package main

import (
	"net/http"
	"log"
	"strings"
	"encoding/json"
	"io/ioutil"
	"regexp"
)

var bangs = loadBangs()

func main() {
	http.HandleFunc("/eval", func(w http.ResponseWriter, r *http.Request) {
		searchQuery := r.URL.Query().Get("query")
		searchEngine := r.URL.Query().Get("engine")

		if (searchQuery == "" || searchEngine == "") {
			http.Error(w, "400 Bad Request", http.StatusBadRequest)
			return
		}

		searchQuery, searchEngine = evaluateBang(searchQuery, searchEngine)

		searchURL := buildSearchURL(searchEngine, searchQuery)
		http.Redirect(w, r, searchURL, http.StatusSeeOther)
	})

	log.Fatalf("Failed to start http server: %v", http.ListenAndServe(":8081", nil))
}

func loadBangs() (bangs map[string]string) {
	data, err := ioutil.ReadFile("bangs.json")
    if err != nil {
		log.Fatalf("Failed to read bangs: %v", err)
	}

	err = json.Unmarshal(data, &bangs)
	if err != nil {
		log.Fatalf("Failed to decode bangs: %v", err)
	}

	return
}

func buildSearchURL(template string, query string) (searchUrl string) {
	return strings.Replace(template, "%s", query, 1)
}

func parseBang(searchQuery string) (bang string, query string) {
	regexStartBang, _ := regexp.Compile("\\!(.*) (.*)")
	regexEndBang, _ := regexp.Compile("(.*) \\!(.*)")

	startBang := regexStartBang.FindSubmatch([]byte(searchQuery))
	endBang := regexEndBang.FindSubmatch([]byte(searchQuery))

	if len(endBang) == 3 {
		return string(endBang[2]), string(endBang[1])
	} else if len(startBang) == 3 {
		return string(startBang[1]), string(startBang[2])
	} else {
		return "", searchQuery
	}
}

func evaluateBang(searchQuery string, searchEngine string) (query string, engine string) {
	bang, query := parseBang(searchQuery)
	if bang == "" {
		return query, searchEngine
	} else {
		return query, bangs[bang]
	}
}