feat: Demonstrate asset datetime summary investigation

Looks like it would be simple to extend the `summaries` property to
allow asset-specific summaries by referring back to the definition of
the `summaries` property.

You can try the notebook yourself by running `nix-shell --run 'jupyter
lab extensions/linz/notebooks/asset-datetime-summary.ipynb'`.

extensions/linz/notebooks/asset-datetime-summary.ipynb

@@ -0,0 +1,191 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "id": "4b29124d-9e52-4124-8b9f-efb60762c0dc",
+   "metadata": {},
+   "source": [
+    "# Creating asset summaries"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "d38f9eb9-e10e-4903-9772-8b887e3cdef5",
+   "metadata": {},
+   "source": [
+    "We'll need a *LINZ extension schema validator:*"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "id": "7b2d67c6-3313-4023-9752-49d133d86d59",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from json import load\n",
+    "from sys import stderr\n",
+    "from urllib.request import urlopen\n",
+    "\n",
+    "from jsonschema import Draft7Validator\n",
+    "\n",
+    "with urlopen(\"https://stac.linz.govt.nz/v0.0.10/linz/schema.json\") as schema_pointer:\n",
+    "    schema = load(schema_pointer)\n",
+    "\n",
+    "validator = Draft7Validator(schema)\n",
+    "\n",
+    "def validate(instance: str) -> None:\n",
+    "    for error in validator.iter_errors(instance):\n",
+    "        print(error.message, file=stderr)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "5e32302e-6714-494f-bbe0-23a60d9b383e",
+   "metadata": {
+    "tags": []
+   },
+   "source": [
+    "The *collection example* is valid:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "id": "3931b743-885d-47ec-aff4-48faa8c6da5b",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "with urlopen(\"https://stac.linz.govt.nz/v0.0.10/linz/examples/collection.json\") as example_pointer:\n",
+    "    example = load(example_pointer)\n",
+    "\n",
+    "validate(example)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "f0e21a05-f00f-4923-a457-b3a7f25907d8",
+   "metadata": {},
+   "source": [
+    "Can we *summarise assets?*"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "id": "76ec8b0b-6d5a-4902-a0b1-6b1415b577f3",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "example[\"summaries\"][\"assets\"] = {\n",
+    "    \"created\": {\"minimum\": \"1999-01-01T00:00:00Z\", \"maximum\": \"2010-01-01T00:00:00Z\"},\n",
+    "    \"updated\": {\"minimum\": \"1999-01-02T00:00:00Z\", \"maximum\": \"2010-01-02T00:00:00Z\"},\n",
+    "}\n",
+    "validate(example)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "3cb90d1c-d25f-46e5-9885-c3d4f303ef09",
+   "metadata": {},
+   "source": [
+    "Yes, but *are such properties validated as normal summaries?* What if there's an invalid datetime or unexpected structure?"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "id": "2f043e5c-11a9-4ad8-9d6b-4ce8fe4cb1c0",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "example[\"summaries\"][\"assets\"] = {\n",
+    "    \"created\": None,\n",
+    "    \"updated\": {\"minimum\": \"1999-01-02T00:00:00Z\"},\n",
+    "}\n",
+    "validate(example)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "16355abb-5da3-4486-9ae7-4f450330c508",
+   "metadata": {},
+   "source": [
+    "Oops, that should've caused a *validation exception!* Let's instead extend the extension schema to validate asset summaries as normal summaries:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "id": "4cd36c8b-ac96-4ea3-a4a2-0db92ef07675",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stderr",
+     "output_type": "stream",
+     "text": [
+      "None is not valid under any of the given schemas\n",
+      "{'minimum': 'not a datetime'} is not valid under any of the given schemas\n"
+     ]
+    }
+   ],
+   "source": [
+    "schema[\"definitions\"][\"fields\"][\"properties\"][\"summaries\"][\"properties\"][\"assets\"] = {\n",
+    "    \"$ref\": \"https://schemas.stacspec.org/v1.0.0/collection-spec/json-schema/collection.json#definitions/summaries\"\n",
+    "}\n",
+    "validate(example)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "bdaa981e-5c50-4f9f-a7d2-6b0bef7c314f",
+   "metadata": {},
+   "source": [
+    "Looks like that worked – the assets summary is validated like any other summary. Let's make sure by reverting to the valid summary:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 6,
+   "id": "8e7cfdb5-1232-40fd-957b-9b01f7448401",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "example[\"summaries\"][\"assets\"] = {\n",
+    "    \"created\": {\"minimum\": \"1999-01-01T00:00:00Z\", \"maximum\": \"2010-01-01T00:00:00Z\"},\n",
+    "    \"updated\": {\"minimum\": \"1999-01-02T00:00:00Z\", \"maximum\": \"2010-01-02T00:00:00Z\"},\n",
+    "}\n",
+    "validate(example)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "6ee3378f-5507-4831-8611-ce56c52304ac",
+   "metadata": {},
+   "source": [
+    "And we're golden!"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python3 - stac",
+   "language": "python",
+   "name": "ipython_stac"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.8.9"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}