use std::any::Any;
use std::cmp::Ordering;
use std::fmt::{self, Debug, Formatter};
use std::hash::Hash;
use std::rc::Rc;

use super::{ops, Array, Class, Dict, Function, Node};
use crate::diag::StrResult;
use crate::geom::{Angle, Color, Fractional, Length, Linear, Relative, RgbaColor};
use crate::layout::Layout;
use crate::syntax::Spanned;
use crate::util::EcoString;

/// A computational value.
#[derive(Clone)]
pub enum Value {
    /// The value that indicates the absence of a meaningful value.
    None,
    /// A value that indicates some smart default behaviour.
    Auto,
    /// A boolean: `true, false`.
    Bool(bool),
    /// An integer: `120`.
    Int(i64),
    /// A floating-point number: `1.2`, `10e-4`.
    Float(f64),
    /// A length: `12pt`, `3cm`.
    Length(Length),
    /// An angle: `1.5rad`, `90deg`.
    Angle(Angle),
    /// A relative value: `50%`.
    Relative(Relative),
    /// A combination of an absolute length and a relative value: `20% + 5cm`.
    Linear(Linear),
    /// A fractional value: `1fr`.
    Fractional(Fractional),
    /// A color value: `#f79143ff`.
    Color(Color),
    /// A string: `"string"`.
    Str(EcoString),
    /// An array of values: `(1, "hi", 12cm)`.
    Array(Array),
    /// A dictionary value: `(color: #f79143, pattern: dashed)`.
    Dict(Dict),
    /// A node value: `[*Hi* there]`.
    Node(Node),
    /// An executable function.
    Func(Function),
    /// A class of nodes.
    Class(Class),
    /// A dynamic value.
    Dyn(Dynamic),
}

impl Value {
    /// Create an inline-level node value.
    pub fn inline<T>(node: T) -> Self
    where
        T: Layout + Debug + Hash + 'static,
    {
        Self::Node(Node::inline(node))
    }

    /// Create a block-level node value.
    pub fn block<T>(node: T) -> Self
    where
        T: Layout + Debug + Hash + 'static,
    {
        Self::Node(Node::block(node))
    }

    /// The name of the stored value's type.
    pub fn type_name(&self) -> &'static str {
        match self {
            Self::None => "none",
            Self::Auto => "auto",
            Self::Bool(_) => bool::TYPE_NAME,
            Self::Int(_) => i64::TYPE_NAME,
            Self::Float(_) => f64::TYPE_NAME,
            Self::Length(_) => Length::TYPE_NAME,
            Self::Angle(_) => Angle::TYPE_NAME,
            Self::Relative(_) => Relative::TYPE_NAME,
            Self::Linear(_) => Linear::TYPE_NAME,
            Self::Fractional(_) => Fractional::TYPE_NAME,
            Self::Color(_) => Color::TYPE_NAME,
            Self::Str(_) => EcoString::TYPE_NAME,
            Self::Array(_) => Array::TYPE_NAME,
            Self::Dict(_) => Dict::TYPE_NAME,
            Self::Node(_) => Node::TYPE_NAME,
            Self::Func(_) => Function::TYPE_NAME,
            Self::Class(_) => Class::TYPE_NAME,
            Self::Dyn(v) => v.type_name(),
        }
    }

    /// Try to cast the value into a specific type.
    pub fn cast<T>(self) -> StrResult<T>
    where
        T: Cast<Value>,
    {
        T::cast(self)
    }

    /// Join the value with another value.
    pub fn join(self, rhs: Self) -> StrResult<Self> {
        ops::join(self, rhs)
    }

    /// Return the debug representation of the value.
    pub fn repr(&self) -> EcoString {
        format_eco!("{:?}", self)
    }

    /// Return the display representation of the value.
    pub fn show(self) -> Node {
        match self {
            Value::None => Node::new(),
            Value::Int(v) => Node::Text(format_eco!("{}", v)),
            Value::Float(v) => Node::Text(format_eco!("{}", v)),
            Value::Str(v) => Node::Text(v),
            Value::Node(v) => v,
            // For values which can't be shown "naturally", we print the
            // representation in monospace.
            v => Node::Text(v.repr()).monospaced(),
        }
    }
}

impl Default for Value {
    fn default() -> Self {
        Value::None
    }
}

impl Debug for Value {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        match self {
            Self::None => f.pad("none"),
            Self::Auto => f.pad("auto"),
            Self::Bool(v) => Debug::fmt(v, f),
            Self::Int(v) => Debug::fmt(v, f),
            Self::Float(v) => Debug::fmt(v, f),
            Self::Length(v) => Debug::fmt(v, f),
            Self::Angle(v) => Debug::fmt(v, f),
            Self::Relative(v) => Debug::fmt(v, f),
            Self::Linear(v) => Debug::fmt(v, f),
            Self::Fractional(v) => Debug::fmt(v, f),
            Self::Color(v) => Debug::fmt(v, f),
            Self::Str(v) => Debug::fmt(v, f),
            Self::Array(v) => Debug::fmt(v, f),
            Self::Dict(v) => Debug::fmt(v, f),
            Self::Node(_) => f.pad("<template>"),
            Self::Func(v) => Debug::fmt(v, f),
            Self::Class(v) => Debug::fmt(v, f),
            Self::Dyn(v) => Debug::fmt(v, f),
        }
    }
}

impl PartialEq for Value {
    fn eq(&self, other: &Self) -> bool {
        ops::equal(self, other)
    }
}

impl PartialOrd for Value {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        ops::compare(self, other)
    }
}

impl From<i32> for Value {
    fn from(v: i32) -> Self {
        Self::Int(v as i64)
    }
}

impl From<usize> for Value {
    fn from(v: usize) -> Self {
        Self::Int(v as i64)
    }
}

impl From<RgbaColor> for Value {
    fn from(v: RgbaColor) -> Self {
        Self::Color(v.into())
    }
}

impl From<&str> for Value {
    fn from(v: &str) -> Self {
        Self::Str(v.into())
    }
}

impl From<String> for Value {
    fn from(v: String) -> Self {
        Self::Str(v.into())
    }
}

impl From<Dynamic> for Value {
    fn from(v: Dynamic) -> Self {
        Self::Dyn(v)
    }
}

/// A dynamic value.
#[derive(Clone)]
pub struct Dynamic(Rc<dyn Bounds>);

impl Dynamic {
    /// Create a new instance from any value that satisifies the required bounds.
    pub fn new<T>(any: T) -> Self
    where
        T: Type + Debug + PartialEq + 'static,
    {
        Self(Rc::new(any))
    }

    /// Whether the wrapped type is `T`.
    pub fn is<T: 'static>(&self) -> bool {
        self.0.as_any().is::<T>()
    }

    /// Try to downcast to a reference to a specific type.
    pub fn downcast<T: 'static>(&self) -> Option<&T> {
        self.0.as_any().downcast_ref()
    }

    /// The name of the stored value's type.
    pub fn type_name(&self) -> &'static str {
        self.0.dyn_type_name()
    }
}

impl Debug for Dynamic {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        Debug::fmt(&self.0, f)
    }
}

impl PartialEq for Dynamic {
    fn eq(&self, other: &Self) -> bool {
        self.0.dyn_eq(other)
    }
}

trait Bounds: Debug + 'static {
    fn as_any(&self) -> &dyn Any;
    fn dyn_eq(&self, other: &Dynamic) -> bool;
    fn dyn_type_name(&self) -> &'static str;
}

impl<T> Bounds for T
where
    T: Type + Debug + PartialEq + 'static,
{
    fn as_any(&self) -> &dyn Any {
        self
    }

    fn dyn_eq(&self, other: &Dynamic) -> bool {
        if let Some(other) = other.downcast::<Self>() {
            self == other
        } else {
            false
        }
    }

    fn dyn_type_name(&self) -> &'static str {
        T::TYPE_NAME
    }
}

/// The type of a value.
pub trait Type {
    /// The name of the type.
    const TYPE_NAME: &'static str;
}

/// Cast from a value to a specific type.
pub trait Cast<V>: Sized {
    /// Check whether the value is castable to `Self`.
    fn is(value: &V) -> bool;

    /// Try to cast the value into an instance of `Self`.
    fn cast(value: V) -> StrResult<Self>;
}

/// Implement traits for primitives.
macro_rules! primitive {
    (
        $type:ty: $name:literal, $variant:ident
        $(, $other:ident($binding:ident) => $out:expr)*
    ) => {
        impl Type for $type {
            const TYPE_NAME: &'static str = $name;
        }

        impl Cast<Value> for $type {
            fn is(value: &Value) -> bool {
                matches!(value, Value::$variant(_) $(| Value::$other(_))*)
            }

            fn cast(value: Value) -> StrResult<Self> {
                match value {
                    Value::$variant(v) => Ok(v),
                    $(Value::$other($binding) => Ok($out),)*
                    v => Err(format!(
                        "expected {}, found {}",
                        Self::TYPE_NAME,
                        v.type_name(),
                    )),
                }
            }
        }

        impl From<$type> for Value {
            fn from(v: $type) -> Self {
                Value::$variant(v)
            }
        }
    };
}

/// Implement traits for dynamic types.
macro_rules! dynamic {
    ($type:ty: $name:literal, $($tts:tt)*) => {
        impl $crate::eval::Type for $type {
            const TYPE_NAME: &'static str = $name;
        }

        castable! {
            $type,
            Expected: <Self as $crate::eval::Type>::TYPE_NAME,
            $($tts)*
            @this: Self => this.clone(),
        }

        impl From<$type> for $crate::eval::Value {
            fn from(v: $type) -> Self {
                $crate::eval::Value::Dyn($crate::eval::Dynamic::new(v))
            }
        }
    };
}

/// Make a type castable from a value.
macro_rules! castable {
    (
        $type:ty,
        Expected: $expected:expr,
        $($pattern:pat => $out:expr,)*
        $(@$dyn_in:ident: $dyn_type:ty => $dyn_out:expr,)*
    ) => {
        impl $crate::eval::Cast<$crate::eval::Value> for $type {
            fn is(value: &Value) -> bool {
                #[allow(unused_variables)]
                match value {
                    $($pattern => true,)*
                    $crate::eval::Value::Dyn(dynamic) => {
                        false $(|| dynamic.is::<$dyn_type>())*
                    }
                    _ => false,
                }
            }

            fn cast(value: $crate::eval::Value) -> $crate::diag::StrResult<Self> {
                let found = match value {
                    $($pattern => return Ok($out),)*
                    $crate::eval::Value::Dyn(dynamic) => {
                        $(if let Some($dyn_in) = dynamic.downcast::<$dyn_type>() {
                            return Ok($dyn_out);
                        })*
                        dynamic.type_name()
                    }
                    v => v.type_name(),
                };

                Err(format!("expected {}, found {}", $expected, found))
            }
        }
    };
}

primitive! { bool: "boolean", Bool }
primitive! { i64: "integer", Int }
primitive! { f64: "float", Float, Int(v) => v as f64 }
primitive! { Length: "length", Length }
primitive! { Angle: "angle", Angle }
primitive! { Relative: "relative", Relative }
primitive! { Linear: "relative length", Linear, Length(v) => v.into(), Relative(v) => v.into() }
primitive! { Fractional: "fractional length", Fractional }
primitive! { Color: "color", Color }
primitive! { EcoString: "string", Str }
primitive! { Array: "array", Array }
primitive! { Dict: "dictionary", Dict }
primitive! { Node: "template", Node }
primitive! { Function: "function", Func }
primitive! { Class: "class", Class }

impl Cast<Value> for Value {
    fn is(_: &Value) -> bool {
        true
    }

    fn cast(value: Value) -> StrResult<Self> {
        Ok(value)
    }
}

impl<T> Cast<Spanned<Value>> for T
where
    T: Cast<Value>,
{
    fn is(value: &Spanned<Value>) -> bool {
        T::is(&value.v)
    }

    fn cast(value: Spanned<Value>) -> StrResult<Self> {
        T::cast(value.v)
    }
}

impl<T> Cast<Spanned<Value>> for Spanned<T>
where
    T: Cast<Value>,
{
    fn is(value: &Spanned<Value>) -> bool {
        T::is(&value.v)
    }

    fn cast(value: Spanned<Value>) -> StrResult<Self> {
        let span = value.span;
        T::cast(value.v).map(|t| Spanned::new(t, span))
    }
}

/// A value that can be automatically determined.
#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
pub enum Smart<T> {
    /// The value should be determined smartly based on the
    /// circumstances.
    Auto,
    /// A forced, specific value.
    Custom(T),
}

impl<T> Smart<T> {
    /// Returns the contained custom value or a provided default value.
    pub fn unwrap_or(self, default: T) -> T {
        match self {
            Self::Auto => default,
            Self::Custom(x) => x,
        }
    }
}

impl<T> Default for Smart<T> {
    fn default() -> Self {
        Self::Auto
    }
}

impl<T> Cast<Value> for Option<T>
where
    T: Cast<Value>,
{
    fn is(value: &Value) -> bool {
        matches!(value, Value::None) || T::is(value)
    }

    fn cast(value: Value) -> StrResult<Self> {
        match value {
            Value::None => Ok(None),
            v => T::cast(v).map(Some).map_err(|msg| with_alternative(msg, "none")),
        }
    }
}

impl<T> Cast<Value> for Smart<T>
where
    T: Cast<Value>,
{
    fn is(value: &Value) -> bool {
        matches!(value, Value::Auto) || T::is(value)
    }

    fn cast(value: Value) -> StrResult<Self> {
        match value {
            Value::Auto => Ok(Self::Auto),
            v => T::cast(v)
                .map(Self::Custom)
                .map_err(|msg| with_alternative(msg, "auto")),
        }
    }
}

/// Transform `expected X, found Y` into `expected X or A, found Y`.
fn with_alternative(msg: String, alt: &str) -> String {
    let mut parts = msg.split(", found ");
    if let (Some(a), Some(b)) = (parts.next(), parts.next()) {
        format!("{} or {}, found {}", a, alt, b)
    } else {
        msg
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[track_caller]
    fn test(value: impl Into<Value>, exp: &str) {
        assert_eq!(format!("{:?}", value.into()), exp);
    }

    #[test]
    fn test_value_debug() {
        // Primitives.
        test(Value::None, "none");
        test(false, "false");
        test(12i64, "12");
        test(3.14, "3.14");
        test(Length::pt(5.5), "5.5pt");
        test(Angle::deg(90.0), "90deg");
        test(Relative::one() / 2.0, "50%");
        test(Relative::new(0.3) + Length::cm(2.0), "30% + 2cm");
        test(Fractional::one() * 7.55, "7.55fr");
        test(Color::Rgba(RgbaColor::new(1, 1, 1, 0xff)), "#010101");

        // Collections.
        test("hello", r#""hello""#);
        test("\n", r#""\n""#);
        test("\\", r#""\\""#);
        test("\"", r#""\"""#);
        test(array![], "()");
        test(array![Value::None], "(none,)");
        test(array![1, 2], "(1, 2)");
        test(dict![], "(:)");
        test(dict!["one" => 1], "(one: 1)");
        test(dict!["two" => false, "one" => 1], "(one: 1, two: false)");

        // Functions.
        test(Function::new(None, |_, _| Ok(Value::None)), "<function>");
        test(
            Function::new(Some("nil".into()), |_, _| Ok(Value::None)),
            "<function nil>",
        );

        // Dynamics.
        test(Dynamic::new(1), "1");
    }
}