use super::conversation::LibPamConversation;
use crate::constants::{ErrorCode, Result};
use crate::conv::Message;
use crate::environ::EnvironMapMut;
use crate::handle::PamShared;
use crate::libpam::environ::{LibPamEnviron, LibPamEnvironMut};
pub use crate::libpam::pam_ffi::LibPamHandle;
use crate::libpam::{memory, pam_ffi};
use crate::logging::Level;
use crate::{Conversation, EnvironMap, Flags, PamHandleApplication, PamHandleModule};
use num_enum::{IntoPrimitive, TryFromPrimitive};
use std::cell::Cell;
use std::ffi::{c_char, c_int, CString};
use std::ops::{Deref, DerefMut};
use std::ptr;

/// Owner for a PAM handle.
struct HandleWrap(*mut LibPamHandle);

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

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

/// An owned PAM handle.
pub struct OwnedLibPamHandle<'a> {
    /// The handle itself.
    handle: HandleWrap,
    /// The last return value from the handle.
    last_return: Cell<Result<()>>,
    /// If set, the Conversation that this PAM handle owns.
    ///
    /// We have to hold on to this because the PAM specification doesn't
    /// actually say what the PAM library should do with a passed-in
    /// conversation. Linux-PAM copies the contents of the `pam_conv` struct
    /// that you pass in to `pam_start`, but OpenPAM uses the pointer itself,
    /// so you have to keep it in one place.
    conversation: Option<Box<LibPamConversation<'a>>>,
}

#[derive(Debug, PartialEq)]
pub struct HandleBuilder {
    service_name: String,
    username: Option<String>,
}

impl HandleBuilder {
    /// Updates the service name.
    pub fn service_name(mut self, service_name: String) -> Self {
        self.service_name = service_name;
        self
    }
    /// Sets the username. Setting this will avoid the need for an extra
    /// round trip through the conversation and may otherwise improve
    /// the login experience.
    pub fn username(mut self, username: String) -> Self {
        self.username = Some(username);
        self
    }
    /// Builds a PAM handle and starts the transaction.
    pub fn build(self, conv: &impl Conversation) -> Result<OwnedLibPamHandle> {
        OwnedLibPamHandle::start(self.service_name, self.username, conv)
    }
}

impl OwnedLibPamHandle<'_> {
    /// Creates a builder to start a PAM transaction for the given service.
    ///
    /// The service name is what controls the steps and checks PAM goes through
    /// when authenticating a user. This corresponds to the configuration file
    /// named <code>/etc/pam.d/<var>service_name</var></code>.
    ///
    /// For more information, see the [`pam_start` man page][man], or
    /// [`pam_start` in the PAM Application Developers' Guide][adg].
    ///
    /// [man]: https://www.man7.org/linux/man-pages/man3/pam_start.3.html
    /// [adg]: https://www.chiark.greenend.org.uk/doc/libpam-doc/html/adg-interface-by-app-expected.html#adg-pam_start
    pub fn build_with_service(service_name: String) -> HandleBuilder {
        HandleBuilder { service_name, username: None }
    }

    fn start(
        service_name: String,
        username: Option<String>,
        conversation: &impl Conversation,
    ) -> Result<Self> {
        let conv = Box::new(LibPamConversation::wrap(conversation));
        let service_cstr = CString::new(service_name).map_err(|_| ErrorCode::ConversationError)?;
        let username_cstr = memory::prompt_ptr(memory::option_cstr(username.as_deref())?.as_ref());

        let mut handle: *mut LibPamHandle = ptr::null_mut();
        // SAFETY: We've set everything up properly to call `pam_start`.
        // The returned value will be a valid pointer provided the result is OK.
        let result = unsafe {
            pam_ffi::pam_start(
                service_cstr.as_ptr(),
                username_cstr,
                conv.as_ref(),
                &mut handle,
            )
        };
        ErrorCode::result_from(result)?;
        Ok(Self {
            handle: HandleWrap(handle),
            last_return: Cell::new(Ok(())),
            conversation: Some(conv),
        })
    }
}

impl PamHandleApplication for OwnedLibPamHandle<'_> {
    fn authenticate(&mut self, flags: Flags) -> Result<()> {
        let ret = unsafe { pam_ffi::pam_authenticate(self.handle.0, flags.bits() as c_int) };
        let result = ErrorCode::result_from(ret);
        self.last_return.set(result);
        result
    }

    fn account_management(&mut self, flags: Flags) -> Result<()> {
        let ret = unsafe { pam_ffi::pam_acct_mgmt(self.handle.0, flags.bits() as c_int) };
        let result = ErrorCode::result_from(ret);
        self.last_return.set(result);
        result
    }

    fn change_authtok(&mut self, flags: Flags) -> Result<()> {
        let ret = unsafe { pam_ffi::pam_chauthtok(self.handle.0, flags.bits() as c_int) };
        let result = ErrorCode::result_from(ret);
        self.last_return.set(result);
        result
    }
}

// TODO: pam_authenticate - app
//       pam_setcred - app
//       pam_acct_mgmt - app
//       pam_chauthtok - app
//       pam_open_session - app
//       pam_close_session - app
//       pam_putenv - shared
//       pam_getenv - shared
//       pam_getenvlist - shared

impl Drop for OwnedLibPamHandle<'_> {
    /// Closes the PAM session on an owned PAM handle.
    ///
    /// See the [`pam_end` manual page][man] for more information.
    ///
    /// [man]: https://www.man7.org/linux/man-pages/man3/pam_end.3.html
    fn drop(&mut self) {
        unsafe {
            pam_ffi::pam_end(
                self.handle.0,
                ErrorCode::result_to_c(self.last_return.get()),
            );
        }
    }
}

/// Macro to implement getting/setting a CStr-based item.
macro_rules! cstr_item {
    (get = $getter:ident, item = $item_type:path) => {
        fn $getter(&self) -> Result<Option<String>> {
            unsafe { self.get_cstr_item($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 log(&self, level: Level, entry: &str) {
        let entry = match CString::new(entry).or_else(|_| CString::new(dbg!(entry))) {
            Ok(cstr) => cstr,
            _ => return,
        };
        #[cfg(pam_impl = "linux-pam")]
        {
            // SAFETY: We're calling this function with a known value.
            unsafe {
                pam_ffi::pam_syslog(self, level as c_int, c"%s".as_ptr().cast(), entry.as_ptr())
            }
        }
        #[cfg(pam_impl = "openpam")]
        {
            // SAFETY: We're calling this function with a known value.
            unsafe {
                pam_ffi::openpam_log(self, level as c_int, c"%s".as_ptr().cast(), entry.as_ptr())
            }
        }
    }

    fn username(&mut self, prompt: Option<&str>) -> Result<String> {
        let prompt = memory::option_cstr(prompt)?;
        let mut output: *const c_char = ptr::null();
        let ret = unsafe {
            pam_ffi::pam_get_user(self, &mut output, memory::prompt_ptr(prompt.as_ref()))
        };
        ErrorCode::result_from(ret)?;
        unsafe { memory::copy_pam_string(output) }
            .transpose()
            .unwrap_or(Err(ErrorCode::ConversationError))
    }

    fn environ(&self) -> impl EnvironMap {
        LibPamEnviron::new(self)
    }

    fn environ_mut(&mut self) -> impl EnvironMapMut {
        LibPamEnvironMut::new(self)
    }

    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 communicate(&self, messages: &[Message]) {
        match self.conversation_item() {
            Ok(conv) => conv.communicate(messages),
            Err(e) => {
                for msg in messages {
                    msg.set_error(e)
                }
            }
        }
    }
}

impl PamHandleModule for LibPamHandle {
    fn authtok(&mut self, prompt: Option<&str>) -> Result<String> {
        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 {
            pam_ffi::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::copy_pam_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());
    }
}

impl LibPamHandle {
    /// Gets a C string item.
    ///
    /// # Safety
    ///
    /// You better be requesting an item which is a C string.
    unsafe fn get_cstr_item(&self, item_type: ItemType) -> Result<Option<String>> {
        let mut output = ptr::null();
        let ret = unsafe { pam_ffi::pam_get_item(self, item_type as c_int, &mut output) };
        ErrorCode::result_from(ret)?;
        memory::copy_pam_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 {
            pam_ffi::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(&self) -> Result<&mut LibPamConversation<'_>> {
        let output: *mut LibPamConversation = ptr::null_mut();
        let result = unsafe {
            pam_ffi::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)
    }
}

macro_rules! delegate {
    // First have the kind that save the result after delegation.
    (fn $meth:ident(&self $(, $param:ident: $typ:ty)*) -> Result<$ret:ty>) => {
        fn $meth(&self $(, $param: $typ)*) -> Result<$ret> {
            let result = self.handle.$meth($($param),*);
            self.last_return.set(split(&result));
            result
        }
    };
    (fn $meth:ident(&mut self $(, $param:ident: $typ:ty)*) -> Result<$ret:ty>) => {
        fn $meth(&mut self $(, $param: $typ)*) -> Result<$ret> {
            let result = self.handle.$meth($($param),*);
            self.last_return.set(split(&result));
            result
        }
    };
    // Then have the kind that are just raw delegates
    (fn $meth:ident(&self $(, $param:ident: $typ:ty)*) -> $ret:ty) => {
        fn $meth(&self $(, $param: $typ)*) -> $ret {
            self.handle.$meth($($param),*)
        }
    };
    (fn $meth:ident(&mut self $(, $param:ident: $typ:ty)*) -> $ret:ty) => {
        fn $meth(&mut self $(, $param: $typ)*) -> $ret {
            self.handle.$meth($($param),*)
        }
    };
    // Then have item getters / setters
    (get = $get:ident$(, set = $set:ident)?) => {
        delegate!(fn $get(&self) -> Result<Option<String>>);
        $(delegate!(set = $set);)?
    };
    (set = $set:ident) => {
        delegate!(fn $set(&mut self, value: Option<&str>) -> Result<()>);
    };
}

fn split<T>(result: &Result<T>) -> Result<()> {
    result.as_ref().map(drop).map_err(|&e| e)
}

impl PamShared for OwnedLibPamHandle<'_> {
    delegate!(fn log(&self, level: Level, entry: &str) -> ());
    delegate!(fn environ(&self) -> impl EnvironMap);
    delegate!(fn environ_mut(&mut self) -> impl EnvironMapMut);
    delegate!(fn username(&mut self, prompt: Option<&str>) -> Result<String>);
    delegate!(get = user_item, set = set_user_item);
    delegate!(get = service, set = set_service);
    delegate!(get = user_prompt, set = set_user_prompt);
    delegate!(get = tty_name, set = set_tty_name);
    delegate!(get = remote_user, set = set_remote_user);
    delegate!(get = remote_host, set = set_remote_host);
    delegate!(set = set_authtok_item);
    delegate!(set = set_old_authtok_item);
}

/// Identifies what is being gotten or set with `pam_get_item`
/// or `pam_set_item`.
#[derive(TryFromPrimitive, IntoPrimitive)]
#[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,
}