//! Provides access to a Nitrokey device using the native libnitrokey API.
//!
//! # Usage
//!
//! Operations on the Nitrokey require different authentication levels.  Some
//! operations can be performed without authentication, some require user
//! access, and some require admin access.  This is modelled using the types
//! [`UnauthenticatedDevice`][], [`UserAuthenticatedDevice`][] and
//! [`AdminAuthenticatedDevice`][].
//!
//! Use [`connect`][] or [`connect_model`][] to obtain an
//! [`UnauthenticatedDevice`][].  You can then use [`authenticate_user`][] or
//! [`authenticate_admin`][] to get an authenticated device.  You can then use
//! [`device`][] to go back to the unauthenticated device.
//!
//! This makes sure that you can only execute a command if you have the
//! required access rights.  Otherwise, your code will not compile.  The only
//! exception are the methods to generate one-time passwords –
//! [`get_hotp_code`][] and [`get_totp_code`][].  Depending on the stick
//! configuration, these operations are available without authentication or
//! with user authentication.
//!
//! Per default, libnitrokey writes log messages, for example the packets that
//! are sent to and received from the stick, to the standard output.  To
//! change this behaviour, use [`set_debug`][] or [`set_log_level`][].
//!
//! # Examples
//!
//! Connect to any Nitrokey and print its serial number:
//!
//! ```no_run
//! use nitrokey::Device;
//! # use nitrokey::CommandError;
//!
//! # fn try_main() -> Result<(), CommandError> {
//! let device = nitrokey::connect()?;
//! println!("{}", device.get_serial_number()?);
//! #     Ok(())
//! # }
//! ```
//!
//! Configure an HOTP slot:
//!
//! ```no_run
//! use nitrokey::{CommandStatus, Device, OtpMode, OtpSlotData};
//! # use nitrokey::CommandError;
//!
//! # fn try_main() -> Result<(), (CommandError)> {
//! let device = nitrokey::connect()?;
//! let slot_data = OtpSlotData::new(1, "test", "01234567890123456689", OtpMode::SixDigits);
//! match device.authenticate_admin("12345678") {
//!     Ok(admin) => {
//!         match admin.write_hotp_slot(slot_data, 0) {
//!             CommandStatus::Success => println!("Successfully wrote slot."),
//!             CommandStatus::Error(err) => println!("Could not write slot: {:?}", err),
//!         }
//!     },
//!     Err((_, err)) => println!("Could not authenticate as admin: {:?}", err),
//! }
//! #     Ok(())
//! # }
//! ```
//!
//! Generate an HOTP one-time password:
//!
//! ```no_run
//! use nitrokey::Device;
//! # use nitrokey::CommandError;
//!
//! # fn try_main() -> Result<(), (CommandError)> {
//! let device = nitrokey::connect()?;
//! match device.get_hotp_code(1) {
//!     Ok(code) => println!("Generated HOTP code: {:?}", code),
//!     Err(err) => println!("Could not generate HOTP code: {:?}", err),
//! }
//! #     Ok(())
//! # }
//! ```
//!
//! [`authenticate_admin`]: struct.UnauthenticatedDevice.html#method.authenticate_admin
//! [`authenticate_user`]: struct.UnauthenticatedDevice.html#method.authenticate_user
//! [`connect`]: fn.connect.html
//! [`connect_model`]: fn.connect_model.html
//! [`device`]: struct.AuthenticatedDevice.html#method.device
//! [`get_hotp_code`]: trait.Device.html#method.get_hotp_code
//! [`get_totp_code`]: trait.Device.html#method.get_totp_code
//! [`set_debug`]: fn.set_debug.html
//! [`set_log_level`]: fn.set_log_level.html
//! [`AdminAuthenticatedDevice`]: struct.AdminAuthenticatedDevice.html
//! [`UserAuthenticatedDevice`]: struct.UserAuthenticatedDevice.html
//! [`UnauthenticatedDevice`]: struct.UnauthenticatedDevice.html

extern crate libc;
extern crate nitrokey_sys;
extern crate rand;

use std::ffi::CString;
use std::ffi::CStr;
use libc::c_int;
use rand::Rng;

#[cfg(test)]
mod tests;

/// Modes for one-time password generation.
#[derive(Debug, PartialEq)]
pub enum OtpMode {
    /// Generate one-time passwords with six digits.
    SixDigits,
    /// Generate one-time passwords with eight digits.
    EightDigits,
}

/// Error types returned by Nitrokey device or by the library.
#[derive(Debug, PartialEq)]
pub enum CommandError {
    /// A packet with a wrong checksum has been sent or received.
    WrongCrc,
    /// A command tried to access an OTP slot that does not exist.
    WrongSlot,
    /// A command tried to generate an OTP on a slot that is not configured.
    SlotNotProgrammed,
    /// The provided password is wrong.
    WrongPassword,
    /// You are not authorized for this command or provided a wrong temporary
    /// password.
    NotAuthorized,
    /// An error occured when getting or setting the time.
    Timestamp,
    /// You did not provide a name for the OTP slot.
    NoName,
    /// This command is not supported by this device.
    NotSupported,
    /// This command is unknown.
    UnknownCommand,
    /// AES decryptionfailed.
    AesDecryptionFailed,
    /// An unknown error occured.
    Unknown,
    /// You passed a string containing a null byte.
    InvalidString,
    /// You passed an invalid slot.
    InvalidSlot,
    /// An error occured during random number generation.
    RngError,
}

/// Command execution status.
#[derive(Debug, PartialEq)]
pub enum CommandStatus {
    /// The command was successful.
    Success,
    /// An error occured during command execution.
    Error(CommandError),
}

/// Log level for libnitrokey.
#[derive(Debug, PartialEq)]
pub enum LogLevel {
    /// Only log error messages.
    Error,
    /// Log error messages and warnings.
    Warning,
    /// Log error messages, warnings and info messages.
    Info,
    /// Log error messages, warnings, info messages and debug messages.
    DebugL1,
    /// Log error messages, warnings, info messages and detailed debug
    /// messages.
    Debug,
    /// Log error messages, warnings, info messages and very detailed debug
    /// messages.
    DebugL2,
}

/// Available Nitrokey models.
#[derive(Debug, PartialEq)]
pub enum Model {
    /// The Nitrokey Storage.
    Storage,
    /// The Nitrokey Pro.
    Pro,
}

/// The configuration for a Nitrokey.
#[derive(Clone, Copy, Debug, PartialEq)]
pub struct Config {
    /// If set, the stick will generate a code from the HOTP slot with the
    /// given number if numlock is pressed.  The slot number must be 0, 1 or 2.
    pub numlock: Option<u8>,
    /// If set, the stick will generate a code from the HOTP slot with the
    /// given number if capslock is pressed.  The slot number must be 0, 1 or 2.
    pub capslock: Option<u8>,
    /// If set, the stick will generate a code from the HOTP slot with the
    /// given number if scrollock is pressed.  The slot number must be 0, 1 or 2.
    pub scrollock: Option<u8>,
    /// If set, OTP generation using [`get_hotp_code`][] or [`get_totp_code`][]
    /// requires user authentication.  Otherwise, OTPs can be generated without
    /// authentication.
    ///
    /// [`get_hotp_code`]: struct.Device.html#method.get_hotp_code
    /// [`get_totp_code`]: struct.Device.html#method.get_totp_code
    pub user_password: bool,
}

#[derive(Debug)]
struct RawConfig {
    pub numlock: u8,
    pub capslock: u8,
    pub scrollock: u8,
    pub user_password: bool,
}

#[derive(Debug)]
/// A Nitrokey device without user or admin authentication.
///
/// Use [`connect`][] or [`connect_model`][] to obtain an instance.  If you
/// want to execute a command that requires user or admin authentication,
/// use [`authenticate_admin`][] or [`authenticate_user`][].
///
/// # Examples
///
/// Authentication with error handling:
///
/// ```no_run
/// use nitrokey::{UnauthenticatedDevice, UserAuthenticatedDevice};
/// # use nitrokey::CommandError;
///
/// fn perform_user_task(device: &UserAuthenticatedDevice) {}
/// fn perform_other_task(device: &UnauthenticatedDevice) {}
///
/// # fn try_main() -> Result<(), CommandError> {
/// let device = nitrokey::connect()?;
/// let device = match device.authenticate_user("123456") {
///     Ok(user) => {
///         perform_user_task(&user);
///         user.device()
///     },
///     Err((device, err)) => {
///         println!("Could not authenticate as user: {:?}", err);
///         device
///     },
/// };
/// perform_other_task(&device);
/// #     Ok(())
/// # }
/// ```
///
/// [`authenticate_admin`]: #method.authenticate_admin
/// [`authenticate_user`]: #method.authenticate_user
/// [`connect`]: fn.connect.html
/// [`connect_model`]: fn.connect_model.html
pub struct UnauthenticatedDevice {}

/// A Nitrokey device with user authentication.
///
/// To obtain an instance of this struct, use the [`authenticate_user`][]
/// method on an [`UnauthenticatedDevice`][].  To get back to an
/// unauthenticated device, use the [`device`][] method.
///
/// [`authenticate_admin`]: struct.UnauthenticatedDevice#method.authenticate_admin
/// [`device`]: #method.device
/// [`UnauthenticatedDevice`]: struct.UnauthenticatedDevice.html
pub struct UserAuthenticatedDevice {
    device: UnauthenticatedDevice,
    temp_password: Vec<u8>,
}

/// A Nitrokey device with admin authentication.
///
/// To obtain an instance of this struct, use the [`authenticate_admin`][]
/// method on an [`UnauthenticatedDevice`][].  To get back to an
/// unauthenticated device, use the [`device`][] method.
///
/// [`authenticate_admin`]: struct.UnauthenticatedDevice#method.authenticate_admin
/// [`device`]: #method.device
/// [`UnauthenticatedDevice`]: struct.UnauthenticatedDevice.html
pub struct AdminAuthenticatedDevice {
    device: UnauthenticatedDevice,
    temp_password: Vec<u8>,
}

/// The configuration for an OTP slot.
#[derive(Debug)]
pub struct OtpSlotData {
    /// The number of the slot – must be less than three for HOTP and less than
    /// 15 for TOTP.
    pub number: u8,
    /// The name of the slot – must not be empty.
    pub name: String,
    /// The secret for the slot.
    pub secret: String,
    /// The OTP generation mode.
    pub mode: OtpMode,
    /// If true, press the enter key after sending an OTP code using double-pressed
    /// numlock, capslock or scrolllock.
    pub use_enter: bool,
    /// Set the token ID [OATH Token Identifier Specification][tokspec], section
    /// “Class A”.
    ///
    /// [tokspec]: https://openauthentication.org/token-specs/
    pub token_id: Option<String>,
}

#[derive(Debug)]
struct RawOtpSlotData {
    pub number: u8,
    pub name: CString,
    pub secret: CString,
    pub mode: OtpMode,
    pub use_enter: bool,
    pub use_token_id: bool,
    pub token_id: CString,
}

static TEMPORARY_PASSWORD_LENGTH: usize = 25;

/// A Nitrokey device.
///
/// This trait provides the commands that can be executed without
/// authentication.  The only exception are the [`get_hotp_code`][] and
/// [`get_totp_code`][] methods:  It depends on the device configuration
/// ([`get_config`][]) whether these commands require user authentication
/// or not.
///
/// [`get_config`]: #method.get_config
/// [`get_hotp_code`]: #method.get_hotp_code
/// [`get_totp_code`]: #method.get_totp_code
pub trait Device {
    /// Closes the connection to this device.  This method consumes the device.
    ///
    /// # Example
    ///
    /// ```no_run
    /// use nitrokey::Device;
    /// # use nitrokey::CommandError;
    ///
    /// # fn try_main() -> Result<(), CommandError> {
    /// let device = nitrokey::connect()?;
    /// // perform tasks ...
    /// device.disconnect();
    /// #     Ok(())
    /// # }
    /// ```
    fn disconnect(self)
    where
        Self: std::marker::Sized,
    {
        unsafe {
            nitrokey_sys::NK_logout();
        }
    }

    /// Sets the time on the Nitrokey.  This command may set the time to
    /// arbitrary values.  `time` is the number of seconds since January 1st,
    /// 1970 (Unix timestamp).
    ///
    /// The time is used for TOTP generation (see [`get_totp_code`][]).
    ///
    /// # Errors
    ///
    /// - [`Timestamp`][] if the time could not be set
    ///
    /// [`get_totp_code`]: #method.get_totp_code
    /// [`Timestamp`]: enum.CommandError.html#variant.Timestamp
    // TODO: example
    fn set_time(&self, time: u64) -> CommandStatus {
        unsafe { CommandStatus::from(nitrokey_sys::NK_totp_set_time(time)) }
    }

    /// Returns the serial number of the Nitrokey device.  The serial number
    /// is the string representation of a hex number.
    ///
    /// # Example
    ///
    /// ```no_run
    /// use nitrokey::Device;
    /// # use nitrokey::CommandError;
    ///
    /// # fn try_main() -> Result<(), CommandError> {
    /// let device = nitrokey::connect()?;
    /// match device.get_serial_number() {
    ///     Ok(number) => println!("serial no: {:?}", number),
    ///     Err(err) => println!("Could not get serial number: {:?}", err),
    /// };
    /// #     Ok(())
    /// # }
    /// ```
    fn get_serial_number(&self) -> Result<String, CommandError> {
        unsafe { result_from_string(nitrokey_sys::NK_device_serial_number()) }
    }

    /// Returns the name of the given HOTP slot.
    ///
    /// # Errors
    ///
    /// - [`SlotNotProgrammed`][] if the given slot is not configured
    /// - [`WrongSlot`][] if there is no slot with the given number
    ///
    /// # Example
    ///
    /// ```no_run
    /// use nitrokey::{CommandError, Device};
    ///
    /// # fn try_main() -> Result<(), CommandError> {
    /// let device = nitrokey::connect()?;
    /// match device.get_hotp_slot_name(1) {
    ///     Ok(name) => println!("HOTP slot 1: {:?}", name),
    ///     Err(CommandError::SlotNotProgrammed) => println!("HOTP slot 1 not programmed"),
    ///     Err(err) => println!("Could not get slot name: {:?}", err),
    /// };
    /// #     Ok(())
    /// # }
    /// ```
    ///
    /// [`SlotNotProgrammed`]: enum.CommandError.html#variant.SlotNotProgrammed
    /// [`WrongSlot`]: enum.CommandError.html#variant.WrongSlot
    fn get_hotp_slot_name(&self, slot: u8) -> Result<String, CommandError> {
        unsafe { result_from_string(nitrokey_sys::NK_get_hotp_slot_name(slot)) }
    }

    /// Returns the name of the given TOTP slot.
    ///
    /// # Errors
    ///
    /// - [`SlotNotProgrammed`][] if the given slot is not configured
    /// - [`WrongSlot`][] if there is no slot with the given number
    ///
    /// # Example
    ///
    /// ```no_run
    /// use nitrokey::{CommandError, Device};
    ///
    /// # fn try_main() -> Result<(), CommandError> {
    /// let device = nitrokey::connect()?;
    /// match device.get_totp_slot_name(1) {
    ///     Ok(name) => println!("TOTP slot 1: {:?}", name),
    ///     Err(CommandError::SlotNotProgrammed) => println!("TOTP slot 1 not programmed"),
    ///     Err(err) => println!("Could not get slot name: {:?}", err),
    /// };
    /// #     Ok(())
    /// # }
    /// ```
    ///
    /// [`SlotNotProgrammed`]: enum.CommandError.html#variant.SlotNotProgrammed
    /// [`WrongSlot`]: enum.CommandError.html#variant.WrongSlot
    fn get_totp_slot_name(&self, slot: u8) -> Result<String, CommandError> {
        unsafe { result_from_string(nitrokey_sys::NK_get_totp_slot_name(slot)) }
    }

    /// Returns the number of remaining authentication attempts for the user.  The
    /// total number of available attempts is three.
    ///
    /// # Example
    ///
    /// ```no_run
    /// use nitrokey::Device;
    /// # use nitrokey::CommandError;
    ///
    /// # fn try_main() -> Result<(), CommandError> {
    /// let device = nitrokey::connect()?;
    /// let count = device.get_user_retry_count();
    /// println!("{} remaining authentication attempts (user)", count);
    /// #     Ok(())
    /// # }
    /// ```
    fn get_user_retry_count(&self) -> u8 {
        unsafe { nitrokey_sys::NK_get_user_retry_count() }
    }

    /// Returns the number of remaining authentication attempts for the admin.  The
    /// total number of available attempts is three.
    ///
    /// # Example
    ///
    /// ```no_run
    /// use nitrokey::Device;
    /// # use nitrokey::CommandError;
    ///
    /// # fn try_main() -> Result<(), CommandError> {
    /// let device = nitrokey::connect()?;
    /// let count = device.get_admin_retry_count();
    /// println!("{} remaining authentication attempts (admin)", count);
    /// #     Ok(())
    /// # }
    /// ```
    fn get_admin_retry_count(&self) -> u8 {
        unsafe { nitrokey_sys::NK_get_admin_retry_count() }
    }

    /// Returns the major part of the firmware version (should be zero).
    ///
    /// # Example
    ///
    /// ```no_run
    /// use nitrokey::Device;
    /// # use nitrokey::CommandError;
    ///
    /// # fn try_main() -> Result<(), CommandError> {
    /// let device = nitrokey::connect()?;
    /// println!(
    ///     "Firmware version: {}.{}",
    ///     device.get_major_firmware_version(),
    ///     device.get_minor_firmware_version(),
    /// );
    /// #     Ok(())
    /// # }
    /// ```
    fn get_major_firmware_version(&self) -> i32 {
        unsafe { nitrokey_sys::NK_get_major_firmware_version() }
    }

    /// Returns the minor part of the firmware version (for example 8 for
    /// version 0.8).
    ///
    /// # Example
    ///
    /// ```no_run
    /// use nitrokey::Device;
    /// # use nitrokey::CommandError;
    ///
    /// # fn try_main() -> Result<(), CommandError> {
    /// let device = nitrokey::connect()?;
    /// println!(
    ///     "Firmware version: {}.{}",
    ///     device.get_major_firmware_version(),
    ///     device.get_minor_firmware_version(),
    /// );
    /// #     Ok(())
    /// # }
    fn get_minor_firmware_version(&self) -> i32 {
        unsafe { nitrokey_sys::NK_get_minor_firmware_version() }
    }

    /// Returns the current configuration of the Nitrokey device.
    ///
    /// # Example
    ///
    /// ```no_run
    /// use nitrokey::Device;
    /// # use nitrokey::CommandError;
    ///
    /// # fn try_main() -> Result<(), CommandError> {
    /// let device = nitrokey::connect()?;
    /// let config = device.get_config()?;
    /// println!("numlock binding:          {:?}", config.numlock);
    /// println!("capslock binding:         {:?}", config.capslock);
    /// println!("scrollock binding:        {:?}", config.scrollock);
    /// println!("require password for OTP: {:?}", config.user_password);
    /// #     Ok(())
    /// # }
    /// ```
    fn get_config(&self) -> Result<Config, CommandError> {
        unsafe {
            let config_ptr = nitrokey_sys::NK_read_config();
            if config_ptr.is_null() {
                return Err(get_last_error());
            }
            let config_array_ptr = config_ptr as *const [u8; 5];
            let raw_config = RawConfig::from(*config_array_ptr);
            libc::free(config_ptr as *mut libc::c_void);
            return Ok(raw_config.into());
        }
    }

    /// Generates an HOTP code on the given slot.  This operation may require
    /// user authorization, depending on the device configuration (see
    /// [`get_config`][]).
    ///
    /// # Errors
    ///
    /// - [`NotAuthorized`][] if OTP generation requires user authentication
    /// - [`SlotNotProgrammed`][] if the given slot is not configured
    /// - [`WrongSlot`][] if there is no slot with the given number
    ///
    /// # Example
    ///
    /// ```no_run
    /// use nitrokey::Device;
    /// # use nitrokey::CommandError;
    ///
    /// # fn try_main() -> Result<(), CommandError> {
    /// let device = nitrokey::connect()?;
    /// let code = device.get_hotp_code(1)?;
    /// println!("Generated HOTP code on slot 1: {:?}", code);
    /// #     Ok(())
    /// # }
    /// ```
    ///
    /// [`get_config`]: #method.get_config
    /// [`NotAuthorized`]: enum.CommandError.html#variant.NotAuthorized
    /// [`SlotNotProgrammed`]: enum.CommandError.html#variant.SlotNotProgrammed
    /// [`WrongSlot`]: enum.CommandError.html#variant.WrongSlot
    fn get_hotp_code(&self, slot: u8) -> Result<String, CommandError> {
        unsafe {
            return result_from_string(nitrokey_sys::NK_get_hotp_code(slot));
        }
    }

    /// Generates a TOTP code on the given slot.  This operation may require
    /// user authorization, depending on the device configuration (see
    /// [`get_config`][]).
    ///
    /// To make sure that the Nitrokey’s time is in sync, consider calling
    /// [`set_time`][] before calling this method.
    ///
    /// # Errors
    ///
    /// - [`NotAuthorized`][] if OTP generation requires user authentication
    /// - [`SlotNotProgrammed`][] if the given slot is not configured
    /// - [`WrongSlot`][] if there is no slot with the given number
    ///
    /// # Example
    ///
    /// ```no_run
    /// use nitrokey::Device;
    /// # use nitrokey::CommandError;
    ///
    /// # fn try_main() -> Result<(), CommandError> {
    /// let device = nitrokey::connect()?;
    /// let code = device.get_totp_code(1)?;
    /// println!("Generated TOTP code on slot 1: {:?}", code);
    /// #     Ok(())
    /// # }
    /// ```
    ///
    /// [`set_time`]: #method.set_time
    /// [`get_config`]: #method.get_config
    /// [`NotAuthorized`]: enum.CommandError.html#variant.NotAuthorized
    /// [`SlotNotProgrammed`]: enum.CommandError.html#variant.SlotNotProgrammed
    /// [`WrongSlot`]: enum.CommandError.html#variant.WrongSlot
    fn get_totp_code(&self, slot: u8) -> Result<String, CommandError> {
        unsafe {
            return result_from_string(nitrokey_sys::NK_get_totp_code(slot, 0, 0, 0));
        }
    }
}

trait AuthenticatedDevice {
    fn new(device: UnauthenticatedDevice, temp_password: Vec<u8>) -> Self;
}

/// Connects to a Nitrokey device.  This method can be used to connect to any
/// connected device, both a Nitrokey Pro and a Nitrokey Storage.
///
/// # Example
///
/// ```
/// use nitrokey::UnauthenticatedDevice;
///
/// fn do_something(device: UnauthenticatedDevice) {}
///
/// match nitrokey::connect() {
///     Ok(device) => do_something(device),
///     Err(err) => println!("Could not connect to a Nitrokey: {:?}", err),
/// }
/// ```
pub fn connect() -> Result<UnauthenticatedDevice, CommandError> {
    unsafe {
        match nitrokey_sys::NK_login_auto() {
            1 => Ok(UnauthenticatedDevice {}),
            _ => Err(CommandError::Unknown),
        }
    }
}

/// Connects to a Nitrokey device of the given model.
///
/// # Example
///
/// ```
/// use nitrokey::{Model, UnauthenticatedDevice};
///
/// fn do_something(device: UnauthenticatedDevice) {}
///
/// match nitrokey::connect_model(Model::Pro) {
///     Ok(device) => do_something(device),
///     Err(err) => println!("Could not connect to a Nitrokey Pro: {:?}", err),
/// }
/// ```
pub fn connect_model(model: Model) -> Result<UnauthenticatedDevice, CommandError> {
    let model = match model {
        Model::Storage => nitrokey_sys::NK_device_model_NK_STORAGE,
        Model::Pro => nitrokey_sys::NK_device_model_NK_PRO,
    };
    unsafe {
        return match nitrokey_sys::NK_login_enum(model) {
            1 => Ok(UnauthenticatedDevice {}),
            rv => Err(CommandError::from(rv)),
        };
    }
}

/// Enables or disables debug output.  Calling this method with `true` is
/// equivalent to setting the log level to `Debug`; calling it with `false` is
/// equivalent to the log level `Error` (see [`set_log_level`][]).
///
/// If debug output is enabled, detailed information about the communication
/// with the Nitrokey device is printed to the standard output.
///
/// [`set_log_level`]: fn.set_log_level.html
pub fn set_debug(state: bool) {
    unsafe {
        nitrokey_sys::NK_set_debug(state);
    }
}

/// Sets the log level for libnitrokey.  All log messages are written to the
/// standard output or standard errror.
pub fn set_log_level(level: LogLevel) {
    unsafe {
        nitrokey_sys::NK_set_debug_level(level.into());
    }
}

fn config_otp_slot_to_option(value: u8) -> Option<u8> {
    if value < 3 {
        return Some(value);
    }
    None
}

fn option_to_config_otp_slot(value: Option<u8>) -> Result<u8, CommandError> {
    match value {
        Some(value) => {
            if value < 3 {
                Ok(value)
            } else {
                Err(CommandError::InvalidSlot)
            }
        }
        None => Ok(255),
    }
}

impl From<c_int> for CommandError {
    fn from(value: c_int) -> Self {
        match value {
            1 => CommandError::WrongCrc,
            2 => CommandError::WrongSlot,
            3 => CommandError::SlotNotProgrammed,
            4 => CommandError::WrongPassword,
            5 => CommandError::NotAuthorized,
            6 => CommandError::Timestamp,
            7 => CommandError::NoName,
            8 => CommandError::NotSupported,
            9 => CommandError::UnknownCommand,
            10 => CommandError::AesDecryptionFailed,
            _ => CommandError::Unknown,
        }
    }
}

impl From<c_int> for CommandStatus {
    fn from(value: c_int) -> Self {
        match value {
            0 => CommandStatus::Success,
            other => CommandStatus::Error(CommandError::from(other)),
        }
    }
}

impl Into<i32> for LogLevel {
    fn into(self) -> i32 {
        match self {
            LogLevel::Error => 0,
            LogLevel::Warning => 1,
            LogLevel::Info => 2,
            LogLevel::DebugL1 => 3,
            LogLevel::Debug => 4,
            LogLevel::DebugL2 => 5,
        }
    }
}

fn get_last_status() -> CommandStatus {
    unsafe {
        let status = nitrokey_sys::NK_get_last_command_status();
        return CommandStatus::from(status as c_int);
    }
}

fn get_last_error() -> CommandError {
    return match get_last_status() {
        CommandStatus::Success => CommandError::Unknown,
        CommandStatus::Error(err) => err,
    };
}

fn owned_str_from_ptr(ptr: *const std::os::raw::c_char) -> String {
    unsafe {
        return CStr::from_ptr(ptr).to_string_lossy().into_owned();
    }
}

fn result_from_string(ptr: *const std::os::raw::c_char) -> Result<String, CommandError> {
    if ptr.is_null() {
        return Err(CommandError::Unknown);
    }
    unsafe {
        let s = owned_str_from_ptr(ptr);
        libc::free(ptr as *mut libc::c_void);
        if s.is_empty() {
            return Err(get_last_error());
        }
        return Ok(s);
    }
}

fn generate_password(length: usize) -> std::io::Result<Vec<u8>> {
    let mut rng = match rand::OsRng::new() {
        Ok(rng) => rng,
        Err(err) => return Err(err),
    };
    let mut data = vec![0u8; length];
    rng.fill_bytes(&mut data[..]);
    return Ok(data);
}

impl OtpSlotData {
    /// Constructs a new instance of this struct.
    pub fn new(number: u8, name: &str, secret: &str, mode: OtpMode) -> OtpSlotData {
        OtpSlotData {
            number,
            name: String::from(name),
            secret: String::from(secret),
            mode,
            use_enter: false,
            token_id: None,
        }
    }
}

impl RawOtpSlotData {
    pub fn new(data: OtpSlotData) -> Result<RawOtpSlotData, CommandError> {
        let name = CString::new(data.name);
        let secret = CString::new(data.secret);
        let use_token_id = data.token_id.is_some();
        let token_id = CString::new(data.token_id.unwrap_or_else(String::new));
        if name.is_err() || secret.is_err() || token_id.is_err() {
            return Err(CommandError::InvalidString);
        }

        Ok(RawOtpSlotData {
            number: data.number,
            name: name.unwrap(),
            secret: secret.unwrap(),
            mode: data.mode,
            use_enter: data.use_enter,
            use_token_id,
            token_id: token_id.unwrap(),
        })
    }
}

impl Config {
    /// Constructs a new instance of this struct.
    pub fn new(
        numlock: Option<u8>,
        capslock: Option<u8>,
        scrollock: Option<u8>,
        user_password: bool,
    ) -> Config {
        Config {
            numlock,
            capslock,
            scrollock,
            user_password,
        }
    }
}

impl RawConfig {
    fn try_from(config: Config) -> Result<RawConfig, CommandError> {
        Ok(RawConfig {
            numlock: option_to_config_otp_slot(config.numlock)?,
            capslock: option_to_config_otp_slot(config.capslock)?,
            scrollock: option_to_config_otp_slot(config.scrollock)?,
            user_password: config.user_password,
        })
    }
}

impl From<[u8; 5]> for RawConfig {
    fn from(data: [u8; 5]) -> Self {
        RawConfig {
            numlock: data[0],
            capslock: data[1],
            scrollock: data[2],
            user_password: data[3] != 0,
        }
    }
}

impl Into<Config> for RawConfig {
    fn into(self) -> Config {
        Config {
            numlock: config_otp_slot_to_option(self.numlock),
            capslock: config_otp_slot_to_option(self.capslock),
            scrollock: config_otp_slot_to_option(self.scrollock),
            user_password: self.user_password,
        }
    }
}

impl UnauthenticatedDevice {
    fn authenticate<D, T>(
        self,
        password: &str,
        callback: T,
    ) -> Result<D, (UnauthenticatedDevice, CommandError)>
    where
        D: AuthenticatedDevice,
        T: Fn(*const i8, *const i8) -> c_int,
    {
        let temp_password = match generate_password(TEMPORARY_PASSWORD_LENGTH) {
            Ok(pw) => pw,
            Err(_) => return Err((self, CommandError::RngError)),
        };
        let password = CString::new(password);
        if password.is_err() {
            return Err((self, CommandError::InvalidString));
        }

        let pw = password.unwrap();
        let password_ptr = pw.as_ptr();
        let temp_password_ptr = temp_password.as_ptr() as *const i8;
        return match callback(password_ptr, temp_password_ptr) {
            0 => Ok(D::new(self, temp_password)),
            rv => Err((self, CommandError::from(rv))),
        };
    }

    /// Performs user authentication.  This method consumes the device.  If
    /// successful, an authenticated device is returned.  Otherwise, the
    /// current unauthenticated device and the error are returned.
    ///
    /// This method generates a random temporary password that is used for all
    /// operations that require user access.
    ///
    /// # Errors
    ///
    /// - [`InvalidString`][] if the provided user password contains a null byte
    /// - [`RngError`][] if the generation of the temporary password failed
    /// - [`WrongPassword`][] if the provided user password is wrong
    ///
    /// # Example
    ///
    /// ```no_run
    /// use nitrokey::{UnauthenticatedDevice, UserAuthenticatedDevice};
    /// # use nitrokey::CommandError;
    ///
    /// fn perform_user_task(device: &UserAuthenticatedDevice) {}
    /// fn perform_other_task(device: &UnauthenticatedDevice) {}
    ///
    /// # fn try_main() -> Result<(), CommandError> {
    /// let device = nitrokey::connect()?;
    /// let device = match device.authenticate_user("123456") {
    ///     Ok(user) => {
    ///         perform_user_task(&user);
    ///         user.device()
    ///     },
    ///     Err((device, err)) => {
    ///         println!("Could not authenticate as user: {:?}", err);
    ///         device
    ///     },
    /// };
    /// perform_other_task(&device);
    /// #     Ok(())
    /// # }
    /// ```
    ///
    /// [`InvalidString`]: enum.CommandError.html#variant.InvalidString
    /// [`RngError`]: enum.CommandError.html#variant.RngError
    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
    pub fn authenticate_user(
        self,
        password: &str,
    ) -> Result<UserAuthenticatedDevice, (UnauthenticatedDevice, CommandError)> {
        return self.authenticate(password, |password_ptr, temp_password_ptr| unsafe {
            nitrokey_sys::NK_user_authenticate(password_ptr, temp_password_ptr)
        });
    }

    /// Performs admin authentication.  This method consumes the device.  If
    /// successful, an authenticated device is returned.  Otherwise, the
    /// current unauthenticated device and the error are returned.
    ///
    /// This method generates a random temporary password that is used for all
    /// operations that require admin access.
    ///
    /// # Errors
    ///
    /// - [`InvalidString`][] if the provided admin password contains a null byte
    /// - [`RngError`][] if the generation of the temporary password failed
    /// - [`WrongPassword`][] if the provided admin password is wrong
    ///
    /// # Example
    ///
    /// ```no_run
    /// use nitrokey::{AdminAuthenticatedDevice, UnauthenticatedDevice};
    /// # use nitrokey::CommandError;
    ///
    /// fn perform_admin_task(device: &AdminAuthenticatedDevice) {}
    /// fn perform_other_task(device: &UnauthenticatedDevice) {}
    ///
    /// # fn try_main() -> Result<(), CommandError> {
    /// let device = nitrokey::connect()?;
    /// let device = match device.authenticate_admin("123456") {
    ///     Ok(admin) => {
    ///         perform_admin_task(&admin);
    ///         admin.device()
    ///     },
    ///     Err((device, err)) => {
    ///         println!("Could not authenticate as admin: {:?}", err);
    ///         device
    ///     },
    /// };
    /// perform_other_task(&device);
    /// #     Ok(())
    /// # }
    /// ```
    ///
    /// [`InvalidString`]: enum.CommandError.html#variant.InvalidString
    /// [`RngError`]: enum.CommandError.html#variant.RngError
    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
    pub fn authenticate_admin(
        self,
        password: &str,
    ) -> Result<AdminAuthenticatedDevice, (UnauthenticatedDevice, CommandError)> {
        return self.authenticate(password, |password_ptr, temp_password_ptr| unsafe {
            nitrokey_sys::NK_first_authenticate(password_ptr, temp_password_ptr)
        });
    }
}

impl Device for UnauthenticatedDevice {}

impl UserAuthenticatedDevice {
    /// Forgets the user authentication and returns an unauthenticated
    /// device.  This method consumes the authenticated device.  It does not
    /// perform any actual commands on the Nitrokey.
    pub fn device(self) -> UnauthenticatedDevice {
        self.device
    }
}

impl Device for UserAuthenticatedDevice {
    /// Generates an HOTP code on the given slot.  This operation may not
    /// require user authorization, depending on the device configuration (see
    /// [`get_config`][]).
    ///
    /// # Errors
    ///
    /// - [`SlotNotProgrammed`][] if the given slot is not configured
    /// - [`WrongSlot`][] if there is no slot with the given number
    ///
    /// # Example
    ///
    /// ```no_run
    /// use nitrokey::Device;
    /// # use nitrokey::CommandError;
    ///
    /// # fn try_main() -> Result<(), CommandError> {
    /// let device = nitrokey::connect()?;
    /// match device.authenticate_user("123456") {
    ///     Ok(user) => {
    ///         let code = user.get_hotp_code(1)?;
    ///         println!("Generated HOTP code on slot 1: {:?}", code);
    ///     },
    ///     Err(err) => println!("Could not authenticate: {:?}", err),
    /// };
    /// #     Ok(())
    /// # }
    /// ```
    ///
    /// [`get_config`]: #method.get_config
    /// [`SlotNotProgrammed`]: enum.CommandError.html#variant.SlotNotProgrammed
    /// [`WrongSlot`]: enum.CommandError.html#variant.WrongSlot
    fn get_hotp_code(&self, slot: u8) -> Result<String, CommandError> {
        unsafe {
            let temp_password_ptr = self.temp_password.as_ptr() as *const i8;
            return result_from_string(nitrokey_sys::NK_get_hotp_code_PIN(slot, temp_password_ptr));
        }
    }

    /// Generates a TOTP code on the given slot.  This operation may not
    /// require user authorization, depending on the device configuration (see
    /// [`get_config`][]).
    ///
    /// To make sure that the Nitrokey’s time is in sync, consider calling
    /// [`set_time`][] before calling this method.
    ///
    /// # Errors
    ///
    /// - [`SlotNotProgrammed`][] if the given slot is not configured
    /// - [`WrongSlot`][] if there is no slot with the given number
    ///
    /// # Example
    ///
    /// ```no_run
    /// use nitrokey::Device;
    /// # use nitrokey::CommandError;
    ///
    /// # fn try_main() -> Result<(), CommandError> {
    /// let device = nitrokey::connect()?;
    /// match device.authenticate_user("123456") {
    ///     Ok(user) => {
    ///         let code = user.get_totp_code(1)?;
    ///         println!("Generated TOTP code on slot 1: {:?}", code);
    ///     },
    ///     Err(err) => println!("Could not authenticate: {:?}", err),
    /// };
    /// #     Ok(())
    /// # }
    /// ```
    ///
    /// [`get_config`]: #method.get_config
    /// [`set_time`]: trait.Device.html#method.set_time
    /// [`SlotNotProgrammed`]: enum.CommandError.html#variant.SlotNotProgrammed
    /// [`WrongSlot`]: enum.CommandError.html#variant.WrongSlot
    fn get_totp_code(&self, slot: u8) -> Result<String, CommandError> {
        unsafe {
            let temp_password_ptr = self.temp_password.as_ptr() as *const i8;
            return result_from_string(nitrokey_sys::NK_get_totp_code_PIN(
                slot,
                0,
                0,
                0,
                temp_password_ptr,
            ));
        }
    }
}

impl AuthenticatedDevice for UserAuthenticatedDevice {
    fn new(device: UnauthenticatedDevice, temp_password: Vec<u8>) -> Self {
        UserAuthenticatedDevice {
            device,
            temp_password,
        }
    }
}

impl AdminAuthenticatedDevice {
    /// Forgets the user authentication and returns an unauthenticated
    /// device.  This method consumes the authenticated device.  It does not
    /// perform any actual commands on the Nitrokey.
    pub fn device(self) -> UnauthenticatedDevice {
        self.device
    }

    /// Writes the given configuration to the Nitrokey device.
    ///
    /// # Errors
    ///
    /// - [`InvalidSlot`][] if the provided numlock, capslock or scrolllock
    ///   slot is larger than two
    ///
    /// # Example
    ///
    /// ```no_run
    /// use nitrokey::Config;
    /// # use nitrokey::CommandError;
    ///
    /// # fn try_main() -> Result<(), CommandError> {
    /// let device = nitrokey::connect()?;
    /// let config = Config::new(None, None, None, false);
    /// match device.authenticate_admin("12345678") {
    ///     Ok(admin) => {
    ///         admin.write_config(config);
    ///         ()
    ///     },
    ///     Err((_, err)) => println!("Could not authenticate as admin: {:?}", err),
    /// };
    /// #     Ok(())
    /// # }
    /// ```
    ///
    /// [`InvalidSlot`]: enum.CommandError.html#variant.InvalidSlot
    pub fn write_config(&self, config: Config) -> CommandStatus {
        let raw_config = match RawConfig::try_from(config) {
            Ok(raw_config) => raw_config,
            Err(err) => return CommandStatus::Error(err),
        };
        unsafe {
            let rv = nitrokey_sys::NK_write_config(
                raw_config.numlock,
                raw_config.capslock,
                raw_config.scrollock,
                raw_config.user_password,
                false,
                self.temp_password.as_ptr() as *const i8,
            );
            return CommandStatus::from(rv);
        }
    }

    fn write_otp_slot<T>(&self, data: OtpSlotData, callback: T) -> CommandStatus
    where
        T: Fn(RawOtpSlotData, *const i8) -> c_int,
    {
        let raw_data = match RawOtpSlotData::new(data) {
            Ok(raw_data) => raw_data,
            Err(err) => return CommandStatus::Error(err),
        };
        let temp_password_ptr = self.temp_password.as_ptr() as *const i8;
        let rv = callback(raw_data, temp_password_ptr);
        return CommandStatus::from(rv);
    }

    /// Configure an HOTP slot with the given data and set the HOTP counter to
    /// the given value (default 0).
    ///
    /// # Errors
    ///
    /// - [`InvalidString`][] if the provided token ID contains a null byte
    /// - [`NoName`][] if the provided name is empty
    /// - [`WrongSlot`][] if there is no slot with the given number
    ///
    /// # Example
    ///
    /// ```no_run
    /// use nitrokey::{CommandStatus, Device, OtpMode, OtpSlotData};
    /// # use nitrokey::CommandError;
    ///
    /// # fn try_main() -> Result<(), (CommandError)> {
    /// let device = nitrokey::connect()?;
    /// let slot_data = OtpSlotData::new(1, "test", "01234567890123456689", OtpMode::SixDigits);
    /// match device.authenticate_admin("12345678") {
    ///     Ok(admin) => {
    ///         match admin.write_hotp_slot(slot_data, 0) {
    ///             CommandStatus::Success => println!("Successfully wrote slot."),
    ///             CommandStatus::Error(err) => println!("Could not write slot: {:?}", err),
    ///         }
    ///     },
    ///     Err((_, err)) => println!("Could not authenticate as admin: {:?}", err),
    /// }
    /// #     Ok(())
    /// # }
    /// ```
    ///
    /// [`InvalidString`]: enum.CommandError.html#variant.InvalidString
    /// [`NoName`]: enum.CommandError.html#variant.NoName
    /// [`WrongSlot`]: enum.CommandError.html#variant.WrongSlot
    pub fn write_hotp_slot(&self, data: OtpSlotData, counter: u64) -> CommandStatus {
        return self.write_otp_slot(data, |raw_data: RawOtpSlotData, temp_password_ptr| unsafe {
            nitrokey_sys::NK_write_hotp_slot(
                raw_data.number,
                raw_data.name.as_ptr(),
                raw_data.secret.as_ptr(),
                counter,
                raw_data.mode == OtpMode::EightDigits,
                raw_data.use_enter,
                raw_data.use_token_id,
                raw_data.token_id.as_ptr(),
                temp_password_ptr,
            )
        });
    }

    /// Configure a TOTP slot with the given data and set the TOTP time window
    /// to the given value (default 30).
    ///
    /// # Errors
    ///
    /// - [`InvalidString`][] if the provided token ID contains a null byte
    /// - [`NoName`][] if the provided name is empty
    /// - [`WrongSlot`][] if there is no slot with the given number
    ///
    /// # Example
    ///
    /// ```no_run
    /// use nitrokey::{CommandStatus, Device, OtpMode, OtpSlotData};
    /// # use nitrokey::CommandError;
    ///
    /// # fn try_main() -> Result<(), (CommandError)> {
    /// let device = nitrokey::connect()?;
    /// let slot_data = OtpSlotData::new(1, "test", "01234567890123456689", OtpMode::EightDigits);
    /// match device.authenticate_admin("12345678") {
    ///     Ok(admin) => {
    ///         match admin.write_totp_slot(slot_data, 30) {
    ///             CommandStatus::Success => println!("Successfully wrote slot."),
    ///             CommandStatus::Error(err) => println!("Could not write slot: {:?}", err),
    ///         }
    ///     },
    ///     Err((_, err)) => println!("Could not authenticate as admin: {:?}", err),
    /// }
    /// #     Ok(())
    /// # }
    /// ```
    ///
    /// [`InvalidString`]: enum.CommandError.html#variant.InvalidString
    /// [`NoName`]: enum.CommandError.html#variant.NoName
    /// [`WrongSlot`]: enum.CommandError.html#variant.WrongSlot
    pub fn write_totp_slot(&self, data: OtpSlotData, time_window: u16) -> CommandStatus {
        return self.write_otp_slot(data, |raw_data: RawOtpSlotData, temp_password_ptr| unsafe {
            nitrokey_sys::NK_write_totp_slot(
                raw_data.number,
                raw_data.name.as_ptr(),
                raw_data.secret.as_ptr(),
                time_window,
                raw_data.mode == OtpMode::EightDigits,
                raw_data.use_enter,
                raw_data.use_token_id,
                raw_data.token_id.as_ptr(),
                temp_password_ptr,
            )
        });
    }
}

impl Device for AdminAuthenticatedDevice {}

impl AuthenticatedDevice for AdminAuthenticatedDevice {
    fn new(device: UnauthenticatedDevice, temp_password: Vec<u8>) -> Self {
        AdminAuthenticatedDevice {
            device,
            temp_password,
        }
    }
}