package mssql

import (
	"database/sql"
	"fmt"
	"regexp"
	"strconv"

	_ "github.com/denisenkom/go-mssqldb"
	"github.com/jinzhu/gorm"
	"github.com/jinzhu/gorm/callbacks"
	"github.com/jinzhu/gorm/clause"
	"github.com/jinzhu/gorm/logger"
	"github.com/jinzhu/gorm/migrator"
	"github.com/jinzhu/gorm/schema"
)

type Dialector struct {
	DSN string
}

func Open(dsn string) gorm.Dialector {
	return &Dialector{DSN: dsn}
}

func (dialector Dialector) Initialize(db *gorm.DB) (err error) {
	// register callbacks
	callbacks.RegisterDefaultCallbacks(db, &callbacks.Config{})
	db.Callback().Create().Replace("gorm:create", Create)
	db.ConnPool, err = sql.Open("sqlserver", dialector.DSN)

	for k, v := range dialector.ClauseBuilders() {
		db.ClauseBuilders[k] = v
	}
	return
}

func (dialector Dialector) ClauseBuilders() map[string]clause.ClauseBuilder {
	return map[string]clause.ClauseBuilder{
		"LIMIT": func(c clause.Clause, builder clause.Builder) {
			if limit, ok := c.Expression.(clause.Limit); ok {
				if limit.Offset > 0 {
					builder.WriteString("OFFSET ")
					builder.WriteString(strconv.Itoa(limit.Offset))
					builder.WriteString("ROWS")
				}

				if limit.Limit > 0 {
					if limit.Offset == 0 {
						builder.WriteString(" OFFSET 0 ROWS")
					}
					builder.WriteString(" FETCH NEXT ")
					builder.WriteString(strconv.Itoa(limit.Limit))
					builder.WriteString(" ROWS ONLY")
				}
			}
		},
	}
}

func (dialector Dialector) Migrator(db *gorm.DB) gorm.Migrator {
	return Migrator{migrator.Migrator{Config: migrator.Config{
		DB:                          db,
		Dialector:                   dialector,
		CreateIndexAfterCreateTable: true,
	}}}
}

func (dialector Dialector) BindVarTo(writer clause.Writer, stmt *gorm.Statement, v interface{}) {
	writer.WriteString("@p")
	writer.WriteString(strconv.Itoa(len(stmt.Vars)))
}

func (dialector Dialector) QuoteTo(writer clause.Writer, str string) {
	writer.WriteByte('"')
	writer.WriteString(str)
	writer.WriteByte('"')
}

var numericPlaceholder = regexp.MustCompile("@p(\\d+)")

func (dialector Dialector) Explain(sql string, vars ...interface{}) string {
	return logger.ExplainSQL(sql, numericPlaceholder, `'`, vars...)
}

func (dialector Dialector) DataTypeOf(field *schema.Field) string {
	switch field.DataType {
	case schema.Bool:
		return "bit"
	case schema.Int, schema.Uint:
		var sqlType string
		switch {
		case field.Size < 16:
			sqlType = "smallint"
		case field.Size < 31:
			sqlType = "int"
		default:
			sqlType = "bigint"
		}

		if field.AutoIncrement || field == field.Schema.PrioritizedPrimaryField {
			return sqlType + " IDENTITY(1,1)"
		}
		return sqlType
	case schema.Float:
		return "float"
	case schema.String:
		size := field.Size
		if field.PrimaryKey && size == 0 {
			size = 256
		}
		if size > 0 && size <= 4000 {
			return fmt.Sprintf("nvarchar(%d)", size)
		}
		return "nvarchar(MAX)"
	case schema.Time:
		return "datetimeoffset"
	case schema.Bytes:
		return "varbinary(MAX)"
	}

	return ""
}