Add function to allow getting string-valued auth_asym_id/chain-labels…

… from residues.

Related to #96.

src/freesasa.h

@@ -945,6 +945,9 @@ int freesasa_structure_add_cif_atom(freesasa_structure *structure,
     \private
     Add atoms from a mmCIF file to a structure using strings for chain labels (LCL)
 
+    This is an intermediate function added in the process of migrating to long chain labels.
+    It is not meant to be part of the public API for now.
+
     @param structure The structure to add to.
     @param atom An atom site from a mmCIF file with long chain labels
     @param classifier A ::freesasa_classifier to determine radius of atom and to
@@ -1136,6 +1139,9 @@ char freesasa_structure_atom_chain(const freesasa_structure *structure,
 
     Asserts that index i is within bounds.
 
+    This is an intermediate function added in the process of migrating to long chain labels.
+    It is not meant to be part of the public API for now.
+
     @param structure The structure.
     @param i Atom index.
     @return Chain label (`'A'`, `'B'`, etc.)
@@ -1231,6 +1237,22 @@ freesasa_structure_residue_number(const freesasa_structure *structure,
 char freesasa_structure_residue_chain(const freesasa_structure *structure,
                                       int r_i);
 
+/**
+    \private
+    Get long form chain residue belongs to.
+
+    This is an intermediate function added in the process of migrating to long chain labels.
+    It is not meant to be part of the public API for now.
+
+    @param structure The structure.
+    @param r_i Residue index (in whole structure).
+    @return Chain label.
+
+    @ingroup structure
+ */
+const char *
+freesasa_structure_residue_chain_lcl(const freesasa_structure *structure,
+                                     int r_i);
 /**
     Get model number for structure.
 

src/structure.c

@@ -1182,6 +1182,16 @@ char freesasa_structure_residue_chain(const freesasa_structure *structure,
     return structure->atoms.atom[structure->residues.first_atom[r_i]]->chain_label[0];
 }
 
+const char *
+freesasa_structure_residue_chain_lcl(const freesasa_structure *structure,
+                                     int r_i)
+{
+    assert(structure);
+    assert(r_i < structure->residues.n && r_i >= 0);
+
+    return structure->atoms.atom[structure->residues.first_atom[r_i]]->chain_label;
+}
+
 int freesasa_structure_n_chains(const freesasa_structure *structure)
 {
     return structure->chains.n;

tests/test_structure.c

@@ -148,6 +148,8 @@ START_TEST(test_cif)
         ck_assert_int_eq(freesasa_structure_atom_chain(s, i), lcl[i][0]);
         ck_assert_str_eq(freesasa_structure_atom_chain_lcl(s, i), lcl[i]);
     }
+    ck_assert_int_eq(freesasa_structure_residue_chain(s, 0), lcl[0][0]);
+    ck_assert_str_eq(freesasa_structure_residue_chain_lcl(s, 0), lcl[0]);
 
     struct freesasa_cif_atom_lcl atom = {
         .group_PDB = "",