# IDNA CONTEXT RULES (including BIDI)
# Mark Davis
# Provides a table-based mechanism for determining whether a label is a U-Label or not.

# For testing, this turns on a Verbose mode, that displays the resolved sets and rules.

VERBOSE:true

# If any of the following regex expressions is found in the label, then the label is not a valid U-Label.
# These rules provide a machine-readable way to test that. This is intended for a reference (test) version;
# implementations would typically use hand-coded versions that would be much more optimized.
# The context rules are derived from http://tools.ietf.org/html/draft-ietf-idnabis-tables-05#appendix-A
# However, they do contain quite a number of corrections and proposed changes.

# FILE FORMAT

# Everything at and after # is a comment, and ignored.
# Blank lines are ignored.
# Leading and trailing spaces are ignored.
# There are 3 kinds of lines: titles, rules and variable definitions

# A variable is defined with a line of the form $X = <unicodeSet>
# They are a single unicodeSet (character range) according to http://www.unicode.org/reports/tr18/
# These variables are substituted in the rules before evaluation

# Rules have the following formats:
# <before>; <at>; <result>
# <before> ; <result>
# Key:
#   <before> and <at> are both regex expressions
#   <result> is either "fail" or "next"
# Everything other kind of line is an error

# A title is of the form "Title: ...". It is just informational, but allows the test to show why a character causes a failure.

# Function
# Logically, a label is processed by iterating through its character positions
# In each iteration, each rule is checked.
# If <before> and <at> both match, then the result is applied as follows:
#   fail: stop, the label is invalid
#   next: skip to the next rule that has a "next" result (skipping any "fail" or "next2" results)
#   next2: skip to the next rule that has a "next" or "next2" result (skipping any "fail" results)
# If the processing reaches the end of the string, then the label is valid.

# The regex expressions use Java / Perl syntax, with Unicode properties. 
# If the regex does not support Unicode Properties (the latest version!), then explicit ranges can be substituted.
# For example, for [:bc=nsm:], using the set on http://unicode.org/cldr/utility/list-unicodeset.jsp?a=[:bc=nsm:]
# Interior spaces are ignored, and may be used for readability.

# The expressions are limited to a basic format which should work in any regex engine (perhaps with some syntax tweeks).
# In particular, the <before> and <at> split is used to avoid lookbehind, which can vary in results depending on regex engines.
# <before> is matched before the current position. Logically, it is equivalent to matching label[0,n] against /.*<before>/
# <at> is matched at the current position. Logically, it is equivalent to matching label[n,end] against /<at>.*/

# ===================================
# Mapping would be done before this table, and only for Lookup
# ===================================

Title: 4.2.2. Rejection of Characters that are not Permitted: fail if DISALLOWED or UNASSIGNED

# Tables

# 2.1. LetterDigits (A)

$LetterDigits = [[:Ll:] [:Lu:] [:Lo:] [:Nd:] [:Lm:] [:Mn:] [:Mc:]]

# 2.2. Unstable (B)

$Unstable = [:^nfkc_casefolded:]

# 2.3. IgnorableProperties (C) // default ignoreable or whitespace or nonchar

$Ignorable = [[:di:] [:WSpace:] [:NChar:]]

# 2.4. IgnorableBlocks (D)

$IgnorableBlocks = [[:block=Combining_Diacritical_Marks_For_Symbols:] [:block=Musical_Symbols:] [:block=Ancient_Greek_Musical_Notation:]]

# 2.5. LDH (E)

$LDH = [\u002D\u0030-\u0039\u0061-\u007A]

# 2.6. Exceptions (F)
# Note: added Tatweel to these, since that seems to be the current consensus.

$ExceptionDisallowed = [\u302E \u302F \u0640]
$ExceptionPvalid = [\u00DF \u03C2 \u06FD \u06FE \u0F0B \u3007]
$ExceptionContexto = [\u002D \u00B7 \u02B9 \u0375 \u0483 \u05F3 \u05F4 \u0660 \u0661 \u0662 \u0663 \u0664 \u0665 \u0666 \u0667 \u0668 \u0669 \u06F0 \u06F1 \u06F2 \u06F3 \u06F4 \u06F5 \u06F6 \u06F7 \u06F8 \u06F9 \u3005 \u303B \u30FB]
   
# 2.7. BackwardCompatible (G)

$BackwardCompatibleDisallowed = []
$BackwardCompatiblePvalid = []
$BackwardCompatibleContexto = []

# 2.8. JoinControl (H)

$JoinControl = [:JoinControl:]

# 2.9. OldHangulJamo (I)

$OldHangulJamo = [[:HST=L:] [:HST=V:] [:HST=T:]]

# 2.10. Unassigned (J)

$Unassigned = [[:unassigned:] - [:nchar:]]

# If .cp. .in.  Exceptions Then Exceptions(cp);
# Else If .cp. .in.  BackwardCompatible Then BackwardCompatible(cp);
# Else If .cp. .in.  Unassigned Then UNASSIGNED;
# Else If .cp. .in.  LDH Then PVALID;
# Else If .cp. .in.  JoinControl Then CONTEXTJ;
# Else If .cp. .in.  Unstable Then DISALLOWED;
# Else If .cp. .in.  IgnorableProperties Then DISALLOWED;
# Else If .cp. .in.  IgnorableBlocks Then DISALLOWED;
# Else If .cp. .in.  OldHangulJamo Then DISALLOWED;
# Else If .cp. .in.  LetterDigits Then PVALID; 
# Else DISALLOWED;

# We compute when invalid.
# There is no functional difference between DISALLOWED and UNASSIGNED: we can just call them invalid.

# The rules in Tables obfuscates the true situation, which is that:
#   A. some characters are always valid
#   B. otherwise LetterDigits are valid - with some subtractions
#   C. otherwise everything is invalid

# There is no functional difference between CONTEXTJ and CONTEXTO, and none at this point from PVALID either
# We record all of them for later

$Context = [$ExceptionContexto $BackwardCompatibleContexto $JoinControl]

$ValidAlways = [$ExceptionPvalid $BackwardCompatiblePvalid $LDH]

$InvalidLetterDigits = [$ExceptionDisallowed $BackwardCompatibleDisallowed $Unassigned $Unstable $IgnorableProperties $IgnorableBlocks $OldHangulJamo]

$Valid = [$ValidAlways $Context [$LetterDigits - $InvalidLetterDigits]]
$Valid2 = [[:nfkc_casefolded:]-[:c:]-[:z:]-[:s:]-[:p:]-[:nl:]-[:no:]-[:me:]-[:di:]-[:HST=L:]-[:HST=V:]-[:HST=V:]-[:block=Combining_Diacritical_Marks_For_Symbols:]-[:block=Musical_Symbols:]-[:block=Ancient_Greek_Musical_Notation:]-[\u0640\u07FA\u302E\u302F\u3031-\u3035\u303B][:JoinControl:][\u00DF\u03C2\u06FD\u06FE\u0F0B\u3007][\u002D\u00B7\u0375\u05F3\u05F4\u30FB]]

$Invalid = [^ $Valid]

# ===================================

# At this point, we have the final list of everything that is invalid, so there is a single test

$Invalid ; fail

# ===================================

Title: 4.2.3.1. Rejection of Hyphen Sequences in U-labels // just xx--

^.. ; -- ; fail

# ===================================

Title: 4.2.3.2. Leading Combining Marks

$M = [:M:]

^ ; $M ; fail

# ===================================

# CONTEXT: 4.2.3.3. Contextual Rules
# The details here are all from Tables

Title: Appendix A.1. HYPHEN-MINUS - Can't be at start or end; that is, ok only if medial

. ; -. ; next
- ; fail

# See comment in http://www.alvestrand.no/pipermail/idna-update/2008-November/003021.html

# ==========================

# ZWNJ and ZWJ is the trickiest section
# Tables is all messed up. Following UAX 31 instead, from which these are derived
# http://www.unicode.org/reports/tr31/#Layout_and_Format_Control_Characters

# There are two different kinds of rules that have to be combined.
# We don't try a script test for Arabic, because it is not needed (and is complicated)

# Variables for Arabic

$T = [:Joining_Type=Transparent:]
$R = [[:Joining_Type=Dual_Joining:][:Joining_Type=Right_Joining:]]
$L = [[:Joining_Type=Dual_Joining:][:Joining_Type=Left_Joining:]] 

# Appendix A.2. ZERO WIDTH NON-JOINER

Title: A1. Allow ZWNJ in the following context: /$L $T* ZWNJ $T* $R/

$L $T* ; \u200C $T* $R ; next

# Variables for Indic

$Lt = [:General_Category=Letter:]
$V = [:Canonical_Combining_Class=Virama:]

# $deva = [:sc=deva:]
# $Ndeva = [^$deva]
# $beng = [:sc=beng:]
# $Nbeng = [^$beng]
# $guru = [:sc=guru:]
# $Nguru = [^$guru]
# $noVirama = [^ $deva $beng $guru]

# WARNING: There is a nasty bug in Java regex before 1.6; the work-around is to do the negations
# above, instead of in the regexes.

# To do the script test for both ZWNJ and ZWJ, use the following.
# The first line lists all the acceptable scripts

Title: ZWJ/ZWNJ apply to letter+virama
# WARNING: rule must come after Arabic!

# $noVirama ; [\u200C\u200D] ; fail

# The remainder makes sure that each script is paired
# Subsequent rules will make sure that there are two characters

# $Ndeva $deva; [\u200C\u200D] ; fail
# $Nbeng $beng; [\u200C\u200D] ; fail
# $Nguru $guru; [\u200C\u200D] ; fail

# Now we do the script-independent rules

Title: A2. Allow ZWNJ in the following context: /$L $V ZWNJ/

$Lt $V ; \u200C ; next2
\u200C ; fail

# Appendix A.3. ZERO WIDTH JOINER

Title: B. Allow ZWJ (U+200D) in the following context:  /$L $V ZWJ/

$Lt $V ; \u200D ; next2
\u200D ; fail

# ==========================

Title: Appendix A.4. MIDDLE DOT

l ; \u00B7 l ; next
\u00B7 ; fail

# Appendix A.5. GREEK LOWER NUMERAL SIGN (KERAIA)
Title: The script of the following character MUST be Greek.
$grek = [:script=greek:]
\u0375 ; $grek ; next
\u0375 ; fail

Title: Appendix A.6. HEBREW PUNCTUATION GERESH - \u05F3 - The script of the preceding character MUST be Hebrew.

$hebr = [:script=hebrew:]
$hebr ; \u05F3 ; next
\u05F3 ; fail

Title: Appendix A.7. HEBREW PUNCTUATION GERSHAYIM - \u05F4 - The script of the preceding character MUST be Hebrew.

$hebr ; \u05F4 ; next
\u05F4 ; fail

Title: Appendix A.12. KATAKANA MIDDLE DOT - \u30FB - Adjacent characters MUST be Hiragana, Katakana, or Han.
$han = [[:script=Hiragana:][:script=Katakana:][:script=Han:]]
$han ; \u30FB $han; next
\u30FB ; fail

Title: Appendix A.13. ARABIC-INDIC DIGITS - 0660..0669
# Rules broken, since they simply forbid them entirely
# Rewrite to exclude mixing with western (ASCII) or extended Arabic digits

$WD = [0-9]
$AD = [\u0660-\u0669]
$EAD = [\u06F0-\u06F9]

[$WD $EAD].*$AD ; fail
$AD.*[$WD $EAD] ; fail

Title: Appendix A.14. EXTENDED ARABIC-INDIC DIGITS
# Rules broken, since they simply forbid them entirely
# Rewrite to exclude mixing with western (ASCII) or Arabic digits

$EAD .* [$WD $AD] ; fail
[$WD $AD] .* $EAD ; fail

# ==========================

# BIDI Rules: 4.2.3.4. Labels Containing Characters Written Right to Left
# The details here are all from http://tools.ietf.org/html/draft-ietf-idnabis-bidi-03

# Note that $NSM != Non-spacing Marks in the general sense
# See http://unicode.org/cldr/utility/unicodeset.jsp?a=[:bc=nsm:]&b=[[:me:][:mn:]]

$NSM = [:bc=NSM:]
$ESON = [[:bc=ES:][:bc=ON:]]
$ENAN = [[:bc=EN:][:bc=AN:]]
$RALAN = [[:bc=R:][:bc=AL:][:bc=AN:]]
$BCL = [:bc=L:]
$BDisallowed = [^[:bc=L:][:bc=R:][:bc=AL:][:bc=AN:][:bc=EN:][:bc=ES:][:bc=BN:][:bc=ON:][:bc=NSM:]]

# Note: 
# The only tables-valid [:bc=ES:] character is: -
# The only tables-valid [:bc=BN:] characters are: [\u200C \u200D]
# The only tables-valid [:bc=ON:] characters are: [・ · ʹ ͵ ʺ ˆ-ˏ ˬ ꜗ-ꜟ ꞈ ⸯ ꙿ]

Title: 1.  Only characters with the BIDI properties L, R, AL, AN, EN, ES, BN, ON and NSM are allowed.

# No rules really necessary, since anything else is excluded by Tables

$BDisallowed ; fail

Title: 2.  ES and ON are not allowed in the first position

^ ; $ESON .* $RALAN ; fail

Title: 3.  ES and ON, followed by zero or more NSM, is not allowed in the last position

$RALAN .* ; $ESON $NSM* $ ; fail

Title: 4.  If an R, AL or AN is present, no L may be present.

$RALAN .* $BCL ; fail
$BCL .* $RALAN ; fail

Title: 5.  If an EN is present, no AN may be present, and vice versa.

# Overlaps with A.13/14 above, not necessary to restate

Title: 6.  The first character may not be an NSM.

^ ; $NSM ; fail

Title: 7.  The first character may not be an EN (European Number) or an AN (Arabic Number).

^ ; $ENAN .* $RALAN ; fail

# NOTE: all of the "not allowed in first position" rules could be combined together

# ===================================

# 4.2.4. Registration Validation Summary: if at least one non-ASCII then <= 59 bytes of PunyCode
# Needs to be done outside of this table