-1`, `-2`, etc. on collision.
///
/// If `dir/name` doesn't exist, returns it as-is. Otherwise increments a
/// counter on the stem: `photo.jpg` → `photo-1.jpg` → `photo-2.jpg` ...
pub fn resolve_unique_filename(dir: &std::path::Path, name: &str) -> std::path::PathBuf {
    let candidate = dir.join(name);
    if !candidate.exists() {
        return candidate;
    }

    let stem = std::path::Path::new(name)
        .file_stem()
        .and_then(|s| s.to_str())
        .unwrap_or(name);
    let ext = std::path::Path::new(name)
        .extension()
        .and_then(|s| s.to_str())
        .unwrap_or("");

    let mut counter = 1u32;
    loop {
        let suffixed = if ext.is_empty() {
            format!("{}-{}", stem, counter)
        } else {
            format!("{}-{}.{}", stem, counter, ext)
        };
        let candidate = dir.join(&suffixed);
        if !candidate.exists() {
            return candidate;
        }
        counter += 1;
    }
}

/// Decrypt a DM file attachment and save to the download directory.
///
/// Uses AES-GCM decryption with the key/nonce from the attachment metadata.
/// Saves with atomic write (temp file + rename). Returns (path, content_hash).
/// If an identical file already exists (same name + size + hash), reuses it.
pub fn decrypt_and_save_attachment(
    encrypted_data: &[u8],
    key: &str,
    nonce: &str,
    name: &str,
    extension: &str,
) -> Result<(std::path::PathBuf, String), String> {
    let decrypted = decrypt_data(encrypted_data, key, nonce)?;
    let file_hash = sha256_hex(&decrypted);

    let dir = crate::db::get_download_dir();
    std::fs::create_dir_all(&dir).map_err(|e| format!("Failed to create directory: {}", e))?;

    let target_name = if name.is_empty() {
        format!("{}.{}", file_hash, extension)
    } else {
        name.to_string()
    };

    // Content dedup: reuse if same name + size + hash
    let candidate = dir.join(&target_name);
    let already_exists = candidate.exists()
        && std::fs::metadata(&candidate).map(|m| m.len() == decrypted.len() as u64).unwrap_or(false)
        && std::fs::read(&candidate).map(|b| sha256_hex(&b) == file_hash).unwrap_or(false);

    if already_exists {
        return Ok((candidate, file_hash));
    }

    let file_path = resolve_unique_filename(&dir, &target_name);

    // Atomic write: temp file then rename
    let tmp_path = dir.join(format!(".{}.{}.tmp", file_hash, extension));
    std::fs::write(&tmp_path, &decrypted).map_err(|e| format!("Failed to write file: {}", e))?;
    std::fs::rename(&tmp_path, &file_path).map_err(|e| format!("Failed to rename file: {}", e))?;

    Ok((file_path, file_hash))
}

/// Format bytes into human-readable format (KB, MB, GB).
pub fn format_bytes(bytes: u64) -> String {
    const KB: f64 = 1024.0;
    const MB: f64 = KB * 1024.0;
    const GB: f64 = MB * 1024.0;

    if bytes < KB as u64 {
        format!("{} B", bytes)
    } else if bytes < MB as u64 {
        format!("{:.1} KB", bytes as f64 / KB)
    } else if bytes < GB as u64 {
        format!("{:.1} MB", bytes as f64 / MB)
    } else {
        format!("{:.1} GB", bytes as f64 / GB)
    }
}

/// Returns true if the provided MIME type is an image/*.
pub fn is_image_mime(mime: &str) -> bool {
    mime.trim().starts_with("image/")
}

/// Convert a file extension to a MIME type, with an optional restriction to image/* types.
pub fn mime_from_extension_safe(extension: &str, image_only: bool) -> Result<String, String> {
    let mime = mime_from_extension(extension).to_string();
    if image_only && !is_image_mime(&mime) {
        return Err(mime);
    }
    Ok(mime)
}

/// Detect MIME type from file magic bytes.
/// Supports PNG, JPEG, GIF, WebP, TIFF, ICO, and SVG.
/// Returns "application/octet-stream" for unrecognized formats.
pub fn mime_from_magic_bytes(bytes: &[u8]) -> &'static str {
    if bytes.len() < 4 {
        return "application/octet-stream";
    }
    match bytes[0] {
        0x89 if bytes[1..4] == [0x50, 0x4E, 0x47] => "image/png",
        0xFF if bytes[1..3] == [0xD8, 0xFF] => "image/jpeg",
        b'G' if bytes.len() >= 6 && (bytes[..6] == *b"GIF87a" || bytes[..6] == *b"GIF89a") => "image/gif",
        b'R' if bytes.len() > 12 && bytes[..4] == *b"RIFF" && bytes[8..12] == *b"WEBP" => "image/webp",
        0x49 if bytes[1..4] == [0x49, 0x2A, 0x00] => "image/tiff",
        0x4D if bytes[1..4] == [0x4D, 0x00, 0x2A] => "image/tiff",
        0x00 if bytes[1..4] == [0x00, 0x01, 0x00] => "image/x-icon",
        b'<' if bytes.starts_with(b"<?xml") || bytes.starts_with(b"<svg") => "image/svg+xml",
        _ => "application/octet-stream",
    }
}

// ============================================================================
// Conditional Encryption — maybe_encrypt / maybe_decrypt
// ============================================================================

use rand::Rng;
use chacha20poly1305::Nonce;

/// Check if a string looks like encrypted content (hex-encoded ChaCha20 output).
/// Minimum (empty message): 12 + 0 + 16 = 28 bytes = 56 hex chars.
#[inline]
pub fn looks_encrypted(s: &str) -> bool {
    if s.len() < 56 { return false; }
    is_all_lowercase_hex(s.as_bytes())
}

/// NEON: check if all bytes are lowercase hex [0-9a-f].
#[cfg(target_arch = "aarch64")]
#[inline]
fn is_all_lowercase_hex(bytes: &[u8]) -> bool {
    use std::arch::aarch64::*;
    unsafe {
        let mut i = 0;
        while i + 16 <= bytes.len() {
            let chunk = vld1q_u8(bytes.as_ptr().add(i));
            let is_digit = vandq_u8(vcgeq_u8(chunk, vdupq_n_u8(b'0')),
                                    vcleq_u8(chunk, vdupq_n_u8(b'9')));
            let is_af = vandq_u8(vcgeq_u8(chunk, vdupq_n_u8(b'a')),
                                 vcleq_u8(chunk, vdupq_n_u8(b'f')));
            if vminvq_u8(vorrq_u8(is_digit, is_af)) == 0 { return false; }
            i += 16;
        }
        while i < bytes.len() {
            let b = bytes[i];
            if !matches!(b, b'0'..=b'9' | b'a'..=b'f') { return false; }
            i += 1;
        }
    }
    true
}

/// SSE2: check if all bytes are lowercase hex [0-9a-f].
#[cfg(target_arch = "x86_64")]
#[inline]
fn is_all_lowercase_hex(bytes: &[u8]) -> bool {
    use std::arch::x86_64::*;
    unsafe {
        let mut i = 0;
        while i + 16 <= bytes.len() {
            let chunk = _mm_loadu_si128(bytes.as_ptr().add(i) as *const __m128i);
            let is_digit = _mm_cmpeq_epi8(
                _mm_subs_epu8(_mm_sub_epi8(chunk, _mm_set1_epi8(b'0' as i8)), _mm_set1_epi8(9)),
                _mm_setzero_si128());
            let is_af = _mm_cmpeq_epi8(
                _mm_subs_epu8(_mm_sub_epi8(chunk, _mm_set1_epi8(b'a' as i8)), _mm_set1_epi8(5)),
                _mm_setzero_si128());
            if _mm_movemask_epi8(_mm_or_si128(is_digit, is_af)) != 0xFFFF { return false; }
            i += 16;
        }
        while i < bytes.len() {
            let b = bytes[i];
            if !matches!(b, b'0'..=b'9' | b'a'..=b'f') { return false; }
            i += 1;
        }
    }
    true
}

/// Scalar fallback for platforms without SIMD.
#[cfg(not(any(target_arch = "aarch64", target_arch = "x86_64")))]
#[inline]
fn is_all_lowercase_hex(bytes: &[u8]) -> bool {
    const IS_LOWER_HEX: [bool; 256] = {
        let mut t = [false; 256];
        t[b'0' as usize] = true; t[b'1' as usize] = true; t[b'2' as usize] = true;
        t[b'3' as usize] = true; t[b'4' as usize] = true; t[b'5' as usize] = true;
        t[b'6' as usize] = true; t[b'7' as usize] = true; t[b'8' as usize] = true;
        t[b'9' as usize] = true; t[b'a' as usize] = true; t[b'b' as usize] = true;
        t[b'c' as usize] = true; t[b'd' as usize] = true; t[b'e' as usize] = true;
        t[b'f' as usize] = true;
        t
    };
    bytes.iter().all(|&b| IS_LOWER_HEX[b as usize])
}

/// Encrypt a string using ENCRYPTION_KEY vault (ChaCha20-Poly1305).
/// If `password` is Some, derives a key from it instead.
pub async fn maybe_encrypt_inner(mut input: String, password: Option<String>) -> String {
    let mut key: [u8; 32] = if password.is_none() {
        crate::state::ENCRYPTION_KEY.get().expect("Encryption key must be set")
    } else {
        hash_pass(&password.unwrap()).await
    };

    let mut rng = rand::thread_rng();
    let nonce_bytes: [u8; 12] = rng.gen();

    let cipher = ChaCha20Poly1305::new_from_slice(&key)
        .expect("Key should be valid");
    let nonce: Nonce = nonce_bytes.into();

    let ciphertext = cipher
        .encrypt(&nonce, input.as_bytes())
        .expect("Encryption should not fail");
    input.zeroize();

    let mut buffer = Vec::with_capacity(nonce_bytes.len() + ciphertext.len());
    buffer.extend_from_slice(&nonce_bytes);
    buffer.extend_from_slice(&ciphertext);

    if !crate::state::ENCRYPTION_KEY.has_key() {
        crate::state::ENCRYPTION_KEY.set(key, &[&crate::state::MY_SECRET_KEY]);
    }

    key.zeroize();

    crate::simd::hex::bytes_to_hex_string(&buffer)
}

/// Decrypt a hex-encoded ChaCha20-Poly1305 ciphertext using ENCRYPTION_KEY vault.
/// If `password` is Some, derives a key from it instead.
pub async fn maybe_decrypt_inner(ciphertext: String, password: Option<String>) -> Result<String, ()> {
    let has_password = password.is_some();

    let mut key: [u8; 32] = if let Some(pass) = password {
        hash_pass(&pass).await
    } else {
        match crate::state::ENCRYPTION_KEY.get() {
            Some(k) => k,
            None => return Err(()),
        }
    };

    let encrypted_data = crate::simd::hex::hex_string_to_bytes(ciphertext.as_str());
    if encrypted_data.len() < 12 {
        key.zeroize();
        return Err(());
    }

    let (nonce_bytes, actual_ciphertext) = encrypted_data.split_at(12);

    let cipher = match ChaCha20Poly1305::new_from_slice(&key) {
        Ok(c) => c,
        Err(_) => { key.zeroize(); return Err(()) }
    };

    let nonce_arr: [u8; 12] = match nonce_bytes.try_into() {
        Ok(n) => n,
        Err(_) => { key.zeroize(); return Err(()) }
    };
    let nonce: Nonce = nonce_arr.into();
    let plaintext = match cipher.decrypt(&nonce, actual_ciphertext) {
        Ok(pt) => pt,
        Err(_) => { key.zeroize(); return Err(()) }
    };

    if has_password && !crate::state::ENCRYPTION_KEY.has_key() {
        crate::state::ENCRYPTION_KEY.set(key, &[&crate::state::MY_SECRET_KEY]);
    }

    key.zeroize();

    // SAFETY: plaintext was originally valid UTF-8, authenticated decryption ensures integrity
    unsafe { Ok(String::from_utf8_unchecked(plaintext)) }
}

/// Conditionally encrypt content based on encryption_enabled setting.
pub async fn maybe_encrypt(input: String) -> String {
    if crate::state::is_encryption_enabled_fast() {
        maybe_encrypt_inner(input, None).await
    } else {
        input
    }
}

/// Conditionally decrypt content. Handles crash recovery — if decryption fails
/// on non-encrypted-looking content, returns it as-is.
pub async fn maybe_decrypt(input: String) -> Result<String, ()> {
    if crate::state::is_encryption_enabled_fast() {
        match maybe_decrypt_inner(input.clone(), None).await {
            Ok(decrypted) => Ok(decrypted),
            Err(_) => {
                if looks_encrypted(&input) { Err(()) } else { Ok(input) }
            }
        }
    } else {
        if looks_encrypted(&input) {
            match maybe_decrypt_inner(input.clone(), None).await {
                Ok(decrypted) => Ok(decrypted),
                Err(_) => Ok(input),
            }
        } else {
            Ok(input)
        }
    }
}

// ============================================================================
// Synchronous at-rest helpers (Concord tables, sync DB code)
// ============================================================================
//
// `maybe_encrypt`/`maybe_decrypt` are async (they may derive a key from a
// password). The Concord DB layer is synchronous and only ever uses the live
// ENCRYPTION_KEY vault, so these sync variants wrap the field-level primitives
// against the vault + the enabled flag. Discriminators for the half-migrated
// case: a key BLOB is 32 bytes raw vs 12+len+16 encrypted; a text field uses
// `looks_encrypted` (>=56 lowercase-hex chars).

/// ChaCha20-Poly1305 encrypt raw bytes with an explicit key → `nonce(12) || ct || tag(16)`.
pub fn encrypt_blob_with_key(plaintext: &[u8], key: &[u8; 32]) -> Result<Vec<u8>, String> {
    use rand::Rng;
    let cipher = ChaCha20Poly1305::new_from_slice(key).map_err(|e| e.to_string())?;
    let nonce_bytes: [u8; 12] = rand::thread_rng().gen();
    let nonce = chacha20poly1305::Nonce::from(nonce_bytes);
    let ct = cipher
        .encrypt(&nonce, plaintext)
        .map_err(|e| format!("blob encryption failed: {}", e))?;
    let mut out = Vec::with_capacity(12 + ct.len());
    out.extend_from_slice(&nonce_bytes);
    out.extend_from_slice(&ct);
    Ok(out)
}

/// ChaCha20-Poly1305 decrypt `nonce(12) || ct || tag(16)` with an explicit key.
pub fn decrypt_blob_with_key(stored: &[u8], key: &[u8; 32]) -> Result<Vec<u8>, String> {
    if stored.len() < 12 + 16 {
        return Err("blob too short to be ciphertext".to_string());
    }
    let cipher = ChaCha20Poly1305::new_from_slice(key).map_err(|e| e.to_string())?;
    let (nonce_bytes, ct) = stored.split_at(12);
    let nonce_arr: [u8; 12] = nonce_bytes.try_into().map_err(|_| "bad nonce".to_string())?;
    let nonce = chacha20poly1305::Nonce::from(nonce_arr);
    cipher
        .decrypt(&nonce, ct)
        .map_err(|_| "blob decryption failed (wrong key or corrupted)".to_string())
}

/// Encrypt a secret key BLOB for at-rest storage. Off → unchanged. Enabled but
/// the vault is empty → Err (never silently persists a secret in plaintext).
pub fn maybe_encrypt_blob(plaintext: &[u8]) -> Result<Vec<u8>, String> {
    if !crate::state::is_encryption_enabled_fast() {
        return Ok(plaintext.to_vec());
    }
    let mut key = crate::state::ENCRYPTION_KEY
        .get()
        .ok_or_else(|| "encryption enabled but key vault is empty".to_string())?;
    let out = encrypt_blob_with_key(plaintext, &key);
    key.zeroize();
    out
}

/// Decrypt a secret key BLOB. Tolerant of the half-migrated DB: a 32-byte value
/// is a raw (not-yet-wrapped / encryption-off) key, and anything that fails to
/// authenticate is returned as-is, so a mixed store always reads back correctly.
pub fn maybe_decrypt_blob(stored: &[u8]) -> Vec<u8> {
    // 32 bytes = a raw key (encryption off, or a row written before the at-rest pass).
    if stored.len() == 32 {
        return stored.to_vec();
    }
    match crate::state::ENCRYPTION_KEY.get() {
        Some(mut key) => {
            let out = decrypt_blob_with_key(stored, &key).unwrap_or_else(|_| stored.to_vec());
            key.zeroize();
            out
        }
        None => stored.to_vec(),
    }
}

/// Encrypt a text field for at-rest storage. Off → unchanged. Enabled but the
/// vault is empty → Err.
pub fn maybe_encrypt_text(plaintext: &str) -> Result<String, String> {
    if !crate::state::is_encryption_enabled_fast() {
        return Ok(plaintext.to_string());
    }
    let mut key = crate::state::ENCRYPTION_KEY
        .get()
        .ok_or_else(|| "encryption enabled but key vault is empty".to_string())?;
    let out = encrypt_with_key(plaintext, &key);
    key.zeroize();
    out
}

/// Decrypt a text field. A value that doesn't look encrypted (or can't be
/// decrypted) is returned as-is — pre-migration rows and encryption-off rows.
pub fn maybe_decrypt_text(stored: &str) -> String {
    if !looks_encrypted(stored) {
        return stored.to_string();
    }
    match crate::state::ENCRYPTION_KEY.get() {
        Some(mut key) => {
            let out = decrypt_with_key(stored, &key).unwrap_or_else(|_| stored.to_string());
            key.zeroize();
            out
        }
        None => stored.to_string(),
    }
}

#[cfg(test)]
mod at_rest_tests {
    use super::*;

    #[test]
    fn blob_roundtrip_with_explicit_key() {
        let key = [7u8; 32];
        let secret = [0x42u8; 32];
        let ct = encrypt_blob_with_key(&secret, &key).unwrap();
        assert_eq!(ct.len(), 12 + 32 + 16, "nonce + ciphertext + tag");
        assert_ne!(&ct[12..44], &secret[..], "ciphertext must not equal plaintext");
        assert_eq!(decrypt_blob_with_key(&ct, &key).unwrap(), secret.to_vec());
    }

    #[test]
    fn blob_wrong_key_fails() {
        let ct = encrypt_blob_with_key(&[1u8; 32], &[7u8; 32]).unwrap();
        assert!(decrypt_blob_with_key(&ct, &[9u8; 32]).is_err());
    }

    #[test]
    fn encrypted_text_is_always_detected_as_encrypted() {
        // Even the shortest fields ("[]", "{}", "") must exceed the looks_encrypted floor
        // so they round-trip through maybe_decrypt_text.
        let key = [3u8; 32];
        for s in ["", "[]", "{}", "a"] {
            let ct = encrypt_with_key(s, &key).unwrap();
            assert!(looks_encrypted(&ct), "ciphertext for {:?} must look encrypted", s);
            assert_eq!(decrypt_with_key(&ct, &key).unwrap(), s);
        }
    }
}

// ============================================================================
// Image Metadata — thumbhash + dimensions for file attachments
// ============================================================================

/// Re-export SIMD nearest-neighbor downsample from simd::image.
pub use crate::simd::image::nearest_neighbor_downsample_rgba;

/// Generate a thumbhash from RGBA8 pixel data.
///
/// Downscales to fit within 100x100 (ThumbHash's max) using fast nearest-neighbor,
/// then hashes. Returns the base91-encoded thumbhash string.
pub fn generate_thumbhash_from_rgba(pixels: &[u8], width: u32, height: u32) -> Option<String> {
    use fast_thumbhash::{rgba_to_thumb_hash, base91_encode};

    const MAX_DIM: u32 = 100;

    let (thumb_w, thumb_h) = if width <= MAX_DIM && height <= MAX_DIM {
        (width, height)
    } else if width > height {
        (MAX_DIM, (MAX_DIM * height / width).max(1))
    } else {
        ((MAX_DIM * width / height).max(1), MAX_DIM)
    };

    let thumbnail = if thumb_w == width && thumb_h == height {
        pixels.to_vec()
    } else {
        nearest_neighbor_downsample_rgba(pixels, width, height, thumb_w, thumb_h)
    };

    let hash = rgba_to_thumb_hash(thumb_w as usize, thumb_h as usize, &thumbnail);
    Some(base91_encode(&hash))
}

/// Decode an image with allocation limits. A tiny file declaring 60000×60000
/// would otherwise allocate ~14 GB before a single pixel decodes — every
/// decode of bytes we didn't author must go through this.
///
/// Applies EXIF orientation to the pixels. Camera photos store their pixels in
/// the sensor's native axis plus an orientation tag; `<img>` honours that tag,
/// but our re-encode strips all metadata, so an un-baked decode would ship the
/// sensor pixels with no tag and the receiver sees the photo rotated. Baking it
/// in here keeps every downstream path (compress, thumbhash, dimensions) upright.
pub fn decode_image_bounded(bytes: &[u8]) -> Result<image::DynamicImage, String> {
    use image::ImageDecoder;
    let mut reader = image::ImageReader::new(std::io::Cursor::new(bytes))
        .with_guessed_format()
        .map_err(|e| format!("image format: {e}"))?;
    reader.limits(bounded_image_limits());
    let mut decoder = reader.into_decoder().map_err(|e| format!("image decode: {e}"))?;
    // Read the tag before consuming the decoder; formats without one report NoTransforms.
    let orientation = decoder.orientation().map_err(|e| format!("image orientation: {e}"))?;
    let mut img = image::DynamicImage::from_decoder(decoder)
        .map_err(|e| format!("image decode: {e}"))?;
    img.apply_orientation(orientation);
    Ok(img)
}

/// Shared decode limits for [`decode_image_bounded`] and call sites that need
/// their own `ImageReader` (fixed-format decodes).
pub fn bounded_image_limits() -> image::Limits {
    let mut limits = image::Limits::default();
    limits.max_image_width = Some(16_384);
    limits.max_image_height = Some(16_384);
    limits.max_alloc = Some(256 * 1024 * 1024);
    limits
}

/// Generate image metadata (thumbhash + dimensions) from raw file bytes.
///
/// Returns None if the bytes can't be decoded as an image.
/// Used by `send_file_dm` to automatically include preview metadata for images.
pub fn generate_image_metadata(file_bytes: &[u8]) -> Option<crate::types::ImageMetadata> {
    let img = decode_image_bounded(file_bytes).ok()?;
    let width = img.width();
    let height = img.height();

    let rgba = img.to_rgba8();
    let thumbhash = generate_thumbhash_from_rgba(rgba.as_raw(), width, height)?;

    Some(crate::types::ImageMetadata {
        thumbhash,
        width,
        height,
    })
}

#[cfg(test)]
mod tests {
    use super::*;

    // ========================================================================
    // encrypt_with_key / decrypt_with_key roundtrip tests
    // ========================================================================

    fn test_key() -> [u8; 32] {
        [0x42u8; 32]
    }

    fn alt_key() -> [u8; 32] {
        [0x99u8; 32]
    }

    #[test]
    fn encrypt_decrypt_roundtrip_simple() {
        let key = test_key();
        let plaintext = "hello world";
        let encrypted = encrypt_with_key(plaintext, &key).expect("encryption should succeed");
        let decrypted = decrypt_with_key(&encrypted, &key).expect("decryption should succeed");
        assert_eq!(decrypted, plaintext, "roundtrip should preserve plaintext");
    }

    #[test]
    fn encrypt_decrypt_100_random_strings() {
        use rand::Rng;
        let key = test_key();
        let mut rng = rand::thread_rng();
        for i in 0..100 {
            let len = rng.gen_range(1..=200);
            let s: String = (0..len).map(|_| rng.gen_range(0x20u8..0x7f) as char).collect();
            let enc = encrypt_with_key(&s, &key)
                .unwrap_or_else(|e| panic!("encryption failed on iteration {}: {}", i, e));
            let dec = decrypt_with_key(&enc, &key)
                .unwrap_or_else(|e| panic!("decryption failed on iteration {}: {}", i, e));
            assert_eq!(dec, s, "roundtrip failed on iteration {}", i);
        }
    }

    #[test]
    fn encrypt_decrypt_empty_string() {
        let key = test_key();
        let encrypted = encrypt_with_key("", &key).expect("encrypting empty string should succeed");
        let decrypted = decrypt_with_key(&encrypted, &key).expect("decrypting empty string should succeed");
        assert_eq!(decrypted, "", "empty string roundtrip should produce empty string");
    }

    #[test]
    fn encrypt_decrypt_large_string() {
        let key = test_key();
        let plaintext = "A".repeat(10 * 1024); // 10 KB
        let encrypted = encrypt_with_key(&plaintext, &key).expect("encrypting 10KB should succeed");
        let decrypted = decrypt_with_key(&encrypted, &key).expect("decrypting 10KB should succeed");
        assert_eq!(decrypted, plaintext, "10KB roundtrip should preserve content");
    }

    #[test]
    fn decrypt_with_wrong_key_fails() {
        let key = test_key();
        let wrong_key = alt_key();
        let encrypted = encrypt_with_key("secret data", &key).expect("encryption should succeed");
        let result = decrypt_with_key(&encrypted, &wrong_key);
        assert!(result.is_err(), "decryption with wrong key should fail");
    }

    #[test]
    fn decrypt_corrupted_ciphertext_fails() {
        let key = test_key();
        let mut encrypted = encrypt_with_key("secret data", &key).expect("encryption should succeed");
        // Corrupt a byte in the ciphertext portion (past the 24-char nonce)
        let bytes: Vec<u8> = encrypted.bytes().collect();
        if bytes.len() > 30 {
            let mut chars: Vec<char> = encrypted.chars().collect();
            // Flip a hex digit in the ciphertext area
            chars[30] = if chars[30] == '0' { 'f' } else { '0' };
            encrypted = chars.into_iter().collect();
        }
        let result = decrypt_with_key(&encrypted, &key);
        assert!(result.is_err(), "decryption of corrupted ciphertext should fail");
    }

    #[test]
    fn different_keys_produce_different_ciphertext() {
        let key1 = test_key();
        let key2 = alt_key();
        let plaintext = "same plaintext";
        let enc1 = encrypt_with_key(plaintext, &key1).expect("enc1 should succeed");
        let enc2 = encrypt_with_key(plaintext, &key2).expect("enc2 should succeed");
        // Ciphertexts after the nonce portion should differ (nonces differ too since random)
        assert_ne!(enc1, enc2, "different keys should produce different ciphertext");
    }

    #[test]
    fn nonce_is_always_different() {
        let key = test_key();
        let plaintext = "same string encrypted twice";
        let enc1 = encrypt_with_key(plaintext, &key).expect("enc1 should succeed");
        let enc2 = encrypt_with_key(plaintext, &key).expect("enc2 should succeed");
        // The first 24 hex chars are the nonce
        let nonce1 = &enc1[..24];
        let nonce2 = &enc2[..24];
        assert_ne!(nonce1, nonce2, "nonces should differ between encryptions of the same plaintext");
    }

    #[test]
    fn unicode_content_preserved() {
        let key = test_key();
        let plaintext = "Hello \u{1F600} \u{1F4A9} \u{1F30D} \u{00E9}\u{00E0}\u{00FC} \u{4E16}\u{754C} \u{0410}\u{0411}\u{0412}";
        let encrypted = encrypt_with_key(plaintext, &key).expect("encrypting unicode should succeed");
        let decrypted = decrypt_with_key(&encrypted, &key).expect("decrypting unicode should succeed");
        assert_eq!(decrypted, plaintext, "unicode content should be preserved through encrypt/decrypt");
    }

    #[test]
    fn decrypt_too_short_ciphertext_fails() {
        let key = test_key();
        let result = decrypt_with_key("abcdef", &key);
        assert!(result.is_err(), "ciphertext shorter than 24 hex chars should fail");
        assert!(result.unwrap_err().contains("too short"), "error should mention too short");
    }

    #[test]
    fn encrypt_output_is_hex_encoded() {
        let key = test_key();
        let encrypted = encrypt_with_key("test", &key).expect("encryption should succeed");
        assert!(encrypted.chars().all(|c| c.is_ascii_hexdigit()),
            "encrypted output should be entirely hex characters");
    }

    #[test]
    fn encrypt_output_has_correct_structure() {
        let key = test_key();
        let encrypted = encrypt_with_key("test", &key).expect("encryption should succeed");
        // Must be at least 24 hex chars (nonce) + some ciphertext
        assert!(encrypted.len() > 24,
            "encrypted output should have nonce (24 hex chars) plus ciphertext");
        // Length should be even (hex pairs)
        assert_eq!(encrypted.len() % 2, 0,
            "encrypted output length should be even (hex pairs)");
    }

    #[test]
    fn encrypt_decrypt_special_characters() {
        let key = test_key();
        let plaintext = r#"!@#$%^&*()_+-=[]{}|;':",.<>?/\`~"#;
        let encrypted = encrypt_with_key(plaintext, &key).expect("encrypting special chars should succeed");
        let decrypted = decrypt_with_key(&encrypted, &key).expect("decrypting special chars should succeed");
        assert_eq!(decrypted, plaintext, "special characters should survive roundtrip");
    }

    #[test]
    fn encrypt_decrypt_newlines_and_whitespace() {
        let key = test_key();
        let plaintext = "line1\nline2\r\nline3\ttab\0null";
        let encrypted = encrypt_with_key(plaintext, &key).expect("encrypting whitespace should succeed");
        let decrypted = decrypt_with_key(&encrypted, &key).expect("decrypting whitespace should succeed");
        assert_eq!(decrypted, plaintext, "whitespace and control chars should survive roundtrip");
    }

    #[test]
    fn decrypt_invalid_hex_in_nonce_fails() {
        let key = test_key();
        // 24 chars of invalid hex + some ciphertext
        let bad = "zzzzzzzzzzzzzzzzzzzzzzzz0000000000000000";
        let result = decrypt_with_key(bad, &key);
        assert!(result.is_err(), "invalid hex in nonce should fail");
    }

    #[test]
    fn decrypt_invalid_hex_in_ciphertext_fails() {
        let key = test_key();
        // Valid nonce (24 hex chars) + invalid ciphertext hex
        let bad = "000000000000000000000000gggggggg";
        let result = decrypt_with_key(bad, &key);
        assert!(result.is_err(), "invalid hex in ciphertext should fail");
    }

    // ========================================================================
    // hex module tests
    // ========================================================================

    #[test]
    fn hex_encode_decode_roundtrip() {
        let data = vec![0x00, 0x01, 0xff, 0x80, 0x7f];
        let encoded = hex::encode(&data);
        let decoded = hex::decode(&encoded).expect("decode should succeed");
        assert_eq!(decoded, data, "hex encode/decode roundtrip should preserve bytes");
    }

    #[test]
    fn hex_decode_odd_length_error() {
        let result = hex::decode("abc");
        assert!(result.is_err(), "odd-length hex string should fail");
        assert!(result.unwrap_err().contains("Odd-length"), "error should mention odd-length");
    }

    #[test]
    fn hex_decode_invalid_hex_error() {
        let result = hex::decode("zzzz");
        assert!(result.is_err(), "invalid hex characters should fail");
    }

    #[test]
    fn hex_encode_empty() {
        assert_eq!(hex::encode(&[]), "", "encoding empty bytes should produce empty string");
    }

    #[test]
    fn hex_decode_empty() {
        let decoded = hex::decode("").expect("decoding empty string should succeed");
        assert!(decoded.is_empty(), "decoding empty string should produce empty vec");
    }

    // ========================================================================
    // hash_pass tests
    // ========================================================================

    #[tokio::test]
    async fn hash_pass_deterministic() {
        let key1 = hash_pass("my_password").await;
        let key2 = hash_pass("my_password").await;
        assert_eq!(key1, key2, "same password should always produce the same key");
    }

    #[tokio::test]
    async fn hash_pass_different_passwords_different_keys() {
        let key1 = hash_pass("password_one").await;
        let key2 = hash_pass("password_two").await;
        assert_ne!(key1, key2, "different passwords should produce different keys");
    }

    #[tokio::test]
    async fn hash_pass_output_is_32_bytes() {
        let key = hash_pass("test_password").await;
        assert_eq!(key.len(), 32, "hash_pass should produce exactly 32 bytes");
        // Ensure it is not all zeros (i.e. hashing actually happened)
        assert!(key.iter().any(|&b| b != 0), "hash output should not be all zeros");
    }

    #[test]
    fn generate_thumbhash_from_bytes_basic() {
        // 2x2 red pixel image in RGBA
        let pixels: Vec<u8> = vec![
            255, 0, 0, 255,  255, 0, 0, 255,
            255, 0, 0, 255,  255, 0, 0, 255,
        ];
        let result = super::generate_thumbhash_from_rgba(&pixels, 2, 2);
        assert!(result.is_some());
        assert!(!result.unwrap().is_empty());
    }

    #[test]
    fn generate_image_metadata_from_bytes() {
        // Create a 4x4 blue PNG in memory
        let img = image::RgbaImage::from_pixel(4, 4, image::Rgba([0, 0, 255, 255]));
        let mut buf = Vec::new();
        let mut cursor = std::io::Cursor::new(&mut buf);
        img.write_to(&mut cursor, image::ImageFormat::Png).unwrap();

        let meta = super::generate_image_metadata(&buf);
        assert!(meta.is_some());
        let meta = meta.unwrap();
        assert_eq!(meta.width, 4);
        assert_eq!(meta.height, 4);
        assert!(!meta.thumbhash.is_empty());
    }

    #[test]
    fn generate_image_metadata_non_image() {
        let text_bytes = b"this is not an image";
        let meta = super::generate_image_metadata(text_bytes);
        assert!(meta.is_none());
    }
}