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// This file is part of Substrate.

// Copyright (C) 2019-2022 Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0

// 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.

//! This module defines `HostState` struct which provide logic and state
//! required for execution of host.

use sp_allocator::{AllocationStats, FreeingBumpHeapAllocator};

/// The state required to construct a HostContext context. The context only lasts for one host
/// call, whereas the state is maintained for the duration of a Wasm runtime call, which may make
/// many different host calls that must share state.
pub struct HostState {
	/// The allocator instance to keep track of allocated memory.
	///
	/// This is stored as an `Option` as we need to temporarly set this to `None` when we are
	/// allocating/deallocating memory. The problem being that we can only mutable access `caller`
	/// once.
	pub allocator: Option<FreeingBumpHeapAllocator>,
	pub panic_message: Option<String>,
}

impl HostState {
	/// Constructs a new `HostState`.
	pub fn new(allocator: FreeingBumpHeapAllocator) -> Self {
		HostState { allocator: Some(allocator), panic_message: None }
	}

	/// Takes the error message out of the host state, leaving a `None` in its place.
	pub fn take_panic_message(&mut self) -> Option<String> {
		self.panic_message.take()
	}

	pub fn allocation_stats(&self) -> AllocationStats {
		self.allocator.as_ref()
			.expect("Allocator is always set and only unavailable when doing an allocation/deallocation; qed")
			.stats()
	}
}