/*
 *	Scope - A simple and minimal metasearch engine
 *	Copyright (C) 2021 Arsen Musayelyan
 *
 *	This program is free software: you can redistribute it and/or modify
 *	it under the terms of the GNU Affero General Public License as published by
 *	the Free Software Foundation, either version 3 of the License, or
 *	(at your option) any later version.
 *
 *	This program is distributed in the hope that it will be useful,
 *	but WITHOUT ANY WARRANTY; without even the implied warranty of
 *	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *	GNU Affero General Public License for more details.
 *
 *	You should have received a copy of the GNU Affero General Public License
 *	along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

package main

import (
	"embed"
	"fmt"
	"html/template"
	"io/fs"
	"net"
	"net/http"
	"os"
	"path"
	"path/filepath"
	"strconv"
	"strings"
	"time"

	"github.com/DataHenHQ/useragent"
	"github.com/Masterminds/sprig"
	"github.com/rs/zerolog"
	"github.com/rs/zerolog/log"
	"github.com/spf13/viper"
	"go.arsenm.dev/scope/internal/cards"
	"go.arsenm.dev/scope/search/web"
)

//go:embed templates
var templates embed.FS

//go:embed static
var static embed.FS

var engines = map[string]web.Engine{
	"google": &web.Google{},
	"ddg":    &web.DDG{},
	"bing":   &web.Bing{},
}

var funcs = template.FuncMap{
	"html": func(s string) template.HTML {
		return template.HTML(s)
	},
}

// TmplContext represents context passed to a template
type TmplContext struct {
	BaseContext
	Results []*web.Result
	Keyword string
	Page    int
	Card    cards.Card
}

// ErrTmplContext represents context passed to an error template
type ErrTmplContext struct {
	BaseContext
	Error     string
	ErrExists bool
	Message   string
	Status    int
}

// BaseContext is the common context between all templates
type BaseContext struct {
	LoadTime time.Duration
}

// Config returns a viper config value
func (bc BaseContext) Config(key string) interface{} {
	return viper.Get(key)
}

func init() {
	// Set logger
	log.Logger = log.Output(zerolog.ConsoleWriter{Out: os.Stderr})

	// Set config options
	viper.AddConfigPath(".")
	viper.AddConfigPath("$HOME/.config")
	viper.AddConfigPath("/etc")
	viper.SetConfigName("scope")
	viper.SetConfigType("toml")

	// Read configuration
	viper.WatchConfig()
	viper.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
	viper.SetEnvPrefix("scope")
	if err := viper.ReadInConfig(); err != nil {
		log.Fatal().Err(err).Msg("Error reading config")
	}
	viper.AutomaticEnv()
}

func main() {
	// Get embedded templates directory
	tmplRoot, err := fs.Sub(templates, "templates")
	if err != nil {
		log.Fatal().Err(err).Msg("Error getting embedded templates directory")
	}

	// Create new template for results
	resultTmpl, err := template.New("base.html").
		Funcs(sprig.FuncMap()).
		Funcs(funcs).
		ParseFS(tmplRoot, "result.html", "base.html")
	if err != nil {
		log.Fatal().Err(err).Msg("Error parsing result template")
	}

	// Create new template for home page
	homeTmpl, err := template.New("base.html").
		Funcs(sprig.FuncMap()).
		ParseFS(tmplRoot, "home.html", "base.html")
	if err != nil {
		log.Fatal().Err(err).Msg("Error parsing home template")
	}

	// Create new template for home page
	errorTmpl, err := template.New("base.html").
		Funcs(sprig.FuncMap()).
		ParseFS(tmplRoot, "error.html", "base.html")
	if err != nil {
		log.Fatal().Err(err).Msg("Error parsing error template")
	}

	// Create new template for home page
	opensearchTmpl, err := template.New("opensearch.xml").
		ParseFS(tmplRoot, "opensearch.xml")
	if err != nil {
		log.Fatal().Err(err).Msg("Error parsing opensearch template")
	}

	// GET / (Home page)
	http.HandleFunc("/", func(res http.ResponseWriter, req *http.Request) {
		start := time.Now()
		homeTmpl.Execute(res, TmplContext{
			BaseContext: BaseContext{
				LoadTime: time.Since(start),
			},
		})
	})

	// GET /search (Results page)
	http.HandleFunc("/search", func(res http.ResponseWriter, req *http.Request) {
		// Get request start time
		start := time.Now()

		// Get queryParams parameters
		queryParams := req.URL.Query()
		// Get parameter "q"
		query := queryParams.Get("q")

		// If no keyword
		if query == "" {
			// Redirect to homepage
			http.Redirect(res, req, "/", http.StatusFound)
			return
		}

		// Get parameter "page"
		pageNumStr := queryParams.Get("page")
		// Attempt to convert to integer, otherwise assume 0
		pageNum, err := strconv.Atoi(pageNumStr)
		if err != nil {
			pageNum = 0
		}

		// Get random user agent
		randUA, _ := useragent.Desktop()

		var cardCh chan cards.Card
		if viper.GetBool("search.cards.enabled") {
			cardCh = make(chan cards.Card, 1)
			// Create channel for instant answer
			if pageNum == 0 {
				go func() {
					// Get matching card for query
					card := cards.GetCard(query, randUA)

					// Run query
					err := card.RunQuery()
					if err != nil || !card.Returned() {
						cardCh <- nil
					}

					// Send card to channel
					cardCh <- card
				}()
			} else {
				cardCh <- nil
			}
		}

		// Search web using all specified engines
		results, err := web.Search(
			web.Options{
				Keyword:   query,
				UserAgent: randUA,
				Page:      pageNum,
			},
			getEngines(viper.GetStringSlice("search.engines"))...,
		)
		if err != nil {
			httpErr(res, http.StatusInternalServerError, err, "Error performing search", start, errorTmpl)
			return
		}

		// Create new template context
		tmplCtx := TmplContext{
			BaseContext: BaseContext{
				LoadTime: time.Since(start),
			},
			Results: results,
			Keyword: query,
			Page:    pageNum,
		}

		// If cards are enabled in config
		if viper.GetBool("search.cards.enabled") {
			// Set card to response
			tmplCtx.Card = <-cardCh
		}

		// Execute result template for search response
		err = resultTmpl.Execute(res, tmplCtx)
		if err != nil {
			httpErr(res, http.StatusInternalServerError, err, "Error executing result template", start, errorTmpl)
			return
		}
	})

	// GET /static/{path} (Static file server, 12 day cache)
	http.Handle("/static/", maxAgeHandler(time.Hour*24*12, http.FileServer(http.FS(static))))

	// GET /opensearch (OpenSearch description file)
	http.HandleFunc("/opensearch", func(res http.ResponseWriter, req *http.Request) {
		opensearchTmpl.Execute(res, TmplContext{})
	})

	// Join address and port from config
	addr := net.JoinHostPort(viper.GetString("server.addr"), viper.GetString("server.port"))

	// Log server starting with address
	log.Info().Str("address", addr).Msg("Starting HTTP server")
	// Start server
	if err := http.ListenAndServe(addr, nil); err != nil {
		log.Fatal().Err(err).Msg("Error while serving")
	}
}

func httpErr(res http.ResponseWriter, statusCode int, err error, msg string, start time.Time, errTmpl *template.Template) {
	if err != nil {
		// Log error with message
		log.Error().Err(err).Msg(msg)
		// Write status code to connection
		res.WriteHeader(statusCode)
		// Execute error template with error
		errTmpl.Execute(res, ErrTmplContext{
			BaseContext: BaseContext{
				LoadTime: time.Since(start),
			},
			Error:     err.Error(),
			ErrExists: true,
			Message:   msg,
			Status:    statusCode,
		})
	} else {
		// Log error without message
		log.Error().Msg(msg)
		// Write status code to connection
		res.WriteHeader(statusCode)
		// Execute error template without error
		errTmpl.Execute(res, ErrTmplContext{
			BaseContext: BaseContext{
				LoadTime: time.Since(start),
			},
			ErrExists: false,
			Message:   msg,
			Status:    statusCode,
		})
	}
}

// Get search endine from names
func getEngines(names []string) []web.Engine {
	var out []web.Engine
	// For every provided name
	for _, name := range names {
		// If engine with that name does not exist, skip
		engine, ok := engines[name]
		if !ok {
			continue
		}
		// Add endine to output
		out = append(out, engine)
	}
	return out
}

// maxAgeHandler adds a cache header to the response with the duration provided
func maxAgeHandler(d time.Duration, h http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// Set Cache-Control header
		w.Header().Add("Cache-Control", fmt.Sprintf("max-age=%d, public, must-revalidate, proxy-revalidate", int(d.Seconds())))
		// Pass to next handler
		h.ServeHTTP(w, r)
	})
}