package image

import (
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"strings"
)

const etagDigestLength = 32

type VariantRequestError struct {
	cause  error
	Detail string
}

func NewUnknownVariantError(name string) error {
	return VariantRequestError{cause: ErrUnknownVariant, Detail: name}
}

func NewUnsupportedParameterError(parameter string) error {
	return VariantRequestError{cause: ErrUnsupportedParameter, Detail: parameter}
}

func (e VariantRequestError) Error() string {
	return e.cause.Error() + ": " + e.Detail
}

func (e VariantRequestError) Unwrap() error {
	return e.cause
}

func VariantRequestDetail(err error) string {
	var requestError VariantRequestError
	if errors.As(err, &requestError) {
		return requestError.Detail
	}
	return ""
}

func VariantETag(settings VariantSettings, sourceName string) string {
	digest := sha256.Sum256([]byte(settings.Fingerprint() + "|" + sourceName))
	return `"` + hex.EncodeToString(digest[:])[:etagDigestLength] + `"`
}

func ETagMatches(ifNoneMatch string, etag string) bool {
	for _, candidate := range strings.Split(ifNoneMatch, ",") {
		trimmed := strings.TrimPrefix(strings.TrimSpace(candidate), "W/")
		if trimmed == "*" || trimmed == etag {
			return true
		}
	}
	return false
}