From d1970ccbb637ea7c55f05a679ef221be667365fa Mon Sep 17 00:00:00 2001
From: Jeremy Hooke <jez@stulk.com>
Date: Tue, 12 Oct 2021 11:53:55 +1100
Subject: [PATCH] Improve error message for chaning CRSes

---
 cubedash/generate.py        |  7 ++++---
 cubedash/summary/_schema.py |  2 +-
 cubedash/summary/_stores.py | 33 +++++++++++++++++++++++++++++++--
 3 files changed, 36 insertions(+), 6 deletions(-)

diff --git a/cubedash/generate.py b/cubedash/generate.py
index 96a223eaf..de29753a4 100755
--- a/cubedash/generate.py
+++ b/cubedash/generate.py
@@ -265,9 +265,10 @@ def convert(self, value, param, ctx):
     "--epsg",
     "epsg_code",
     type=int,
-    default=DEFAULT_EPSG,
-    show_default=True,
-    help="The equal-area epsg code to use internally for grouping spatial data",
+    # We default to None as we want to know later if they explicitly specified one or not.
+    default=None,
+    help=f"The equal-area epsg code to use internally for grouping spatial data. "
+    f"(default: {DEFAULT_EPSG})",
 )
 @click.option(
     "--verbose",
diff --git a/cubedash/summary/_schema.py b/cubedash/summary/_schema.py
index bccca136d..233243dc8 100644
--- a/cubedash/summary/_schema.py
+++ b/cubedash/summary/_schema.py
@@ -197,7 +197,7 @@
 )
 
 # An SQLAlchemy expression to read the configured SRID.
-FOOTPRINT_SRID_EXPRESSION = func.FindSRID(
+FOOTPRINT_SRID_EXPRESSION = func.Find_SRID(
     TIME_OVERVIEW.schema, TIME_OVERVIEW.name, "footprint_geometry"
 )
 
diff --git a/cubedash/summary/_stores.py b/cubedash/summary/_stores.py
index 11270b810..9590bf882 100644
--- a/cubedash/summary/_stores.py
+++ b/cubedash/summary/_stores.py
@@ -203,6 +203,9 @@ class ProductLocationSample:
     example_uris: List[str]
 
 
+_NOT_SET = object()
+
+
 class SummaryStore:
     def __init__(self, index: Index, summariser: Summariser, log=_LOG) -> None:
         self.index = index
@@ -253,7 +256,7 @@ def is_schema_compatible(self, for_writing_operations_too=False) -> bool:
         else:
             return _schema.is_compatible_schema(self._engine)
 
-    def init(self, grouping_epsg_code: int = DEFAULT_EPSG):
+    def init(self, grouping_epsg_code: int = None):
         """
         Initialise any schema elements that don't exist.
 
@@ -261,8 +264,34 @@ def init(self, grouping_epsg_code: int = DEFAULT_EPSG):
 
         (Requires `create` permissions in the db)
         """
+
         # Add any missing schema items or patches.
-        _schema.create_schema(self._engine, epsg_code=grouping_epsg_code)
+        _schema.create_schema(
+            self._engine, epsg_code=grouping_epsg_code or DEFAULT_EPSG
+        )
+
+        # If they specified an epsg code, make sure the existing schema uses it.
+        if grouping_epsg_code:
+            crs_used_by_schema = self.grouping_crs
+            if crs_used_by_schema != f"EPSG:{grouping_epsg_code}":
+                raise RuntimeError(
+                    f"""
+                Tried to initialise with EPSG:{grouping_epsg_code!r},
+                but the schema is already using {crs_used_by_schema}.
+
+                To change the CRS, you need to drop Explorer's schema first.
+
+                Eg.
+
+                    cubedash-gen --drop
+
+                And create with the new code:
+
+                    cubedash-gen --init --epsg {grouping_epsg_code}
+
+                (Warning: this can take a long time!)
+                """
+                )
         refresh_also = _schema.update_schema(self._engine)
 
         if refresh_also: