1 files changed, 112 insertions, 0 deletions
diff --git a/command.go b/command.go
new file mode 100644
index 0000000..7d36ce0
--- /dev/null
+++ b/command.go
@@ -0,0 +1,112 @@
+package main
+
+// handle the command infrastructure
+
+import (
+  "fmt"
+  "flag"
+  "os"
+)
+
+type (
+  Command struct {
+    Use   string // command name (used for matching)
+    Short string // a short description  to display
+    Long  string // a long help text
+    Example string // an example string
+    Run   func(*Command, []string)
+
+    flagSet *flag.FlagSet
+    commands []*Command
+  }
+)
+
+func (c *Command) AddCommand(cmds... *Command) {
+  res := c.commands
+  for _, cmd := range cmds {
+    res = append(res, cmd)
+  }
+  c.commands = res
+}
+
+func (c *Command) eval(args []string) error {
+  var name string = ""
+  var rest []string = []string{}
+
+  if len(args) > 0 {
+    name = args[0]
+  }
+  if len(args) > 1 {
+    rest = args[1:]
+  }
+
+  if name == "help" {
+    c.Help(rest)
+    return nil
+  }
+
+  for _, cmd := range c.commands {
+    if cmd.Use == name {
+      return cmd.eval(rest)
+    }
+  }
+  if err := c.Flags().Parse(rest); err != nil { return err }
+  if c.Run != nil {
+    c.Run(c, rest)
+  } else {
+    c.Help(rest)
+  }
+  return nil
+}
+
+func (c *Command) Execute() error {
+  return c.eval(os.Args[1:])
+}
+
+func (c *Command) Flags() *flag.FlagSet {
+  if c.flagSet == nil { c.flagSet = flag.NewFlagSet(c.Use, flag.ContinueOnError) }
+  return c.flagSet
+}
+
+func (c *Command) Help(args []string) {
+  if len(args) > 0 {
+    for _, cmd := range c.commands {
+      if args[0] == cmd.Use {
+        cmd.Help([]string{})
+        return
+      }
+    }
+  }
+  if c.Long != "" { fmt.Println(c.Long, "\n") }
+  c.Usage()
+}
+
+func (c *Command) Usage() {
+  usage := ""
+  if c.Use != "" {
+    usage = usage + " " + c.Use
+  }
+  if len(c.commands) > 0 {
+    usage = usage + " command"
+  }
+  if c.flagSet != nil {
+    usage = usage + " [flags]"
+  }
+  fmt.Printf("Usage: %s%s\n", os.Args[0], usage)
+
+  if len(c.commands) > 0 {
+    fmt.Printf("\nwhere command is one of:\n")
+    for _, cmd := range c.commands {
+      fmt.Printf("\t%s\t\t%s\n", cmd.Use, cmd.Short)
+    }
+  }
+  if c.flagSet != nil {
+    fmt.Printf("\nwhere flags is any of:\n")
+    c.Flags().SetOutput(os.Stdout)
+    c.Flags().PrintDefaults()
+  }
+  if c.Example != "" {
+    fmt.Println("\nexample:")
+    fmt.Printf("\t%s\n", c.Example)
+  }
+}