use alloc::vec::Vec;
use crate::elements;
use super::{
	invoke::{Invoke, Identity},
	misc::{ValueTypeBuilder, ValueTypesBuilder, OptionalValueTypeBuilder},
};

/// Signature template description
pub enum Signature {
	TypeReference(u32),
	Inline(elements::FunctionType),
}

/// Signature builder
pub struct SignatureBuilder<F=Identity> {
	callback: F,
	signature: elements::FunctionType,
}

impl SignatureBuilder {
	/// New signature builder
	pub fn new() -> Self {
		SignatureBuilder::with_callback(Identity)
	}
}

impl<F> SignatureBuilder<F> where F: Invoke<elements::FunctionType> {
	/// New builder with callback function specified
	pub fn with_callback(callback: F) -> Self {
		SignatureBuilder {
			callback: callback,
			signature: elements::FunctionType::default(),
		}
	}

	/// Add argument to signature builder
	pub fn with_param(mut self, value_type: elements::ValueType) -> Self {
		self.signature.params_mut().push(value_type);
		self
	}

	/// Add multiple arguments to signature builder
	pub fn with_params(mut self, value_types: Vec<elements::ValueType>) -> Self {
		self.signature.params_mut().extend(value_types);
		self
	}

	/// Override signature return type
	pub fn with_return_type(mut self, return_type: Option<elements::ValueType>) -> Self {
		*self.signature.return_type_mut() = return_type;
		self
	}

	/// Start build new argument
	pub fn param(self) -> ValueTypeBuilder<Self> {
		ValueTypeBuilder::with_callback(self)
	}

	/// Start build multiple arguments
	pub fn params(self) -> ValueTypesBuilder<Self> {
		ValueTypesBuilder::with_callback(self)
	}

	/// Start building return type
	pub fn return_type(self) -> OptionalValueTypeBuilder<Self> {
		OptionalValueTypeBuilder::with_callback(self)
	}

	/// Finish current builder
	pub fn build(self) -> F::Result {
		self.callback.invoke(self.signature)
	}

	/// Finish current builder returning intermediate `Signature` struct
	pub fn build_sig(self) -> Signature {
		Signature::Inline(self.signature)
	}
}

impl<F> Invoke<Vec<elements::ValueType>> for SignatureBuilder<F>
	where F: Invoke<elements::FunctionType>
{
	type Result = Self;

	fn invoke(self, args: Vec<elements::ValueType>) -> Self {
		self.with_params(args)
	}
}

impl<F> Invoke<Option<elements::ValueType>> for SignatureBuilder<F>
	where F: Invoke<elements::FunctionType>
{
	type Result = Self;

	fn invoke(self, arg: Option<elements::ValueType>) -> Self {
		self.with_return_type(arg)
	}
}

impl<F> Invoke<elements::ValueType> for SignatureBuilder<F>
	where F: Invoke<elements::FunctionType>
{
	type Result = Self;

	fn invoke(self, arg: elements::ValueType) -> Self {
		self.with_param(arg)
	}
}

/// Type (signature) reference builder (for function/import/indirect call)
pub struct TypeRefBuilder<F=Identity> {
	callback: F,
	type_ref: u32,
}

impl<F> TypeRefBuilder<F> where F: Invoke<u32> {
	/// New builder chained with specified callback
	pub fn with_callback(callback: F) -> Self {
		TypeRefBuilder {
			callback: callback,
			type_ref: 0
		}
	}

	/// Set/override of type reference
	pub fn val(mut self, val: u32) -> Self {
		self.type_ref = val;
		self
	}

	/// Finish current builder
	pub fn build(self) -> F::Result { self.callback.invoke(self.type_ref) }
}

/// Multiple signatures builder
pub struct SignaturesBuilder<F=Identity> {
	callback: F,
	section: Vec<Signature>,
}

impl SignaturesBuilder {
	/// New empty functions section builder
	pub fn new() -> Self {
		SignaturesBuilder::with_callback(Identity)
	}
}

impl<F> SignaturesBuilder<F> {
	/// New builder chained with specified callback
	pub fn with_callback(callback: F) -> Self {
		SignaturesBuilder {
			callback: callback,
			section: Vec::new(),
		}
	}

	/// Push new signature into the builder output
	pub fn with_signature(mut self, signature: Signature) -> Self {
		self.section.push(signature);
		self
	}

	/// Start building new signature with `TypeRefBuilder`
	pub fn type_ref(self) -> TypeRefBuilder<Self> {
		TypeRefBuilder::with_callback(self)
	}
}

impl<F> SignaturesBuilder<F> where F: Invoke<SignatureBindings> {
	/// Start building new signature with dedicated builder
	pub fn signature(self) -> SignatureBuilder<Self> {
		SignatureBuilder::with_callback(self)
	}
}

impl<F> Invoke<elements::FunctionType> for SignaturesBuilder<F> {
	type Result = Self;

	fn invoke(self, signature: elements::FunctionType) -> Self {
		self.with_signature(Signature::Inline(signature))
	}
}

impl<F> Invoke<u32> for SignaturesBuilder<F> {
	type Result = Self;

	fn invoke(self, type_ref: u32) -> Self {
		self.with_signature(Signature::TypeReference(type_ref))
	}
}

impl<F> SignaturesBuilder<F> where F: Invoke<elements::FunctionSection> {

	/// Finalize builder spawning element
	pub fn build(self) -> F::Result {
		let mut result = elements::FunctionSection::default();
		for f in self.section.into_iter() {
			if let Signature::TypeReference(type_ref) = f {
				result.entries_mut().push(elements::Func::new(type_ref));
			} else {
				unreachable!(); // never possible with current generics impl-s
			}
		}
		self.callback.invoke(result)
	}
}

/// Signature bindings
pub type SignatureBindings = Vec<Signature>;

impl<F> SignaturesBuilder<F> where F: Invoke<SignatureBindings> {
	/// Bind signature list
	pub fn bind(self) -> F::Result {
		self.callback.invoke(self.section)
	}
}

/// Function body (code) builder
pub struct FuncBodyBuilder<F=Identity> {
	callback: F,
	body: elements::FuncBody,
}

impl<F> FuncBodyBuilder<F> {
	/// New body (code) builder given the chain callback
	pub fn with_callback(callback: F) -> Self {
		FuncBodyBuilder {
			callback: callback,
			body: elements::FuncBody::new(Vec::new(), elements::Instructions::empty()),
		}
	}
}

impl<F> FuncBodyBuilder<F> where F: Invoke<elements::FuncBody> {
	/// Set/override entirely with FuncBody struct
	pub fn with_func(mut self, func: elements::FuncBody) -> Self {
		self.body = func;
		self
	}

	/// Extend function local list with new entries
	pub fn with_locals(mut self, locals: Vec<elements::Local>) -> Self {
		self.body.locals_mut().extend(locals);
		self
	}

	/// Set code of the function
	pub fn with_instructions(mut self, instructions: elements::Instructions) -> Self {
		*self.body.code_mut() = instructions;
		self
	}

	/// Finish current builder spawning resulting struct
	pub fn build(self) -> F::Result {
		self.callback.invoke(self.body)
	}
}

/// Function definition (extended structure to specify function entirely, incl. signature, mainness and code)
pub struct FunctionDefinition {
	/// Is this function is start function
	pub is_main: bool,
	/// Signature description
	pub signature: Signature,
	/// Body (code) of the function
	pub code: elements::FuncBody,
}

impl Default for FunctionDefinition {
	fn default() -> Self {
		FunctionDefinition {
			is_main: false,
			signature: Signature::TypeReference(0),
			code: elements::FuncBody::empty(),
		}
	}
}

/// Function definition builder
pub struct FunctionBuilder<F=Identity> {
	callback: F,
	func: FunctionDefinition,
}

impl FunctionBuilder {
	/// New function builder
	pub fn new() -> Self {
		FunctionBuilder::with_callback(Identity)
	}
}

impl<F> FunctionBuilder<F> where F: Invoke<FunctionDefinition> {
	/// New function builder with chained callback
	pub fn with_callback(callback: F) -> Self {
		FunctionBuilder {
			callback: callback,
			func: Default::default(),
		}
	}

	/// Set that this function is main entry point
	pub fn main(mut self) -> Self {
		self.func.is_main = true;
		self
	}

	/// Start signature builder of the function
	pub fn signature(self) -> SignatureBuilder<Self> {
		SignatureBuilder::with_callback(self)
	}

	/// Override current signature entirely with new one from known struct
	pub fn with_signature(mut self, signature: Signature) -> Self {
		self.func.signature = signature;
		self
	}

	/// Start code (body) builder
	pub fn body(self) -> FuncBodyBuilder<Self> {
		FuncBodyBuilder::with_callback(self)
	}

	/// Set body (code) for this function
	pub fn with_body(mut self, body: elements::FuncBody) -> Self {
		self.func.code = body;
		self
	}

	/// Finalize current builder spawning resulting struct in the callback
	pub fn build(self) -> F::Result {
		self.callback.invoke(self.func)
	}
}

impl<F> Invoke<elements::FunctionType> for FunctionBuilder<F> where F: Invoke<FunctionDefinition> {
	type Result = Self;

	fn invoke(self, signature: elements::FunctionType) -> Self {
		self.with_signature(Signature::Inline(signature))
	}
}

impl<F> Invoke<u32> for FunctionBuilder<F> where F: Invoke<FunctionDefinition> {
	type Result = Self;

	fn invoke(self, type_ref: u32) -> Self {
		self.with_signature(Signature::TypeReference(type_ref))
	}
}

impl<F> Invoke<elements::FuncBody> for FunctionBuilder<F> where F: Invoke<FunctionDefinition> {
	type Result = Self;

	fn invoke(self, body: elements::FuncBody) -> Self::Result {
		self.with_body(body)
	}
}

/// New builder of signature list
pub fn signatures() -> SignaturesBuilder {
	SignaturesBuilder::new()
}

/// New signature builder
pub fn signature() -> SignatureBuilder {
	SignatureBuilder::new()
}

/// New builder of function (signature & body)
pub fn function() -> FunctionBuilder {
	FunctionBuilder::new()
}

#[cfg(test)]
mod tests {

	use super::{signatures, function};
	use crate::elements;

	#[test]
	fn example() {
		let result = signatures()
			.type_ref().val(1).build()
			.build();

		assert_eq!(result.entries().len(), 1);

		let result = signatures()
			.signature()
				.param().i32()
				.param().i32()
				.return_type().i64()
				.build()
			.bind();

		assert_eq!(result.len(), 1);
	}

	#[test]
	fn func_example() {
		let func = function()
			.signature()
				.param().i32()
				.return_type().i32()
				.build()
			.body()
				.with_instructions(elements::Instructions::empty())
				.build()
			.build();

		assert_eq!(func.code.locals().len(), 0);
		assert_eq!(func.code.code().elements().len(), 1);
	}
}