From c4f30559d331f28e01de4202ffa141bfd1c87d15 Mon Sep 17 00:00:00 2001
From: mockturtl <mockturtl@gmail.com>
Date: Sat, 9 May 2015 20:03:34 -0400
Subject: [PATCH] wip subs

---
 CHANGELOG.md          |  2 +-
 README.md             |  2 +-
 lib/src/parser.dart   | 19 ++++++++++++++-----
 test/parser_test.dart | 25 +++++++++++++++++++++++++
 4 files changed, 41 insertions(+), 7 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 94ab6fc..064d0a1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,7 +12,7 @@ HEAD
 ----
 
 - [deprecated] `Parser` methods will become private. [#3][]
-    - `#unquote` `#strip`, `#swallow`, `#parseOne`, `#surroundingQuote`
+    - `#unquote` `#strip`, `#swallow`, `#parseOne`, `#surroundingQuote`, `#interpolate`
 - [deps] migrate to [test][]
 - [deps] bump [logging][]
 
diff --git a/README.md b/README.md
index 3c21a44..4f88588 100644
--- a/README.md
+++ b/README.md
@@ -38,7 +38,7 @@ bool get hasEnv => dotenv.isEveryDefined(_requiredEnvVars);
 
 ### limitations
 
-Does **not** yet support escaping or substitution.  Pull requests gleefully considered.
+Does **not** yet support escaping.  Pull requests gleefully considered.
 
 ###### prior art
 
diff --git a/lib/src/parser.dart b/lib/src/parser.dart
index 8d13690..c5d8e5e 100644
--- a/lib/src/parser.dart
+++ b/lib/src/parser.dart
@@ -8,6 +8,7 @@ class Parser {
   static final _comment = new RegExp(r'#.*$');
   static final _keyword = 'export';
   static final _surroundQuotes = new RegExp(r'''^(['"])(.*)\1$''');
+  static final _bashVar = new RegExp(r'(?:\\)?(\$)([a-zA-Z_][\w]*)+');
 
   const Parser();
 
@@ -16,7 +17,7 @@ class Parser {
   Map<String, String> parse(Iterable<String> lines) {
     var out = {};
     lines.forEach((line) {
-      var kv = parseOne(line);
+      var kv = parseOne(line, env: out);
       if (kv.isEmpty) return;
       out.putIfAbsent(kv.keys.single, () => kv.values.single);
     });
@@ -26,7 +27,8 @@ class Parser {
 
   /// Parse a single line into a key-value pair.
   @Deprecated('Exposed for testing') // FIXME
-  Map<String, String> parseOne(String line) {
+  Map<String, String> parseOne(String line,
+      {Map<String, String> env: const {}}) {
     var stripped = strip(line);
     if (!_isValid(stripped)) return {};
 
@@ -42,11 +44,18 @@ class Parser {
     if (quotChar == "'") // skip substitution in single-quoted values
         return {k: v};
 
-    // TODO: variable substitution
-
-    return {k: v};
+    return {k: interpolate(v, env)};
   }
 
+  /// Substitute $bash_vars in [val] with values from [env].
+  @Deprecated('Exposed for testing') // FIXME
+  String interpolate(String val, Map<String, String> env) => val
+      .replaceAllMapped(_bashVar, (m) {
+    var k = m.group(2);
+    if (!env.containsKey(k) || env[k] == null) return '';
+    return env[k];
+  });
+
   /// If [val] is wrapped in single or double quotes, return the quote character.
   /// Otherwise, return the empty string.
   @Deprecated('Exposed for testing') // FIXME
diff --git a/test/parser_test.dart b/test/parser_test.dart
index 38dc11b..1336f92 100644
--- a/test/parser_test.dart
+++ b/test/parser_test.dart
@@ -16,16 +16,36 @@ void main() {
 
     test('it skips empty lines', subj.parse_empty);
     test('it ignores duplicate keys', subj.parse_dup);
+    test('it substitutes known variables into other values', subj.parse_subs);
 
     test('it detects unquoted values', subj.surroundingQuote_none);
     test('it detects double-quoted values', subj.surroundingQuote_double);
     test('it detects single-quoted values', subj.surroundingQuote_single);
+
+    test('it performs variable substitution', subj.interpolate);
+    test('it skips undefined variables', subj.interpolate_missing);
+    test('it handles explicitly null values in env', subj.interpolate_missing2);
   });
 }
 
 const _psr = const Parser();
 
 class ParserTest {
+  void interpolate() {
+    var out = _psr.interpolate(r'a$foo$baz', {'foo': 'bar', 'baz': 'qux'});
+    expect(out, equals('abarqux'));
+  }
+
+  void interpolate_missing() {
+    var out = _psr.interpolate(r'a$foo$baz', {});
+    expect(out, equals('a'));
+  }
+
+  void interpolate_missing2() {
+    var out = _psr.interpolate(r'a$foo$baz', {'foo': null});
+    expect(out, equals('a'));
+  }
+
   void surroundingQuote_none() {
     var out = _psr.surroundingQuote('no quotes here!');
     expect(out, isEmpty);
@@ -93,4 +113,9 @@ class ParserTest {
     var out = _psr.parse(['foo=bar', 'foo=baz']);
     expect(out, equals({'foo': 'bar'}));
   }
+
+  void parse_subs() {
+    var out = _psr.parse(['foo=bar', r'baz=super$foo']);
+    expect(out, equals({'foo': 'bar', 'baz': 'superbar'}));
+  }
 }