1build-feed-paginated.go

package main

import (
	"encoding/json"
	"math"
	"net/http"
	"os"
	"strconv"

	"github.com/aws/aws-lambda-go/events"
	"github.com/aws/aws-lambda-go/lambda"
)

// Post - Shape of each post fetched from the server and sent to the frontend
type Post struct {
	Title  string  `json:"title"`
	Author string  `json:"author"`
	Posted float64 `json:"posted"`
}

// Content - Shape of raw response
type Content struct {
	Posts []Post
}

// ResponseBody - Shape of lambda response body
type ResponseBody struct {
	Posts   []Post `json:"posts"`
	PerPage int    `json:"perPage"`
	Page    int    `json:"page"`
	Pages   int    `json:"pages"`
}

// Paginate - Provides relevant slice of posts
func Paginate(posts []Post, PerPage int, Page int) []Post {
	PostsCount := float64(len(posts))
	return posts[int(math.Min(float64((Page-1)*PerPage), PostsCount)):int(math.Min(float64((Page*PerPage)), PostsCount))]
}

// HandleRequest - Lambda request handler
func HandleRequest(request events.APIGatewayProxyRequest) (events.APIGatewayProxyResponse, error) {
	var client = &http.Client{}

	content := Content{}
	r, err := client.Get(os.Getenv("URL"))
	if err != nil {
		return events.APIGatewayProxyResponse{}, err
	}
	defer r.Body.Close()

	json.NewDecoder(r.Body).Decode(&content)

	PerPage, _ := strconv.Atoi(request.QueryStringParameters["perPage"])
	Page, _ := strconv.Atoi(request.QueryStringParameters["page"])

	body := ResponseBody{
		PerPage: PerPage,
		Page:    Page,
		Posts:   Paginate(content.Posts, PerPage, Page),
		Pages:   int(math.Ceil(float64(len(content.Posts)) / float64(int(PerPage)))),
	}

	Body, err := json.Marshal(body)
	if err != nil {
		return events.APIGatewayProxyResponse{}, err
	}

	return events.APIGatewayProxyResponse{
		Body:       string(Body),
		StatusCode: 200,
		Headers: map[string]string{
			"Access-Control-Allow-Origin":  "*",
			"Content-Type":                 "application/json",
			"Access-Control-Allow-Methods": "GET, OPTIONS, POST",
			"Access-Control-Allow-Headers": "Content-Type",
		},
	}, nil
}

func main() {
	lambda.Start(HandleRequest)
}