split configuration parsing out into separate packages, split api out as well

1 files changed, 52 insertions, 0 deletions

diff --git a/srv/cfg/cfg.go b/srv/cfg/cfg.go
new file mode 100644
index 0000000..08a9e53
--- /dev/null
+++ b/srv/cfg/cfg.go
@@ -0,0 +1,52 @@
+// Package cfg implements a simple wrapper around go's flag package, in order to
+// implement initialization hooks.
+package cfg
+
+import (
+	"context"
+	"flag"
+	"os"
+)
+
+// Cfger is a component which can be used with Cfg to setup its initialization.
+type Cfger interface {
+	SetupCfg(*Cfg)
+}
+
+// Cfg is a wrapper around the stdlib's FlagSet and a set of initialization
+// hooks.
+type Cfg struct {
+	*flag.FlagSet
+
+	hooks []func(ctx context.Context) error
+}
+
+// New initializes and returns a new instance of *Cfg.
+func New() *Cfg {
+	return &Cfg{
+		FlagSet: flag.NewFlagSet("", flag.ExitOnError),
+	}
+}
+
+// OnInit appends the given callback to the sequence of hooks which will run on
+// a call to Init.
+func (c *Cfg) OnInit(cb func(context.Context) error) {
+	c.hooks = append(c.hooks, cb)
+}
+
+// Init runs all hooks registered using OnInit, in the same order OnInit was
+// called. If one returns an error that error is returned and no further hooks
+// are run.
+func (c *Cfg) Init(ctx context.Context) error {
+	if err := c.FlagSet.Parse(os.Args[1:]); err != nil {
+		return err
+	}
+
+	for _, h := range c.hooks {
+		if err := h(ctx); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}