bangs/evaluator.go

package main

import (
	"log"
	"net/http"
	"net/url"
	"os"
	"regexp"
	"strings"
)

//go:generate go run scripts/includebangs.go

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)
	})

	listenAddress := getSetting("LISTEN_ADDRESS", ":8081")
	log.Printf("Listening at %s", listenAddress)

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

func getenv(name string, fallback string) (value string) {
	value = os.Getenv(name)
	if value == "" {
		return fallback
	}
	return
}

func getSetting(name, fallback string) (value string) {
	return getenv("BANG_EVALUATOR_"+name, fallback)
}

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

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

func evaluateBang(searchQuery string, searchEngine string) (query string, engine string) {
	bang, query := parseBang(searchQuery)
	engine = getBang(bang)

	if bang == "" || engine == "" {
		return searchQuery, searchEngine
	} else {
		return query, engine
	}
}