package main

import (
	"bytes"
	"crypto/sha1"
	"database/sql"
	"encoding/hex"
	"errors"
	"fmt"
	"html/template"
	"io"
	"io/fs"
	"log"
	"net"
	"net/http"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
	"time"

	_ "github.com/mattn/go-sqlite3"
)

var (
	db *sql.DB // sqlite database
	gd string  // gallery directory
)

func openDB(directory string) error {
	var err error
	db, err = sql.Open("sqlite3",
		"file:"+filepath.Join(directory, "gallery.db?_foreign_keys=1"))
	gd = directory
	return err
}

func imagePath(sha1 string) string {
	return filepath.Join(gd, "images", sha1[:2], sha1)
}

func thumbPath(sha1 string) string {
	return filepath.Join(gd, "thumbs", sha1[:2], sha1+".webp")
}

func dbCollectStrings(query string) ([]string, error) {
	rows, err := db.Query(query)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var result []string
	for rows.Next() {
		var s string
		if err := rows.Scan(&s); err != nil {
			return nil, err
		}
		result = append(result, s)
	}
	if err := rows.Err(); err != nil {
		return nil, err
	}
	return result, nil
}

type directoryManager struct {
	cache map[string]int64 // Unix-style paths to directory.id
}

func (dm *directoryManager) IDForDirectoryPath(path string) (int64, error) {
	// Relative paths could be handled differently,
	// but right now, they're assumed to start at the root.
	list := strings.Split(filepath.ToSlash(filepath.Clean(path)), "/")
	if len(list) > 1 && list[0] == "" {
		list = list[1:]
	}
	if len(list) == 0 {
		return 0, nil
	}

	var parent sql.NullInt64
	for _, name := range list {
		if err := db.QueryRow(
			`SELECT id FROM directory WHERE name = ? AND parent IS ?`,
			name, parent).Scan(&parent); err == nil {
			continue
		} else if !errors.Is(err, sql.ErrNoRows) {
			return 0, err
		}

		if result, err := db.Exec(
			`INSERT INTO directory(name, parent) VALUES (?, ?)`,
			name, parent); err != nil {
			return 0, err
		} else if id, err := result.LastInsertId(); err != nil {
			return 0, err
		} else {
			parent = sql.NullInt64{Int64: id, Valid: true}
		}
	}
	return parent.Int64, nil
}

// XXX: This is preliminary.
type entry struct {
	Parent int64
	Name   string
	Mtime  int64
	Sha1   string

	Thumbw int
	Thumbh int
	Dhash  int64
}

// XXX: This is preliminary.
type directory struct {
	Id       int64
	Name     string
	Parent   int64
	Children []int64
	Entries  []entry
}

func dbCollectDirectory(id int64) (directory, error) {
	d := directory{Id: id}
	dbID := sql.NullInt64{Int64: id, Valid: id != 0}
	if id != 0 {
		err := db.QueryRow(`SELECT name, IFNULL(parent, 0)
			FROM directory WHERE id IS ?`, dbID).Scan(&d.Name, &d.Parent)
		if err != nil {
			return d, err
		}
	}

	rows1, err := db.Query(`SELECT id FROM directory WHERE parent IS ?`, dbID)
	if err != nil {
		return d, err
	}
	defer rows1.Close()
	for rows1.Next() {
		var child int64
		if err := rows1.Scan(&child); err != nil {
			return d, err
		}
		d.Children = append(d.Children, child)
	}
	if err := rows1.Err(); err != nil {
		return d, err
	}

	rows2, err := db.Query(`SELECT IFNULL(entry.parent, 0),
		entry.name, entry.mtime, entry.sha1,
		IFNULL(image.thumbw, 0), IFNULL(image.thumbh, 0), IFNULL(image.dhash, 0)
		FROM entry JOIN image ON entry.sha1 = image.sha1
		WHERE entry.parent IS ?`, dbID)
	if err != nil {
		return d, err
	}
	defer rows2.Close()
	for rows2.Next() {
		var e entry
		if err := rows2.Scan(&e.Parent, &e.Name, &e.Mtime, &e.Sha1,
			&e.Thumbw, &e.Thumbh, &e.Dhash); err != nil {
			return d, err
		}
		d.Entries = append(d.Entries, e)
	}
	return d, rows2.Err()
}

// cmdInit initializes a "gallery directory" that contains gallery.sqlite,
// images, thumbs.
func cmdInit(args []string) error {
	if len(args) != 1 {
		return errors.New("usage: GD")
	}

	if err := openDB(args[0]); err != nil {
		return err
	}
	if _, err := db.Exec(initializeSQL); err != nil {
		return err
	}

	// XXX: There's technically no reason to keep images as symlinks,
	// we might just keep absolute paths in the database as well.
	if err := os.MkdirAll(filepath.Join(gd, "images"), 0755); err != nil {
		return err
	}
	if err := os.MkdirAll(filepath.Join(gd, "thumbs"), 0755); err != nil {
		return err
	}
	return nil
}

var hashRE = regexp.MustCompile(`^/.*?/([0-9a-f]{40})$`)
var staticHandler http.Handler

var page = template.Must(template.New("/").Parse(`<!DOCTYPE html><html><head>
	<title>Gallery</title>
	<meta charset="utf-8" />
	<meta name="viewport" content="width=device-width, initial-scale=1">
	<link rel=stylesheet href=style.css>
</head><body>
	<h1>{{ .Name }}</h1>
	<ul>
		{{ range .Children }}
		<li><a href="?id={{ . }}">{{ . }}</a></li>
		{{ end }}
	</ul>

	{{ range .Entries }}
	<a href="/image/{{ .Sha1 }}">
		<img width={{ .Thumbw }} height={{ .Thumbh }} src="/thumb/{{ .Sha1 }}"
			title="{{ .Name }}">
	</a>
	{{ end }}

	<script src=gallery.js></script>
</body></html>`))

func handleRequest(w http.ResponseWriter, r *http.Request) {
	if r.URL.Path != "/" {
		staticHandler.ServeHTTP(w, r)
		return
	}

	id, _ := strconv.ParseInt(r.URL.Query().Get("id"), 10, 64)
	d, err := dbCollectDirectory(id)
	if err != nil {
		http.Error(w, err.Error(), 500)
		return
	}
	if err := page.Execute(w, d); err != nil {
		log.Println(err)
	}
}

func handleImages(w http.ResponseWriter, r *http.Request) {
	if m := hashRE.FindStringSubmatch(r.URL.Path); m == nil {
		http.NotFound(w, r)
	} else {
		http.ServeFile(w, r, imagePath(m[1]))
	}
}

func handleThumbs(w http.ResponseWriter, r *http.Request) {
	if m := hashRE.FindStringSubmatch(r.URL.Path); m == nil {
		http.NotFound(w, r)
	} else {
		http.ServeFile(w, r, thumbPath(m[1]))
	}
}

// cmdRun runs a web UI against GD on ADDRESS.
func cmdRun(args []string) error {
	if len(args) != 2 {
		return errors.New("usage: GD ADDRESS")
	}
	if err := openDB(args[0]); err != nil {
		return err
	}

	address := args[1]

	// This separation is not strictly necessary,
	// but having an elementary level of security doesn't hurt either.
	staticHandler = http.FileServer(http.Dir("public"))

	http.HandleFunc("/", handleRequest)
	http.HandleFunc("/image/", handleImages)
	http.HandleFunc("/thumb/", handleThumbs)
	// TODO: Add a few API endpoints.

	host, port, err := net.SplitHostPort(address)
	if err != nil {
		log.Println(err)
	} else if host == "" {
		log.Println("http://" + net.JoinHostPort("localhost", port))
	} else {
		log.Println("http://" + address)
	}

	s := &http.Server{
		Addr:           address,
		ReadTimeout:    60 * time.Second,
		WriteTimeout:   60 * time.Second,
		MaxHeaderBytes: 32 << 10,
	}
	return s.ListenAndServe()
}

func isImage(path string) (bool, error) {
	cmd := exec.Command("xdg-mime", "query", "filetype", path)
	stdout, err := cmd.StdoutPipe()
	if err != nil {
		return false, err
	}
	if err := cmd.Start(); err != nil {
		return false, err
	}
	out, err := io.ReadAll(stdout)
	if err != nil {
		return false, err
	}
	if err := cmd.Wait(); err != nil {
		return false, err
	}
	return bytes.HasPrefix(out, []byte("image/")), nil
}

func importFunc(path string, d fs.DirEntry, err error) error {
	if err != nil || d.IsDir() {
		return err
	}

	// The input may be a relative path, and we want to remember it as such,
	// but symlinks for the images must be absolute.
	absPath, err := filepath.Abs(path)
	if err != nil {
		return err
	}

	// Skip videos, which ImageMagick can process, but we don't want it to,
	// so that they're not converted 1:1 to WebP.
	pathIsImage, err := isImage(path)
	if err != nil {
		return err
	}
	if !pathIsImage {
		return nil
	}

	f, err := os.Open(path)
	if err != nil {
		return err
	}
	defer f.Close()

	s, err := f.Stat()
	if err != nil {
		return err
	}

	hash := sha1.New()
	_, err = io.CopyBuffer(hash, f, make([]byte, 65536))
	if err != nil {
		return err
	}

	hexSHA1 := hex.EncodeToString(hash.Sum(nil))
	pathImage := imagePath(hexSHA1)
	imageDirname, _ := filepath.Split(pathImage)
	if err := os.MkdirAll(imageDirname, 0755); err != nil {
		return err
	}
	if err := os.Symlink(absPath, pathImage); err != nil &&
		!errors.Is(err, fs.ErrExist) {
		return err
	}

	// TODO: This should all run in a transaction.
	if _, err = db.Exec(`INSERT INTO image(sha1) VALUES (?)
		ON CONFLICT(sha1) DO NOTHING`, hexSHA1); err != nil {
		return err
	}

	// TODO: Maintain the cache across calls.
	dm := directoryManager{}
	dbDirname, dbBasename := filepath.Split(path)
	dbParent, err := dm.IDForDirectoryPath(dbDirname)
	if err != nil {
		return err
	}

	_, err = db.Exec(`INSERT INTO entry(
		parent, name, mtime, sha1
	) VALUES (?, ?, ?, ?)`, dbParent, dbBasename, s.ModTime().Unix(), hexSHA1)
	return err
}

// cmdImport adds files to the "entry" table.
func cmdImport(args []string) error {
	if len(args) < 1 {
		return errors.New("usage: GD ROOT...")
	}
	if err := openDB(args[0]); err != nil {
		return err
	}

	// TODO: This would better be done in parallel (making hashes).
	// TODO: Show progress in some manner. Perhaps port my propeller code.
	for _, name := range args[1:] {
		if err := filepath.WalkDir(name, importFunc); err != nil {
			return err
		}
	}
	return nil
}

// cmdSync is like import, but clears the "entry" table beforehands.
func cmdSync(args []string) error {
	if len(args) < 1 {
		return errors.New("usage: GD ROOT...")
	}
	if err := openDB(args[0]); err != nil {
		return err
	}

	// TODO
	return nil
}

// cmdCheck checks if all files tracked in the DB are accessible.
func cmdCheck(args []string) error {
	if len(args) != 1 {
		return errors.New("usage: GD")
	}
	if err := openDB(args[0]); err != nil {
		return err
	}

	// TODO: Check if all hashes of DB entries have a statable image file,
	// and that all images with thumb{w,h} have a thumbnail file. Perhaps.
	return nil
}

func makeThumbnail(pathImage, pathThumb string) (int, int, error) {
	thumbDirname, _ := filepath.Split(pathThumb)
	if err := os.MkdirAll(thumbDirname, 0755); err != nil {
		return 0, 0, err
	}

	// Create a normalized thumbnail. Since we don't particularly need
	// any complex processing, such as surrounding of metadata,
	// simply push it through ImageMagick.
	//
	//  - http://www.ericbrasseur.org/gamma.html
	//  - https://www.imagemagick.org/Usage/thumbnails/
	//  - https://imagemagick.org/script/command-line-options.php#layers
	//
	// "info:" output is written for each frame, which is why we delete
	// all of them but the first one beforehands.
	//
	// TODO: See if we can optimize resulting WebP animations.
	// (Do -layers optimize* apply to this format at all?)
	cmd := exec.Command("convert", pathImage, "-coalesce", "-colorspace", "RGB",
		"-auto-orient", "-strip", "-resize", "256x128>", "-colorspace", "sRGB",
		"-format", "%w %h", "+write", pathThumb, "-delete", "1--1", "info:")

	stdout, err := cmd.StdoutPipe()
	if err != nil {
		return 0, 0, err
	}
	if err := cmd.Start(); err != nil {
		return 0, 0, err
	}
	out, err := io.ReadAll(stdout)
	if err != nil {
		return 0, 0, err
	}
	if err := cmd.Wait(); err != nil {
		return 0, 0, err
	}

	var w, h int
	_, err = fmt.Fscanf(bytes.NewReader(out), "%d %d", &w, &h)
	return w, h, err
}

// cmdThumbnail generates missing thumbnails, in parallel.
func cmdThumbnail(args []string) error {
	if len(args) < 1 {
		return errors.New("usage: GD [SHA1...]")
	}
	if err := openDB(args[0]); err != nil {
		return err
	}

	hexSHA1 := args[1:]
	if len(hexSHA1) == 0 {
		// Get all unique images in the database with no thumbnail.
		var err error
		hexSHA1, err = dbCollectStrings(`SELECT sha1 FROM image
			WHERE thumbw IS NULL OR thumbh IS NULL`)
		if err != nil {
			return err
		}
	}

	// TODO: Try to run the thumbnailer in parallel, somehow.
	// Then run convert with `-limit thread 1`.
	// TODO: Show progress in some manner. Perhaps port my propeller code.
	for _, sha1 := range hexSHA1 {
		pathImage := imagePath(sha1)
		pathThumb := thumbPath(sha1)
		w, h, err := makeThumbnail(pathImage, pathThumb)
		if err != nil {
			return err
		}

		_, err = db.Exec(`UPDATE image SET thumbw = ?, thumbh = ?
			WHERE sha1 = ?`, w, h, sha1)
		if err != nil {
			return err
		}
	}
	return nil
}

func makeDhash(hasher, pathThumb string) (uint64, error) {
	cmd := exec.Command(hasher, pathThumb)
	stdout, err := cmd.StdoutPipe()
	if err != nil {
		return 0, err
	}
	if err := cmd.Start(); err != nil {
		return 0, err
	}
	out, err := io.ReadAll(stdout)
	if err != nil {
		return 0, err
	}
	if err := cmd.Wait(); err != nil {
		return 0, err
	}

	var hash uint64
	_, err = fmt.Fscanf(bytes.NewReader(out), "%x", &hash)
	return hash, err
}

// cmdDhash generates perceptual hash from thumbnails.
func cmdDhash(args []string) error {
	if len(args) < 1 {
		return errors.New("usage: GD HASHER [SHA1...]")
	}
	if err := openDB(args[0]); err != nil {
		return err
	}

	hasher, hexSHA1 := args[1], args[2:]
	if len(hexSHA1) == 0 {
		var err error
		hexSHA1, err = dbCollectStrings(`SELECT sha1 FROM image
			WHERE dhash IS NULL`)
		if err != nil {
			return err
		}
	}

	// TODO: Try to run the hasher in parallel, somehow.
	// TODO: Show progress in some manner. Perhaps port my propeller code.
	for _, sha1 := range hexSHA1 {
		pathThumb := thumbPath(sha1)
		hash, err := makeDhash(hasher, pathThumb)
		if err != nil {
			return err
		}

		_, err = db.Exec(`UPDATE image SET dhash = ? WHERE sha1 = ?`,
			int64(hash), sha1)
		if err != nil {
			return err
		}
	}
	return nil
}

var commands = map[string]struct {
	handler func(args []string) error
}{
	"init":      {cmdInit},
	"run":       {cmdRun},
	"import":    {cmdImport},
	"sync":      {cmdSync},
	"check":     {cmdCheck},
	"thumbnail": {cmdThumbnail},
	"dhash":     {cmdDhash},
}

func main() {
	if len(os.Args) <= 2 {
		log.Fatalln("Missing arguments")
	}

	cmd, ok := commands[os.Args[1]]
	if !ok {
		log.Fatalln("Unknown command: " + os.Args[1])
	}

	err := cmd.handler(os.Args[2:])

	// Note that the database object has a closing finalizer,
	// we just additionally print any errors coming from there.
	if db != nil {
		if err := db.Close(); err != nil {
			log.Println(err)
		}
	}

	if err != nil {
		log.Fatalln(err)
	}
}