use std::cmp;
use std::marker::PhantomData;
use std::os::raw::c_char;

#[cfg(all(debug_assertions, feature = "assert_process_allocs"))]
#[global_allocator]
static A: assert_no_alloc::AllocDisabler = assert_no_alloc::AllocDisabler;

/// A Rabin fingerprint based string hash for parameter ID strings.
pub fn hash_param_id(id: &str) -> u32 {
    let mut hash: u32 = 0;
    for char in id.bytes() {
        hash = hash.wrapping_mul(31).wrapping_add(char as u32);
    }

    // In VST3 the last bit is reserved for parameters provided by the host
    // https://developer.steinberg.help/display/VST/Parameters+and+Automation
    hash &= !(1 << 31);

    hash
}

/// The equivalent of the `strlcpy()` C function. Copy `src` to `dest` as a null-terminated
/// C-string. If `dest` does not have enough capacity, add a null terminator at the end to prevent
/// buffer overflows.
pub fn strlcpy(dest: &mut [c_char], src: &str) {
    if dest.is_empty() {
        return;
    }

    let src_bytes: &[u8] = src.as_bytes();
    // NOTE: `c_char` is i8 on x86 based archs, and u8 on AArch64. There this line won't do
    //       anything.
    let src_bytes_signed: &[c_char] = unsafe { &*(src_bytes as *const [u8] as *const [c_char]) };

    // Make sure there's always room for a null terminator
    let copy_len = cmp::min(dest.len() - 1, src.len());
    dest[..copy_len].copy_from_slice(&src_bytes_signed[..copy_len]);
    dest[copy_len] = 0;
}

/// A wrapper around the entire process function, including the plugin wrapper parts. This sets up
/// `assert_no_alloc` if needed, while also making sure that things like FTZ are set up correctly if
/// the host has not already done so.
pub fn process_wrapper<T, F: FnOnce() -> T>(f: F) -> T {
    // Make sure FTZ is always enabled, even if the host doesn't do it for us
    let _ftz_guard = ScopedFtz::enable();

    cfg_if::cfg_if! {
        if #[cfg(all(debug_assertions, feature = "assert_process_allocs"))] {
            assert_no_alloc::assert_no_alloc(f)
        } else {
            f()
        }
    }
}

/// Enable the CPU's Flush To Zero flag while this object is in scope. If the flag was not already
/// set, it will be restored to its old value when this gets dropped.
struct ScopedFtz {
    /// Whether FTZ should be disabled again, i.e. if FTZ was not enabled before.
    should_disable_again: bool,
    /// We can't directly implement !Send and !Sync, but this will do the same thing. This object
    /// affects the current thread's floating point registers, so it may only be dropped on the
    /// current thread.
    _send_sync_marker: PhantomData<*const ()>,
}

impl ScopedFtz {
    fn enable() -> Self {
        // TODO: Implement this for AArch64/neon
        cfg_if::cfg_if! {
            if #[cfg(target_feature = "sse")] {
                let mode = unsafe { std::arch::x86_64::_MM_GET_FLUSH_ZERO_MODE() };
                if mode != std::arch::x86_64::_MM_FLUSH_ZERO_ON {
                    unsafe { std::arch::x86_64::_MM_SET_FLUSH_ZERO_MODE(std::arch::x86_64::_MM_FLUSH_ZERO_ON) };

                    Self {
                        should_disable_again: true,
                        _send_sync_marker: PhantomData,
                    }
                } else {
                    Self {
                        should_disable_again: false,
                        _send_sync_marker: PhantomData,
                    }
                }
            } else {
                Self {
                    should_disable_again: false,
                    _send_sync_marker: PhantomData,
                }
            }
        }
    }
}

impl Drop for ScopedFtz {
    fn drop(&mut self) {
        if self.should_disable_again {
            cfg_if::cfg_if! {
                if #[cfg(target_feature = "sse")] {
                    unsafe { std::arch::x86_64::_MM_SET_FLUSH_ZERO_MODE(std::arch::x86_64::_MM_FLUSH_ZERO_OFF) };
                }
            };
        }
    }
}

#[cfg(test)]
mod miri {
    use std::ffi::CStr;

    use super::*;

    #[test]
    fn strlcpy_normal() {
        let mut dest = [0; 256];
        strlcpy(&mut dest, "Hello, world!");

        assert_eq!(
            unsafe { CStr::from_ptr(dest.as_ptr()) }.to_str(),
            Ok("Hello, world!")
        );
    }

    #[test]
    fn strlcpy_overflow() {
        let mut dest = [0; 6];
        strlcpy(&mut dest, "Hello, world!");

        assert_eq!(
            unsafe { CStr::from_ptr(dest.as_ptr()) }.to_str(),
            Ok("Hello")
        );
    }
}