use super::conversation::LibPamConversation;
use crate::constants::{ErrorCode, InvalidEnum, Result};
use crate::conv::Message;
use crate::handle::{PamApplicationOnly, PamModuleOnly, PamShared};
use crate::pam_ffi::memory;
use crate::pam_ffi::memory::Immovable;
use crate::{Conversation, Response};
use num_derive::FromPrimitive;
use num_traits::FromPrimitive;
use std::ffi::{c_char, c_int};
use std::ops::{Deref, DerefMut};
use std::result::Result as StdResult;
use std::{mem, ptr};

/// An owned PAM handle.
#[repr(transparent)]
pub struct OwnedLibPamHandle(*mut LibPamHandle);

/// An opaque structure that a PAM handle points to.
#[repr(C)]
pub struct LibPamHandle {
    _data: (),
    _marker: Immovable,
}

impl LibPamHandle {
    /// Gets a C string item.
    ///
    /// # Safety
    ///
    /// You better be requesting an item which is a C string.
    unsafe fn get_cstr_item(&mut self, item_type: ItemType) -> Result<Option<&str>> {
        let mut output = ptr::null();
        let ret = unsafe { super::pam_get_item(self, item_type as c_int, &mut output) };
        ErrorCode::result_from(ret)?;
        memory::wrap_string(output.cast())
    }

    /// Sets a C string item.
    ///
    /// # Safety
    ///
    /// You better be setting an item which is a C string.
    unsafe fn set_cstr_item(&mut self, item_type: ItemType, data: Option<&str>) -> Result<()> {
        let data_str = memory::option_cstr(data)?;
        let ret = unsafe {
            super::pam_set_item(
                self,
                item_type as c_int,
                memory::prompt_ptr(data_str.as_ref()).cast(),
            )
        };
        ErrorCode::result_from(ret)
    }

    /// Gets the `PAM_CONV` item from the handle.
    fn conversation_item(&mut self) -> Result<&mut LibPamConversation> {
        let output: *mut LibPamConversation = ptr::null_mut();
        let result = unsafe {
            super::pam_get_item(
                self,
                ItemType::Conversation.into(),
                &mut output.cast_const().cast(),
            )
        };
        ErrorCode::result_from(result)?;
        // SAFETY: We got this result from PAM, and we're checking if it's null.
        unsafe { output.as_mut() }.ok_or(ErrorCode::ConversationError)
    }
}

impl PamApplicationOnly for OwnedLibPamHandle {
    fn close(self, status: Result<()>) -> Result<()> {
        let ret = unsafe { super::pam_end(self.0, ErrorCode::result_to_c(status)) };
        // Forget rather than dropping, since dropping also calls pam_end.
        mem::forget(self);
        ErrorCode::result_from(ret)
    }
}

impl Deref for OwnedLibPamHandle {
    type Target = LibPamHandle;
    fn deref(&self) -> &Self::Target {
        unsafe { &*self.0 }
    }
}

impl DerefMut for OwnedLibPamHandle {
    fn deref_mut(&mut self) -> &mut Self::Target {
        unsafe { &mut *self.0 }
    }
}

impl Drop for OwnedLibPamHandle {
    /// Ends the PAM session with a zero error code.
    /// You probably want to call [`close`](Self::close) instead of
    /// letting this drop by itself.
    fn drop(&mut self) {
        unsafe {
            super::pam_end(self.0, 0);
        }
    }
}

macro_rules! cstr_item {
    (get = $getter:ident, item = $item_type:path) => {
        fn $getter(&mut self) -> Result<Option<&str>> {
            unsafe { self.get_cstr_item($item_type) }
        }
    };
    (set = $setter:ident, item = $item_type:path) => {
        fn $setter(&mut self, value: Option<&str>) -> Result<()> {
            unsafe { self.set_cstr_item($item_type, value) }
        }
    };
}

impl PamShared for LibPamHandle {
    fn get_user(&mut self, prompt: Option<&str>) -> Result<&str> {
        let prompt = memory::option_cstr(prompt)?;
        let mut output: *const c_char = ptr::null();
        let ret =
            unsafe { super::pam_get_user(self, &mut output, memory::prompt_ptr(prompt.as_ref())) };
        ErrorCode::result_from(ret)?;
        unsafe { memory::wrap_string(output) }
            .transpose()
            .unwrap_or(Err(ErrorCode::ConversationError))
    }

    cstr_item!(get = user_item, item = ItemType::User);
    cstr_item!(set = set_user_item, item = ItemType::User);
    cstr_item!(get = service, item = ItemType::Service);
    cstr_item!(set = set_service, item = ItemType::Service);
    cstr_item!(get = user_prompt, item = ItemType::UserPrompt);
    cstr_item!(set = set_user_prompt, item = ItemType::UserPrompt);
    cstr_item!(get = tty_name, item = ItemType::Tty);
    cstr_item!(set = set_tty_name, item = ItemType::Tty);
    cstr_item!(get = remote_user, item = ItemType::RemoteUser);
    cstr_item!(set = set_remote_user, item = ItemType::RemoteUser);
    cstr_item!(get = remote_host, item = ItemType::RemoteHost);
    cstr_item!(set = set_remote_host, item = ItemType::RemoteHost);
    cstr_item!(set = set_authtok_item, item = ItemType::AuthTok);
    cstr_item!(set = set_old_authtok_item, item = ItemType::OldAuthTok);
}

impl Conversation for LibPamHandle {
    fn converse(&mut self, messages: &[Message]) -> Result<Vec<Response>> {
        self.conversation_item()?.converse(messages)
    }
}

impl PamModuleOnly for LibPamHandle {
    fn get_authtok(&mut self, prompt: Option<&str>) -> Result<&str> {
        let prompt = memory::option_cstr(prompt)?;
        let mut output: *const c_char = ptr::null_mut();
        // SAFETY: We're calling this with known-good values.
        let res = unsafe {
            super::pam_get_authtok(
                self,
                ItemType::AuthTok.into(),
                &mut output,
                memory::prompt_ptr(prompt.as_ref()),
            )
        };
        ErrorCode::result_from(res)?;
        // SAFETY: We got this string from PAM.
        unsafe { memory::wrap_string(output) }
            .transpose()
            .unwrap_or(Err(ErrorCode::ConversationError))
    }

    cstr_item!(get = authtok_item, item = ItemType::AuthTok);
    cstr_item!(get = old_authtok_item, item = ItemType::OldAuthTok);
}

/// Function called at the end of a PAM session that is called to clean up
/// a value previously provided to PAM in a `pam_set_data` call.
///
/// You should never call this yourself.
extern "C" fn set_data_cleanup<T>(_: *const libc::c_void, c_data: *mut libc::c_void, _: c_int) {
    unsafe {
        let _data: Box<T> = Box::from_raw(c_data.cast());
    }
}

/// Identifies what is being gotten or set with `pam_get_item`
/// or `pam_set_item`.
#[derive(FromPrimitive)]
#[repr(i32)]
#[non_exhaustive] // because C could give us anything!
pub enum ItemType {
    /// The PAM service name.
    Service = 1,
    /// The user's login name.
    User = 2,
    /// The TTY name.
    Tty = 3,
    /// The remote host (if applicable).
    RemoteHost = 4,
    /// The conversation struct (not a CStr-based item).
    Conversation = 5,
    /// The authentication token (password).
    AuthTok = 6,
    /// The old authentication token (when changing passwords).
    OldAuthTok = 7,
    /// The remote user's name.
    RemoteUser = 8,
    /// The prompt shown when requesting a username.
    UserPrompt = 9,
    /// App-supplied function to override failure delays.
    FailDelay = 10,
    /// X display name.
    XDisplay = 11,
    /// X server authentication data.
    XAuthData = 12,
    /// The type of `pam_get_authtok`.
    AuthTokType = 13,
}

impl TryFrom<c_int> for ItemType {
    type Error = InvalidEnum<Self>;
    fn try_from(value: c_int) -> StdResult<Self, Self::Error> {
        Self::from_i32(value).ok_or(value.into())
    }
}

impl From<ItemType> for c_int {
    fn from(val: ItemType) -> Self {
        val as Self
    }
}