From 87e65b43d7a9a6a4ed4e3550e2e0c079bce8a896 Mon Sep 17 00:00:00 2001
From: Don Cross <cosinekitty@gmail.com>
Date: Mon, 20 May 2019 15:23:15 -0400
Subject: [PATCH] Implemented C function Seasons, but not yet tested.

---
 generate/template/astronomy.c | 31 ++++++++++++++++++++++++++++++-
 source/c/astronomy.c          | 31 ++++++++++++++++++++++++++++++-
 source/c/astronomy.h          | 12 ++++++++++++
 3 files changed, 72 insertions(+), 2 deletions(-)

diff --git a/generate/template/astronomy.c b/generate/template/astronomy.c
index acb01cf0..2c6b4608 100644
--- a/generate/template/astronomy.c
+++ b/generate/template/astronomy.c
@@ -1801,6 +1801,35 @@ static int QuadInterp(
     return 1;   /* success */
 }
 
+static astro_status_t FindSeasonChange(double targetLon, int year, int month, int day, astro_time_t *time)
+{
+    astro_time_t startDate = Astronomy_MakeTime(year, month, day, 0, 0, 0.0);
+    astro_search_result_t result = Astronomy_SearchSunLongitude(targetLon, startDate, 4.0);
+    *time = result.time;
+    return result.status;
+}
+
+astro_seasons_t Astronomy_Seasons(int year)
+{
+    astro_seasons_t seasons;
+    astro_status_t  status;
+
+    seasons.status = ASTRO_SUCCESS;
+
+    status = FindSeasonChange(  0, year,  3, 19, &seasons.mar_equinox);
+    if (status != ASTRO_SUCCESS) seasons.status = status;
+
+    status = FindSeasonChange( 90, year,  6, 19, &seasons.jun_solstice);
+    if (status != ASTRO_SUCCESS) seasons.status = status;
+
+    status = FindSeasonChange(180, year,  9, 21, &seasons.sep_equinox);
+    if (status != ASTRO_SUCCESS) seasons.status = status;
+
+    status = FindSeasonChange(270, year, 12, 20, &seasons.dec_solstice);
+    if (status != ASTRO_SUCCESS) seasons.status = status;
+
+    return seasons;
+}
 
 #ifdef __cplusplus
 }
@@ -1831,6 +1860,6 @@ static int QuadInterp(
     X   SearchRelativeLongitude
     X   SearchRiseSet
     -   SearchSunLongitude
-    X   Seasons
+    -   Seasons
     -   SunPosition
 */
diff --git a/source/c/astronomy.c b/source/c/astronomy.c
index b19232b1..4bef4411 100644
--- a/source/c/astronomy.c
+++ b/source/c/astronomy.c
@@ -2857,6 +2857,35 @@ static int QuadInterp(
     return 1;   /* success */
 }
 
+static astro_status_t FindSeasonChange(double targetLon, int year, int month, int day, astro_time_t *time)
+{
+    astro_time_t startDate = Astronomy_MakeTime(year, month, day, 0, 0, 0.0);
+    astro_search_result_t result = Astronomy_SearchSunLongitude(targetLon, startDate, 4.0);
+    *time = result.time;
+    return result.status;
+}
+
+astro_seasons_t Astronomy_Seasons(int year)
+{
+    astro_seasons_t seasons;
+    astro_status_t  status;
+
+    seasons.status = ASTRO_SUCCESS;
+
+    status = FindSeasonChange(  0, year,  3, 19, &seasons.mar_equinox);
+    if (status != ASTRO_SUCCESS) seasons.status = status;
+
+    status = FindSeasonChange( 90, year,  6, 19, &seasons.jun_solstice);
+    if (status != ASTRO_SUCCESS) seasons.status = status;
+
+    status = FindSeasonChange(180, year,  9, 21, &seasons.sep_equinox);
+    if (status != ASTRO_SUCCESS) seasons.status = status;
+
+    status = FindSeasonChange(270, year, 12, 20, &seasons.dec_solstice);
+    if (status != ASTRO_SUCCESS) seasons.status = status;
+
+    return seasons;
+}
 
 #ifdef __cplusplus
 }
@@ -2887,6 +2916,6 @@ static int QuadInterp(
     X   SearchRelativeLongitude
     X   SearchRiseSet
     -   SearchSunLongitude
-    X   Seasons
+    -   Seasons
     -   SunPosition
 */
diff --git a/source/c/astronomy.h b/source/c/astronomy.h
index 6512df0c..84ba60f3 100644
--- a/source/c/astronomy.h
+++ b/source/c/astronomy.h
@@ -134,6 +134,16 @@ typedef struct
 }
 astro_search_result_t;
 
+typedef struct
+{
+    astro_status_t  status;
+    astro_time_t    mar_equinox;
+    astro_time_t    jun_solstice;
+    astro_time_t    sep_equinox;
+    astro_time_t    dec_solstice;
+}
+astro_seasons_t;
+
 typedef double (* astro_search_func_t) (void *context, astro_time_t time);
 
 /*---------- functions ----------*/
@@ -169,6 +179,8 @@ astro_search_result_t Astronomy_SearchSunLongitude(
     astro_time_t dateStart,
     double limitDays);
 
+astro_seasons_t Astronomy_Seasons(int calendar_year);
+
 #ifdef __cplusplus
 }
 #endif