[nit.git] / lib / sax / helpers / namespace_support.nit

# This file is part of NIT ( http://www.nitlanguage.org ).
#
# This file is free software, which comes along with NIT. This software is
# distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
# without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
# PARTICULAR PURPOSE. You can modify it is you want, provided this header
# is kept unaltered, and a notification of the changes is added.
# You are allowed to redistribute it and sell it, alone or is a part of
# another product.

# Encapsulates Namespace logic for use by applications using SAX, or internally by SAX drivers.
module sax::helpers::namespace_support

# Encapsulates Namespace logic for use by applications using SAX, or internally by SAX drivers.
#
# This class encapsulates the logic of Namespace processing:
# it tracks the declarations currently in force for each context
# and automatically processes qualified XML names into their
# Namespace parts; it can also be used in reverse for generating
# XML qualified names from Namespaces.
#
# Namespace support objects are reusable, but the reset method
# must be invoked between each session.
#
# Here is a simple session:
#
#     var parts: Array[String] = new Array[String].with_capacity(3)
#     var support = new NamespaceSupport
#     #
#     support.push_context
#     support.declare_prefix("", "http://www.w3.org/1999/xhtml")
#     support.declare_prefix("dc", "http://www.purl.org/dc#")
#     #
#     parts = support.process_name("p", parts, false).as(not null)
#     assert parts[0] == "http://www.w3.org/1999/xhtml"
#     assert parts[1] == "p"
#     assert parts[2] == "p"
#     #
#     parts = support.process_name("dc:title", parts, false).as(not null)
#     assert parts[0] == "http://www.purl.org/dc#"
#     assert parts[1] == "title"
#     assert parts[2] == "dc:title"
#     #
#     support.pop_context
#
# Note that this class is optimized for the use case where most
# elements do not contain Namespace declarations: if the same
# prefix/URI mapping is repeated for each context (for example), this
# class will be somewhat less efficient.
#
# Although SAX drivers (parsers) may choose to use this class to
# implement namespace handling, they are not required to do so.
# Applications must track namespace information themselves if they
# want to use namespace information.
#
# Note: The original source code and documentation of this class comes, in part,
# from [SAX 2.0](http://www.saxproject.org).
class NamespaceSupport
        # The XML Namespace URI as a constant.
        #
        # The value is `http://www.w3.org/XML/1998/namespace`
        # as defined in the “Namespaces in XML” specification.
        #
        # This is the Namespace URI that is automatically mapped
        # to the `xml` prefix.
        var xmlns = "http://www.w3.org/XML/1998/namespace"

        # The namespace declaration URI as a constant.
        #
        # The value is `http://www.w3.org/xmlns/2000/`, as defined
        # in a erratum to the “Namespaces in XML” recommendation.
        #
        # This is the Namespace URI that is automatically mapped
        # to the `xmlns` prefix.
        var nsdecl = "http://www.w3.org/xmlns/2000/"

        private var contexts: Array[Context] = new Array[Context].with_capacity(32)
        private var current_context: Context = new Context
        private var context_position: Int = 0

        init do
                contexts.push(current_context)
                current_context.declare_prefix("xml", xmlns)
                current_context.declare_prefix("xmlns", nsdecl)
        end

        # Reset this Namespace support object for reuse.
        #
        # It is necessary to invoke this method before reusing the
        # Namespace support object for a new session.
        fun reset do
                contexts.clear
                contexts.enlarge(32)
                context_position = 0
                current_context = new Context
                contexts.push(current_context)
                current_context.declare_prefix("xml", xmlns)
                current_context.declare_prefix("xmlns", nsdecl)
        end

        # Start a new Namespace context.
        #
        # The new context will automatically inherit
        # the declarations of its parent context, but it will also keep
        # track of which declarations were made within this context.
        #
        # Event callback code should start a new context once per element.
        # This means being ready to call this in either of two places.
        # For elements that don't include namespace declarations, the
        # `ContentHandler.start_element` callback is the right place.
        # For elements with such a declaration, it'd done in the first
        # `ContentHandler.start_prefix_mapping` callback.
        # A boolean flag can be used to
        # track whether a context has been started yet. When either of
        # those methods is called, it checks the flag to see if a new context
        # needs to be started. If so, it starts the context and sets the
        # flag. After `ContentHandler.start_element` does that, it always clears
        # the flag.
        #
        # Normally, SAX drivers would push a new context at the beginning
        # of each XML element. Then they perform a first pass over the
        # attributes to process all namespace declarations, making
        # `ContentHandler.start_prefix_mapping` callbacks.
        # Then a second pass is made, to determine the namespace-qualified
        # names for all attributes and for the element name.
        # Finally all the information for the
        # `ContentHandler.start_element` callback is available,
        # so it can then be made.
        #
        # The Namespace support object always starts with a base context
        # already in force: in this context, only the `xml` prefix is
        # declared.
        #
        # SEE: `sax::ContentHandler`
        #
        # SEE: `pop_context`
        fun push_context do
                current_context.decls_ok = false
                context_position += 1

                # Extend the array if necessary.
                if context_position >= contexts.length then
                        current_context = new Context
                        contexts.push(current_context)
                else
                        current_context = contexts[context_position]
                end

                # Set the parent, if any.
                if context_position > 0 then
                        current_context.parent = contexts[context_position - 1]
                end
        end

        # Revert to the previous Namespace context.
        #
        # Normally, you should pop the context at the end of each
        # XML element. After popping the context, all Namespace prefix
        # mappings that were previously in force are restored.
        #
        # You must not attempt to declare additional Namespace
        # prefixes after popping a context, unless you push another
        # context first.
        #
        # SEE: `push_context`
        fun pop_context do
                assert stack_not_empty: context_position > 0
                current_context.clear
                context_position -= 1
                current_context = contexts[context_position]
        end

        # Declare a Namespace prefix.
        #
        # All prefixes must be declared before they are referenced.
        # For example, a SAX driver (parser)
        # would scan an element's attributes
        # in two passes: first for namespace declarations,
        # then a second pass using `process_name` to
        # interpret prefixes against (potentially redefined) prefixes.
        #
        # This method declares a prefix in the current Namespace
        # context; the prefix will remain in force until this context
        # is popped, unless it is shadowed in a descendant context.
        #
        # To declare the default element Namespace, use the empty string as
        # the prefix.
        #
        # Note that you must *not* declare a prefix after
        # you've pushed and popped another Namespace context, or
        # treated the declarations phase as complete by processing
        # a prefixed name.
        #
        # Note that there is an asymmetry in this library:
        # `prefix` will not return the `""` prefix,
        # even if you have declared a default element namespace.
        # To check for a default namespace,
        # you have to look it up explicitly using `uri`.
        # This asymmetry exists to make it easier to look up prefixes
        # for attribute names, where the default prefix is not allowed.
        #
        # Parameters:
        #
        # * `prefix`: prefix to declare, or the empty string to
        # indicate the default element namespace. This may never have
        # the value `xml` or `xmlns`.
        # * `uri`: The Namespace URI to associate with the prefix.
        #
        #
        # Returns:
        #
        # `true` if the prefix and the URI are legal, `false` otherwise.
        #
        # SEE: `process_name`
        #
        # SEE: `uri`
        #
        # SEE: `prefix`
        fun declare_prefix(prefix: String, uri: String): Bool do
                if prefix == "xml" or prefix == "xmlns" or
                                        uri == xmlns or uri == nsdecl then
                        return false
                else
                        current_context.declare_prefix(prefix, uri)
                        return true
                end
        end

        # Process a raw XML qualified name, after all declarations in the current context have been handled by `declare_prefix`.
        #
        # This method processes a raw XML qualified name in the current
        # context by removing the prefix and looking it up among the
        # prefixes currently declared. The return value will be the
        # array supplied by the caller, filled in as follows:
        #
        # * `parts[0]`: Namespace URI, or an empty string if none is in use.
        # * `parts[1]`: local name (without prefix).
        # * `parts[2]`: original raw name.
        #
        # If the raw name has a prefix that has not been declared, then
        # the return value will be `null`.
        #
        # Note that attribute names are processed differently than
        # element names: an unprefixed element name will receive the
        # default Namespace (if any), while an unprefixed attribute name
        # will not.
        #
        # Parameters:
        #
        # * `qname`: raw XML qualified name to be processed.
        # * `parts`: array supplied by the caller. Will be enlarged to 3 elements if
        # needed. If the specified array contains more than 3 elements, its length
        # will be kept intact.
        # * `is_attribute`: flag indicating whether this is an attribute name
        # (`true`) or an element name (`false`).
        #
        # SEE: `declare_prefix`
        fun process_name(qname: String, parts: Array[String], is_attribute: Bool):
                        nullable Array[String] do
                var my_parts = current_context.process_name(qname, is_attribute)

                if my_parts == null then
                        return null
                else
                        parts[0] = my_parts[0]
                        parts[1] = my_parts[1]
                        parts[2] = my_parts[2]
                        if parts[0] == "" and qname == "xmlns" and is_attribute then
                                parts[0] = nsdecl
                                parts[1] = ""
                        end
                        return parts
                end
        end

        # Look up a prefix and get the currently-mapped Namespace URI.
        #
        # This method looks up the prefix in the current context.
        # Use the empty string (`""`) for the default Namespace.
        #
        # Parameters:
        #
        # * `prefix`: The prefix to look up.
        #
        # Returns:
        #
        # The associated Namespace URI, or `null` if the prefix
        # is undeclared in this context.
        #
        # SEE: `prefix`
        #
        # SEE: `prefixes_of`
        fun uri(prefix: String): nullable String do
                return current_context.uri(prefix)
        end

        # Return all prefixes currently declared.
        #
        # Note: if there is a default prefix, it will not be
        # returned in this enumeration; check for the default prefix
        # using the `uri` with an argument of `""` or use `declared_prefixes`.
        #
        # Returns:
        #
        # All prefixes declared in the current context except
        # for the empty (default) prefix.
        #
        # SEE: `declared_prefixes`
        #
        # SEE: `uri`
        fun prefixes: Collection[String] do return current_context.prefixes

        # Return one of the prefixes mapped to a Namespace URI.
        #
        # If more than one prefix is currently mapped to the same
        # URI, this method will make an arbitrary selection; if you
        # want all of the prefixes, use the `prefixes_of` method instead.
        #
        # Note: this will never return the empty (default) prefix;
        # to check for a default prefix, use the `uri`
        # method with an argument of `""`.
        #
        # Parameters:
        #
        # * `uri`: Namespace URI.
        #
        # Returns:
        #
        # One of the prefixes currently mapped to the URI supplied,
        # or `null` if none is mapped or if the URI is assigned to
        # the default Namespace.
        #
        # SEE: `prefixes_of`
        #
        # SEE: `uri`
        fun prefix(uri: String): nullable String do
                return current_context.prefix(uri)
        end

        # Return all prefixes currently declared for an URI.
        #
        # This method returns prefixes mapped to a specific Namespace
        # URI. The `xml` prefix will be included. If you want only one
        # prefix that's mapped to the Namespace URI, and you don't care
        # which one you get, use the `prefix` method instead.
        #
        # Note: the empty (default) prefix is *never* included
        # in this enumeration; to check for the presence of a default
        # Namespace, use the `uri` method with an argument of `""`.
        #
        # Parameters:
        #
        # * `uri`: The Namespace URI.
        #
        # SEE: `prefix`
        #
        # SEE: `declared_prefixes`
        #
        # SEE: `uri`
        fun prefixes_of(uri: String): Collection[String] do
                var prefixes = new Array[String]
                var all_prefixes = self.prefixes

                for prefix in all_prefixes do
                        if uri == self.uri(prefix) then
                                prefixes.push(prefix)
                        end
                end
                return prefixes
        end

        # Return all prefixes declared (and undeclared) in this context.
        #
        # The empty (default) prefix will be included in this
        # enumeration; note that this behaviour differs from that of
        # `prefix`, `prefixes` and `prefixes_of`.
        #
        # SEE: `prefixes`
        #
        # SEE: `uri`
        fun declared_prefixes: Collection[String] do
                return current_context.declared_prefixes
        end
end


# Internal class for a single Namespace context.
#
# This module caches and reuses Namespace contexts,
# so the number allocated
# will be equal to the element depth of the document, not to the total
# number of elements (i.e. 5-10 rather than tens of thousands).
# Also, data structures used to represent contexts are shared when
# possible (child contexts without declarations) to further reduce
# the amount of memory that's consumed.
#
# Note: The original source code and documentation of this class comes, in part,
# from [SAX 2.0](http://www.saxproject.org).
private class Context

        private var empty: Collection[String] = new Array[String].with_capacity(0)

        # `prefix` -> `uri`
        private var prefix_table: nullable Map[String, String] = null

        # Cache of `process_name` for elements.
        #
        # `qname -> [uri, local_name, qname]`
        private var element_name_table: nullable Map[String, Array[String]] = null

        # Cache of `process_name` for attributes.
        #
        # `qname -> [uri, local_name, qname]`
        private var attribute_name_table: nullable Map[String, Array[String]] = null

        # Namespace in absence of prefix.
        private var default_ns: nullable String = null

        # Can we currently declare prefixes in this context?
        var decls_ok: Bool = true is writable

        # All prefixes declared in this context.
        private var declarations: nullable Array[String] = null

        # Was `copy_tables` called since the last call to `parent=`?
        private var decl_seen: Bool = false

        # Parent context.
        private var p_parent: nullable Context = null

        init do
        end

        # (Re)set the parent of this Namespace context.
        #
        # The context must either have been freshly constructed,
        # or must have been cleared.
        #
        # Parameters:
        #
        # * `context`: parent Namespace context object.
        fun parent=(parent: Context) do
                p_parent = parent
                declarations = null
                prefix_table = parent.prefix_table
                element_name_table = parent.element_name_table
                attribute_name_table = parent.attribute_name_table
                default_ns = parent.default_ns
                decl_seen = false
                decls_ok = true
        end

        # Makes associated state become collectible, invalidating this context.
        #
        # `parent=` must be called before this context may be used again.
        fun clear do
                p_parent = null
                prefix_table = null
                element_name_table = null
                attribute_name_table = null
                default_ns = null
                declarations = null
        end

        # Declare a Namespace prefix for this context.
        #
        # Parameters:
        #
        # * `prefix`: prefix to declare.
        # * `uri`: associated Namespace URI.
        #
        # SEE: `NamespaceSupport.declare_prefix`
        fun declare_prefix(prefix: String, uri: String) do
                assert legal_state: decls_ok else
                        sys.stderr.write("Can't declare any more prefixes in this context.\n")
                end

                # Lazy processing...
                if not decl_seen then
                        copy_tables
                end

                if "" == prefix then
                        if "" == uri then
                                default_ns = null
                        else
                                default_ns = uri
                        end
                else if "" == uri then
                        prefix_table.keys.remove(prefix)
                else
                        prefix_table[prefix] = uri
                end
                declarations.push(prefix)
        end

        # Process a raw XML qualified name in this context.
        #
        # Parameters:
        #
        # * `qname`: raw XML qualified name.
        # * `is_attribute`: `true` if this is an attribute name.
        #
        # Returns:
        #
        # An array of three strings containing the URI part (or empty string),
        # the local part and the raw name, or `null` if there is an undeclared
        # prefix.
        #
        # SEE: `NamespaceSupport.process_name`
        fun process_name(qname: String, is_attribute: Bool):
                        nullable Array[String] do
                var name: Array[String]
                var table: Map[String, Array[String]]
                var match: nullable Match

                # Detect errors in call sequence.
                decls_ok = false
                # Select the appropriate table.
                if is_attribute then
                        table = attribute_name_table.as(not null)
                else
                        table = element_name_table.as(not null)
                end

                # Start by looking in the cache, and
                # return immediately if the name
                # is already known in this content.
                if table.keys.has(qname) then
                        return table[qname]
                end

                # We haven't seen this name in this
                # context before. Maybe in the parent
                # context, but we can't assume prefix
                # bindings are the same.
                name = new Array[String].with_capacity(3)
                match = qname.search(':')

                if match == null then
                        # No prefix
                        if is_attribute then
                                name.push("")
                        else
                                name.push(default_ns or else "")
                        end
                        name.push(qname)
                        name.push(qname)
                else
                        # Prefix
                        var prefix = qname.substring(0, match.from)

                        if prefix == "" then
                                if is_attribute then
                                        name.push("")
                                else
                                        name.push(default_ns or else "")
                                end
                                name.push(qname.substring_from(match.after))
                                name.push(qname)
                        else if (not is_attribute) and "xmlns" == prefix then
                                return null
                        else if prefix_table.keys.has(prefix) then
                                name.push(prefix_table[prefix])
                                name.push(qname.substring_from(match.after))
                                name.push(qname)
                        else
                                return null
                        end
                end

                # Save in the cache for future use.
                # (Could be shared with parent context...)
                table[qname] = name
                return name
        end

        # Look up the URI associated with a prefix in this context.
        #
        # Return `null` if no URI is associated with a specified prefix.
        #
        # Parameters:
        #
        # * `prefix`: prefix to look up.
        #
        # SEE: `NamespaceSupport.uri`
        fun uri(prefix: String): nullable String do
                if "" == prefix then
                        return default_ns
                else if prefix_table == null then
                        return null
                else
                        return prefix_table.get_or_null(prefix)
                end
        end

        # Look up one of the prefixes associated with a URI in this context.
        #
        # Since many prefixes may be mapped to the same URI,
        # the return value may be unreliable.
        #
        # Parameters:
        #
        # * `uri`: URI to look up.
        #
        # Returns:
        #
        # The associated prefix, or `null` if none is declared.
        #
        # SEE: `NamespaceSupport.prefix`
        fun prefix(uri: String): nullable String do
                # Note: We do not use the original code from SAX 2.0.1 because it is
                # buggy with redefined prefixes. For example, with
                # `<x xmlns:y="1"><z xmlns:y="2" /></x>`, when in `z`, `uri("1")`
                # returns `"y"` in the original code while it should return `null`.
                # Our code is slower, but it works.
                var all_prefixes = prefixes

                for prefix in all_prefixes do
                        if uri == self.uri(prefix) then
                                return prefix
                        end
                end
                return null
        end

        # Return all prefixes declared in this context (possibly empty).
        #
        # SEE: `NamespaceSupport.declared_prefixes`
        fun declared_prefixes: Collection[String] do
                return declarations or else empty
        end

        # Return all prefixes currently in force.
        #
        # The default prefix, if in force, is *not*
        # returned, and will have to be checked for separately.
        #
        # SEE: `NamespaceSupport.prefixes`
        fun prefixes: Collection[String] do
                if prefix_table == null then
                        return empty
                else
                        return prefix_table.keys
                end
        end

        # Copy on write for the internal tables in this context.
        #
        # This class is optimized for the normal case where most
        # elements do not contain Namespace declarations.
        private fun copy_tables do
                if prefix_table != null then
                        var old_prefix_table = prefix_table.as(not null)
                        prefix_table = new HashMap[String, String]
                        prefix_table.recover_with(old_prefix_table)
                else
                        prefix_table = new HashMap[String, String]
                end
                element_name_table = new HashMap[String, Array[String]]
                attribute_name_table = new HashMap[String, Array[String]]
                declarations = new Array[String]
                decl_seen = true
        end
end