Make InferString accept any valid JSON value

Author: bombsimon

inferrer.go

@@ -2,6 +2,7 @@ package jtdinfer
 
 import (
 	"encoding/json"
+	"strconv"
 )
 
 // Inferrer represents the `InferredSchema` with its state combined with the
@@ -32,27 +33,63 @@ func (i *Inferrer) IntoSchema() Schema {
 	return i.Inference.IntoSchema(i.Hints)
 }
 
-// InferStrings accepts a slice of strings and will convert them to either a
-// `map[string]any` or []any` and run inference on all the rows. If any of the
-// rows are not valid JSON object or list, the inference up to that point is
-// returned.
-//
-// If you need to infer simple values like strings or integers they can be
-// passed directly to `Infer`.
+// InferStrings accepts a slice of strings and will try to JSON unmarshal each
+// row to the type that the first row looks like. If an error occurs the
+// inferrer will return with the state it had when the error occurred.
+// If you already have the type of your data such as a slice of numbers or a map
+// of strings you can pass them directly to `Infer`. This is just a convenience
+// method if all you got is strings.
 func InferStrings(rows []string, hints *Hints) *Inferrer {
 	inferrer := NewInferrer(hints)
+	if len(rows) == 0 {
+		return inferrer
+	}
+
+	var (
+		firstRow   = rows[0]
+		getToInfer func() any
+	)
+
+	switch {
+	case isBool(firstRow):
+		getToInfer = func() any { return false }
+	case isObject(firstRow):
+		getToInfer = func() any { return make(map[string]any) }
+	case isArray(firstRow):
+		getToInfer = func() any { return make([]any, 0) }
+	case isNumber(firstRow):
+		getToInfer = func() any { return 0.0 }
+	default:
+		getToInfer = func() any { return "" }
+	}
 
 	for _, row := range rows {
-		var toInfer any = make(map[string]any, 0)
+		toInfer := getToInfer()
 		if err := json.Unmarshal([]byte(row), &toInfer); err != nil {
-			toInfer = make([]any, 0)
-			if err := json.Unmarshal([]byte(row), &toInfer); err != nil {
-				return inferrer
-			}
+			return inferrer
 		}
 
 		inferrer = inferrer.Infer(toInfer)
 	}
 
 	return inferrer
 }
+
+func isBool(value string) bool {
+	return value == "true" || value == "false"
+}
+
+func isObject(value string) bool {
+	var m map[string]any
+	return json.Unmarshal([]byte(value), &m) == nil
+}
+
+func isArray(value string) bool {
+	var a []any
+	return json.Unmarshal([]byte(value), &a) == nil
+}
+
+func isNumber(value string) bool {
+	_, err := strconv.ParseFloat(value, 64)
+	return err == nil
+}

inferrer_test.go

@@ -1,13 +1,137 @@
 package jtdinfer
 
 import (
+	"fmt"
+	"math"
+	"strconv"
 	"testing"
+	"time"
 
 	jtd "github.com/jsontypedef/json-typedef-go"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
+func TestInferString(t *testing.T) {
+	cases := []struct {
+		description    string
+		values         []string
+		expectedSchema Schema
+	}{
+		{
+			description: "boolean true value",
+			values:      []string{"true"},
+			expectedSchema: Schema{
+				Type: jtd.TypeBoolean,
+			},
+		},
+		{
+			description: "boolean false value",
+			values:      []string{"false"},
+			expectedSchema: Schema{
+				Type: jtd.TypeBoolean,
+			},
+		},
+		{
+			description: "object",
+			values:      []string{`{"name":"Joe"}`},
+			expectedSchema: Schema{
+				Properties: map[string]Schema{
+					"name": {
+						Type: jtd.TypeString,
+					},
+				},
+			},
+		},
+		{
+			description: "array",
+			values:      []string{`[1, 2, 3]`},
+			expectedSchema: Schema{
+				Elements: &Schema{
+					Type: jtd.TypeUint8,
+				},
+			},
+		},
+		{
+			description: "unsigned integer",
+			values:      []string{"1"},
+			expectedSchema: Schema{
+				Type: jtd.TypeUint8,
+			},
+		},
+		{
+			description: "signed integer",
+			values:      []string{"-1"},
+			expectedSchema: Schema{
+				Type: jtd.TypeInt8,
+			},
+		},
+		{
+			description: "signed max integer",
+			values:      []string{strconv.Itoa(math.MinInt32)},
+			expectedSchema: Schema{
+				Type: jtd.TypeInt32,
+			},
+		},
+		{
+			description: "float without fraction",
+			values:      []string{"1.0"},
+			expectedSchema: Schema{
+				Type: jtd.TypeUint8,
+			},
+		},
+		{
+			description: "positive float",
+			values:      []string{"1.1"},
+			expectedSchema: Schema{
+				Type: jtd.TypeFloat64,
+			},
+		},
+		{
+			description: "negative float",
+			values:      []string{"-1.1"},
+			expectedSchema: Schema{
+				Type: jtd.TypeFloat64,
+			},
+		},
+		{
+			description: "string",
+			values:      []string{`"string"`},
+			expectedSchema: Schema{
+				Type: jtd.TypeString,
+			},
+		},
+		{
+			description: "number in string is still string",
+			values:      []string{`"2.2"`},
+			expectedSchema: Schema{
+				Type: jtd.TypeString,
+			},
+		},
+		{
+			description: "timestamp",
+			values:      []string{fmt.Sprintf(`"%s"`, time.Now().Format(time.RFC3339))},
+			expectedSchema: Schema{
+				Type: jtd.TypeTimestamp,
+			},
+		},
+		{
+			description: "null",
+			values:      []string{"null"},
+			expectedSchema: Schema{
+				Nullable: true,
+			},
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.description, func(t *testing.T) {
+			gotSchema := InferStrings(tc.values, NewHints()).IntoSchema()
+			assert.EqualValues(t, tc.expectedSchema, gotSchema)
+		})
+	}
+}
+
 func TestJTDInfer(t *testing.T) {
 	rows := []string{
 		`{"name": "Joe", "age": 42, "hobbies": ["code", "animals"]}`,