Update json functions to more closely match Redshift, fixes HearthSim#3

Redshift returns NULL when a value cannot be found.
Redshift strips quotes from strings returned in the JSON.
Redshift checks for valid index when using json_extract_array_element_text.

sql/01_functions.sql

@@ -1,17 +1,21 @@
 -- json_extract_array_element_text()
-CREATE FUNCTION json_extract_array_element_text(json_array text, array_index int) RETURNS text immutable as $$
-import json
-result = json.loads(json_array)[array_index]
-return json.dumps(result)
+CREATE OR REPLACE FUNCTION json_extract_array_element_text(json_array text, array_index int) RETURNS text immutable as $$
+	import json
+	items = json.loads(json_array)
+	if 0 <= array_index and array_index < len(items):
+		return json.dumps(items[array_index]).strip('"')
+	else:
+		return None
 $$ LANGUAGE plpythonu;
 
 -- json_extract_path_text()
 CREATE FUNCTION json_extract_path_text(json_string text, VARIADIC path_elems character[]) RETURNS text immutable as $$
-import json
-result = json.loads(json_string)
-if path_elem not in result: return ""
-result = result[path_elem]
-return json.dumps(result)
+  import json
+  result = json.loads(json_string)
+  for path_elem in path_elems:
+      if path_elem not in result: return None
+      result = result[path_elem]
+  return json.dumps(result).strip('"')
 $$ LANGUAGE plpythonu;
 
 -- json_array_length()

test/01_functions.sql

@@ -0,0 +1,18 @@
+-- These should work in Redshift and the docker container as of
+-- select version(); -- PostgreSQL 8.0.2 on i686-pc-linux-gnu, compiled by GCC gcc (GCC) 3.4.2 20041017 (Red Hat 3.4.2-6.fc3), Redshift 1.0.34691
+
+SELECT json_extract_array_element_text('[1,2,3]', -1); -- NULL
+SELECT json_extract_array_element_text('[1,2,3]', 0); -- 1
+SELECT json_extract_array_element_text('[1,2,3]', 3); -- NULL
+SELECT json_extract_array_element_text('["a","b","c"]', -1); -- NULL
+SELECT json_extract_array_element_text('["a","b","c"]', 2); -- c
+SELECT json_extract_array_element_text('["a","b","c"]', 3); -- NULL
+
+-- Built in pg_catalog.json_extract_path_text exists so we need to include the schema when calling.
+-- See https://www.postgresql.org/docs/10/functions-json.html
+SELECT public.json_extract_path_text('{"a":{"b":{"c":1}},"d":[2,3],"e":"f"}', 'a'); -- {"b": {"c": 1}}
+SELECT public.json_extract_path_text('{"a":{"b":{"c":1}},"d":[2,3],"e":"f"}','a.b'); -- NULL
+SELECT public.json_extract_path_text('{"a":{"b":{"c":1}},"d":[2,3],"e":"f"}','d'); -- [2, 3]
+SELECT public.json_extract_path_text('{"a":{"b":{"c":1}},"d":[2,3],"e":"f"}','e'); -- f
+
+SELECT NOW(), getdate(); -- 2022-01-18 13:47:09.566 -0500,	2022-01-18 18:47:10.000