feat(service): add list skip / CEL filters, test db (#60)

To provide an illustrative example of CEL's usage as a filter language,
implement it, along with filtering and sending data along to a functional database
(in this case, sqlite).

A small example cel2sql parser was written to illustrate the ability to use
CEL as a query language. However, this will be replaced by some cel -> sql parser,
hopefully contributed as a more general library and dependency.

Example:

```
curl $'http://localhost:8081/publishers?filter=description.startsWith(\'tomorrow\')'
{"results":[{"description":"tomorrow they will write again","path":"publishers/foo"}],"nextPageToken":""}
```

Fixes #59

example/bookstore/v1/bookstore.proto

@@ -531,6 +531,12 @@ message ListPublishersRequest {
 
   // The maximum number of resources to return in a single page.
   int32 max_page_size = 10017;
+
+  // The number of resources to skip before returning the first resource in the page.
+  int32 skip = 10021;
+
+  // The filter to apply to the list.
+  string filter = 10022;
 }
 
 // Response message for the Listpublisher method

example/bookstore/v1/bookstore.swagger.json

@@ -152,6 +152,21 @@
             "required": false,
             "type": "integer",
             "format": "int32"
+          },
+          {
+            "name": "skip",
+            "description": "The number of resources to skip before returning the first resource in the page.",
+            "in": "query",
+            "required": false,
+            "type": "integer",
+            "format": "int32"
+          },
+          {
+            "name": "filter",
+            "description": "The filter to apply to the list.",
+            "in": "query",
+            "required": false,
+            "type": "string"
           }
         ],
         "tags": [

example/bookstore/v1/bookstore.yaml

@@ -14,7 +14,9 @@ resources:
       read: {}
       update: {}
       delete: {}
-      list: {}
+      list:
+        supports_filter: true
+        supports_skip: true
       apply: {}
   # example of a child resource
   - kind: "book"

example/bookstore/v1/bookstore_openapi.json

@@ -125,6 +125,20 @@
             "schema": {
               "type": "string"
             }
+          },
+          {
+            "name": "skip",
+            "in": "query",
+            "schema": {
+              "type": "integer"
+            }
+          },
+          {
+            "name": "filter",
+            "in": "query",
+            "schema": {
+              "type": "string"
+            }
           }
         ],
         "responses": {

example/bookstore/v1/bookstore_openapi.yaml

@@ -174,6 +174,14 @@ paths:
         name: page_token
         schema:
           type: string
+      - in: query
+        name: skip
+        schema:
+          type: integer
+      - in: query
+        name: filter
+        schema:
+          type: string
       responses:
         "200":
           content:

example/service/cel.go

@@ -0,0 +1,29 @@
+package service
+
+import (
+	"github.com/aep-dev/aepc/pkg/cel2ansisql"
+	"github.com/google/cel-go/cel"
+)
+
+func convertCELToSQL(expr string) (string, error) {
+	if expr == "" {
+		return "", nil
+	}
+	env, err := cel.NewEnv(
+		cel.Variable("path", cel.StringType),
+		cel.Variable("description", cel.StringType),
+	)
+	if err != nil {
+		return "", err
+	}
+	ast, iss := env.Compile(expr)
+	if iss.Err() != nil {
+		return "", iss.Err()
+	}
+
+	sql, err := cel2ansisql.ConvertToSQL(ast)
+	if err != nil {
+		return "", err
+	}
+	return sql, nil
+}

example/service/cel_test.go

@@ -0,0 +1,36 @@
+package service
+
+import (
+	"testing"
+)
+
+func TestCELToSQL(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected string
+	}{
+		{
+			name:     "simple expression",
+			input:    "description.startsWith('tomorrow')",
+			expected: "description LIKE CONCAT('tomorrow', '%')",
+		},
+		{
+			name:     "empty",
+			input:    "",
+			expected: "",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := convertCELToSQL(tt.input)
+			if err != nil {
+				t.Errorf("convertCELToSQL() = %v, want %v", err, tt.expected)
+			}
+			if got != tt.expected {
+				t.Errorf("convertCELToSQL() = %v, want %v", got, tt.expected)
+			}
+		})
+	}
+}