From ef8dc85f3c72eec8a071c06a696483515d069bb3 Mon Sep 17 00:00:00 2001
From: Celine Mercier <celine.mercier@metabarcoding.org>
Date: Tue, 27 Nov 2018 16:00:29 +0100
Subject: [PATCH] C, taxonomy: new function to get the lowest common ancestor
 of two taxa

---
 src/obidms_taxonomy.c | 57 +++++++++++++++++++++++++++++++++++++++++++
 src/obidms_taxonomy.h | 12 +++++++++
 2 files changed, 69 insertions(+)

diff --git a/src/obidms_taxonomy.c b/src/obidms_taxonomy.c
index 1e113b5..5822773 100755
--- a/src/obidms_taxonomy.c
+++ b/src/obidms_taxonomy.c
@@ -3528,6 +3528,63 @@ int obi_taxo_add_preferred_name_with_taxon(OBIDMS_taxonomy_p tax, ecotx_t* taxon
 }
 
 
+ecotx_t* obi_taxo_get_lca(ecotx_t* taxon1, ecotx_t* taxon2)  // TODO could be more efficient maybe
+{
+	ecotx_t* current_taxon;
+	ecotx_t* next_taxon;
+	ecotx_t* lca;
+	ecotx_t* path1[1000];
+	ecotx_t* path2[1000];
+	int      i,j;
+
+	if ((taxon1 == NULL) || (taxon2 == NULL))
+	{
+		obi_set_errno(OBI_TAXONOMY_ERROR);
+		obidebug(1, "\nError getting the LCA of two taxons: at least one of the taxon pointers is NULL");
+		return NULL;
+	}
+
+	// Get path of first taxon   // TODO function to get path?
+	current_taxon = taxon1;
+	next_taxon    = current_taxon->parent;
+	path1[0]      = current_taxon;
+	i=0;
+	while (current_taxon != next_taxon)  // root node
+	{
+		current_taxon = next_taxon;
+		next_taxon    = current_taxon->parent;
+		i++;
+		path1[i] = current_taxon;
+	}
+	i--;
+
+	// Get path of second taxon   // TODO function to get path?
+	current_taxon = taxon2;
+	next_taxon    = current_taxon->parent;
+	path2[0]      = current_taxon;
+	j=0;
+	while (current_taxon != next_taxon)  // root node
+	{
+		current_taxon = next_taxon;
+		next_taxon    = current_taxon->parent;
+		j++;
+		path2[j] = current_taxon;
+	}
+	j--;
+
+	while ((i>=0) && (j>=0) && (path1[i] == path2[j]))
+	{
+		i--;
+		j--;
+	}
+	i++;
+
+	lca = path1[i];
+
+	return lca;
+}
+
+
 ecotx_t* obi_taxo_get_parent_at_rank(ecotx_t* taxon, int32_t rankidx)
 {
 	ecotx_t* current_taxon;
diff --git a/src/obidms_taxonomy.h b/src/obidms_taxonomy.h
index 8b5c130..c5ba099 100755
--- a/src/obidms_taxonomy.h
+++ b/src/obidms_taxonomy.h
@@ -320,6 +320,18 @@ int obi_taxo_add_preferred_name_with_taxid(OBIDMS_taxonomy_p tax, int32_t taxid,
 int obi_taxo_add_preferred_name_with_taxon(OBIDMS_taxonomy_p tax, ecotx_t* taxon, const char* preferred_name);
 
 
+/**
+ * @brief Function returning the last common ancestor of two taxa.
+ *
+ * @param taxon1 A pointer on the first taxon.
+ * @param taxon2 A pointer on the second taxon.
+ *
+ * @returns A pointer on the last common ancestor of the two taxa.
+ * @retval NULL if an error occurred.
+ */
+ecotx_t* obi_taxo_get_lca(ecotx_t* taxon1, ecotx_t* taxon2);
+
+
 /**
  * @brief Function returning the parent of a taxon at a given rank.
  *