package ormkv

import (
	"bytes"
	"errors"
	"io"

	"google.golang.org/protobuf/reflect/protoreflect"

	"cosmossdk.io/orm/types/ormerrors"
)

// UniqueKeyCodec is the codec for unique indexes.
type UniqueKeyCodec struct {
	pkFieldOrder []struct {
		inKey bool
		i     int
	}
	keyCodec   *KeyCodec
	valueCodec *KeyCodec
}

var _ IndexCodec = &UniqueKeyCodec{}

// NewUniqueKeyCodec creates a new UniqueKeyCodec with an optional prefix for the
// provided message descriptor, index and primary key fields.
func NewUniqueKeyCodec(prefix []byte, messageType protoreflect.MessageType, indexFields, primaryKeyFields []protoreflect.Name) (*UniqueKeyCodec, error) {
	if len(indexFields) == 0 {
		return nil, ormerrors.InvalidTableDefinition.Wrapf("index fields are empty")
	}

	if len(primaryKeyFields) == 0 {
		return nil, ormerrors.InvalidTableDefinition.Wrapf("primary key fields are empty")
	}

	keyCodec, err := NewKeyCodec(prefix, messageType, indexFields)
	if err != nil {
		return nil, err
	}

	haveFields := map[protoreflect.Name]int{}
	for i, descriptor := range keyCodec.fieldDescriptors {
		haveFields[descriptor.Name()] = i
	}

	var valueFields []protoreflect.Name
	var pkFieldOrder []struct {
		inKey bool
		i     int
	}
	k := 0
	for _, field := range primaryKeyFields {
		if j, ok := haveFields[field]; ok {
			pkFieldOrder = append(pkFieldOrder, struct {
				inKey bool
				i     int
			}{inKey: true, i: j})
		} else {
			valueFields = append(valueFields, field)
			pkFieldOrder = append(pkFieldOrder, struct {
				inKey bool
				i     int
			}{inKey: false, i: k})
			k++
		}
	}

	// if there is nothing in the value we have a trivial unique index
	// which shouldn't actually be a unique index at all
	if len(valueFields) == 0 {
		return nil, ormerrors.InvalidTableDefinition.Wrapf("unique index %s on table %s introduces no new uniqueness constraint not already in the primary key and should not be marked as unique",
			indexFields, messageType.Descriptor().FullName())
	}

	valueCodec, err := NewKeyCodec(nil, messageType, valueFields)
	if err != nil {
		return nil, err
	}

	return &UniqueKeyCodec{
		pkFieldOrder: pkFieldOrder,
		keyCodec:     keyCodec,
		valueCodec:   valueCodec,
	}, nil
}

func (u UniqueKeyCodec) DecodeIndexKey(k, v []byte) (indexFields, primaryKey []protoreflect.Value, err error) {
	ks, err := u.keyCodec.DecodeKey(bytes.NewReader(k))

	// got prefix key
	if errors.Is(err, io.EOF) {
		return ks, nil, err
	} else if err != nil {
		return nil, nil, err
	}

	// got prefix key
	if len(ks) < len(u.keyCodec.fieldCodecs) {
		return ks, nil, err
	}

	vs, err := u.valueCodec.DecodeKey(bytes.NewReader(v))
	if err != nil {
		return nil, nil, err
	}

	pk := u.extractPrimaryKey(ks, vs)
	return ks, pk, nil
}

func (u UniqueKeyCodec) extractPrimaryKey(keyValues, valueValues []protoreflect.Value) []protoreflect.Value {
	numPkFields := len(u.pkFieldOrder)
	pkValues := make([]protoreflect.Value, numPkFields)

	for i := 0; i < numPkFields; i++ {
		fo := u.pkFieldOrder[i]
		if fo.inKey {
			pkValues[i] = keyValues[fo.i]
		} else {
			pkValues[i] = valueValues[fo.i]
		}
	}

	return pkValues
}

func (u UniqueKeyCodec) DecodeEntry(k, v []byte) (Entry, error) {
	idxVals, pk, err := u.DecodeIndexKey(k, v)
	if err != nil {
		return nil, err
	}

	return &IndexKeyEntry{
		TableName:   u.MessageType().Descriptor().FullName(),
		Fields:      u.keyCodec.fieldNames,
		IsUnique:    true,
		IndexValues: idxVals,
		PrimaryKey:  pk,
	}, err
}

func (u UniqueKeyCodec) EncodeEntry(entry Entry) (k, v []byte, err error) {
	indexEntry, ok := entry.(*IndexKeyEntry)
	if !ok {
		return nil, nil, ormerrors.BadDecodeEntry
	}
	k, err = u.keyCodec.EncodeKey(indexEntry.IndexValues)
	if err != nil {
		return nil, nil, err
	}

	n := len(indexEntry.PrimaryKey)
	if n != len(u.pkFieldOrder) {
		return nil, nil, ormerrors.BadDecodeEntry.Wrapf("wrong primary key length")
	}

	var values []protoreflect.Value
	for i := 0; i < n; i++ {
		value := indexEntry.PrimaryKey[i]
		fieldOrder := u.pkFieldOrder[i]
		if !fieldOrder.inKey {
			// goes in values because it is not present in the index key otherwise
			values = append(values, value)
		} else if u.keyCodec.fieldCodecs[fieldOrder.i].Compare(value, indexEntry.IndexValues[fieldOrder.i]) != 0 {
			// does not go in values, but we need to verify that the value in index values matches the primary key value
			return nil, nil, ormerrors.BadDecodeEntry.Wrapf("value in primary key does not match corresponding value in index key")
		}
	}

	v, err = u.valueCodec.EncodeKey(values)
	return k, v, err
}

func (u UniqueKeyCodec) EncodeKVFromMessage(message protoreflect.Message) (k, v []byte, err error) {
	_, k, err = u.keyCodec.EncodeKeyFromMessage(message)
	if err != nil {
		return nil, nil, err
	}

	_, v, err = u.valueCodec.EncodeKeyFromMessage(message)
	return k, v, err
}

func (u UniqueKeyCodec) GetFieldNames() []protoreflect.Name {
	return u.keyCodec.GetFieldNames()
}

func (u UniqueKeyCodec) GetKeyCodec() *KeyCodec {
	return u.keyCodec
}

func (u UniqueKeyCodec) GetValueCodec() *KeyCodec {
	return u.valueCodec
}

func (u UniqueKeyCodec) CompareKeys(key1, key2 []protoreflect.Value) int {
	return u.keyCodec.CompareKeys(key1, key2)
}

func (u UniqueKeyCodec) EncodeKeyFromMessage(message protoreflect.Message) (keyValues []protoreflect.Value, key []byte, err error) {
	return u.keyCodec.EncodeKeyFromMessage(message)
}

func (u UniqueKeyCodec) IsFullyOrdered() bool {
	return u.keyCodec.IsFullyOrdered()
}

func (u UniqueKeyCodec) MessageType() protoreflect.MessageType {
	return u.keyCodec.messageType
}