package bui

import (
	"encoding/json"
	"errors"
	"fmt"
	"strings"
)

var (
	ErrEmptyQuery = errors.New("empty query")
	chunkSize     = 100
)

func BulkSaveBuilder(objects []map[string]interface{}, tableName string) ([]string, error) {
	if len(objects) == 0 {
		return []string{}, ErrEmptyQuery
	}

	chunks := splitToChunks(objects, chunkSize)
	keys := getKeys(objects[0])

	rawKeys := strings.Join(keys, ", ")

	var updateKeys []string
	for _, key := range keys {
		updateKeys = append(updateKeys, fmt.Sprintf("%s = VALUES(%s)", key, key))
	}

	rawUpdate := strings.Join(updateKeys, ", ")

	var queries []string
	for _, chunk := range chunks {
		var valueGroups [][]interface{}
		for _, obj := range chunk {
			var valueGroup []interface{}
			for _, key := range keys {
				valueGroup = append(valueGroup, obj[key])
			}
			valueGroups = append(valueGroups, valueGroup)
		}

		JSONValues, err := json.Marshal(valueGroups)
		if err != nil {
			return []string{}, err
		}

		rawValues := strings.ReplaceAll(fmt.Sprintf("%s", JSONValues), "[", "(")
		rawValues = strings.ReplaceAll(rawValues, "]", ")")

		q := fmt.Sprintf(
			"INSERT INTO `%s` (%s) VALUES %s ON DUPLICATE KEY UPDATE %s",
			tableName, rawKeys, rawValues[1:len(rawValues)-1], rawUpdate,
		)
		queries = append(queries, q)
	}

	return queries, nil
}

func getKeys(myMap map[string]interface{}) []string {
	keys := make([]string, 0, len(myMap))
	for key := range myMap {
		keys = append(keys, key)
	}
	return keys
}

func splitToChunks(arr []map[string]interface{}, lim int) [][]map[string]interface{} {
	var chunk []map[string]interface{}
	chunks := make([][]map[string]interface{}, 0, len(arr)/lim+1)
	for len(arr) >= lim {
		chunk, arr = arr[:lim], arr[lim:]
		chunks = append(chunks, chunk)
	}
	if len(arr) > 0 {
		chunks = append(chunks, arr[:])
	}
	return chunks
}