Refactor: use nrel_spa package instead of bundled SPA

Replace the 1280-line bundled SPA implementation with a dependency on
the nrel_spa package. SpaResult and SpaAnglesResult are now re-exported
from nrel_spa for backwards compatibility. All 24 tests pass unchanged.

CHANGELOG.md

@@ -2,6 +2,13 @@
 
 All notable changes to this project will be documented in this file.
 
+## [Unreleased]
+
+### Changed
+
+- Replaced bundled SPA implementation with the `nrel_spa` package dependency
+- Removed `SpaResult` and `SpaAnglesResult` from local types (now re-exported from `nrel_spa`)
+
 ## [1.0.0] - 2026-03-08
 
 ### Added

README.md

@@ -4,7 +4,7 @@
 [![CI](https://github.com/acamarata/pray-calc-dart/actions/workflows/ci.yml/badge.svg)](https://github.com/acamarata/pray-calc-dart/actions/workflows/ci.yml)
 [![License: MIT](https://img.shields.io/badge/license-MIT-blue.svg)](LICENSE)
 
-Islamic prayer times for Dart and Flutter. Pure Dart port of [pray-calc](https://github.com/acamarata/pray-calc), implementing the NREL Solar Position Algorithm, MCW seasonal model, and dynamic twilight angles. Zero dependencies.
+Islamic prayer times for Dart and Flutter. Pure Dart port of [pray-calc](https://github.com/acamarata/pray-calc), implementing the MCW seasonal model and dynamic twilight angles. Uses [nrel_spa](https://github.com/acamarata/nrel-spa-dart) for the NREL Solar Position Algorithm.
 
 ## Installation
 
@@ -87,7 +87,7 @@ Result: approximately 18 degrees at the equator, approximately 12-14 degrees at
 
 ## Compatibility
 
-Dart SDK 3.7.0+. Works in Flutter (iOS, Android, Web, Desktop), Dart CLI, and server-side Dart. Zero external dependencies.
+Dart SDK 3.7.0+. Works in Flutter (iOS, Android, Web, Desktop), Dart CLI, and server-side Dart. Single dependency: [nrel_spa](https://pub.dev/packages/nrel_spa).
 
 ## Related
 

lib/pray_calc_dart.dart

@@ -12,4 +12,4 @@ export 'src/solar_ephemeris.dart';
 export 'src/msc.dart';
 export 'src/asr.dart';
 export 'src/qiyam.dart';
-export 'src/spa.dart' show getSpa;
+export 'package:nrel_spa/nrel_spa.dart' show getSpa, SpaResult, SpaAnglesResult;

lib/src/get_times.dart

@@ -4,8 +4,9 @@
 /// angle algorithm. Times are in local time as determined by the UTC offset.
 library;
 
+import 'package:nrel_spa/nrel_spa.dart';
+
 import 'types.dart';
-import 'spa.dart';
 import 'solar_ephemeris.dart';
 import 'angles.dart';
 import 'asr.dart';

lib/src/types.dart

@@ -103,40 +103,4 @@ class SolarEphemeris {
   });
 }
 
-/// SPA result from the NREL Solar Position Algorithm.
-class SpaResult {
-  /// Topocentric zenith angle in degrees.
-  final double zenith;
-
-  /// Topocentric azimuth angle, eastward from north, in degrees.
-  final double azimuth;
-
-  /// Local sunrise time as fractional hours (NaN if polar).
-  final double sunrise;
-
-  /// Local sun transit time (solar noon) as fractional hours.
-  final double solarNoon;
-
-  /// Local sunset time as fractional hours (NaN if polar).
-  final double sunset;
-
-  /// Custom zenith angle results (one per angle in the input list).
-  final List<SpaAnglesResult> angles;
-
-  const SpaResult({
-    required this.zenith,
-    required this.azimuth,
-    required this.sunrise,
-    required this.solarNoon,
-    required this.sunset,
-    this.angles = const [],
-  });
-}
-
-/// Sunrise/sunset pair for a custom zenith angle.
-class SpaAnglesResult {
-  final double sunrise;
-  final double sunset;
-
-  const SpaAnglesResult({required this.sunrise, required this.sunset});
-}
+// SpaResult and SpaAnglesResult are provided by the nrel_spa package.

pubspec.yaml

@@ -1,8 +1,8 @@
 name: pray_calc_dart
 description: >
   Islamic prayer times for Dart and Flutter. Pure Dart port of the pray-calc
-  library implementing the NREL Solar Position Algorithm, MCW seasonal model,
-  and dynamic twilight angles. Zero dependencies.
+  library implementing the MCW seasonal model and dynamic twilight angles.
+  Uses nrel_spa for the NREL Solar Position Algorithm.
 version: 1.0.0
 repository: https://github.com/acamarata/pray-calc-dart
 issue_tracker: https://github.com/acamarata/pray-calc-dart/issues
@@ -16,6 +16,10 @@ topics:
 environment:
   sdk: ^3.7.0
 
+dependencies:
+  nrel_spa:
+    path: ../nrel-spa-dart
+
 dev_dependencies:
   lints: ^5.0.0
   test: ^1.25.8