From 92fb6e5161e7b73f2fafc17ecdf4b716278a2e8c Mon Sep 17 00:00:00 2001
From: Qi Xiao <xiaqqaix@gmail.com>
Date: Fri, 26 Feb 2016 04:05:47 +0100
Subject: [PATCH] Support shared variable.

This fixes #15. Only string is supported ATM.
---
 eval/eval.go            |  7 +++++++
 eval/shared.go          | 19 +++++++++++++++++
 store/sharedVar.go      | 35 ++++++++++++++++++++++++++++++++
 store/sharedVar_test.go | 45 +++++++++++++++++++++++++++++++++++++++++
 4 files changed, 106 insertions(+)
 create mode 100644 eval/shared.go
 create mode 100644 store/sharedVar.go
 create mode 100644 store/sharedVar_test.go

diff --git a/eval/eval.go b/eval/eval.go
index a2257237..dfdbe59d 100644
--- a/eval/eval.go
+++ b/eval/eval.go
@@ -349,6 +349,8 @@ func (ev *Evaler) Global() Namespace {
 	return map[string]Variable(ev.global)
 }
 
+var ErrStoreUnconnected = errors.New("store unconnected")
+
 // ResolveVar resolves a variable. When the variable cannot be found, nil is
 // returned.
 func (ec *EvalCtx) ResolveVar(ns, name string) Variable {
@@ -372,6 +374,11 @@ func (ec *EvalCtx) ResolveVar(ns, name string) Variable {
 			return NewRoVariable(ExternalCmd{name[len(FnPrefix):]})
 		}
 		return envVariable{name}
+	case "shared":
+		if ec.store == nil {
+			throw(ErrStoreUnconnected)
+		}
+		return sharedVariable{ec.store, name}
 	default:
 		use(ec, ns, nil)
 		return ec.modules[ns][name]
diff --git a/eval/shared.go b/eval/shared.go
new file mode 100644
index 00000000..659001a2
--- /dev/null
+++ b/eval/shared.go
@@ -0,0 +1,19 @@
+package eval
+
+import "github.com/elves/elvish/store"
+
+type sharedVariable struct {
+	store *store.Store
+	name  string
+}
+
+func (sv sharedVariable) Set(val Value) {
+	err := sv.store.SetSharedVar(sv.name, ToString(val))
+	maybeThrow(err)
+}
+
+func (sv sharedVariable) Get() Value {
+	value, err := sv.store.GetSharedVar(sv.name)
+	maybeThrow(err)
+	return String(value)
+}
diff --git a/store/sharedVar.go b/store/sharedVar.go
new file mode 100644
index 00000000..a8adf549
--- /dev/null
+++ b/store/sharedVar.go
@@ -0,0 +1,35 @@
+package store
+
+import (
+	"database/sql"
+	"errors"
+)
+
+var ErrNoVar = errors.New("no such variable")
+
+func init() {
+	initTable["shared"] = func(db *sql.DB) error {
+		_, err := db.Exec(`create table if not exists shared_var (name text unique primary key, value text)`)
+		return err
+	}
+}
+
+func (s *Store) GetSharedVar(n string) (string, error) {
+	row := s.db.QueryRow(`select value from shared_var where name = ?`, n)
+	var value string
+	err := row.Scan(&value)
+	if err == sql.ErrNoRows {
+		err = ErrNoVar
+	}
+	return value, err
+}
+
+func (s *Store) SetSharedVar(n, v string) error {
+	_, err := s.db.Exec(`insert or replace into shared_var (name, value) values (?, ?)`, n, v)
+	return err
+}
+
+func (s *Store) DelSharedVar(n string) error {
+	_, err := s.db.Exec(`delete from shared_var where name = ?`, n)
+	return err
+}
diff --git a/store/sharedVar_test.go b/store/sharedVar_test.go
new file mode 100644
index 00000000..7079973b
--- /dev/null
+++ b/store/sharedVar_test.go
@@ -0,0 +1,45 @@
+package store
+
+import "testing"
+
+func TestSharedVar(t *testing.T) {
+	varname := "foo"
+	value1 := "lorem ipsum"
+	value2 := "o mores, o tempora"
+
+	// Getting an nonexistent variable should return ErrNoVar.
+	_, err := tStore.GetSharedVar(varname)
+	if err != ErrNoVar {
+		t.Error("want ErrNoVar, got", err)
+	}
+
+	// Setting a variable for the first time creates it.
+	err = tStore.SetSharedVar(varname, value1)
+	if err != nil {
+		t.Error("want no error, got", err)
+	}
+	v, err := tStore.GetSharedVar(varname)
+	if v != value1 || err != nil {
+		t.Errorf("want %q and no error, got %q and %v", value1, v, err)
+	}
+
+	// Setting an existing variable updates its value.
+	err = tStore.SetSharedVar(varname, value2)
+	if err != nil {
+		t.Error("want no error, got", err)
+	}
+	v, err = tStore.GetSharedVar(varname)
+	if v != value2 || err != nil {
+		t.Errorf("want %q and no error, got %q and %v", value2, v, err)
+	}
+
+	// After deleting a variable, access to it cause ErrNoVar.
+	err = tStore.DelSharedVar(varname)
+	if err != nil {
+		t.Error("want no error, got", err)
+	}
+	_, err = tStore.GetSharedVar(varname)
+	if err != ErrNoVar {
+		t.Error("want ErrNoVar, got", err)
+	}
+}