/*
Copyright The ORAS Authors.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package errutil

import (
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"strings"
	"unicode"
)

// maxErrorBytes specifies the default limit on how many response bytes are
// allowed in the server's error response.
// A typical error message is around 200 bytes. Hence, 8 KiB should be
// sufficient.
var maxErrorBytes int64 = 8 * 1024 // 8 KiB

// requestError contains a single error.
type requestError struct {
	Code    string `json:"code"`
	Message string `json:"message"`
}

// Error returns a error string describing the error.
func (e requestError) Error() string {
	code := strings.Map(func(r rune) rune {
		if r == '_' {
			return ' '
		}
		return unicode.ToLower(r)
	}, e.Code)
	if e.Message == "" {
		return code
	}
	return fmt.Sprintf("%s: %s", code, e.Message)
}

// requestErrors is a bundle of requestError.
type requestErrors []requestError

// Error returns a error string describing the error.
func (errs requestErrors) Error() string {
	switch len(errs) {
	case 0:
		return "<nil>"
	case 1:
		return errs[0].Error()
	}
	var errmsgs []string
	for _, err := range errs {
		errmsgs = append(errmsgs, err.Error())
	}
	return strings.Join(errmsgs, "; ")
}

// ParseErrorResponse parses the error returned by the remote registry.
func ParseErrorResponse(resp *http.Response) error {
	var errmsg string
	var body struct {
		Errors requestErrors `json:"errors"`
	}
	lr := io.LimitReader(resp.Body, maxErrorBytes)
	if err := json.NewDecoder(lr).Decode(&body); err == nil && len(body.Errors) > 0 {
		errmsg = body.Errors.Error()
	} else {
		errmsg = http.StatusText(resp.StatusCode)
	}
	return fmt.Errorf("%s %q: unexpected status code %d: %s", resp.Request.Method, resp.Request.URL, resp.StatusCode, errmsg)
}