Slice

README.md

@@ -6,7 +6,6 @@
 - [x] Recursive descent (`$..`)
 - [x] Wildcard (`$.store.*`)
 - [x] Square-bracket field notation (`['foo']`, `$['"some" \'special\' [chars]']`)
-- [ ] Subscript (`books[:2]`)
 - [ ] Slice (`articles[1:10:2]`)
 - [ ] Union (`book[0, 1]`, `book[author, title, price]`)
 - [ ] Basic filtering (`book[?(@.price - 1)]`)

lib/src/selector/slice.dart

@@ -0,0 +1,46 @@
+import 'dart:math';
+
+import 'package:json_path/src/result.dart';
+import 'package:json_path/src/selector/selector.dart';
+
+class Slice extends Selector {
+  Slice({int first, this.last, int step})
+      : first = first ?? 0,
+        step = step ?? 1;
+
+  final int first;
+
+  final int last;
+
+  final int step;
+
+  @override
+  Iterable<Result> call(Iterable<Result> results) => results.map((r) {
+        if (step > 0 && r.value is List) {
+          return _filterList(r.value, r.path);
+        }
+        return const <Result>[];
+      }).expand((_) => _);
+
+  @override
+  String get expression =>
+      '[${first == 0 ? '' : first}:${last ?? ''}${step != 1 ? ':$step' : ''}]';
+
+  Iterable<Result> _filterList(List list, String path) =>
+      _for(_actualFirst(list.length), _actualLast(list.length), step)
+          .map((i) => Result(list[i], path + '[$i]'));
+
+  int _actualFirst(int len) => max(0, first < 0 ? (len + first) : first);
+
+  int _actualLast(int len) {
+    if (last == null) return len;
+    if (last < 0) return min(len, len + last);
+    return min(len, last);
+  }
+
+  Iterable<int> _for(int from, int to, int step) sync* {
+    for (var i = from; i < to; i += step) {
+      yield i;
+    }
+  }
+}

lib/src/state.dart

@@ -5,6 +5,7 @@ import 'package:json_path/src/selector/field.dart';
 import 'package:json_path/src/selector/index.dart';
 import 'package:json_path/src/selector/recursive.dart';
 import 'package:json_path/src/selector/selector.dart';
+import 'package:json_path/src/selector/slice.dart';
 
 /// AST parser state
 abstract class State {
@@ -26,7 +27,7 @@ class Ready implements State {
   State process(Node node) {
     switch (node.value) {
       case '[':
-        return Ready(selector.then(_bracketExpression(node.children)));
+        return Ready(selector.then(_bracketSelector(node.children)));
       case '.':
         return AwaitingField(selector);
       case '..':
@@ -38,15 +39,39 @@ class Ready implements State {
     }
   }
 
-  Selector _bracketExpression(List<Node> nodes) {
-    final node = nodes.single;
-    if (node.value == '*') return AllInArray();
-    if (node.isNumber) return Index(int.parse(nodes.first.value));
-    if (node.value.startsWith("'")) return Field(_unquote(node.value));
+  Selector _bracketSelector(List<Node> nodes) {
+    if (nodes.length == 1) {
+      final node = nodes.single;
+      if (node.value == '*') return AllInArray();
+      if (node.isNumber) return Index(int.parse(nodes.first.value));
+      if (node.value.startsWith("'")) {
+        return Field(node.value.substring(1, node.value.length - 1));
+      }
+    } else if (nodes.length > 1) {
+      int first;
+      int last;
+      int step;
+      var colons = 0;
+      nodes.map((_) => _.value).forEach((val) {
+        if (val == ':') {
+          colons++;
+          return;
+        }
+        if (colons == 0) {
+          first = int.parse(val);
+          return;
+        }
+        if (colons == 1) {
+          last = int.parse(val);
+          return;
+        }
+        step = int.parse(val);
+      });
+      return Slice(first: first, last: last, step: step);
+    }
+
     throw StateError('Unexpected bracket expression');
   }
-
-  String _unquote(String s) => s.substring(1, s.length - 1);
 }
 
 class AwaitingField implements State {

lib/src/tokenize.dart

@@ -46,12 +46,14 @@ List<String> tokenize(String expr) {
   return tokens;
 }
 
+
 const _singles = [
   r'$',
   '[',
   ']',
   '.',
   '*',
+  ':',
 ];
 
 const _doubles = [

pubspec.yaml

@@ -3,6 +3,7 @@ version: 0.0.0+dev.4
 description: JSONPath for Dart. JSONPath is XPath for JSON. It is a path in a JSON document.
 homepage: "https://github.com/f3ath/jessie"
 
+
 dev_dependencies:
   pedantic: ^1.9.0
   test: ^1.9.0

test/json_path_test.dart

@@ -36,11 +36,11 @@ void main() {
     });
 
     test('Mixed brackets and fields', () {
-      final store = JsonPath(r"$['store'].bicycle['price']");
-      expect(store.toString(), r"$['store']['bicycle']['price']");
+      final price = JsonPath(r"$['store'].bicycle['price']");
+      expect(price.toString(), r"$['store']['bicycle']['price']");
       expect(
-          store.select(json).single.value, json['store']['bicycle']['price']);
-      expect(store.select(json).single.path, r"$['store']['bicycle']['price']");
+          price.select(json).single.value, json['store']['bicycle']['price']);
+      expect(price.select(json).single.path, r"$['store']['bicycle']['price']");
     });
   });
 
@@ -51,6 +51,122 @@ void main() {
     });
   });
 
+  group('Slices', () {
+    final abc = 'abcdefg'.split('');
+    test('1:3', () {
+      final slice = JsonPath(r'$[1:3]');
+      expect(slice.toString(), r'$[1:3]');
+      expect(slice.select(abc).length, 2);
+      expect(slice.select(abc).first.value, 'b');
+      expect(slice.select(abc).first.path, r'$[1]');
+      expect(slice.select(abc).last.value, 'c');
+      expect(slice.select(abc).last.path, r'$[2]');
+    });
+    test('1:5:2', () {
+      final slice = JsonPath(r'$[1:5:2]');
+      expect(slice.toString(), r'$[1:5:2]');
+      expect(slice.select(abc).length, 2);
+      expect(slice.select(abc).first.value, 'b');
+      expect(slice.select(abc).first.path, r'$[1]');
+      expect(slice.select(abc).last.value, 'd');
+      expect(slice.select(abc).last.path, r'$[3]');
+    });
+    test('1:5:-2', () {
+      final slice = JsonPath(r'$[1:5:-2]');
+      expect(slice.toString(), r'$[1:5:-2]');
+      expect(slice.select(abc).length, 0);
+    });
+    test(':3', () {
+      final slice = JsonPath(r'$[:3]');
+      expect(slice.toString(), r'$[:3]');
+      expect(slice.select(abc).length, 3);
+      expect(slice.select(abc).first.value, 'a');
+      expect(slice.select(abc).first.path, r'$[0]');
+      expect(slice.select(abc).last.value, 'c');
+      expect(slice.select(abc).last.path, r'$[2]');
+    });
+    test(':3:2', () {
+      final slice = JsonPath(r'$[:3:2]');
+      expect(slice.toString(), r'$[:3:2]');
+      expect(slice.select(abc).length, 2);
+      expect(slice.select(abc).first.value, 'a');
+      expect(slice.select(abc).first.path, r'$[0]');
+      expect(slice.select(abc).last.value, 'c');
+      expect(slice.select(abc).last.path, r'$[2]');
+    });
+    test('3::2', () {
+      final slice = JsonPath(r'$[3::2]');
+      expect(slice.toString(), r'$[3::2]');
+      expect(slice.select(abc).length, 2);
+      expect(slice.select(abc).first.value, 'd');
+      expect(slice.select(abc).first.path, r'$[3]');
+      expect(slice.select(abc).last.value, 'f');
+      expect(slice.select(abc).last.path, r'$[5]');
+    });
+    test('100:', () {
+      final slice = JsonPath(r'$[100:]');
+      expect(slice.toString(), r'$[100:]');
+      expect(slice.select(abc).length, 0);
+    });
+    test('3:', () {
+      final slice = JsonPath(r'$[3:]');
+      expect(slice.toString(), r'$[3:]');
+      expect(slice.select(abc).length, 4);
+      expect(slice.select(abc).first.value, 'd');
+      expect(slice.select(abc).first.path, r'$[3]');
+      expect(slice.select(abc).last.value, 'g');
+      expect(slice.select(abc).last.path, r'$[6]');
+    });
+    test(':-5', () {
+      final slice = JsonPath(r'$[:-5]');
+      expect(slice.toString(), r'$[:-5]');
+      expect(slice.select(abc).length, 2);
+      expect(slice.select(abc).first.value, 'a');
+      expect(slice.select(abc).first.path, r'$[0]');
+      expect(slice.select(abc).last.value, 'b');
+      expect(slice.select(abc).last.path, r'$[1]');
+    });
+
+    test('-5:', () {
+      final slice = JsonPath(r'$[-5:]');
+      expect(slice.toString(), r'$[-5:]');
+      expect(slice.select(abc).length, 5);
+      expect(slice.select(abc).first.value, 'c');
+      expect(slice.select(abc).first.path, r'$[2]');
+      expect(slice.select(abc).last.value, 'g');
+      expect(slice.select(abc).last.path, r'$[6]');
+    });
+    test('0:6', () {
+      final slice = JsonPath(r'$[0:6]');
+      expect(slice.toString(), r'$[:6]');
+      expect(slice.select(abc).length, 6);
+      expect(slice.select(abc).first.value, 'a');
+      expect(slice.select(abc).first.path, r'$[0]');
+      expect(slice.select(abc).last.value, 'f');
+      expect(slice.select(abc).last.path, r'$[5]');
+    });
+    test('0:100', () {
+      final slice = JsonPath(r'$[0:100]');
+      expect(slice.toString(), r'$[:100]');
+      expect(slice.select(abc).length, 7);
+      expect(slice.select(abc).first.value, 'a');
+      expect(slice.select(abc).first.path, r'$[0]');
+      expect(slice.select(abc).last.value, 'g');
+      expect(slice.select(abc).last.path, r'$[6]');
+    });
+
+    test('-6:-1', () {
+      final slice = JsonPath(r'$[-6:-1]');
+      expect(slice.toString(), r'$[-6:-1]');
+      expect(slice.select(abc).length, 5);
+      expect(slice.select(abc).first.value, 'b');
+      expect(slice.select(abc).first.path, r'$[1]');
+      expect(slice.select(abc).last.value, 'f');
+      expect(slice.select(abc).last.path, r'$[5]');
+    });
+
+  });
+
   group('Uncommon brackets', () {
     test('Escape single quote', () {
       final j = {r"sq'sq s\s qs\'qs": 'value'};