use crate::ffi;
use std::convert::TryInto;
use std::fmt;
use std::io;
use std::io::prelude::*;
use std::ops::{Deref, DerefMut};
use std::ptr;

use crate::error::ErrorStack;
use crate::ffi::{EVP_MD_CTX_free, EVP_MD_CTX_new};
use crate::nid::Nid;
use crate::{cvt, cvt_p};

#[derive(Copy, Clone, PartialEq, Eq)]
pub struct MessageDigest(*const ffi::EVP_MD);

impl MessageDigest {
    /// Creates a `MessageDigest` from a raw OpenSSL pointer.
    ///
    /// # Safety
    ///
    /// The caller must ensure the pointer is valid.
    pub unsafe fn from_ptr(x: *const ffi::EVP_MD) -> Self {
        MessageDigest(x)
    }

    /// Returns the `MessageDigest` corresponding to an `Nid`.
    ///
    /// This corresponds to [`EVP_get_digestbynid`].
    ///
    /// [`EVP_get_digestbynid`]: https://www.openssl.org/docs/man1.1.0/crypto/EVP_DigestInit.html
    pub fn from_nid(type_: Nid) -> Option<MessageDigest> {
        unsafe {
            let ptr = ffi::EVP_get_digestbynid(type_.as_raw());
            if ptr.is_null() {
                None
            } else {
                Some(MessageDigest(ptr))
            }
        }
    }

    pub fn md5() -> MessageDigest {
        unsafe { MessageDigest(ffi::EVP_md5()) }
    }

    pub fn sha1() -> MessageDigest {
        unsafe { MessageDigest(ffi::EVP_sha1()) }
    }

    pub fn sha224() -> MessageDigest {
        unsafe { MessageDigest(ffi::EVP_sha224()) }
    }

    pub fn sha256() -> MessageDigest {
        unsafe { MessageDigest(ffi::EVP_sha256()) }
    }

    pub fn sha384() -> MessageDigest {
        unsafe { MessageDigest(ffi::EVP_sha384()) }
    }

    pub fn sha512() -> MessageDigest {
        unsafe { MessageDigest(ffi::EVP_sha512()) }
    }

    #[allow(clippy::trivially_copy_pass_by_ref)]
    pub fn as_ptr(&self) -> *const ffi::EVP_MD {
        self.0
    }

    /// The size of the digest in bytes.
    #[allow(clippy::trivially_copy_pass_by_ref)]
    pub fn size(&self) -> usize {
        unsafe { ffi::EVP_MD_size(self.0) }
    }

    /// The name of the digest.
    #[allow(clippy::trivially_copy_pass_by_ref)]
    pub fn type_(&self) -> Nid {
        Nid::from_raw(unsafe { ffi::EVP_MD_type(self.0) })
    }
}

unsafe impl Sync for MessageDigest {}
unsafe impl Send for MessageDigest {}

#[derive(PartialEq, Copy, Clone)]
enum State {
    Reset,
    Updated,
    Finalized,
}

use self::State::*;

/// Provides message digest (hash) computation.
///
/// # Examples
///
/// Calculate a hash in one go:
///
/// ```
/// use boring::hash::{hash, MessageDigest};
///
/// let data = b"\x42\xF4\x97\xE0";
/// let spec = b"\x7c\x43\x0f\x17\x8a\xef\xdf\x14\x87\xfe\xe7\x14\x4e\x96\x41\xe2";
/// let res = hash(MessageDigest::md5(), data).unwrap();
/// assert_eq!(&*res, spec);
/// ```
///
/// Supply the input in chunks:
///
/// ```
/// use boring::hash::{Hasher, MessageDigest};
///
/// let data = [b"\x42\xF4", b"\x97\xE0"];
/// let spec = b"\x7c\x43\x0f\x17\x8a\xef\xdf\x14\x87\xfe\xe7\x14\x4e\x96\x41\xe2";
/// let mut h = Hasher::new(MessageDigest::md5()).unwrap();
/// h.update(data[0]).unwrap();
/// h.update(data[1]).unwrap();
/// let res = h.finish().unwrap();
/// assert_eq!(&*res, spec);
/// ```
///
/// # Warning
///
/// Don't actually use MD5 and SHA-1 hashes, they're not secure anymore.
///
/// Don't ever hash passwords, use the functions in the `pkcs5` module or bcrypt/scrypt instead.
///
/// For extendable output functions (XOFs, i.e. SHAKE128/SHAKE256), you must use finish_xof instead
/// of finish and provide a buf to store the hash. The hash will be as long as the buf.
pub struct Hasher {
    ctx: *mut ffi::EVP_MD_CTX,
    md: *const ffi::EVP_MD,
    type_: MessageDigest,
    state: State,
}

unsafe impl Sync for Hasher {}
unsafe impl Send for Hasher {}

impl Hasher {
    /// Creates a new `Hasher` with the specified hash type.
    pub fn new(ty: MessageDigest) -> Result<Hasher, ErrorStack> {
        ffi::init();

        let ctx = unsafe { cvt_p(EVP_MD_CTX_new())? };

        let mut h = Hasher {
            ctx,
            md: ty.as_ptr(),
            type_: ty,
            state: Finalized,
        };
        h.init()?;
        Ok(h)
    }

    fn init(&mut self) -> Result<(), ErrorStack> {
        match self.state {
            Reset => return Ok(()),
            Updated => {
                self.finish()?;
            }
            Finalized => (),
        }
        unsafe {
            cvt(ffi::EVP_DigestInit_ex(self.ctx, self.md, ptr::null_mut()))?;
        }
        self.state = Reset;
        Ok(())
    }

    /// Feeds data into the hasher.
    pub fn update(&mut self, data: &[u8]) -> Result<(), ErrorStack> {
        if self.state == Finalized {
            self.init()?;
        }
        unsafe {
            cvt(ffi::EVP_DigestUpdate(
                self.ctx,
                data.as_ptr() as *mut _,
                data.len(),
            ))?;
        }
        self.state = Updated;
        Ok(())
    }

    /// Returns the hash of the data written and resets the non-XOF hasher.
    pub fn finish(&mut self) -> Result<DigestBytes, ErrorStack> {
        if self.state == Finalized {
            self.init()?;
        }
        unsafe {
            let mut len = ffi::EVP_MAX_MD_SIZE.try_into().unwrap();
            let mut buf = [0; ffi::EVP_MAX_MD_SIZE as usize];
            cvt(ffi::EVP_DigestFinal_ex(
                self.ctx,
                buf.as_mut_ptr(),
                &mut len,
            ))?;
            self.state = Finalized;
            Ok(DigestBytes {
                buf,
                len: len as usize,
            })
        }
    }

    /// Writes the hash of the data into the supplied buf and resets the XOF hasher.
    /// The hash will be as long as the buf.
    pub fn finish_xof(&mut self, buf: &mut [u8]) -> Result<(), ErrorStack> {
        if self.state == Finalized {
            self.init()?;
        }
        unsafe {
            cvt(ffi::EVP_DigestFinalXOF(
                self.ctx,
                buf.as_mut_ptr(),
                buf.len(),
            ))?;
            self.state = Finalized;
            Ok(())
        }
    }
}

impl Write for Hasher {
    #[inline]
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        self.update(buf)?;
        Ok(buf.len())
    }

    fn flush(&mut self) -> io::Result<()> {
        Ok(())
    }
}

impl Clone for Hasher {
    fn clone(&self) -> Hasher {
        let ctx = unsafe {
            let ctx = EVP_MD_CTX_new();
            assert!(!ctx.is_null());
            let r = ffi::EVP_MD_CTX_copy_ex(ctx, self.ctx);
            assert_eq!(r, 1);
            ctx
        };
        Hasher {
            ctx,
            md: self.md,
            type_: self.type_,
            state: self.state,
        }
    }
}

impl Drop for Hasher {
    fn drop(&mut self) {
        unsafe {
            if self.state != Finalized {
                drop(self.finish());
            }
            EVP_MD_CTX_free(self.ctx);
        }
    }
}

/// The resulting bytes of a digest.
///
/// This type derefs to a byte slice - it exists to avoid allocating memory to
/// store the digest data.
#[derive(Copy)]
pub struct DigestBytes {
    pub(crate) buf: [u8; ffi::EVP_MAX_MD_SIZE as usize],
    pub(crate) len: usize,
}

impl Clone for DigestBytes {
    #[inline]
    fn clone(&self) -> DigestBytes {
        *self
    }
}

impl Deref for DigestBytes {
    type Target = [u8];

    #[inline]
    fn deref(&self) -> &[u8] {
        &self.buf[..self.len]
    }
}

impl DerefMut for DigestBytes {
    #[inline]
    fn deref_mut(&mut self) -> &mut [u8] {
        &mut self.buf[..self.len]
    }
}

impl AsRef<[u8]> for DigestBytes {
    #[inline]
    fn as_ref(&self) -> &[u8] {
        self.deref()
    }
}

impl fmt::Debug for DigestBytes {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        fmt::Debug::fmt(&**self, fmt)
    }
}

/// Computes the hash of the `data` with the non-XOF hasher `t`.
pub fn hash(t: MessageDigest, data: &[u8]) -> Result<DigestBytes, ErrorStack> {
    let mut h = Hasher::new(t)?;
    h.update(data)?;
    h.finish()
}

/// Computes the hash of the `data` with the XOF hasher `t` and stores it in `buf`.
pub fn hash_xof(t: MessageDigest, data: &[u8], buf: &mut [u8]) -> Result<(), ErrorStack> {
    let mut h = Hasher::new(t)?;
    h.update(data)?;
    h.finish_xof(buf)
}

#[cfg(test)]
mod tests {
    use hex::{self, FromHex};
    use std::io::prelude::*;

    use super::*;

    fn hash_test(hashtype: MessageDigest, hashtest: &(&str, &str)) {
        let res = hash(hashtype, &Vec::from_hex(hashtest.0).unwrap()).unwrap();
        assert_eq!(hex::encode(res), hashtest.1);
    }

    fn hash_recycle_test(h: &mut Hasher, hashtest: &(&str, &str)) {
        h.write_all(&Vec::from_hex(hashtest.0).unwrap()).unwrap();
        let res = h.finish().unwrap();
        assert_eq!(hex::encode(res), hashtest.1);
    }

    // Test vectors from http://www.nsrl.nist.gov/testdata/
    const MD5_TESTS: [(&str, &str); 13] = [
        ("", "d41d8cd98f00b204e9800998ecf8427e"),
        ("7F", "83acb6e67e50e31db6ed341dd2de1595"),
        ("EC9C", "0b07f0d4ca797d8ac58874f887cb0b68"),
        ("FEE57A", "e0d583171eb06d56198fc0ef22173907"),
        ("42F497E0", "7c430f178aefdf1487fee7144e9641e2"),
        ("C53B777F1C", "75ef141d64cb37ec423da2d9d440c925"),
        ("89D5B576327B", "ebbaf15eb0ed784c6faa9dc32831bf33"),
        ("5D4CCE781EB190", "ce175c4b08172019f05e6b5279889f2c"),
        ("81901FE94932D7B9", "cd4d2f62b8cdb3a0cf968a735a239281"),
        ("C9FFDEE7788EFB4EC9", "e0841a231ab698db30c6c0f3f246c014"),
        ("66AC4B7EBA95E53DC10B", "a3b3cea71910d9af56742aa0bb2fe329"),
        ("A510CD18F7A56852EB0319", "577e216843dd11573574d3fb209b97d8"),
        (
            "AAED18DBE8938C19ED734A8D",
            "6f80fb775f27e0a4ce5c2f42fc72c5f1",
        ),
    ];

    #[test]
    fn test_md5() {
        for test in MD5_TESTS.iter() {
            hash_test(MessageDigest::md5(), test);
        }
    }

    #[test]
    fn test_md5_recycle() {
        let mut h = Hasher::new(MessageDigest::md5()).unwrap();
        for test in MD5_TESTS.iter() {
            hash_recycle_test(&mut h, test);
        }
    }

    #[test]
    fn test_finish_twice() {
        let mut h = Hasher::new(MessageDigest::md5()).unwrap();
        h.write_all(&Vec::from_hex(MD5_TESTS[6].0).unwrap())
            .unwrap();
        h.finish().unwrap();
        let res = h.finish().unwrap();
        let null = hash(MessageDigest::md5(), &[]).unwrap();
        assert_eq!(&*res, &*null);
    }

    #[test]
    #[allow(clippy::redundant_clone)]
    fn test_clone() {
        let i = 7;
        let inp = Vec::from_hex(MD5_TESTS[i].0).unwrap();
        assert!(inp.len() > 2);
        let p = inp.len() / 2;
        let h0 = Hasher::new(MessageDigest::md5()).unwrap();

        println!("Clone a new hasher");
        let mut h1 = h0.clone();
        h1.write_all(&inp[..p]).unwrap();
        {
            println!("Clone an updated hasher");
            let mut h2 = h1.clone();
            h2.write_all(&inp[p..]).unwrap();
            let res = h2.finish().unwrap();
            assert_eq!(hex::encode(res), MD5_TESTS[i].1);
        }
        h1.write_all(&inp[p..]).unwrap();
        let res = h1.finish().unwrap();
        assert_eq!(hex::encode(res), MD5_TESTS[i].1);

        println!("Clone a finished hasher");
        let mut h3 = h1.clone();
        h3.write_all(&Vec::from_hex(MD5_TESTS[i + 1].0).unwrap())
            .unwrap();
        let res = h3.finish().unwrap();
        assert_eq!(hex::encode(res), MD5_TESTS[i + 1].1);
    }

    #[test]
    fn test_sha1() {
        let tests = [("616263", "a9993e364706816aba3e25717850c26c9cd0d89d")];

        for test in tests.iter() {
            hash_test(MessageDigest::sha1(), test);
        }
    }

    #[test]
    fn test_sha256() {
        let tests = [(
            "616263",
            "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad",
        )];

        for test in tests.iter() {
            hash_test(MessageDigest::sha256(), test);
        }
    }

    #[test]
    fn from_nid() {
        assert_eq!(
            MessageDigest::from_nid(Nid::SHA256).unwrap().as_ptr(),
            MessageDigest::sha256().as_ptr()
        );
    }
}
