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// Copyright 2019-2020 Parity Technologies (UK) Ltd.
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//
// 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.

#![cfg_attr(not(feature = "std"), no_std)]

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use ink_lang as ink;
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#[ink::contract(version = "0.1.0")]
mod runtime {
    use ink_core::{
        env,
        hash::Blake2x128,
    };
    use ink_prelude::{
        format,
        vec,
        vec::Vec,
    };
    use scale::{
        Decode,
        Encode,
    };
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    /// All balance information for an account, mirroring the structure defined in the runtime.
    /// Copied from [substrate](https://github.com/paritytech/substrate/blob/2c87fe171bc341755a43a3b32d67560469f8daac/frame/system/src/lib.rs#L307)
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    #[derive(Encode, Decode)]
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    pub struct AccountData {
        free: Balance,
        _reserved: Balance,
        _misc_frozen: Balance,
        _fee_frozen: Balance,
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    }

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    /// Information of an account, mirroring the structure defined in the runtime
    /// Copied from [substrate](https://github.com/paritytech/substrate/blob/2c87fe171bc341755a43a3b32d67560469f8daac/frame/system/src/lib.rs#L307)
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    #[derive(Encode, Decode)]
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    pub struct AccountInfo {
        _nonce: u32,
        _refcount: u8,
        data: AccountData,
    }
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    /// This simple contract reads a value from runtime storage
    #[ink(storage)]
    struct RuntimeStorage {}

    impl RuntimeStorage {
        #[ink(constructor)]
        fn new(&mut self) {}

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        /// Returns an account's free balance, read directly from runtime storage
        ///
        /// # Key Scheme
        ///
        /// A key for the [substrate storage map]
        /// (https://github.com/paritytech/substrate/blob/dd97b1478b31a4715df7e88a5ebc6664425fb6c6/frame/support/src/storage/generator/map.rs#L28)
        /// is constructed with:
        ///
        /// ```nocompile
        /// Twox128(module_prefix) ++ Twox128(storage_prefix) ++ Hasher(encode(key))
        /// ```
        ///
        /// For the `System` module's `Account` map, the [hasher implementation]
        /// (https://github.com/paritytech/substrate/blob/2c87fe171bc341755a43a3b32d67560469f8daac/frame/system/src/lib.rs#L349)
        /// is `blake2_128_concat`.
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        #[ink(message)]
        fn get_balance(&self, account: AccountId) -> Balance {
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            let mut key = vec![
                // Precomputed: Twox128("System")
                38, 170, 57, 78, 234, 86, 48, 224, 124, 72, 174, 12, 149, 88, 206, 247,
                // Precomputed: Twox128("Account")
                185, 157, 136, 14, 198, 129, 121, 156, 12, 243, 14, 136, 134, 55, 29, 169,
            ];

            let encoded_account = &account.encode();

            let mut blake2_128 = Blake2x128::from(Vec::new());
            let hashed_account = blake2_128.hash_raw(&encoded_account);

            // The hasher is `Blake2_128Concat` which appends the unhashed account to the hashed account
            key.extend_from_slice(&hashed_account);
            key.extend_from_slice(&encoded_account);

            // fetch from runtime storage
            let result = self.env().get_runtime_storage::<AccountInfo>(&key[..]);
            match result {
                Some(Ok(account_info)) => account_info.data.free,
                Some(Err(err)) => {
                    env::println(&format!("Error reading AccountInfo {:?}", err));
                    0
                }
                None => {
                    env::println(&format!("No data at key {:?}", key));
                    0
                }
            }
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        }
    }

    #[cfg(all(test))]
    mod tests {
        use super::*;
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        use ink_core::env;
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        #[test]
        fn non_existent_account_returns_zero() {
            let contract = RuntimeStorage::new();
            let account: AccountId = [0u8; 32].into();
            assert_eq!(contract.get_balance(account), 0);
        }
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        #[test]
        fn returns_account_balance_from_storage() {
            let contract = RuntimeStorage::new();
            let account: AccountId = [0u8; 32].into();
            let balance = 1_000_000;

            let account_info = AccountInfo {
                data: AccountData {
                    free: balance,
                    _reserved: 0,
                    _fee_frozen: 0,
                    _misc_frozen: 0,
                },
                _nonce: 0,
                _refcount: 0,
            };

            let encoded_account = &account.encode();

            let mut key = vec![
                // Precomputed: Twox128("System")
                38, 170, 57, 78, 234, 86, 48, 224, 124, 72, 174, 12, 149, 88, 206, 247,
                // Precomputed: Twox128("Account")
                185, 157, 136, 14, 198, 129, 121, 156, 12, 243, 14, 136, 134, 55, 29, 169,
            ];

            let mut blake2_128 = Blake2x128::from(Vec::new());
            let hashed_account = blake2_128.hash_raw(&encoded_account);

            key.extend_from_slice(&hashed_account);
            key.extend_from_slice(&encoded_account);

            env::test::set_runtime_storage(&key, account_info);
            assert_eq!(contract.get_balance(account), balance);
        }
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    }
}