Add command package

pkg/cli/command/command.go

@@ -0,0 +1,274 @@
+package command
+
+import (
+	"os"
+	"strings"
+
+	"github.com/dnote/dnote/pkg/cli/log"
+	"github.com/pkg/errors"
+
+	flag "github.com/spf13/pflag"
+)
+
+type Command struct {
+	// Name is the name of the command. This is used to find the subcommand
+	// and is case sensitive.
+	Name string
+
+	// flags is a FlagSet which can parse and hold flags and their values.
+	flags *flag.FlagSet
+
+	// args is a list of arments
+	args []string
+
+	// RunE is a function that contains the logic for the command
+	RunE func(cmd *Command, args []string) error
+
+	// commands is the list of subcommands that this command has.
+	commands []*Command
+
+	// Parent is a pointer to the parent command, if any, of which the command
+	// is a subcommand.
+	Parent *Command
+
+	Use           string
+	Short         string
+	SilenceErrors bool
+	SilenceUsage  bool
+	Example       string
+	Aliases       []string
+	PreRunE       func(cmd *Command, args []string) error
+	Deprecated    string
+	Long          string
+	Run           func(cmd *Command, args []string)
+}
+
+// Flags returns a flag set for the command. If not initialized yet, it initializes
+// one and returns the result.
+func (c *Command) Flags() *flag.FlagSet {
+	if c.flags == nil {
+		c.flags = flag.NewFlagSet(c.Name, flag.ContinueOnError)
+	}
+
+	return c.flags
+}
+
+// ParseFlags parses the given slice of arguments using the flag set of the command.
+func (c *Command) ParseFlags(args []string) error {
+	err := c.Flags().Parse(args)
+	if err != nil {
+		return errors.Wrap(err, "Error parsing flags")
+	}
+
+	return nil
+}
+
+// Root returns the root command of the given command.
+func (c *Command) Root() *Command {
+	if c.Parent != nil {
+		return c.Parent.Root()
+	}
+
+	return c
+}
+
+// flagHasDefaultOption checks whether the given flag has a default value
+// in the given flag set.
+func flagHasDefaultOption(flag *flag.Flag, flagSet *flag.FlagSet) bool {
+	if flag == nil {
+		return false
+	}
+
+	return flag.NoOptDefVal != ""
+}
+
+// isFlagWithAdditionalArg checks whether the given string represents a flag
+// which is followed by an argument. For instance, suppose that there is no
+// default value for a flag "--flag". Then, given "--flag", this function returns
+// true because "--flag" must be followed by an argument. Similar logic applies to
+// a short-hand flag using a single dash. (e.g. "-f")
+func isFlagWithAdditionalArg(flagStr string, flagSet *flag.FlagSet) bool {
+	// --flag arg
+	if strings.HasPrefix(flagStr, "--") && !strings.Contains(flagStr, "=") {
+		flagKey := flagStr[2:]
+		flag := flagSet.Lookup(flagKey)
+
+		return !flagHasDefaultOption(flag, flagSet)
+	}
+
+	// -f arg
+	if strings.HasPrefix(flagStr, "-") && !strings.Contains(flagStr, "=") && len(flagStr) == 2 {
+		flagKey := flagStr[1:]
+		flag := flagSet.ShorthandLookup(flagKey)
+
+		return !flagHasDefaultOption(flag, flagSet)
+	}
+
+	return false
+}
+
+// filterFlags removes flags and their values from the given arguments. It returns
+// a filtered slice which contains only non-flag arguments.
+func filterFlags(args []string, c *Command) []string {
+	ret := []string{}
+	flags := c.Flags()
+
+	idx := 0
+
+	for idx < len(args) {
+		currentArg := args[idx]
+
+		// "--" signifies the end of command line flags
+		if currentArg == "--" {
+			ret = append(ret, args[idx+1:]...)
+			break
+		}
+
+		if isFlagWithAdditionalArg(currentArg, flags) {
+			idx = idx + 2
+			continue
+		}
+
+		if currentArg != "" && !strings.HasPrefix(currentArg, "-") {
+			ret = append(ret, currentArg)
+		}
+
+		idx = idx + 1
+	}
+
+	return ret
+}
+
+// setArgs sets the arguments for the command. It is useful while writing tests.
+func (c *Command) setArgs(args []string) {
+	c.args = args
+}
+
+// Args returns the argument for the command. By default, os.Args[1:] is used.
+func (c *Command) Args() []string {
+	args := c.args
+	if c.args == nil {
+		args = os.Args[1:]
+	}
+
+	return args
+
+}
+
+// Execute runs the root command. It is meant to be called on the root command.
+func (c *Command) Execute() error {
+	// Call Execute on the root command
+	if c.Parent != nil {
+		return c.Root().Execute()
+	}
+
+	args := c.Args()
+	log.Debug("root command received arguments: %s\n", args)
+
+	cmd, flags := c.findSubCommand(args)
+	if cmd == nil {
+		// not found. show suggestion
+		return nil
+	}
+
+	cmd.execute(flags)
+
+	return nil
+}
+
+// execute runs the command.
+func (c *Command) execute(args []string) error {
+	log.Debug("command '%s' called with arguments: %s\n", c.Name, args)
+
+	if err := c.ParseFlags(args); err != nil {
+		return err
+	}
+
+	nonFlagArgs := c.Flags().Args()
+	log.Debug("command '%s' called with non-flag arguments: %s\n", c.Name, nonFlagArgs)
+
+	if err := c.RunE(c, nonFlagArgs); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// hasAlias checks whether the command has the given alias.
+func (c *Command) hasAlias(targetAlias string) bool {
+	for _, alias := range c.Aliases {
+		if alias == targetAlias {
+			return true
+		}
+	}
+
+	return false
+}
+
+// findSubCommand finds and returns an appropriate subcommand to be called, based
+// on the given slice of arguments. It also returns a slice of arguments with which
+// the subcommand should be called.
+func (c *Command) findSubCommand(args []string) (*Command, []string) {
+	nonFlagArgs := filterFlags(args, c)
+	log.Debug("non-flag arguments: %s\n", nonFlagArgs)
+
+	subCommand := nonFlagArgs[0]
+	log.Debug("sub-command: '%s'\n", subCommand)
+
+	for _, cmd := range c.commands {
+		if cmd.Name == subCommand || cmd.hasAlias(subCommand) {
+			return cmd, c.argsWithout(args, subCommand)
+		}
+	}
+
+	return nil, []string{}
+}
+
+// argsWithout removes the fist non-flag occurrence of the given key in the
+// given slice of arguments. It does not modify the given slice.
+func (c *Command) argsWithout(args []string, key string) []string {
+	flags := c.Flags()
+
+	idx := -1
+	pos := 0
+
+	for pos < len(args) {
+		currentArg := args[pos]
+
+		// "--" signifies the end of command line flags
+		if currentArg == "--" {
+			break
+		}
+
+		if isFlagWithAdditionalArg(currentArg, flags) {
+			pos = pos + 2
+			continue
+		}
+
+		if !strings.HasPrefix(currentArg, "-") {
+			if currentArg == key {
+				idx = pos
+				break
+			}
+		}
+
+		pos = pos + 1
+	}
+
+	if idx == -1 {
+		return args
+	}
+
+	ret := []string{}
+	ret = append(ret, args[:pos]...)
+	ret = append(ret, args[pos+1:]...)
+
+	return ret
+}
+
+// AddCommand adds the given command as a subcommand.
+func (c *Command) AddCommand(cmd *Command) {
+	cmd.Parent = c
+
+	c.commands = append(c.commands, cmd)
+}