package asterisc

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"math"
	"os"
	"path/filepath"

	"github.com/ethereum-optimism/optimism/op-challenger/config"
	"github.com/ethereum-optimism/optimism/op-challenger/game/fault/trace/utils"
	"github.com/ethereum-optimism/optimism/op-challenger/game/fault/types"
	"github.com/ethereum-optimism/optimism/op-program/host/kvstore"
	"github.com/ethereum-optimism/optimism/op-service/ioutil"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/log"
)

const (
	proofsDir      = "proofs"
	diskStateCache = "state.json.gz"
)

type AsteriscMetricer interface {
	RecordAsteriscExecutionTime(t float64)
}

type AsteriscTraceProvider struct {
	logger         log.Logger
	dir            string
	prestate       string
	generator      utils.ProofGenerator
	gameDepth      types.Depth
	preimageLoader *utils.PreimageLoader

	types.PrestateProvider

	// lastStep stores the last step in the actual trace if known. 0 indicates unknown.
	// Cached as an optimisation to avoid repeatedly attempting to execute beyond the end of the trace.
	lastStep uint64
}

func NewTraceProvider(logger log.Logger, m AsteriscMetricer, cfg *config.Config, prestateProvider types.PrestateProvider, localInputs utils.LocalGameInputs, dir string, gameDepth types.Depth) *AsteriscTraceProvider {
	return &AsteriscTraceProvider{
		logger:           logger,
		dir:              dir,
		prestate:         cfg.AsteriscAbsolutePreState,
		generator:        NewExecutor(logger, m, cfg, localInputs),
		gameDepth:        gameDepth,
		preimageLoader:   utils.NewPreimageLoader(kvstore.NewDiskKV(utils.PreimageDir(dir)).Get),
		PrestateProvider: prestateProvider,
	}
}

func (p *AsteriscTraceProvider) Get(ctx context.Context, pos types.Position) (common.Hash, error) {
	traceIndex := pos.TraceIndex(p.gameDepth)
	if !traceIndex.IsUint64() {
		return common.Hash{}, errors.New("trace index out of bounds")
	}
	proof, err := p.loadProof(ctx, traceIndex.Uint64())
	if err != nil {
		return common.Hash{}, err
	}
	value := proof.ClaimValue

	if value == (common.Hash{}) {
		return common.Hash{}, errors.New("proof missing post hash")
	}
	return value, nil
}

func (p *AsteriscTraceProvider) GetStepData(ctx context.Context, pos types.Position) ([]byte, []byte, *types.PreimageOracleData, error) {
	traceIndex := pos.TraceIndex(p.gameDepth)
	if !traceIndex.IsUint64() {
		return nil, nil, nil, errors.New("trace index out of bounds")
	}
	proof, err := p.loadProof(ctx, traceIndex.Uint64())
	if err != nil {
		return nil, nil, nil, err
	}
	value := ([]byte)(proof.StateData)
	if len(value) == 0 {
		return nil, nil, nil, errors.New("proof missing state data")
	}
	data := ([]byte)(proof.ProofData)
	if data == nil {
		return nil, nil, nil, errors.New("proof missing proof data")
	}
	oracleData, err := p.preimageLoader.LoadPreimage(proof)
	if err != nil {
		return nil, nil, nil, fmt.Errorf("failed to load preimage: %w", err)
	}
	return value, data, oracleData, nil
}

func (p *AsteriscTraceProvider) GetL2BlockNumberChallenge(_ context.Context) (*types.InvalidL2BlockNumberChallenge, error) {
	return nil, types.ErrL2BlockNumberValid
}

// loadProof will attempt to load or generate the proof data at the specified index
// If the requested index is beyond the end of the actual trace it is extended with no-op instructions.
func (p *AsteriscTraceProvider) loadProof(ctx context.Context, i uint64) (*utils.ProofData, error) {
	// Attempt to read the last step from disk cache
	if p.lastStep == 0 {
		step, err := utils.ReadLastStep(p.dir)
		if err != nil {
			p.logger.Warn("Failed to read last step from disk cache", "err", err)
		} else {
			p.lastStep = step
		}
	}
	// If the last step is tracked, set i to the last step to generate or load the final proof
	if p.lastStep != 0 && i > p.lastStep {
		i = p.lastStep
	}
	path := filepath.Join(p.dir, proofsDir, fmt.Sprintf("%d.json.gz", i))
	file, err := ioutil.OpenDecompressed(path)
	if errors.Is(err, os.ErrNotExist) {
		if err := p.generator.GenerateProof(ctx, p.dir, i); err != nil {
			return nil, fmt.Errorf("generate asterisc trace with proof at %v: %w", i, err)
		}
		// Try opening the file again now and it should exist.
		file, err = ioutil.OpenDecompressed(path)
		if errors.Is(err, os.ErrNotExist) {
			// Expected proof wasn't generated, check if we reached the end of execution
			state, err := p.finalState()
			if err != nil {
				return nil, err
			}
			if state.Exited && state.Step <= i {
				p.logger.Warn("Requested proof was after the program exited", "proof", i, "last", state.Step)
				// The final instruction has already been applied to this state, so the last step we can execute
				// is one before its Step value.
				p.lastStep = state.Step - 1
				// Extend the trace out to the full length using a no-op instruction that doesn't change any state
				// No execution is done, so no proof-data or oracle values are required.
				proof := &utils.ProofData{
					ClaimValue:   state.StateHash,
					StateData:    state.Witness,
					ProofData:    []byte{},
					OracleKey:    nil,
					OracleValue:  nil,
					OracleOffset: 0,
				}
				if err := utils.WriteLastStep(p.dir, proof, p.lastStep); err != nil {
					p.logger.Warn("Failed to write last step to disk cache", "step", p.lastStep)
				}
				return proof, nil
			} else {
				return nil, fmt.Errorf("expected proof not generated but final state was not exited, requested step %v, final state at step %v", i, state.Step)
			}
		}
	}
	if err != nil {
		return nil, fmt.Errorf("cannot open proof file (%v): %w", path, err)
	}
	defer file.Close()
	var proof utils.ProofData
	err = json.NewDecoder(file).Decode(&proof)
	if err != nil {
		return nil, fmt.Errorf("failed to read proof (%v): %w", path, err)
	}
	return &proof, nil
}

func (c *AsteriscTraceProvider) finalState() (*VMState, error) {
	state, err := parseState(filepath.Join(c.dir, utils.FinalState))
	if err != nil {
		return nil, fmt.Errorf("cannot read final state: %w", err)
	}
	return state, nil
}

// AsteriscTraceProviderForTest is a AsteriscTraceProvider that can find the step referencing the preimage read
// Only to be used for testing
type AsteriscTraceProviderForTest struct {
	*AsteriscTraceProvider
}

func NewTraceProviderForTest(logger log.Logger, m AsteriscMetricer, cfg *config.Config, localInputs utils.LocalGameInputs, dir string, gameDepth types.Depth) *AsteriscTraceProviderForTest {
	p := &AsteriscTraceProvider{
		logger:         logger,
		dir:            dir,
		prestate:       cfg.AsteriscAbsolutePreState,
		generator:      NewExecutor(logger, m, cfg, localInputs),
		gameDepth:      gameDepth,
		preimageLoader: utils.NewPreimageLoader(kvstore.NewDiskKV(utils.PreimageDir(dir)).Get),
	}
	return &AsteriscTraceProviderForTest{p}
}

func (p *AsteriscTraceProviderForTest) FindStep(ctx context.Context, start uint64, preimage utils.PreimageOpt) (uint64, error) {
	// Run asterisc to find the step that meets the preimage conditions
	if err := p.generator.(*Executor).generateProof(ctx, p.dir, start, math.MaxUint64, preimage()...); err != nil {
		return 0, fmt.Errorf("generate asterisc trace (until preimage read): %w", err)
	}
	// Load the step from the state asterisc finished with
	state, err := p.finalState()
	if err != nil {
		return 0, fmt.Errorf("failed to load final state: %w", err)
	}
	// Check we didn't get to the end of the trace without finding the preimage read we were looking for
	if state.Exited {
		return 0, fmt.Errorf("preimage read not found: %w", io.EOF)
	}
	// The state is the post-state so the step we want to execute to read the preimage is step - 1.
	return state.Step - 1, nil
}
