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package acme

import (
	"bytes"
	"encoding/json"
	"errors"
	"net/http"
	"net/textproto"
	"regexp"
	"time"
)

// Solver decribes a solving interface
type Solver interface {
	Solve()
}

// Links to the next stage
type Links map[string]string

// Client ...
type Client struct {
	Dir   Directory
	nonce chan string
	Links Links
}

// NewClient fetches directory and initializes nonce
func NewClient(uri string) (*Client, error) {
	resp, err := http.Get(uri)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()
	c := &Client{nonce: make(chan string, 10)}
	c.nonce <- replyNonce(resp)
	err = json.NewDecoder(resp.Body).Decode(&c.Dir)
	if err != nil {
		return nil, err
	}
	return c, nil
}

var errNoNonces = errors.New("No nonces available")

// Nonce implements jose nonce provider
func (c Client) Nonce() (string, error) {
	select {
	case nonce := <-c.nonce:
		return nonce, nil
	default:
		return "", errNoNonces
	}
}

// Important header fields
//
// Replay-Nonce		each response, required for next request
// Link			links to next stage
// Retry-After		polling interval

// Action		Request		Response
//
// Register		POST new-reg	201 -> reg
// Request challenges	POST new-authz	201 -> authz
// Answer challenges	POST challenge	200
// Poll for status	GET  authz	200
// Request issuance	POST new-cert	201 -> cert
// Check for new cert	GET  cert	200

// Post is used for
// new-reg, new-authz, challenge, new-cert
func (c *Client) Post(s Signer, uri string, v interface{}) (*http.Response, error) {
	body, err := json.Marshal(v)
	if err != nil {
		return nil, err
	}

	signed, err := s.Sign(body, c)
	if err != nil {
		return nil, err
	}

	resp, err := http.Post(uri, "application/jose+json",
		bytes.NewReader(signed))
	if err != nil {
		return nil, err
	}

	c.nonce <- replyNonce(resp)
	c.Links = links(resp)

	if resp.StatusCode >= http.StatusBadRequest {
		return nil, handleError(resp)
	}

	return resp, nil
}

func links(r *http.Response) Links {
	links := make(Links)
	key := textproto.CanonicalMIMEHeaderKey("Link")
	reg := regexp.MustCompile(`^<(.*)>;rel="(.*)"`)
	for _, l := range r.Header[key] {
		re := reg.FindStringSubmatch(l)
		if len(re) == 3 {
			links[re[2]] = re[1]
		}
	}
	return links
}

func retryAfter(r *http.Response) time.Duration {
	ra := r.Header.Get("Retry-After")
	if d, err := time.ParseDuration(ra + "s"); err == nil {
		return d
	}
	return time.Second
}

func replyNonce(r *http.Response) string {
	return r.Header.Get("Replay-Nonce")
}