<?php
/**
 * This source file is part of the open source project
 * ExpressionEngine (https://expressionengine.com)
 *
 * @link      https://expressionengine.com/
 * @copyright Copyright (c) 2003-2022, Packet Tide, LLC (https://www.packettide.com)
 * @license   https://expressionengine.com/license Licensed under Apache License, Version 2.0
 */

namespace ExpressionEngine\Library\Parser\Conditional;

use ExpressionEngine\Library\Parser\AbstractParser;
use ExpressionEngine\Library\Parser\Conditional\Exception\ParserException;
use ExpressionEngine\Library\Parser\Conditional\Exception\BooleanExpressionException;
use ExpressionEngine\Library\Parser\Conditional\Token\Boolean;

/**
 * Core Conditional Parser
 *
 * Implemented as a recursive descent parser.
 *
 * The Grammar, written without left recursion for clarity.
 *
 *  template = [TEMPLATE_STRING | conditional]*
 *  conditional = LD IF expr RD template (ELSEIF expr RD template)* (ELSE template)? ENDIF
 *  expr = bool_expr | value
 *  bool_expr = value OPERATOR expr | parenthetical_expr OPERATOR expr
 *  parenthetical_expr = LP expr RP
 *  value = NUMBER | STRING | BOOL | VARIABLE | TAG
 *
 * The grammar as it stands should be LL(1) and LALR compatible. If anyone
 * goes really code happy, be my guest.
 */
class Parser extends AbstractParser
{
    protected $output = '';
    protected $output_buffers = array();

    protected $variables = array();

    protected $safety = false;

    protected $last_conditional_annotation;

    private $ignore_whitespace = false;

    public function parse()
    {
        $this->openBuffer();

        do {
            $this->next();
            $this->template();
        } while (count($this->tokens));

        $this->expect('EOS');

        $out = $this->closeBuffer(false);

        // If the output starts with \n and ends with \n remove just the first
        // and last (not trim() which will remove ALL); this is to remove any
        // whitespace we added with annotations
        if ($out && $out[0] == "\n" && substr($out, -1) == "\n") {
            $out = substr($out, 1);
            $out = substr($out, 0, strlen($out) - 1);
        }

        return $out;
    }

    /**
     * Set the variables to use for the parsing
     */
    public function setVariables($vars)
    {
        $this->variables = $vars;
    }

    /**
     * Turn safety on.
     *
     * When safety is on, any non-scalars are turned into FALSE so that
     * the conditional can fully execute
     */
    public function safetyOn()
    {
        $this->safety = true;
    }

    /**
     * Output the last conditional annotation.
     *
     * Do *NOT* call this unless you know why. It's used by the conditional
     * statement class to re-insert conditional annotations when it has to
     * write a conditional back out.
     */
    public function outputLastAnnotation()
    {
        if (! isset($this->last_conditional_annotation)) {
            return;
        }

        $this->output($this->last_conditional_annotation->lexeme);
    }

    /**
     * Template production rule
     */
    protected function template()
    {
        // this loop is identical to calling $this->template() at the
        // end of both if branches, but avoids the added weight on the stack
        while (true) {
            if ($this->is('TEMPLATE_STRING')) {
                $this->output($this->value());
                $this->next();
            } elseif ($this->acceptTag('IF')) {
                $token = $this->token;

                $conditional = new Statement($this);

                try {
                    $this->conditional($conditional);
                } catch (BooleanExpressionException $e) {
                    throw new ParserException(
                        $this->getRethrowMessage($e, $token)
                    );
                }

                $this->expectTag('ENDIF', $token);
                $this->expect('RD');

                $conditional->closeIf();
            } else {
                break;
            }
        }
    }

    /**
     * Conditional production rule
     *
     * {if condition}
     *     template
     * {if:else condition}
     *     template
     * {if:else}
     *     template
     * {/if}
     */
    protected function conditional($conditional)
    {
        $if_expression = $this->condition();

        if ($conditional->addIf($if_expression)) {
            $this->next();
            $this->template();
        } else {
            $this->next(false);
            $this->skipConditionalBody();
        }

        while ($this->acceptTag('ELSEIF')) {
            $elseif_expression = $this->condition();

            if ($conditional->addElseIf($elseif_expression)) {
                $this->next();
                $this->template();
            } else {
                $this->next(false);
                $this->skipConditionalBody();
            }
        }

        if ($this->acceptTag('ELSE')) {
            $this->expect('RD');

            if ($conditional->addElse()) {
                $this->template();
            } else {
                $this->skipConditionalBody();
            }
        }
    }

    /**
     * Seek past the body of the conditional. This method
     * will also skip any nested conditionals since we don't
     * need to evaluate those if they are not going to be output.
     */
    protected function skipConditionalBody()
    {
        $conditional_depth = 0;
        $this->ignore_whitespace = true;

        do {
            if ($this->isTag('ENDIF')) {
                if ($conditional_depth == 0) {
                    break;
                }

                $conditional_depth--;

                // skip the LD and ENDIF and expect an RD
                // to form {/if}.
                $this->next();
                $this->next();
                $this->expect('RD');

                continue;
            } elseif ($this->isTag('IF')) {
                $conditional_depth++;
                $this->next();
            } elseif ($this->is('TEMPLATE_STRING') || $this->is('COMMENT')) {
                $this->next(false);

                continue;
            } elseif ($conditional_depth == 0) {
                break;
            }

            $this->next(false);
        } while ($this->valid());

        $this->ignore_whitespace = false;
    }

    /**
     * The condition and closing brace.
     *
     * 5 == 7 && bob - mary}
     */
    protected function condition()
    {
        $this->openBuffer();

        $expression = $this->expression();

        // Expect an RD, but don't move to the next token
        // as it may be a comment annotating the next conditional
        // when we're not actually there yet
        // e.g. {if current}{!-- don't touch this yet --}{if nested}...
        if (! $this->is('RD')) {
            throw new ParserException(
                $this->expectedMessage('RD')
            );
        }

        $this->closeBuffer(); // discard whitespace added by next()

        return $expression;
    }

    /**
     * Boolean Expressions
     *
     * This does the left side of the expression and then loops if that ends
     * in an operator.
     */
    protected function expression()
    {
        $expression = new BooleanExpression();

        do {
            $continue_loop = false;

            while ($this->is('LP')) {
                $expression->add($this->token);
                $this->next();
            }

            if ($this->is('BOOL') ||
                $this->is('NUMBER') ||
                $this->is('STRING')) {
                if (! $this->token->canEvaluate()) {
                    $this->addSafely($expression);
                } else {
                    $expression->add($this->token);
                }

                $this->next();
            } elseif ($this->is('VARIABLE')) {
                $this->variable($expression);
                $this->next();
            } elseif ($this->is('MISC')) {
                $this->addSafely($expression);
                $this->next();
            }

            // A closing parenthesis would be before the operator
            while ($this->is('RP')) {
                $expression->add($this->token);
                $this->next();
            }

            // If we hit an operator, we need to go around again
            // looking for the right hand value.
            if ($this->is('OPERATOR')) {
                $expression->add($this->token);
                $this->next();

                $continue_loop = true;
            }

            // Seek past tags, adding them to output, but pretending that
            // they are basically not there. This allows for arbitrary tag
            // embedding in places where we would otherwise consider variables
            // illegal. This is fine because we don't know what those tags will
            // evaluate to.
            while ($this->is('TAG')) {
                $this->addSafely($expression);
                $this->next();
                $continue_loop = true;
            }
        } while ($continue_loop == true);

        return $expression;
    }

    /**
     * Variable Values
     */
    protected function variable($expression)
    {
        $name = $this->value();

        if (array_key_exists($name, $this->variables)) {
            $value = $this->variables[$name];

            // can't do arrays
            if (is_array($value)) {
                return $this->addFalse($expression);
            }

            // can't do objects
            if (is_object($value) and ! method_exists($value, '__toString')) {
                return $this->addFalse($expression);
            }

            $this->token->setValue($value);
        } elseif ($this->safety === true) {
            return $this->addFalse($expression);
        }

        $expression->add($this->token);
    }

    /**
     * Embedded Tags and Miscellaneous Junk
     */
    protected function addSafely($expression)
    {
        if ($this->safety === true) {
            $expression->add(new Boolean(false));
        } else {
            $expression->add($this->token);
        }
    }

    /**
     * Add a false token
     *
     * These are used to replace invalid values.
     */
    protected function addFalse($expression)
    {
        $expression->add(new Boolean(false));
    }

    /**
     * Add to the current output buffer
     */
    public function output($value)
    {
        $this->output .= $value;
    }

    /**
     * Move to the next token
     */
    protected function next($skip_and_output_comments = true)
    {
        parent::next();

        if ($this->is('WHITESPACE')) {
            $this->whitespace();
            $this->next();
        }

        if ($this->is('COMMENT')) {
            if ($this->token->conditional_annotation) {
                $this->last_conditional_annotation = $this->token;

                if ($skip_and_output_comments) {
                    return $this->next();
                }
            }

            if ($skip_and_output_comments) {
                $this->output($this->value());
                $this->next();
            }
        }
    }

    /**
     * Add whitespace
     */
    protected function whitespace()
    {
        if (! $this->ignore_whitespace && substr($this->output, -1) != ' ') {
            $this->output(' ');
        }
    }

    /**
     * Open a new output buffer
     */
    protected function openBuffer()
    {
        $this->output_buffers[] = '';
        $this->initBuffer();
    }

    /**
     * Close and flush the current output buffer
     */
    protected function closeBuffer($trim = true)
    {
        $out = array_pop($this->output_buffers);
        $this->initBuffer();

        return $trim ? trim($out) : $out;
    }

    /**
     * Initialize the buffer pointer so we can append
     * to `$this->output` without worrying about which
     * buffer to use.
     */
    protected function initBuffer()
    {
        $this->output = & $this->output_buffers[count($this->output_buffers) - 1];
    }

    /**
     * Check if there is a tag at the current offset
     *
     * Works like is() but enforces an LD and then compares
     * to the next token.
     *
     * @param String $type The type to check against
     * @return Bool  Current token is LD and next is type
     */
    protected function isTag($type)
    {
        if ($this->is('LD')) {
            $next = current($this->tokens);

            if ($next->type == $type) {
                return true;
            }
        }

        return false;
    }

    /**
     * Enforce an expected token.
     *
     * Overrides the abstract one to throw an exception.
     *
     * @param String $expect_type The type to check against
     * @return Bool  Expected token was found
     * @throws ParserException If expected token is not found
     */
    protected function expect($expect_type, $open = null)
    {
        if (parent::expect($expect_type) === false) {
            throw new ParserException(
                $this->expectedMessage($expect_type, $open)
            );
        }

        return true;
    }

    /**
     * Accept a tag token.
     *
     * Works like accept, but assumes that the token is preceded by an LD.
     */
    protected function acceptTag($type)
    {
        if (! $this->isTag($type)) {
            return false;
        }

        $this->openBuffer();
        $this->next();
        $this->next();
        $this->closeBuffer(); // discard next()'s whitespace

        return true;
    }

    /**
     * Expect a tag token
     *
     * Works like expect, but assumes that the token is preceded by an LD.
     */
    protected function expectTag($expect_type, $open = null)
    {
        if (! $this->acceptTag($expect_type)) {
            throw new ParserException(
                $this->expectedMessage($expect_type . ' tag', $open)
            );
        }

        return true;
    }

    /**
     * Rethrow an error message.
     *
     * Since a rethrow can happen after tokens have been consumed,
     * we require that a token is given for state information.
     */
    private function getRethrowMessage($exception, $token = null)
    {
        $message = $exception->getMessage();

        $location = $token->context;
        $lineno = $token->lineno;

        return $message . "\n\nIn $location on line $lineno";
    }

    /**
     * Construct an error message for when we find ourselves in a state
     * we can't resolve.
     *
     * We try to be as verbose and intelligent as possible. This is not
     * hit during regular execution, so it can be pretty heavy.
     *
     * @param String $expected Expected token type
     * @param Token $open The token that last opened a tag
     */
    private function expectedMessage($expected, $open = null)
    {
        $value = $this->value();
        $found_type = $this->token->type;
        $location = $this->token->context;
        $lineno = $this->token->lineno;

        if ($found_type != 'VARIABLE' && strlen($value) > 23) {
            $value = substr($value, 0, 20) . '...';
        }

        if ($found_type == 'EOS') {
            $found_description = "end of $location on line $lineno";
            $expected_description = "$expected";

            if ($open) {
                $expected_description .= " for opening on line " . $open->lineno;

                if ($open->context != $location) {
                    $expected_description .= ' in ' . $open->context;
                }
            }
        } else {
            $found_description = "'$value' ($found_type)";
            $expected_description = "$expected in $location on line $lineno";
        }

        $message = "Unexpected $found_description; expected $expected_description.";

        return $message;
    }
}

// EOF
