1 files changed, 156 insertions, 0 deletions
diff --git a/commands/select/select.go b/commands/select/select.go
new file mode 100644
index 00000000..b821ba59
--- /dev/null
+++ b/commands/select/select.go
@@ -0,0 +1,156 @@
+package _select
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+
+	"github.com/pkg/errors"
+
+	"github.com/MichaelMure/git-bug/cache"
+	"github.com/MichaelMure/git-bug/entity"
+)
+
+type ErrNoValidId struct {
+	typename string
+}
+
+func NewErrNoValidId(typename string) *ErrNoValidId {
+	return &ErrNoValidId{typename: typename}
+}
+
+func (e ErrNoValidId) Error() string {
+	return fmt.Sprintf("you must provide a %s id or use the \"select\" command first", e.typename)
+}
+
+func IsErrNoValidId(err error) bool {
+	_, ok := err.(*ErrNoValidId)
+	return ok
+}
+
+type Resolver[CacheT cache.CacheEntity] interface {
+	Resolve(id entity.Id) (CacheT, error)
+	ResolvePrefix(prefix string) (CacheT, error)
+}
+
+// Resolve first try to resolve an entity using the first argument of the command
+// line. If it fails, it falls back to the select mechanism.
+//
+// Returns:
+// - the entity if any
+// - the new list of command line arguments with the entity prefix removed if it
+//   has been used
+// - an error if the process failed
+func Resolve[CacheT cache.CacheEntity](repo *cache.RepoCache,
+	typename string, namespace string, resolver Resolver[CacheT],
+	args []string) (CacheT, []string, error) {
+	// At first, try to use the first argument as an entity prefix
+	if len(args) > 0 {
+		cached, err := resolver.ResolvePrefix(args[0])
+
+		if err == nil {
+			return cached, args[1:], nil
+		}
+
+		if !entity.IsErrNotFound(err) {
+			return *new(CacheT), nil, err
+		}
+	}
+
+	// first arg is not a valid entity prefix, we can safely use the preselected entity if any
+
+	cached, err := selected(repo, resolver, namespace)
+
+	// selected entity is invalid
+	if entity.IsErrNotFound(err) {
+		// we clear the selected bug
+		err = Clear(repo, namespace)
+		if err != nil {
+			return *new(CacheT), nil, err
+		}
+		return *new(CacheT), nil, NewErrNoValidId(typename)
+	}
+
+	// another error when reading the entity
+	if err != nil {
+		return *new(CacheT), nil, err
+	}
+
+	// entity is successfully retrieved
+	if cached != nil {
+		return *cached, args, nil
+	}
+
+	// no selected bug and no valid first argument
+	return *new(CacheT), nil, NewErrNoValidId(typename)
+}
+
+func selectFileName(namespace string) string {
+	return filepath.Join("select", namespace)
+}
+
+// Select will select a bug for future use
+func Select(repo *cache.RepoCache, namespace string, id entity.Id) error {
+	filename := selectFileName(namespace)
+	f, err := repo.LocalStorage().OpenFile(filename, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0666)
+	if err != nil {
+		return err
+	}
+
+	_, err = f.Write([]byte(id.String()))
+	if err != nil {
+		return err
+	}
+
+	return f.Close()
+}
+
+// Clear will clear the selected entity, if any
+func Clear(repo *cache.RepoCache, namespace string) error {
+	filename := selectFileName(namespace)
+	return repo.LocalStorage().Remove(filename)
+}
+
+func selected[CacheT cache.CacheEntity](repo *cache.RepoCache, resolver Resolver[CacheT], namespace string) (*CacheT, error) {
+	filename := selectFileName(namespace)
+	f, err := repo.LocalStorage().Open(filename)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, nil
+		} else {
+			return nil, err
+		}
+	}
+
+	buf, err := ioutil.ReadAll(io.LimitReader(f, 100))
+	if err != nil {
+		return nil, err
+	}
+	if len(buf) == 100 {
+		return nil, fmt.Errorf("the select file should be < 100 bytes")
+	}
+
+	id := entity.Id(buf)
+	if err := id.Validate(); err != nil {
+		err = repo.LocalStorage().Remove(filename)
+		if err != nil {
+			return nil, errors.Wrap(err, "error while removing invalid select file")
+		}
+
+		return nil, fmt.Errorf("select file in invalid, removing it")
+	}
+
+	cached, err := resolver.Resolve(id)
+	if err != nil {
+		return nil, err
+	}
+
+	err = f.Close()
+	if err != nil {
+		return nil, err
+	}
+
+	return &cached, nil
+}