lazy/lazy.go

package lazy

import (
	"database/sql/driver"
	"errors"
	"fmt"
	"math/rand/v2"
	"reflect"
	"regexp"

	"github.com/jmoiron/sqlx"
)

const (
	DB_TAG    = "db"   //tag used to parse sql fields in example struct
	LAZY_TAG  = "lazy" //tag label for KEY_VALUE
	KEY_VALUE = "key"  //tag value for LAZY_TAG
)

var (
	ErrBadExample  = errors.New("example field must be a non-nil struct")
	ErrMissingKeys = errors.New("there must be a key for each row requested with RowCount")
	//contains placeholder to inject type on runtime
	ErrUnsupportedType = errors.New("type: %s is not yet supported")
)

// mock data generated based on config
type RowMock struct {
	Query   string
	Columns []string
	Rows    [][]driver.Value
}

// configuration for RandomGenerate
type Config struct {
	Query    string
	Example  any
	Keys     []any
	RowCount int
}

type StructMock struct {
	Query       string
	Args        []driver.Value
	MockStructs []any
	Result      driver.Result
}

// generates mock data based on configuration to be used for sqlmock
func RandomRows(m Config) (*RowMock, error) {
	//example struct cannot be nil and must be a struct
	if m.Example == nil {
		return nil, ErrBadExample
	}
	if reflect.ValueOf(m.Example).Kind() != reflect.Struct {
		return nil, ErrBadExample
	}

	//any weirdness, just pull one row
	if m.RowCount <= 0 {
		m.RowCount = 1
	}

	//if keys are set, ensure there are enough to populate requested rows
	primaryKey := false
	if len(m.Keys) > 0 {
		primaryKey = true
		if len(m.Keys) != m.RowCount {
			return nil, ErrMissingKeys
		}
	}

	retType := reflect.TypeOf(m.Example)
	maxFieldCount := retType.NumField()
	columns := make([]string, 0, maxFieldCount)
	rows := make([][]driver.Value, 0)

	for y := 0; y < m.RowCount; y++ {
		rows = append(rows, make([]driver.Value, 0))
		for x := 0; x < maxFieldCount; x++ {
			field := retType.Field(x)
			dbTag := field.Tag.Get(DB_TAG)
			if dbTag == "" {
				continue
			}

			//track columns only once
			if y == 0 {
				columns = append(columns, dbTag)
			}

			//if field has lazy:"key" tag and tags are present inject primary key
			if field.Tag.Get(LAZY_TAG) == KEY_VALUE && primaryKey {
				rows[y] = append(rows[y], m.Keys[y])
				continue
			}

			//generate random values
			nv := kindToRandom(field)
			if nv == nil {
				return nil, fmt.Errorf(ErrUnsupportedType.Error(), field.Type.Name())
			}

			rows[y] = append(rows[y], nv)
		}
	}

	return &RowMock{
		//sql is rebound and escaped for sqlmock.ExpectQuery
		Query:   sqlx.Rebind(sqlx.AT, regexp.QuoteMeta(m.Query)),
		Columns: columns,
		Rows:    rows,
	}, nil
}

func RandomStruct(c Config) (*StructMock, error) {
	if c.Example == nil {
		return nil, ErrBadExample
	}
	if reflect.ValueOf(c.Example).Kind() != reflect.Struct {
		return nil, ErrBadExample
	}

	if c.RowCount <= 0 {
		c.RowCount = 1
	}

	retType := reflect.TypeOf(c.Example)
	maxFieldCount := retType.NumField()
	//create slice of structs
	ft := reflect.SliceOf(retType)
	filled := reflect.MakeSlice(ft, 0, c.RowCount).Elem()
	args := make([]driver.Value, 0, maxFieldCount)

	for x := 0; x < c.RowCount; x++ {
		for y := 0; y < maxFieldCount; y++ {
			field := retType.Field(y)
			dbTag := field.Tag.Get(DB_TAG)
			if dbTag == "" {
				continue
			}

			nv := kindToRandom(field)
			if nv == nil {
				return nil, fmt.Errorf(ErrUnsupportedType.Error(), field.Type.Name())
			}

			args[y] = nv
			if x == 0 {
				nf := filled.Index(x).Field(y)
				if nf.CanSet() {
					filled.Index(x).Field(y).Set(reflect.ValueOf(nv))
				}
			}
		}
	}

	return &StructMock{
		Query:       sqlx.Rebind(sqlx.AT, regexp.QuoteMeta(c.Query)),
		Args:        args,
		MockStructs: reflect.ValueOf(filled).Interface().([]any),
		Result: &sqlResult{
			rowsAffected: int64(c.RowCount),
			err:          nil,
		},
	}, nil
}

// converts basic reflect Kind's to psuedo-random data, slices are given a random amount of entries
func kindToRandom(field reflect.StructField) any {
	kind := field.Type.Kind()
	switch kind {
	case reflect.Int:
		return rand.Int()
	case reflect.Int32:
		return rand.Int32()
	case reflect.Int64:
		return rand.Int64()
	case reflect.Float32:
		return rand.Float32()
	case reflect.Float64:
		return rand.Float64()
	case reflect.String:
		return fmt.Sprintf("%d", rand.Int())
	case reflect.Bool:
		return rand.Int()%2 == 0
	case reflect.Array:
		underlying := field.Type.Elem().Kind()
		count := reflect.ValueOf(field).Len() //fill entire length
		switch underlying {
		case reflect.Int:
			var intslice []int
			for x := 0; x < count; x++ {
				intslice = append(intslice, rand.Int())
			}
			return intslice
		case reflect.Int32:
			var int32slice []int32
			for x := 0; x < count; x++ {
				int32slice = append(int32slice, rand.Int32())
			}
			return int32slice
		case reflect.Int64:
			var int64slice []int64
			for x := 0; x < count; x++ {
				int64slice = append(int64slice, rand.Int64())
			}
			return int64slice
		case reflect.Float32:
			var float32slice []float32
			for x := 0; x < count; x++ {
				float32slice = append(float32slice, rand.Float32())
			}
			return float32slice
		case reflect.Float64:
			var float64slice []float64
			for x := 0; x < count; x++ {
				float64slice = append(float64slice, rand.Float64())
			}
			return float64slice
		case reflect.String:
			var strslice []string
			for x := 0; x < count; x++ {
				strslice = append(strslice, fmt.Sprintf("%d", rand.Int()))
			}
			return strslice
		case reflect.Bool:
			var boolslice []bool
			for x := 0; x < count; x++ {
				boolslice = append(boolslice, (rand.Int()%2 == 0))
			}
			return boolslice
		}
	case reflect.Slice:
		underlying := field.Type.Elem().Kind()
		count := (rand.Int() % 10) + 1 //amount of entries to append to slice
		switch underlying {
		case reflect.Int:
			var intslice []int
			for x := 0; x < count; x++ {
				intslice = append(intslice, rand.Int())
			}
			return intslice
		case reflect.Int32:
			var int32slice []int32
			for x := 0; x < count; x++ {
				int32slice = append(int32slice, rand.Int32())
			}
			return int32slice
		case reflect.Int64:
			var int64slice []int64
			for x := 0; x < count; x++ {
				int64slice = append(int64slice, rand.Int64())
			}
			return int64slice
		case reflect.Float32:
			var float32slice []float32
			for x := 0; x < count; x++ {
				float32slice = append(float32slice, rand.Float32())
			}
			return float32slice
		case reflect.Float64:
			var float64slice []float64
			for x := 0; x < count; x++ {
				float64slice = append(float64slice, rand.Float64())
			}
			return float64slice
		case reflect.String:
			var strslice []string
			for x := 0; x < count; x++ {
				strslice = append(strslice, fmt.Sprintf("%d", rand.Int()))
			}
			return strslice
		case reflect.Bool:
			var boolslice []bool
			for x := 0; x < count; x++ {
				boolslice = append(boolslice, (rand.Int()%2 == 0))
			}
			return boolslice
		}
	}

	return nil
}