From c471a64ab8a4d3e90fb0050b5b4f68a187c2b02e Mon Sep 17 00:00:00 2001
From: Přemysl Eric Janouch <p@janouch.name>
Date: Sun, 17 Dec 2023 20:44:03 +0100
Subject: Implement the check command

---
 main.go | 125 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 122 insertions(+), 3 deletions(-)

diff --git a/main.go b/main.go
index 44214b9..0a96007 100644
--- a/main.go
+++ b/main.go
@@ -22,6 +22,7 @@ import (
 	"path/filepath"
 	"regexp"
 	"runtime"
+	"slices"
 	"strconv"
 	"strings"
 	"sync"
@@ -853,7 +854,74 @@ func cmdTag(args []string) error {
 
 // --- Check -------------------------------------------------------------------
 
-// cmdCheck checks if all files tracked in the DB are accessible.
+func isValidSHA1(hash string) bool {
+	if len(hash) != sha1.Size*2 || strings.ToLower(hash) != hash {
+		return false
+	}
+	if _, err := hex.DecodeString(hash); err != nil {
+		return false
+	}
+	return true
+}
+
+func hashesToFileListing(root, suffix string, hashes []string) []string {
+	// Note that we're semi-duplicating {image,thumb}Path().
+	paths := []string{root}
+	for _, hash := range hashes {
+		dir := filepath.Join(root, hash[:2])
+		paths = append(paths, dir, filepath.Join(dir, hash+suffix))
+	}
+	slices.Sort(paths)
+	return slices.Compact(paths)
+}
+
+func collectFileListing(root string) (paths []string, err error) {
+	err = filepath.WalkDir(root,
+		func(path string, d fs.DirEntry, err error) error {
+			paths = append(paths, path)
+			return err
+		})
+
+	// Even though it should already be sorted somehow.
+	slices.Sort(paths)
+	return
+}
+
+func checkFiles(root, suffix string, hashes []string) (bool, []string, error) {
+	db := hashesToFileListing(root, suffix, hashes)
+	fs, err := collectFileListing(root)
+	if err != nil {
+		return false, nil, err
+	}
+
+	iDB, iFS, ok, intersection := 0, 0, true, []string{}
+	for iDB < len(db) && iFS < len(fs) {
+		if db[iDB] == fs[iFS] {
+			intersection = append(intersection, db[iDB])
+			iDB++
+			iFS++
+		} else if db[iDB] < fs[iFS] {
+			ok = false
+			fmt.Printf("only in DB: %s\n", db[iDB])
+			iDB++
+		} else {
+			ok = false
+			fmt.Printf("only in FS: %s\n", fs[iFS])
+			iFS++
+		}
+	}
+	for _, path := range db[iDB:] {
+		ok = false
+		fmt.Printf("only in DB: %s\n", path)
+	}
+	for _, path := range fs[iFS:] {
+		ok = false
+		fmt.Printf("only in FS: %s\n", path)
+	}
+	return ok, intersection, nil
+}
+
+// cmdCheck carries out various database consistency checks.
 func cmdCheck(args []string) error {
 	if len(args) != 1 {
 		return errors.New("usage: GD")
@@ -862,8 +930,59 @@ func cmdCheck(args []string) error {
 		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.
+	// Check if hashes are in the right format.
+	log.Println("checking image hashes")
+
+	allSHA1, err := dbCollectStrings(`SELECT sha1 FROM image`)
+	if err != nil {
+		return err
+	}
+
+	ok := true
+	for _, hash := range allSHA1 {
+		if !isValidSHA1(hash) {
+			ok = false
+			fmt.Printf("invalid image SHA1: %s\n", hash)
+		}
+	}
+
+	// This is, rather obviously, just a strict subset.
+	// Although it doesn't run in the same transaction.
+	thumbSHA1, err := dbCollectStrings(`SELECT sha1 FROM image
+		WHERE thumbw IS NOT NULL OR thumbh IS NOT NULL`)
+	if err != nil {
+		return err
+	}
+
+	// This somewhat duplicates {image,thumb}Path().
+	log.Println("checking SQL against filesystem")
+	okImages, intersection, err := checkFiles(
+		filepath.Join(galleryDirectory, "images"), "", allSHA1)
+	if err != nil {
+		return err
+	}
+
+	okThumbs, _, err := checkFiles(
+		filepath.Join(galleryDirectory, "thumbs"), ".webp", thumbSHA1)
+	if err != nil {
+		return err
+	}
+	if !okImages || !okThumbs {
+		ok = false
+	}
+
+	// NOTE: We could also compare mtime, and on mismatch the current SHA1,
+	// though that's more of a "sync" job.
+	log.Println("checking for dead symlinks")
+	for _, path := range intersection {
+		if _, err := os.Stat(path); err != nil {
+			ok = false
+			fmt.Printf("%s: %s\n", path, err)
+		}
+	}
+	if !ok {
+		return errors.New("detected inconsistencies")
+	}
 	return nil
 }
 
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