package callbacks

import (
	"fmt"
	"reflect"
	"sort"
	"strings"

	"gorm.io/gorm"
	"gorm.io/gorm/clause"
	"gorm.io/gorm/schema"
)

func Query(db *gorm.DB) {
	if db.Error == nil {
		BuildQuerySQL(db)

		if !db.DryRun && db.Error == nil {
			rows, err := db.Statement.ConnPool.QueryContext(db.Statement.Context, db.Statement.SQL.String(), db.Statement.Vars...)
			if err != nil {
				db.AddError(err)
				return
			}
			defer rows.Close()

			gorm.Scan(rows, db, false)
		}
	}
}

func BuildQuerySQL(db *gorm.DB) {
	if db.Statement.Schema != nil && !db.Statement.Unscoped {
		for _, c := range db.Statement.Schema.QueryClauses {
			db.Statement.AddClause(c)
		}
	}

	if db.Statement.SQL.String() == "" {
		db.Statement.SQL.Grow(100)
		clauseSelect := clause.Select{Distinct: db.Statement.Distinct}

		if db.Statement.ReflectValue.Kind() == reflect.Struct && db.Statement.ReflectValue.Type() == db.Statement.Schema.ModelType {
			var conds []clause.Expression
			for _, primaryField := range db.Statement.Schema.PrimaryFields {
				if v, isZero := primaryField.ValueOf(db.Statement.ReflectValue); !isZero {
					conds = append(conds, clause.Eq{Column: clause.Column{Table: db.Statement.Table, Name: primaryField.DBName}, Value: v})
				}
			}

			if len(conds) > 0 {
				db.Statement.AddClause(clause.Where{Exprs: conds})
			}
		}

		if len(db.Statement.Selects) > 0 {
			clauseSelect.Columns = make([]clause.Column, len(db.Statement.Selects))
			for idx, name := range db.Statement.Selects {
				if db.Statement.Schema == nil {
					clauseSelect.Columns[idx] = clause.Column{Name: name, Raw: true}
				} else if f := db.Statement.Schema.LookUpField(name); f != nil {
					clauseSelect.Columns[idx] = clause.Column{Name: f.DBName}
				} else {
					clauseSelect.Columns[idx] = clause.Column{Name: name, Raw: true}
				}
			}
		} else if db.Statement.Schema != nil && len(db.Statement.Omits) > 0 {
			selectColumns, _ := db.Statement.SelectAndOmitColumns(false, false)
			clauseSelect.Columns = make([]clause.Column, 0, len(db.Statement.Schema.DBNames))
			for _, dbName := range db.Statement.Schema.DBNames {
				if v, ok := selectColumns[dbName]; (ok && v) || !ok {
					clauseSelect.Columns = append(clauseSelect.Columns, clause.Column{Table: db.Statement.Table, Name: dbName})
				}
			}
		} else if db.Statement.Schema != nil && db.Statement.ReflectValue.IsValid() {
			queryFields := db.QueryFields
			if !queryFields {
				switch db.Statement.ReflectValue.Kind() {
				case reflect.Struct:
					queryFields = db.Statement.ReflectValue.Type() != db.Statement.Schema.ModelType
				case reflect.Slice:
					queryFields = db.Statement.ReflectValue.Type().Elem() != db.Statement.Schema.ModelType
				}
			}

			if queryFields {
				stmt := gorm.Statement{DB: db}
				// smaller struct
				if err := stmt.Parse(db.Statement.Dest); err == nil && (db.QueryFields || stmt.Schema.ModelType != db.Statement.Schema.ModelType) {
					clauseSelect.Columns = make([]clause.Column, len(stmt.Schema.DBNames))

					for idx, dbName := range stmt.Schema.DBNames {
						clauseSelect.Columns[idx] = clause.Column{Table: db.Statement.Table, Name: dbName}
					}
				}
			}
		}

		// inline joins
		if len(db.Statement.Joins) != 0 {
			if len(db.Statement.Selects) == 0 && db.Statement.Schema != nil {
				clauseSelect.Columns = make([]clause.Column, len(db.Statement.Schema.DBNames))
				for idx, dbName := range db.Statement.Schema.DBNames {
					clauseSelect.Columns[idx] = clause.Column{Table: db.Statement.Table, Name: dbName}
				}
			}

			joins := []clause.Join{}
			for _, join := range db.Statement.Joins {
				if db.Statement.Schema == nil {
					joins = append(joins, clause.Join{
						Expression: clause.NamedExpr{SQL: join.Name, Vars: join.Conds},
					})
				} else if relation, ok := db.Statement.Schema.Relationships.Relations[join.Name]; ok {
					tableAliasName := relation.Name

					for _, s := range relation.FieldSchema.DBNames {
						clauseSelect.Columns = append(clauseSelect.Columns, clause.Column{
							Table: tableAliasName,
							Name:  s,
							Alias: tableAliasName + "__" + s,
						})
					}

					exprs := make([]clause.Expression, len(relation.References))
					for idx, ref := range relation.References {
						if ref.OwnPrimaryKey {
							exprs[idx] = clause.Eq{
								Column: clause.Column{Table: clause.CurrentTable, Name: ref.PrimaryKey.DBName},
								Value:  clause.Column{Table: tableAliasName, Name: ref.ForeignKey.DBName},
							}
						} else {
							if ref.PrimaryValue == "" {
								exprs[idx] = clause.Eq{
									Column: clause.Column{Table: clause.CurrentTable, Name: ref.ForeignKey.DBName},
									Value:  clause.Column{Table: tableAliasName, Name: ref.PrimaryKey.DBName},
								}
							} else {
								exprs[idx] = clause.Eq{
									Column: clause.Column{Table: tableAliasName, Name: ref.ForeignKey.DBName},
									Value:  ref.PrimaryValue,
								}
							}
						}
					}

					joins = append(joins, clause.Join{
						Type:  clause.LeftJoin,
						Table: clause.Table{Name: relation.FieldSchema.Table, Alias: tableAliasName},
						ON:    clause.Where{Exprs: exprs},
					})
				} else {
					joins = append(joins, clause.Join{
						Expression: clause.NamedExpr{SQL: join.Name, Vars: join.Conds},
					})
				}
			}

			db.Statement.AddClause(clause.From{Joins: joins})
		} else {
			db.Statement.AddClauseIfNotExists(clause.From{})
		}

		db.Statement.AddClauseIfNotExists(clauseSelect)

		db.Statement.Build("SELECT", "FROM", "WHERE", "GROUP BY", "ORDER BY", "LIMIT", "FOR")
	}
}

func Preload(db *gorm.DB) {
	if db.Error == nil && len(db.Statement.Preloads) > 0 {
		preloadMap := map[string][]string{}
		for name := range db.Statement.Preloads {
			if name == clause.Associations {
				for _, rel := range db.Statement.Schema.Relationships.Relations {
					if rel.Schema == db.Statement.Schema {
						preloadMap[rel.Name] = []string{rel.Name}
					}
				}
			} else {
				preloadFields := strings.Split(name, ".")
				for idx := range preloadFields {
					preloadMap[strings.Join(preloadFields[:idx+1], ".")] = preloadFields[:idx+1]
				}
			}
		}

		preloadNames := make([]string, len(preloadMap))
		idx := 0
		for key := range preloadMap {
			preloadNames[idx] = key
			idx++
		}
		sort.Strings(preloadNames)

		for _, name := range preloadNames {
			var (
				curSchema     = db.Statement.Schema
				preloadFields = preloadMap[name]
				rels          = make([]*schema.Relationship, len(preloadFields))
			)

			for idx, preloadField := range preloadFields {
				if rel := curSchema.Relationships.Relations[preloadField]; rel != nil {
					rels[idx] = rel
					curSchema = rel.FieldSchema
				} else {
					db.AddError(fmt.Errorf("%v: %w", name, gorm.ErrUnsupportedRelation))
				}
			}

			if db.Error == nil {
				preload(db, rels, db.Statement.Preloads[name])
			}
		}
	}
}

func AfterQuery(db *gorm.DB) {
	if db.Error == nil && db.Statement.Schema != nil && !db.Statement.SkipHooks && db.Statement.Schema.AfterFind {
		callMethod(db, func(value interface{}, tx *gorm.DB) bool {
			if i, ok := value.(AfterFindInterface); ok {
				db.AddError(i.AfterFind(tx))
				return true
			}
			return false
		})
	}
}