Add strlen and strcat_max functions

src/calibre/manual/template_lang.rst

@@ -273,7 +273,9 @@ The following functions are available in addition to those described in single-f
     * ``print(a, b, ...)`` -- prints the arguments to standard output. Unless you start calibre from the command line (``calibre-debug -g``), the output will go to a black hole.
     * ``raw_field(name)`` -- returns the metadata field named by name without applying any formatting.
     * ``strcat(a, b, ...)`` -- can take any number of arguments. Returns a string formed by concatenating all the arguments.
+    * ``strcat_max(max, string1, prefix2, string2, ...)`` -- Returns a string formed by concatenating the arguments. The returned value is initialized to string1. `Prefix, string` pairs are added to the end of the value as long as the resulting string length is less than `max`. String1 is returned even if string1 is longer than max. You can pass as many `prefix, string` pairs as you wish.
     * ``strcmp(x, y, lt, eq, gt)`` -- does a case-insensitive comparison x and y as strings. Returns ``lt`` if x < y. Returns ``eq`` if x == y. Otherwise returns ``gt``.
+    * ``strlen(a)`` -- Returns the length of the string passed as the argument.
     * ``substr(str, start, end)`` -- returns the ``start``'th through the ``end``'th characters of ``str``. The first character in ``str`` is the zero'th character. If end is negative, then it indicates that many characters counting from the right. If end is zero, then it indicates the last character. For example, ``substr('12345', 1, 0)`` returns ``'2345'``, and ``substr('12345', 1, -1)`` returns ``'234'``.
     * ``subtract(x, y)`` -- returns x - y. Throws an exception if either x or y are not numbers.
     * ``today()`` -- return a date string for today. This value is designed for use in format_date or days_between, but can be manipulated like any other string. The date is in ISO format.

src/calibre/utils/formatter_functions.py

@@ -136,6 +136,19 @@ class BuiltinStrcat(BuiltinFormatterFunction):
             res += args[i]
         return res
 
+class BuiltinStrlen(BuiltinFormatterFunction):
+    name = 'strlen'
+    arg_count = 1
+    category = 'String Manipulation'
+    __doc__ = doc = _('strlen(a) -- Returns the length of the string passed as '
+            'the argument')
+
+    def evaluate(self, formatter, kwargs, mi, locals, a):
+        try:
+            return len(a)
+        except:
+            return -1
+
 class BuiltinAdd(BuiltinFormatterFunction):
     name = 'add'
     arg_count = 2
@@ -345,6 +358,40 @@ class BuiltinSwitch(BuiltinFormatterFunction):
                 return args[i+1]
             i += 2
 
+class BuiltinStrcatMax(BuiltinFormatterFunction):
+    name = 'strcat_max'
+    arg_count = -1
+    category = 'String Manipulation'
+    __doc__ = doc = _('strcat_max(max, string1, prefix2, string2, ...) -- '
+            'Returns a string formed by concatenating the arguments. The '
+            'returned value is initialized to string1. `Prefix, string` '
+            'pairs are added to the end of the value as long as the '
+            'resulting string length is less than `max`. String1 is returned '
+            'even if string1 is longer than max. You can pass as many '
+            '`prefix, string` pairs as you wish.')
+
+    def evaluate(self, formatter, kwargs, mi, locals, *args):
+        if len(args) < 2:
+            raise ValueError(_('strcat_max requires 2 or more arguments'))
+        if (len(args) % 2) != 0:
+            raise ValueError(_('strcat_max requires an even number of arguments'))
+        try:
+            max = int(args[0])
+        except:
+            raise ValueError(_('first argument to strcat_max must be an integer'))
+
+        i = 2
+        result = args[1]
+        try:
+            while i < len(args):
+                if (len(result) + len(args[i]) + len(args[i+1])) > max:
+                    break
+                result = result + args[i] + args[i+1]
+                i += 2
+        except:
+            pass
+        return result.strip()
+
 class BuiltinInList(BuiltinFormatterFunction):
     name = 'in_list'
     arg_count = 5
@@ -956,7 +1003,8 @@ _formatter_builtins = [
     BuiltinLowercase(), BuiltinMultiply(), BuiltinNot(),
     BuiltinOndevice(), BuiltinOr(), BuiltinPrint(), BuiltinRawField(),
     BuiltinRe(), BuiltinSelect(), BuiltinShorten(), BuiltinStrcat(),
-    BuiltinStrcmp(), BuiltinStrInList(), BuiltinSubitems(),
+    BuiltinStrcatMax(),
+    BuiltinStrcmp(), BuiltinStrInList(), BuiltinStrlen(), BuiltinSubitems(),
     BuiltinSublist(),BuiltinSubstr(), BuiltinSubtract(), BuiltinSwapAroundComma(),
     BuiltinSwitch(), BuiltinTemplate(), BuiltinTest(), BuiltinTitlecase(),
     BuiltinToday(), BuiltinUppercase(),