feat(chat): interactive diff view for file edit and patch tool output (#738) (#741)

* feat(chat): interactive diff view for patch and file edit tool output

* fix(chat): address agy review feedback for diff viewer UX and layout

* fix(chat): suppress raw text/json when diff view renders and fix sync message ordering race (#741)

* fix(tests): resolve nullable smart-cast errors in ToolBubbleParsingTest

---------

Co-authored-by: M57 <hy4ri@users.noreply.github.com>

app/src/main/java/com/m57/hermescontrol/theme/Color.kt

@@ -98,3 +98,11 @@ val CodeTerminalBg = Color(0xFF1E1E1E)
 val CodeTerminalBorder = Color(0xFF333333)
 val CodeTerminalText = Color(0xFFD4D4D4)
 val CodeTerminalMuted = Color(0xFF808080)
+
+// ── Diff viewer tokens (issue #738) ──────────────────────────────────
+val CodeDiffAddBg = Color(0x263DDC84)
+val CodeDiffAddText = Color(0xFF3DDC84)
+val CodeDiffDeleteBg = Color(0x26FF5C5C)
+val CodeDiffDeleteText = Color(0xFFFF5C5C)
+val CodeDiffHunkBg = Color(0x264DA8FF)
+val CodeDiffHunkText = Color(0xFF4DA8FF)

app/src/main/java/com/m57/hermescontrol/ui/chat/ChatBubble.kt

@@ -85,6 +85,7 @@ import com.m57.hermescontrol.theme.HermesStatusColors
 import com.m57.hermescontrol.theme.LightOnSurface
 import com.m57.hermescontrol.theme.LocalHermesStatusColors
 import com.m57.hermescontrol.theme.onColorFor
+import com.m57.hermescontrol.ui.chat.components.DiffViewCard
 import com.m57.hermescontrol.ui.chat.components.ReasoningCard
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.launch
@@ -560,6 +561,8 @@ data class ParsedToolData(
     val mainOutput: String? = null,
     val extraFields: Map<String, String> = emptyMap(),
     val isRunning: Boolean = false,
+    val diffOutput: String? = null,
+    val diffPath: String? = null,
 )
 
 private fun formatTodoToolOutput(
@@ -1688,7 +1691,19 @@ fun parseToolOutput(
         val hasStderr = dataSource.has("stderr")
         val hasExitCode = dataSource.has("exit_code") || dataSource.has("exitCode")
 
-        if (hasOutput || hasStdout || hasStderr || hasExitCode) {
+        val isTerminalTool =
+            resolvedToolName == "terminal" ||
+                resolvedToolName == "bash" ||
+                resolvedToolName == "sh" ||
+                resolvedToolName == "cmd" ||
+                resolvedToolName == "exec"
+
+        val isDiffTool =
+            resolvedToolName == "patch" ||
+                resolvedToolName == "write_file" ||
+                resolvedToolName == "edit"
+
+        if (!isDiffTool && (isTerminalTool || hasOutput || hasStdout || hasStderr || hasExitCode)) {
             val terminalOutput =
                 (
                     dataSource.get("output")?.takeIf { !it.isJsonNull }?.asString
@@ -1760,6 +1775,50 @@ fun parseToolOutput(
                 }
             }
 
+            val diffCandidate =
+                dataSource.get("diff")?.takeIf { !it.isJsonNull }?.let {
+                    if (it.isJsonPrimitive) it.asString else it.toString()
+                }
+                    ?: dataSource.get("patch")?.takeIf { !it.isJsonNull }?.let {
+                        if (it.isJsonPrimitive) it.asString else it.toString()
+                    }
+                    ?: mainOutput
+
+            val filePathArg =
+                args["path"]?.toString()
+                    ?: argsObj?.get("path")?.takeIf { !it.isJsonNull }?.asString
+
+            val oldStrArg = args["old_string"]?.toString()
+            val newStrArg = args["new_string"]?.toString()
+
+            val isDiffTool =
+                resolvedToolName == "patch" ||
+                    resolvedToolName == "edit" ||
+                    resolvedToolName == "write_file"
+
+            val extractedDiffOutput =
+                when {
+                    diffCandidate != null && (
+                        diffCandidate.contains("\n-") ||
+                            diffCandidate.contains("\n+") ||
+                            diffCandidate.startsWith("--- ") ||
+                            diffCandidate.startsWith("+++ ") ||
+                            diffCandidate.startsWith("*** ") ||
+                            diffCandidate.startsWith("@@ ")
+                    ) -> diffCandidate
+
+                    isDiffTool && oldStrArg != null && newStrArg != null -> {
+                        val pathHeader = filePathArg ?: "file"
+                        "--- $pathHeader\n+++ $pathHeader\n@@ -1,1 +1,1 @@\n-$oldStrArg\n+$newStrArg"
+                    }
+
+                    isDiffTool && args["patch"] != null -> {
+                        args["patch"].toString()
+                    }
+
+                    else -> null
+                }
+
             val duration = obj.get("duration_s")?.takeIf { !it.isJsonNull }?.asDouble
 
             ParsedToolData(
@@ -1771,6 +1830,8 @@ fun parseToolOutput(
                 extraFields = extraFields,
                 durationSec = duration,
                 isRunning = isRunning,
+                diffOutput = extractedDiffOutput,
+                diffPath = filePathArg,
             )
         }
     } catch (e: Exception) {
@@ -1848,7 +1909,13 @@ private fun ExpandedToolContent(
                 )
             }
         } else {
-            // ── Generic tool output ──
+            // ── Generic tool output / Diff view ──
+            if (parsed.diffOutput != null) {
+                DiffViewCard(
+                    diffText = parsed.diffOutput,
+                    filePath = parsed.diffPath,
+                )
+            } else {
                 parsed.mainOutput?.let {
                     Text(
                         text = it,
@@ -1882,7 +1949,8 @@ private fun ExpandedToolContent(
                         )
                     }
                 }
-
+            }
+        }
         // Duration footer
         parsed.durationSec?.let { dur ->
             Text(
@@ -1895,7 +1963,6 @@ private fun ExpandedToolContent(
         }
     }
 }
-}
 
 @Composable
 private fun ToolBubble(

app/src/main/java/com/m57/hermescontrol/ui/chat/ChatViewModel.kt

@@ -1571,21 +1571,39 @@ class ChatViewModel(
                         withContext(Dispatchers.IO) { repo.persistMessages(incoming, sessionId) }
                         _uiState.update { current ->
                             if (current.currentSessionId != sessionId) return@update current
-                            val unmatched = incoming.map { it.role to it.content }.toMutableList()
+                            val unmatchedIncoming = incoming.toMutableList()
-                            val retained =
+                            val mergedList = mutableListOf<ChatMessage>()
-                                current.messages.filter { existing ->
+
-                                    if (serverMessageIndex(existing.id, sessionId) != null) {
+                            for (existing in current.messages) {
-                                        true
+                                val existingServerIndex = serverMessageIndex(existing.id, sessionId)
+                                if (existingServerIndex != null) {
+                                    val matchIdx = unmatchedIncoming.indexOfFirst { it.id == existing.id }
+                                    if (matchIdx >= 0) {
+                                        mergedList.add(unmatchedIncoming.removeAt(matchIdx))
                                     } else {
-                                        val duplicate =
+                                        mergedList.add(existing)
-                                            unmatched.indexOfFirst { (role, content) ->
-                                                role == existing.role && content == existing.content
                                     }
-                                        if (duplicate >= 0) unmatched.removeAt(duplicate)
+                                } else {
-                                        duplicate < 0
+                                    val matchIdx =
+                                        unmatchedIncoming.indexOfFirst { inc ->
+                                            inc.role == existing.role && (
+                                                inc.content == existing.content ||
+                                                    (
+                                                        existing.role == MessageRole.TOOL &&
+                                                            inc.toolName != null &&
+                                                            inc.toolName == existing.toolName
+                                                    )
+                                            )
+                                        }
+                                    if (matchIdx >= 0) {
+                                        mergedList.add(unmatchedIncoming.removeAt(matchIdx))
+                                    } else {
+                                        mergedList.add(existing)
                                     }
                                 }
-                            val merged = (retained + incoming).distinctBy { it.id }
+                            }
+                            mergedList.addAll(unmatchedIncoming)
+                            val merged = mergedList.distinctBy { it.id }
                             if (sameMessages(current.messages, merged)) current else current.copy(messages = merged)
                         }
                     }

app/src/main/java/com/m57/hermescontrol/ui/chat/components/DiffViewCard.kt

@@ -0,0 +1,352 @@
+package com.m57.hermescontrol.ui.chat.components
+
+import android.content.ClipData
+import android.content.ClipboardManager
+import android.content.Context
+import androidx.compose.animation.animateContentSize
+import androidx.compose.foundation.BorderStroke
+import androidx.compose.foundation.background
+import androidx.compose.foundation.horizontalScroll
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.IntrinsicSize
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.heightIn
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.layout.width
+import androidx.compose.foundation.rememberScrollState
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.foundation.verticalScroll
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.automirrored.filled.InsertDriveFile
+import androidx.compose.material.icons.filled.Check
+import androidx.compose.material.icons.filled.ContentCopy
+import androidx.compose.material.icons.filled.ExpandLess
+import androidx.compose.material.icons.filled.ExpandMore
+import androidx.compose.material3.Icon
+import androidx.compose.material3.IconButton
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Surface
+import androidx.compose.material3.Text
+import androidx.compose.material3.TextButton
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.platform.testTag
+import androidx.compose.ui.text.font.FontFamily
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.text.style.TextOverflow
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
+import com.m57.hermescontrol.theme.CodeDiffAddBg
+import com.m57.hermescontrol.theme.CodeDiffAddText
+import com.m57.hermescontrol.theme.CodeDiffDeleteBg
+import com.m57.hermescontrol.theme.CodeDiffDeleteText
+import com.m57.hermescontrol.theme.CodeDiffHunkBg
+import com.m57.hermescontrol.theme.CodeDiffHunkText
+import com.m57.hermescontrol.theme.CodeTerminalBg
+import com.m57.hermescontrol.theme.CodeTerminalBorder
+import com.m57.hermescontrol.theme.CodeTerminalMuted
+import com.m57.hermescontrol.theme.CodeTerminalText
+import kotlinx.coroutines.delay
+
+enum class DiffLineType {
+    FILE_HEADER,
+    HUNK_HEADER,
+    ADDED,
+    DELETED,
+    CONTEXT,
+}
+
+data class ParsedDiffLine(
+    val type: DiffLineType,
+    val text: String,
+)
+
+data class ParsedDiffResult(
+    val filePath: String?,
+    val lines: List<ParsedDiffLine>,
+    val additionsCount: Int,
+    val deletionsCount: Int,
+)
+
+/**
+ * Parses unified diff or patch text into structured lines and line counts.
+ */
+fun parseDiffText(
+    diffText: String,
+    defaultPath: String? = null,
+): ParsedDiffResult {
+    if (diffText.isBlank()) {
+        return ParsedDiffResult(
+            filePath = defaultPath,
+            lines = emptyList(),
+            additionsCount = 0,
+            deletionsCount = 0,
+        )
+    }
+
+    val rawLines = diffText.lines()
+    val parsedLines = mutableListOf<ParsedDiffLine>()
+    var extractedPath: String? = defaultPath
+    var additions = 0
+    var deletions = 0
+
+    for (line in rawLines) {
+        when {
+            line.startsWith("--- ") || line.startsWith("+++ ") -> {
+                if (extractedPath == null || extractedPath == defaultPath) {
+                    val candidate =
+                        line.drop(4)
+                            .trim()
+                            .removePrefix("a/")
+                            .removePrefix("b/")
+                            .split("\t")
+                            .firstOrNull()
+                    if (!candidate.isNullOrBlank() && candidate != "/dev/null") {
+                        extractedPath = candidate
+                    }
+                }
+                parsedLines.add(ParsedDiffLine(DiffLineType.FILE_HEADER, line))
+            }
+
+            line.startsWith("*** Update File:") ||
+                line.startsWith("*** Add File:") ||
+                line.startsWith("*** Delete File:") -> {
+                val candidate = line.substringAfter(":").trim()
+                if (candidate.isNotBlank()) {
+                    extractedPath = candidate
+                }
+                parsedLines.add(ParsedDiffLine(DiffLineType.FILE_HEADER, line))
+            }
+
+            line.startsWith("@@ ") || line.startsWith("*** ") -> {
+                parsedLines.add(ParsedDiffLine(DiffLineType.HUNK_HEADER, line))
+            }
+
+            line.startsWith("+") -> {
+                additions++
+                parsedLines.add(ParsedDiffLine(DiffLineType.ADDED, line))
+            }
+
+            line.startsWith("-") -> {
+                deletions++
+                parsedLines.add(ParsedDiffLine(DiffLineType.DELETED, line))
+            }
+
+            else -> {
+                parsedLines.add(ParsedDiffLine(DiffLineType.CONTEXT, line))
+            }
+        }
+    }
+
+    return ParsedDiffResult(
+        filePath = extractedPath ?: defaultPath,
+        lines = parsedLines,
+        additionsCount = additions,
+        deletionsCount = deletions,
+    )
+}
+
+/**
+ * Interactive diff view card for file edit & patch tool outputs.
+ */
+@Composable
+fun DiffViewCard(
+    diffText: String,
+    filePath: String? = null,
+    onCopy: (String) -> Unit = {},
+    modifier: Modifier = Modifier,
+) {
+    val context = LocalContext.current
+    val parsed = remember(diffText, filePath) { parseDiffText(diffText, filePath) }
+    var expanded by remember { mutableStateOf(false) }
+    var copied by remember { mutableStateOf(false) }
+
+    LaunchedEffect(copied) {
+        if (copied) {
+            delay(2000)
+            copied = false
+        }
+    }
+
+    val displayLines =
+        if (expanded || parsed.lines.size <= 16) {
+            parsed.lines
+        } else {
+            parsed.lines.take(16)
+        }
+
+    Surface(
+        modifier =
+            modifier
+                .fillMaxWidth()
+                .testTag("diff_view_card"),
+        shape = RoundedCornerShape(8.dp),
+        color = CodeTerminalBg,
+        border = BorderStroke(1.dp, CodeTerminalBorder),
+    ) {
+        Column(modifier = Modifier.animateContentSize()) {
+            // Header bar
+            Row(
+                modifier =
+                    Modifier
+                        .fillMaxWidth()
+                        .padding(horizontal = 10.dp, vertical = 6.dp),
+                verticalAlignment = Alignment.CenterVertically,
+            ) {
+                Row(
+                    modifier = Modifier.weight(1f),
+                    verticalAlignment = Alignment.CenterVertically,
+                ) {
+                    Icon(
+                        imageVector = Icons.AutoMirrored.Filled.InsertDriveFile,
+                        contentDescription = null,
+                        tint = CodeTerminalMuted,
+                        modifier = Modifier.size(16.dp),
+                    )
+                    Spacer(Modifier.width(6.dp))
+                    Text(
+                        text = parsed.filePath ?: "diff",
+                        style =
+                            MaterialTheme.typography.labelMedium.copy(
+                                fontWeight = FontWeight.Bold,
+                                fontFamily = FontFamily.Monospace,
+                                color = CodeTerminalText,
+                            ),
+                        maxLines = 1,
+                        overflow = TextOverflow.Ellipsis,
+                        modifier = Modifier.weight(1f, fill = false),
+                    )
+                    Spacer(Modifier.width(8.dp))
+
+                    // Addition / Deletion badges
+                    if (parsed.additionsCount > 0) {
+                        Text(
+                            text = "+${parsed.additionsCount}",
+                            style =
+                                MaterialTheme.typography.labelSmall.copy(
+                                    fontWeight = FontWeight.Bold,
+                                    color = CodeDiffAddText,
+                                ),
+                        )
+                        Spacer(Modifier.width(6.dp))
+                    }
+                    if (parsed.deletionsCount > 0) {
+                        Text(
+                            text = "-${parsed.deletionsCount}",
+                            style =
+                                MaterialTheme.typography.labelSmall.copy(
+                                    fontWeight = FontWeight.Bold,
+                                    color = CodeDiffDeleteText,
+                                ),
+                        )
+                        Spacer(Modifier.width(6.dp))
+                    }
+                }
+
+                IconButton(
+                    onClick = {
+                        val clipboard =
+                            context.getSystemService(Context.CLIPBOARD_SERVICE) as? ClipboardManager
+                        clipboard?.setPrimaryClip(ClipData.newPlainText("diff", diffText))
+                        copied = true
+                        onCopy(diffText)
+                    },
+                    modifier = Modifier.size(28.dp),
+                ) {
+                    Icon(
+                        imageVector = if (copied) Icons.Filled.Check else Icons.Filled.ContentCopy,
+                        contentDescription = if (copied) "Copied" else "Copy diff",
+                        tint = CodeTerminalMuted,
+                        modifier = Modifier.size(14.dp),
+                    )
+                }
+            }
+
+            // Diff lines body
+            val verticalScrollModifier =
+                if (expanded) {
+                    Modifier.heightIn(max = 400.dp).verticalScroll(rememberScrollState())
+                } else {
+                    Modifier
+                }
+
+            Column(
+                modifier =
+                    Modifier
+                        .fillMaxWidth()
+                        .then(verticalScrollModifier)
+                        .horizontalScroll(rememberScrollState())
+                        .width(IntrinsicSize.Max),
+            ) {
+                displayLines.forEach { line ->
+                    val (bgColor, textColor) =
+                        when (line.type) {
+                            DiffLineType.ADDED -> CodeDiffAddBg to CodeDiffAddText
+                            DiffLineType.DELETED -> CodeDiffDeleteBg to CodeDiffDeleteText
+                            DiffLineType.HUNK_HEADER -> CodeDiffHunkBg to CodeDiffHunkText
+                            DiffLineType.FILE_HEADER -> Color.Transparent to CodeTerminalMuted
+                            DiffLineType.CONTEXT -> Color.Transparent to CodeTerminalText
+                        }
+
+                    Box(
+                        modifier =
+                            Modifier
+                                .fillMaxWidth()
+                                .background(bgColor)
+                                .padding(horizontal = 10.dp, vertical = 2.dp),
+                    ) {
+                        Text(
+                            text = line.text,
+                            style =
+                                MaterialTheme.typography.bodySmall.copy(
+                                    fontFamily = FontFamily.Monospace,
+                                    fontSize = 11.sp,
+                                    color = textColor,
+                                ),
+                        )
+                    }
+                }
+            }
+
+            // Expand / Collapse footer button for diffs > 16 lines
+            if (parsed.lines.size > 16) {
+                TextButton(
+                    onClick = { expanded = !expanded },
+                    modifier = Modifier.fillMaxWidth(),
+                ) {
+                    Row(verticalAlignment = Alignment.CenterVertically) {
+                        Text(
+                            text =
+                                if (expanded) {
+                                    "Collapse diff"
+                                } else {
+                                    "Show full diff (${parsed.lines.size} lines)"
+                                },
+                            style = MaterialTheme.typography.labelSmall,
+                            color = CodeTerminalMuted,
+                        )
+                        Spacer(Modifier.width(4.dp))
+                        Icon(
+                            imageVector = if (expanded) Icons.Filled.ExpandLess else Icons.Filled.ExpandMore,
+                            contentDescription = null,
+                            tint = CodeTerminalMuted,
+                            modifier = Modifier.size(16.dp),
+                        )
+                    }
+                }
+            }
+        }
+    }
+}

app/src/test/java/com/m57/hermescontrol/ui/chat/ToolBubbleParsingTest.kt

@@ -1,5 +1,7 @@
 package com.m57.hermescontrol.ui.chat
 
+import com.m57.hermescontrol.ui.chat.components.DiffLineType
+import com.m57.hermescontrol.ui.chat.components.parseDiffText
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertFalse
 import org.junit.Assert.assertNotNull
@@ -244,4 +246,77 @@ class ToolBubbleParsingTest {
         assertEquals(0, parsed.exitCode)
         assertNull(parsed.summaryText) // no args → no summary
     }
+
+    // ── Diff parsing & Patch tool tests ───────────────────────
+
+    @Test
+    fun testParseDiffText_unifiedDiff() {
+        val rawDiff =
+            """
+            --- app/src/Main.kt
+            +++ app/src/Main.kt
+            @@ -1,3 +1,3 @@
+             fun main() {
+            -    println("hello")
+            +    println("hello world")
+             }
+            """.trimIndent()
+
+        val result = parseDiffText(rawDiff)
+        assertEquals("app/src/Main.kt", result.filePath)
+        assertEquals(1, result.additionsCount)
+        assertEquals(1, result.deletionsCount)
+
+        val addedLine = result.lines.find { it.type == DiffLineType.ADDED }
+        assertNotNull(addedLine)
+        assertEquals("+    println(\"hello world\")", addedLine!!.text)
+    }
+
+    @Test
+    fun testParseToolOutput_patchReplaceMode() {
+        val json =
+            """{
+            "tool_id": "call_patch_1",
+            "name": "patch",
+            "args": {
+                "path": "app/config.json",
+                "old_string": "debug=false",
+                "new_string": "debug=true"
+            },
+            "result": {
+                "output": "--- app/config.json\n+++ app/config.json\n@@ -1,1 +1,1 @@\n-debug=false\n+debug=true"
+            }
+        }"""
+        val parsed = parseToolOutput(json, "patch", false)
+        assertNotNull(parsed)
+        assertEquals("app/config.json", parsed!!.diffPath)
+        val diffOutput = parsed.diffOutput
+        assertNotNull(diffOutput)
+        assertTrue(diffOutput!!.contains("-debug=false"))
+        assertTrue(diffOutput.contains("+debug=true"))
+    }
+
+    @Test
+    fun testParseToolOutput_editTool() {
+        val json =
+            """{
+            "tool_id": "call_edit_1",
+            "name": "edit",
+            "args": {
+                "path": "app/src/Main.kt",
+                "old_string": "val x = 1",
+                "new_string": "val x = 2"
+            },
+            "result": {
+                "output": "--- app/src/Main.kt\n+++ app/src/Main.kt\n@@ -1,1 +1,1 @@\n-val x = 1\n+val x = 2"
+            }
+        }"""
+        val parsed = parseToolOutput(json, "edit", false)
+        assertNotNull(parsed)
+        assertEquals("app/src/Main.kt", parsed!!.diffPath)
+        val editDiff = parsed.diffOutput
+        assertNotNull(editDiff)
+        assertTrue(editDiff!!.contains("-val x = 1"))
+        assertTrue(editDiff.contains("+val x = 2"))
+    }
 }