feat(num): implement number string decode

dec_num.go

@@ -16,22 +16,40 @@ func (d *Decoder) NumAppend(v Num) (Num, error) {
 
 // num decodes number.
 func (d *Decoder) num(v Num, forceAppend bool) (Num, error) {
+	var str bool
 	switch d.Next() {
 	case String:
-		// Consume start of the string.
-		d.head++
+		str = true
 	case Number: // float or integer
 	default:
 		return v, errors.Errorf("unexpected %s", d.Next())
 	}
 	if d.reader == nil && !forceAppend {
 		// Can use underlying buffer directly.
-		v = d.number()
+		start := d.head
+		d.head++
+		d.number()
+		if str {
+			if err := d.consume('"'); err != nil {
+				return nil, errors.Wrap(err, "end of string")
+			}
+		}
+		v = d.buf[start:d.head]
 	} else {
-		buf, err := d.numberAppend(v[:0])
+		if str {
+			d.head++ // '"'
+			v = append(v, '"')
+		}
+		buf, err := d.numberAppend(v)
 		if err != nil {
 			return v, errors.Wrap(err, "decode")
 		}
+		if str {
+			if err := d.consume('"'); err != nil {
+				return nil, errors.Wrap(err, "end of string")
+			}
+			buf = append(buf, '"')
+		}
 		v = buf
 	}
 
@@ -47,6 +65,9 @@ func (d *Decoder) num(v Num, forceAppend bool) (Num, error) {
 	}
 
 	// TODO(ernado): Additional validity checks
+	// Current invariants:
+	// 1) Zero or one dot
+	// 2) Only: +, -, ., e, E, 0-9
 
 	return v, nil
 }

dec_num_test.go

@@ -0,0 +1,43 @@
+package jx
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestDecoder_Num(t *testing.T) {
+	t.Run("Positive", func(t *testing.T) {
+		for _, s := range []string{
+			`100`,
+			`100.0`,
+			`-100.0`,
+			`-100`,
+			`"-100"`,
+			`"-100.0"`,
+		} {
+			v, err := DecodeStr(s).Num()
+			require.NoError(t, err)
+			require.Equal(t, s, v.String())
+
+			v, err = DecodeStr(s).NumAppend(nil)
+			require.NoError(t, err)
+			require.Equal(t, s, v.String())
+		}
+	})
+	t.Run("Negative", func(t *testing.T) {
+		for _, s := range []string{
+			`1.00.0`,
+			`"-100`,
+			`"-100.0.0"`,
+			"false",
+			`"false"`,
+		} {
+			_, err := DecodeStr(s).Num()
+			require.Error(t, err, s)
+
+			_, err = DecodeStr(s).NumAppend(nil)
+			require.Error(t, err, s)
+		}
+	})
+}

num.go

@@ -141,7 +141,7 @@ func (n Num) Zero() bool {
 	}
 	for _, c := range n {
 		switch c {
-		case '.', '0':
+		case '.', '0', '-':
 			continue
 		default:
 			return false

num_test.go

@@ -8,9 +8,16 @@ import (
 )
 
 func TestEncoder_Num(t *testing.T) {
-	var e Encoder
-	e.Num(Num{'1', '2', '3'})
-	require.Equal(t, e.String(), "123")
+	t.Run("Valid", func(t *testing.T) {
+		var e Encoder
+		e.Num(Num{'1', '2', '3'})
+		require.Equal(t, e.String(), "123")
+	})
+	t.Run("Invalid", func(t *testing.T) {
+		var e Encoder
+		e.Num(Num{})
+		require.Equal(t, e.String(), "null")
+	})
 }
 
 func TestNum(t *testing.T) {
@@ -48,6 +55,8 @@ func TestNum(t *testing.T) {
 		assert.True(t, v.Equal(v))
 		assert.True(t, v.IsInt())
 		assert.False(t, v.Equal(Num{}))
+
+		assert.Equal(t, 0, Num{'"'}.Sign())
 	})
 	t.Run("ZeroValue", func(t *testing.T) {
 		// Zero value is invalid because there is no Num.Value.
@@ -59,6 +68,24 @@ func TestNum(t *testing.T) {
 		require.False(t, v.Str())
 		require.Equal(t, "<invalid>", v.String())
 	})
+	t.Run("IntZero", func(t *testing.T) {
+		v := Num{'0'}
+		require.True(t, v.Zero())
+		require.False(t, v.Positive())
+		require.False(t, v.Negative())
+		require.True(t, v.IsInt())
+		require.False(t, v.Str())
+		require.Equal(t, "0", v.String())
+	})
+	t.Run("FloatZero", func(t *testing.T) {
+		v := Num{'-', '0', '.', '0'}
+		require.True(t, v.Zero())
+		require.False(t, v.Positive())
+		require.True(t, v.Negative())
+		require.False(t, v.IsInt())
+		require.False(t, v.Str())
+		require.Equal(t, "-0.0", v.String())
+	})
 	t.Run("Integer", func(t *testing.T) {
 		t.Run("Int", func(t *testing.T) {
 			v := Num{'1', '2', '3'}