Add rudimentary command-line history (up/down arrow)

This commit adds very rudimentary command-line history support. Use the
up/down arrow to navigate the history.

This commit also adds an additional command, "history" to view the
history.

refterm_example_terminal.c

@@ -1039,6 +1039,18 @@ static void ExecuteCommandLine(example_terminal *Terminal)
     {
         AppendOutput(Terminal, "%s\n", B);
     }
+    else if (StringsAreEqual(Terminal->CommandLine, "history"))
+    {
+        const int ovr = Terminal->CommandLineHistoryCount > CommandLineHistorySize;
+        AppendOutput(Terminal, "History size: %u (max: %u)\n",
+                     ovr ? CommandLineHistorySize : Terminal->CommandLineHistoryCount,
+                     CommandLineHistorySize);
+        for (uint32_t n = 0, i = ovr ? Terminal->CommandLineHistoryCount - CommandLineHistorySize : 0;
+             i < Terminal->CommandLineHistoryCount;
+             ++i, ++n) {
+            AppendOutput(Terminal, "%3u  %s\n", n, Terminal->CommandLineHistory[i % CommandLineHistorySize].CommandLine);
+        }
+    }
     else if(StringsAreEqual(Terminal->CommandLine, ""))
     {
     }
@@ -1060,6 +1072,72 @@ static void ExecuteCommandLine(example_terminal *Terminal)
     }
 }
 
+static void PushCommandHistory(example_terminal *Terminal)
+{
+    if (!Terminal->CommandLineCount) {
+        Terminal->CommandLineHistoryCursor = 0; // indicate we are not going back/forth through history
+        return; // don't push empty lines to history
+    }
+    if (Terminal->CommandLineHistoryCount) {
+        // check that top and command line don't match (don't push dupes)
+        const uint32_t top = (Terminal->CommandLineHistoryCount - 1) % CommandLineHistorySize;
+        char cmdTmp[CommandLineSize + 1];
+        memcpy(cmdTmp, Terminal->CommandLine, Terminal->CommandLineCount);
+        cmdTmp[Terminal->CommandLineCount] = 0;
+        if (StringsAreEqual(Terminal->CommandLineHistory[top].CommandLine, cmdTmp)) {
+            Terminal->CommandLineHistoryCursor = 0; // indicate we are not going back/forth through history
+            return; // don't push dupes to history
+        }
+    }
+    const uint32_t index = Terminal->CommandLineHistoryCount++ % CommandLineHistorySize;
+    Terminal->CommandLineHistory[index].CommandLineCount = Terminal->CommandLineCount;
+    memcpy(Terminal->CommandLineHistory[index].CommandLine, Terminal->CommandLine, CommandLineSize);
+    Terminal->CommandLineHistory[index].CommandLine[Terminal->CommandLineCount] = 0; // ensure NUL termination
+    Terminal->CommandLineHistoryCursor = 0; // indicate we are not going back/forth through history
+}
+
+static void CopyCommandHistoryCursorToCommandLine(example_terminal *Terminal)
+{
+    if (Terminal->CommandLineHistoryCount && Terminal->CommandLineHistoryCursor) {
+        const uint32_t index = (Terminal->CommandLineHistoryCursor - 1) % CommandLineHistorySize;
+        memcpy(Terminal->CommandLine, Terminal->CommandLineHistory[index].CommandLine, CommandLineSize);
+        Terminal->CommandLineCount = Terminal->CommandLineHistory[index].CommandLineCount;
+    }
+}
+
+static void CommandHistoryPrev(example_terminal *Terminal)
+{
+    if (!Terminal->CommandLineHistoryCount) {
+        // no history
+        Terminal->CommandLineHistoryCursor = 0;
+        return;
+    }
+    if (!Terminal->CommandLineHistoryCursor) {
+        // no cursor set, initialize to 1 past end of history
+        Terminal->CommandLineHistoryCursor = 1 + Terminal->CommandLineHistoryCount;
+    }
+    else if (Terminal->CommandLineHistoryCount - (Terminal->CommandLineHistoryCursor-1) >= CommandLineHistorySize) {
+        // at beginning of history
+        return;
+    }
+    Terminal->CommandLineHistoryCursor--;
+    CopyCommandHistoryCursorToCommandLine(Terminal);
+}
+
+static void CommandHistoryNext(example_terminal *Terminal)
+{
+    if (!Terminal->CommandLineHistoryCursor
+            || Terminal->CommandLineHistoryCursor >= Terminal->CommandLineHistoryCount) {
+        // not iterating back through history, or at top of history/no history
+        // clear line, clear cursor
+        Terminal->CommandLineCount = 0;
+        Terminal->CommandLineHistoryCursor = 0;
+        return;
+    }
+    Terminal->CommandLineHistoryCursor++;
+    CopyCommandHistoryCursorToCommandLine(Terminal);
+}
+
 static int IsUTF8Extension(char A)
 {
     int Result = ((A & 0xc0) == 0x80);
@@ -1091,6 +1169,16 @@ static void ProcessMessages(example_terminal *Terminal)
                     {
                         Terminal->ViewingLineOffset += Terminal->ScreenBuffer.DimY/2;
                     } break;
+
+                    case VK_UP:
+                    {
+                        CommandHistoryPrev(Terminal);
+                    } break;
+
+                    case VK_DOWN:
+                    {
+                        CommandHistoryNext(Terminal);
+                    } break;
                 }
 
                 if(Terminal->ViewingLineOffset > 0)
@@ -1124,6 +1212,7 @@ static void ProcessMessages(example_terminal *Terminal)
 
                     case VK_RETURN:
                     {
+                        PushCommandHistory(Terminal);
                         ExecuteCommandLine(Terminal);
                         Terminal->CommandLineCount = 0;
                         Terminal->ViewingLineOffset = 0;

refterm_example_terminal.h

@@ -88,7 +88,17 @@ typedef struct
 
     wchar_t LastChar;
     uint32_t CommandLineCount;
-    char CommandLine[256];
+#define CommandLineSize 256
+    char CommandLine[CommandLineSize];
+
+#define CommandLineHistorySize 96
+    // TODO(Calin): This should really be a linked-list
+    struct {
+        uint32_t CommandLineCount;
+        char CommandLine[CommandLineSize];
+    } CommandLineHistory[CommandLineHistorySize];
+    uint32_t CommandLineHistoryCount;
+    uint32_t CommandLineHistoryCursor;
 
     int NoThrottle;
     int DebugHighlighting;
@@ -120,4 +130,3 @@ typedef struct
 #define MaxDirectCodepoint 126
     gpu_glyph_index ReservedTileTable[MaxDirectCodepoint - MinDirectCodepoint + 1];
 } example_terminal;
-