updated cache

ios-icons/cache.lua

@@ -1,38 +1,56 @@
+local format = string.format
 local cache = {}
 
-function cache.new(path)
-    local c = { }
+-- add a function to get a list of keys
+-- add delete function
+-- what about a protocol so that we can have caches with a backend other than the file system?
+-- (then what about Lua FUSE?)
 
-    -- add a function to get keys
-    -- add delete function
-    -- what about a protocol so that we can have caches with a backend other than the file system?
-    -- (then what about Lua FUSE?)
-
-
-    _,_,rc = os.execute("test -d " .. path)
-    if rc == 1 then os.execute("mkdir -p " .. path) end
 
-    c.get = function(k, generate)
-        local data = nil
-        local fd = io.open(path .. "/" .. k, "rb")
-        if fd then data = fd:read("*all") ; fd:close() end
-        if not data and type(generate) == "function" then
-            data = generate()
-            c.store(k, data)
-        end
-        return data        
-    end
+function cache.new(path, keytransform)
+   assert(type(path) == 'string' and #path > 0, 'path must be a non-empty string')
+   assert(type(keytransform) == 'nil' or type(keytransform) == 'function', 'keytransform must be a function')
+
+   local c = { }
+
+   _,_,rc = os.execute('test -d ' .. path)
+   if rc == 1 then os.execute('mkdir -p ' .. path) end
 
-    c.store = function(k, v)
-        local fd = io.open(path .. "/" .. k, "wb")
-        fd:write(v)
-        fd:close()
-    end
-
-    setmetatable(c, {
-        __tostring = function() return "cache[" .. path .. "]" end,
-    })
-    return c
+   c.keytransform = keytransform or function(k) return k end
+   c.key = function(k)
+      local kprime = c.keytransform(k)
+      if not kprime then return nil end
+      return format('%s/%s', path, kprime)
+   end
+
+   c.get = function(k, generate)
+      local data = nil
+      local key = c.key(k)
+      if not key then error('invalid key: ' .. tostring(k)) end
+
+      local fd = io.open(key, "rb")
+      if fd then data = fd:read("*all") ; fd:close() end
+      if not data and type(generate) == "function" then
+         data = generate(k)
+         c.store(k, data)
+      end
+      return data        
+   end
+
+   c.set = function(k, v)
+      local key = c.key(k)
+      if not key then error('invalid key: ' .. tostring(k)) end
+
+      local fd = io.open(key, "wb")
+      fd:write(v)
+      fd:close()
+   end
+
+   setmetatable(c, {
+                   __tostring = function() return "cache[" .. path .. "]" end,
+                   })
+   return c
 end
 
+
 return cache