use std::ffi::{CStr, CString};
use std::os::raw::{c_char, c_int};

use libc::{c_void, free};
use rand_core::RngCore;
use rand_os::OsRng;

use crate::error::{CommandError, Error};

/// Log level for libnitrokey.
///
/// Setting the log level to a lower level enables all output from higher levels too.  Currently,
/// only the log levels `Warning`, `DebugL1`, `Debug` and `DebugL2` are actually used.
#[derive(Clone, Copy, Debug, PartialEq)]
pub enum LogLevel {
    /// Error messages.  Currently not used.
    Error,
    /// Warning messages.
    Warning,
    /// Informational messages.  Currently not used.
    Info,
    /// Basic debug messages, especially basic information on the sent and received packets.
    DebugL1,
    /// Detailed debug messages, especially detailed information on the sent and received packets.
    Debug,
    /// Very detailed debug messages, especially detailed information about the control flow for
    /// device communication (for example function entries and exits).
    DebugL2,
}

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

pub fn result_from_string(ptr: *const c_char) -> Result<String, Error> {
    if ptr.is_null() {
        return Err(CommandError::Undefined.into());
    }
    unsafe {
        let s = owned_str_from_ptr(ptr);
        free(ptr as *mut c_void);
        // An empty string can both indicate an error or be a valid return value.  In this case, we
        // have to check the last command status to decide what to return.
        if s.is_empty() {
            get_last_result().map(|_| s)
        } else {
            Ok(s)
        }
    }
}

pub fn get_command_result(value: c_int) -> Result<(), Error> {
    match value {
        0 => Ok(()),
        other => Err(CommandError::from(other).into()),
    }
}

pub fn get_last_result() -> Result<(), Error> {
    let value = unsafe { nitrokey_sys::NK_get_last_command_status() } as c_int;
    get_command_result(value)
}

pub fn get_last_error() -> Error {
    return match get_last_result() {
        Ok(()) => CommandError::Undefined.into(),
        Err(err) => err,
    };
}

pub fn generate_password(length: usize) -> Result<Vec<u8>, Error> {
    let mut rng = OsRng::new().map_err(CommandError::from)?;
    let mut data = vec![0u8; length];
    rng.fill_bytes(&mut data[..]);
    Ok(data)
}

pub fn get_cstring<T: Into<Vec<u8>>>(s: T) -> Result<CString, Error> {
    CString::new(s).or(Err(CommandError::InvalidString.into()))
}

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,
        }
    }
}