package gorm

import (
	"errors"
	"fmt"
	"reflect"

	"github.com/jinzhu/gorm/clause"
	"github.com/jinzhu/gorm/schema"
	"github.com/jinzhu/gorm/utils"
)

// Association Mode contains some helper methods to handle relationship things easily.
type Association struct {
	DB           *DB
	Relationship *schema.Relationship
	Error        error
}

func (db *DB) Association(column string) *Association {
	association := &Association{DB: db}

	if err := db.Statement.Parse(db.Statement.Model); err == nil {
		association.Relationship = db.Statement.Schema.Relationships.Relations[column]

		if association.Relationship == nil {
			association.Error = fmt.Errorf("%w: %v", ErrUnsupportedRelation, column)
		}

		db.Statement.ReflectValue = reflect.Indirect(reflect.ValueOf(db.Statement.Model))
	} else {
		association.Error = err
	}

	return association
}

func (association *Association) Find(out interface{}, conds ...interface{}) error {
	if association.Error == nil {
		var (
			queryConds = association.Relationship.ToQueryConditions(association.DB.Statement.ReflectValue)
			tx         = association.DB.Model(out).Table("")
		)

		if association.Relationship.JoinTable != nil {
			for _, queryClause := range association.Relationship.JoinTable.QueryClauses {
				tx.Clauses(queryClause)
			}

			tx.Clauses(clause.From{Joins: []clause.Join{{
				Table: clause.Table{Name: association.Relationship.JoinTable.Table},
				ON:    clause.Where{Exprs: queryConds},
			}}})
		} else {
			tx.Clauses(clause.Where{Exprs: queryConds})
		}

		association.Error = tx.Find(out, conds...).Error
	}

	return association.Error
}

func (association *Association) Append(values ...interface{}) error {
	if association.Error == nil {
		switch association.Relationship.Type {
		case schema.HasOne, schema.BelongsTo:
			if len(values) > 0 {
				association.Error = association.Replace(values...)
			}
		default:
			association.saveAssociation(false, values...)
		}
	}

	return association.Error
}

func (association *Association) Replace(values ...interface{}) error {
	if association.Error == nil {
		association.saveAssociation(true, values...)
		reflectValue := association.DB.Statement.ReflectValue
		rel := association.Relationship

		switch rel.Type {
		case schema.HasOne, schema.HasMany:
			var (
				primaryFields []*schema.Field
				foreignKeys   []string
				updateMap     = map[string]interface{}{}
				modelValue    = reflect.New(rel.FieldSchema.ModelType).Interface()
			)

			for _, ref := range rel.References {
				if ref.OwnPrimaryKey {
					primaryFields = append(primaryFields, ref.PrimaryKey)
				} else {
					foreignKeys = append(foreignKeys, ref.ForeignKey.DBName)
					updateMap[ref.ForeignKey.DBName] = nil
				}
			}

			_, values := schema.GetIdentityFieldValuesMap(reflectValue, primaryFields)
			column, queryValues := schema.ToQueryValues(foreignKeys, values)
			association.DB.Model(modelValue).Where(clause.IN{Column: column, Values: queryValues}).UpdateColumns(updateMap)
		case schema.Many2Many:
			var primaryFields, relPrimaryFields []*schema.Field
			var foreignKeys, relForeignKeys []string
			modelValue := reflect.New(rel.JoinTable.ModelType).Interface()
			conds := []clause.Expression{}

			for _, ref := range rel.References {
				if ref.OwnPrimaryKey {
					primaryFields = append(primaryFields, ref.PrimaryKey)
					foreignKeys = append(foreignKeys, ref.ForeignKey.DBName)
				} else if ref.PrimaryValue != "" {
					conds = append(conds, clause.Eq{
						Column: clause.Column{Table: rel.JoinTable.Table, Name: ref.ForeignKey.DBName},
						Value:  ref.PrimaryValue,
					})
				} else {
					relPrimaryFields = append(relPrimaryFields, ref.PrimaryKey)
					relForeignKeys = append(relForeignKeys, ref.ForeignKey.DBName)
				}
			}

			generateConds := func(rv reflect.Value) {
				_, values := schema.GetIdentityFieldValuesMap(rv, primaryFields)
				column, queryValues := schema.ToQueryValues(foreignKeys, values)

				relValue := rel.Field.ReflectValueOf(rv)
				_, relValues := schema.GetIdentityFieldValuesMap(relValue, relPrimaryFields)
				relColumn, relQueryValues := schema.ToQueryValues(relForeignKeys, relValues)

				conds = append(conds, clause.And(
					clause.IN{Column: column, Values: queryValues},
					clause.Not(clause.IN{Column: relColumn, Values: relQueryValues}),
				))
			}

			switch reflectValue.Kind() {
			case reflect.Struct:
				generateConds(reflectValue)
			case reflect.Slice, reflect.Array:
				for i := 0; i < reflectValue.Len(); i++ {
					generateConds(reflectValue.Index(i))
				}
			}

			association.DB.Where(conds).Delete(modelValue)
		}
	}
	return association.Error
}

func (association *Association) Delete(values ...interface{}) error {
	if association.Error == nil {
		var (
			tx           = association.DB
			rel          = association.Relationship
			reflectValue = tx.Statement.ReflectValue
			conds        = rel.ToQueryConditions(reflectValue)
			relFields    []*schema.Field
			foreignKeys  []string
			updateAttrs  = map[string]interface{}{}
		)

		for _, ref := range rel.References {
			if ref.PrimaryValue == "" {
				if rel.JoinTable == nil || !ref.OwnPrimaryKey {
					if ref.OwnPrimaryKey {
						relFields = append(relFields, ref.ForeignKey)
					} else {
						relFields = append(relFields, ref.PrimaryKey)
					}

					foreignKeys = append(foreignKeys, ref.ForeignKey.DBName)
					updateAttrs[ref.ForeignKey.DBName] = nil
				}
			}
		}

		relValuesMap, relQueryValues := schema.GetIdentityFieldValuesMapFromValues(values, relFields)
		column, values := schema.ToQueryValues(foreignKeys, relQueryValues)
		tx.Where(clause.IN{Column: column, Values: values})

		switch rel.Type {
		case schema.HasOne, schema.HasMany:
			modelValue := reflect.New(rel.FieldSchema.ModelType).Interface()
			tx.Model(modelValue).Clauses(clause.Where{Exprs: conds}).UpdateColumns(updateAttrs)
		case schema.BelongsTo:
			tx.Clauses(clause.Where{Exprs: conds}).UpdateColumns(updateAttrs)
		case schema.Many2Many:
			modelValue := reflect.New(rel.JoinTable.ModelType).Interface()
			tx.Clauses(clause.Where{Exprs: conds}).Delete(modelValue)
		}

		if tx.Error == nil {
			cleanUpDeletedRelations := func(data reflect.Value) {
				if _, zero := rel.Field.ValueOf(data); !zero {
					fieldValue := reflect.Indirect(rel.Field.ReflectValueOf(data))

					fieldValues := make([]reflect.Value, len(relFields))
					switch fieldValue.Kind() {
					case reflect.Slice, reflect.Array:
						validFieldValues := reflect.Zero(rel.Field.FieldType)
						for i := 0; i < fieldValue.Len(); i++ {
							for idx, field := range relFields {
								fieldValues[idx] = field.ReflectValueOf(fieldValue.Index(i))
							}

							if _, ok := relValuesMap[utils.ToStringKey(fieldValues...)]; !ok {
								validFieldValues = reflect.Append(validFieldValues, fieldValue.Index(i))
							}
						}

						rel.Field.Set(data, validFieldValues)
					case reflect.Struct:
						for idx, field := range relFields {
							fieldValues[idx] = field.ReflectValueOf(data)
						}
						if _, ok := relValuesMap[utils.ToStringKey(fieldValues...)]; ok {
							rel.Field.Set(data, reflect.Zero(rel.FieldSchema.ModelType))
						}
					}
				}
			}

			switch reflectValue.Kind() {
			case reflect.Slice, reflect.Array:
				for i := 0; i < reflectValue.Len(); i++ {
					cleanUpDeletedRelations(reflect.Indirect(reflectValue.Index(i)))
				}
			case reflect.Struct:
				cleanUpDeletedRelations(reflectValue)
			}
		} else {
			association.Error = tx.Error
		}
	}
	return association.Error
}

func (association *Association) Clear() error {
	return association.Replace()
}

func (association *Association) Count() (count int) {
	if association.Error == nil {
		var (
			tx    = association.DB
			conds = association.Relationship.ToQueryConditions(tx.Statement.ReflectValue)
		)

		if association.Relationship.JoinTable != nil {
			for _, queryClause := range association.Relationship.JoinTable.QueryClauses {
				tx.Clauses(queryClause)
			}

			tx.Clauses(clause.From{Joins: []clause.Join{{
				Table: clause.Table{Name: association.Relationship.JoinTable.Table},
				ON:    clause.Where{Exprs: conds},
			}}})
		} else {
			tx.Clauses(clause.Where{Exprs: conds})
		}

		association.Error = tx.Count(&count).Error
	}

	return
}

func (association *Association) saveAssociation(clear bool, values ...interface{}) {
	reflectValue := association.DB.Statement.ReflectValue

	appendToRelations := func(source, rv reflect.Value, clear bool) {
		switch association.Relationship.Type {
		case schema.HasOne, schema.BelongsTo:
			switch rv.Kind() {
			case reflect.Slice, reflect.Array:
				if rv.Len() > 0 {
					association.Error = association.Relationship.Field.Set(source, rv.Index(0))
				}
			case reflect.Struct:
				association.Error = association.Relationship.Field.Set(source, rv)
			}
		case schema.HasMany, schema.Many2Many:
			elemType := association.Relationship.Field.IndirectFieldType.Elem()
			fieldValue := reflect.Indirect(association.Relationship.Field.ReflectValueOf(reflectValue))
			if clear {
				fieldValue = reflect.New(association.Relationship.Field.IndirectFieldType)
			}

			appendToFieldValues := func(ev reflect.Value) {
				if ev.Type().AssignableTo(elemType) {
					fieldValue = reflect.Append(fieldValue, ev)
				} else if ev.Type().Elem().AssignableTo(elemType) {
					fieldValue = reflect.Append(fieldValue, ev.Elem())
				} else {
					association.Error = fmt.Errorf("unsupported data type: %v for relation %v", ev.Type(), association.Relationship.Name)
				}
			}

			switch rv.Kind() {
			case reflect.Slice, reflect.Array:
				for i := 0; i < rv.Len(); i++ {
					appendToFieldValues(reflect.Indirect(rv.Index(i)))
				}
			case reflect.Struct:
				appendToFieldValues(rv)
			}

			if association.Error == nil {
				association.Error = association.Relationship.Field.Set(source, fieldValue)
			}
		}
	}

	selectedColumns := []string{association.Relationship.Name}
	hasZero := false
	for _, ref := range association.Relationship.References {
		if !ref.OwnPrimaryKey {
			selectedColumns = append(selectedColumns, ref.ForeignKey.Name)
		}
	}

	switch reflectValue.Kind() {
	case reflect.Slice, reflect.Array:
		if len(values) != reflectValue.Len() {
			if clear && len(values) == 0 {
				for i := 0; i < reflectValue.Len(); i++ {
					association.Relationship.Field.Set(reflectValue.Index(i), reflect.New(association.Relationship.Field.IndirectFieldType))
				}
				break
			}
			association.Error = errors.New("invalid association values, length doesn't match")
		}

		for i := 0; i < reflectValue.Len(); i++ {
			appendToRelations(reflectValue.Index(i), reflect.Indirect(reflect.ValueOf(values[i])), clear)

			if !hasZero {
				_, hasZero = association.DB.Statement.Schema.PrioritizedPrimaryField.ValueOf(reflectValue.Index(i))
			}
		}
	case reflect.Struct:
		if clear && len(values) == 0 {
			association.Relationship.Field.Set(reflectValue, reflect.New(association.Relationship.Field.IndirectFieldType))
		}

		for idx, value := range values {
			appendToRelations(reflectValue, reflect.Indirect(reflect.ValueOf(value)), clear && idx == 0)
		}

		_, hasZero = association.DB.Statement.Schema.PrioritizedPrimaryField.ValueOf(reflectValue)
	}

	if hasZero {
		association.DB.Save(reflectValue.Interface())
	} else {
		association.DB.Select(selectedColumns).Save(reflectValue.Interface())
	}
}