Improve support for MM .? modifiers.

The previous commit permitted these to exist, but didn't make the data
available to the caller.

This extends the API with additional queries to distinguish the
specifics about the modification types present.

htslib/sam.h

@@ -2271,6 +2271,44 @@ int bam_mods_at_qpos(const bam1_t *b, int qpos, hts_base_mod_state *state,
                      hts_base_mod *mods, int n_mods);
 
 
+/// Returns data about a specific modification type for the alignment record.
+/**
+ * @param b          BAM alignment record
+ * @param state      The base modification state pointer.
+ * @param code       Modification code.  If positive this is a character code,
+ *                   if negative it is a -ChEBI code.
+ *
+ * @param strand     Boolean for top (0) or bottom (1) strand
+ * @param implicit   Boolean for whether unlisted positions should be
+ *                   implicitly assumed to be unmodified, or require an
+ *                   explicit score and should be considered as unknown.
+ *                   Returned.
+ * @param canonical  Canonical base type associated with this modification
+ *                   Returned.
+ *
+ * @return 0 on success or -1 if not found.  The strand, implicit and canonical
+ * fields are filled out if passed in as non-NULL pointers.
+ */
+HTSLIB_EXPORT
+int bam_mods_query_type(hts_base_mod_state *state, int code,
+                        int *strand, int *implicit, char *canonical);
+
+/// Returns the list of base modification codes provided for this
+/// alignment record as an array of character codes (+ve) or ChEBI numbers
+/// (negative).
+/*
+ * @param b          BAM alignment record
+ * @param state      The base modification state pointer.
+ * @param ntype      Filled out with the number of array elements returned
+ *
+ * @return the type array, with *ntype filled out with the size.
+ *         The array returned should not be freed.
+ *         It is a valid pointer until the state is freed using
+ *         hts_base_mod_free().
+ */
+HTSLIB_EXPORT
+int *bam_mods_recorded(hts_base_mod_state *state, int *ntype);
+
 #ifdef __cplusplus
 }
 #endif

sam.c

@@ -6092,6 +6092,7 @@ struct hts_base_mod_state {
     char *MMend[MAX_BASE_MOD];  // end of pos-delta string
     uint8_t *ML[MAX_BASE_MOD];  // next qual
     int MLstride[MAX_BASE_MOD]; // bytes between quals for this type
+    int implicit[MAX_BASE_MOD]; // treat unlisted positions as non-modified?
     int seq_pos;                // current position along sequence
     int nmods;                  // used array size (0 to MAX_BASE_MOD-1).
 };
@@ -6160,6 +6161,7 @@ int bam_parse_basemod(const bam1_t *b, hts_base_mod_state *state) {
 
     char *cp = (char *)mm+1;
     int mod_num = 0;
+    int implicit = 1;
     while (*cp) {
         for (; *cp; cp++) {
             // cp should be [ACGTNU][+-]([a-zA-Z]+|[0-9]+)[.?]?(,\d+)*;
@@ -6192,16 +6194,15 @@ int bam_parse_basemod(const bam1_t *b, hts_base_mod_state *state) {
                 if (*cp == '\0')
                     return -1;
             }
+
             me = cp;
 
-            // Optional explicit vs implicit marker.
-            // Right now we ignore this field.  A proper API for
-            // querying it will follow later.
+            // Optional explicit vs implicit marker
             if (*cp == '.') {
-                // implicit = 1;
+                // default is implicit = 1;
                 cp++;
             } else if (*cp == '?') {
-                // implicit = 0;
+                implicit = 0;
                 cp++;
             } else if (*cp != ',' && *cp != ';') {
                 // parse error
@@ -6257,6 +6258,7 @@ int bam_parse_basemod(const bam1_t *b, hts_base_mod_state *state) {
                 state->strand   [mod_num] = (strand == '-');
                 state->canonical[mod_num] = btype;
                 state->MLstride [mod_num] = stride;
+                state->implicit [mod_num] = implicit;
 
                 state->MMcount  [mod_num] = delta;
                 if (b->core.flag & BAM_FREVERSE) {
@@ -6473,3 +6475,44 @@ int bam_mods_at_qpos(const bam1_t *b, int qpos, hts_base_mod_state *state,
 
     return r;
 }
+
+/*
+ * Returns the list of base modification codes provided for this
+ * alignment record as an array of character codes (+ve) or ChEBI numbers
+ * (negative).
+ *
+ * Returns the array, with *ntype filled out with the size.
+ *         The array returned should not be freed.
+ *         It is a valid pointer until the state is freed using
+ *         hts_base_mod_free().
+ */
+int *bam_mods_recorded(hts_base_mod_state *state, int *ntype) {
+    *ntype = state->nmods;
+    return state->type;
+}
+
+/*
+ * Returns data about a specific modification type for the alignment record.
+ * Code is either positive (eg 'm') or negative for ChEBI numbers.
+ *
+ * Return 0 on success or -1 if not found.  The strand, implicit and canonical
+ * fields are filled out if passed in as non-NULL pointers.
+ */
+int bam_mods_query_type(hts_base_mod_state *state, int code,
+                        int *strand, int *implicit, char *canonical) {
+    // Find code entry
+    int i;
+    for (i = 0; i < state->nmods; i++) {
+        if (state->type[i] == code)
+            break;
+    }
+    if (i == state->nmods)
+        return -1;
+
+    // Return data
+    if (strand)    *strand    = state->strand[i];
+    if (implicit)  *implicit  = state->implicit[i];
+    if (canonical) *canonical = "?AC?G???T??????N"[state->canonical[i]];
+
+    return 0;
+}

test/base_mods/MM-chebi.out

@@ -35,6 +35,7 @@
 34	C	C+m204 C+(76792)33 
 35	A	
 ---
+Present: m #-76792 n
 6	C	C+m102 
 15	N	N+n212 
 17	C	C+m128 

test/base_mods/MM-double.out

@@ -35,6 +35,7 @@
 34	A	
 35	T	
 ---
+Present: m m o
 1	G	G-m115 
 7	C	C+m128 
 12	G	G-m141 

test/base_mods/MM-explicit-x.out

@@ -0,0 +1,103 @@
+0	A	
+1	T	
+2	C	
+3	A	
+4	T	
+5	C	
+6	A	
+7	T	
+8	T	
+9	C	C+m.200 C+h.10 
+10	C	C+m.50 C+h.170 
+11	T	
+12	A	
+13	C	
+14	C	C+m.160 C+h.20 
+15	G	
+16	C	
+17	T	
+18	A	
+19	T	
+20	A	
+21	G	
+22	C	
+23	C	
+24	T	
+---
+Present: m h
+9	C	C+m200 C+h10 
+10	C	C+m50 C+h170 
+14	C	C+m160 C+h20 
+
+===
+
+0	A	
+1	T	
+2	C	
+3	A	
+4	T	
+5	C	
+6	A	
+7	T	
+8	T	
+9	C	C+m?200 C+h?10 
+10	C	C+m?50 C+h?170 
+11	T	
+12	A	
+13	C	C+m?10 C+h?5 
+14	C	C+m?160 C+h?20 
+15	G	
+16	C	C+m?10 C+h?5 
+17	T	
+18	A	
+19	T	
+20	A	
+21	G	
+22	C	
+23	C	
+24	T	
+---
+Present: m h
+9	C	C+m200 C+h10 
+10	C	C+m50 C+h170 
+13	C	C+m10 C+h5 
+14	C	C+m160 C+h20 
+16	C	C+m10 C+h5 
+
+===
+
+0	A	
+1	T	
+2	C	
+3	A	
+4	T	
+5	C	
+6	A	
+7	T	
+8	T	
+9	C	C+m.200 C+h?10 
+10	C	C+h?170 
+11	T	
+12	A	
+13	C	C+h?5 
+14	C	C+m.160 C+h?20 
+15	G	
+16	C	C+h?5 
+17	T	
+18	A	
+19	T	
+20	A	
+21	G	
+22	C	
+23	C	
+24	T	
+---
+Present: m h
+9	C	C+m200 C+h10 
+10	C	C+h170 
+13	C	C+h5 
+14	C	C+m160 C+h20 
+16	C	C+h5 
+
+===
+

test/base_mods/MM-explicit.out

@@ -24,6 +24,7 @@
 23	C	
 24	T	
 ---
+Present: m h
 9	C	C+m200 C+h10 
 10	C	C+m50 C+h170 
 14	C	C+m160 C+h20 
@@ -56,6 +57,7 @@
 23	C	
 24	T	
 ---
+Present: m h
 9	C	C+m200 C+h10 
 10	C	C+m50 C+h170 
 13	C	C+m10 C+h5 
@@ -90,6 +92,7 @@
 23	C	
 24	T	
 ---
+Present: m h
 9	C	C+m200 C+h10 
 10	C	C+h170 
 13	C	C+h5 

test/base_mods/MM-explicit.sam

@@ -4,10 +4,24 @@
 @CO	unchecked and require an explicit statement to indicate it was
 @CO	looked at and no base modification was observed.
 @CO	
-@CO	  0  1   23  45 6     78
-@CO	ATCATCATTCCTACCGCTATAGCCT
-@CO	  .  .   m.  .m .     ..  m
-@CO	  ?  ?   .h  .. .     ??  h
+@CO	ATCATCATTCCTACCGCTATAGCCT  r1; implicit
+@CO	  -  -   ..  -. -     --
+@CO	         Mm   M
+@CO	  -  -   ..  -. -     --
+@CO	         hH   h
+@CO	
+@CO	ATCATCATTCCTACCGCTATAGCCT  r2; explicit to a small region
+@CO	  -  -   ??  ?? ?     --
+@CO	         Mm  mM m
+@CO	  -  -   ??  ?? ?     --
+@CO	         hH  hh h
+@CO	
+@CO	ATCATCATTCCTACCGCTATAGCCT  r3; mixture
+@CO	  -  -   .   -. -     --
+@CO	         M    M
+@CO       -  -   ??  ?? ?     --
+@CO	         hH  hh h     --
+@CO	
 r1	0	*	0	0	*	*	0	0	ATCATCATTCCTACCGCTATAGCCT	*	Mm:Z:C+mh,2,0,1;	Ml:B:C,200,10,50,170,160,20
 r2	0	*	0	0	*	*	0	0	ATCATCATTCCTACCGCTATAGCCT	*	Mm:Z:C+mh?,2,0,0,0,0;	Ml:B:C,200,10,50,170,10,5,160,20,10,5
 r3	0	*	0	0	*	*	0	0	ATCATCATTCCTACCGCTATAGCCT	*	Mm:Z:C+m.,2,2;C+h?,2,0,0,0,0;	Ml:B:C,200,160,10,170,5,20,5

test/base_mods/MM-multi.out

@@ -35,6 +35,7 @@
 34	C	C+m230 C+h6 
 35	A	
 ---
+Present: m h n
 6	C	C+m128 
 15	N	N+n215 
 17	C	C+m153 
@@ -83,6 +84,7 @@
 34	C	C+m204 C+h31 
 35	A	
 ---
+Present: m h n
 6	C	C+m77 C+h159 
 15	N	N+n240 
 17	C	C+m103 C+h133 

test/base_mods/base-mods.tst

@@ -33,10 +33,11 @@
 # samtools binary. This can be useful for testing older versions.
 
 # Test files from SAM spec
-P MM-chebi.out     $test_mod MM-chebi.sam
-P MM-double.out    $test_mod MM-double.sam
-P MM-multi.out     $test_mod MM-multi.sam
-P MM-explicit.out  $test_mod MM-explicit.sam
+P MM-chebi.out       $test_mod    MM-chebi.sam
+P MM-double.out      $test_mod    MM-double.sam
+P MM-multi.out       $test_mod    MM-multi.sam
+P MM-explicit.out    $test_mod    MM-explicit.sam
+P MM-explicit-x.out  $test_mod -x MM-explicit.sam
 
 # Pileup testing
 P MM-pileup.out $pileup_mod < MM-pileup.sam