package ics23

import (
	"bytes"
	"encoding/binary"
	"errors"

	// adds sha256 capability to crypto.SHA256

	"crypto/sha256"

	"gno.land/p/nt/ufmt/v0"
)

type HashOp int32

const (
	// NO_HASH is the default if no data passed. Note this is an illegal argument some places.
	HashOp_NO_HASH HashOp = 0
	HashOp_SHA256  HashOp = 1
)

// LengthOp defines how to process the key and value of the LeafOp
// to include length information. After encoding the length with the given
// algorithm, the length will be prepended to the key and value bytes.
// (Each one with it's own encoded length)
type LengthOp int32

const (
	// NO_PREFIX don't include any length info
	LengthOp_NO_PREFIX LengthOp = 0
	// VAR_PROTO uses protobuf (and go-amino) varint encoding of the length
	LengthOp_VAR_PROTO LengthOp = 1
)

// validateIavlOps validates the prefix to ensure it begins with
// the height, size, and version of the IAVL tree. Each varint must be a bounded value.
// In addition, the remaining bytes are validated to ensure they correspond to the correct
// length. The layerNum is the inverse of the tree depth, i.e. depth=0 means leaf, depth>=1 means inner node
func validateIavlOps(op opType, layerNum int) error {
	r := bytes.NewReader(op.GetPrefix())

	height, err := binary.ReadVarint(r)
	if err != nil {
		return ufmt.Errorf("failed to read IAVL height varint: %v", err)
	}
	if int(height) < 0 || int(height) < layerNum {
		return ufmt.Errorf("IAVL height (%d) must be non-negative and greater than or equal to the layer number (%d)", height, layerNum)
	}

	size, err := binary.ReadVarint(r)
	if err != nil {
		return ufmt.Errorf("failed to read IAVL size varint: %v", err)
	}

	if int(size) < 0 {
		return ufmt.Errorf("IAVL size must be non-negative")
	}

	version, err := binary.ReadVarint(r)
	if err != nil {
		return ufmt.Errorf("failed to read IAVL version varint: %v", err)
	}

	if int(version) < 0 {
		return ufmt.Errorf("IAVL version must be non-negative")
	}

	// grab the length of the remainder of the prefix
	remLen := r.Len()
	if layerNum == 0 {
		// leaf node
		if remLen != 0 {
			return ufmt.Errorf("expected remaining prefix length to be 0, got: %d", remLen)
		}
		if height != 0 {
			return ufmt.Errorf("expected leaf node height to be 0, got: %d", remLen)
		}
		if size != 1 {
			return ufmt.Errorf("expected leaf node size to be 1, got: %d", remLen)
		}
	} else {
		// inner node
		//
		// when the child comes from the left, the suffix if filled in
		// prefix: height | size | version | length byte (1 remainder)
		//
		// when the child comes from the right, the suffix is empty
		// prefix: height | size | version | length byte | 32 byte hash | next length byte (34 remainder)
		if remLen != 1 && remLen != 34 {
			return ufmt.Errorf("remainder of prefix must be of length 1 or 34, got: %d", remLen)
		}
		if op.GetHash() != HashOp_SHA256 {
			return ufmt.Errorf("IAVL hash op must be %v", HashOp_SHA256)
		}
	}
	return nil
}

// validateTendermintOps validates the prefix to ensure it begins with []byte{1}.
func validateTendermintOps(op *InnerOp) error {
	if len(op.Prefix) == 0 {
		return ufmt.Errorf("inner op prefix must not be empty")
	}

	innerPrefix := []byte{1}
	if op.Suffix != nil {
		if !bytes.Equal(op.Prefix, innerPrefix) {
			return ufmt.Errorf("expected inner op prefix: %v, got: %v", innerPrefix, op.Prefix)
		}
	}

	if !bytes.HasPrefix(op.Prefix, innerPrefix) {
		return ufmt.Errorf("expected inner op prefix to begin with: %v, got: %v", innerPrefix, op.Prefix[:1])
	}

	return nil
}

// Apply will calculate the leaf hash given the key and value being proven
func (op *LeafOp) Apply(key []byte, value []byte) ([]byte, error) {
	if len(key) == 0 {
		return nil, errors.New("leaf op needs key")
	}
	if len(value) == 0 {
		return nil, errors.New("leaf op needs value")
	}
	pkey, err := prepareLeafData(op.PrehashKey, op.Length, key)
	if err != nil {
		return nil, ufmt.Errorf("prehash key, %v", err)
	}
	pvalue, err := prepareLeafData(op.PrehashValue, op.Length, value)
	if err != nil {
		return nil, ufmt.Errorf("prehash value, %v", err)
	}

	data := op.Prefix
	data = append(data, pkey...)
	data = append(data, pvalue...)

	return doHash(op.Hash, data)
}

// Apply will calculate the hash of the next step, given the hash of the previous step
func (op *InnerOp) Apply(child []byte) ([]byte, error) {
	if len(child) == 0 {
		return nil, errors.New("inner op needs child value")
	}
	preimage := op.Prefix
	preimage = append(preimage, child...)
	preimage = append(preimage, op.Suffix...)
	return doHash(op.Hash, preimage)
}

// CheckAgainstSpec will verify the LeafOp is in the format defined in spec
func (op *LeafOp) CheckAgainstSpec(spec *ProofSpec) error {
	if spec == nil {
		return errors.New("op and spec must be non-nil")
	}
	lspec := spec.LeafSpec
	if lspec == nil {
		return errors.New("spec.LeafSpec must be non-nil")
	}

	if spec.SpecEquals(IavlSpec()) {
		err := validateIavlOps(op, 0)
		if err != nil {
			return err
		}
	}

	if op.Hash != lspec.Hash {
		return ufmt.Errorf("unexpected HashOp: %d", op.Hash)
	}
	if op.PrehashKey != lspec.PrehashKey {
		return ufmt.Errorf("unexpected PrehashKey: %d", op.PrehashKey)
	}
	if op.PrehashValue != lspec.PrehashValue {
		return ufmt.Errorf("unexpected PrehashValue: %d", op.PrehashValue)
	}
	if op.Length != lspec.Length {
		return ufmt.Errorf("unexpected LengthOp: %d", op.Length)
	}
	if !bytes.HasPrefix(op.Prefix, lspec.Prefix) {
		return ufmt.Errorf("leaf Prefix doesn't start with %X", lspec.Prefix)
	}
	return nil
}

// CheckAgainstSpec will verify the InnerOp is in the format defined in spec
func (op *InnerOp) CheckAgainstSpec(spec *ProofSpec, b int) error {
	if spec == nil {
		return errors.New("op and spec must be both non-nil")
	}
	if spec.InnerSpec == nil {
		return errors.New("spec.InnerSpec must be non-nil")
	}
	if spec.LeafSpec == nil {
		return errors.New("spec.LeafSpec must be non-nil")
	}

	if op.Hash != spec.InnerSpec.Hash {
		return ufmt.Errorf("unexpected HashOp: %d", op.Hash)
	}

	if spec.SpecEquals(IavlSpec()) {
		err := validateIavlOps(op, b)
		if err != nil {
			return err
		}
	}

	if spec.SpecEquals(TendermintSpec()) {
		err := validateTendermintOps(op)
		if err != nil {
			return err
		}
	}

	leafPrefix := spec.LeafSpec.Prefix
	if bytes.HasPrefix(op.Prefix, leafPrefix) {
		return ufmt.Errorf("inner Prefix starts with %X", leafPrefix)
	}
	if len(op.Prefix) < int(spec.InnerSpec.MinPrefixLength) {
		return ufmt.Errorf("innerOp prefix too short (%d)", len(op.Prefix))
	}
	maxLeftChildBytes := (len(spec.InnerSpec.ChildOrder) - 1) * int(spec.InnerSpec.ChildSize)
	if len(op.Prefix) > int(spec.InnerSpec.MaxPrefixLength)+maxLeftChildBytes {
		return ufmt.Errorf("innerOp prefix too long (%d)", len(op.Prefix))
	}

	if spec.InnerSpec.ChildSize <= 0 {
		return errors.New("spec.InnerSpec.ChildSize must be >= 1")
	}

	if spec.InnerSpec.MaxPrefixLength >= spec.InnerSpec.MinPrefixLength+spec.InnerSpec.ChildSize {
		return errors.New("spec.InnerSpec.MaxPrefixLength must be < spec.InnerSpec.MinPrefixLength + spec.InnerSpec.ChildSize")
	}

	// ensures soundness, with suffix having to be of correct length
	if len(op.Suffix)%int(spec.InnerSpec.ChildSize) != 0 {
		return ufmt.Errorf("InnerOp suffix malformed")
	}

	return nil
}

// doHash will preform the specified hash on the preimage.
// if hashOp == NONE, it will return an error (use doHashOrNoop if you want different behavior)
func doHash(hashOp HashOp, preimage []byte) ([]byte, error) {
	switch hashOp {
	case HashOp_SHA256:
		h := sha256.Sum256(preimage)
		return h[:], nil
	}
	return nil, ufmt.Errorf("unsupported hashop: %d", hashOp)
}

func prepareLeafData(hashOp HashOp, lengthOp LengthOp, data []byte) ([]byte, error) {
	// TODO: lengthop before or after hash ???
	hdata, err := doHashOrNoop(hashOp, data)
	if err != nil {
		return nil, err
	}

	return doLengthOp(lengthOp, hdata)
}

type opType interface {
	GetPrefix() []byte
	GetHash() HashOp
}

// doLengthOp will calculate the proper prefix and return it prepended
//
//	doLengthOp(op, data) -> length(data) || data
func doLengthOp(lengthOp LengthOp, data []byte) ([]byte, error) {
	switch lengthOp {
	case LengthOp_NO_PREFIX:
		return data, nil
	case LengthOp_VAR_PROTO:
		res := append(encodeVarintProto(len(data)), data...)
		return res, nil
	}
	return nil, ufmt.Errorf("unsupported lengthop: %d", lengthOp)
}

func encodeVarintProto(l int) []byte {
	// avoid multiple allocs for normal case
	res := make([]byte, 0, 8)
	for l >= 1<<7 {
		res = append(res, uint8(l&0x7f|0x80))
		l >>= 7
	}
	res = append(res, uint8(l))
	return res
}

// doHashOrNoop will return the preimage untouched if hashOp == NONE,
// otherwise, perform doHash
func doHashOrNoop(hashOp HashOp, preimage []byte) ([]byte, error) {
	if hashOp == HashOp_NO_HASH {
		return preimage, nil
	}
	return doHash(hashOp, preimage)
}