doc: improve documentation and fix sonar issue

Author: devnied

README.md

@@ -11,17 +11,21 @@ With the Snowflake plugin, you can visualize your Snowflake data in Grafana and
 #### Install the Data Source
 
 1. Install the plugin into the grafana plugin folder:
+
+**With grafana-cli**
 ```shell
-grafana-cli --pluginUrl https://github.com/michelin/snowflake-grafana-datasource/releases/latest/download/snowflake-grafana-datasource.zip plugins install michelin-snowflake-datasource
+grafana cli --pluginUrl https://github.com/michelin/snowflake-grafana-datasource/releases/latest/download/snowflake-grafana-datasource.zip plugins install michelin-snowflake-datasource
 ```
-or
+`--pluginsDir` option can be used to specify a custom plugin directory
+
+**Manually**
 ```shell
 cd /var/lib/grafana/plugins/
 wget https://github.com/michelin/snowflake-grafana-datasource/releases/latest/download/snowflake-grafana-datasource.zip
 unzip snowflake-grafana-datasource.zip
 ```
 
-2. Edit the grafana configuration file to allow unsigned plugins:
+2. Edit the grafana configuration file `grafana.ini` to allow unsigned plugins:
 * Linux：/etc/grafana/grafana.ini
 * macOS：/usr/local/etc/grafana/grafana.ini
 ```shell
@@ -187,6 +191,12 @@ More info about snowflake-side caching: https://docs.snowflake.com/en/user-guide
 
 The snowflake datasource is a data source backend plugin composed of both frontend and backend components.
 
+To build the project you must have the following tools installed:
+* Go
+* Node
+* yarn
+
+
 ### Frontend
 
 1. Install dependencies

pkg/macros.go

@@ -11,6 +11,7 @@ import (
 
 const rsIdentifier = `([_a-zA-Z0-9]+)`
 const sExpr = `\$` + rsIdentifier + `\(([^\)]*)\)`
+const missingColumnMessage = "missing time column argument for macro %v"
 
 func ReplaceAllStringSubmatchFunc(re *regexp.Regexp, str string, repl func([]string) string) string {
 	result := ""
@@ -78,20 +79,21 @@ func SetupFillmode(configStruct *queryConfigStruct, fillmode string) error {
 // evaluateMacro convert macro expression to sql expression
 func evaluateMacro(name string, args []string, configStruct *queryConfigStruct) (string, error) {
 	timeRange := configStruct.TimeRange
+
 	switch name {
 	case "__time":
 		if len(args) == 0 || args[0] == "" {
-			return "", fmt.Errorf("missing time column argument for macro %v", name)
+			return "", fmt.Errorf(missingColumnMessage, name)
 		}
 		return fmt.Sprintf("TRY_TO_TIMESTAMP_NTZ(%s) AS time", args[0]), nil
 	case "__timeEpoch":
 		if len(args) == 0 || args[0] == "" {
-			return "", fmt.Errorf("missing time column argument for macro %v", name)
+			return "", fmt.Errorf(missingColumnMessage, name)
 		}
 		return fmt.Sprintf("extract(epoch from %s) as time", args[0]), nil
 	case "__timeFilter":
 		if len(args) == 0 || args[0] == "" {
-			return "", fmt.Errorf("missing time column argument for macro %v", name)
+			return "", fmt.Errorf(missingColumnMessage, name)
 		}
 		column := args[0]
 		timezone := "'UTC'"
@@ -101,7 +103,7 @@ func evaluateMacro(name string, args []string, configStruct *queryConfigStruct)
 		return fmt.Sprintf("%s > CONVERT_TIMEZONE('UTC', %s, '%s'::timestamp_ntz) AND %s < CONVERT_TIMEZONE('UTC', %s, '%s'::timestamp_ntz)", column, timezone, timeRange.From.UTC().Format(time.RFC3339Nano), column, timezone, timeRange.To.UTC().Format(time.RFC3339Nano)), nil
 	case "__timeTzFilter":
 		if len(args) == 0 || args[0] == "" {
-			return "", fmt.Errorf("missing time column argument for macro %v", name)
+			return "", fmt.Errorf(missingColumnMessage, name)
 		}
 		column := args[0]
 		return fmt.Sprintf("%s > '%s'::timestamp_tz AND %s < '%s'::timestamp_tz", column, timeRange.From.UTC().Format(time.RFC3339Nano), column, timeRange.To.UTC().Format(time.RFC3339Nano)), nil
@@ -164,12 +166,12 @@ func evaluateMacro(name string, args []string, configStruct *queryConfigStruct)
 		return "", err
 	case "__unixEpochFilter":
 		if len(args) == 0 || args[0] == "" {
-			return "", fmt.Errorf("missing time column argument for macro %v", name)
+			return "", fmt.Errorf(missingColumnMessage, name)
 		}
 		return fmt.Sprintf("%s >= %d AND %s <= %d", args[0], timeRange.From.UTC().Unix(), args[0], timeRange.To.UTC().Unix()), nil
 	case "__unixEpochNanoFilter":
 		if len(args) == 0 || args[0] == "" {
-			return "", fmt.Errorf("missing time column argument for macro %v", name)
+			return "", fmt.Errorf(missingColumnMessage, name)
 		}
 		return fmt.Sprintf("%s >= %d AND %s <= %d", args[0], timeRange.From.UTC().UnixNano(), args[0], timeRange.To.UTC().UnixNano()), nil
 	case "__unixEpochNanoFrom":