<?php

#  Copyright (C) 2008,2009 Joshua Grams <josh@qualdan.com>
#
#  This program is free software: you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation, either version 3 of the License, or
#  (at your option) any later version.
#  
#  This program 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.  See the
#  GNU General Public License for more details.
#  
#  You should have received a copy of the GNU General Public License
#  along with this program.  If not, see <http://www.gnu.org/licenses/>.


# This is a simple template-handling system.  You pass it a big data 
# structure with key/value pairs, and a template string to fill out.
#
# Within a template, it recognizes tags of the form ~name [arg...]~, 
# optionally wrapped in HTML comments (which will be removed along with 
# the tag markers when the template is filled out).
#
# { and } as the final argument mark those tags as being the start and 
# end of a sub-template (for optional or repeated sections).  All other 
# tags represent slots to be directly filled by data values.  On a } 
# tag, the name is optional, but must match the corresponding { tag if 
# present.
#
# For a value tag, arguments represent encodings to be applied 
# successively.  For instance, ~foo html~ will encode it to be safe in 
# HTML ('&' to '&amp;', '<' to '&lt;', and so on).
#
# { tags can take one argument, which will call the corresponding 
# tem_auto_* function to munge the data, automating certain common use 
# cases.  See the comments on the tem_auto functions for more details.

require_once('code/wfpl/encode.php');
require_once('code/wfpl/file.php');
require_once('code/wfpl/misc.php');


# Public functions
# ----------------

function template($template, $data) {
	return fill_template(parse_template($template), $data);
}

function template_file($filename, $data) {
	return fill_template(parse_template_file($filename), $data);
}

function parse_template_file($filename) {
	return parse_template(file_get_contents($filename));
}

# First we take the template string and convert it into a tree of
# strings and sub-templates.  A template is a hash with a name string,
# a pieces array, and possibly an args array.

function parse_template($string) {
	# Don't mess with the $stack/$tem assignments!  Since
	# PHP references point to the variable, not the data,
	# it really does have to be written exactly like this.
	$stack[] = array('name' => 'root', 'pieces' => array());
   	$tem = &last($stack);
	# note: for some reason this captures '<!--' but not '-->'.
	$matches = preg_split("/(<!--)?(~[^~]*~)(?(1)-->)/", $string, -1, PREG_SPLIT_DELIM_CAPTURE);
	foreach($matches as $match) {
		if(substr($match,0,1) == '~') {
			$args = explode(' ', substr($match,1,-1));

			if(count($args) == 1 and $args[0] == '}') $name = '';
			else $name = array_shift($args);

			if(last($args) == '{') {  # open block
				array_pop($args);
				$stack[] = array('name' => $name, 'pieces' => array(), 'args' => $args);
				$tem['pieces'][] = &last($stack);
				$tem = &last($stack);
			} elseif(last($args) == '}') {  # close block
				array_pop($args);
				$cur = $stack[count($stack)-1]['name'];
				if($name && $name != $cur) {
				   	die("Invalid template: tried to close '$name', but '$cur' is current.");
				}
				array_pop($stack); $tem = &last($stack);
			} else {  # value slot
				$tem['pieces'][] = array('name' => $name, 'args' => $args);
			}
		} elseif($match and $match != '<!--') {  # static string
			$tem['pieces'][] = $match;
		}
	}
	return $tem;
}

# To fill out a template, we do a depth-first traversal of the template 
# tree, replacing all tags with the data values.

# The data starts out as a nested set of key/value pairs, where the 
# values can be:

	# a string to fill a value slot
	# a hash to fill one instance of a sub-template
	# an array of hashes to fill multiple instances of a sub-template

# The middle form will be converted to the last form as we use it.

function tem_data_as_rows($value) {
	if(is_array($value)) {
		# numeric keys, is already array of arrays -- expand sub-template for each.
		if(array_key_exists(0, $value)) return $value;
		# key/value pairs -- expand sub-template once.
		else return array($value);
	} elseif($value) {
		# value -- expand sub-template once using only parent values
		return array(array());
	} else {
		# empty value -- don't expand sub-template
		return array();
	}
}


# We use dynamic scoping, so we keep a stack of namespaces.
# Each scope references a hash and the parent scope.

function &tem_scope(&$data, $push = true) {
	static $stack = array();

	if($push) {
		$parent =& last($stack);
		$stack[] = array();

		$scope =& last($stack);
		$scope['data'] =& $data;
		if($parent) $scope['parent'] =& $parent;
	} else { # pop
		array_pop($stack);
	}
	return last($stack);
}

function &tem_end_scope() { return tem_scope($x, false); }

# To look up a key, we check each namespace (starting with the
# innermost one) until a value is found.

function tem_find_scope($key, $context) {
	$scope = $context;
	do{
		if(array_key_exists($key, $scope['data'])) {
			return $scope;
		}
	} while($scope = $scope['parent']);

	# not found; return empty scope.
	return array('parent' => $context);
}

function tem_get($key, $context) {
	$scope = tem_find_scope($key, $context);
	if($scope) return $scope['data'][$key];
}

# Return the value for a tag as a set of rows to fill a sub-template.
# If $tag has an arg, call the tem_auto function to munge the data.
function &tem_get_rows($tag, $context)
{
	$key = $tag['name'];
	if(count($tag['args'])) {
		$func = "tem_auto_" . $tag['args'][0];
		function_exists($func)
		   	or die("ERROR: template auto function '$func' not found.<br>\n");
	}
	$scope = tem_find_scope($key, $context);

	if($func) $value = $func($key, $scope);
	else $value = $scope['data'][$key];

	$rows = tem_data_as_rows($value);
	if(is_array($value)) $scope['data'][$key] = $rows;

	return $rows;
}

# Return the value for a tag as an encoded string.
function tem_get_enc($tag, $context)
{
	$key = $tag['name'];
	$value = tem_get($key, $context);
	foreach($tag['args'] as $encoding) {
		$func = "enc_$encoding";
		if(function_exists($func)) $value = $func($value, $key);
		else die("ERROR: encoder function '$func' not found.<br>\n");
	}
	return $value;
}

function fill_template($template, &$data, &$context = NULL) {
	if(!$context) $context =& tem_scope($data);
	foreach($template['pieces'] as $tem) {
		if(is_string($tem)) $output .= $tem;
		elseif($tem['pieces']) {  # sub-template
			$rows =& tem_get_rows($tem, $context);
			foreach($rows as $key => &$row) {
				$context =& tem_scope($row);
				$context['rows'] =& $rows;
					$output .= fill_template($tem, $row, $context);
				$context =& tem_end_scope();

			}
		} else {  # variable
			$output .= tem_get_enc($tem, $context);
		}
	}
	return $output;
}


# Return a hash containing the top-level sub-templates of tem.
function top_sub_templates($tem) {
	$subs = array();
	foreach($tem['pieces'] as $piece) {
		if(is_array($piece) and $piece['pieces']) {
		   	$subs[$piece['name']] = $piece;
		}
	}
	return $subs;
}

# Replace top-level values in $main with top-level templates from $tem.
function merge_templates($main, $tem) {
	$out = array('name' => $main['name'], 'pieces' => array());

	$subs = top_sub_templates($tem);

	foreach($main['pieces'] as $piece) {
		if(is_array($piece) and !$piece['pieces'] and $subs[$piece['name']]) {
			$piece = $subs[$piece['name']];
		}
		$out['pieces'][] = $piece;
	}
	return $out;
}


# tem_auto functions
# ------------------
#
# If a { tag has an argument, the corresponding tem_auto function is called.
# This allows it to mangle the data to automate some common cases.

# 'sep' (separator) sections will be shown for all but the last parent row.
# Sample usage:
# 	<!--~rows~-->
# 		<!--~row~-->
# 			row content...
# 			<!--~separator sep {~--><hr><!--~separator }"-->
# 		<!--~row~-->
# 	<!--~rows~-->
#
function tem_auto_sep($key, $context) {
	$rows =& $context['parent']['rows'];
	if(key($rows)) return true;
	# else we are on the last row (cursor has hit the end and reset).
}

# 'once' sections will be shown once unless the corresponding data value
# is false.  We check only for false; 0 or '' will not work.

function tem_auto_once($key, $context) {
	if($context['data'][$key] !== false)
	   	return tem_data_as_rows(true);
}

# 'evenodd' sections are given an 'evenodd' attribute whose value
# alternates between 'even' and 'odd'.

function tem_auto_evenodd($key, $context) {
	$rows = $context['data'][$key];
	$even = 0;
	$text = array('even', 'odd');
	foreach($rows as $key => $value) {
		$rows[$key]['evenodd'] = $text[$even];
		$even = 1 - $even;
	}
	return tem_data_as_rows($rows);
}

?>