Shorten CWD path

For showing the CWD path in a more compact way, this function

    - shortens path parts before last from right to left, until first
      character of the path stays (directory -> direc~ or d~)
    - combines parts before last from right with left (a~/b~ -> a~~)
    - shortens the last part from middle, preferring to keep characters
      from left (longdirectoryname -> long~ame)

in order (of 2nd and 3rd, the one that removes more characters is
applied first) until given maximum length is reached.

Process.c

@@ -733,6 +733,133 @@ void Process_printPercentage(float val, char* buffer, int n, int* attr) {
    }
 }
 
+typedef struct ShortenCwdContext {
+   char *cwd;
+   size_t maxLength;
+   size_t len;
+   char **parts;
+   size_t partsLen;
+   size_t *partLengths;
+} ShortenCwdContext;
+
+static void shortenCwdParts(ShortenCwdContext *ctx) {
+   for (int i = ctx->partsLen - 2; i >= 0 && ctx->len > ctx->maxLength; i--) {
+      if (ctx->partLengths[i] < 3)
+         continue;
+
+      size_t extraChars = ctx->len - ctx->maxLength;
+      size_t maxRemovableChars = ctx->partLengths[i] - 2;
+      size_t charsToRemove = extraChars < maxRemovableChars ? extraChars : maxRemovableChars;
+
+      ctx->partLengths[i] -= charsToRemove;
+      ctx->len -= charsToRemove;
+      String_safeStrncpy(ctx->parts[i] + (ctx->partLengths[i] - 1), "~", 2);
+   }
+}
+
+static size_t collapseCwdParts(ShortenCwdContext *ctx, bool doActualWork) {
+   if (ctx->len <= ctx->maxLength || ctx->partsLen <= 3)
+      return 0;
+
+   size_t len = ctx->len;
+
+   size_t i;
+   for (i = ctx->partsLen - 2; i > 1; i--) {
+      if (len + (3 - ctx->partLengths[i]) <= ctx->maxLength)
+         break;
+
+      len -= ctx->partLengths[i] + 1;
+
+      if (doActualWork) {
+         ctx->partLengths[i] = 0;
+         free(ctx->parts[i]);
+         ctx->parts[i] = NULL;
+      }
+   }
+
+   len += 3 - ctx->partLengths[i];
+   size_t diff = ctx->len - len;
+
+   if (doActualWork) {
+      char newPart[] = "~~~";
+      newPart[0] = ctx->parts[i][0];
+      free_and_xStrdup(&ctx->parts[i], newPart);
+      ctx->partLengths[i] = 3;
+      ctx->len = len;
+   }
+
+   return diff;
+}
+
+static size_t shortenCwdLastPart(ShortenCwdContext *ctx, bool doActualWork) {
+   if (ctx->len <= ctx->maxLength)
+      return 0;
+
+   size_t lastPartLen = ctx->partLengths[ctx->partsLen - 1];
+   if (lastPartLen <= 3)
+      return 0;
+
+   char *lastPart = ctx->parts[ctx->partsLen - 1];
+   size_t extraChars = ctx->len - ctx->maxLength + 1;
+   size_t maxRemovableChars = lastPartLen - 2;
+   size_t charsToRemove = extraChars < maxRemovableChars ? extraChars : maxRemovableChars;
+
+   if (doActualWork) {
+      size_t charsAtBeginning = (lastPartLen - charsToRemove + 1) / 2;
+      size_t charsAtEnd = lastPartLen - charsToRemove - charsAtBeginning;
+      lastPart[charsAtBeginning] = '~';
+      memmove(lastPart + charsAtBeginning + 1, lastPart + lastPartLen - charsAtEnd, charsAtEnd);
+      lastPart[charsAtBeginning + charsAtEnd + 1] = '\0';
+      ctx->partLengths[ctx->partsLen - 1] = lastPartLen - charsToRemove + 1;
+      ctx->len -= charsToRemove - 1;
+   }
+
+   return charsToRemove - 1;
+}
+
+static void writeCwdUsingParts(ShortenCwdContext *ctx) {
+   ctx->cwd[0] = '\0';
+   for (size_t i = 0, writeIndex = 0; i < ctx->partsLen; i++) {
+      if (!ctx->parts[i])
+         continue;
+
+      String_safeStrncpy(ctx->cwd + writeIndex, ctx->parts[i], ctx->partLengths[i] + 1);
+      writeIndex += ctx->partLengths[i];
+      if (i < ctx->partsLen - 1)
+         ctx->cwd[writeIndex++] = '/';
+   }
+}
+
+static void shortenCwd(char *cwd, const size_t maxLength) {
+   size_t len = strlen(cwd);
+   if (len <= maxLength)
+      return;
+
+   ShortenCwdContext ctx = {
+      .cwd = cwd,
+      .maxLength = maxLength,
+      .len = len,
+   };
+   ctx.parts = String_split(cwd, '/', &ctx.partsLen);
+   ctx.partLengths = xCalloc(ctx.partsLen, sizeof(size_t));
+   for (size_t i = 0; i < ctx.partsLen; i++)
+      ctx.partLengths[i] = strlen(ctx.parts[i]);
+
+   shortenCwdParts(&ctx);
+   if (shortenCwdLastPart(&ctx, false) > collapseCwdParts(&ctx, false)) {
+      shortenCwdLastPart(&ctx, true);
+      collapseCwdParts(&ctx, true);
+   } else {
+      collapseCwdParts(&ctx, true);
+      shortenCwdLastPart(&ctx, true);
+   }
+
+   writeCwdUsingParts(&ctx);
+
+   free(ctx.partLengths);
+   String_freeArray(ctx.parts);
+}
+
 void Process_writeField(const Process* this, RichString* str, ProcessField field) {
    char buffer[256];
    size_t n = sizeof(buffer);
@@ -825,6 +952,7 @@ void Process_writeField(const Process* this, RichString* str, ProcessField field
          attr = CRT_colors[PROCESS_SHADOW];
          cwd = "main thread terminated";
       } else {
+         shortenCwd(this->procCwd, 25);
          cwd = this->procCwd;
       }
       Process_printLeftAlignedField(str, attr, cwd, 25);