/*
Package invoker provides a convenient wrapper to perform test calls via RPC client.

This layer builds on top of the basic RPC client and simplifies performing
test function invocations and script runs. It also makes historic calls (NeoGo
extension) transparent, allowing to use the same API as for regular calls.
Results of these calls can be interpreted by upper layer packages like actor
(to create transactions) or unwrap (to retrieve data from return values).
*/
package invoker

import (
	"errors"
	"fmt"

	"github.com/google/uuid"
	"github.com/nspcc-dev/neo-go/pkg/core/transaction"
	"github.com/nspcc-dev/neo-go/pkg/neorpc/result"
	"github.com/nspcc-dev/neo-go/pkg/smartcontract"
	"github.com/nspcc-dev/neo-go/pkg/util"
	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
)

// DefaultIteratorResultItems is the default number of results to
// request from the iterator. Typically it's the same as server's
// MaxIteratorResultItems, but different servers can have different
// settings.
const DefaultIteratorResultItems = 100

// RPCSessions is a set of RPC methods needed to retrieve values from the
// session-based iterators.
type RPCSessions interface {
	TerminateSession(sessionID uuid.UUID) (bool, error)
	TraverseIterator(sessionID, iteratorID uuid.UUID, maxItemsCount int) ([]stackitem.Item, error)
}

// RPCInvoke is a set of RPC methods needed to execute things at the current
// blockchain height.
type RPCInvoke interface {
	RPCSessions

	InvokeContractVerify(contract util.Uint160, params []smartcontract.Parameter, signers []transaction.Signer, witnesses ...transaction.Witness) (*result.Invoke, error)
	InvokeFunction(contract util.Uint160, operation string, params []smartcontract.Parameter, signers []transaction.Signer) (*result.Invoke, error)
	InvokeScript(script []byte, signers []transaction.Signer) (*result.Invoke, error)
}

// RPCInvokeHistoric is a set of RPC methods needed to execute things at some
// fixed point in blockchain's life.
type RPCInvokeHistoric interface {
	RPCSessions

	InvokeContractVerifyAtHeight(height uint32, contract util.Uint160, params []smartcontract.Parameter, signers []transaction.Signer, witnesses ...transaction.Witness) (*result.Invoke, error)
	InvokeContractVerifyWithState(stateroot util.Uint256, contract util.Uint160, params []smartcontract.Parameter, signers []transaction.Signer, witnesses ...transaction.Witness) (*result.Invoke, error)
	InvokeFunctionAtHeight(height uint32, contract util.Uint160, operation string, params []smartcontract.Parameter, signers []transaction.Signer) (*result.Invoke, error)
	InvokeFunctionWithState(stateroot util.Uint256, contract util.Uint160, operation string, params []smartcontract.Parameter, signers []transaction.Signer) (*result.Invoke, error)
	InvokeScriptAtHeight(height uint32, script []byte, signers []transaction.Signer) (*result.Invoke, error)
	InvokeScriptWithState(stateroot util.Uint256, script []byte, signers []transaction.Signer) (*result.Invoke, error)
}

// Invoker allows to test-execute things using RPC client. Its API simplifies
// reusing the same signers list for a series of invocations and at the
// same time uses regular Go types for call parameters. It doesn't do anything with
// the result of invocation, that's left for upper (contract) layer to deal with.
// Invoker does not produce any transactions and does not change the state of the
// chain.
type Invoker struct {
	client  RPCInvoke
	signers []transaction.Signer
}

type historicConverter struct {
	client RPCInvokeHistoric
	height *uint32
	root   *util.Uint256
}

// New creates an Invoker to test-execute things at the current blockchain height.
// If you only want to read data from the contract using its safe methods normally
// (but contract-specific in general case) it's OK to pass nil for signers (that
// is, use no signers).
func New(client RPCInvoke, signers []transaction.Signer) *Invoker {
	return &Invoker{client, signers}
}

// NewHistoricAtHeight creates an Invoker to test-execute things at some given height.
func NewHistoricAtHeight(height uint32, client RPCInvokeHistoric, signers []transaction.Signer) *Invoker {
	return New(&historicConverter{
		client: client,
		height: &height,
	}, signers)
}

// NewHistoricWithState creates an Invoker to test-execute things with some
// given state or block.
func NewHistoricWithState(rootOrBlock util.Uint256, client RPCInvokeHistoric, signers []transaction.Signer) *Invoker {
	return New(&historicConverter{
		client: client,
		root:   &rootOrBlock,
	}, signers)
}

func (h *historicConverter) InvokeScript(script []byte, signers []transaction.Signer) (*result.Invoke, error) {
	if h.height != nil {
		return h.client.InvokeScriptAtHeight(*h.height, script, signers)
	}
	if h.root != nil {
		return h.client.InvokeScriptWithState(*h.root, script, signers)
	}
	panic("uninitialized historicConverter")
}

func (h *historicConverter) InvokeFunction(contract util.Uint160, operation string, params []smartcontract.Parameter, signers []transaction.Signer) (*result.Invoke, error) {
	if h.height != nil {
		return h.client.InvokeFunctionAtHeight(*h.height, contract, operation, params, signers)
	}
	if h.root != nil {
		return h.client.InvokeFunctionWithState(*h.root, contract, operation, params, signers)
	}
	panic("uninitialized historicConverter")
}

func (h *historicConverter) InvokeContractVerify(contract util.Uint160, params []smartcontract.Parameter, signers []transaction.Signer, witnesses ...transaction.Witness) (*result.Invoke, error) {
	if h.height != nil {
		return h.client.InvokeContractVerifyAtHeight(*h.height, contract, params, signers, witnesses...)
	}
	if h.root != nil {
		return h.client.InvokeContractVerifyWithState(*h.root, contract, params, signers, witnesses...)
	}
	panic("uninitialized historicConverter")
}

func (h *historicConverter) TerminateSession(sessionID uuid.UUID) (bool, error) {
	return h.client.TerminateSession(sessionID)
}

func (h *historicConverter) TraverseIterator(sessionID, iteratorID uuid.UUID, maxItemsCount int) ([]stackitem.Item, error) {
	return h.client.TraverseIterator(sessionID, iteratorID, maxItemsCount)
}

// Signers returns the set of current invoker signers which is mostly useful
// when working with upper-layer actors. Returned slice is a newly allocated
// one (if this invoker has them), so it's safe to modify.
func (v *Invoker) Signers() []transaction.Signer {
	if v.signers == nil {
		return nil
	}
	var res = make([]transaction.Signer, len(v.signers))
	for i := range v.signers {
		res[i] = *v.signers[i].Copy()
	}
	return res
}

// Call invokes a method of the contract with the given parameters (and
// Invoker-specific list of signers) and returns the result as is.
func (v *Invoker) Call(contract util.Uint160, operation string, params ...any) (*result.Invoke, error) {
	ps, err := smartcontract.NewParametersFromValues(params...)
	if err != nil {
		return nil, err
	}
	return v.client.InvokeFunction(contract, operation, ps, v.signers)
}

// CallAndExpandIterator creates a script containing a call of the specified method
// of a contract with given parameters (similar to how Call operates). But then this
// script contains additional code that expects that the result of the first call is
// an iterator. This iterator is traversed extracting values from it and adding them
// into an array until maxItems is reached or iterator has no more elements. The
// result of the whole script is an array containing up to maxResultItems elements
// from the iterator returned from the contract's method call. This script is executed
// using regular JSON-API (according to the way Iterator is set up).
func (v *Invoker) CallAndExpandIterator(contract util.Uint160, method string, maxItems int, params ...any) (*result.Invoke, error) {
	bytes, err := smartcontract.CreateCallAndUnwrapIteratorScript(contract, method, maxItems, params...)
	if err != nil {
		return nil, fmt.Errorf("iterator unwrapper script: %w", err)
	}
	return v.Run(bytes)
}

// Verify invokes contract's verify method in the verification context with
// Invoker-specific signers and given witnesses and parameters.
func (v *Invoker) Verify(contract util.Uint160, witnesses []transaction.Witness, params ...any) (*result.Invoke, error) {
	ps, err := smartcontract.NewParametersFromValues(params...)
	if err != nil {
		return nil, err
	}
	return v.client.InvokeContractVerify(contract, ps, v.signers, witnesses...)
}

// Run executes given bytecode with Invoker-specific list of signers.
func (v *Invoker) Run(script []byte) (*result.Invoke, error) {
	return v.client.InvokeScript(script, v.signers)
}

// TerminateSession closes the given session, returning an error if anything
// goes wrong. It's not strictly required to close the session (it'll expire on
// the server anyway), but it helps to release server resources earlier.
func (v *Invoker) TerminateSession(sessionID uuid.UUID) error {
	return termSession(v.client, sessionID)
}

func termSession(rpc RPCSessions, sessionID uuid.UUID) error {
	r, err := rpc.TerminateSession(sessionID)
	if err != nil {
		return err
	}
	if !r {
		return errors.New("terminatesession returned false")
	}
	return nil
}

// TraverseIterator allows to retrieve the next batch of items from the given
// iterator in the given session (previously returned from Call or Run). It works
// both with session-backed iterators and expanded ones (which one you have
// depends on the RPC server). It can change the state of the iterator in the
// process. If num <= 0 then DefaultIteratorResultItems number of elements is
// requested. If result contains no elements, then either Iterator has no
// elements or session was expired and terminated by the server.
func (v *Invoker) TraverseIterator(sessionID uuid.UUID, iterator *result.Iterator, num int) ([]stackitem.Item, error) {
	return iterateNext(v.client, sessionID, iterator, num)
}

func iterateNext(rpc RPCSessions, sessionID uuid.UUID, iterator *result.Iterator, num int) ([]stackitem.Item, error) {
	if num <= 0 {
		num = DefaultIteratorResultItems
	}

	if iterator.ID != nil {
		return rpc.TraverseIterator(sessionID, *iterator.ID, num)
	}
	num = min(num, len(iterator.Values))
	items := iterator.Values[:num]
	iterator.Values = iterator.Values[num:]

	return items, nil
}