Track HID report offsets per report ID per USB spec

Per USB HID spec section 6.2.2.7, each report ID defines an independent
report structure with its own bit offset tracking. Previously, offsets
were reset when encountering a new report ID or at collection boundaries,
causing incorrect parsing of descriptors with multiple reports.

Changes:
- Add report_offset_map_t to map report IDs to their offsets
- Track offsets separately for each report ID in parser state
- Remove incorrect offset resets on report ID change and collection end
- Add helper functions for offset lookup and creation

Local items still reset after Main items and Global items persist,
matching spec requirements.

Author: rygwdn

src/hid_parser.c

@@ -33,16 +33,39 @@ uint32_t get_descriptor_value(uint8_t const *report, int size) {
     }
 }
 
+uint32_t *get_or_create_report_offset(parser_state_t *parser, uint8_t report_id) {
+    for (int i = 0; i < parser->num_report_offsets; i++) {
+        if (parser->report_offsets[i].report_id == report_id) {
+            return &parser->report_offsets[i].offset_in_bits;
+        }
+    }
+
+    if (parser->num_report_offsets < MAX_REPORTS) {
+        parser->report_offsets[parser->num_report_offsets].report_id = report_id;
+        parser->report_offsets[parser->num_report_offsets].offset_in_bits = 0;
+        return &parser->report_offsets[parser->num_report_offsets++].offset_in_bits;
+    }
+
+    return NULL;
+}
+
+uint32_t get_current_offset(parser_state_t *parser) {
+    uint32_t *offset = get_or_create_report_offset(parser, parser->report_id);
+    return offset ? *offset : 0;
+}
+
 void update_usage(parser_state_t *parser, int i) {
     /* If we don't have as many usages as elements, the usage for the previous element applies */
     if (i > 0 && i >= parser->usage_count && i < HID_MAX_USAGES)
         *(parser->p_usage + i) = *(parser->p_usage + i - 1);
 }
 
 void store_element(parser_state_t *parser, report_val_t *val, int i, uint32_t data, uint16_t size, hid_interface_t *iface) {
+    uint32_t current_offset = get_current_offset(parser);
+
     *val = (report_val_t){
-        .offset     = parser->offset_in_bits,
-        .offset_idx = parser->offset_in_bits >> 3,
+        .offset     = current_offset,
+        .offset_idx = current_offset >> 3,
         .size       = size,
 
         .usage_max = parser->locals[RI_LOCAL_USAGE_MAX].val,
@@ -62,8 +85,6 @@ void store_element(parser_state_t *parser, report_val_t *val, int i, uint32_t da
 
 void handle_global_item(parser_state_t *parser, item_t *item) {
     if (item->hdr.tag == RI_GLOBAL_REPORT_ID) {
-        /* Reset offset for a new page */
-        parser->offset_in_bits = 0;
         parser->report_id = item->val;
     }
 
@@ -98,6 +119,10 @@ void handle_main_input(parser_state_t *parser, item_t *item, hid_interface_t *if
         count = 1;
     }
 
+    uint32_t *current_offset = get_or_create_report_offset(parser, parser->report_id);
+    if (!current_offset)
+        return;
+
     for (int i = 0; i < count; i++) {
         update_usage(parser, i);
         store_element(parser, &val, i, item->val, size, iface);
@@ -106,7 +131,7 @@ void handle_main_input(parser_state_t *parser, item_t *item, hid_interface_t *if
         extract_data(iface, &val);
 
         /* Iterate <count> times and increase offset by <size> amount, moving by <count> x <size> bits */
-        parser->offset_in_bits += size;
+        *current_offset += size;
     }
 
     /* Advance the usage array pointer by global report count and reset the count variable */
@@ -117,9 +142,6 @@ void handle_main_input(parser_state_t *parser, item_t *item, hid_interface_t *if
 }
 
 void handle_main_item(parser_state_t *parser, item_t *item, hid_interface_t *iface) {
-    if (IS_BLOCK_END)
-        parser->offset_in_bits = 0;
-
     switch (item->hdr.tag) {
         case RI_MAIN_COLLECTION:
             parser->collection.start++;

src/include/hid_parser.h

@@ -38,6 +38,12 @@ typedef struct {
     uint8_t end;
 } collection_t;
 
+/* Maps a report ID to its current bit offset */
+typedef struct {
+    uint8_t report_id;
+    uint32_t offset_in_bits;
+} report_offset_map_t;
+
 /* Header byte is unpacked to size/type/tag using this struct */
 typedef struct TU_ATTR_PACKED {
     uint8_t size : 2;
@@ -149,13 +155,15 @@ typedef struct {
     int report_id; /* Report ID of the current section we're parsing */
 
     uint32_t usage_count;
-    uint32_t offset_in_bits;
     uint16_t usages[HID_MAX_USAGES];
     uint16_t *p_usage;
     uint16_t global_usage;
 
     collection_t collection;
 
+    report_offset_map_t report_offsets[MAX_REPORTS];
+    uint8_t num_report_offsets;
+
     /* as tag is 4 bits, there can be 16 different tags in global header type */
     item_t globals[16];