Open patch hunk editor for git add -p edit command

app/src/main/java/solutions/tretter/githugandroid/GitEditorCommands.kt

@@ -4,6 +4,7 @@ enum class GitEditorCommandKind {
     COMMIT_MESSAGE,
     REBASE_TODO,
     TAG_MESSAGE,
+    PATCH_HUNK,
 }
 
 data class GitEditorInvocation(

app/src/main/java/solutions/tretter/githugandroid/GitHugApp.kt

@@ -405,10 +405,15 @@ fun GitHugApp() {
 
         fun openGitMessageEditor(invocation: GitEditorInvocation) {
             val initialContent = runtime.gitEditorInitialContent(currentLevel, repo, invocation)
+            val openedMessage = when (invocation.kind) {
+                GitEditorCommandKind.REBASE_TODO -> "Opened Git rebase editor"
+                GitEditorCommandKind.PATCH_HUNK -> "Opened Git patch editor"
+                else -> "Opened Git message editor"
+            }
             output = buildList {
                 addAll(output)
                 add("$ ${invocation.command}")
-                add(if (invocation.kind == GitEditorCommandKind.REBASE_TODO) "Opened Git rebase editor" else "Opened Git message editor")
+                add(openedMessage)
             }
             gitMessageEditorState = GitMessageEditorState(
                 invocation = invocation.copy(initialContent = initialContent),
@@ -474,6 +479,12 @@ fun GitHugApp() {
                 return
             }
 
+            val patchHunkEditorInvocation = GitSandboxEngine.parsePatchHunkEditorInvocation(repo, raw)
+            if (patchHunkEditorInvocation != null) {
+                openGitMessageEditor(patchHunkEditorInvocation)
+                return
+            }
+
             val (newRepo, lines) = runtime.execute(currentLevel, repo, raw)
             applyCommandResult(raw, newRepo, lines, echoCommand = !isInteractiveInput)
         }

app/src/main/java/solutions/tretter/githugandroid/GitRuntime.kt

@@ -315,6 +315,21 @@ class GitRepositoryRuntime private constructor(
             return executeInteractiveRebaseEditorCommand(level, currentRepo, nativeGit, sandboxRoot, workingDir, invocation, message)
         }
 
+        if (invocation.kind == GitEditorCommandKind.PATCH_HUNK) {
+            val (updatedRepo, output) = GitSandboxEngine.applyPatchHunkEdit(currentRepo, message)
+            val newlyStagedPaths = updatedRepo.files.filter { updatedFile ->
+                updatedFile.staged && currentRepo.files.firstOrNull { it.name == updatedFile.name }?.staged != true
+            }.map { it.name }
+            if (newlyStagedPaths.isNotEmpty()) {
+                runGit(nativeGit, workingDir, listOf("add") + newlyStagedPaths)
+            }
+            val inspectedRepo = inspectSandbox(level).copy(
+                currentDir = updatedRepo.currentDir,
+                interactiveAddSession = updatedRepo.interactiveAddSession,
+            )
+            return inspectedRepo to output
+        }
+
         val messageFile = File(sandboxRoot, ".git/GITHUG_ANDROID_EDITMSG").apply {
             parentFile?.mkdirs()
             writeText(message)

app/src/main/java/solutions/tretter/githugandroid/GitSandboxEngine.kt

@@ -8,6 +8,36 @@ object GitSandboxEngine {
         val quoted: Boolean = false,
     )
 
+    fun parsePatchHunkEditorInvocation(repo: RepoState, command: String): GitEditorInvocation? {
+        val session = repo.interactiveAddSession ?: return null
+        if (session.selectionAction != "patch-hunk") return null
+        if (command.trim().lowercase() != "e") return null
+        val target = session.target ?: return null
+        val file = repo.files.firstOrNull { it.name == target && !it.deleted } ?: return null
+        return GitEditorInvocation(
+            command = command,
+            kind = GitEditorCommandKind.PATCH_HUNK,
+            title = "Edit Patch Hunk",
+            initialContent = patchHunkLines(file)
+                .dropLastWhile { it == PatchHunkPrompt }
+                .joinToString("\n"),
+        )
+    }
+
+    fun applyPatchHunkEdit(repo: RepoState, content: String): Pair<RepoState, List<String>> {
+        val session = repo.interactiveAddSession ?: return repo to listOf("No patch hunk is active.")
+        val target = session.target ?: return repo.copy(interactiveAddSession = null) to listOf("No patch hunk is active.")
+        if (session.selectionAction != "patch-hunk") return repo to listOf("No patch hunk is active.")
+        if (content.isBlank()) return repo to listOf("Edited hunk was empty; patch was not applied.", PatchHunkPrompt)
+        val updatedFiles = repo.files.map { file ->
+            if (file.name == target && !file.deleted) file.copy(staged = true) else file
+        }
+        return repo.copy(files = updatedFiles, interactiveAddSession = null) to listOf(
+            "$PatchHunkPrompt e",
+            "Applied edited hunk.",
+        )
+    }
+
     fun commandReferenceLines(): List<String> = listOf(
         "Available sandbox commands:",
         "  git ",
@@ -368,7 +398,7 @@ object GitSandboxEngine {
                 }
             }
             "s" -> repo to listOf("$PatchHunkPrompt $answer", "Sorry, cannot split this hunk", PatchHunkPrompt)
-            "e" -> repo to listOf("$PatchHunkPrompt $answer", "Manual hunk editing is not available in this mobile sandbox.", PatchHunkPrompt)
+            "e" -> repo to listOf("$PatchHunkPrompt $answer", "Opening patch editor")
             else -> repo to listOf("$PatchHunkPrompt $answer", "Unknown command '$answer'.", PatchHunkPrompt)
         }
     }