package callbacks

import (
	"fmt"
	"gorm.io/gorm"
	"gorm.io/gorm/clause"
	"gorm.io/gorm/schema"
	"gorm.io/gorm/utils"
	"reflect"
)

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 func() {
				db.AddError(rows.Close())
			}()
			gorm.Scan(rows, db, 0)
		}
	}
}

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

	if db.Statement.SQL.Len() == 0 {
		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.Context, 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}
					}
				}
			}
		}

		HandleJoins(
			db,
			func(db *gorm.DB) {
				if len(db.Statement.Selects) == 0 && len(db.Statement.Omits) == 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}
					}
				}
			},
			func(db *gorm.DB, tableAliasName string, join gorm.Join, relation *schema.Relationship) {
				columnStmt := gorm.Statement{
					Table: tableAliasName, DB: db, Schema: relation.FieldSchema,
					Selects: join.Selects, Omits: join.Omits,
				}

				selectColumns, restricted := columnStmt.SelectAndOmitColumns(false, false)
				for _, s := range relation.FieldSchema.DBNames {
					if v, ok := selectColumns[s]; (ok && v) || (!ok && !restricted) {
						clauseSelect.Columns = append(clauseSelect.Columns, clause.Column{
							Table: tableAliasName,
							Name:  s,
							Alias: utils.NestedRelationName(tableAliasName, s),
						})
					}
				}
			},
		)

		db.Statement.AddClauseIfNotExists(clauseSelect)

		db.Statement.Build(db.Statement.BuildClauses...)
	}
}

func Preload(db *gorm.DB) {
	if db.Error == nil && len(db.Statement.Preloads) > 0 {
		if db.Statement.Schema == nil {
			db.AddError(fmt.Errorf("%w when using preload", gorm.ErrModelValueRequired))
			return
		}

		joins := make([]string, 0, len(db.Statement.Joins))
		for _, join := range db.Statement.Joins {
			joins = append(joins, join.Name)
		}

		tx := preloadDB(db, db.Statement.ReflectValue, db.Statement.Dest)
		if tx.Error != nil {
			return
		}

		db.AddError(preloadEntryPoint(tx, joins, &tx.Statement.Schema.Relationships, db.Statement.Preloads, db.Statement.Preloads[clause.Associations]))
	}
}

func AfterQuery(db *gorm.DB) {
	// clear the joins after query because preload need it
	if v, ok := db.Statement.Clauses["FROM"].Expression.(clause.From); ok {
		fromClause := db.Statement.Clauses["FROM"]
		fromClause.Expression = clause.From{Tables: v.Tables, Joins: v.Joins[:len(v.Joins)-len(db.Statement.Joins)]} // keep the original From Joins
		db.Statement.Clauses["FROM"] = fromClause
	}
	if db.Error == nil && db.Statement.Schema != nil && !db.Statement.SkipHooks && db.Statement.Schema.AfterFind && db.RowsAffected > 0 {
		callMethod(db, func(value interface{}, tx *gorm.DB) bool {
			if i, ok := value.(AfterFindInterface); ok {
				db.AddError(i.AfterFind(tx))
				return true
			}
			return false
		})
	}
}