Created the method handler and the initial version for handling requests without country code

handlers/historyHandler.go

@@ -3,16 +3,107 @@ package handlers
 import (
 	"Assignment02/utils"
 	"encoding/json"
-	"fmt"
 	"log"
 	"net/http"
 	"strconv"
+	"strings"
 )
 
-func createRenewableEnergyDatasetTask2(data [][]string) []utils.RenewableEnergy {
+// This function is the entry point for historical renewable energy percentage statistics
+func HandleGetRequestForHistoricalPercentage(w http.ResponseWriter, r *http.Request) {
+
+	//only accept GET method requests
+	switch r.Method {
+	case http.MethodGet:
+		getHandler(w, r)
+	default:
+		http.Error(w, "REST Method "+r.Method+" not supported. Currently only "+http.MethodGet+
+			" is supported.", http.StatusNotImplemented)
+		return
+	}
+}
+
+func getHandler(w http.ResponseWriter, r *http.Request) {
+
+	//Setting the header
+	w.Header().Set("content-type", "application/json")
+
+	// Retrieve the dataset variable
+	data := parse(utils.RenewableEnergyDataset)
+
+	//Retrieve the URL path
+	parts := strings.Split(r.URL.Path, "/")
+
+	//Check the path length and return an error in case there are too many parts
+	if len(parts) != 6 {
+		http.Error(w, "Malformed URL. Expected format: ... "+utils.HISTORY_PATH+"<country code>?begin=<year>&end=<year>", http.StatusBadRequest)
+		return
+	}
+
+	// In case of no country code was provided
+	if parts[5] == "" {
+
+		//check if any time boundaries were specified
+		if r.URL.RawQuery == "" { //In case no time boundaries were not specified
+			//Return the information for all years
+			meanHistoricalPercentage(w, data, 1965, 2021)
+		}
+	}
+
+	//Return OK status code when finished
+	http.Error(w, "OK", http.StatusOK)
+
+}
+
+// This function calculates the mean renewable energy percentage in a specific time frame and writes it to the response writer
+func meanHistoricalPercentage(w http.ResponseWriter, data []utils.RenewableEnergy, start int, finish int) {
+
+	//Instantiate the response variable to be returned to the client
+	var response []utils.MeanRenewableEnergy
+
+	//A variable to keep track of the sum of percentages for each country
+	var sum float64 = 0
+
+	//A variable to keep track of the number of percentages in the sum
+	num := 0
+
+	//Loop over the dataset calculating the mean percentage within the time boundaries for each country
+	name := data[0].Entity
+	for _, element := range data {
+		// Reset the variables and register the results whenever the loop encounters a new country
+		if element.Entity != name {
+
+			if num == 0 {
+				log.Println(element)
+				num += 1
+			}
+			temp := utils.MeanRenewableEnergy{Entity: name, Code: element.Code, Renewables: sum / float64(num)}
+
+			response = append(response, temp)
+			name = element.Entity
+			sum = 0
+			num = 0
+		}
+
+		//Check that the year is within the time limits before updating the variables
+		if element.Year >= start && element.Year <= finish {
+			sum += element.Renewables
+			num += 1
+		}
+	}
+	//Encode and send the response to the client or return an error if the encoding fails
+	err := json.NewEncoder(w).Encode(response)
+	if err != nil {
+		http.Error(w, "Error occurred while encoding coding the response "+err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+}
+
+func parse(dataset [][]string) []utils.RenewableEnergy {
 	// convert csv lines to array of structs
 	var RenewableEnergyDataset []utils.RenewableEnergy
-	for i, line := range data {
+	for i, line := range dataset {
 		if i > 0 { // omit header line
 			var rec utils.RenewableEnergy
 			var err error
@@ -35,18 +126,3 @@ func createRenewableEnergyDatasetTask2(data [][]string) []utils.RenewableEnergy
 	}
 	return RenewableEnergyDataset
 }
-
-func HandleGetRequestForHistoricalPercentage(w http.ResponseWriter, r *http.Request) {
-
-	// Assign successive lines of raw CSV data to fields of the created structs
-	var RenewableEnergyDataset = createRenewableEnergyDatasetTask2(utils.RenewableEnergyDataset)
-
-	// Convert an array of structs to JSON using marshaling functions from the encoding/json package
-	jsonData, err := json.MarshalIndent(RenewableEnergyDataset, "", "  ")
-	if err != nil {
-		log.Fatal(err)
-	}
-
-	//fmt.Println(string(jsonData)) // Print the JSON data to the console
-	fmt.Fprintf(w, "%v", string(jsonData)) // Print the JSON data to the browser
-}