Initial support for CLI commands

README.md

@@ -1,7 +1,8 @@
 # configstruct
-Simple Go module to parse a configuration from environment and cli flags using struct tags.
+Simple Go module to parse a configuration from environment values and CLI flags using struct tags.
+Starting with v1.3.0 there there is also support for CLI commands and subcommands
 
-Usage
+## Usage without commands
 ```Go
 // define a struct with tags for env name, cli flag and usage
 type Config struct {
@@ -33,7 +34,49 @@ if err != nil {...}
 port := conf.Port
 host := conf.Hostname
 if conf.Debug {...}
+```
 
+## Usage with commands
+The program with global flags and a command `count` should be called like this:
+````bash
+mycmd -hostname localhost count -number 2
 
+```` 
 
-```
+This is the code to model this behaviour:
+
+```Go
+// define a struct with tags for env name, cli flag and usage
+type RootConfig struct {
+	Hostname string `env:"CONFIGSTRUCT_HOSTNAME" cli:"hostname" usage:"hostname value"`
+	Debug    bool   `env:"CONFIGSTRUCT_DEBUG" cli:"debug" usage:"debug mode"`
+}
+
+type CountConfig struct {
+    Number int `cli:"number" usage:"number to count"`
+} 
+
+// create a variable of the struct type and define defaults if needed
+rootCfg := RootConfig{
+    Hostname: "localhost",
+    Debug:    true,
+}
+
+countCfg := CountConfig {
+    Number: 1
+}
+
+countCmd := NewCommand("count", &subConfig, func(cfg interface{}) error {
+    cfgValues := cfg.(*CountConfig)
+    ...
+    return nil
+})
+
+cmd := NewCommand("", &rootCfg, func(cfg interface{}) error {
+    cfgValues := cfg.(*RootConfig)
+    ...
+    return nil
+}, subCmd)
+
+err := cmd.ParseAndRun(os.Args)
+```

commands.go

@@ -0,0 +1,56 @@
+package configstruct
+
+import (
+	"flag"
+	"strings"
+)
+
+// Command defines a command that consists of a name (empty for root command), a struct that models all
+// flags, a function that is executed if the command matches and that gets the config struct as argument
+// several sub-commands can be added
+type Command struct {
+	fs          *flag.FlagSet
+	config      interface{}
+	f           func(cfg interface{}) error
+	subCommands []*Command
+}
+
+// NewCommand creates a command that is triggered by the given name in the command line
+// all flags are defined by a struct that is parsed and filled with real values
+// this struct is then set as argument for the function that is executed if the name matches
+func NewCommand(name string, config interface{}, f func(cfg interface{}) error, subCommands ...*Command) *Command {
+	fs := flag.NewFlagSet(name, flag.ExitOnError)
+
+	return &Command{
+		fs:          fs,
+		config:      config,
+		f:           f,
+		subCommands: subCommands,
+	}
+}
+
+// ParseAndRun parses the given arguments and executes command functions
+func (c *Command) ParseAndRun(args []string, opts ...Option) error {
+	err := ParseWithFlagSet(c.fs, args, c.config, opts...)
+	if err != nil {
+		return err
+	}
+
+	if c.fs.Name() == "" || strings.EqualFold(c.fs.Name(), args[0]) {
+		err := c.f(c.config)
+		if err != nil {
+			return err
+		}
+	}
+
+	args = c.fs.Args()
+	if len(args) > 0 {
+		for i := range c.subCommands {
+			if strings.EqualFold(c.subCommands[i].fs.Name(), args[0]) {
+				c.subCommands[i].ParseAndRun(args)
+			}
+		}
+	}
+
+	return nil
+}

commands_test.go

@@ -0,0 +1,40 @@
+package configstruct
+
+import (
+	"testing"
+)
+
+type rootCmdConfig struct {
+	Hostname   string  `env:"CONFIGSTRUCT_HOSTNAME" cli:"hostname" usage:"hostname value"`
+	Port       int     `env:"CONFIGSTRUCT_PORT" cli:"port" usage:"listen port"`
+	Debug      bool    `env:"CONFIGSTRUCT_DEBUG" cli:"debug" usage:"debug mode"`
+	FloatValue float64 `env:"CONFIGSTRUCT_FLOAT" cli:"floatValue" usage:"float value"`
+}
+
+type subCmdConfig struct {
+	Number int `cli:"number" usage:"number to count"`
+}
+
+func TestCommand_ParseAndRun(t *testing.T) {
+	args := []string{"cliName", "-hostname", "localhost", "count", "-number", "2"}
+
+	var rootConfig rootCmdConfig
+	var subConfig subCmdConfig
+
+	subCmd := NewCommand("count", &subConfig, func(cfg interface{}) error {
+		cfgValues := cfg.(*subCmdConfig)
+		t.Log("sub command", cfgValues.Number)
+		return nil
+	})
+
+	cmd := NewCommand("", &rootConfig, func(cfg interface{}) error {
+		cfgValues := cfg.(*rootCmdConfig)
+		t.Log("root command", cfgValues.Hostname)
+		return nil
+	}, subCmd)
+
+	err := cmd.ParseAndRun(args)
+	if err != nil {
+		t.Errorf("error should be nil but is %v", err)
+	}
+}