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// Copyright 2018-2022 Parity Technologies (UK) Ltd.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

/// Trait implemented by chain extensions.
///
/// Allows to use the `self.env().extension().my_chain_extension(...)` syntax.
///
/// # Note
///
/// This trait is automatically implemented when using `#[ink::chain_extension]`
/// procedural macro.
pub trait ChainExtensionInstance {
    /// The type of the chain extension instance.
    type Instance;

    /// Creates a new instance of the chain extension to use methods with method chaining
    /// syntax.
    fn instantiate() -> Self::Instance;
}

/// Implemented by chain extension types.
///
/// Every chain extension defines a set of chain extension methods
/// that share a common error code type.
pub trait ChainExtension {
    /// The error code that determines whether a chain extension method call was
    /// successful.
    type ErrorCode: ink_env::chain_extension::FromStatusCode;
}

/// Only implemented for `Result<T, E>`.
///
/// Used to check at compile time if the chain extension method return type
/// is a `Result` type using the type system instead of the syntactic structure.
#[doc(hidden)]
pub trait IsResultType: private::IsResultSealed {
    /// The `T` type of the `Result<T, E>`.
    type Ok;
    /// The `E` type of the `Result<T, E>`.
    type Err;
}

impl<T, E> private::IsResultSealed for Result<T, E> {}
impl<T, E> IsResultType for Result<T, E> {
    type Ok = T;
    type Err = E;
}

/// Only implemented for [`ValueReturned`].
///
/// Used to deduce the correct return type of a chain extension method at compile time
/// based on 2 flags: `const IS_RESULT: bool` and `const HANDLE_STATUS: bool`.
///
/// If `IS_RESULT` is set to `false` and `HANDLE_STATUS` is `true`, then
/// `type ReturnType = Result<T, E>`. Otherwise `type ReturnType = T`.
pub trait Output<const IS_RESULT: bool, const HANDLE_STATUS: bool, T, E>:
    private::OutputSealed
{
    type ReturnType;
}

/// Represents some abstract value that is returned by a function.
/// Currently acts as a placeholder.
pub struct ValueReturned;
impl private::OutputSealed for ValueReturned {}

impl<T, E> Output<false, false, T, E> for ValueReturned {
    type ReturnType = T;
}

impl<T, E> Output<false, true, T, E> for ValueReturned {
    type ReturnType = core::result::Result<T, E>;
}

impl<T, E> Output<true, false, T, E> for ValueReturned {
    type ReturnType = T;
}

impl<T, E> Output<true, true, T, E> for ValueReturned {
    type ReturnType = T;
}

mod private {
    /// Seals the `IsResultType` trait so that it cannot be implemented outside this
    /// module.
    pub trait IsResultSealed {}
    /// Seals the `Output` trait so that it cannot be implemented outside this module.
    pub trait OutputSealed {}
}