package main

import (
	"os"
	"fmt"
	"log"
	"sort"
	"time"
	"bufio"
	"errors"
	"context"
	"strconv"
	"strings"
	"net/url"
	"crypto/x509"
	"encoding/xml"
	"path/filepath"

	"git.sr.ht/~adnano/go-gemini"
	"git.sr.ht/~adnano/go-gemini/tofu"
)

var (
	hosts     tofu.KnownHosts
	hostsfile *tofu.HostWriter
	predirs   map[string]*url.URL
	perrors   map[string]PError
)

func xdgDataHome() string {
	if s, ok := os.LookupEnv("XDG_DATA_HOME"); ok {
		return s
	}
	return filepath.Join(os.Getenv("HOME"), ".local", "share")
}

func init() {
	path := filepath.Join(xdgDataHome(), "konbata", "known_hosts")
	err := hosts.Load(path)
	if err != nil {
		log.Fatal(err)
	}

	hostsfile, err = tofu.OpenHostsFile(path)
	if err != nil {
		log.Fatal(err)
	}

	err = populatePRedirs()
	if err != nil {
		log.Fatal(err)
	}

	err = populatePErrors()
	if err != nil {
		log.Fatal(err)
	}
}

func populatePRedirs() error {
	file, err := os.OpenFile(filepath.Join(xdgDataHome(), "konbata", "predirs"), os.O_RDONLY|os.O_CREATE, 0600)
	if err != nil {
		return err
	}
	defer file.Close()
	scanner := bufio.NewScanner(file)
	predirs = make(map[string]*url.URL)
	for scanner.Scan() {
		urls := strings.Split(scanner.Text(), " ")
		if len(urls) != 2 {
			continue
		}
		url0, err := url.Parse(urls[0])
		if err != nil {
			continue
		}
		if url0.Scheme != "gemini" {
			continue
		}
		url1, err := url.Parse(urls[1])
		if err != nil {
			continue
		}
		if url1.Scheme != "gemini" {
			continue
		}
		predirs[url0.String()] = url1
	}
	return nil
}

func savePRedirs() error {
	file, err := os.OpenFile(filepath.Join(xdgDataHome(), "konbata", "predirs"), os.O_WRONLY|os.O_CREATE, 0600)
	if err != nil {
		return err
	}
	defer file.Close()
	err = file.Truncate(0)
	if err != nil {
		return err
	}
	writer := bufio.NewWriter(file)
	for url0, url1 := range predirs {
		_, err = writer.WriteString(url0)
		if err != nil {
			return err
		}
		_, err = writer.WriteRune(' ')
		if err != nil {
			return err
		}
		_, err = writer.WriteString(url1.String())
		if err != nil {
			return err
		}
		_, err = writer.WriteRune('\n')
		if err != nil {
			return err
		}
	}
	return writer.Flush()
}

func populatePErrors() error {
	file, err := os.OpenFile(filepath.Join(xdgDataHome(), "konbata", "perrors"), os.O_RDONLY|os.O_CREATE, 0600)
	if err != nil {
		return err
	}
	defer file.Close()
	scanner := bufio.NewScanner(file)
	perrors = make(map[string]PError)
	unescaper := strings.NewReplacer("\\n", "\n", "\\\\", "\\")
	for scanner.Scan() {
		values := strings.SplitN(scanner.Text(), " ", 3)
		if len(values) != 3 {
			continue
		}
		url, err := url.Parse(values[0])
		if err != nil {
			continue
		}
		if url.Scheme != "gemini" {
			continue
		}
		code, err := strconv.Atoi(values[1])
		if err != nil {
			continue
		}
		perrors[url.String()] = PError{
			Code: gemini.Status(code),
			Message: unescaper.Replace(values[2]),
		}
	}
	return nil
}

func savePErrors() error {
	file, err := os.OpenFile(filepath.Join(xdgDataHome(), "konbata", "perrors"), os.O_WRONLY|os.O_CREATE, 0600)
	if err != nil {
		return err
	}
	defer file.Close()
	err = file.Truncate(0)
	if err != nil {
		return err
	}
	writer := bufio.NewWriter(file)
	escaper := strings.NewReplacer("\\", "\\\\", "\n", "\\n")
	for url, perror := range perrors {
		_, err = writer.WriteString(url)
		if err != nil {
			return err
		}
		_, err = writer.WriteRune(' ')
		if err != nil {
			return err
		}
		_, err = writer.WriteString(strconv.Itoa(int(perror.Code)))
		if err != nil {
			return err
		}
		_, err = writer.WriteRune(' ')
		if err != nil {
			return err
		}
		_, err = escaper.WriteString(writer, perror.Message)
		if err != nil {
			return err
		}
		_, err = writer.WriteRune('\n')
		if err != nil {
			return err
		}
	}
	return writer.Flush()
}

func trustCertificate(hostname string, cert *x509.Certificate) error {
	host := tofu.NewHost(hostname, cert.Raw)
	knownHost, ok := hosts.Lookup(hostname)
	if ok {
		// Check fingerprint
		if knownHost.Fingerprint != host.Fingerprint {
			return errors.New("fingerprint does not match!")
		}
		return nil
	}

	hosts.Add(host)
	hostsfile.WriteHost(host)
	return nil
}

func do(client gemini.Client, ctx context.Context, req *gemini.Request, via []*gemini.Request) (*gemini.Response, *gemini.Request, error) {
	if target, exists := predirs[req.URL.String()]; exists {
		via = append(via, req)
		if len(via) > 5 {
			return nil, req, errors.New("too many redirects")
		}

		redirect := *req
		redirect.URL = target
		return do(client, ctx, &redirect, via)
	}
	if perror, exists := perrors[req.URL.String()]; exists {
		return nil, req, errors.New(fmt.Sprintf("%d %s", perror.Code, perror.Message))
	}
	resp, err := client.Do(ctx, req)
	if err != nil {
		return resp, req, err
	}

	if resp.Status == gemini.StatusPermanentRedirect {
		target, err := url.Parse(resp.Meta)
		if err != nil {
			return resp, req, err
		}
		if target.Scheme != "gemini" && target.Scheme != "" {
			return resp, req, errors.New(fmt.Sprintf("tried to redirect to scheme %s", target.Scheme))
		}
		target = req.URL.ResolveReference(target)
		predirs[req.URL.String()] = target
		err = savePRedirs()
		if err != nil {
			return resp, req, err
		}
	}
	if resp.Status.Class() == gemini.StatusPermanentFailure {
		perrors[req.URL.String()] = PError{
			Code: resp.Status,
			Message: resp.Meta,
		}
		err = savePErrors()
		if err != nil {
			return resp, req, err
		}
	}
	if resp.Status.Class() == gemini.StatusRedirect {
		via = append(via, req)
		if len(via) > 5 {
			return resp, req, errors.New("too many redirects")
		}

		target, err := url.Parse(resp.Meta)
		if err != nil {
			return resp, req, err
		}
		if target.Scheme != "gemini" && target.Scheme != "" {
			return resp, req, errors.New(fmt.Sprintf("tried to redirect to scheme %s", target.Scheme))
		}
		target = req.URL.ResolveReference(target)
		redirect := *req
		redirect.URL = target
		return do(client, ctx, &redirect, via)
	}
	if resp.Status.Class() != gemini.StatusSuccess {
		return resp, req, errors.New(fmt.Sprintf("%d %s", resp.Status, resp.Meta))
	}

	return resp, req, err
}

func main() {
	if len(os.Args) == 0 {
		fmt.Fprintf(os.Stderr, "Usage: konbata <url>\n")
		os.Exit(1)
	}
	if len(os.Args) != 2 {
		fmt.Fprintf(os.Stderr, "Usage: %s <url>\n", os.Args[0])
		os.Exit(1)
	}

	req, err := gemini.NewRequest(os.Args[1])
	if err != nil {
		log.Fatal(err)
	}

	client := gemini.Client{
		TrustCertificate: trustCertificate,
	}
	ctx := context.Background()
	resp, req, err := do(client, ctx, req, nil)
	if err != nil {
		log.Fatal(err)
	}
	defer resp.Body.Close()

	if resp.Meta != "text/gemini" && !strings.HasPrefix(resp.Meta, "text/gemini;") {
		log.Fatal("mime type is not text/gemini")
	}
	aw := AtomWriter{
		Title: "",
		Items: nil,
	}
	gemini.ParseLines(resp.Body, aw.Handle)
	sort.Sort(ByTime(aw.Items))
	feed := &Feed{
		XMLNS: "http://www.w3.org/2005/Atom",
		Link: &FeedLink{
			Href: req.URL.String(),
		},
		Id: req.URL.String(),
		Entries: nil,
	}
	if aw.Title == "" {
		feed.Title = req.URL.String()
	} else {
		feed.Title = aw.Title
	}
	if len(aw.Items) == 0 {
		feed.Updated = time.Now().Format(time.RFC3339)
	} else {
		feed.Updated = aw.Items[len(aw.Items) - 1].Date.Format(time.RFC3339)
	}
	for i := len(aw.Items); i != 0; i-- {
		item := aw.Items[i - 1]
		link, err := req.URL.Parse(item.Link)
		if err != nil {
			log.Fatal(err)
		}
		feed.Entries = append(feed.Entries, &FeedEntry{
			Title: item.Title,
			Link: &EntryLink{
				Href: link.String(),
				Rel: "alternate",
			},
			Id: link.String(),
			Updated: item.Date.Format(time.RFC3339),
		})
	}
	out, err := xml.MarshalIndent(feed, "", "    ")
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(string(out))
}

type Feed struct {
	XMLName xml.Name `xml:"feed"`
	XMLNS   string `xml:"xmlns,attr"`
	Title   string `xml:"title"`
	Link    *FeedLink `xml:"link"`
	Updated string `xml:"updated"`
	Id      string `xml:"id"`
	Entries []*FeedEntry `xml:"entry"`
}
type FeedLink struct {
	XMLName xml.Name `xml:"link"`
	Href    string `xml:"href,attr"`
}
type FeedEntry struct {
	XMLName xml.Name `xml:"entry"`
	Title   string `xml:"title"`
	Link    *EntryLink `xml:"link"`
	Id      string `xml:"id"`
	Updated string `xml:"updated"`
}
type EntryLink struct {
	XMLName xml.Name `xml:"link"`
	Href    string `xml:"href,attr"`
	Rel    string `xml:"rel,attr"`
}

type FeedItem struct {
	Date  time.Time
	Title string
	Link  string
}

type ByTime []FeedItem
func (a ByTime) Len() int {
	return len(a)
}
func (a ByTime) Less(i, j int) bool {
	return a[i].Date.Before(a[j].Date)
}
func (a ByTime) Swap(i, j int) {
	a[i], a[j] = a[j], a[i]
}

type PError struct {
	Code    gemini.Status
	Message string
}

type AtomWriter struct {
	Title string
	Items []FeedItem
}

func (a *AtomWriter) Handle(line gemini.Line) {
	switch line := line.(type) {
	case gemini.LineLink:
		runes := []rune(line.Name)
		t, err := time.Parse("2006-01-02", string(runes[:10]))
		if err == nil {
			a.Items = append(a.Items, FeedItem{
				Date: t,
				Title: strings.TrimSpace(strings.TrimLeft(strings.TrimSpace(string(runes[10:])), ":-")),
				Link: string(line.URL),
			})
		}
	case gemini.LineHeading1:
		if a.Title == "" {
			a.Title = string(line)
		}
	}
}