Add a file-like lua JSON wrapper

library/lua/json.lua

@@ -1,5 +1,6 @@
 local _ENV = mkmodule('json')
 local internal = require 'json.internal'
+local fs = dfhack.filesystem
 
 encode_defaults = {
     -- For compatibility with jsonxx (C++)
@@ -14,11 +15,8 @@ function encode(data, options, msg)
     return internal:encode(data, msg, opts)
 end
 
-function encode_file(data, path, overwrite, ...)
-    if dfhack.filesystem.exists(path) and not overwrite then
-        error('File exists: ' .. path)
-    end
-    if dfhack.filesystem.isdir(path) then
+function encode_file(data, path, ...)
+    if fs.isdir(path) then
         error('Is a directory: ' .. path)
     end
     local contents = encode(data, ...)
@@ -41,4 +39,42 @@ function decode_file(path, ...)
     return decode(contents, ...)
 end
 
+local _file = defclass()
+function _file:init(opts)
+    self.path = opts.path
+    self.data = {}
+    self.exists = false
+    self:read(opts.strict)
+end
+
+function _file:read(strict)
+    if not fs.exists(self.path) then
+        if strict then
+            error('cannot read file: ' .. self.path)
+        else
+            self.data = {}
+        end
+    else
+        self.exists = true
+        self.data = decode_file(self.path)
+    end
+    return self.data
+end
+
+function _file:write(data)
+    if data then
+        self.data = data
+    end
+    encode_file(self.data, self.path)
+    self.exists = true
+end
+
+function _file:__tostring()
+    return ('<json file: %s>'):format(self.path)
+end
+
+function open(path, strict)
+    return _file{path=path, strict=strict}
+end
+
 return _ENV