Datasette.render_template() method, closes #577

Pull request #664.

datasette/app.py

@@ -1,6 +1,8 @@
 import asyncio
 import collections
 import hashlib
+import itertools
+import json
 import os
 import re
 import sys
@@ -12,7 +14,8 @@ from pathlib import Path
 
 import click
 from markupsafe import Markup
-from jinja2 import ChoiceLoader, Environment, FileSystemLoader, PrefixLoader
+from jinja2 import ChoiceLoader, Environment, FileSystemLoader, PrefixLoader, escape
+from jinja2.environment import Template
 import uvicorn
 
 from .views.base import DatasetteError, ureg, AsgiRouter
@@ -27,6 +30,7 @@ from .utils import (
     QueryInterrupted,
     escape_css_string,
     escape_sqlite,
+    format_bytes,
     get_plugins,
     module_from_path,
     sqlite3,
@@ -35,6 +39,7 @@ from .utils import (
 from .utils.asgi import (
     AsgiLifespan,
     NotFound,
+    Response,
     asgi_static,
     asgi_send,
     asgi_send_html,
@@ -526,6 +531,96 @@ class Datasette:
         for renderer in hook_renderers:
             self.renderers[renderer["extension"]] = renderer["callback"]
 
+    async def render_template(
+        self, templates, context=None, request=None, view_name=None
+    ):
+        context = context or {}
+        if isinstance(templates, Template):
+            template = templates
+            select_templates = []
+        else:
+            if isinstance(templates, str):
+                templates = [templates]
+            template = self.jinja_env.select_template(templates)
+            select_templates = [
+                "{}{}".format(
+                    "*" if template_name == template.name else "", template_name
+                )
+                for template_name in templates
+            ]
+        body_scripts = []
+        # pylint: disable=no-member
+        for script in pm.hook.extra_body_script(
+            template=template.name,
+            database=context.get("database"),
+            table=context.get("table"),
+            view_name=view_name,
+            datasette=self,
+        ):
+            body_scripts.append(Markup(script))
+
+        extra_template_vars = {}
+        # pylint: disable=no-member
+        for extra_vars in pm.hook.extra_template_vars(
+            template=template.name,
+            database=context.get("database"),
+            table=context.get("table"),
+            view_name=view_name,
+            request=request,
+            datasette=self,
+        ):
+            if callable(extra_vars):
+                extra_vars = extra_vars()
+            if asyncio.iscoroutine(extra_vars):
+                extra_vars = await extra_vars
+            assert isinstance(extra_vars, dict), "extra_vars is of type {}".format(
+                type(extra_vars)
+            )
+            extra_template_vars.update(extra_vars)
+
+        template_context = {
+            **context,
+            **{
+                "app_css_hash": self.app_css_hash(),
+                "select_templates": select_templates,
+                "zip": zip,
+                "body_scripts": body_scripts,
+                "format_bytes": format_bytes,
+                "extra_css_urls": self._asset_urls("extra_css_urls", template, context),
+                "extra_js_urls": self._asset_urls("extra_js_urls", template, context),
+            },
+            **extra_template_vars,
+        }
+        return await template.render_async(template_context)
+
+    def _asset_urls(self, key, template, context):
+        # Flatten list-of-lists from plugins:
+        seen_urls = set()
+        for url_or_dict in itertools.chain(
+            itertools.chain.from_iterable(
+                getattr(pm.hook, key)(
+                    template=template.name,
+                    database=context.get("database"),
+                    table=context.get("table"),
+                    datasette=self,
+                )
+            ),
+            (self.metadata(key) or []),
+        ):
+            if isinstance(url_or_dict, dict):
+                url = url_or_dict["url"]
+                sri = url_or_dict.get("sri")
+            else:
+                url = url_or_dict
+                sri = None
+            if url in seen_urls:
+                continue
+            seen_urls.add(url)
+            if sri:
+                yield {"url": url, "sri": sri}
+            else:
+                yield {"url": url}
+
     def app(self):
         "Returns an ASGI app function that serves the whole of Datasette"
         default_templates = str(app_root / "datasette" / "templates")