lazyhandler/magic/path.go

package magic

import (
	"fmt"
	"net/http"
	"reflect"
	"regexp"
	"strconv"
	"strings"
)

var (
	cachedStructPathValueFields      = make(map[reflect.Type][]structPathValueFields)
	cachedUnsupportedPathValueFields = make(map[reflect.Type]reflect.StructField)
)

type UnsupportedPathValueType struct {
	inner reflect.Type
}

func (err UnsupportedPathValueType) Error() string {
	return "unsupported type for path value: " + err.inner.String()
}

type structPathValueFields struct {
	PathKey  string
	FieldKey string

	Type     reflect.Type
	Optional bool
	Match    *regexp.Regexp
}

type PathValue[T any] struct {
	Data T
}

type PathValueNotFound struct {
	Key string
}

func (err PathValueNotFound) Error() string {
	return "path value not found: " + err.Key
}

type InvalidPathValueType struct {
	Kind  reflect.Kind
	Value string
}

func (err InvalidPathValueType) Error() string {
	return fmt.Sprintf("invalid value for kind %v: %v", err.Kind, err.Value)
}

type InvalidPathValue struct {
	Match *regexp.Regexp
	Value string
}

func (err InvalidPathValue) Error() string {
	return fmt.Sprintf("value not matched with regexp %v: %v", err.Match, err.Value)
}

func findReflectPathValueFields(v reflect.Value) ([]structPathValueFields, error) {
	if cached, ok := cachedStructPathValueFields[v.Type()]; ok {
		return cached, nil
	}
	if cached, ok := cachedUnsupportedPathValueFields[v.Type()]; ok {
		return nil, UnsupportedPathValueType{inner: cached.Type}
	}

	var fields []structPathValueFields
	if v.Kind() == reflect.Struct {
		t := v.Type()
		for idx := 0; idx < t.NumField(); idx++ {
			field := t.Field(idx)

			pathKey := field.Name
			var match *regexp.Regexp

			if tags, ok := field.Tag.Lookup("pathvalue"); ok {
				parts := strings.Split(strings.TrimSpace(tags), ",")
				if len(parts) == 0 {
					// do nothing
				} else {
					if parts[0] != "" {
						pathKey = parts[0]
					}

					for _, part := range parts[1:] {
						part = strings.TrimSpace(part)
						if strings.HasPrefix(part, "match=") {
							part := strings.TrimPrefix(part, "match=")
							if unquoted, err := strconv.Unquote(part); err != nil {
								return nil, err
							} else {
								part = unquoted
							}
							exp, err := regexp.Compile(part)
							if err != nil {
								return nil, err
							}
							match = exp
						}
					}
				}

			}

			fieldType := field.Type
			optional := false

			if fieldType.Kind() == reflect.Ptr {
				fieldType = fieldType.Elem()
				optional = true
			}

			if pathValueConvertTable[fieldType.Kind()] == nil {
				if _, ok := fieldType.MethodByName("FromString"); !ok {
					cachedUnsupportedPathValueFields[t] = field
					return nil, UnsupportedPathValueType{inner: field.Type}
				}
			}

			fields = append(fields, structPathValueFields{
				PathKey:  pathKey,
				FieldKey: field.Name,

				Type:     fieldType,
				Optional: optional,

				Match: match,
			})
		}
		cachedStructPathValueFields[t] = fields
	} else {
		return nil, UnsupportedPathValueType{inner: v.Type()}
	}

	return fields, nil
}

func (pathValue *PathValue[T]) FromRequest(r *http.Request) error {
	v := reflect.ValueOf(pathValue).Elem().FieldByName("Data")
	fields, err := findReflectPathValueFields(v)
	if err != nil {
		return err
	}

	for _, field := range fields {
		str := r.PathValue(field.PathKey)
		if str == "" {
			if !field.Optional {
				return PathValueNotFound{Key: field.PathKey}
			}
			continue
		}
		if field.Match != nil && !field.Match.MatchString(str) {
			return InvalidPathValue{Match: field.Match, Value: str}
		}
		convert := pathValueConvertTable[field.Type.Kind()]
		result, err := convert(str)
		if err != nil {
			return err
		}

		reflectValue := reflect.ValueOf(result)

		if field.Optional {
			newReflectedValue := reflect.New(reflectValue.Type())
			newReflectedValue.Elem().Set(reflect.ValueOf(result))
			reflectValue = newReflectedValue
		}
		v.FieldByName(field.FieldKey).Set(reflectValue)
	}

	return nil
}