package main

import (
	_ "embed"
	"encoding/gob"
	"errors"
	"fmt"
	"html/template"
	"io"
	"log"
	"net/http"
	"os"
	"os/signal"
	"runtime/debug"
	"time"
)

// File for persistent storage
var DataFilename = "ideas.data"

// Version number used for debugging compatibility with the .data file
var Version string

// layout for how the date should be output in html
var DateLayout string = "02/01/2006 on 15:04"

// template for ideas html
var (
	//go:embed t_idea/index.html
	ideas_html string
	//go:embed t_idea/edit.html
	idea_edit_html string
)

var Ideas []Idea

// ToDo's
// - [ ] Create a Server out of this so you can run multiple instances
// - [x] edit a post
// - [x] Store ideas to a file (encoder/gob)
// - [x] Change the date format printing
// - [x] outsource removing the posts to a separate cli tool
// - [x] Add a post
// - [x] Remove a post

// Represents an idea
// CreatedAt is a formatted date string
// out of 5 rating of the idea
// formatted time string with DateLayout
type Idea struct {
	Title     string
	Text      string
	Author    string
	CreatedAt string
}

// Data passed to the ideas_html template
type PageData struct {
	Ideas []Idea
	Error string
}

func GetVersion() string {
	buildinfo, ok := debug.ReadBuildInfo()
	if !ok {
		log.Fatalln("Could not read buildinfo to know package version.")
	}
	return buildinfo.Main.Version
}

func main() {
	Version = GetVersion()

	// If the .data file does not exist, create it in the cache directory
	{
		p := os.Getenv("XDG_CACHE_HOME")
		if p == "" {
			p = "."
		}
		DataFilename = p + "/" + DataFilename

		f, err := os.Open(DataFilename)
		if errors.Is(err, os.ErrNotExist) {
			// The file does not exist, so create one with only Version encoded
			log.Println("File does not exist, creating", DataFilename)
			f, err = os.Create(DataFilename)
			if err != nil {
				log.Fatalln("Error while creating data file:", err)
			}

			enc := gob.NewEncoder(f)
			if err := enc.Encode(Version); err != nil {
				log.Fatalln("Error while encoding Version:", err)
			}
		} else if err != nil {
			log.Fatalln("Error while opening data file:", err)
		} else {
			dec := gob.NewDecoder(f)

			// Check the version
			var v string
			if err := dec.Decode(&v); err != io.EOF && err != nil {
				log.Fatalln("Error while decoding version:", err)
			}
			if v != Version {
				log.Fatalf("Version mismatch for datafile@%s != package@%s\n", v, Version)
			}

			// Decode the data and import it into Ideas
			err = dec.Decode(&Ideas)
			if err != nil && err != io.EOF {
				log.Fatalln("Error while decoding ideas:", err)
			}
			log.Printf("Imported @%s: %d ideas\n", v, len(Ideas))
			if err := f.Close(); err != nil {
				log.Fatalln("Error while closing file:", err)
			}
		}

	}

	// Handle SIGINT
	// Save all Ideas into the data file
	// NOTE (Luca): This system might seem dumb, but it only adds overhead at startup
	// and exit of the program which is fine.
	go func() {
		c := make(chan os.Signal, 1)
		signal.Notify(c, os.Interrupt)
		<-c

		f, err := os.Create(DataFilename)
		if err != nil {
			log.Fatalln(err)
		}
		defer f.Close()

		enc := gob.NewEncoder(f)
		if err := enc.Encode(Version); err != nil {
			log.Fatalln(err)
		}

		if err := enc.Encode(Ideas); err != nil {
			log.Fatalln("Error while saving ideas:", err)
		}

		log.Println("data saved.")
		os.Exit(0)
	}()

	// Handling http

	tmpl, err := template.New("ideas_html").Parse(ideas_html)
	if err != nil {
		log.Fatalln(err)
	}
	_, err = tmpl.New("edit").Parse(idea_edit_html)
	if err != nil {
		log.Fatalln(err)
	}

	// TODO (Luca): Make the app more interactive by using websockets instead,
	// such that adding or editing does not require to
	// refresh the page.
	// Another approach would be to use htmx?
	//

	mux := http.NewServeMux()

	fs := http.FileServer(http.Dir("assets/"))
	mux.Handle("/static/", http.StripPrefix("/static/", fs))

	mux.HandleFunc("GET /{$}", func(w http.ResponseWriter, r *http.Request) {
		http.Redirect(w, r, "/ideas/", http.StatusMovedPermanently)
	})

	mux.HandleFunc("GET /ideas/", func(w http.ResponseWriter, r *http.Request) {
		tmpl.Execute(w, PageData{Ideas, ""})
	})

	mux.HandleFunc("POST /idea/create/", func(w http.ResponseWriter, r *http.Request) {
		i := Idea{
			Title:     r.FormValue("title"),
			Author:    r.FormValue("author"),
			CreatedAt: time.Now().Format(DateLayout),
			Text:      r.FormValue("text"),
		}
		if i.Title == "" || i.Author == "" || i.Text == "" {
			tmpl.Execute(w, PageData{Ideas, "All fields are required"})
			return
		}

		for _, v := range Ideas {
			if i.Title == v.Title {
				tmpl.Execute(w, PageData{Ideas, "An idea with title '" + v.Title + "' already exists!"})
				return
			}
		}

		Ideas = append(Ideas, i)
		log.Println("Added new idea:", i.Title)
		http.Redirect(w, r, "/ideas/", http.StatusMovedPermanently)
	})

	mux.HandleFunc("GET /idea/edit/", func(w http.ResponseWriter, r *http.Request) {
		t := r.URL.Query().Get("t")
		if t == "" {
			tmpl.Execute(w, PageData{Ideas, "You must provide a title."})
			return
		}

		for _, i := range Ideas {
			if i.Title == t {
				tmpl.ExecuteTemplate(w, "edit", i)
				return
			}
		}
		tmpl.Execute(w, PageData{Ideas, "No idea with title '" + t + "'."})
	})

	mux.HandleFunc("POST /idea/edit/", func(w http.ResponseWriter, r *http.Request) {
		t := r.FormValue("title")
		if t == "" {
			tmpl.Execute(w, PageData{Ideas, "You must provide a title."})
			return
		}

		var i *Idea
		for j := range Ideas {
			if Ideas[j].Title == t {
				i = &Ideas[j]
				break
			}
		}
		if i.Title == "" {
			tmpl.Execute(w, PageData{Ideas, "No idea with title '" + t + "'."})
		}

		i.Title = r.FormValue("title")
		i.Text = r.FormValue("text")
		log.Printf("Edited '%s'\n", i.Title)

		http.Redirect(w, r, "/ideas/", http.StatusMovedPermanently)
	})

	mux.HandleFunc("POST /idea/delete/", func(w http.ResponseWriter, r *http.Request) {
		t := r.FormValue("title")
		if t == "" {
			tmpl.Execute(w, PageData{Ideas, "You must provide a title."})
			return
		}
		for i, v := range Ideas {
			if t == v.Title {
				log.Println("Deleted:", v.Title)
				Ideas = append(Ideas[:i], Ideas[i+1:]...)
				http.Redirect(w, r, "/ideas/", http.StatusMovedPermanently)
				return
			}
		}
		tmpl.Execute(w, PageData{Ideas, "No idea with title '" + t + "'."})
	})

	mux.HandleFunc("POST /comment/create/", func(w http.ResponseWriter, r *http.Request) {
		fmt.Fprintln(w, "Not implemented yet.")
	})

	log.Println("Listening on http://localhost:8080/ideas")
	err = http.ListenAndServe(":8080", mux)
	if err != nil {
		log.Fatalln(err)
	}
}