From 6c055d0255c16ccfe0fc2ced5780ede9df8d6c80 Mon Sep 17 00:00:00 2001
From: Brian Picciano <mediocregopher@gmail.com>
Date: Sun, 28 Oct 2018 15:59:49 -0400
Subject: [PATCH] m: WIP on moving the child logic out of mcfg.Cfg and into
 contexts

---
 m/ctx.go      | 73 +++++++++++++++++++++++++++++++++++++++++++++++++++
 m/ctx_test.go | 39 +++++++++++++++++++++++++++
 m/m.go        |  5 ++--
 3 files changed, 115 insertions(+), 2 deletions(-)
 create mode 100644 m/ctx.go
 create mode 100644 m/ctx_test.go

diff --git a/m/ctx.go b/m/ctx.go
new file mode 100644
index 0000000..279e232
--- /dev/null
+++ b/m/ctx.go
@@ -0,0 +1,73 @@
+package m
+
+import (
+	"context"
+	"sync"
+)
+
+type ctxKey int
+
+const (
+	ctxStateKey ctxKey = iota
+)
+
+type ctxState struct {
+	path     []string
+	l        sync.RWMutex
+	children map[string]context.Context
+}
+
+func newCtxState() *ctxState {
+	return &ctxState{
+		children: map[string]context.Context{},
+	}
+}
+
+// Ctx returns a new context which can be used as the root context for all
+// purposes in this framework.
+func Ctx() context.Context {
+	return context.WithValue(context.Background(), ctxStateKey, newCtxState())
+}
+
+func getCtxState(ctx context.Context) *ctxState {
+	s, _ := ctx.Value(ctxStateKey).(*ctxState)
+	if s == nil {
+		panic("non-conforming context used")
+	}
+	return s
+}
+
+// Path returns the sequence of names which were used to produce this context
+// via the ChildOf function.
+func Path(ctx context.Context) []string {
+	return getCtxState(ctx).path
+}
+
+// Children returns all children of this context which have been created by
+// ChildOf, mapped by their name.
+func Children(ctx context.Context) map[string]context.Context {
+	s := getCtxState(ctx)
+	out := map[string]context.Context{}
+	s.l.RLock()
+	defer s.l.RUnlock()
+	for name, childCtx := range s.children {
+		out[name] = childCtx
+	}
+	return out
+}
+
+// ChildOf creates a child of the given context with the given name and returns
+// it. The Path of the returned context will be the path of the parent with its
+// name appended to it. The Children function can be called on the parent to
+// retrieve all children which have been made using this function.
+func ChildOf(ctx context.Context, name string) context.Context {
+	s, childS := getCtxState(ctx), newCtxState()
+	s.l.Lock()
+	defer s.l.Unlock()
+	childS.path = make([]string, 0, len(s.path)+1)
+	childS.path = append(childS.path, s.path...)
+	childS.path = append(childS.path, name)
+	childCtx := context.WithValue(ctx, ctxStateKey, childS)
+	s.children[name] = childCtx
+	return childCtx
+}
diff --git a/m/ctx_test.go b/m/ctx_test.go
new file mode 100644
index 0000000..19b5d69
--- /dev/null
+++ b/m/ctx_test.go
@@ -0,0 +1,39 @@
+package m
+
+import (
+	"context"
+	. "testing"
+
+	"github.com/mediocregopher/mediocre-go-lib/mtest/massert"
+)
+
+func TestContext(t *T) {
+	ctx := Ctx()
+	ctx1 := ChildOf(ctx, "1")
+	ctx1a := ChildOf(ctx1, "a")
+	ctx1b := ChildOf(ctx1, "b")
+	ctx2 := ChildOf(ctx, "2")
+
+	massert.Fatal(t, massert.All(
+		massert.Len(Path(ctx), 0),
+		massert.Equal(Path(ctx1), []string{"1"}),
+		massert.Equal(Path(ctx1a), []string{"1", "a"}),
+		massert.Equal(Path(ctx1b), []string{"1", "b"}),
+		massert.Equal(Path(ctx2), []string{"2"}),
+	))
+
+	massert.Fatal(t, massert.All(
+		massert.Equal(
+			map[string]context.Context{"1": ctx1, "2": ctx2},
+			Children(ctx),
+		),
+		massert.Equal(
+			map[string]context.Context{"a": ctx1a, "b": ctx1b},
+			Children(ctx1),
+		),
+		massert.Equal(
+			map[string]context.Context{},
+			Children(ctx2),
+		),
+	))
+}
diff --git a/m/m.go b/m/m.go
index e52ad2d..fbe6ef0 100644
--- a/m/m.go
+++ b/m/m.go
@@ -36,12 +36,13 @@ func CfgSource() mcfg.Source {
 // If the cfg is nil then mlog.DefaultLogger is returned.
 func Log(cfg *mcfg.Cfg, kvs ...mlog.KVer) *mlog.Logger {
 	fn := cfg.FullName()
-	l := mlog.DefaultLogger.WithWriteFn(func(w io.Writer, msg mlog.Message) error {
+	l := mlog.DefaultLogger.Clone()
+	l.SetWriteFn(func(w io.Writer, msg mlog.Message) error {
 		msg.Msg = "(" + fn + ") " + msg.Msg
 		return mlog.DefaultWriteFn(w, msg)
 	})
 	if len(kvs) > 0 {
-		l = l.WithKV(kvs...)
+		l.AddKV(kvs...)
 	}
 	return l
 }