From 9f6a85cff7113989394255519ef1745f15b0d872 Mon Sep 17 00:00:00 2001
From: Devin Gunay <devingunay@gmail.com>
Date: Thu, 27 Oct 2022 11:00:44 -0700
Subject: [PATCH] add partial ProcessBitMap example

---
 go/examples/processbitmap/process_bitmap.go | 105 ++++++++++++++++++++
 go/go.mod                                   |   1 +
 go/go.sum                                   |   2 +
 3 files changed, 108 insertions(+)
 create mode 100644 go/examples/processbitmap/process_bitmap.go

diff --git a/go/examples/processbitmap/process_bitmap.go b/go/examples/processbitmap/process_bitmap.go
new file mode 100644
index 0000000..7a6745f
--- /dev/null
+++ b/go/examples/processbitmap/process_bitmap.go
@@ -0,0 +1,105 @@
+package changeeventheader
+
+import (
+	"context"
+	"encoding/hex"
+	"fmt"
+	"strings"
+
+	"github.com/boljen/go-bitmap"
+)
+
+var ErrUnexpectedType = fmt.Errorf("unexpected type")
+
+// ProcessBitMap takes the bitmap-encoded list of changed fields and returns a list of field names.
+// See Salesforce pub-sub docs for more details:
+// https://developer.salesforce.com/docs/platform/pub-sub-api/guide/event-deserialization-considerations.html
+func ProcessBitMap(ctx context.Context, avroSchema map[string]any, bitmapFields []string) ([]string, error) {
+	changedFieldNames := []string{}
+	if len(bitmapFields) == 0 {
+		return changedFieldNames, nil
+	}
+
+	// Replace top field level bitmap with list of fields
+	if strings.HasPrefix(bitmapFields[0], "0x") {
+		// Convert hex to bytes
+		hexStr := bitmapFields[0][2:]
+		bytes, err := hex.DecodeString(hexStr)
+		if err != nil {
+			return nil, fmt.Errorf("decode hex string '%s': %w", hexStr, err)
+		}
+
+		// Reverse to little-endian
+		reversedBytes := []byte{}
+		for i := len(bytes) - 1; i >= 0; i-- {
+			reversedBytes = append(reversedBytes, bytes[i])
+		}
+
+		bitMap := bitmap.Bitmap(reversedBytes)
+
+		schemaFieldNames, err := getSchemaFieldNames(avroSchema)
+		if err != nil {
+			return nil, fmt.Errorf("get schema field names: %w", err)
+		}
+
+		changedFieldNames = append(
+			changedFieldNames,
+			getFieldNamesFromBitString(bitMap, schemaFieldNames)...,
+		)
+		bitmapFields = bitmapFields[1:] // shift off the front
+	}
+
+	// There can be other bitmaps present in the message of the form:
+	// parentPos-childBitMap
+	// If we end up needing that, we can implement it here.
+	// Check the example repository for Python or Java examples (no Go examples exist yet).
+
+	return changedFieldNames, nil
+}
+
+func getSchemaFieldNames(schema map[string]any) ([]string, error) {
+	fields := []string{}
+	fieldsSlice, ok := schema["fields"].([]any)
+	if !ok {
+		return nil, ErrCouldNotConvertType(schema["fields"], []any{})
+	}
+
+	for _, fieldObj := range fieldsSlice {
+		field, ok := fieldObj.(map[string]any)
+		if !ok {
+			return nil, ErrCouldNotConvertType(fieldObj, map[string]any{})
+		}
+
+		asString, ok := field["name"].(string)
+		if !ok {
+			return nil, ErrCouldNotConvertType(field["name"], "")
+		}
+		fields = append(fields, asString)
+	}
+	return fields, nil
+}
+
+func ErrCouldNotConvertType(from any, to any) error {
+	return fmt.Errorf("could not convert %T to type %T: %w", from, to, ErrUnexpectedType)
+}
+
+func getFieldNamesFromBitString(
+	bitMap bitmap.Bitmap,
+	// A list of all of the schema field names
+	schemaFieldNames []string,
+) []string {
+	// Find indices of "1" bits
+	oneIndices := []int{}
+	for i := 0; i < bitMap.Len(); i++ {
+		if bitMap.Get(i) {
+			oneIndices = append(oneIndices, i)
+		}
+	}
+
+	// And then pick the schema field names with those indices
+	changedFieldNames := []string{}
+	for _, index := range oneIndices {
+		changedFieldNames = append(changedFieldNames, schemaFieldNames[index])
+	}
+	return changedFieldNames
+}
diff --git a/go/go.mod b/go/go.mod
index 485001b..46fa7b4 100644
--- a/go/go.mod
+++ b/go/go.mod
@@ -3,6 +3,7 @@ module github.com/developerforce/pub-sub-api/go
 go 1.18
 
 require (
+	github.com/boljen/go-bitmap v0.0.0-20151001105940-23cd2fb0ce7d
 	github.com/linkedin/goavro/v2 v2.11.0
 	google.golang.org/grpc v1.37.0
 	google.golang.org/protobuf v1.26.0
diff --git a/go/go.sum b/go/go.sum
index 6038168..2f0cdc0 100644
--- a/go/go.sum
+++ b/go/go.sum
@@ -1,5 +1,7 @@
 cloud.google.com/go v0.26.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw=
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
+github.com/boljen/go-bitmap v0.0.0-20151001105940-23cd2fb0ce7d h1:zsO4lp+bjv5XvPTF58Vq+qgmZEYZttJK+CWtSZhKenI=
+github.com/boljen/go-bitmap v0.0.0-20151001105940-23cd2fb0ce7d/go.mod h1:f1iKL6ZhUWvbk7PdWVmOaak10o86cqMUYEmn1CZNGEI=
 github.com/census-instrumentation/opencensus-proto v0.2.1/go.mod h1:f6KPmirojxKA12rnyqOA5BBL4O983OfeGPqjHWSTneU=
 github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDkc90ppPyw=
 github.com/cncf/udpa/go v0.0.0-20201120205902-5459f2c99403/go.mod h1:WmhPx2Nbnhtbo57+VJT5O0JRkEi1Wbu0z5j0R8u5Hbk=