use std::mem::{forget, transmute};
use std::ops::{Deref, DerefMut};

use parking_lot::{
    MappedRwLockReadGuard,
    MappedRwLockWriteGuard,
    RwLock,
    RwLockReadGuard,
    RwLockWriteGuard,
};

use crate::type_name::TypeName;

#[derive(Debug, Default)]
pub struct Lock<Value>
where
    Value: TypeName,
{
    inner: RwLock<Value>,
}

impl<Value> Lock<Value>
where
    Value: TypeName,
{
    pub fn new(value: Value) -> Self
    {
        Self { inner: RwLock::new(value) }
    }

    /// Tries to a acquire a handle to the resource with read access.
    ///
    /// # Errors
    /// Returns `Err` if unavailable (A mutable handle is hold).
    pub fn read_nonblock(&self) -> Result<ReadGuard<Value>, Error>
    {
        let guard = self.inner.try_read().ok_or(Error::ReadUnavailable)?;

        tracing::trace!("Acquired lock to value of type {}", guard.type_name());

        Ok(ReadGuard { inner: guard })
    }

    /// Tries to a acquire a handle to the resource with mutable access.
    ///
    /// # Errors
    /// Returns `Err` if unavailable (A mutable or immutable handle is hold).
    pub fn write_nonblock(&self) -> Result<WriteGuard<Value>, Error>
    {
        let guard = self.inner.try_write().ok_or(Error::WriteUnavailable)?;

        tracing::trace!(
            "Acquired mutable lock to value of type {}",
            guard.type_name()
        );

        Ok(WriteGuard { inner: guard })
    }

    pub fn into_inner(self) -> Value
    {
        self.inner.into_inner()
    }
}

#[derive(Debug, thiserror::Error)]
pub enum Error
{
    #[error("Lock is unavailable for reading")]
    ReadUnavailable,

    #[error("Lock is unavailable for writing")]
    WriteUnavailable,
}

#[derive(Debug)]
pub struct ReadGuard<'guard, Value>
where
    Value: TypeName,
{
    inner: RwLockReadGuard<'guard, Value>,
}

impl<'guard, Value> ReadGuard<'guard, Value>
where
    Value: TypeName,
{
    pub fn map<NewValue>(
        self,
        func: impl FnOnce(&Value) -> &NewValue,
    ) -> MappedReadGuard<'guard, NewValue>
    where
        NewValue: TypeName,
    {
        // The 'inner' field cannot be moved out of ReadGuard in a normal way since
        // ReadGuard implements Drop
        let inner = unsafe { std::ptr::read(&self.inner) };
        forget(self);

        MappedReadGuard {
            inner: RwLockReadGuard::map(inner, func),
        }
    }

    /// Converts the `ReadGuard` to a `ReadGuard` with a possibly longer lifetime.
    ///
    /// # Safety
    /// The returned `ReadGuard` must **NOT** be used for longer than the original
    /// lifetime.
    #[must_use]
    pub unsafe fn upgrade_lifetime<'new>(self) -> ReadGuard<'new, Value>
    {
        unsafe { transmute(self) }
    }
}

impl<'guard, Value> Deref for ReadGuard<'guard, Value>
where
    Value: TypeName,
{
    type Target = Value;

    fn deref(&self) -> &Self::Target
    {
        &self.inner
    }
}

impl<'guard, Value> Drop for ReadGuard<'guard, Value>
where
    Value: TypeName,
{
    fn drop(&mut self)
    {
        tracing::trace!("Dropped lock to value of type {}", self.type_name());
    }
}

#[derive(Debug)]
pub struct MappedReadGuard<'guard, Value>
where
    Value: TypeName,
{
    inner: MappedRwLockReadGuard<'guard, Value>,
}

impl<'guard, Value> Deref for MappedReadGuard<'guard, Value>
where
    Value: TypeName,
{
    type Target = Value;

    fn deref(&self) -> &Self::Target
    {
        &self.inner
    }
}

impl<'guard, Value> Drop for MappedReadGuard<'guard, Value>
where
    Value: TypeName,
{
    fn drop(&mut self)
    {
        tracing::trace!("Dropped mapped lock to value of type {}", self.type_name());
    }
}

#[derive(Debug)]
pub struct WriteGuard<'guard, Value>
where
    Value: TypeName,
{
    inner: RwLockWriteGuard<'guard, Value>,
}

impl<'guard, Value> WriteGuard<'guard, Value>
where
    Value: TypeName,
{
    pub fn map<NewValue>(
        self,
        func: impl FnOnce(&mut Value) -> &mut NewValue,
    ) -> MappedWriteGuard<'guard, NewValue>
    where
        NewValue: TypeName,
    {
        // The 'inner' field cannot be moved out of ReadGuard in a normal way since
        // ReadGuard implements Drop
        let inner = unsafe { std::ptr::read(&self.inner) };
        forget(self);

        MappedWriteGuard {
            inner: RwLockWriteGuard::map(inner, func),
        }
    }
}

impl<'guard, Value> Deref for WriteGuard<'guard, Value>
where
    Value: TypeName,
{
    type Target = Value;

    fn deref(&self) -> &Self::Target
    {
        &self.inner
    }
}

impl<'guard, Value> DerefMut for WriteGuard<'guard, Value>
where
    Value: TypeName,
{
    fn deref_mut(&mut self) -> &mut Self::Target
    {
        &mut self.inner
    }
}

impl<'guard, Value> Drop for WriteGuard<'guard, Value>
where
    Value: TypeName,
{
    fn drop(&mut self)
    {
        tracing::trace!("Dropped mutable lock to value of type {}", self.type_name());
    }
}

#[derive(Debug)]
pub struct MappedWriteGuard<'guard, Value>
where
    Value: TypeName,
{
    inner: MappedRwLockWriteGuard<'guard, Value>,
}

impl<'guard, Value> Deref for MappedWriteGuard<'guard, Value>
where
    Value: TypeName,
{
    type Target = Value;

    fn deref(&self) -> &Self::Target
    {
        &self.inner
    }
}

impl<'guard, Value> DerefMut for MappedWriteGuard<'guard, Value>
where
    Value: TypeName,
{
    fn deref_mut(&mut self) -> &mut Self::Target
    {
        &mut self.inner
    }
}

impl<'guard, Value> Drop for MappedWriteGuard<'guard, Value>
where
    Value: TypeName,
{
    fn drop(&mut self)
    {
        tracing::trace!(
            "Dropped mapped mutable lock to value of type {}",
            self.type_name()
        );
    }
}