use {
	Error, Signature, Externals, FuncInstance, FuncRef, HostError, ImportsBuilder,
	MemoryInstance, MemoryRef, TableInstance, TableRef, ModuleImportResolver, ModuleInstance, ModuleRef,
	RuntimeValue, RuntimeArgs, Module, TableDescriptor, MemoryDescriptor, Trap,
};
use types::ValueType;
use wabt::wat2wasm;

#[derive(Debug, Clone, PartialEq)]
struct HostErrorWithCode {
	error_code: u32,
}

impl ::std::fmt::Display for HostErrorWithCode {
	fn fmt(&self, f: &mut ::std::fmt::Formatter) -> Result<(), ::std::fmt::Error> {
		write!(f, "{}", self.error_code)
	}
}

impl HostError for HostErrorWithCode {}

/// Host state for the test environment.
///
/// This struct can be used as an external function executor and
/// as imports provider. This has a drawback: this struct
/// should be provided upon an instantiation of the module.
///
/// However, this limitation can be lifted by implementing `Externals`
/// and `ModuleImportResolver` traits for different structures.
/// See `defer_providing_externals` test for details.
struct TestHost {
	memory: Option<MemoryRef>,
	instance: Option<ModuleRef>,
}

impl TestHost {
	fn new() -> TestHost {
		TestHost {
			memory: Some(MemoryInstance::alloc(1, Some(1)).unwrap()),
			instance: None,
		}
	}
}

/// sub(a: i32, b: i32) -> i32
///
/// This function just substracts one integer from another,
/// returning the subtraction result.
const SUB_FUNC_INDEX: usize = 0;

/// err(error_code: i32) -> !
///
/// This function traps upon a call.
/// The trap have a special type - HostErrorWithCode.
const ERR_FUNC_INDEX: usize = 1;

/// inc_mem(ptr: *mut u8)
///
/// Increments value at the given address in memory. This function
/// requires attached memory.
const INC_MEM_FUNC_INDEX: usize = 2;

/// get_mem(ptr: *mut u8) -> u8
///
/// Returns value at the given address in memory. This function
/// requires attached memory.
const GET_MEM_FUNC_INDEX: usize = 3;

/// recurse<T>(val: T) -> T
///
/// If called, resolves exported function named 'recursive' from the attached
/// module instance and then calls into it with the provided argument.
/// Note that this function is polymorphic over type T.
/// This function requires attached module instance.
const RECURSE_FUNC_INDEX: usize = 4;

impl Externals for TestHost {
	fn invoke_index(
		&mut self,
		index: usize,
		args: RuntimeArgs,
	) -> Result<Option<RuntimeValue>, Trap> {
		match index {
			SUB_FUNC_INDEX => {
				let a: i32 = args.nth(0);
				let b: i32 = args.nth(1);

				let result: RuntimeValue = (a - b).into();

				Ok(Some(result))
			}
			ERR_FUNC_INDEX => {
				let error_code: u32 = args.nth(0);
				let error = HostErrorWithCode { error_code };
				Err(Trap::Host(Box::new(error)))
			}
			INC_MEM_FUNC_INDEX => {
				let ptr: u32 = args.nth(0);

				let memory = self.memory.as_ref().expect(
					"Function 'inc_mem' expects attached memory",
				);
				let mut buf = [0u8; 1];
				memory.get_into(ptr, &mut buf).unwrap();
				buf[0] += 1;
				memory.set(ptr, &buf).unwrap();

				Ok(None)
			}
			GET_MEM_FUNC_INDEX => {
				let ptr: u32 = args.nth(0);

				let memory = self.memory.as_ref().expect(
					"Function 'get_mem' expects attached memory",
				);
				let mut buf = [0u8; 1];
				memory.get_into(ptr, &mut buf).unwrap();

				Ok(Some(RuntimeValue::I32(buf[0] as i32)))
			}
			RECURSE_FUNC_INDEX => {
				let val = args.nth_value_checked(0).expect("Exactly one argument expected");

				let instance = self.instance
					.as_ref()
					.expect("Function 'recurse' expects attached module instance")
					.clone();
				let result = instance
					.invoke_export("recursive", &[val.into()], self)
					.expect("Failed to call 'recursive'")
					.expect("expected to be Some");

				if val.value_type() != result.value_type() {
					return Err(Trap::Host(Box::new(HostErrorWithCode { error_code: 123 })));
				}
				Ok(Some(result))
			}
			_ => panic!("env doesn't provide function at index {}", index),
		}
	}
}

impl TestHost {
	fn check_signature(&self, index: usize, signature: &Signature) -> bool {
		if index == RECURSE_FUNC_INDEX {
			// This function requires special handling because it is polymorphic.
			if signature.params().len() != 1 {
				return false;
			}
			let param_type = signature.params()[0];
			return signature.return_type() == Some(param_type);
		}

		let (params, ret_ty): (&[ValueType], Option<ValueType>) = match index {
			SUB_FUNC_INDEX => (&[ValueType::I32, ValueType::I32], Some(ValueType::I32)),
			ERR_FUNC_INDEX => (&[ValueType::I32], None),
			INC_MEM_FUNC_INDEX => (&[ValueType::I32], None),
			GET_MEM_FUNC_INDEX => (&[ValueType::I32], Some(ValueType::I32)),
			_ => return false,
		};

		signature.params() == params && signature.return_type() == ret_ty
	}
}

impl ModuleImportResolver for TestHost {
	fn resolve_func(&self, field_name: &str, signature: &Signature) -> Result<FuncRef, Error> {
		let index = match field_name {
			"sub" => SUB_FUNC_INDEX,
			"err" => ERR_FUNC_INDEX,
			"inc_mem" => INC_MEM_FUNC_INDEX,
			"get_mem" => GET_MEM_FUNC_INDEX,
			"recurse" => RECURSE_FUNC_INDEX,
			_ => {
				return Err(Error::Instantiation(
					format!("Export {} not found", field_name),
				))
			}
		};

		if !self.check_signature(index, signature) {
			return Err(Error::Instantiation(format!(
				"Export `{}` doesnt match expected type {:?}",
				field_name,
				signature
			)));
		}

		Ok(FuncInstance::alloc_host(signature.clone(), index))
	}

	fn resolve_memory(
		&self,
		field_name: &str,
		_memory_type: &MemoryDescriptor,
	) -> Result<MemoryRef, Error> {
		Err(Error::Instantiation(
			format!("Export {} not found", field_name),
		))
	}
}

fn parse_wat(source: &str) -> Module {
	let wasm_binary = wat2wasm(source).expect("Failed to parse wat source");
	Module::from_buffer(wasm_binary).expect("Failed to load parsed module")
}

#[test]
fn call_host_func() {
	let module = parse_wat(
		r#"
(module
	(import "env" "sub" (func $sub (param i32 i32) (result i32)))

	(func (export "test") (result i32)
		(call $sub
			(i32.const 5)
			(i32.const 7)
		)
	)
)
"#,
	);

	let mut env = TestHost::new();

	let instance = ModuleInstance::new(&module, &ImportsBuilder::new().with_resolver("env", &env))
		.expect("Failed to instantiate module")
		.assert_no_start();

	assert_eq!(
		instance.invoke_export("test", &[], &mut env).expect(
			"Failed to invoke 'test' function",
		),
		Some(RuntimeValue::I32(-2))
	);
}

#[test]
fn host_err() {
	let module = parse_wat(
		r#"
(module
	(import "env" "err" (func $err (param i32)))

	(func (export "test")
		(call $err
			(i32.const 228)
		)
	)
)
"#,
	);

	let mut env = TestHost::new();

	let instance = ModuleInstance::new(&module, &ImportsBuilder::new().with_resolver("env", &env))
		.expect("Failed to instantiate module")
		.assert_no_start();

	let error = instance.invoke_export("test", &[], &mut env).expect_err(
		"`test` expected to return error",
	);

	let host_error: Box<HostError> = match error {
		Error::Trap(Trap::Host(err)) => err,
		err => panic!("Unexpected error {:?}", err),
	};

	let error_with_code = host_error.downcast_ref::<HostErrorWithCode>().expect(
		"Failed to downcast to expected error type",
	);
	assert_eq!(error_with_code.error_code, 228);
}

#[test]
fn modify_mem_with_host_funcs() {
	let module = parse_wat(
		r#"
(module
	(import "env" "inc_mem" (func $inc_mem (param i32)))
	;; (import "env" "get_mem" (func $get_mem (param i32) (result i32)))

	(func (export "modify_mem")
		;; inc memory at address 12 for 4 times.
		(call $inc_mem (i32.const 12))
		(call $inc_mem (i32.const 12))
		(call $inc_mem (i32.const 12))
		(call $inc_mem (i32.const 12))
	)
)
"#,
	);

	let mut env = TestHost::new();

	let instance = ModuleInstance::new(&module, &ImportsBuilder::new().with_resolver("env", &env))
		.expect("Failed to instantiate module")
		.assert_no_start();

	instance.invoke_export("modify_mem", &[], &mut env).expect(
		"Failed to invoke 'test' function",
	);

	// Check contents of memory at address 12.
	let mut buf = [0u8; 1];
	env.memory.unwrap().get_into(12, &mut buf).unwrap();

	assert_eq!(&buf, &[4]);
}

#[test]
fn pull_internal_mem_from_module() {
	let module = parse_wat(
		r#"
(module
	(import "env" "inc_mem" (func $inc_mem (param i32)))
	(import "env" "get_mem" (func $get_mem (param i32) (result i32)))

	;; declare internal memory and export it under name "mem"
	(memory (export "mem") 1 1)

	(func (export "test") (result i32)
		;; Increment value at address 1337
		(call $inc_mem (i32.const 1337))

		;; Return value at address 1337
		(call $get_mem (i32.const 1337))
	)
)
"#,
	);

	let mut env = TestHost {
		memory: None,
		instance: None,
	};

	let instance = ModuleInstance::new(&module, &ImportsBuilder::new().with_resolver("env", &env))
		.expect("Failed to instantiate module")
		.assert_no_start();

	// Get memory instance exported by name 'mem' from the module instance.
	let internal_mem = instance
		.export_by_name("mem")
		.expect("Module expected to have 'mem' export")
		.as_memory()
		.cloned()
		.expect("'mem' export should be a memory");

	env.memory = Some(internal_mem);

	assert_eq!(
		instance.invoke_export("test", &[], &mut env).unwrap(),
		Some(RuntimeValue::I32(1))
	);
}

#[test]
fn recursion() {
	let module = parse_wat(
		r#"
(module
	;; Import 'recurse' function. Upon a call it will call back inside
	;; this module, namely to function 'recursive' defined below.
	(import "env" "recurse" (func $recurse (param i64) (result i64)))

	;; Note that we import same function but with different type signature
	;; this is possible since 'recurse' is a host function and it is defined
	;; to be polymorphic.
	(import "env" "recurse" (func (param f32) (result f32)))

	(func (export "recursive") (param i64) (result i64)
		;; return arg_0 + 42;
		(i64.add
			(get_local 0)
			(i64.const 42)
		)
	)

	(func (export "test") (result i64)
		(call $recurse (i64.const 321))
	)
)
"#,
	);

	let mut env = TestHost::new();

	let instance = ModuleInstance::new(&module, &ImportsBuilder::new().with_resolver("env", &env))
		.expect("Failed to instantiate module")
		.assert_no_start();

	// Put instance into the env, because $recurse function expects
	// attached module instance.
	env.instance = Some(instance.clone());

	assert_eq!(
		instance.invoke_export("test", &[], &mut env).expect(
			"Failed to invoke 'test' function",
		),
		// 363 = 321 + 42
		Some(RuntimeValue::I64(363))
	);
}

#[test]
fn defer_providing_externals() {
	const INC_FUNC_INDEX: usize = 0;

	/// `HostImportResolver` will be passed at instantiation time.
	///
	/// Main purpose of this struct is to statsify imports of
	/// the module being instantiated.
	struct HostImportResolver {
		mem: MemoryRef,
	}

	impl ModuleImportResolver for HostImportResolver {
		fn resolve_func(
			&self,
			field_name: &str,
			signature: &Signature,
		) -> Result<FuncRef, Error> {
			if field_name != "inc" {
				return Err(Error::Instantiation(
					format!("Export {} not found", field_name),
				));
			}
			if signature.params() != &[ValueType::I32] || signature.return_type() != None {
				return Err(Error::Instantiation(format!(
					"Export `{}` doesnt match expected type {:?}",
					field_name,
					signature
				)));
			}

			Ok(FuncInstance::alloc_host(signature.clone(), INC_FUNC_INDEX))
		}

		fn resolve_memory(
			&self,
			field_name: &str,
			_memory_type: &MemoryDescriptor,
		) -> Result<MemoryRef, Error> {
			if field_name == "mem" {
				Ok(self.mem.clone())
			} else {
				Err(Error::Instantiation(
					format!("Export {} not found", field_name),
				))
			}
		}
	}

	/// This struct implements external functions that can be called
	/// by wasm module.
	struct HostExternals<'a> {
		acc: &'a mut u32,
	}

	impl<'a> Externals for HostExternals<'a> {
		fn invoke_index(
			&mut self,
			index: usize,
			args: RuntimeArgs,
		) -> Result<Option<RuntimeValue>, Trap> {
			match index {
				INC_FUNC_INDEX => {
					let a = args.nth::<u32>(0);
					*self.acc += a;
					Ok(None)
				}
				_ => panic!("env module doesn't provide function at index {}", index),
			}
		}
	}

	let module = parse_wat(
		r#"
(module
	;; Just to require 'mem' from 'host'.
	(import "host" "mem" (memory 1))
	(import "host" "inc" (func $inc (param i32)))

	(func (export "test")
		(call $inc (i32.const 1))
	)
)
"#,
	);

	// Create HostImportResolver with some initialized memory instance.
	// This memory instance will be provided as 'mem' export.
	let host_import_resolver =
		HostImportResolver { mem: MemoryInstance::alloc(1, Some(1)).unwrap() };

	// Instantiate module with `host_import_resolver` as import resolver for "host" module.
	let instance = ModuleInstance::new(
		&module,
		&ImportsBuilder::new().with_resolver("host", &host_import_resolver),
	).expect("Failed to instantiate module")
		.assert_no_start();

	let mut acc = 89;
	{
		let mut host_externals = HostExternals { acc: &mut acc };

		instance
			.invoke_export("test", &[], &mut host_externals)
			.unwrap(); // acc += 1;
		instance
			.invoke_export("test", &[], &mut host_externals)
			.unwrap(); // acc += 1;
	}
	assert_eq!(acc, 91);
}

#[test]
fn two_envs_one_externals() {
	const PRIVILEGED_FUNC_INDEX: usize = 0;
	const ORDINARY_FUNC_INDEX: usize = 1;

	struct HostExternals;

	impl Externals for HostExternals {
		fn invoke_index(
			&mut self,
			index: usize,
			_args: RuntimeArgs,
		) -> Result<Option<RuntimeValue>, Trap> {
			match index {
				PRIVILEGED_FUNC_INDEX => {
					println!("privileged!");
					Ok(None)
				}
				ORDINARY_FUNC_INDEX => Ok(None),
				_ => panic!("env module doesn't provide function at index {}", index),
			}
		}
	}

	struct PrivilegedResolver;
	struct OrdinaryResolver;

	impl ModuleImportResolver for PrivilegedResolver {
		fn resolve_func(
			&self,
			field_name: &str,
			signature: &Signature,
		) -> Result<FuncRef, Error> {
			let index = match field_name {
				"ordinary" => ORDINARY_FUNC_INDEX,
				"privileged" => PRIVILEGED_FUNC_INDEX,
				_ => {
					return Err(Error::Instantiation(
						format!("Export {} not found", field_name),
					))
				}
			};

			Ok(FuncInstance::alloc_host(signature.clone(), index))
		}
	}

	impl ModuleImportResolver for OrdinaryResolver {
		fn resolve_func(
			&self,
			field_name: &str,
			signature: &Signature,
		) -> Result<FuncRef, Error> {
			let index = match field_name {
				"ordinary" => ORDINARY_FUNC_INDEX,
				"privileged" => {
					return Err(Error::Instantiation(
						"'priveleged' can be imported only in privileged context".into(),
					))
				}
				_ => {
					return Err(Error::Instantiation(
						format!("Export {} not found", field_name),
					))
				}
			};

			Ok(FuncInstance::alloc_host(signature.clone(), index))
		}
	}

	let trusted_module = parse_wat(
		r#"
(module
	;; Trusted module can import both ordinary and privileged functions.
	(import "env" "ordinary" (func $ordinary))
	(import "env" "privileged" (func $privileged))
	(func (export "do_trusted_things")
		(call $ordinary)
		(call $privileged)
	)
)
"#,
	);

	let untrusted_module = parse_wat(
		r#"
(module
	;; Untrusted module can import only ordinary functions.
	(import "env" "ordinary" (func $ordinary))
	(import "trusted" "do_trusted_things" (func $do_trusted_things))
	(func (export "test")
		(call $ordinary)
		(call $do_trusted_things)
	)
)
"#,
	);

	let trusted_instance = ModuleInstance::new(
		&trusted_module,
		&ImportsBuilder::new().with_resolver("env", &PrivilegedResolver),
	).expect("Failed to instantiate module")
		.assert_no_start();

	let untrusted_instance = ModuleInstance::new(
		&untrusted_module,
		&ImportsBuilder::new()
			.with_resolver("env", &OrdinaryResolver)
			.with_resolver("trusted", &trusted_instance),
	).expect("Failed to instantiate module")
		.assert_no_start();

	untrusted_instance
		.invoke_export("test", &[], &mut HostExternals)
		.expect("Failed to invoke 'test' function");
}

#[test]
fn dynamically_add_host_func() {
	const ADD_FUNC_FUNC_INDEX: usize = 0;

	struct HostExternals {
		table: TableRef,
		added_funcs: u32,
	}

	impl Externals for HostExternals {
		fn invoke_index(
			&mut self,
			index: usize,
			_args: RuntimeArgs,
		) -> Result<Option<RuntimeValue>, Trap> {
			match index {
				ADD_FUNC_FUNC_INDEX => {
					// Allocate indicies for the new function.
					// host_func_index is in host index space, and first index is occupied by ADD_FUNC_FUNC_INDEX.
					let table_index = self.added_funcs;
					let host_func_index = table_index + 1;
					self.added_funcs += 1;

					let added_func = FuncInstance::alloc_host(
						Signature::new(&[][..], Some(ValueType::I32)),
						host_func_index as usize,
					);
					self.table.set(table_index, Some(added_func))
						.map_err(|_| Trap::TableAccessOutOfBounds)?;

					Ok(Some(RuntimeValue::I32(table_index as i32)))
				}
				index if index as u32 <= self.added_funcs => {
					Ok(Some(RuntimeValue::I32(index as i32)))
				}
				_ => panic!("'env' module doesn't provide function at index {}", index),
			}
		}
	}

	impl ModuleImportResolver for HostExternals {
		fn resolve_func(
			&self,
			field_name: &str,
			signature: &Signature,
		) -> Result<FuncRef, Error> {
			let index = match field_name {
				"add_func" => ADD_FUNC_FUNC_INDEX,
				_ => {
					return Err(Error::Instantiation(
						format!("Export {} not found", field_name),
					))
				}
			};
			Ok(FuncInstance::alloc_host(signature.clone(), index))
		}

		fn resolve_table(
			&self,
			field_name: &str,
			_table_type: &TableDescriptor,
		) -> Result<TableRef, Error> {
			if field_name == "table" {
				Ok(self.table.clone())
			} else {
				Err(Error::Instantiation(
					format!("Export {} not found", field_name),
				))
			}
		}
	}

	let mut host_externals = HostExternals {
		table: TableInstance::alloc(10, None).unwrap(),
		added_funcs: 0,
	};

	let module = parse_wat(
		r#"
(module
	(type $t0 (func (result i32)))
	(import "env" "add_func" (func $add_func (result i32)))
	(import "env" "table" (table 10 anyfunc))
	(func (export "test") (result i32)
		;; Call add_func but discard the result
		call $add_func
		drop

		;; Call add_func and then make an indirect call with the returned index
		call $add_func
		call_indirect (type $t0)
	)
)
"#,
	);

	let instance = ModuleInstance::new(
		&module,
		&ImportsBuilder::new().with_resolver("env", &host_externals),
	).expect("Failed to instantiate module")
		.assert_no_start();

	assert_eq!(
		instance
			.invoke_export("test", &[], &mut host_externals)
			.expect("Failed to invoke 'test' function"),
		Some(RuntimeValue::I32(2))
	);
}