// Copyright (c) Mainflux
// SPDX-License-Identifier: Apache-2.0

package mongodb

import (
	"context"

	"github.com/mainflux/mainflux/pkg/errors"
	"github.com/mainflux/mainflux/pkg/transformers/senml"
	"github.com/mainflux/mainflux/readers"
	"go.mongodb.org/mongo-driver/bson"
	"go.mongodb.org/mongo-driver/mongo"
	"go.mongodb.org/mongo-driver/mongo/options"
)

const collection = "mainflux"

var errReadMessages = errors.New("failed to read messages from mongodb database")

var _ readers.MessageRepository = (*mongoRepository)(nil)

type mongoRepository struct {
	db *mongo.Database
}

// Message struct is used as a MongoDB representation of Mainflux message.
type message struct {
	Channel     string   `bson:"channel,omitempty"`
	Subtopic    string   `bson:"subtopic,omitempty"`
	Publisher   string   `bson:"publisher,omitempty"`
	Protocol    string   `bson:"protocol,omitempty"`
	Name        string   `bson:"name,omitempty"`
	Unit        string   `bson:"unit,omitempty"`
	Value       *float64 `bson:"value,omitempty"`
	StringValue *string  `bson:"stringValue,omitempty"`
	BoolValue   *bool    `bson:"boolValue,omitempty"`
	DataValue   *string  `bson:"dataValue,omitempty"`
	Sum         *float64 `bson:"sum,omitempty"`
	Time        float64  `bson:"time,omitempty"`
	UpdateTime  float64  `bson:"updateTime,omitempty"`
}

// New returns new MongoDB reader.
func New(db *mongo.Database) readers.MessageRepository {
	return mongoRepository{
		db: db,
	}
}

func (repo mongoRepository) ReadAll(chanID string, offset, limit uint64, query map[string]string) (readers.MessagesPage, error) {
	col := repo.db.Collection(collection)
	sortMap := map[string]interface{}{
		"time": -1,
	}

	filter := fmtCondition(chanID, query)
	cursor, err := col.Find(context.Background(), filter, options.Find().SetSort(sortMap).SetLimit(int64(limit)).SetSkip(int64(offset)))
	if err != nil {
		return readers.MessagesPage{}, errors.Wrap(errReadMessages, err)
	}
	defer cursor.Close(context.Background())

	messages := []senml.Message{}
	for cursor.Next(context.Background()) {
		var m message
		if err := cursor.Decode(&m); err != nil {
			return readers.MessagesPage{}, errors.Wrap(errReadMessages, err)
		}

		msg := senml.Message{
			Channel:    m.Channel,
			Subtopic:   m.Subtopic,
			Publisher:  m.Publisher,
			Protocol:   m.Protocol,
			Name:       m.Name,
			Unit:       m.Unit,
			Time:       m.Time,
			UpdateTime: m.UpdateTime,
			Sum:        m.Sum,
		}

		switch {
		case m.Value != nil:
			msg.Value = m.Value
		case m.StringValue != nil:
			msg.StringValue = m.StringValue
		case m.DataValue != nil:
			msg.DataValue = m.DataValue
		case m.BoolValue != nil:
			msg.BoolValue = m.BoolValue
		}

		messages = append(messages, msg)
	}

	total, err := col.CountDocuments(context.Background(), filter)
	if err != nil {
		return readers.MessagesPage{}, errors.Wrap(errReadMessages, err)
	}
	if total < 0 {
		return readers.MessagesPage{}, nil
	}

	return readers.MessagesPage{
		Total:    uint64(total),
		Offset:   offset,
		Limit:    limit,
		Messages: messages,
	}, nil
}

func fmtCondition(chanID string, query map[string]string) *bson.D {
	filter := bson.D{
		bson.E{
			Key:   "channel",
			Value: chanID,
		},
	}
	for name, value := range query {
		switch name {
		case
			"channel",
			"subtopic",
			"publisher",
			"name",
			"protocol":
			filter = append(filter, bson.E{Key: name, Value: value})
		}
	}

	return &filter
}