// Package rest allows for quick and easy access any REST or REST-like API.

package rest

import (

	"bytes"

	"io/ioutil"

	"net/http"

	"net/url"

)

// Method contains the supported HTTP verbs.

type Method string

// Supported HTTP verbs.

const (

	Get    Method = "GET"

	Post   Method = "POST"

	Put    Method = "PUT"

	Patch  Method = "PATCH"

	Delete Method = "DELETE"

)

// Request holds the request to an API Call.

type Request struct {

	Method      Method

	BaseURL     string // e.g. https://api.sendgrid.com

	Headers     map[string]string

	QueryParams map[string]string

	Body        []byte

}

// RestError is a struct for an error handling.

type RestError struct {

	Response *Response

}

// Error is the implementation of the error interface.

func (e *RestError) Error() string {

	return e.Response.Body

}

// DefaultClient is used if no custom HTTP client is defined

var DefaultClient = &Client{HTTPClient: http.DefaultClient}

// Client allows modification of client headers, redirect policy

// and other settings

// See https://golang.org/pkg/net/http

type Client struct {

	HTTPClient *http.Client

}

// Response holds the response from an API call.

type Response struct {

	StatusCode int                 // e.g. 200

	Body       string              // e.g. {"result: success"}

	Headers    map[string][]string // e.g. map[X-Ratelimit-Limit:[600]]

}

// AddQueryParameters adds query parameters to the URL.

func AddQueryParameters(baseURL string, queryParams map[string]string) string {

	baseURL += "?"

	params := url.Values{}

	for key, value := range queryParams {

		params.Add(key, value)

	}

	return baseURL + params.Encode()

}

// BuildRequestObject creates the HTTP request object.

func BuildRequestObject(request Request) (*http.Request, error) {

	// Add any query parameters to the URL.

	if len(request.QueryParams) != 0 {

		request.BaseURL = AddQueryParameters(request.BaseURL, request.QueryParams)

	}

	req, err := http.NewRequest(string(request.Method), request.BaseURL, bytes.NewBuffer(request.Body))

	if err != nil {

		return req, err

	}

	for key, value := range request.Headers {

		req.Header.Set(key, value)

	}

	_, exists := req.Header["Content-Type"]

	if len(request.Body) > 0 && !exists {

		req.Header.Set("Content-Type", "application/json")

	}

	return req, err

}

// MakeRequest makes the API call.

func MakeRequest(req *http.Request) (*http.Response, error) {

	return DefaultClient.HTTPClient.Do(req)

}

// BuildResponse builds the response struct.

func BuildResponse(res *http.Response) (*Response, error) {

	body, err := ioutil.ReadAll(res.Body)

	if err != nil {

		return nil, err

	}

	defer func() {

		if err := res.Body.Close(); err != nil {

			return // maybe log in the future

		}

	}()

	response := Response{

		StatusCode: res.StatusCode,

		Body:       string(body),

		Headers:    res.Header,

	}

	return &response, nil

}

// API supports old implementation (deprecated)

func API(request Request) (*Response, error) {

	return Send(request)

}

// Send uses the DefaultClient to send your request

func Send(request Request) (*Response, error) {

	return DefaultClient.Send(request)

}

// The following functions enable the ability to define a

// custom HTTP Client

// MakeRequest makes the API call.

func (c *Client) MakeRequest(req *http.Request) (*http.Response, error) {

	return c.HTTPClient.Do(req)

}

// API supports old implementation (deprecated)

func (c *Client) API(request Request) (*Response, error) {

	return c.Send(request)

}

// Send will build your request, make the request, and build your response.

func (c *Client) Send(request Request) (*Response, error) {

	// Build the HTTP request object.

	req, err := BuildRequestObject(request)

	if err != nil {

		return nil, err

	}

	// Build the HTTP client and make the request.

	res, err := c.MakeRequest(req)

	if err != nil {

		return nil, err

	}

	// Build Response object.

	response, err := BuildResponse(res)

	if err != nil {

		return nil, err

	}

	return response, nil

}