//! Types used when dealing with PAM conversations.

use crate::pam_ffi::memory;
use crate::pam_ffi::memory::{CBinaryData, Immovable, NulError, TooBigError};
use std::ffi::{c_char, c_int, c_void, CStr};
use std::ops::{Deref, DerefMut};
use std::result::Result as StdResult;
use std::str::Utf8Error;
use std::{mem, ptr, slice};

#[repr(transparent)]
#[derive(Debug)]
pub struct RawTextResponse(RawResponse);

impl RawTextResponse {
    /// Allocates a new text response on the C heap.
    ///
    /// Both `self` and its internal pointer are located on the C heap.
    /// You are responsible for calling [`free`](Self::free_contents)
    /// on the pointer you get back when you're done with it.
    pub fn fill(dest: &mut RawResponse, text: impl AsRef<str>) -> StdResult<&mut Self, NulError> {
        dest.data = memory::malloc_str(text)?.cast();
        Ok(unsafe { &mut *(dest as *mut RawResponse as *mut Self) })
    }

    /// Gets the string stored in this response.
    pub fn contents(&self) -> StdResult<&str, Utf8Error> {
        // SAFETY: This data is either passed from PAM (so we are forced to
        // trust it) or was created by us in TextResponseInner::alloc.
        // In either case, it's going to be a valid null-terminated string.
        unsafe { CStr::from_ptr(self.0.data as *const c_char) }.to_str()
    }

    /// Releases memory owned by this response.
    ///
    /// # Safety
    ///
    /// You are responsible for no longer using this after calling free.
    pub unsafe fn free_contents(&mut self) {
        let data = self.0.data;
        memory::zero_c_string(data);
        libc::free(data);
        self.0.data = ptr::null_mut()
    }
}

/// A [`RawResponse`] with [`CBinaryData`] in it.
#[repr(transparent)]
#[derive(Debug)]
pub struct RawBinaryResponse(RawResponse);

impl RawBinaryResponse {
    /// Allocates a new binary response on the C heap.
    ///
    /// The `data_type` is a tag you can use for whatever.
    /// It is passed through PAM unchanged.
    ///
    /// The referenced data is copied to the C heap. We do not take ownership.
    /// You are responsible for calling [`free`](Self::free_contents)
    /// on the pointer you get back when you're done with it.
    pub fn fill<'a>(
        dest: &'a mut RawResponse,
        data: &[u8],
        data_type: u8,
    ) -> StdResult<&'a mut Self, TooBigError> {
        dest.data = CBinaryData::alloc(data, data_type)? as *mut c_void;
        Ok(unsafe {
            (dest as *mut RawResponse)
                .cast::<RawBinaryResponse>()
                .as_mut()
                .unwrap()
        })
    }

    /// Gets the binary data in this response.
    pub fn contents(&self) -> &[u8] {
        self.data().contents()
    }

    /// Gets the `data_type` tag that was embedded with the message.
    pub fn data_type(&self) -> u8 {
        self.data().data_type()
    }

    #[inline]
    fn data(&self) -> &CBinaryData {
        // SAFETY: This was either something we got from PAM (in which case
        // we trust it), or something that was created with
        // BinaryResponseInner::alloc. In both cases, it points to valid data.
        unsafe { &*(self.0.data as *const CBinaryData) }
    }

    /// Releases memory owned by this response.
    ///
    /// # Safety
    ///
    /// You are responsible for not using this after calling free.
    pub unsafe fn free_contents(&mut self) {
        let data_ref = (self.0.data as *mut CBinaryData).as_mut();
        if let Some(d) = data_ref {
            d.zero_contents()
        }
        libc::free(self.0.data);
        self.0.data = ptr::null_mut()
    }
}

/// Generic version of response data.
///
/// This has the same structure as [`RawBinaryResponse`]
/// and [`RawTextResponse`].
#[repr(C)]
#[derive(Debug)]
pub struct RawResponse {
    /// Pointer to the data returned in a response.
    /// For most responses, this will be a [`CStr`], but for responses to
    /// [`MessageStyle::BinaryPrompt`]s, this will be [`CBinaryData`]
    /// (a Linux-PAM extension).
    data: *mut c_void,
    /// Unused.
    return_code: c_int,
    _marker: Immovable,
}

/// A contiguous block of responses.
#[derive(Debug)]
#[repr(C)]
pub struct OwnedResponses {
    base: *mut RawResponse,
    count: usize,
}

impl OwnedResponses {
    /// Allocates an owned list of responses on the C heap.
    fn alloc(count: usize) -> Self {
        OwnedResponses {
            // SAFETY: We are doing allocation here.
            base: unsafe { libc::calloc(count, size_of::<RawResponse>()) } as *mut RawResponse,
            count,
        }
    }

    /// Takes ownership of a list of responses allocated on the C heap.
    ///
    /// # Safety
    ///
    /// It's up to you to make sure you pass a valid pointer.
    unsafe fn from_c_heap(base: *mut RawResponse, count: usize) -> Self {
        OwnedResponses { base, count }
    }
}

impl From<OwnedResponses> for *mut RawResponse {
    /// Converts this into a pointer to `RawResponse`.
    ///
    /// The backing data is no longer freed.
    fn from(value: OwnedResponses) -> Self {
        let ret = value.base;
        mem::forget(value);
        ret
    }
}

impl Deref for OwnedResponses {
    type Target = [RawResponse];
    fn deref(&self) -> &Self::Target {
        // SAFETY: We allocated this ourselves, or it was provided to us by PAM.
        unsafe { slice::from_raw_parts(self.base, self.count) }
    }
}

impl DerefMut for OwnedResponses {
    fn deref_mut(&mut self) -> &mut Self::Target {
        // SAFETY: We allocated this ourselves, or it was provided to us by PAM.
        unsafe { slice::from_raw_parts_mut(self.base, self.count) }
    }
}

impl Drop for OwnedResponses {
    fn drop(&mut self) {
        // SAFETY: We allocated this ourselves, or it was provided to us by PAM.
        unsafe {
            for resp in self.iter_mut() {
                libc::free(resp.data)
            }
            libc::free(self.base as *mut c_void)
        }
    }
}

#[cfg(test)]
mod tests {

    use super::{OwnedResponses, RawBinaryResponse, RawTextResponse};

    #[test]
    fn test_text_response() {
        let mut responses = OwnedResponses::alloc(2);
        let text = RawTextResponse::fill(&mut responses[0], "hello").unwrap();
        let data = text.contents().expect("valid");
        assert_eq!("hello", data);
        unsafe {
            text.free_contents();
            text.free_contents();
        }
        RawTextResponse::fill(&mut responses[1], "hell\0").expect_err("should error; contains nul");
    }

    #[test]
    fn test_binary_response() {
        let mut responses = OwnedResponses::alloc(1);
        let real_data = [1, 2, 3, 4, 5, 6, 7, 8];
        let resp = RawBinaryResponse::fill(&mut responses[0], &real_data, 7)
            .expect("alloc should succeed");
        let data = resp.contents();
        assert_eq!(&real_data, data);
        assert_eq!(7, resp.data_type());
        unsafe {
            resp.free_contents();
            resp.free_contents();
        }
    }

    #[test]
    #[ignore]
    fn test_binary_response_too_big() {
        let big_data: Vec<u8> = vec![0xFFu8; 10_000_000_000];
        let mut responses = OwnedResponses::alloc(1);
        RawBinaryResponse::fill(&mut responses[0], &big_data, 0).expect_err("this is too big!");
    }
}