add api endpoint to preview babycode

apps/api.lua

@@ -1,8 +1,13 @@
 local app = require("lapis").Application()
+local json_params = require("lapis.application").json_params
+
 local sse = require("lib.sse")
 
 local db = require("lapis.db")
 
+local html_escape = require("lapis.html").escape
+local babycode = require("lib.babycode")
+
 local util = require("util")
 
 app:get("sse_thread_updates", "/thread-updates/:thread_id", function(self)
@@ -33,4 +38,20 @@ app:get("sse_thread_updates", "/thread-updates/:thread_id", function(self)
   return {skip_render = true}
 end)
 
+app:post("babycode_preview", "/babycode-preview", json_params(function(self)
+  local user = util.get_logged_in_user(self)
+  if not user then
+    return {json = {error = "not authorized"}, status = 401}
+  end
+  if not util.rate_limit_allowed(user.id, "babycode_preview", 5) then
+    return {json = {error = "too many requests"}, status = 429}
+  end
+  local markup = self.params.markup
+  if not markup or type(markup) ~= "string" then
+    return {json = {error = "markup field missing or invalid type"}, status = 400}
+  end
+  local rendered = babycode.to_html(markup, html_escape)
+  return {json = {html = rendered}}
+end))
+
 return app

migrations.lua

@@ -91,4 +91,15 @@ return {
     
     db.query("COMMIT")
   end,
+  
+  [12] = function ()
+    schema.create_table("api_rate_limits", {
+      {"id", types.integer{primary_key = true}},
+      {"method", types.text{null = false}},
+      {"user_id", "INTEGER REFERENCES users(id) ON DELETE CASCADE"},
+      {"logged_at", "INTEGER DEFAULT (unixepoch(CURRENT_TIMESTAMP))"},
+    })
+    
+    db.query("CREATE INDEX idx_rate_limit_user_method ON api_rate_limits (user_id, method)")
+  end,
 }

util.lua

@@ -316,4 +316,25 @@ function util.inject_warn_infobox(req, message)
   req.session.infobox = ib
 end
 
+function util.rate_limit_allowed(user_id, method, seconds)
+  local last_call = db.query([[
+    SELECT logged_at FROM api_rate_limits
+    WHERE user_id = ? AND method = ?
+    ORDER BY logged_at DESC LIMIT 1
+  ]], user_id, method)
+  if #last_call == 0 or (os.time() - last_call[1].logged_at) >= seconds then
+    db.query(
+      "DELETE FROM api_rate_limits WHERE user_id = ? AND method = ?",
+      user_id, method
+    )
+    db.query(
+      "INSERT INTO api_rate_limits (user_id, method) VALUES (?, ?)",
+      user_id, method
+    )
+    return true
+  else
+    return false
+  end
+end
+
 return util