From 62cb08c3dce9d2579c70dcad157c6634f471f29e Mon Sep 17 00:00:00 2001
From: Keith Burzinski <kbx81x@gmail.com>
Date: Fri, 9 Jan 2026 04:05:47 -0600
Subject: [PATCH] [api] Add methods supporting efficient packed repeated sint32
 field encoding for #12985 (#13094)

---
 esphome/components/api/proto.h | 63 +++++++++++++++++++++++++++++++---
 1 file changed, 58 insertions(+), 5 deletions(-)

diff --git a/esphome/components/api/proto.h b/esphome/components/api/proto.h
index 2d93adbb47..a336a9493d 100644
--- a/esphome/components/api/proto.h
+++ b/esphome/components/api/proto.h
@@ -39,6 +39,24 @@ inline constexpr int64_t decode_zigzag64(uint64_t value) {
   return (value & 1) ? static_cast<int64_t>(~(value >> 1)) : static_cast<int64_t>(value >> 1);
 }
 
+/// Count number of varints in a packed buffer
+inline uint16_t count_packed_varints(const uint8_t *data, size_t len) {
+  uint16_t count = 0;
+  while (len > 0) {
+    // Skip varint bytes until we find one without continuation bit
+    while (len > 0 && (*data & 0x80)) {
+      data++;
+      len--;
+    }
+    if (len > 0) {
+      data++;
+      len--;
+      count++;
+    }
+  }
+  return count;
+}
+
 /*
  * StringRef Ownership Model for API Protocol Messages
  * ===================================================
@@ -180,9 +198,10 @@ class ProtoVarInt {
   uint64_t value_;
 };
 
-// Forward declaration for decode_to_message and encode_to_writer
-class ProtoMessage;
+// Forward declarations for decode_to_message, encode_message and encode_packed_sint32
 class ProtoDecodableMessage;
+class ProtoMessage;
+class ProtoSize;
 
 class ProtoLengthDelimited {
  public:
@@ -334,6 +353,8 @@ class ProtoWriteBuffer {
   void encode_sint64(uint32_t field_id, int64_t value, bool force = false) {
     this->encode_uint64(field_id, encode_zigzag64(value), force);
   }
+  /// Encode a packed repeated sint32 field (zero-copy from vector)
+  void encode_packed_sint32(uint32_t field_id, const std::vector<int32_t> &values);
   void encode_message(uint32_t field_id, const ProtoMessage &value);
   std::vector<uint8_t> *get_buffer() const { return buffer_; }
 
@@ -341,9 +362,6 @@ class ProtoWriteBuffer {
   std::vector<uint8_t> *buffer_;
 };
 
-// Forward declaration
-class ProtoSize;
-
 class ProtoMessage {
  public:
   virtual ~ProtoMessage() = default;
@@ -792,8 +810,43 @@ class ProtoSize {
       }
     }
   }
+
+  /**
+   * @brief Calculate size of a packed repeated sint32 field
+   */
+  inline void add_packed_sint32(uint32_t field_id_size, const std::vector<int32_t> &values) {
+    if (values.empty())
+      return;
+
+    size_t packed_size = 0;
+    for (int value : values) {
+      packed_size += varint(encode_zigzag32(value));
+    }
+
+    // field_id + length varint + packed data
+    total_size_ += field_id_size + varint(static_cast<uint32_t>(packed_size)) + static_cast<uint32_t>(packed_size);
+  }
 };
 
+// Implementation of encode_packed_sint32 - must be after ProtoSize is defined
+inline void ProtoWriteBuffer::encode_packed_sint32(uint32_t field_id, const std::vector<int32_t> &values) {
+  if (values.empty())
+    return;
+
+  // Calculate packed size
+  size_t packed_size = 0;
+  for (int value : values) {
+    packed_size += ProtoSize::varint(encode_zigzag32(value));
+  }
+
+  // Write tag (LENGTH_DELIMITED) + length + all zigzag-encoded values
+  this->encode_field_raw(field_id, WIRE_TYPE_LENGTH_DELIMITED);
+  this->encode_varint_raw(packed_size);
+  for (int value : values) {
+    this->encode_varint_raw(encode_zigzag32(value));
+  }
+}
+
 // Implementation of encode_message - must be after ProtoMessage is defined
 inline void ProtoWriteBuffer::encode_message(uint32_t field_id, const ProtoMessage &value) {
   this->encode_field_raw(field_id, 2);  // type 2: Length-delimited message