From b8430c9f12103a2674d6c651f5dcd37a411ed204 Mon Sep 17 00:00:00 2001
From: Juri Pakaste <juri@juripakaste.fi>
Date: Tue, 11 Jul 2023 09:35:57 +0300
Subject: [PATCH 1/2] Add a helper function for Decoder

---
 .../Documentation.docc/Documentation.md       |  4 ++
 Sources/Parse3339/Parse3339.swift             | 30 ++++++++++++++
 Tests/Parse3339Tests/Parse3339Tests.swift     | 40 +++++++++++++++++++
 3 files changed, 74 insertions(+)

diff --git a/Sources/Parse3339/Documentation.docc/Documentation.md b/Sources/Parse3339/Documentation.docc/Documentation.md
index 2534f63..f8bb91c 100644
--- a/Sources/Parse3339/Documentation.docc/Documentation.md
+++ b/Sources/Parse3339/Documentation.docc/Documentation.md
@@ -43,3 +43,7 @@ print(date.timeIntervalSinceReferenceDate)
 ### Parser output
 
 - ``Parts``
+
+### Codable support
+
+- ``parseFromDecoder(_:)``
diff --git a/Sources/Parse3339/Parse3339.swift b/Sources/Parse3339/Parse3339.swift
index b81e451..cee67da 100644
--- a/Sources/Parse3339/Parse3339.swift
+++ b/Sources/Parse3339/Parse3339.swift
@@ -308,6 +308,36 @@ public func parse(_ seq: some Sequence<UInt8>) -> Parts? {
     return nil
 }
 
+// MARK: JSONDecoder support
+
+/// Helper function for using Parse3339 with Codable types.
+///
+/// Use `parseFromDecoder(_:)` with a custom date decoding strategy. The mechanism depends on
+/// the `TopLevelDecoder` implementation. With `JSONDecoder` you can use the `dateDecodingStrategy`
+/// property with a `custom` value like this:
+///
+/// ```swift
+/// let decoder = JSONDecoder()
+/// decoder.dateDecodingStrategy = .custom(Parse3339.parseFromDecoder(_:))
+/// ```
+///
+/// `parseFromDecoder` first decodes a `String` and then parses the string. For formats other than JSON you may get
+/// better performance by using an implementation that feeds bytes to ``parse(_:)-9on3x``.
+public func parseFromDecoder(_ decoder: some Decoder) throws -> Date {
+    let container = try decoder.singleValueContainer()
+    let str = try container.decode(String.self)
+    guard let parsed = parse(str) else {
+        throw DecodingError.typeMismatch(
+            Date.self,
+            DecodingError.Context(
+                codingPath: [],
+                debugDescription: "The string '\(str)' could not be parsed as a date"
+            )
+        )
+    }
+    return parsed.date
+}
+
 // MARK: - Private
 
 private enum ZoneDirection {
diff --git a/Tests/Parse3339Tests/Parse3339Tests.swift b/Tests/Parse3339Tests/Parse3339Tests.swift
index 89d1364..d97888e 100644
--- a/Tests/Parse3339Tests/Parse3339Tests.swift
+++ b/Tests/Parse3339Tests/Parse3339Tests.swift
@@ -622,6 +622,46 @@ final class Parse3339Tests: XCTestCase {
             }
         }
     }
+
+    // MARK: Decodable
+
+    func testDecodable() throws {
+        struct Payload: Codable {
+            let message: String
+            let date: Date
+        }
+
+        let dateComponents = DateComponents(
+            timeZone: TimeZone(identifier: "Europe/Helsinki"),
+            year: 2023,
+            month: 7,
+            day: 11,
+            hour: 8,
+            minute: 49,
+            second: 0
+        )
+        let date = Calendar(identifier: .gregorian).date(from: dateComponents)!
+        let payload = Payload(message: "hello world", date: date)
+
+        let encoder = JSONEncoder()
+        encoder.dateEncodingStrategy = .iso8601
+
+        let json = try encoder.encode(payload)
+
+        var didCallParse = false
+        func wrappedParse(_ decoder: any Decoder) throws -> Date {
+            didCallParse = true
+            return try parseFromDecoder(decoder)
+        }
+
+        let decoder = JSONDecoder()
+        decoder.dateDecodingStrategy = .custom(wrappedParse(_:))
+        let decoded = try decoder.decode(Payload.self, from: json)
+
+        XCTAssertTrue(didCallParse)
+        XCTAssertEqual(decoded.message, "hello world")
+        XCTAssertEqual(decoded.date, date)
+    }
 }
 
 let isoFormatter: ISO8601DateFormatter = {

From de2c33d2d26f823f2b6a68a00520f2021e5b7f42 Mon Sep 17 00:00:00 2001
From: Juri Pakaste <juri@juripakaste.fi>
Date: Tue, 11 Jul 2023 09:38:19 +0300
Subject: [PATCH 2/2] Add usage note to README for JSONDecoder

---
 README.md | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/README.md b/README.md
index 00bacb1..688483b 100644
--- a/README.md
+++ b/README.md
@@ -31,6 +31,15 @@ print(date.timeIntervalSinceReferenceDate)
 // output: 710590440.0
 ```
 
+There's a helper function you can use with Foundation's `JSONDecoder`:
+
+```swift
+import Parse3339
+
+let decoder = JSONDecoder()
+decoder.dateDecodingStrategy = .custom(Parse3339.parseFromDecoder(_:))
+```
+
 For `Package.swift` snippets and documentation, visit the [Swift Package Index page](https://swiftpackageindex.com/juri/Parse3339).
 
 ## Speed and memory usage