d-lua-stuff · September 2, 2020 02:34 · Sep 2, 2020
diff --git a/json.lua b/json.lua
@@ -0,0 +1,140 @@
+-- Extracts values from a JSON string with pattern matching
+-- This is faster than using dkjson when only a few fields are needed
+
+-- Use this only with trusted data sources! Limitations:
+-- * Character escapes are not supported
+-- * Field nesting is ignored
+
+local find, gsub = string.find, string.gsub
+
+---@param json string
+---@param key string
+---@param init number|nil
+---@return string|nil, number|nil, number|nil
+local function extractStringJsonValue (json, key, init)
+  local pattern = [["]] .. key .. [["%s*:%s*"([^"]*)"]]
+  local startIndex, endIndex, valueStr = find(json, pattern, init)
+  return valueStr, startIndex, endIndex
+end
+
+---@param json string
+---@param key string
+---@param init number|nil
+---@return number|nil, number|nil, number|nil
+local function extractNumberJsonValue (json, key, init)
+  local pattern = [["]] .. key .. [["%s*:%s*(-?[0-9.e-]+)]]
+  local startIndex, endIndex, valueStr = find(json, pattern, init)
+  return tonumber(valueStr), startIndex, endIndex
+end
+
+---@param json string
+---@param key string
+---@param init number|nil
+---@return boolean|nil, number|nil, number|nil
+local function extractBooleanJsonValue (json, key, init)
+  local pattern = [["]] .. key .. [["%s*:%s*([truefals]+)]]
+  local startIndex, endIndex, valueStr = find(json, pattern, init)
+
+  if valueStr == "true" then
+    return true, startIndex, endIndex
+  elseif valueStr == "false" then
+    return false, startIndex, endIndex
+  else
+    return nil
+  end
+end
+
+---@param extractJsonValue function
+---@param json string
+---@param key string
+---@param stopAfterIndex number|nil
+---@param stopAfterValue any|nil
+---@return any[]
+local function extractAllJsonValues (extractJsonValue, json, key, stopAfterIndex, stopAfterValue)
+  local values = {}
+  local valuesLen = 0
+
+  local jsonPos = 1
+  local value, valueStartIndex, valueEndIndex -- luacheck: ignore valueStartIndex -- unused
+
+  repeat
+    value, valueStartIndex, valueEndIndex = extractJsonValue(json, key, jsonPos)
+
+    if value ~= nil then
+      valuesLen = valuesLen + 1
+      values[valuesLen] = value
+
+      jsonPos = valueEndIndex + 1
+    end
+
+    if value == stopAfterValue then break end
+    if valuesLen == stopAfterIndex then break end
+  until value == nil
+
+  return values
+end
+
+---@param json string
+---@param key string
+---@param stopAfterIndex number|nil
+---@param stopAfterValue string|nil
+---@return string[]
+local function extractAllStringJsonValues (json, key, stopAfterIndex, stopAfterValue)
+  return extractAllJsonValues(extractStringJsonValue, json, key, stopAfterIndex, stopAfterValue)
+end
+
+---@param json string
+---@param key string
+---@param stopAfterIndex number|nil
+---@param stopAfterValue number|nil
+---@return number[]
+local function extractAllNumberJsonValues (json, key, stopAfterIndex, stopAfterValue)
+  return extractAllJsonValues(extractNumberJsonValue, json, key, stopAfterIndex, stopAfterValue)
+end
+
+---@param json string
+---@param key string
+---@param stopAfterIndex number|nil
+---@param stopAfterValue boolean|nil
+---@return boolean[]
+local function extractAllBooleanJsonValues (json, key, stopAfterIndex, stopAfterValue)
+  return extractAllJsonValues(extractBooleanJsonValue, json, key, stopAfterIndex, stopAfterValue)
+end
+
+---@param json string
+---@param key string
+---@return string
+local function deleteAllStringJsonValues (json, key)
+  local pattern = [[%s*"]] .. key .. [["%s*:%s*"[^"]*"%s*,?]]
+  return (gsub(json, pattern, ""))
+end
+
+---@param json string
+---@param key string
+---@return string
+local function deleteAllNumberJsonValues (json, key)
+  local pattern = [[%s*"]] .. key .. [["%s*:%s*-?[0-9.e-]+%s*,?]]
+  return (gsub(json, pattern, ""))
+end
+
+---@param json string
+---@param key string
+---@return string
+local function deleteAllBooleanJsonValue (json, key)
+  local pattern = [[%s*"]] .. key .. [["%s*:%s*[truefals]+%s*,?]]
+  return (gsub(json, pattern, ""))
+end
+
+return {
+  extractStringJsonValue = extractStringJsonValue,
+  extractNumberJsonValue = extractNumberJsonValue,
+  extractBooleanJsonValue = extractBooleanJsonValue,
+
+  extractAllStringJsonValues = extractAllStringJsonValues,
+  extractAllNumberJsonValues = extractAllNumberJsonValues,
+  extractAllBooleanJsonValues = extractAllBooleanJsonValues,
+
+  deleteAllStringJsonValues = deleteAllStringJsonValues,
+  deleteAllNumberJsonValues = deleteAllNumberJsonValues,
+  deleteAllBooleanJsonValue = deleteAllBooleanJsonValue
+}