// Copyright 2017 CoreOS, Inc.
//
// 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 client

import (
	"bytes"
	"encoding/xml"
	"fmt"
	"io"
	"net/http"
	"time"

	"git.thisco.de/vbatts/go-omaha/omaha"
)

const (
	defaultTimeout = 90 * time.Second
)

// httpClient extends the standard http.Client to support xml encoding
// and decoding as well as automatic retries on transient failures.
type httpClient struct {
	http.Client
}

func newHTTPClient() *httpClient {
	return &httpClient{http.Client{
		Timeout: defaultTimeout,
	}}
}

// doPost sends a single HTTP POST, returning a parsed omaha response.
func (hc *httpClient) doPost(url string, reqBody []byte) (*omaha.Response, error) {
	resp, err := hc.Post(url, "text/xml; charset=utf-8", bytes.NewReader(reqBody))
	if err != nil {
		return nil, &omahaError{err, ExitCodeOmahaRequestError}
	}
	defer resp.Body.Close()

	// A response over 1M in size is certainly bogus.
	respBody := &io.LimitedReader{R: resp.Body, N: 1024 * 1024}
	contentType := resp.Header.Get("Content-Type")
	omahaResp, err := omaha.ParseResponse(contentType, respBody)

	// Report a more sensible error if we truncated the body.
	if isUnexpectedEOF(err) && respBody.N <= 0 {
		err = bodySizeError
	} else if err == io.EOF {
		err = bodyEmptyError
	} else if err != nil {
		err = &omahaError{err, ExitCodeOmahaRequestXMLParseError}
	}

	// Prefer reporting HTTP errors over XML parsing errors.
	if resp.StatusCode != http.StatusOK {
		err = &httpError{resp}
	}

	return omahaResp, err
}

// Omaha encodes and sends an omaha request, retrying on any transient errors.
func (hc *httpClient) Omaha(url string, req *omaha.Request) (resp *omaha.Response, err error) {
	buf := bytes.NewBufferString(xml.Header)
	enc := xml.NewEncoder(buf)
	if err := enc.Encode(req); err != nil {
		return nil, fmt.Errorf("omaha: failed to encode request: %v", err)
	}

	expNetBackoff(func() error {
		resp, err = hc.doPost(url, buf.Bytes())
		return err
	})

	return resp, err
}