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

package avm

import (
	"bytes"
	"errors"
	"sort"

	"github.com/ava-labs/gecko/chains/atomic"
	"github.com/ava-labs/gecko/database/versiondb"

	"github.com/ava-labs/gecko/database"
	"github.com/ava-labs/gecko/ids"
	"github.com/ava-labs/gecko/snow"
	"github.com/ava-labs/gecko/utils"
	"github.com/ava-labs/gecko/vms/components/ava"
	"github.com/ava-labs/gecko/vms/components/codec"
	"github.com/ava-labs/gecko/vms/components/verify"
)

var (
	errNilUTXOID = errors.New("nil utxo ID is not valid")
)

// ImportInput ...
type ImportInput struct {
	UTXOID    ids.ID `serialize:"true"`
	ava.Asset `serialize:"true"`

	In FxTransferable `serialize:"true"`
}

// Input returns the feature extension input that this Input is using.
func (in *ImportInput) Input() FxTransferable { return in.In }

// Verify implements the verify.Verifiable interface
func (in *ImportInput) Verify() error {
	switch {
	case in == nil:
		return errNilTransferableInput
	case in.UTXOID.IsZero():
		return errNilUTXOID
	case in.In == nil:
		return errNilTransferableFxInput
	default:
		return verify.All(&in.Asset, in.In)
	}
}

type innerSortImportInputs []*ImportInput

func (ins innerSortImportInputs) Less(i, j int) bool {
	return bytes.Compare(ins[i].AssetID().Bytes(), ins[j].AssetID().Bytes()) == -1
}
func (ins innerSortImportInputs) Len() int      { return len(ins) }
func (ins innerSortImportInputs) Swap(i, j int) { ins[j], ins[i] = ins[i], ins[j] }

func sortImportInputs(ins []*ImportInput) { sort.Sort(innerSortImportInputs(ins)) }
func isSortedAndUniqueImportInputs(ins []*ImportInput) bool {
	return utils.IsSortedAndUnique(innerSortImportInputs(ins))
}

// ImportTx is a transaction that imports an asset from another blockchain.
type ImportTx struct {
	BaseTx `serialize:"true"`

	Outs []*TransferableOutput `serialize:"true"` // The outputs of this transaction
	Ins  []*ImportInput        `serialize:"true"` // The inputs to this transaction
}

// InputUTXOs track which UTXOs this transaction is consuming.
func (t *ImportTx) InputUTXOs() []*ava.UTXOID {
	utxos := t.BaseTx.InputUTXOs()
	for _, in := range t.Ins {
		utxos = append(utxos, &ava.UTXOID{
			TxID:   in.UTXOID,
			Symbol: true,
		})
	}
	return utxos
}

// AssetIDs returns the IDs of the assets this transaction depends on
func (t *ImportTx) AssetIDs() ids.Set {
	assets := t.BaseTx.AssetIDs()
	for _, in := range t.Ins {
		assets.Add(in.AssetID())
	}
	return assets
}

// UTXOs returns the UTXOs transaction is producing.
func (t *ImportTx) UTXOs() []*ava.UTXO {
	txID := t.ID()
	utxos := t.BaseTx.UTXOs()

	for _, out := range t.Outs {
		utxos = append(utxos, &ava.UTXO{
			UTXOID: ava.UTXOID{
				TxID:        txID,
				OutputIndex: uint32(len(utxos)),
			},
			Asset: ava.Asset{ID: out.AssetID()},
			Out:   out.Out,
		})
	}

	return utxos
}

var (
	errNoInputs = errors.New("no import inputs")
)

// SyntacticVerify that this transaction is well-formed.
func (t *ImportTx) SyntacticVerify(ctx *snow.Context, c codec.Codec, numFxs int) error {
	switch {
	case t == nil:
		return errNilTx
	case len(t.Ins) == 0:
		return errNoInputs
	}

	if err := t.BaseTx.SyntacticVerify(ctx, c, numFxs); err != nil {
		return err
	}

	fc := ava.NewFlowChecker()
	for _, out := range t.Outs {
		if err := out.Verify(); err != nil {
			return err
		}
		fc.Produce(out.AssetID(), out.Output().Amount())
	}
	if !IsSortedTransferableOutputs(t.Outs, c) {
		return errOutputsNotSorted
	}

	for _, in := range t.Ins {
		if err := in.Verify(); err != nil {
			return err
		}
		fc.Consume(in.AssetID(), in.Input().Amount())
	}
	if !isSortedAndUniqueImportInputs(t.Ins) {
		return errInputsNotSortedUnique
	}

	// TODO: Add the Tx fee to the produced side

	if err := fc.Verify(); err != nil {
		return err
	}

	return nil
}

// SemanticVerify that this transaction is well-formed.
func (t *ImportTx) SemanticVerify(vm *VM, uTx *UniqueTx, creds []verify.Verifiable) error {
	if err := t.BaseTx.SemanticVerify(vm, uTx, creds); err != nil {
		return err
	}

	bID := ids.Empty // TODO: Needs to be set to the platform chain
	smDB := vm.ctx.SharedMemory.GetDatabase(bID)
	defer vm.ctx.SharedMemory.ReleaseDatabase(bID)

	state := ava.NewPrefixedState(smDB, vm.codec)

	offset := len(t.BaseTx.Ins)
	for i, in := range t.Ins {
		cred := creds[i+offset]

		fxIndex, err := vm.getFx(cred)
		if err != nil {
			return err
		}
		fx := vm.fxs[fxIndex].Fx

		utxoID := in.UTXOID
		utxo, err := state.PlatformUTXO(utxoID)
		if err != nil {
			return err
		}
		utxoAssetID := utxo.AssetID()
		inAssetID := in.AssetID()
		if !utxoAssetID.Equals(inAssetID) {
			return errAssetIDMismatch
		}

		if !vm.verifyFxUsage(fxIndex, inAssetID) {
			return errIncompatibleFx
		}

		if err := fx.VerifyTransfer(uTx, utxo.Out, in.In, cred); err != nil {
			return err
		}
	}
	return nil
}

// ExecuteWithSideEffects writes the batch with any additional side effects
func (t *ImportTx) ExecuteWithSideEffects(vm *VM, batch database.Batch) error {
	bID := ids.Empty // TODO: Needs to be set to the platform chain
	smDB := vm.ctx.SharedMemory.GetDatabase(bID)
	defer vm.ctx.SharedMemory.ReleaseDatabase(bID)

	vsmDB := versiondb.New(smDB)

	state := ava.NewPrefixedState(vsmDB, vm.codec)
	for _, in := range t.Ins {
		utxoID := in.UTXOID
		if err := state.SetPlatformUTXO(utxoID, nil); err != nil {
			return err
		}
	}

	sharedBatch, err := vsmDB.CommitBatch()
	if err != nil {
		return err
	}

	return atomic.WriteAll(batch, sharedBatch)
}