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// This file is part of Substrate.

// Copyright (C) 2021-2022 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.

//! Migrations to version [`4.0.0`], as denoted by the changelog.

use frame_support::{
	traits::{Get, StorageVersion},
	weights::Weight,
};

/// The old prefix.
pub const OLD_PREFIX: &[u8] = b"PhragmenElection";

/// Migrate the entire storage of this pallet to a new prefix.
///
/// This new prefix must be the same as the one set in construct_runtime. For safety, use
/// `PalletInfo` to get it, as:
/// `<Runtime as frame_system::Config>::PalletInfo::name::<ElectionsPhragmenPallet>`.
///
/// The old storage prefix, `PhragmenElection` is hardcoded in the migration code.
pub fn migrate<T: crate::Config, N: AsRef<str>>(new_pallet_name: N) -> Weight {
	if new_pallet_name.as_ref().as_bytes() == OLD_PREFIX {
		log::info!(
			target: "runtime::elections-phragmen",
			"New pallet name is equal to the old prefix. No migration needs to be done.",
		);
		return Weight::zero()
	}
	let storage_version = StorageVersion::get::<crate::Pallet<T>>();
	log::info!(
		target: "runtime::elections-phragmen",
		"Running migration to v4 for elections-phragmen with storage version {:?}",
		storage_version,
	);

	if storage_version <= 3 {
		log::info!("new prefix: {}", new_pallet_name.as_ref());
		frame_support::storage::migration::move_pallet(
			OLD_PREFIX,
			new_pallet_name.as_ref().as_bytes(),
		);

		StorageVersion::new(4).put::<crate::Pallet<T>>();

		<T as frame_system::Config>::BlockWeights::get().max_block
	} else {
		log::warn!(
			target: "runtime::elections-phragmen",
			"Attempted to apply migration to v4 but failed because storage version is {:?}",
			storage_version,
		);
		Weight::zero()
	}
}

/// Some checks prior to migration. This can be linked to
/// [`frame_support::traits::OnRuntimeUpgrade::pre_upgrade`] for further testing.
///
/// Panics if anything goes wrong.
pub fn pre_migration<T: crate::Config, N: AsRef<str>>(new: N) {
	let new = new.as_ref();
	log::info!("pre-migration elections-phragmen test with new = {}", new);

	// the next key must exist, and start with the hash of `OLD_PREFIX`.
	let next_key = sp_io::storage::next_key(OLD_PREFIX).unwrap();
	assert!(next_key.starts_with(&sp_io::hashing::twox_128(OLD_PREFIX)));

	// ensure nothing is stored in the new prefix.
	assert!(
		sp_io::storage::next_key(new.as_bytes()).map_or(
			// either nothing is there
			true,
			// or we ensure that it has no common prefix with twox_128(new).
			|next_key| !next_key.starts_with(&sp_io::hashing::twox_128(new.as_bytes()))
		),
		"unexpected next_key({}) = {:?}",
		new,
		sp_core::hexdisplay::HexDisplay::from(&sp_io::storage::next_key(new.as_bytes()).unwrap())
	);
	// ensure storage version is 3.
	assert_eq!(StorageVersion::get::<crate::Pallet<T>>(), 3);
}

/// Some checks for after migration. This can be linked to
/// [`frame_support::traits::OnRuntimeUpgrade::post_upgrade`] for further testing.
///
/// Panics if anything goes wrong.
pub fn post_migration<T: crate::Config>() {
	log::info!("post-migration elections-phragmen");
	// ensure we've been updated to v4 by the automatic write of crate version -> storage version.
	assert_eq!(StorageVersion::get::<crate::Pallet<T>>(), 4);
}