From 7fc53ab11410c91a0e17f5c7087fd6cc02565fce Mon Sep 17 00:00:00 2001
From: Alberto Restifo <alberto@restifo.dev>
Date: Fri, 8 May 2020 11:40:18 +0200
Subject: [PATCH] Add support for BigDecimal and BigInt

---
 .vscode/settings.json       |  3 +++
 README.md                   |  2 +-
 spec/cbor/from_cbor_spec.cr |  3 +++
 src/cbor/from_cbor.cr       | 49 ++++++++++++++++++++++++++++++++-----
 4 files changed, 50 insertions(+), 7 deletions(-)
 create mode 100644 .vscode/settings.json

diff --git a/.vscode/settings.json b/.vscode/settings.json
new file mode 100644
index 0000000..f5df97a
--- /dev/null
+++ b/.vscode/settings.json
@@ -0,0 +1,3 @@
+{
+    "crystal-lang.mainFile": "${workspaceRoot}/src/cbor.cr"
+}
\ No newline at end of file
diff --git a/README.md b/README.md
index abfb633..77efb91 100644
--- a/README.md
+++ b/README.md
@@ -50,7 +50,7 @@ and the values are encoded in the respective Crystal types:
 
 - `Time`
 - `BigInt`
-- `BigFloat`
+- `BigDecimal`
 
 ## Development
 
diff --git a/spec/cbor/from_cbor_spec.cr b/spec/cbor/from_cbor_spec.cr
index ba31c6b..b9b4629 100644
--- a/spec/cbor/from_cbor_spec.cr
+++ b/spec/cbor/from_cbor_spec.cr
@@ -40,6 +40,9 @@ describe "CBOR helpers on basic types" do
       {Tuple(Int8, Int8), Bytes[0x82, 0x01, 0x02], {1_i8, 2_i8}},
       {NamedTuple(a: UInt8, b: Array(UInt8)), Bytes[0xa2, 0x61, 0x61, 0x01, 0x61, 0x62, 0x82, 0x02, 0x03], {a: 1_u8, b: [2_u8, 3_u8]}},
       {BigInt, Bytes[0xc2, 0x49, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00], BigInt.new("18446744073709551616")},
+      {BigInt, Bytes[0x18, 0x18], BigInt.new(24)}, # BigInt from int
+      {BigDecimal, Bytes[0xc4, 0x82, 0x21, 0x19, 0x6a, 0xb3], BigDecimal.new(273.15)},
+      {BigDecimal, Bytes[0xc5, 0x82, 0x20, 0x03], BigDecimal.new(1.5)},
     ]
 
     tests.each do |tt|
diff --git a/src/cbor/from_cbor.cr b/src/cbor/from_cbor.cr
index 8b0a53a..439d440 100644
--- a/src/cbor/from_cbor.cr
+++ b/src/cbor/from_cbor.cr
@@ -149,12 +149,20 @@ def Time.new(decoder : CBOR::Decoder)
   end
 end
 
-# Reads the CBOR value as a BigInt. The value must be surrounded by a tag with
-# value 2 (positive) or 3 (negative).
+# Reads the CBOR value as a BigInt.
+# If the next token is an integer, then the integer will be transformed as a
+# BigInt, otherwhise the value must be surrounded by a tag with value 2
+# (positive) or 3 (negative).
 def BigInt.new(decoder : CBOR::Decoder)
-  case tag = decoder.read_tag
-  when CBOR::Tag::PositiveBigNum,
-       CBOR::Tag::NegativeBigNum
+  case token = decoder.current_token
+  when CBOR::Token::TagT
+    decoder.finish_token!
+
+    tag = token.value
+    unless tag == CBOR::Tag::PositiveBigNum || tag == CBOR::Tag::NegativeBigNum
+      raise CBOR::ParseError.new("Expected tag to have value 2 or 3, got #{tag.value}")
+    end
+
     big = new(decoder.read_bytes.hexstring, 16)
 
     if tag == CBOR::Tag::NegativeBigNum
@@ -163,8 +171,37 @@ def BigInt.new(decoder : CBOR::Decoder)
     end
 
     big
+  when CBOR::Token::IntT
+    decoder.finish_token!
+    new(token.value)
   else
-    raise CBOR::ParseError.new("Expected tag to have value 2 or 3, got #{tag.value}")
+    decoder.unexpected_token(token, "IntT or TagT")
+  end
+end
+
+# Reads the CBOR value as a BigDecimal.
+# If the next token is a flaot, then it'll be transformed to a BigDecimal,
+# otherwhise the value must be correctly tagged with value 4 (decimal fraction)
+# or 5 (big float).
+def BigDecimal.new(decoder : CBOR::Decoder)
+  case token = decoder.current_token
+  when CBOR::Token::TagT
+    decoder.finish_token!
+
+    tag = token.value
+    unless tag == CBOR::Tag::Decimal || tag == CBOR::Tag::BigFloat
+      raise CBOR::ParseError.new("Expected tag to have value 4 or 5, got #{tag.value}")
+    end
+
+    exponent, matissa = Tuple(Int128, BigInt).new(decoder)
+
+    base = tag == CBOR::Tag::Decimal ? 10.0 : 2.0
+    e = base**exponent
+    new(matissa) * new(e)
+  when CBOR::Token::FloatT
+    new(token.value)
+  else
+    decoder.unexpected_token(token, "FloatT or TagT")
   end
 end