package db

import (
	"database/sql"
	"database/sql/driver"
	"encoding/json"
	"fmt"
	"gorm.io/gorm"
	"gorm.io/gorm/callbacks"
	"gorm.io/gorm/clause"
	"gorm.io/gorm/schema"
	"reflect"
)

type Version sql.NullInt64

func (n *Version) Scan(value interface{}) error {
	return (*sql.NullInt64)(n).Scan(value)
}

func (n Version) Value() (driver.Value, error) {
	if !n.Valid {
		return 0, nil
	}
	return n.Int64, nil
}

func (n Version) MarshalJSON() ([]byte, error) {
	if n.Valid {
		return json.Marshal(n.Int64)
	}
	return json.Marshal(0)
}

func (n *Version) UnmarshalJSON(b []byte) error {
	if string(b) == "null" {
		n.Valid = false
		return nil
	}
	err := json.Unmarshal(b, &n.Int64)
	if err == nil {
		n.Valid = true
	}
	return err
}

func (Version) UpdateClauses(f *schema.Field) []clause.Interface {
	return []clause.Interface{OptimisticLockUpdateClause{Field: f}}
}

type OptimisticLockUpdateClause struct {
	Field *schema.Field
}

func (sd OptimisticLockUpdateClause) Name() string {
	return ""
}

func (sd OptimisticLockUpdateClause) Build(clause.Builder) {
}

func (sd OptimisticLockUpdateClause) MergeClause(*clause.Clause) {
}

func (sd OptimisticLockUpdateClause) ModifyStatement(stmt *gorm.Statement) {
	versionValue := clause.Expr{SQL: fmt.Sprintf("%s+1", sd.Field.DBName)}
	if stmt.SQL.String() == "" {
		if set := callbacks.ConvertToAssignments(stmt); len(set) > 0 {
			exists := false
			for i, c := range set {
				if c.Column.Name == sd.Field.DBName {
					c.Value = versionValue
					set[i] = c
					exists = true
					break
				}
			}
			if !exists {
				set = append(set, clause.Assignment{Column: clause.Column{Name: sd.Field.DBName}, Value: versionValue})
			}
			stmt.AddClause(set)
		} else {
			stmt.AddClause(clause.Set{{Column: clause.Column{Name: sd.Field.DBName}, Value: versionValue}})
		}
		stmt.SetColumn(sd.Field.DBName, versionValue, true)

		if stmt.Schema != nil {
			_, queryValues := schema.GetIdentityFieldValuesMap(stmt.ReflectValue, stmt.Schema.PrimaryFields)
			column, values := schema.ToQueryValues(stmt.Table, stmt.Schema.PrimaryFieldDBNames, queryValues)

			if len(values) > 0 {
				stmt.AddClause(clause.Where{Exprs: []clause.Expression{clause.IN{Column: column, Values: values}}})
			}

			if stmt.ReflectValue.CanAddr() && stmt.Dest != stmt.Model && stmt.Model != nil {
				_, queryValues = schema.GetIdentityFieldValuesMap(reflect.ValueOf(stmt.Model), stmt.Schema.PrimaryFields)
				column, values = schema.ToQueryValues(stmt.Table, stmt.Schema.PrimaryFieldDBNames, queryValues)

				if len(values) > 0 {
					stmt.AddClause(clause.Where{Exprs: []clause.Expression{clause.IN{Column: column, Values: values}}})
				}
			}
		}

		if _, ok := stmt.Clauses["WHERE"]; !stmt.DB.AllowGlobalUpdate && !ok {
			stmt.DB.AddError(gorm.ErrMissingWhereClause)
		} else {
			oldVersion := sd.getVersionValue(stmt)
			if _, ok := stmt.Clauses["optimistic_lock_enabled"]; !ok && oldVersion > 0 {
				if c, ok := stmt.Clauses["WHERE"]; ok {
					if where, ok := c.Expression.(clause.Where); ok && len(where.Exprs) > 1 {
						for _, expr := range where.Exprs {
							if orCond, ok := expr.(clause.OrConditions); ok && len(orCond.Exprs) == 1 {
								where.Exprs = []clause.Expression{clause.And(where.Exprs...)}
								c.Expression = where
								stmt.Clauses["WHERE"] = c
								break
							}
						}
					}
				}

				stmt.AddClause(clause.Where{Exprs: []clause.Expression{
					clause.Eq{Column: clause.Column{Table: clause.CurrentTable, Name: sd.Field.DBName}, Value: oldVersion},
				}})
				stmt.Clauses["optimistic_lock_enabled"] = clause.Clause{}
			}
		}

		stmt.AddClauseIfNotExists(clause.Update{})
		stmt.Build("UPDATE", "SET", "WHERE")
	}

}

func (sd OptimisticLockUpdateClause) getVersionValue(stmt *gorm.Statement) int64 {
	if stmt.Dest != nil {
		v := reflect.ValueOf(stmt.Dest)
		k := reflect.ValueOf(stmt.Dest).Kind()
		if k == reflect.Ptr {
			v = v.Elem()
			k = v.Kind()
		}

		if k == reflect.Struct {
			fv := v.FieldByName(sd.Field.Name)
			if fv.Kind() == reflect.Ptr {
				fv = fv.Elem()
			}
			iv := fv.FieldByName("Int64")
			return iv.Int()
		}
	}
	return 0
}