use crate::{Runtime, Scope, ScopeId, ScopeProperty};
use serde::{Deserialize, Serialize};
use std::{fmt::Debug, marker::PhantomData};

/// Creates a signal, the basic reactive primitive.
///
/// A signal is a piece of data that may change over time,
/// and notifies other code when it has changed. This is the
/// core primitive of Leptos’s reactive system.
///
/// Takes a reactive [Scope] and the initial value as arguments,
/// and returns a tuple containing a [ReadSignal] and a [WriteSignal],
/// each of which can be called as a function.
///
/// ```
/// # use leptos_reactive::*;
/// # create_scope(|cx| {
/// let (count, set_count) = create_signal(cx, 0);
///
/// // ✅ calling the getter clones and returns the value
/// assert_eq!(count(), 0);
///
/// // ✅ calling the setter sets the value
/// set_count(1);
/// assert_eq!(count(), 1);
///
/// // ❌ don't try to call the getter within the setter
/// // set_count(count() + 1);
///
/// // ✅ instead, use .update() to mutate the value in place
/// set_count.update(|count: &mut i32| *count += 1);
/// assert_eq!(count(), 2);
///
/// // ✅ you can create "derived signals" with the same Fn() -> T interface
/// let double_count = move || count() * 2; // signals are `Copy` so you can `move` them anywhere
/// set_count(0);
/// assert_eq!(double_count(), 0);
/// set_count(1);
/// assert_eq!(double_count(), 2);
/// # }).dispose();
/// #
/// ```
pub fn create_signal<T>(cx: Scope, value: T) -> (ReadSignal<T>, WriteSignal<T>) {
    let s = cx.runtime.create_signal(value);
    cx.with_scope_property(|prop| prop.push(ScopeProperty::Signal(s.0.id)));
    s
}

/// The getter for a reactive signal.
///
/// A signal is a piece of data that may change over time,
/// and notifies other code when it has changed. This is the
/// core primitive of Leptos’s reactive system.
///
/// Calling [ReadSignal::get] within an effect will cause that effect
/// to subscribe to the signal, and to re-run whenever the value of
/// the signal changes.
///
/// `ReadSignal` implements [Fn], so that `value()` and `value.get()` are identical.
///
/// `ReadSignal` is also [Copy] and `'static`, so it can very easily moved into closures
/// or copied structs.
///
/// ```
/// # use leptos_reactive::*;
/// # create_scope(|cx| {
/// let (count, set_count) = create_signal(cx, 0);
///
/// // ✅ calling the getter clones and returns the value
/// assert_eq!(count(), 0);
///
/// // ✅ calling the setter sets the value
/// set_count(1);
/// assert_eq!(count(), 1);
///
/// // ❌ don't try to call the getter within the setter
/// // set_count(count() + 1);
///
/// // ✅ instead, use .update() to mutate the value in place
/// set_count.update(|count: &mut i32| *count += 1);
/// assert_eq!(count(), 2);
///
/// // ✅ you can create "derived signals" with the same Fn() -> T interface
/// let double_count = move || count() * 2; // signals are `Copy` so you can `move` them anywhere
/// set_count(0);
/// assert_eq!(double_count(), 0);
/// set_count(1);
/// assert_eq!(double_count(), 2);
/// # }).dispose();
/// #
/// ```
#[derive(Debug, PartialEq, Eq, Hash)]
pub struct ReadSignal<T>
where
    T: 'static,
{
    pub(crate) runtime: &'static Runtime,
    pub(crate) id: SignalId,
    pub(crate) ty: PhantomData<T>,
}

impl<T> ReadSignal<T>
where
    T: 'static,
{
    /// Applies a function to the current value of the signal, and subscribes
    /// the running effect to this signal.
    ///
    /// If you want to get the value without cloning it, use [ReadSignal::with].
    /// ```
    /// # use leptos_reactive::*;
    /// # create_scope(|cx| {
    /// let (name, set_name) = create_signal(cx, "Alice".to_string());
    ///
    /// // ❌ unnecessarily clones the string
    /// let first_char = move || name().chars().next().unwrap();
    /// assert_eq!(first_char(), 'A');
    ///
    /// // ✅ gets the first char without cloning the `String`
    /// let first_char = move || name.with(|n| n.chars().next().unwrap());
    /// assert_eq!(first_char(), 'A');
    /// set_name("Bob".to_string());
    /// assert_eq!(first_char(), 'B');
    /// });
    /// ```
    pub fn with<U>(&self, f: impl FnOnce(&T) -> U) -> U {
        self.id.with(self.runtime, f)
    }

    /// Clones and returns the current value of the signal, and subscribes
    /// the running effect to this signal.
    ///
    /// If you want to get the value without cloning it, use [ReadSignal::with].
    /// (`value.get()` is equivalent to `value.with(T::clone)`.)
    /// ```
    /// # use leptos_reactive::*;
    /// # create_scope(|cx| {
    /// let (count, set_count) = create_signal(cx, 0);
    ///
    /// // calling the getter clones and returns the value
    /// assert_eq!(count(), 0);
    /// });
    /// ```
    pub fn get(&self) -> T
    where
        T: Clone,
    {
        self.id.with(self.runtime, T::clone)
    }
}

impl<T> Clone for ReadSignal<T> {
    fn clone(&self) -> Self {
        Self {
            runtime: self.runtime,
            id: self.id,
            ty: PhantomData,
        }
    }
}

impl<T> Copy for ReadSignal<T> {}

impl<T> FnOnce<()> for ReadSignal<T>
where
    T: Debug + Clone,
{
    type Output = T;

    extern "rust-call" fn call_once(self, _args: ()) -> Self::Output {
        self.get()
    }
}

impl<T> FnMut<()> for ReadSignal<T>
where
    T: Debug + Clone,
{
    extern "rust-call" fn call_mut(&mut self, _args: ()) -> Self::Output {
        self.get()
    }
}

impl<T> Fn<()> for ReadSignal<T>
where
    T: Debug + Clone,
{
    extern "rust-call" fn call(&self, _args: ()) -> Self::Output {
        self.get()
    }
}

/// The setter for a reactive signal.
///
/// A signal is a piece of data that may change over time,
/// and notifies other code when it has changed. This is the
/// core primitive of Leptos’s reactive system.
///
/// Calling [WriteSignal::update] will mutate the signal’s value in place,
/// and notify all subscribers that the signal’s value has changed.
///
/// `ReadSignal` implements [Fn], such that `set_value(new_value)` is equivalent to
/// `set_value.update(|value| *value = new_value)`.
///
/// `WriteSignal` is [Copy] and `'static`, so it can very easily moved into closures
/// or copied structs.
///
/// ```
/// # use leptos_reactive::*;
/// # create_scope(|cx| {
/// let (count, set_count) = create_signal(cx, 0);
///
/// // ✅ calling the setter sets the value
/// set_count(1);
/// assert_eq!(count(), 1);
///
/// // ❌ don't try to call the getter within the setter
/// // set_count(count() + 1);
///
/// // ✅ instead, use .update() to mutate the value in place
/// set_count.update(|count: &mut i32| *count += 1);
/// assert_eq!(count(), 2);
/// # }).dispose();
/// #
/// ```
#[derive(Debug, PartialEq, Eq, Hash)]
pub struct WriteSignal<T>
where
    T: 'static,
{
    pub(crate) runtime: &'static Runtime,
    pub(crate) id: SignalId,
    pub(crate) ty: PhantomData<T>,
}

impl<T> WriteSignal<T>
where
    T: Clone + 'static,
{
    /// Applies a function to the current value and notifies subscribers
    /// that the signal has changed.
    ///
    /// **Note:** `update()` does not auto-memoize, i.e., it will notify subscribers
    /// even if the value has not actually changed.
    /// ```
    /// # use leptos_reactive::*;
    /// # create_scope(|cx| {
    /// let (count, set_count) = create_signal(cx, 0);
    ///
    /// // notifies subscribers
    /// set_count.update(|n| *n = 1); // it's easier just to call set_count(1), though!
    /// assert_eq!(count(), 1);
    ///
    /// // you can include arbitrary logic in this update function
    /// // also notifies subscribers, even though the value hasn't changed
    /// set_count.update(|n| if *n > 3 { *n += 1 });
    /// assert_eq!(count(), 1);
    /// # }).dispose();
    /// ```
    pub fn update(&self, f: impl FnOnce(&mut T)) {
        self.id.update(self.runtime, f)
    }
}

impl<T> Clone for WriteSignal<T>
where
    T: Clone,
{
    fn clone(&self) -> Self {
        Self {
            runtime: self.runtime,
            id: self.id,
            ty: PhantomData,
        }
    }
}

impl<T> Copy for WriteSignal<T> where T: Clone {}

impl<T> FnOnce<(T,)> for WriteSignal<T>
where
    T: Clone + 'static,
{
    type Output = ();

    extern "rust-call" fn call_once(self, args: (T,)) -> Self::Output {
        self.update(move |n| *n = args.0)
    }
}

impl<T> FnMut<(T,)> for WriteSignal<T>
where
    T: Clone + 'static,
{
    extern "rust-call" fn call_mut(&mut self, args: (T,)) -> Self::Output {
        self.update(move |n| *n = args.0)
    }
}

impl<T> Fn<(T,)> for WriteSignal<T>
where
    T: Clone + 'static,
{
    extern "rust-call" fn call(&self, args: (T,)) -> Self::Output {
        self.update(move |n| *n = args.0)
    }
}

/// Creates a reactive signal with the getter and setter unified in one value.
/// You may prefer this style, or it may be easier to pass around in a context
/// or as a function argument.
/// /// ```
/// # use leptos_reactive::*;
/// # create_scope(|cx| {
/// let count = create_rw_signal(cx, 0);
///
/// // ✅ set the value
/// count.set(1);
/// assert_eq!(count(), 1);
///
/// // ❌ don't try to call the getter within the setter
/// // count.set(count.get() + 1);
///
/// // ✅ instead, use .update() to mutate the value in place
/// count.update(|count: &mut i32| *count += 1);
/// assert_eq!(count(), 2);
/// # }).dispose();
/// #
/// ```
pub fn create_rw_signal<T>(cx: Scope, value: T) -> RwSignal<T> {
    let s = cx.runtime.create_rw_signal(value);
    cx.with_scope_property(|prop| prop.push(ScopeProperty::Signal(s.id)));
    s
}

/// A signal that combines the getter and setter into one value, rather than
/// separating them into a [ReadSignal] and a [WriteSignal]. You may prefer this
/// its style, or it may be easier to pass around in a context or as a function argument.
/// ```
/// # use leptos_reactive::*;
/// # create_scope(|cx| {
/// let count = create_rw_signal(cx, 0);
///
/// // ✅ set the value
/// count.set(1);
/// assert_eq!(count(), 1);
///
/// // ❌ don't try to call the getter within the setter
/// // count.set(count.get() + 1);
///
/// // ✅ instead, use .update() to mutate the value in place
/// count.update(|count: &mut i32| *count += 1);
/// assert_eq!(count(), 2);
/// # }).dispose();
/// #
/// ```
#[derive(Copy, Clone)]
pub struct RwSignal<T>
where
    T: 'static,
{
    pub(crate) runtime: &'static Runtime,
    pub(crate) id: SignalId,
    pub(crate) ty: PhantomData<T>,
}

impl<T> RwSignal<T>
where
    T: 'static,
{
    pub fn with<U>(&self, f: impl FnOnce(&T) -> U) -> U {
        self.id.with(self.runtime, f)
    }

    pub fn get(&self) -> T
    where
        T: Clone,
    {
        self.id.with(self.runtime, T::clone)
    }

    pub fn update(&self, f: impl FnOnce(&mut T)) {
        self.id.update(self.runtime, f)
    }

    pub fn set(&self, value: T) {
        self.id.update(self.runtime, |n| *n = value)
    }
}

impl<T> FnOnce<()> for RwSignal<T>
where
    T: Debug + Clone,
{
    type Output = T;

    extern "rust-call" fn call_once(self, _args: ()) -> Self::Output {
        self.get()
    }
}

impl<T> FnMut<()> for RwSignal<T>
where
    T: Debug + Clone,
{
    extern "rust-call" fn call_mut(&mut self, _args: ()) -> Self::Output {
        self.get()
    }
}

impl<T> Fn<()> for RwSignal<T>
where
    T: Debug + Clone,
{
    extern "rust-call" fn call(&self, _args: ()) -> Self::Output {
        self.get()
    }
}

// Internals
slotmap::new_key_type! { pub struct SignalId; }

impl SignalId {
    pub(crate) fn with<T, U>(&self, runtime: &Runtime, f: impl FnOnce(&T) -> U) -> U
    where
        T: 'static,
    {
        // add subscriber
        if let Some(observer) = runtime.observer.get() {
            let mut subs = runtime.signal_subscribers.borrow_mut();
            if let Some(subs) = subs.entry(*self) {
                subs.or_default().borrow_mut().insert(observer);
            }
        }

        // get the value
        let value = {
            let signals = runtime.signals.borrow();
            signals.get(*self).cloned().unwrap_or_else(|| {
                panic!("tried to access a signal that has been disposed: {self:?}")
            })
        };
        let value = value.borrow();
        let value = value.downcast_ref::<T>().unwrap_or_else(|| {
            panic!(
                "error casting signal {:?} to type {:?}",
                self,
                std::any::type_name::<T>()
            )
        });
        f(value)
    }

    pub(crate) fn update<T>(&self, runtime: &Runtime, f: impl FnOnce(&mut T))
    where
        T: 'static,
    {
        // update the value
        {
            let value = {
                let signals = runtime.signals.borrow();
                signals.get(*self).cloned().unwrap_or_else(|| {
                    panic!("tried to access a signal that has been disposed: {self:?}")
                })
            };
            let mut value = value.borrow_mut();
            let value = value.downcast_mut::<T>().unwrap_or_else(|| {
                panic!(
                    "error casting signal {:?} to type {:?}",
                    self,
                    std::any::type_name::<T>()
                )
            });
            f(value);
        }

        // notify subscribers
        let subs = {
            let subs = runtime.signal_subscribers.borrow();
            let subs = subs.get(*self);
            subs.map(|subs| subs.borrow().clone())
        };
        if let Some(subs) = subs {
            for sub in subs {
                let effect = {
                    let effects = runtime.effects.borrow();
                    effects.get(sub).cloned()
                };
                if let Some(effect) = effect {
                    effect.borrow_mut().run(sub, runtime);
                }
            }
        }
    }
}