// (c) 2019-2020, Ava Labs, Inc. All rights reserved.
// See the file LICENSE for licensing terms.

package platformvm

import (
	"container/heap"
	"errors"
	"fmt"

	"github.com/ava-labs/gecko/database"
	"github.com/ava-labs/gecko/database/versiondb"
	"github.com/ava-labs/gecko/ids"
	"github.com/ava-labs/gecko/utils/math"
)

var (
	errShouldBeDSValidator = errors.New("expected validator to be in the default subnet")
)

// rewardValidatorTx is a transaction that represents a proposal to remove a
// validator that is currently validating from the validator set.
//
// If this transaction is accepted and the next block accepted is a *Commit
// block, the validator is removed and the account that the validator specified
// receives the staked $AVA as well as a validating reward.
//
// If this transaction is accepted and the next block accepted is an *Abort
// block, the validator is removed and the account that the validator specified
// receives the staked $AVA but no reward.
type rewardValidatorTx struct {
	// ID of the tx that created the delegator/validator being removed/rewarded
	TxID ids.ID `serialize:"true"`

	vm *VM
}

func (tx *rewardValidatorTx) initialize(vm *VM) error {
	tx.vm = vm
	return nil
}

// SyntacticVerify that this transaction is well formed
func (tx *rewardValidatorTx) SyntacticVerify() error {
	switch {
	case tx == nil:
		return errNilTx
	case tx.TxID.IsZero():
		return errInvalidID
	default:
		return nil
	}
}

// SemanticVerify this transaction performs a valid state transition.
//
// The current validating set must have at least one member.
// The next validator to be removed must be the validator specified in this block.
// The next validator to be removed must be have an end time equal to the current
//   chain timestamp.
func (tx *rewardValidatorTx) SemanticVerify(db database.Database) (*versiondb.Database, *versiondb.Database, func(), func(), error) {
	if err := tx.SyntacticVerify(); err != nil {
		return nil, nil, nil, nil, err
	}
	if db == nil {
		return nil, nil, nil, nil, errDbNil
	}

	currentEvents, err := tx.vm.getCurrentValidators(db, DefaultSubnetID)
	if err != nil {
		return nil, nil, nil, nil, errDBCurrentValidators
	}
	if currentEvents.Len() == 0 { // there is no validator to remove
		return nil, nil, nil, nil, errEmptyValidatingSet
	}

	vdrTx := currentEvents.Peek()

	if txID := vdrTx.ID(); !txID.Equals(tx.TxID) {
		return nil, nil, nil, nil, fmt.Errorf("attempting to remove TxID: %s. Should be removing %s",
			tx.TxID,
			txID)
	}

	// Verify that the chain's timestamp is the validator's end time
	currentTime, err := tx.vm.getTimestamp(db)
	if err != nil {
		return nil, nil, nil, nil, err
	}
	if endTime := vdrTx.EndTime(); !endTime.Equal(currentTime) {
		return nil, nil, nil, nil, fmt.Errorf("attempting to remove TxID: %s before their end time %s",
			tx.TxID,
			endTime)
	}

	heap.Pop(currentEvents) // Remove validator from the validator set

	onCommitDB := versiondb.New(db)
	// If this tx's proposal is committed, remove the validator from the validator set and update the
	// account balance to reflect the return of staked $AVA and their reward.
	if err := tx.vm.putCurrentValidators(onCommitDB, currentEvents, DefaultSubnetID); err != nil {
		return nil, nil, nil, nil, errDBPutCurrentValidators
	}

	onAbortDB := versiondb.New(db)
	// If this tx's proposal is aborted, remove the validator from the validator set and update the
	// account balance to reflect the return of staked $AVA. The validator receives no reward.
	if err := tx.vm.putCurrentValidators(onAbortDB, currentEvents, DefaultSubnetID); err != nil {
		return nil, nil, nil, nil, errDBPutCurrentValidators
	}

	switch vdrTx := vdrTx.(type) {
	case *addDefaultSubnetValidatorTx:
		duration := vdrTx.Duration()
		amount := vdrTx.Wght
		reward := reward(duration, amount, InflationRate)
		amountWithReward, err := math.Add64(amount, reward)
		if err != nil {
			amountWithReward = amount
			tx.vm.Ctx.Log.Error("error while calculating balance with reward: %s", err)
		}

		accountID := vdrTx.Destination
		account, err := tx.vm.getAccount(db, accountID) // account receiving staked $AVA (and, if applicable, reward)
		// Error is likely because the staked $AVA is being sent to a new
		// account that isn't in the platform chain's state yet.
		// Create the account
		// TODO: We should have a keyNotFound error to distinguish this case from others
		if err != nil {
			account = newAccount(accountID, 0, 0)
		}

		accountWithReward := account // The state of the account if the validator earned a validating reward
		accountNoReward := account   // The state of the account if the validator didn't earn a validating reward
		if newAccount, err := account.Add(amountWithReward); err == nil {
			accountWithReward = newAccount
		} else {
			tx.vm.Ctx.Log.Error("error while calculating account balance: %v", err)
		}
		if newAccount, err := account.Add(amount); err == nil {
			accountNoReward = newAccount
		} else {
			tx.vm.Ctx.Log.Error("error while calculating account balance: %v", err)
		}

		if err := tx.vm.putAccount(onCommitDB, accountWithReward); err != nil {
			return nil, nil, nil, nil, errDBPutAccount
		}
		if err := tx.vm.putAccount(onAbortDB, accountNoReward); err != nil {
			return nil, nil, nil, nil, errDBPutAccount
		}
	case *addDefaultSubnetDelegatorTx:
		parentTx, err := currentEvents.getDefaultSubnetStaker(vdrTx.NodeID)
		if err != nil {
			return nil, nil, nil, nil, err
		}

		duration := vdrTx.Duration()
		amount := vdrTx.Wght
		reward := reward(duration, amount, InflationRate)

		// Because parentTx.Shares <= NumberOfShares this will never underflow
		delegatorShares := NumberOfShares - uint64(parentTx.Shares)
		// Because delegatorShares <= NumberOfShares this will never overflow
		delegatorReward := delegatorShares * (reward / NumberOfShares)
		// Delay rounding as long as possible for small numbers
		if optimisticReward, err := math.Mul64(delegatorShares, reward); err == nil {
			delegatorReward = optimisticReward / NumberOfShares
		}

		// Because delegatorReward <= reward this will never underflow
		validatorReward := reward - delegatorReward

		delegatorAmountWithReward, err := math.Add64(amount, delegatorReward)
		if err != nil {
			delegatorAmountWithReward = amount
			tx.vm.Ctx.Log.Error("error while calculating balance with reward: %s", err)
		}

		delegatorAccountID := vdrTx.Destination
		delegatorAccount, err := tx.vm.getAccount(db, delegatorAccountID) // account receiving staked $AVA (and, if applicable, reward)
		// Error is likely because the staked $AVA is being sent to a new
		// account that isn't in the platform chain's state yet.
		// Create the account
		// TODO: We should have a keyNotFound error to distinguish this case from others
		if err != nil {
			delegatorAccount = newAccount(delegatorAccountID, 0, 0)
		}

		delegatorAccountWithReward := delegatorAccount // The state of the account if the validator earned a validating reward
		delegatorAccountNoReward := delegatorAccount   // The state of the account if the validator didn't earn a validating reward
		if newAccount, err := delegatorAccount.Add(delegatorAmountWithReward); err == nil {
			delegatorAccountWithReward = newAccount
		} else {
			tx.vm.Ctx.Log.Error("error while calculating account balance: %v", err)
		}
		if newAccount, err := delegatorAccount.Add(amount); err == nil {
			delegatorAccountNoReward = newAccount
		} else {
			tx.vm.Ctx.Log.Error("error while calculating account balance: %v", err)
		}

		if err := tx.vm.putAccount(onCommitDB, delegatorAccountWithReward); err != nil {
			return nil, nil, nil, nil, errDBPutAccount
		}
		if err := tx.vm.putAccount(onAbortDB, delegatorAccountNoReward); err != nil {
			return nil, nil, nil, nil, errDBPutAccount
		}

		validatorAccountID := parentTx.Destination
		validatorAccount, err := tx.vm.getAccount(onCommitDB, validatorAccountID) // account receiving staked $AVA (and, if applicable, reward)
		// Error is likely because the staked $AVA is being sent to a new
		// account that isn't in the platform chain's state yet.
		// Create the account
		// TODO: We should have a keyNotFound error to distinguish this case from others
		if err != nil {
			validatorAccount = newAccount(validatorAccountID, 0, 0)
		}

		validatorAccountWithReward := validatorAccount // The state of the account if the validator earned a validating reward
		if newAccount, err := validatorAccount.Add(validatorReward); err == nil {
			validatorAccountWithReward = newAccount
		} else {
			tx.vm.Ctx.Log.Error("error while calculating account balance: %v", err)
		}

		if err := tx.vm.putAccount(onCommitDB, validatorAccountWithReward); err != nil {
			return nil, nil, nil, nil, errDBPutAccount
		}
	default:
		return nil, nil, nil, nil, errShouldBeDSValidator
	}

	// Regardless of whether this tx is committed or aborted, update the
	// validator set to remove the staker. onAbortDB or onCommitDB should commit
	// (flush to vm.DB) before this is called
	updateValidators := func() {
		if err := tx.vm.updateValidators(DefaultSubnetID); err != nil {
			tx.vm.Ctx.Log.Fatal("failed to update validators on the default subnet: %s", err)
		}
	}

	return onCommitDB, onAbortDB, updateValidators, updateValidators, nil
}

// InitiallyPrefersCommit returns true.
//
// Right now, *Commit (that is, remove the validator and reward them) is always
// preferred over *Abort (remove the validator but don't reward them.)
//
// TODO: A validator should receive a reward only if they are sufficiently
// responsive and correct during the time they are validating.
func (tx *rewardValidatorTx) InitiallyPrefersCommit() bool { return true }

// RewardStakerTx creates a new transaction that proposes to remove the staker
// [validatorID] from the default validator set.
func (vm *VM) newRewardValidatorTx(txID ids.ID) (*rewardValidatorTx, error) {
	tx := &rewardValidatorTx{
		TxID: txID,
	}
	return tx, tx.initialize(vm)
}