Cleanup: move tag functions into own translation unit

Make dive.h a bit slimmer. It's only a drop in the bucket - but at
least when modifying tag functions not the *whole* application is
rebuilt anymore.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

25 files changed, 321 insertions, 267 deletions

diff --git a/core/CMakeLists.txt b/core/CMakeLists.txt
index 17a2bd0c7..9d3f3e493 100644
--- a/core/CMakeLists.txt
+++ b/core/CMakeLists.txt
@@ -144,6 +144,8 @@ set(SUBSURFACE_CORE_LIB_SRCS
 	subsurfacestartup.h
 	subsurfacesysinfo.cpp
 	subsurfacesysinfo.h
+	tag.c
+	tag.h
 	taxonomy.c
 	taxonomy.h
 	time.c
diff --git a/core/datatrak.c b/core/datatrak.c
index 5e806f08f..43c7346cd 100644
--- a/core/datatrak.c
+++ b/core/datatrak.c
@@ -17,6 +17,7 @@
 #include "file.h"
 #include "divesite.h"
 #include "ssrf.h"
+#include "tag.h"
 
 static unsigned int two_bytes_to_int(unsigned char x, unsigned char y)
 {
diff --git a/core/dive.c b/core/dive.c
index 907ad40e7..5191402a5 100644
--- a/core/dive.c
+++ b/core/dive.c
@@ -14,24 +14,14 @@
 #include "qthelper.h"
 #include "metadata.h"
 #include "membuffer.h"
+#include "tag.h"
+#include "structured_list.h"
 
 /* one could argue about the best place to have this variable -
  * it's used in the UI, but it seems to make the most sense to have it
  * here */
 struct dive displayed_dive;
 
-struct tag_entry *g_tag_list = NULL;
-
-static const char *default_tags[] = {
-	QT_TRANSLATE_NOOP("gettextFromC", "boat"), QT_TRANSLATE_NOOP("gettextFromC", "shore"), QT_TRANSLATE_NOOP("gettextFromC", "drift"),
-	QT_TRANSLATE_NOOP("gettextFromC", "deep"), QT_TRANSLATE_NOOP("gettextFromC", "cavern"), QT_TRANSLATE_NOOP("gettextFromC", "ice"),
-	QT_TRANSLATE_NOOP("gettextFromC", "wreck"), QT_TRANSLATE_NOOP("gettextFromC", "cave"), QT_TRANSLATE_NOOP("gettextFromC", "altitude"),
-	QT_TRANSLATE_NOOP("gettextFromC", "pool"), QT_TRANSLATE_NOOP("gettextFromC", "lake"), QT_TRANSLATE_NOOP("gettextFromC", "river"),
-	QT_TRANSLATE_NOOP("gettextFromC", "night"), QT_TRANSLATE_NOOP("gettextFromC", "fresh"), QT_TRANSLATE_NOOP("gettextFromC", "student"),
-	QT_TRANSLATE_NOOP("gettextFromC", "instructor"), QT_TRANSLATE_NOOP("gettextFromC", "photo"), QT_TRANSLATE_NOOP("gettextFromC", "video"),
-	QT_TRANSLATE_NOOP("gettextFromC", "deco")
-};
-
 const char *cylinderuse_text[] = {
 	QT_TRANSLATE_NOOP("gettextFromC", "OC-gas"), QT_TRANSLATE_NOOP("gettextFromC", "diluent"), QT_TRANSLATE_NOOP("gettextFromC", "oxygen"), QT_TRANSLATE_NOOP("gettextFromC", "not used")
 };
@@ -474,31 +464,6 @@ struct dive *alloc_dive(void)
 	return dive;
 }
 
-/* Clear everything but the first element;
- * this works for taglist, picturelist, even dive computers */
-#define STRUCTURED_LIST_FREE(_type, _start, _free) \
-	{                                          \
-		_type *_ptr = _start;              \
-		while (_ptr) {                     \
-			_type *_next = _ptr->next; \
-			_free(_ptr);               \
-			_ptr = _next;              \
-		}                                  \
-	}
-
-#define STRUCTURED_LIST_COPY(_type, _first, _dest, _cpy) \
-	{                                                \
-		_type *_sptr = _first;                   \
-		_type **_dptr = &_dest;                  \
-		while (_sptr) {                          \
-			*_dptr = malloc(sizeof(_type));  \
-			_cpy(_sptr, *_dptr);             \
-			_sptr = _sptr->next;             \
-			_dptr = &(*_dptr)->next;         \
-		}                                        \
-		*_dptr = 0;                              \
-	}
-
 static void free_dc(struct divecomputer *dc);
 static void free_dc_contents(struct divecomputer *dc);
 
@@ -548,14 +513,6 @@ static void copy_pl(struct picture *sp, struct picture *dp)
 	dp->filename = copy_string(sp->filename);
 }
 
-/* copy an element in a list of tags */
-static void copy_tl(struct tag_entry *st, struct tag_entry *dt)
-{
-	dt->tag = malloc(sizeof(struct divetag));
-	dt->tag->name = copy_string(st->tag->name);
-	dt->tag->source = copy_string(st->tag->source);
-}
-
 static void free_dive_structures(struct dive *d)
 {
 	if (!d)
@@ -3253,182 +3210,6 @@ static void join_dive_computers(struct dive *d, struct divecomputer *res,
 	remove_redundant_dc(res, prefer_downloaded);
 }
 
-static bool tag_seen_before(struct tag_entry *start, struct tag_entry *before)
-{
-	while (start && start != before) {
-		if (same_string(start->tag->name, before->tag->name))
-			return true;
-		start = start->next;
-	}
-	return false;
-}
-
-/* remove duplicates and empty nodes */
-void taglist_cleanup(struct tag_entry **tag_list)
-{
-	struct tag_entry **tl = tag_list;
-	while (*tl) {
-		/* skip tags that are empty or that we have seen before */
-		if (empty_string((*tl)->tag->name) || tag_seen_before(*tag_list, *tl)) {
-			*tl = (*tl)->next;
-			continue;
-		}
-		tl = &(*tl)->next;
-	}
-}
-
-char *taglist_get_tagstring(struct tag_entry *tag_list)
-{
-	bool first_tag = true;
-	struct membuffer b = { 0 };
-	struct tag_entry *tmp = tag_list;
-	while (tmp != NULL) {
-		if (!empty_string(tmp->tag->name)) {
-			if (first_tag) {
-				put_format(&b, "%s", tmp->tag->name);
-				first_tag = false;
-			} else {
-				put_format(&b, ", %s", tmp->tag->name);
-			}
-		}
-		tmp = tmp->next;
-	}
-	/* Ensures we do return null terminated empty string for:
-	 *  - empty tag list
-	 *  - tag list with empty tag only
-	 */
-	mb_cstring(&b);
-	return detach_buffer(&b);
-}
-
-static inline void taglist_free_divetag(struct divetag *tag)
-{
-	if (tag->name != NULL)
-		free(tag->name);
-	if (tag->source != NULL)
-		free(tag->source);
-	free(tag);
-}
-
-/* Add a tag to the tag_list, keep the list sorted */
-static struct divetag *taglist_add_divetag(struct tag_entry **tag_list, struct divetag *tag)
-{
-	struct tag_entry *next, *entry;
-
-	while ((next = *tag_list) != NULL) {
-		int cmp = strcmp(next->tag->name, tag->name);
-
-		/* Already have it? */
-		if (!cmp)
-			return next->tag;
-		/* Is the entry larger? If so, insert here */
-		if (cmp > 0)
-			break;
-		/* Continue traversing the list */
-		tag_list = &next->next;
-	}
-
-	/* Insert in front of it */
-	entry = malloc(sizeof(struct tag_entry));
-	entry->next = next;
-	entry->tag = tag;
-	*tag_list = entry;
-	return tag;
-}
-
-struct divetag *taglist_add_tag(struct tag_entry **tag_list, const char *tag)
-{
-	size_t i = 0;
-	int is_default_tag = 0;
-	struct divetag *ret_tag, *new_tag;
-	const char *translation;
-	new_tag = malloc(sizeof(struct divetag));
-
-	for (i = 0; i < sizeof(default_tags) / sizeof(char *); i++) {
-		if (strcmp(default_tags[i], tag) == 0) {
-			is_default_tag = 1;
-			break;
-		}
-	}
-	/* Only translate default tags */
-	if (is_default_tag) {
-		translation = translate("gettextFromC", tag);
-		new_tag->name = malloc(strlen(translation) + 1);
-		memcpy(new_tag->name, translation, strlen(translation) + 1);
-		new_tag->source = malloc(strlen(tag) + 1);
-		memcpy(new_tag->source, tag, strlen(tag) + 1);
-	} else {
-		new_tag->source = NULL;
-		new_tag->name = malloc(strlen(tag) + 1);
-		memcpy(new_tag->name, tag, strlen(tag) + 1);
-	}
-	/* Try to insert new_tag into g_tag_list if we are not operating on it */
-	if (tag_list != &g_tag_list) {
-		ret_tag = taglist_add_divetag(&g_tag_list, new_tag);
-		/* g_tag_list already contains new_tag, free the duplicate */
-		if (ret_tag != new_tag)
-			taglist_free_divetag(new_tag);
-		ret_tag = taglist_add_divetag(tag_list, ret_tag);
-	} else {
-		ret_tag = taglist_add_divetag(tag_list, new_tag);
-		if (ret_tag != new_tag)
-			taglist_free_divetag(new_tag);
-	}
-	return ret_tag;
-}
-
-void taglist_free(struct tag_entry *entry)
-{
-	STRUCTURED_LIST_FREE(struct tag_entry, entry, free)
-}
-
-struct tag_entry *taglist_copy(struct tag_entry *s)
-{
-	struct tag_entry *res;
-	STRUCTURED_LIST_COPY(struct tag_entry, s, res, copy_tl);
-	return res;
-}
-
-/* Merge src1 and src2, write to *dst */
-static void taglist_merge(struct tag_entry **dst, struct tag_entry *src1, struct tag_entry *src2)
-{
-	struct tag_entry *entry;
-
-	for (entry = src1; entry; entry = entry->next)
-		taglist_add_divetag(dst, entry->tag);
-	for (entry = src2; entry; entry = entry->next)
-		taglist_add_divetag(dst, entry->tag);
-}
-
-void taglist_init_global()
-{
-	size_t i;
-
-	for (i = 0; i < sizeof(default_tags) / sizeof(char *); i++)
-		taglist_add_tag(&g_tag_list, default_tags[i]);
-}
-
-bool taglist_contains(struct tag_entry *tag_list, const char *tag)
-{
-	while (tag_list) {
-		if (same_string(tag_list->tag->name, tag))
-			return true;
-		tag_list = tag_list->next;
-	}
-	return false;
-}
-
-struct tag_entry *taglist_added(struct tag_entry *original_list, struct tag_entry *new_list)
-{
-	struct tag_entry *added_list = NULL;
-	while (new_list) {
-		if (!taglist_contains(original_list, new_list->tag->name))
-			taglist_add_tag(&added_list, new_list->tag->name);
-		new_list = new_list->next;
-	}
-	return added_list;
-}
-
 bool is_dc_planner(const struct divecomputer *dc)
 {
 	return same_string(dc->model, "planned dive");
diff --git a/core/dive.h b/core/dive.h
index c115f5c0f..a68336494 100644
--- a/core/dive.h
+++ b/core/dive.h
@@ -177,52 +177,6 @@ struct sample                         // BASE TYPE BYTES  UNITS    RANGE
 					  //                                               not calculated when planning a dive
 };	                                  // Total size of structure: 57 bytes, excluding padding at end
 
-struct divetag {
-	/*
-	 * The name of the divetag. If a translation is available, name contains
-	 * the translated tag
-	 */
-	char *name;
-	/*
-	 * If a translation is available, we write the original tag to source.
-	 * This enables us to write a non-localized tag to the xml file.
-	 */
-	char *source;
-};
-
-struct tag_entry {
-	struct divetag *tag;
-	struct tag_entry *next;
-};
-
-/*
- * divetags are only stored once, each dive only contains
- * a list of tag_entries which then point to the divetags
- * in the global g_tag_list
- */
-
-extern struct tag_entry *g_tag_list;
-
-struct divetag *taglist_add_tag(struct tag_entry **tag_list, const char *tag);
-struct tag_entry *taglist_added(struct tag_entry *original_list, struct tag_entry *new_list);
-
-/*
- * Writes all divetags form tag_list into internally allocated buffer
- * Function returns pointer to allocated buffer
- * Buffer contains comma separated list of tags names or null terminated string
- *
- * NOTE! The returned buffer must be freed once used.
- */
-char *taglist_get_tagstring(struct tag_entry *tag_list);
-
-/* cleans up a list: removes empty tags and duplicates */
-void taglist_cleanup(struct tag_entry **tag_list);
-
-void taglist_init_global();
-void taglist_free(struct tag_entry *tag_list);
-struct tag_entry *taglist_copy(struct tag_entry *s);
-bool taglist_contains(struct tag_entry *tag_list, const char *tag);
-
 struct extra_data {
 	const char *key;
 	const char *value;
diff --git a/core/import-suunto.c b/core/import-suunto.c
index 078593700..060ed113b 100644
--- a/core/import-suunto.c
+++ b/core/import-suunto.c
@@ -12,6 +12,7 @@
 #include "device.h"
 #include "membuffer.h"
 #include "gettext.h"
+#include "tag.h"
 
 static int dm4_events(void *param, int columns, char **data, char **column)
 {
diff --git a/core/load-git.c b/core/load-git.c
index a0baedecd..91d8f8cd1 100644
--- a/core/load-git.c
+++ b/core/load-git.c
@@ -22,6 +22,7 @@
 #include "membuffer.h"
 #include "git-access.h"
 #include "qthelper.h"
+#include "tag.h"
 
 const char *saved_git_id = NULL;
 
diff --git a/core/parse-xml.c b/core/parse-xml.c
index 43d0049a7..f4a7d60a9 100644
--- a/core/parse-xml.c
+++ b/core/parse-xml.c
@@ -29,6 +29,7 @@
 #include "device.h"
 #include "membuffer.h"
 #include "qthelper.h"
+#include "tag.h"
 
 int verbose, quit, force_root;
 int last_xml_version = -1;
diff --git a/core/qthelper.cpp b/core/qthelper.cpp
index 65c55414d..e9bab9ebd 100644
--- a/core/qthelper.cpp
+++ b/core/qthelper.cpp
@@ -17,6 +17,7 @@
 #include <sys/time.h>
 #include "exif.h"
 #include "file.h"
+#include "tag.h"
 #include "imagedownloader.h"
 #include <QFile>
 #include <QRegExp>
diff --git a/core/save-git.c b/core/save-git.c
index a5f6f0dde..bbf70c373 100644
--- a/core/save-git.c
+++ b/core/save-git.c
@@ -26,6 +26,7 @@
 #include "version.h"
 #include "qthelper.h"
 #include "gettext.h"
+#include "tag.h"
 
 #define VA_BUF(b, fmt) do { va_list args; va_start(args, fmt); put_vformat(b, fmt, args); va_end(args); } while (0)
 
diff --git a/core/save-html.c b/core/save-html.c
index f9d7049a9..3c54efd6f 100644
--- a/core/save-html.c
+++ b/core/save-html.c
@@ -8,6 +8,7 @@
 #include "qthelper.h"
 #include "gettext.h"
 #include "divesite.h"
+#include "tag.h"
 #include <stdio.h>
 
 void write_attribute(struct membuffer *b, const char *att_name, const char *value, const char *separator)
diff --git a/core/save-xml.c b/core/save-xml.c
index f043ab6d8..658f05e1b 100644
--- a/core/save-xml.c
+++ b/core/save-xml.c
@@ -22,6 +22,7 @@
 #include "git-access.h"
 #include "qthelper.h"
 #include "gettext.h"
+#include "tag.h"
 
 /*
  * We're outputting utf8 in xml.
diff --git a/core/structured_list.h b/core/structured_list.h
new file mode 100644
index 000000000..232e4ee34
--- /dev/null
+++ b/core/structured_list.h
@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-2.0
+#ifndef STRUCTURED_LIST_H
+#define STRUCTURED_LIST_H
+
+/* Clear everything but the first element;
+ * this works for taglist, picturelist, even dive computers */
+#define STRUCTURED_LIST_FREE(_type, _start, _free) \
+	{                                          \
+		_type *_ptr = _start;              \
+		while (_ptr) {                     \
+			_type *_next = _ptr->next; \
+			_free(_ptr);               \
+			_ptr = _next;              \
+		}                                  \
+	}
+
+#define STRUCTURED_LIST_COPY(_type, _first, _dest, _cpy) \
+	{                                                \
+		_type *_sptr = _first;                   \
+		_type **_dptr = &_dest;                  \
+		while (_sptr) {                          \
+			*_dptr = malloc(sizeof(_type));  \
+			_cpy(_sptr, *_dptr);             \
+			_sptr = _sptr->next;             \
+			_dptr = &(*_dptr)->next;         \
+		}                                        \
+		*_dptr = 0;                              \
+	}
+
+#endif
diff --git a/core/tag.c b/core/tag.c
new file mode 100644
index 000000000..ba88ab879
--- /dev/null
+++ b/core/tag.c
@@ -0,0 +1,206 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "tag.h"
+#include "structured_list.h"
+#include "subsurface-string.h"
+#include "membuffer.h"
+#include "gettext.h"
+
+#include <stdlib.h>
+
+struct tag_entry *g_tag_list = NULL;
+
+static const char *default_tags[] = {
+	QT_TRANSLATE_NOOP("gettextFromC", "boat"), QT_TRANSLATE_NOOP("gettextFromC", "shore"), QT_TRANSLATE_NOOP("gettextFromC", "drift"),
+	QT_TRANSLATE_NOOP("gettextFromC", "deep"), QT_TRANSLATE_NOOP("gettextFromC", "cavern"), QT_TRANSLATE_NOOP("gettextFromC", "ice"),
+	QT_TRANSLATE_NOOP("gettextFromC", "wreck"), QT_TRANSLATE_NOOP("gettextFromC", "cave"), QT_TRANSLATE_NOOP("gettextFromC", "altitude"),
+	QT_TRANSLATE_NOOP("gettextFromC", "pool"), QT_TRANSLATE_NOOP("gettextFromC", "lake"), QT_TRANSLATE_NOOP("gettextFromC", "river"),
+	QT_TRANSLATE_NOOP("gettextFromC", "night"), QT_TRANSLATE_NOOP("gettextFromC", "fresh"), QT_TRANSLATE_NOOP("gettextFromC", "student"),
+	QT_TRANSLATE_NOOP("gettextFromC", "instructor"), QT_TRANSLATE_NOOP("gettextFromC", "photo"), QT_TRANSLATE_NOOP("gettextFromC", "video"),
+	QT_TRANSLATE_NOOP("gettextFromC", "deco")
+};
+
+/* copy an element in a list of tags */
+static void copy_tl(struct tag_entry *st, struct tag_entry *dt)
+{
+	dt->tag = malloc(sizeof(struct divetag));
+	dt->tag->name = copy_string(st->tag->name);
+	dt->tag->source = copy_string(st->tag->source);
+}
+
+static bool tag_seen_before(struct tag_entry *start, struct tag_entry *before)
+{
+	while (start && start != before) {
+		if (same_string(start->tag->name, before->tag->name))
+			return true;
+		start = start->next;
+	}
+	return false;
+}
+
+/* remove duplicates and empty nodes */
+void taglist_cleanup(struct tag_entry **tag_list)
+{
+	struct tag_entry **tl = tag_list;
+	while (*tl) {
+		/* skip tags that are empty or that we have seen before */
+		if (empty_string((*tl)->tag->name) || tag_seen_before(*tag_list, *tl)) {
+			*tl = (*tl)->next;
+			continue;
+		}
+		tl = &(*tl)->next;
+	}
+}
+
+char *taglist_get_tagstring(struct tag_entry *tag_list)
+{
+	bool first_tag = true;
+	struct membuffer b = { 0 };
+	struct tag_entry *tmp = tag_list;
+	while (tmp != NULL) {
+		if (!empty_string(tmp->tag->name)) {
+			if (first_tag) {
+				put_format(&b, "%s", tmp->tag->name);
+				first_tag = false;
+			} else {
+				put_format(&b, ", %s", tmp->tag->name);
+			}
+		}
+		tmp = tmp->next;
+	}
+	/* Ensures we do return null terminated empty string for:
+	 *  - empty tag list
+	 *  - tag list with empty tag only
+	 */
+	mb_cstring(&b);
+	return detach_buffer(&b);
+}
+
+static inline void taglist_free_divetag(struct divetag *tag)
+{
+	if (tag->name != NULL)
+		free(tag->name);
+	if (tag->source != NULL)
+		free(tag->source);
+	free(tag);
+}
+
+/* Add a tag to the tag_list, keep the list sorted */
+static struct divetag *taglist_add_divetag(struct tag_entry **tag_list, struct divetag *tag)
+{
+	struct tag_entry *next, *entry;
+
+	while ((next = *tag_list) != NULL) {
+		int cmp = strcmp(next->tag->name, tag->name);
+
+		/* Already have it? */
+		if (!cmp)
+			return next->tag;
+		/* Is the entry larger? If so, insert here */
+		if (cmp > 0)
+			break;
+		/* Continue traversing the list */
+		tag_list = &next->next;
+	}
+
+	/* Insert in front of it */
+	entry = malloc(sizeof(struct tag_entry));
+	entry->next = next;
+	entry->tag = tag;
+	*tag_list = entry;
+	return tag;
+}
+
+struct divetag *taglist_add_tag(struct tag_entry **tag_list, const char *tag)
+{
+	size_t i = 0;
+	int is_default_tag = 0;
+	struct divetag *ret_tag, *new_tag;
+	const char *translation;
+	new_tag = malloc(sizeof(struct divetag));
+
+	for (i = 0; i < sizeof(default_tags) / sizeof(char *); i++) {
+		if (strcmp(default_tags[i], tag) == 0) {
+			is_default_tag = 1;
+			break;
+		}
+	}
+	/* Only translate default tags */
+	if (is_default_tag) {
+		translation = translate("gettextFromC", tag);
+		new_tag->name = malloc(strlen(translation) + 1);
+		memcpy(new_tag->name, translation, strlen(translation) + 1);
+		new_tag->source = malloc(strlen(tag) + 1);
+		memcpy(new_tag->source, tag, strlen(tag) + 1);
+	} else {
+		new_tag->source = NULL;
+		new_tag->name = malloc(strlen(tag) + 1);
+		memcpy(new_tag->name, tag, strlen(tag) + 1);
+	}
+	/* Try to insert new_tag into g_tag_list if we are not operating on it */
+	if (tag_list != &g_tag_list) {
+		ret_tag = taglist_add_divetag(&g_tag_list, new_tag);
+		/* g_tag_list already contains new_tag, free the duplicate */
+		if (ret_tag != new_tag)
+			taglist_free_divetag(new_tag);
+		ret_tag = taglist_add_divetag(tag_list, ret_tag);
+	} else {
+		ret_tag = taglist_add_divetag(tag_list, new_tag);
+		if (ret_tag != new_tag)
+			taglist_free_divetag(new_tag);
+	}
+	return ret_tag;
+}
+
+void taglist_free(struct tag_entry *entry)
+{
+	STRUCTURED_LIST_FREE(struct tag_entry, entry, free)
+}
+
+struct tag_entry *taglist_copy(struct tag_entry *s)
+{
+	struct tag_entry *res;
+	STRUCTURED_LIST_COPY(struct tag_entry, s, res, copy_tl);
+	return res;
+}
+
+/* Merge src1 and src2, write to *dst */
+void taglist_merge(struct tag_entry **dst, struct tag_entry *src1, struct tag_entry *src2)
+{
+	struct tag_entry *entry;
+
+	for (entry = src1; entry; entry = entry->next)
+		taglist_add_divetag(dst, entry->tag);
+	for (entry = src2; entry; entry = entry->next)
+		taglist_add_divetag(dst, entry->tag);
+}
+
+void taglist_init_global()
+{
+	size_t i;
+
+	for (i = 0; i < sizeof(default_tags) / sizeof(char *); i++)
+		taglist_add_tag(&g_tag_list, default_tags[i]);
+}
+
+bool taglist_contains(struct tag_entry *tag_list, const char *tag)
+{
+	while (tag_list) {
+		if (same_string(tag_list->tag->name, tag))
+			return true;
+		tag_list = tag_list->next;
+	}
+	return false;
+}
+
+struct tag_entry *taglist_added(struct tag_entry *original_list, struct tag_entry *new_list)
+{
+	struct tag_entry *added_list = NULL;
+	while (new_list) {
+		if (!taglist_contains(original_list, new_list->tag->name))
+			taglist_add_tag(&added_list, new_list->tag->name);
+		new_list = new_list->next;
+	}
+	return added_list;
+}
+
diff --git a/core/tag.h b/core/tag.h
new file mode 100644
index 000000000..1f50dc920
--- /dev/null
+++ b/core/tag.h
@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: GPL-2.0
+// Dive tag related structures and helpers
+#ifndef TAG_H
+#define TAG_H
+
+#include <stdbool.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct divetag {
+	/*
+	 * The name of the divetag. If a translation is available, name contains
+	 * the translated tag
+	 */
+	char *name;
+	/*
+	 * If a translation is available, we write the original tag to source.
+	 * This enables us to write a non-localized tag to the xml file.
+	 */
+	char *source;
+};
+
+struct tag_entry {
+	struct divetag *tag;
+	struct tag_entry *next;
+};
+
+/*
+ * divetags are only stored once, each dive only contains
+ * a list of tag_entries which then point to the divetags
+ * in the global g_tag_list
+ */
+extern struct tag_entry *g_tag_list;
+
+struct divetag *taglist_add_tag(struct tag_entry **tag_list, const char *tag);
+struct tag_entry *taglist_added(struct tag_entry *original_list, struct tag_entry *new_list);
+
+/*
+ * Writes all divetags form tag_list into internally allocated buffer
+ * Function returns pointer to allocated buffer
+ * Buffer contains comma separated list of tags names or null terminated string
+ *
+ * NOTE! The returned buffer must be freed once used.
+ */
+char *taglist_get_tagstring(struct tag_entry *tag_list);
+
+/* cleans up a list: removes empty tags and duplicates */
+void taglist_cleanup(struct tag_entry **tag_list);
+
+void taglist_init_global();
+void taglist_free(struct tag_entry *tag_list);
+struct tag_entry *taglist_copy(struct tag_entry *s);
+bool taglist_contains(struct tag_entry *tag_list, const char *tag);
+void taglist_merge(struct tag_entry **dst, struct tag_entry *src1, struct tag_entry *src2);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
diff --git a/core/uemis-downloader.c b/core/uemis-downloader.c
index 593b94617..83f37545b 100644
--- a/core/uemis-downloader.c
+++ b/core/uemis-downloader.c
@@ -26,6 +26,7 @@
 #include "uemis.h"
 #include "divelist.h"
 #include "divesite.h"
+#include "tag.h"
 #include "core/subsurface-string.h"
 
 #define ERR_FS_ALMOST_FULL QT_TRANSLATE_NOOP("gettextFromC", "Uemis Zurich: the file system is almost full.\nDisconnect/reconnect the dive computer\nand click \'Retry\'")
diff --git a/desktop-widgets/command_edit.cpp b/desktop-widgets/command_edit.cpp
index 2c9d56ba5..89b864f60 100644
--- a/desktop-widgets/command_edit.cpp
+++ b/desktop-widgets/command_edit.cpp
@@ -5,6 +5,7 @@
 #include "core/divelist.h"
 #include "core/qthelper.h" // for copy_qstring
 #include "core/subsurface-string.h"
+#include "core/tag.h"
 #include "desktop-widgets/mapwidget.h" // TODO: Replace desktop-dependency by signal
 
 namespace Command {
diff --git a/desktop-widgets/divelogexportdialog.cpp b/desktop-widgets/divelogexportdialog.cpp
index 4fef543a0..1059d9bd0 100644
--- a/desktop-widgets/divelogexportdialog.cpp
+++ b/desktop-widgets/divelogexportdialog.cpp
@@ -17,6 +17,7 @@
 #include "profile-widget/profilewidget2.h"
 #include "core/save-profiledata.h"
 #include "core/divesite.h"
+#include "core/tag.h"
 
 // Retrieves the current unit settings defined in the Subsurface preferences.
 #define GET_UNIT(name, field, f, t)           \
diff --git a/desktop-widgets/simplewidgets.cpp b/desktop-widgets/simplewidgets.cpp
index 660a8a433..acb66c0c5 100644
--- a/desktop-widgets/simplewidgets.cpp
+++ b/desktop-widgets/simplewidgets.cpp
@@ -22,6 +22,7 @@
 #include "profile-widget/profilewidget2.h"
 #include "desktop-widgets/command.h"
 #include "core/metadata.h"
+#include "core/tag.h"
 
 double MinMaxAvgWidget::average() const
 {
diff --git a/packaging/ios/Subsurface-mobile.pro b/packaging/ios/Subsurface-mobile.pro
index ea6a378ea..a0caf4886 100644
--- a/packaging/ios/Subsurface-mobile.pro
+++ b/packaging/ios/Subsurface-mobile.pro
@@ -70,6 +70,7 @@ SOURCES += ../../subsurface-mobile-main.cpp \
 	../../core/membuffer.c \
 	../../core/sha1.c \
 	../../core/strtod.c \
+	../../core/tag.c \
 	../../core/taxonomy.c \
 	../../core/time.c \
 	../../core/uemis.c \
diff --git a/qt-models/completionmodels.cpp b/qt-models/completionmodels.cpp
index b4e166de3..957b8c7fd 100644
--- a/qt-models/completionmodels.cpp
+++ b/qt-models/completionmodels.cpp
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 #include "qt-models/completionmodels.h"
 #include "core/dive.h"
+#include "core/tag.h"
 #include <QSet>
 #include <QString>
 
diff --git a/qt-models/divetripmodel.cpp b/qt-models/divetripmodel.cpp
index 59069164f..7795b3563 100644
--- a/qt-models/divetripmodel.cpp
+++ b/qt-models/divetripmodel.cpp
@@ -6,6 +6,7 @@
 #include "core/divelist.h"
 #include "core/qthelper.h"
 #include "core/subsurface-string.h"
+#include "core/tag.h"
 #include <QIcon>
 #include <QDebug>
 #include <memory>
diff --git a/smtk-import/smartrak.c b/smtk-import/smartrak.c
index 31c7e4dc3..64c6d8e5f 100644
--- a/smtk-import/smartrak.c
+++ b/smtk-import/smartrak.c
@@ -33,6 +33,7 @@
 #include "core/libdivecomputer.h"
 #include "core/divesite.h"
 #include "core/membuffer.h"
+#include "core/tag.h"
 
 /* SmartTrak version, constant for every single file */
 int smtk_version;
diff --git a/subsurface-desktop-main.cpp b/subsurface-desktop-main.cpp
index cec1a159b..7922b01e1 100644
--- a/subsurface-desktop-main.cpp
+++ b/subsurface-desktop-main.cpp
@@ -12,6 +12,7 @@
 #include "core/qthelper.h"
 #include "core/subsurfacestartup.h"
 #include "core/settings/qPref.h"
+#include "core/tag.h"
 #include "desktop-widgets/diveplanner.h"
 #include "desktop-widgets/mainwindow.h"
 #include "desktop-widgets/preferences/preferencesdialog.h"
diff --git a/subsurface-mobile-main.cpp b/subsurface-mobile-main.cpp
index a9e4b424d..93c81f5a1 100644
--- a/subsurface-mobile-main.cpp
+++ b/subsurface-mobile-main.cpp
@@ -13,6 +13,7 @@
 #include "core/subsurfacestartup.h"
 #include "core/settings/qPref.h"
 #include "core/settings/qPrefDisplay.h"
+#include "core/tag.h"
 
 #include <QApplication>
 #include <QLocale>
diff --git a/tests/testtaglist.cpp b/tests/testtaglist.cpp
index afe5049f1..cd7e59c43 100644
--- a/tests/testtaglist.cpp
+++ b/tests/testtaglist.cpp
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 #include "testtaglist.h"
 #include "core/dive.h"
+#include "core/tag.h"
 
 void TestTagList::initTestCase()
 {