package api

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"io/ioutil"
	"net"
	"net/http"
	"net/url"
	"strconv"
	"strings"
	"sync"
	"time"

	"git.j3s.sh/cascade/lib/cleanhttp"
)

// Config is used to configure the creation of a client
type Config struct {
	// Address is the address of the Consul server
	Address string

	// Scheme is the URI scheme for the Consul server
	Scheme string

	// Transport is the Transport to use for the http client.
	Transport *http.Transport

	// HttpClient is the client to use. Default will be
	// used if not provided.
	HttpClient *http.Client

	// WaitTime limits how long a Watch will block. If not provided,
	// the agent default values will be used.
	WaitTime time.Duration
}

// DefaultConfig returns a default configuration for the client. By default this
// will pool and reuse idle connections to cascade. If you have a long-lived
// client object, this is the desired behavior and should make the most efficient
// use of the connections to cascade. If you don't reuse a client object, which
// is not recommended, then you may notice idle connections building up over
// time. To avoid this, use the DefaultNonPooledConfig() instead.
func DefaultConfig() *Config {
	return defaultConfig(cleanhttp.DefaultPooledTransport)
}

// DefaultNonPooledConfig returns a default configuration for the client which
// does not pool connections. This isn't a recommended configuration because it
// will reconnect to cascade on every request, but this is useful to avoid the
// accumulation of idle connections if you make many client objects during the
// lifetime of your application.
func DefaultNonPooledConfig() *Config {
	return defaultConfig(cleanhttp.DefaultTransport)
}

// defaultConfig returns the default configuration for the client, using the
// given function to make the transport.
func defaultConfig(transportFn func() *http.Transport) *Config {
	config := &Config{
		Address:   "127.0.0.1:8500",
		Scheme:    "http",
		Transport: transportFn(),
	}

	return config
}

// Client provides a client to the Consul API
type Client struct {
	modifyLock sync.RWMutex
	headers    http.Header

	config Config
}

// Headers gets the current set of headers used for requests. This returns a
// copy; to modify it call AddHeader or SetHeaders.
func (c *Client) Headers() http.Header {
	c.modifyLock.RLock()
	defer c.modifyLock.RUnlock()

	if c.headers == nil {
		return nil
	}

	ret := make(http.Header)
	for k, v := range c.headers {
		for _, val := range v {
			ret[k] = append(ret[k], val)
		}
	}

	return ret
}

// AddHeader allows a single header key/value pair to be added
// in a race-safe fashion.
func (c *Client) AddHeader(key, value string) {
	c.modifyLock.Lock()
	defer c.modifyLock.Unlock()
	c.headers.Add(key, value)
}

// SetHeaders clears all previous headers and uses only the given
// ones going forward.
func (c *Client) SetHeaders(headers http.Header) {
	c.modifyLock.Lock()
	defer c.modifyLock.Unlock()
	c.headers = headers
}

// NewClient returns a new client
func NewClient(config *Config) (*Client, error) {
	// bootstrap the config
	defConfig := DefaultConfig()

	if config.Address == "" {
		config.Address = defConfig.Address
	}

	if config.Scheme == "" {
		config.Scheme = defConfig.Scheme
	}

	if config.Transport == nil {
		config.Transport = defConfig.Transport
	}

	if config.HttpClient == nil {
		config.HttpClient = NewHttpClient(config.Transport)
	}

	parts := strings.SplitN(config.Address, "://", 2)
	if len(parts) == 2 {
		switch parts[0] {
		case "http":
			config.Scheme = "http"
		// TODO: unix socket support? do i care? no???
		default:
			return nil, fmt.Errorf("Unknown protocol scheme: %s", parts[0])
		}
		config.Address = parts[1]
	}

	return &Client{config: *config, headers: make(http.Header)}, nil
}

// NewHttpClient returns an http client configured with the given Transport
func NewHttpClient(transport *http.Transport) *http.Client {
	client := &http.Client{
		Transport: transport,
	}
	return client
}

// request is used to help build up a request
type request struct {
	config *Config
	method string
	url    *url.URL
	params url.Values
	body   io.Reader
	header http.Header
	obj    interface{}
	ctx    context.Context
}

// QueryMeta is used to return meta data about a query
type QueryMeta struct {
	// LastIndex. This can be used as a WaitIndex to perform
	// a blocking query
	LastIndex uint64

	// LastContentHash. This can be used as a WaitHash to perform a blocking query
	// for endpoints that support hash-based blocking. Endpoints that do not
	// support it will return an empty hash.
	LastContentHash string

	// How long did the request take
	RequestTime time.Duration

	// Is address translation enabled for HTTP responses on this agent
	AddressTranslationEnabled bool
}

// QueryOptions are used to parameterize a query
type QueryOptions struct {
	// WaitIndex is used to enable a blocking query. Waits
	// until the timeout or the next index is reached
	WaitIndex uint64

	// WaitHash is used by some endpoints instead of WaitIndex to perform blocking
	// on state based on a hash of the response rather than a monotonic index.
	// This is required when the state being blocked on is not stored in Raft, for
	// example agent-local proxy configuration.
	WaitHash string

	// WaitTime is used to bound the duration of a wait.
	// Defaults to that of the Config, but can be overridden.
	WaitTime time.Duration

	// Near is used to provide a node name that will sort the results
	// in ascending order based on the estimated round trip time from
	// that node. Setting this to "_agent" will use the agent's node
	// for the sort.
	Near string

	// NodeMeta is used to filter results by nodes with the given
	// metadata key/value pairs. Currently, only one key/value pair can
	// be provided for filtering.
	NodeMeta map[string]string

	// ctx is an optional context pass through to the underlying HTTP
	// request layer. Use Context() and WithContext() to manage this.
	ctx context.Context

	// Filter requests filtering data prior to it being returned. The string
	// is a go-bexpr compatible expression.
	Filter string
}

// setQueryOptions is used to annotate the request with
// additional query options
func (r *request) setQueryOptions(q *QueryOptions) {
	if q == nil {
		return
	}
	if q.WaitIndex != 0 {
		r.params.Set("index", strconv.FormatUint(q.WaitIndex, 10))
	}
	if q.WaitTime != 0 {
		r.params.Set("wait", durToMsec(q.WaitTime))
	}
	if q.WaitHash != "" {
		r.params.Set("hash", q.WaitHash)
	}
	if q.Near != "" {
		r.params.Set("near", q.Near)
	}
	if q.Filter != "" {
		r.params.Set("filter", q.Filter)
	}
	if len(q.NodeMeta) > 0 {
		for key, value := range q.NodeMeta {
			r.params.Add("node-meta", key+":"+value)
		}
	}

	r.ctx = q.ctx
}

// durToMsec converts a duration to a millisecond specified string. If the
// user selected a positive value that rounds to 0 ms, then we will use 1 ms
// so they get a short delay, otherwise Consul will translate the 0 ms into
// a huge default delay.
func durToMsec(dur time.Duration) string {
	ms := dur / time.Millisecond
	if dur > 0 && ms == 0 {
		ms = 1
	}
	return fmt.Sprintf("%dms", ms)
}

// serverError is a string we look for to detect 500 errors.
const serverError = "Unexpected response code: 500"

// IsRetryableError returns true for 500 errors from the Consul servers, and
// network connection errors. These are usually retryable at a later time.
// This applies to reads but NOT to writes. This may return true for errors
// on writes that may have still gone through, so do not use this to retry
// any write operations.
func IsRetryableError(err error) bool {
	if err == nil {
		return false
	}

	if _, ok := err.(net.Error); ok {
		return true
	}

	// TODO (slackpad) - Make a real error type here instead of using
	// a string check.
	return strings.Contains(err.Error(), serverError)
}

// toHTTP converts the request to an HTTP request
func (r *request) toHTTP() (*http.Request, error) {
	// Encode the query parameters
	r.url.RawQuery = r.params.Encode()

	// Check if we should encode the body
	if r.body == nil && r.obj != nil {
		b, err := encodeBody(r.obj)
		if err != nil {
			return nil, err
		}
		r.body = b
	}

	// Create the HTTP request
	req, err := http.NewRequest(r.method, r.url.RequestURI(), r.body)
	if err != nil {
		return nil, err
	}

	req.URL.Host = r.url.Host
	req.URL.Scheme = r.url.Scheme
	req.Host = r.url.Host
	req.Header = r.header

	// Content-Type must always be set when a body is present
	// See https://github.com/hashicorp/consul/issues/10011
	if req.Body != nil && req.Header.Get("Content-Type") == "" {
		req.Header.Set("Content-Type", "application/json")
	}

	if r.ctx != nil {
		return req.WithContext(r.ctx), nil
	}

	return req, nil
}

// newRequest is used to create a new request
func (c *Client) newRequest(method, path string) *request {
	r := &request{
		config: &c.config,
		method: method,
		url: &url.URL{
			Scheme: c.config.Scheme,
			Host:   c.config.Address,
			Path:   path,
		},
		params: make(map[string][]string),
		header: c.Headers(),
	}

	if c.config.WaitTime != 0 {
		r.params.Set("wait", durToMsec(r.config.WaitTime))
	}

	return r
}

// doRequest runs a request with our client
func (c *Client) doRequest(r *request) (time.Duration, *http.Response, error) {
	req, err := r.toHTTP()
	if err != nil {
		return 0, nil, err
	}
	start := time.Now()
	resp, err := c.config.HttpClient.Do(req)
	diff := time.Since(start)
	return diff, resp, err
}

// Query is used to do a GET request against an endpoint
// and deserialize the response into an interface using
// standard cascade conventions.
func (c *Client) query(endpoint string, out interface{}, q *QueryOptions) (*QueryMeta, error) {
	r := c.newRequest("GET", endpoint)
	r.setQueryOptions(q)
	rtt, resp, err := c.doRequest(r)
	if err != nil {
		return nil, err
	}
	defer closeResponseBody(resp)

	qm := &QueryMeta{}
	err = parseQueryMeta(resp, qm)
	if err != nil {
		return nil, err
	}
	qm.RequestTime = rtt

	if err := decodeBody(resp, out); err != nil {
		return nil, err
	}
	return qm, nil
}

// parseQueryMeta is used to help parse query meta-data
func parseQueryMeta(resp *http.Response, q *QueryMeta) error {
	header := resp.Header

	// Parse the X-Consul-Index (if it's set - hash based blocking queries don't
	// set this)
	//	if indexStr := header.Get("X-Consul-Index"); indexStr != "" {
	//		index, err := strconv.ParseUint(indexStr, 10, 64)
	//		if err != nil {
	//			return fmt.Errorf("Failed to parse X-Consul-Index: %v", err)
	//		}
	//		q.LastIndex = index
	//	}
	//	q.LastContentHash = header.Get("X-Consul-ContentHash")

	// Parse X-Consul-Translate-Addresses
	switch header.Get("X-Consul-Translate-Addresses") {
	case "true":
		q.AddressTranslationEnabled = true
	default:
		q.AddressTranslationEnabled = false
	}

	return nil
}

// decodeBody is used to JSON decode a body
func decodeBody(resp *http.Response, out interface{}) error {
	dec := json.NewDecoder(resp.Body)
	return dec.Decode(out)
}

// encodeBody is used to encode a request body
func encodeBody(obj interface{}) (io.Reader, error) {
	buf := bytes.NewBuffer(nil)
	enc := json.NewEncoder(buf)
	if err := enc.Encode(obj); err != nil {
		return nil, err
	}
	return buf, nil
}

// requireOK is used to wrap doRequest and check for a 200
func requireOK(d time.Duration, resp *http.Response, e error) (time.Duration, *http.Response, error) {
	if e != nil {
		if resp != nil {
			closeResponseBody(resp)
		}
		return d, nil, e
	}
	if resp.StatusCode != 200 {
		return d, nil, generateUnexpectedResponseCodeError(resp)
	}
	return d, resp, nil
}

// closeResponseBody reads resp.Body until EOF, and then closes it. The read
// is necessary to ensure that the http.Client's underlying RoundTripper is able
// to re-use the TCP connection. See godoc on net/http.Client.Do.
func closeResponseBody(resp *http.Response) error {
	_, _ = io.Copy(ioutil.Discard, resp.Body)
	return resp.Body.Close()
}

func (req *request) filterQuery(filter string) {
	if filter == "" {
		return
	}

	req.params.Set("filter", filter)
}

// generateUnexpectedResponseCodeError consumes the rest of the body, closes
// the body stream and generates an error indicating the status code was
// unexpected.
func generateUnexpectedResponseCodeError(resp *http.Response) error {
	var buf bytes.Buffer
	io.Copy(&buf, resp.Body)
	closeResponseBody(resp)
	return fmt.Errorf("Unexpected response code: %d (%s)", resp.StatusCode, buf.Bytes())
}

func requireNotFoundOrOK(d time.Duration, resp *http.Response, e error) (bool, time.Duration, *http.Response, error) {
	if e != nil {
		if resp != nil {
			closeResponseBody(resp)
		}
		return false, d, nil, e
	}
	switch resp.StatusCode {
	case 200:
		return true, d, resp, nil
	case 404:
		return false, d, resp, nil
	default:
		return false, d, nil, generateUnexpectedResponseCodeError(resp)
	}
}