use std::collections::HashMap;
use std::io::{BufRead, BufReader, Read, Write};
use std::marker::PhantomData;
use std::ops::{Deref, DerefMut};
use std::process::{Child, ChildStdin, ChildStdout, Command, Stdio};
use std::ptr::NonNull;
use std::sync::mpsc::{self, Receiver, Sender};
use std::sync::{Arc, Barrier};

use parking_lot::{Mutex, MutexGuard, RwLock};

use crate::{ActionTarget, LiveMod, Parameter};

/// A handle to an external livemod viewer.
///
/// This handle is used to create [`ModVar`]s and track [`StaticModVar`]s. It must be kept alive
/// for the user interface to continue running.
pub struct LiveModHandle {
    sender: Sender<Message>,
    variables: Arc<RwLock<HashMap<String, ModVarHandle>>>,
    barrier: Arc<Barrier>,
}

impl LiveModHandle {
    /// Initialise livemod with the external `livemod-gui` user interface
    pub fn new_gui() -> LiveModHandle {
        Self::new_with_ui("livemod-gui")
    }

    /// Initialise livemod with an external user interface, for which the specified command will be run.
    pub fn new_with_ui(command: &str) -> LiveModHandle {
        let mut child = Command::new(command)
            .stdin(Stdio::piped())
            .stdout(Stdio::piped())
            .spawn()
            .unwrap();
        let (sender, recv) = mpsc::channel();
        let output_sender = sender.clone();

        let stdin = child.stdin.take().unwrap();
        let stdout = child.stdout.take().unwrap();

        let child_arc1 = Arc::new(child);
        let child_arc2 = child_arc1.clone();

        let variables_arc1 = Arc::new(RwLock::new(HashMap::new()));
        let variables_arc2 = variables_arc1.clone();
        let variables_arc3 = variables_arc1.clone();

        let barrier_arc1 = Arc::new(Barrier::new(2));
        let barrier_arc2 = barrier_arc1.clone();

        std::thread::Builder::new()
            .name("livemod_input".to_owned())
            .spawn(|| {
                input_thread(stdin, recv, variables_arc2);
                drop(child_arc1);
            })
            .unwrap();
        std::thread::Builder::new()
            .name("livemod_output".to_owned())
            .spawn(|| {
                output_thread(stdout, output_sender, variables_arc3, barrier_arc2);
                drop(child_arc2);
            })
            .unwrap();

        LiveModHandle {
            sender,
            variables: variables_arc1,
            barrier: barrier_arc1,
        }
    }

    /// Track an existing [`StaticModVar`]
    pub fn track_variable<T: LiveMod + 'static>(&self, name: &str, var: &'static StaticModVar<T>) {
        let var_handle = ModVarHandle {
            var: NonNull::from(&var.value),
        };
        self.sender
            .send(Message::NewVariable(name.to_owned(), var_handle))
            .unwrap();
    }

    /// Create a variable and send it to the external viewer to be tracked.
    ///
    /// The variable will be removed from the external viewer when it is dropped.
    pub fn create_variable<T: LiveMod + 'static>(&self, name: &str, var: T) -> ModVar<T> {
        let mod_var = ModVar {
            name: name.to_owned(),
            value: Box::new(Mutex::new(var)),
            sender: self.sender.clone(),
            variables: self.variables.clone(),
        };
        let var_handle = ModVarHandle {
            var: NonNull::from(&*mod_var.value),
        };
        self.sender
            .send(Message::NewVariable(name.to_owned(), var_handle))
            .unwrap();
        //TODO: Duplicate name prevention
        mod_var
    }

    /// Create a variable and send it to the external viewer to be tracked.
    ///
    /// The variable will be removed from the external viewer when it is dropped.
    ///
    /// # Safety
    /// You must ensure the returned variable is dropped before any of the variables it references.
    pub unsafe fn create_variable_unchecked<'a, T: LiveMod + 'a>(
        &self,
        name: &str,
        var: T,
    ) -> ModVar<T> {
        let mod_var = ModVar {
            name: name.to_owned(),
            value: Box::new(Mutex::new(var)),
            sender: self.sender.clone(),
            variables: self.variables.clone(),
        };
        let var_handle = ModVarHandle {
            var: std::mem::transmute::<
                NonNull<Mutex<dyn LiveMod + 'a>>,
                NonNull<Mutex<dyn LiveMod + 'static>>,
            >(NonNull::from(&*mod_var.value)),
        };
        self.sender
            .send(Message::NewVariable(name.to_owned(), var_handle))
            .unwrap();
        //TODO: Duplicate name prevention
        mod_var
    }
}

impl Drop for LiveModHandle {
    fn drop(&mut self) {
        self.sender.send(Message::Quit).unwrap();
        self.barrier.wait();
    }
}

/// A variable tracked by an external livemod viewer
///
/// A `ModVar` cannot be created directly, and must be created using the [`LiveModHandle::create_variable`] method.
pub struct ModVar<T> {
    name: String,
    value: Box<Mutex<T>>,
    sender: Sender<Message>,
    variables: Arc<RwLock<HashMap<String, ModVarHandle>>>,
}

impl<T: LiveMod> ModVar<T> {
    /// Get an immutable reference to the value in this `ModVar`. The value will not be changed
    /// by the external viewer while this reference is held.
    pub fn lock(&self) -> ModVarGuard<T> {
        ModVarGuard(self.value.lock())
    }

    /// Get a mutable reference to the value in thie `ModVar` The value will not be changed
    /// by the external viewer while this reference is held. The value in the external viewer
    /// will be updated if and only if the `ModVarMutGuard` is dereferenced mutably.
    pub fn lock_mut(&mut self) -> ModVarMutGuard<T> {
        ModVarMutGuard(self.value.lock(), Some(UpdateMessage::new(self)))
    }
}

impl<T> Drop for ModVar<T> {
    fn drop(&mut self) {
        self.sender
            .send(Message::RemoveVariable(self.name.clone()))
            .unwrap();
        self.variables.write().remove(&self.name);
    }
}

/// A static trackable livemod variable.
pub struct StaticModVar<T> {
    value: Mutex<T>,
}

impl<T> StaticModVar<T> {
    pub const fn new(value: T) -> StaticModVar<T> {
        StaticModVar {
            value: parking_lot::const_mutex(value),
        }
    }

    /// Get an immutable reference to the value in this `ModVar`. The value will not be changed
    /// by the external viewer while this reference is held.
    pub fn lock(&self) -> ModVarGuard<T> {
        ModVarGuard(self.value.lock())
    }
}

/// An immutable lock of a [`ModVar`] or [`StaticModVar`]. Can be dereferenced to get the contained data.
pub struct ModVarGuard<'a, T>(MutexGuard<'a, T>);

impl<'a, T> Deref for ModVarGuard<'a, T> {
    type Target = T;

    fn deref(&self) -> &Self::Target {
        &*self.0
    }
}

/// A mutable lock of a [`ModVar`]. Can be dereferenced to get the contained data, and modified.
///
/// The value is updated in the external viewer if and only if this guard is dereferenced mutably.
pub struct ModVarMutGuard<'a, T>(MutexGuard<'a, T>, Option<UpdateMessage<'a>>);

impl<'a, T> Deref for ModVarMutGuard<'a, T> {
    type Target = T;

    fn deref(&self) -> &Self::Target {
        &*self.0
    }
}

impl<'a, T> DerefMut for ModVarMutGuard<'a, T> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        if let Some(msg) = self.1.take() {
            msg.send();
        }
        &mut *self.0
    }
}

struct UpdateMessage<'a> {
    name: String,
    handle: ModVarHandle,
    sender: Sender<Message>,
    _marker: PhantomData<&'a ModVarHandle>,
}

impl UpdateMessage<'_> {
    fn new<'a, T: LiveMod + 'a>(var: &'a ModVar<T>) -> UpdateMessage<'a> {
        UpdateMessage {
            name: var.name.clone(),
            handle: ModVarHandle {
                var: unsafe {
                    // SAFETY: The value lives as long as the ModVar which we are borrowing
                    //TODO: Check soundness of reference
                    std::mem::transmute::<
                        NonNull<Mutex<dyn LiveMod + 'a>>,
                        NonNull<Mutex<dyn LiveMod + 'static>>,
                    >(NonNull::from(&*var.value))
                },
            },
            sender: var.sender.clone(),
            _marker: std::marker::PhantomData,
        }
    }

    fn send(self) {
        self.sender
            .send(Message::UpdatedVariable(self.name, self.handle))
            .unwrap();
    }
}

#[derive(Clone, Copy)]
struct ModVarHandle {
    var: NonNull<Mutex<dyn LiveMod>>,
}

unsafe impl Send for ModVarHandle {}
unsafe impl Sync for ModVarHandle {}

enum Message {
    NewVariable(String, ModVarHandle),
    UpdatedVariable(String, ModVarHandle),
    RemoveVariable(String),
    UpdatedRepr(String),
    Quit,
}

struct ChildDropper {
    child: Child,
}

impl Drop for ChildDropper {
    fn drop(&mut self) {
        self.child.wait().unwrap();
    }
}

fn input_thread(
    mut input: ChildStdin,
    recv: Receiver<Message>,
    variables: Arc<RwLock<HashMap<String, ModVarHandle>>>,
) {
    while let Ok(message) = recv.recv() {
        match message {
            Message::NewVariable(name, handle) => {
                let var = unsafe { handle.var.as_ref() }.lock();
                let repr = var.repr_default(ActionTarget::This).serialize();
                let value = var.get_self(ActionTarget::This).serialize();
                writeln!(
                    input,
                    "n{};{}-{};{}-{}",
                    &name,
                    repr.as_bytes().len(),
                    repr,
                    value.as_bytes().len(),
                    value,
                )
                .unwrap();
                variables.write().insert(name, handle);
            }
            Message::UpdatedVariable(name, handle) => {
                let var = unsafe { handle.var.as_ref() }.lock();
                let value = var.get_self(ActionTarget::This).serialize();
                writeln!(input, "s{};{}-{}", &name, value.as_bytes().len(), value,).unwrap();
            }
            Message::UpdatedRepr(name) => {
                // Get the 'base' variable from our HashMap
                let var_handle =
                    unsafe { &mut *variables.read().get(&name).unwrap().var.as_ref().lock() };

                let repr = var_handle.repr_default(ActionTarget::This).serialize();

                let value = var_handle.get_self(ActionTarget::This).serialize();

                writeln!(
                    input,
                    "u{};{}-{};{}-{}",
                    name,
                    repr.as_bytes().len(),
                    repr,
                    value.as_bytes().len(),
                    value,
                )
                .unwrap();
            }
            Message::RemoveVariable(name) => {
                writeln!(input, "r{}", &name).unwrap();
            }
            Message::Quit => {
                break;
            }
        }
    }

    // Stdin is closed on drop.
}

fn output_thread(
    output: ChildStdout,
    sender: Sender<Message>,
    variables: Arc<RwLock<HashMap<String, ModVarHandle>>>,
    barrier: Arc<Barrier>,
) {
    let mut reader = BufReader::new(output);

    loop {
        let message_type = {
            let mut message_type = [0u8];
            match reader.read_exact(&mut message_type) {
                Ok(()) => message_type[0],
                Err(_) => break,
            }
        };

        match message_type {
            b's' => {
                // Data is to be changed
                let name = {
                    let mut name = Vec::new();
                    reader.read_until(b';', &mut name).unwrap();
                    name.pop(); // Remove trailing ';'
                    String::from_utf8(name).unwrap()
                };

                let namespaced_name = name.split('.').collect::<Vec<_>>();

                let value = {
                    let len = {
                        let mut len = Vec::new();
                        reader.read_until(b'-', &mut len).unwrap();
                        len.pop(); // Pop delimiter
                        String::from_utf8(len).unwrap().parse::<usize>().unwrap()
                    };

                    let mut value = vec![0u8; len];
                    reader.read_exact(&mut value).unwrap();
                    Parameter::deserialize(&mut value.into_iter()).unwrap()
                };

                // Get the 'base' variable from our HashMap
                let base = namespaced_name.first().unwrap();
                let referenced_var = unsafe {
                    &mut *match variables.read().get(*base) {
                        Some(base_handle) => base_handle,
                        None => {
                            // The variable has already been removed
                            continue;
                        }
                    }
                    .var
                    // SAFETY: Pointers are valid as long as they are in the map
                    //TODO: Convert to Arcs because there really is no need for raw pointers
                    .as_ref()
                    .lock()
                };

                // Set the variable
                if referenced_var
                    .accept(ActionTarget::from_name_and_fields(&namespaced_name), value)
                {
                    sender
                        .send(Message::UpdatedRepr(namespaced_name[0].to_owned()))
                        .unwrap();
                }
            }
            _ => {}
        }
    }

    barrier.wait();
}