Begin refactoring gui

This begins a big refactor of moving more code out of the Gui struct into contexts, controllers, and helpers. We also move some code into structs in the
gui package purely for the sake of better encapsulation

pkg/gui/controllers/helpers/diff_helper.go

@@ -0,0 +1,114 @@
+package helpers
+
+import (
+	"fmt"
+
+	"github.com/jesseduffield/lazygit/pkg/gui/context"
+	"github.com/jesseduffield/lazygit/pkg/gui/modes/diffing"
+	"github.com/jesseduffield/lazygit/pkg/gui/types"
+	"github.com/samber/lo"
+)
+
+type DiffHelper struct {
+	c *types.HelperCommon
+}
+
+func NewDiffHelper(c *types.HelperCommon) *DiffHelper {
+	return &DiffHelper{
+		c: c,
+	}
+}
+
+func (self *DiffHelper) DiffStr() string {
+	output := self.c.Modes().Diffing.Ref
+
+	right := self.currentDiffTerminal()
+	if right != "" {
+		output += " " + right
+	}
+
+	if self.c.Modes().Diffing.Reverse {
+		output += " -R"
+	}
+
+	if self.c.State().GetIgnoreWhitespaceInDiffView() {
+		output += " --ignore-all-space"
+	}
+
+	file := self.currentlySelectedFilename()
+	if file != "" {
+		output += " -- " + file
+	} else if self.c.Modes().Filtering.Active() {
+		output += " -- " + self.c.Modes().Filtering.GetPath()
+	}
+
+	return output
+}
+
+func (self *DiffHelper) ExitDiffMode() error {
+	self.c.Modes().Diffing = diffing.New()
+	return self.c.Refresh(types.RefreshOptions{Mode: types.ASYNC})
+}
+
+func (self *DiffHelper) RenderDiff() error {
+	cmdObj := self.c.OS().Cmd.New(
+		fmt.Sprintf("git diff --submodule --no-ext-diff --color %s", self.DiffStr()),
+	)
+	task := types.NewRunPtyTask(cmdObj.GetCmd())
+
+	return self.c.RenderToMainViews(types.RefreshMainOpts{
+		Pair: self.c.MainViewPairs().Normal,
+		Main: &types.ViewUpdateOpts{
+			Title: "Diff",
+			Task:  task,
+		},
+	})
+}
+
+// CurrentDiffTerminals returns the current diff terminals of the currently selected item.
+// in the case of a branch it returns both the branch and it's upstream name,
+// which becomes an option when you bring up the diff menu, but when you're just
+// flicking through branches it will be using the local branch name.
+func (self *DiffHelper) CurrentDiffTerminals() []string {
+	c := self.c.CurrentSideContext()
+
+	if c.GetKey() == "" {
+		return nil
+	}
+
+	switch v := c.(type) {
+	case types.DiffableContext:
+		return v.GetDiffTerminals()
+	}
+
+	return nil
+}
+
+func (self *DiffHelper) currentDiffTerminal() string {
+	names := self.CurrentDiffTerminals()
+	if len(names) == 0 {
+		return ""
+	}
+	return names[0]
+}
+
+func (self *DiffHelper) currentlySelectedFilename() string {
+	currentContext := self.c.CurrentContext()
+
+	switch currentContext := currentContext.(type) {
+	case types.IListContext:
+		if lo.Contains([]types.ContextKey{context.FILES_CONTEXT_KEY, context.COMMIT_FILES_CONTEXT_KEY}, currentContext.GetKey()) {
+			return currentContext.GetSelectedItemId()
+		}
+	}
+
+	return ""
+}
+
+func (self *DiffHelper) WithDiffModeCheck(f func() error) error {
+	if self.c.Modes().Diffing.Active() {
+		return self.RenderDiff()
+	}
+
+	return f()
+}