package dbi

import (
	"database/sql"
	"reflect"
	"strings"
)

// scanRow scans a single row into val, using reflection to map columns to struct fields.
// Supports sql.Scanner, structs (column names mapped by lowercasing and stripping underscores),
// and single-value types.
func scanRow(rows *sql.Rows, cols []string, val any) error {
	rv := reflect.ValueOf(val).Elem()
	rt := rv.Type()

	if _, ok := val.(sql.Scanner); ok {
		return rows.Scan(val)
	}

	if rt.Kind() == reflect.Struct {
		fieldMap := make(map[string]int, rt.NumField())
		for i := 0; i < rt.NumField(); i++ {
			f := rt.Field(i)
			if f.IsExported() {
				fieldMap[strings.ToLower(f.Name)] = i
			}
		}

		dest := make([]any, len(cols))
		for i, col := range cols {
			// TODO get rid of this subtlety. just require exact name/case match
			if fi, ok := fieldMap[strings.ReplaceAll(col, "_", "")]; ok {
				dest[i] = rv.Field(fi).Addr().Interface()
			} else {
				dest[i] = new(any)
			}
		}
		return rows.Scan(dest...)
	}

	return rows.Scan(val)
}