lib.rs 34.9 KB
Newer Older
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109
// Copyright 2018-2020 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.

//! # Plain Multisig Wallet
//!
//! This implements a plain multi owner wallet.
//!
//! ## Warning
//!
//! This contract is an *example*. It is neither audited nor endorsed for production use.
//! Do **not** rely on it to keep anything of value secure.
//!
//! ## Overview
//!
//! Each instantiation of this contract has a set of `owners` and a `requirement` of
//! how many of them need to agree on a `Transaction` for it to be able to be executed.
//! Every owner can submit a transaction and when enough of the other owners confirm
//! it will be able to be executed. The following invariant is enforced by the contract:
//!
//! ```ignore
//! 0 < requirement && requirement <= owners && owners <= MAX_OWNERS
//! ```
//!
//! ## Error Handling
//!
//! With the exeception of `execute_transaction` no error conditions are signalled
//! through return types. Any error or invariant violation triggers a panic and therefore
//! rolls back the transaction.
//!
//! ## Interface
//!
//! The interface is modelled after the popular gnosis multisig wallet. However, there
//! are subtle variations from the interface. For example the `confirm_transaction`
//! will never trigger the execution of a `Transaction` even if the treshold is reached.
//! A call of `execute_transaction` is always required. This can be called by anyone.
//!
//! All the messages that are declared as only callable by the wallet must go through
//! the usual submit, confirm, execute cycle as any other transaction that should be
//! called by the wallet. For example to add an owner you would submit a transaction
//! that calls the wallets own `add_owner` message through `submit_transaction`.
//!
//! ### Owner Management
//!
//! The messages `add_owner`, `remove_owner`, and `replace_owner` can be used to manage
//! the owner set after instantiation.
//!
//! ### Changing the Requirement
//!
//! `change_requirement` can be used to tighten or relax the `requirement` of how many
//! owner signatures are needed to execute a `Transaction`.
//!
//! ### Transaction Management
//!
//! `submit_transaction`, `cancel_transaction`, `confirm_transaction`,
//! `revoke_confirmation` and `execute_transaction` are the bread and butter messages
//! of this contract. Use them to dispatch arbitrary messages to other contracts
//! with the wallet as a sender.

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

use ink_lang as ink;

#[ink::contract(version = "0.1.0")]
mod multisig_plain {
    use ink_core::{
        env::call::{
            state::{
                Sealed,
                Unsealed,
            },
            CallBuilder,
            CallParams,
        },
        storage,
    };
    use ink_prelude::vec::Vec;
    use scale::Output;

    /// Tune this to your liking but be wary that allowing too many owners will not perform well.
    const MAX_OWNERS: u32 = 50;

    type TransactionId = u32;
    const WRONG_TRANSACTION_ID: &str =
        "The user specified an invalid transaction id. Abort.";

    /// A wrapper that allows us to encode a blob of bytes.
    ///
    /// We use this to pass the set of untyped (bytes) parameters to the `CallBuilder`.
    struct CallInput<'a>(&'a [u8]);

    impl<'a> scale::Encode for CallInput<'a> {
        fn encode_to<T: Output>(&self, dest: &mut T) {
            dest.write(self.0);
        }
    }

    /// Indicates whether a transaction is already confirmed or needs further confirmations.
    #[derive(scale::Encode, scale::Decode, Clone, Copy)]
110
    #[cfg_attr(feature = "ink-generate-abi", derive(type_metadata::Metadata))]
111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958
    pub enum ConfirmationStatus {
        /// The transaction is already confirmed.
        Confirmed,
        /// Indicates how many confirmations are remaining.
        ConfirmationsNeeded(u32),
    }

    /// A Transaction is what every `owner` can submit for confirmation by other owners.
    /// If enough owners agree it will be executed by the contract.
    #[derive(scale::Encode, scale::Decode, storage::Flush)]
    #[cfg_attr(feature = "ink-generate-abi", derive(type_metadata::Metadata))]
    #[cfg_attr(feature = "std", derive(Debug, PartialEq, Eq))]
    pub struct Transaction {
        /// The AccountId of the contract that is called in this transaction.
        callee: AccountId,
        /// The selector bytes that identifies the function of the callee that should be called.
        selector: [u8; 4],
        /// The SCALE encoded parameters that are passed to the called function.
        input: Vec<u8>,
        /// The amount of chain balance that is transferred to the callee.
        transferred_value: Balance,
        /// Gas limit for the execution of the call.
        gas_limit: u64,
    }

    #[ink(storage)]
    struct MultisigPlain {
        /// Every entry in this map represents the confirmation of an owner for a
        /// transaction. This is effecively a set rather than a map.
        confirmations: storage::BTreeMap<(TransactionId, AccountId), ()>,
        /// The amount of confirmations for every transaction. This is a redundant
        /// information and is kept in order to prevent iterating through the
        /// confirmation set to check if a transaction is confirmed.
        confirmation_count: storage::BTreeMap<TransactionId, u32>,
        /// Just the list of transactions. It is a stash as stable ids are necessary
        /// for referencing them in confirmation calls.
        transactions: storage::Stash<Transaction>,
        /// The list is a vector because iterating over it is necessary when cleaning
        /// up the confirmation set.
        owners: storage::Vec<AccountId>,
        /// Redundant information to speed up the check whether a caller is an owner.
        is_owner: storage::BTreeMap<AccountId, ()>,
        /// Minimum number of owners that have to confirm a transaction to be executed.
        requirement: storage::Value<u32>,
    }

    /// Emitted when an owner confirms a transaction.
    #[ink(event)]
    struct Confirmation {
        /// The transaction that was confirmed.
        #[ink(topic)]
        transaction: TransactionId,
        /// The owner that sent the confirmation.
        #[ink(topic)]
        from: AccountId,
        /// The confirmation status after this confirmation was applied.
        #[ink(topic)]
        status: ConfirmationStatus,
    }

    /// Emitted when an owner revoked a confirmation.
    #[ink(event)]
    struct Revokation {
        /// The transaction that was revoked.
        #[ink(topic)]
        transaction: TransactionId,
        /// The owner that sent the revokation.
        #[ink(topic)]
        from: AccountId,
    }

    /// Emitted when an owner submits a transaction.
    #[ink(event)]
    struct Submission {
        /// The transaction that was submitted.
        #[ink(topic)]
        transaction: TransactionId,
    }

    /// Emitted when a transaction was canceled.
    #[ink(event)]
    struct Cancelation {
        /// The transaction that was canceled.
        #[ink(topic)]
        transaction: TransactionId,
    }

    /// Emitted when a transaction was executed.
    #[ink(event)]
    struct Execution {
        /// The transaction that was executed.
        #[ink(topic)]
        transaction: TransactionId,
        /// Indicates whether the transaction executed successfully. If so the `Ok` value holds
        /// the output in bytes. The Option is `None` when the transaction was executed through
        /// `invoke_transaction` rather than `evaluate_transaction`.
        #[ink(topic)]
        result: Result<Option<Vec<u8>>, ()>,
    }

    /// Emitted when an owner is added to the wallet.
    #[ink(event)]
    struct OwnerAddition {
        /// The owner that was added.
        #[ink(topic)]
        owner: AccountId,
    }

    /// Emitted when an owner is removed from the wallet.
    #[ink(event)]
    struct OwnerRemoval {
        /// The owner that was removed.
        #[ink(topic)]
        owner: AccountId,
    }

    /// Emitted when the requirement changed.
    #[ink(event)]
    struct RequirementChange {
        /// The new requirement value.
        new_requirement: u32,
    }

    impl MultisigPlain {
        /// The only constructor of the contract.
        ///
        /// A list of owners must be supplied and a number of how many of them must
        /// confirm a transaction. Duplicate owners are silently dropped.
        ///
        /// # Panics
        ///
        /// If `requirement` violates our invariant.
        #[ink(constructor)]
        fn new(&mut self, requirement: u32, owners: Vec<AccountId>) {
            for owner in &owners {
                self.is_owner.insert(*owner, ());
                self.owners.push(*owner);
            }
            ensure_requirement_is_valid(self.owners.len(), requirement);
            assert!(self.is_owner.len() == self.owners.len());
            self.requirement.set(requirement);
        }

        /// Add a new owner to the contract.
        ///
        /// Only callable by the wallet itself.
        ///
        /// # Panics
        ///
        /// If the owner already exists.
        ///
        /// # Examples
        ///
        /// Since this message must be send by the wallet itself it has to be build as a
        /// `Transaction` and dispatched through `submit_transaction` + `invoke_transaction`:
        /// ```
        /// use ink_core::env::call{CallData, CallParams, Selector};
        ///
        /// // address of an existing MultiSigPlain contract
        /// let wallet_id: AccountId = [7u8; 32].into();
        ///
        /// // first create the transaction that adds `alice` through `add_owner`
        /// let alice: AccountId = [1u8; 32].into();
        /// let mut call = CallData::new(Selector::from_str("add_owner"));
        /// call.push_arg(&alice);
        /// let transaction = Transaction {
        ///     callee: wallet_id,
        ///     selector: call.selector().to_bytes(),
        ///     input: call.params().to_owned(),
        ///     transferred_value: 0,
        ///     gas_limit: 0
        /// };
        ///
        /// // submit the transaction for confirmation
        /// let mut submit = CallParams::eval(wallet_id, Selector::from_str("submit_transaction"));
        /// let (id, _)  = submit.push_arg(&transaction)
        ///     .fire()
        ///     .expect("submit_transaction won't panic.");
        ///
        /// // wait until all required owners have confirmed and then execute the transaction
        /// let mut invoke = CallParams::eval(wallet_id, Selector::from_str("invoke_transaction"));
        /// invoke.push_arg(&id).fire();
        /// ```
        #[ink(message)]
        fn add_owner(&mut self, new_owner: AccountId) {
            self.ensure_from_wallet();
            self.ensure_no_owner(&new_owner);
            ensure_requirement_is_valid(self.owners.len() + 1, *self.requirement);
            self.is_owner.insert(new_owner, ());
            self.owners.push(new_owner);
            self.env().emit_event(OwnerAddition { owner: new_owner });
        }

        /// Remove an owner from the contract.
        ///
        /// Only callable by the wallet itself. If by doing this the amount of owners
        /// would be smaller than the requirement it is adjusted to be exactly the
        /// number of owners.
        ///
        /// # Panics
        ///
        /// If `owner` is no owner of the wallet.
        #[ink(message)]
        fn remove_owner(&mut self, owner: AccountId) {
            self.ensure_from_wallet();
            self.ensure_owner(&owner);
            let len = self.owners.len() - 1;
            let requirement = u32::min(len, *self.requirement);
            ensure_requirement_is_valid(len, requirement);
            self.owners.swap_remove(self.owner_index(&owner));
            self.is_owner.remove(&owner);
            self.requirement.set(requirement);
            self.clean_owner_confirmations(&owner);
            self.env().emit_event(OwnerRemoval { owner });
        }

        /// Replace an owner from the contract with a new one.
        ///
        /// Only callable by the wallet itself.
        ///
        /// # Panics
        ///
        /// If `old_owner` is no owner or if `new_owner` already is one.
        #[ink(message)]
        fn replace_owner(&mut self, old_owner: AccountId, new_owner: AccountId) {
            self.ensure_from_wallet();
            self.ensure_owner(&old_owner);
            self.ensure_no_owner(&new_owner);
            self.owners
                .replace(self.owner_index(&old_owner), || new_owner);
            self.is_owner.remove(&old_owner);
            self.is_owner.insert(new_owner, ());
            self.clean_owner_confirmations(&old_owner);
            self.env().emit_event(OwnerRemoval { owner: old_owner });
            self.env().emit_event(OwnerAddition { owner: new_owner });
        }

        /// Change the requirement to a new value.
        ///
        /// Only callable by the wallet itself.
        ///
        /// # Panics
        ///
        /// If the `new_requirement` violates our invariant.
        #[ink(message)]
        fn change_requirement(&mut self, new_requirement: u32) {
            self.ensure_from_wallet();
            ensure_requirement_is_valid(self.owners.len(), new_requirement);
            self.requirement.set(new_requirement);
            self.env().emit_event(RequirementChange { new_requirement });
        }

        /// Add a new transaction candiate to the contract.
        ///
        /// This also confirms the transaction for the caller. This can be called by any owner.
        #[ink(message)]
        fn submit_transaction(
            &mut self,
            transaction: Transaction,
        ) -> (TransactionId, ConfirmationStatus) {
            self.ensure_caller_is_owner();
            let trans_id = self.transactions.put(transaction);
            self.env().emit_event(Submission {
                transaction: trans_id,
            });
            (
                trans_id,
                self.confirm_by_caller(self.env().caller(), trans_id),
            )
        }

        /// Remove a transaction from the contract.
        /// Only callable by the wallet itself.
        ///
        /// # Panics
        ///
        /// If `trans_id` is no valid transaction id.
        #[ink(message)]
        fn cancel_transaction(&mut self, trans_id: TransactionId) {
            self.ensure_from_wallet();
            if self.take_transaction(trans_id).is_some() {
                self.env().emit_event(Cancelation {
                    transaction: trans_id,
                });
            }
        }

        /// Confirm a transaction for the sender that was submitted by any owner.
        ///
        /// This can be called by any owner.
        ///
        /// # Panics
        ///
        /// If `trans_id` is no valid transaction id.
        #[ink(message)]
        fn confirm_transaction(&mut self, trans_id: TransactionId) -> ConfirmationStatus {
            self.ensure_caller_is_owner();
            self.ensure_transaction_exists(trans_id);
            self.confirm_by_caller(self.env().caller(), trans_id)
        }

        /// Revoke the senders confirmation.
        ///
        /// This can be called by any owner.
        ///
        /// # Panics
        ///
        /// If `trans_id` is no valid transaction id.
        #[ink(message)]
        fn revoke_confirmation(&mut self, trans_id: TransactionId) {
            self.ensure_caller_is_owner();
            let caller = self.env().caller();
            if self.confirmations.remove(&(trans_id, caller)).is_some() {
                *self.confirmation_count.entry(trans_id).or_insert(1) -= 1;
                self.env().emit_event(Revokation {
                    transaction: trans_id,
                    from: caller,
                });
            }
        }

        /// Invoke a confirmed execution without getting its output.
        ///
        /// Its return value indicates whether the called transaction was successful.
        /// This can be called by anyone.
        #[ink(message)]
        fn invoke_transaction(&mut self, trans_id: TransactionId) -> Result<(), ()> {
            self.ensure_confirmed(trans_id);
            let t = self.take_transaction(trans_id).expect(WRONG_TRANSACTION_ID);
            let result = parameterize_call(
                &t,
                CallParams::<EnvTypes, ()>::invoke(t.callee, t.selector.into()),
            )
            .fire()
            .map_err(|_| ());
            self.env().emit_event(Execution {
                transaction: trans_id,
                result: result.map(|_| None),
            });
            result
        }

        /// Evaluate a confirmed execution and return its output as bytes.
        ///
        /// Its return value indicates whether the called transaction was successful and contains
        /// its output when sucesful.
        /// This can be called by anyone.
        #[ink(message)]
        fn eval_transaction(&mut self, trans_id: TransactionId) -> Result<Vec<u8>, ()> {
            self.ensure_confirmed(trans_id);
            let t = self.take_transaction(trans_id).expect(WRONG_TRANSACTION_ID);
            let result = parameterize_call(
                &t,
                CallParams::<EnvTypes, Vec<u8>>::eval(t.callee, t.selector.into()),
            )
            .fire()
            .map_err(|_| ());
            self.env().emit_event(Execution {
                transaction: trans_id,
                result: result.clone().map(Some),
            });
            result
        }

        /// Set the `transaction` as confirmed by `confirmer`.
        /// Idempotent operation regarding an already confirmed `transaction`
        /// by `confirmer`.
        fn confirm_by_caller(
            &mut self,
            confirmer: AccountId,
            transaction: TransactionId,
        ) -> ConfirmationStatus {
            let count = self.confirmation_count.entry(transaction).or_insert(0);
            let new_confirmation = self
                .confirmations
                .insert((transaction, confirmer), ())
                .is_none();
            if new_confirmation {
                *count += 1;
            }
            let status = {
                if *count >= *self.requirement {
                    ConfirmationStatus::Confirmed
                } else {
                    ConfirmationStatus::ConfirmationsNeeded(*self.requirement - *count)
                }
            };
            if new_confirmation {
                self.env().emit_event(Confirmation {
                    transaction,
                    from: confirmer,
                    status,
                });
            }
            status
        }

        /// Get the index of `owner` in `self.owners`.
        /// Panics if `owner` is not found in `self.owners`.
        fn owner_index(&self, owner: &AccountId) -> u32 {
            self.owners.iter().position(|x| *x == *owner).expect(
                "This is only called after it was already verified that the id is
                 actually an owner.",
            ) as u32
        }

        /// Remove the transaction identified by `trans_id` from `self.transactions`.
        /// Also removes all confirmation state associated with it.
        fn take_transaction(&mut self, trans_id: TransactionId) -> Option<Transaction> {
            let transaction = self.transactions.take(trans_id);
            if transaction.is_some() {
                self.clean_transaction_confirmations(trans_id);
            }
            transaction
        }

        /// Remove all confirmation state associated with `owner`.
        /// Also adjusts the `self.confirmation_count` variable.
        fn clean_owner_confirmations(&mut self, owner: &AccountId) {
            for (trans_id, _) in self.transactions.iter() {
                if self.confirmations.remove(&(trans_id, *owner)).is_some() {
                    *self.confirmation_count.entry(trans_id).or_insert(0) += 1;
                }
            }
        }

        /// This removes all confirmation state associated with `transaction`.
        fn clean_transaction_confirmations(&mut self, transaction: TransactionId) {
            for owner in self.owners.iter() {
                self.confirmations.remove(&(transaction, *owner));
            }
            self.confirmation_count.remove(&transaction);
        }

        /// Panic if transaction `trans_id` is not confirmed by at least
        /// `self.requirement` owners.
        fn ensure_confirmed(&self, trans_id: TransactionId) {
            assert!(
                self.confirmation_count
                    .get(&trans_id)
                    .expect(WRONG_TRANSACTION_ID)
                    >= self.requirement.get()
            );
        }

        /// Panic if the transaction `trans_id` does not exit.
        fn ensure_transaction_exists(&self, trans_id: TransactionId) {
            self.transactions.get(trans_id).expect(WRONG_TRANSACTION_ID);
        }

        /// Panic if the sender is no owner of the wallet.
        fn ensure_caller_is_owner(&self) {
            self.ensure_owner(&self.env().caller());
        }

        /// Panic if the sender is not this wallet.
        fn ensure_from_wallet(&self) {
            assert_eq!(self.env().caller(), self.env().account_id());
        }

        /// Panic if `owner` is not an owner,
        fn ensure_owner(&self, owner: &AccountId) {
            assert!(self.is_owner.contains_key(owner));
        }

        /// Panic if `owner` is an owner.
        fn ensure_no_owner(&self, owner: &AccountId) {
            assert!(!self.is_owner.contains_key(owner));
        }
    }

    /// Parameterize a call with the arguments stored inside a transaction.
    fn parameterize_call<R>(
        t: &Transaction,
        builder: CallBuilder<EnvTypes, R, Unsealed>,
    ) -> CallBuilder<EnvTypes, R, Sealed> {
        builder
            .gas_limit(t.gas_limit)
            .transferred_value(t.transferred_value)
            .push_arg(&CallInput(&t.input))
            .seal()
    }

    /// Panic if the number of `owners` under a `requirement` violates our
    /// requirement invariant.
    fn ensure_requirement_is_valid(owners: u32, requirement: u32) {
        assert!(0 < requirement && requirement <= owners && owners <= MAX_OWNERS);
    }

    #[cfg(test)]
    mod tests {
        use super::*;
        use ink_core::env::{
            call,
            test,
        };
        type Accounts = test::DefaultAccounts<EnvTypes>;
        const WALLET: [u8; 32] = [7; 32];

        impl Transaction {
            fn change_requirement(requirement: u32) -> Self {
                let mut call =
                    call::CallData::new(call::Selector::from_str("change_requirement"));
                call.push_arg(&requirement);
                Self {
                    callee: WALLET.into(),
                    selector: call.selector().to_bytes(),
                    input: call.params().to_owned(),
                    transferred_value: 0,
                    gas_limit: 1000000,
                }
            }
        }

        fn set_sender(sender: AccountId) {
            test::push_execution_context::<EnvTypes>(
                sender,
                WALLET.into(),
                1000000,
                1000000,
                call::CallData::new(call::Selector::from_str("dummy")),
            );
        }

        fn set_from_wallet() {
            set_sender(WALLET.into());
        }

        fn set_from_owner() {
            let accounts = default_accounts();
            set_sender(accounts.alice);
        }

        fn set_from_noowner() {
            let accounts = default_accounts();
            set_sender(accounts.django);
        }

        fn default_accounts() -> Accounts {
            test::default_accounts()
                .expect("Test environment is expected to be initialized.")
        }

        fn build_contract() -> MultisigPlain {
            let accounts = default_accounts();
            let owners = ink_prelude::vec![accounts.alice, accounts.bob, accounts.eve];
            MultisigPlain::new(2, owners)
        }

        fn submit_transaction() -> MultisigPlain {
            let mut contract = build_contract();
            let accounts = default_accounts();
            set_from_owner();
            contract.submit_transaction(Transaction::change_requirement(1));
            assert_eq!(contract.transactions.len(), 1);
            assert_eq!(test::recorded_events().count(), 2);
            let transaction = contract.transactions.get(0).unwrap();
            assert_eq!(*transaction, Transaction::change_requirement(1));
            contract.confirmations.get(&(0, accounts.alice)).unwrap();
            assert_eq!(contract.confirmations.len(), 1);
            assert_eq!(*contract.confirmation_count.get(&0).unwrap(), 1);
            contract
        }

        #[test]
        fn construction_works() {
            let accounts = default_accounts();
            let owners = ink_prelude::vec![accounts.alice, accounts.bob, accounts.eve];
            let contract = build_contract();

            assert_eq!(contract.owners.len(), 3);
            assert_eq!(*contract.requirement.get(), 2);
            assert!(contract.owners.iter().eq(owners.iter()));
            assert!(contract.is_owner.get(&accounts.alice).is_some());
            assert!(contract.is_owner.get(&accounts.bob).is_some());
            assert!(contract.is_owner.get(&accounts.eve).is_some());
            assert!(contract.is_owner.get(&accounts.charlie).is_none());
            assert!(contract.is_owner.get(&accounts.django).is_none());
            assert!(contract.is_owner.get(&accounts.frank).is_none());
            assert_eq!(contract.confirmations.len(), 0);
            assert_eq!(contract.confirmation_count.len(), 0);
            assert_eq!(contract.transactions.len(), 0);
        }

        #[test]
        #[should_panic]
        fn empty_owner_construction_fails() {
            MultisigPlain::new(0, vec![]);
        }

        #[test]
        #[should_panic]
        fn zero_requirement_construction_fails() {
            let accounts = default_accounts();
            MultisigPlain::new(0, vec![accounts.alice, accounts.bob]);
        }

        #[test]
        #[should_panic]
        fn too_large_requirement_construction_fails() {
            let accounts = default_accounts();
            MultisigPlain::new(3, vec![accounts.alice, accounts.bob]);
        }

        #[test]
        fn add_owner_works() {
            let accounts = default_accounts();
            let mut contract = build_contract();
            set_from_wallet();
            let owners = contract.owners.len();
            contract.add_owner(accounts.frank);
            assert_eq!(contract.owners.len(), owners + 1);
            assert!(contract.is_owner.get(&accounts.frank).is_some());
            assert_eq!(test::recorded_events().count(), 1);
        }

        #[test]
        #[should_panic]
        fn add_existing_owner_fails() {
            let accounts = default_accounts();
            let mut contract = build_contract();
            set_from_wallet();
            contract.add_owner(accounts.bob);
        }

        #[test]
        #[should_panic]
        fn add_owner_permission_denied() {
            let accounts = default_accounts();
            let mut contract = build_contract();
            set_from_owner();
            contract.add_owner(accounts.frank);
        }

        #[test]
        fn remove_owner_works() {
            let accounts = default_accounts();
            let mut contract = build_contract();
            set_from_wallet();
            let owners = contract.owners.len();
            contract.remove_owner(accounts.alice);
            assert_eq!(contract.owners.len(), owners - 1);
            assert!(contract.is_owner.get(&accounts.alice).is_none());
            assert_eq!(test::recorded_events().count(), 1);
        }

        #[test]
        #[should_panic]
        fn remove_owner_nonexisting_fails() {
            let accounts = default_accounts();
            let mut contract = build_contract();
            set_from_wallet();
            contract.remove_owner(accounts.django);
        }

        #[test]
        #[should_panic]
        fn remove_owner_permission_denied() {
            let accounts = default_accounts();
            let mut contract = build_contract();
            set_from_owner();
            contract.remove_owner(accounts.alice);
        }

        #[test]
        fn replace_owner_works() {
            let accounts = default_accounts();
            let mut contract = build_contract();
            set_from_wallet();
            let owners = contract.owners.len();
            contract.replace_owner(accounts.alice, accounts.django);
            assert_eq!(contract.owners.len(), owners);
            assert!(contract.is_owner.get(&accounts.alice).is_none());
            assert!(contract.is_owner.get(&accounts.django).is_some());
            assert_eq!(test::recorded_events().count(), 2);
        }

        #[test]
        #[should_panic]
        fn replace_owner_existing_fails() {
            let accounts = default_accounts();
            let mut contract = build_contract();
            set_from_wallet();
            contract.replace_owner(accounts.alice, accounts.bob);
        }

        #[test]
        #[should_panic]
        fn replace_owner_nonexisting_fails() {
            let accounts = default_accounts();
            let mut contract = build_contract();
            set_from_wallet();
            contract.replace_owner(accounts.django, accounts.frank);
        }

        #[test]
        #[should_panic]
        fn replace_owner_permission_denied() {
            let accounts = default_accounts();
            let mut contract = build_contract();
            set_from_owner();
            contract.replace_owner(accounts.alice, accounts.django);
        }

        #[test]
        fn change_requirement_works() {
            let mut contract = build_contract();
            assert_eq!(*contract.requirement.get(), 2);
            set_from_wallet();
            contract.change_requirement(3);
            assert_eq!(*contract.requirement.get(), 3);
            assert_eq!(test::recorded_events().count(), 1);
        }

        #[test]
        #[should_panic]
        fn change_requirement_too_high() {
            let mut contract = build_contract();
            set_from_wallet();
            contract.change_requirement(4);
        }

        #[test]
        #[should_panic]
        fn change_requirement_zero_fails() {
            let mut contract = build_contract();
            set_from_wallet();
            contract.change_requirement(0);
        }

        #[test]
        fn submit_transaction_works() {
            submit_transaction();
        }

        #[test]
        #[should_panic]
        fn submit_transaction_noowner_fails() {
            let mut contract = build_contract();
            set_from_noowner();
            contract.submit_transaction(Transaction::change_requirement(1));
        }

        #[test]
        #[should_panic]
        fn submit_transaction_wallet_fails() {
            let mut contract = build_contract();
            set_from_wallet();
            contract.submit_transaction(Transaction::change_requirement(1));
        }

        #[test]
        fn cancel_transaction_works() {
            let mut contract = submit_transaction();
            set_from_wallet();
            contract.cancel_transaction(0);
            assert_eq!(contract.transactions.len(), 0);
            assert_eq!(test::recorded_events().count(), 3);
        }

        #[test]
        fn cancel_transaction_nonexisting() {
            let mut contract = submit_transaction();
            set_from_wallet();
            contract.cancel_transaction(1);
            assert_eq!(contract.transactions.len(), 1);
            assert_eq!(test::recorded_events().count(), 2);
        }

        #[test]
        #[should_panic]
        fn cancel_transaction_no_permission() {
            let mut contract = submit_transaction();
            contract.cancel_transaction(0);
        }

        #[test]
        fn confirm_transaction_works() {
            let mut contract = submit_transaction();
            let accounts = default_accounts();
            set_sender(accounts.bob);
            contract.confirm_transaction(0);
            assert_eq!(test::recorded_events().count(), 3);
            contract.confirmations.get(&(0, accounts.bob)).unwrap();
            assert_eq!(contract.confirmations.len(), 2);
            assert_eq!(*contract.confirmation_count.get(&0).unwrap(), 2);
        }

        #[test]
        fn confirm_transaction_already_confirmed() {
            let mut contract = submit_transaction();
            let accounts = default_accounts();
            set_sender(accounts.alice);
            contract.confirm_transaction(0);
            assert_eq!(test::recorded_events().count(), 2);
            contract.confirmations.get(&(0, accounts.alice)).unwrap();
            assert_eq!(contract.confirmations.len(), 1);
            assert_eq!(*contract.confirmation_count.get(&0).unwrap(), 1);
        }

        #[test]
        #[should_panic]
        fn confirm_transaction_noowner_fail() {
            let mut contract = submit_transaction();
            set_from_noowner();
            contract.confirm_transaction(0);
        }

        #[test]
        fn revoke_transaction_works() {
            let mut contract = submit_transaction();
            let accounts = default_accounts();
            set_sender(accounts.alice);
            contract.revoke_confirmation(0);
            assert_eq!(test::recorded_events().count(), 3);
            assert!(contract.confirmations.get(&(0, accounts.alice)).is_none());
            assert_eq!(contract.confirmations.len(), 0);
            assert_eq!(*contract.confirmation_count.get(&0).unwrap(), 0);
        }

        #[test]
        fn revoke_transaction_no_confirmer() {
            let mut contract = submit_transaction();
            let accounts = default_accounts();
            set_sender(accounts.bob);
            contract.revoke_confirmation(0);
            assert_eq!(test::recorded_events().count(), 2);
            assert!(contract.confirmations.get(&(0, accounts.alice)).is_some());
            assert_eq!(contract.confirmations.len(), 1);
            assert_eq!(*contract.confirmation_count.get(&0).unwrap(), 1);
        }

        #[test]
        #[should_panic]
        fn revoke_transaction_noowner_fail() {
            let mut contract = submit_transaction();
            let accounts = default_accounts();
            set_sender(accounts.django);
            contract.revoke_confirmation(0);
        }

        #[test]
        fn execute_transaction_works() {
            // Execution of calls is currently unsupported in off-chain test.
            // Calling execute_transaction panics in any case.
        }
    }
}