just horrific, fixes #1

Author: cldellow

README.md

@@ -15,7 +15,18 @@ Install this plugin in the same environment as Datasette.
 
 ## Usage
 
-Usage instructions go here.
+Write a hook like:
+
+```python
+from datasette import hookimpl
+
+@hookimpl
+def rewrite_sql(sql):
+  if sql == 'select 123':
+    return 'select 234'
+
+  return sql
+```
 
 ## Development
 

datasette_rewrite_sql/__init__.py

@@ -1 +1,89 @@
+from datasette.utils import await_me_maybe
 from datasette import hookimpl
+from datasette.plugins import pm
+from datasette.database import Database
+from . import hookspecs
+
+original_execute = Database.execute
+original_execute_write = Database.execute_write
+original_execute_write_script = Database.execute_write_script
+original_execute_write_many = Database.execute_write_many
+
+async def patched_execute(
+    self,
+    sql,
+    params=None,
+    truncate=False,
+    custom_time_limit=None,
+    page_size=None,
+    log_sql_errors=True,
+):
+    rewritten = await rewrite(self.ds, self, 'execute', sql, params)
+    return await original_execute(
+        self,
+        rewritten,
+        params,
+        truncate,
+        custom_time_limit,
+        page_size,
+        log_sql_errors
+    )
+
+async def patched_execute_write(self, sql, params=None, block=True):
+    rewritten = await rewrite(self.ds, self, 'execute_write', sql, params)
+
+    return await original_execute_write(self, rewritten, params, block)
+
+async def patched_execute_write_script(self, sql, block=True):
+    rewritten = await rewrite(self.ds, self, 'execute_write_script', sql, None)
+
+    return await original_execute_write_script(self, rewritten, block)
+
+async def patched_execute_write_many(self, sql, params_seq, block=True):
+    rewritten = await rewrite(self.ds, self, 'execute_write_many', sql, params_seq)
+    return await original_execute_write_many(self, rewritten, params_seq, block)
+
+Database.execute = patched_execute
+Database.execute_write = patched_execute_write
+Database.execute_write_many = patched_execute_write_many
+Database.execute_write_script = patched_execute_write_script
+
+
+@hookimpl
+def startup():
+    pm.add_hookspecs(hookspecs)
+
+async def rewrite(datasette, database, fn, sql, params):
+    # A challenge: if two plugins are participating in rewriting, who wins?
+    #
+    # Option 1: the first one registered wins.
+    # Option 2: the output of the first is fed into the second.
+    #
+    # With option 2, if two plugins rewrite the output, ought the first one
+    # get another kick at the can to rewrite the output of the second? That is,
+    # should rewrites continue until no plugin wants to rewrite again?
+    #
+    # That feels like the "right" solution, but is probably hard for programmers
+    # to reason about -- I can imagine easily getting into an infinite loop.
+    #
+    # Instead, let's let each hook rewrite exactly once.
+    #
+    # This seems to not be a supported case for pluggy. So, let's do
+    # some vaguely evil things to do it ourselves.
+    caller_kwargs = {
+        'datasette': datasette,
+        'database': database,
+        'fn': fn,
+        'sql': sql,
+        'params': params
+    }
+
+    for hook_impl in pm.hook.rewrite_sql.get_hookimpls():
+        args = [caller_kwargs[argname] for argname in hook_impl.argnames]
+        res = await await_me_maybe(hook_impl.function(*args))
+
+        if res is not None:
+            sql = res
+            caller_kwargs['sql'] = sql
+
+    return sql

datasette_rewrite_sql/hookspecs.py

@@ -0,0 +1,8 @@
+from pluggy import HookspecMarker
+
+hookspec = HookspecMarker("datasette")
+
+
+@hookspec
+def rewrite_sql(datasette, database, fn, sql, params):
+    "Inspect or rewrite the SQL request."

go

@@ -0,0 +1,3 @@
+#!/bin/bash
+set -euo pipefail
+datasette --reload --plugins-dir plugins/

plugins/test.py

@@ -0,0 +1,7 @@
+from datasette import hookimpl
+
+@hookimpl
+def rewrite_sql(sql):
+    if sql == 'SELECT 123':
+        return 'SELECT 234'
+    return sql