<?php
namespace JmesPath;

/**
 * Tree visitor used to compile JMESPath expressions into native PHP code.
 */
class TreeCompiler
{
    private $indentation;
    private $source;
    private $vars;

    /**
     * @param array  $ast    AST to compile.
     * @param string $fnName The name of the function to generate.
     * @param string $expr   Expression being compiled.
     *
     * @return string
     */
    public function visit(array $ast, $fnName, $expr)
    {
        $this->vars = [];
        $this->source = $this->indentation = '';
        $this->write("<?php\n")
            ->write('use JmesPath\\TreeInterpreter as Ti;')
            ->write('use JmesPath\\FnDispatcher as Fd;')
            ->write('use JmesPath\\Utils;')
            ->write('')
            ->write('function %s(Ti $interpreter, $value) {', $fnName)
            ->indent()
                ->dispatch($ast)
                ->write('')
                ->write('return $value;')
            ->outdent()
        ->write('}');

        return $this->source;
    }

    /**
     * @param array $node
     * @return mixed
     */
    private function dispatch(array $node)
    {
        return $this->{"visit_{$node['type']}"}($node);
    }

    /**
     * Creates a monotonically incrementing unique variable name by prefix.
     *
     * @param string $prefix Variable name prefix
     *
     * @return string
     */
    private function makeVar($prefix)
    {
        if (!isset($this->vars[$prefix])) {
            $this->vars[$prefix] = 0;
            return '$' . $prefix;
        }

        return '$' . $prefix . ++$this->vars[$prefix];
    }

    /**
     * Writes the given line of source code. Pass positional arguments to write
     * that match the format of sprintf.
     *
     * @param string $str String to write
     * @return $this
     */
    private function write($str)
    {
        $this->source .= $this->indentation;
        if (func_num_args() == 1) {
            $this->source .= $str . "\n";
            return $this;
        }
        $this->source .= vsprintf($str, array_slice(func_get_args(), 1)) . "\n";
        return $this;
    }

    /**
     * Decreases the indentation level of code being written
     * @return $this
     */
    private function outdent()
    {
        $this->indentation = substr($this->indentation, 0, -4);
        return $this;
    }

    /**
     * Increases the indentation level of code being written
     * @return $this
     */
    private function indent()
    {
        $this->indentation .= '    ';
        return $this;
    }

    private function visit_or(array $node)
    {
        $a = $this->makeVar('beforeOr');
        return $this
            ->write('%s = $value;', $a)
            ->dispatch($node['children'][0])
            ->write('if (!Utils::isTruthy($value)) {')
                ->indent()
                ->write('$value = %s;', $a)
                ->dispatch($node['children'][1])
                ->outdent()
            ->write('}');
    }

    private function visit_and(array $node)
    {
        $a = $this->makeVar('beforeAnd');
        return $this
            ->write('%s = $value;', $a)
            ->dispatch($node['children'][0])
            ->write('if (Utils::isTruthy($value)) {')
                ->indent()
                ->write('$value = %s;', $a)
                ->dispatch($node['children'][1])
                ->outdent()
            ->write('}');
    }

    private function visit_not(array $node)
    {
        return $this
            ->write('// Visiting not node')
            ->dispatch($node['children'][0])
            ->write('// Applying boolean not to result of not node')
            ->write('$value = !Utils::isTruthy($value);');
    }

    private function visit_subexpression(array $node)
    {
        return $this
            ->dispatch($node['children'][0])
            ->write('if ($value !== null) {')
                ->indent()
                ->dispatch($node['children'][1])
                ->outdent()
            ->write('}');
    }

    private function visit_field(array $node)
    {
        $arr = '$value[' . var_export($node['value'], true) . ']';
        $obj = '$value->{' . var_export($node['value'], true) . '}';
        $this->write('if (is_array($value) || $value instanceof \\ArrayAccess) {')
                ->indent()
                ->write('$value = isset(%s) ? %s : null;', $arr, $arr)
                ->outdent()
            ->write('} elseif ($value instanceof \\stdClass) {')
                ->indent()
                ->write('$value = isset(%s) ? %s : null;', $obj, $obj)
                ->outdent()
            ->write("} else {")
                ->indent()
                ->write('$value = null;')
                ->outdent()
            ->write("}");

        return $this;
    }

    private function visit_index(array $node)
    {
        if ($node['value'] >= 0) {
            $check = '$value[' . $node['value'] . ']';
            return $this->write(
                '$value = (is_array($value) || $value instanceof \\ArrayAccess)'
                    . ' && isset(%s) ? %s : null;',
                $check, $check
            );
        }

        $a = $this->makeVar('count');
        return $this
            ->write('if (is_array($value) || ($value instanceof \\ArrayAccess && $value instanceof \\Countable)) {')
                ->indent()
                ->write('%s = count($value) + %s;', $a, $node['value'])
                ->write('$value = isset($value[%s]) ? $value[%s] : null;', $a, $a)
                ->outdent()
            ->write('} else {')
                ->indent()
                ->write('$value = null;')
                ->outdent()
            ->write('}');
    }

    private function visit_literal(array $node)
    {
        return $this->write('$value = %s;', var_export($node['value'], true));
    }

    private function visit_pipe(array $node)
    {
        return $this
            ->dispatch($node['children'][0])
            ->dispatch($node['children'][1]);
    }

    private function visit_multi_select_list(array $node)
    {
        return $this->visit_multi_select_hash($node);
    }

    private function visit_multi_select_hash(array $node)
    {
        $listVal = $this->makeVar('list');
        $value = $this->makeVar('prev');
        $this->write('if ($value !== null) {')
            ->indent()
            ->write('%s = [];', $listVal)
            ->write('%s = $value;', $value);

        $first = true;
        foreach ($node['children'] as $child) {
            if (!$first) {
                $this->write('$value = %s;', $value);
            }
            $first = false;
            if ($node['type'] == 'multi_select_hash') {
                $this->dispatch($child['children'][0]);
                $key = var_export($child['value'], true);
                $this->write('%s[%s] = $value;', $listVal, $key);
            } else {
                $this->dispatch($child);
                $this->write('%s[] = $value;', $listVal);
            }
        }

        return $this
            ->write('$value = %s;', $listVal)
            ->outdent()
            ->write('}');
    }

    private function visit_function(array $node)
    {
        $value = $this->makeVar('val');
        $args = $this->makeVar('args');
        $this->write('%s = $value;', $value)
            ->write('%s = [];', $args);

        foreach ($node['children'] as $arg) {
            $this->dispatch($arg);
            $this->write('%s[] = $value;', $args)
                ->write('$value = %s;', $value);
        }

        return $this->write(
            '$value = Fd::getInstance()->__invoke(%s, %s);',
            var_export($node['value'], true), $args
        );
    }

    private function visit_slice(array $node)
    {
        return $this
            ->write('$value = !is_string($value) && !Utils::isArray($value)')
            ->write('    ? null : Utils::slice($value, %s, %s, %s);',
                var_export($node['value'][0], true),
                var_export($node['value'][1], true),
                var_export($node['value'][2], true)
            );
    }

    private function visit_current(array $node)
    {
        return $this->write('// Visiting current node (no-op)');
    }

    private function visit_expref(array $node)
    {
        $child = var_export($node['children'][0], true);
        return $this->write('$value = function ($value) use ($interpreter) {')
            ->indent()
            ->write('return $interpreter->visit(%s, $value);', $child)
            ->outdent()
        ->write('};');
    }

    private function visit_flatten(array $node)
    {
        $this->dispatch($node['children'][0]);
        $merged = $this->makeVar('merged');
        $val = $this->makeVar('val');

        $this
            ->write('// Visiting merge node')
            ->write('if (!Utils::isArray($value)) {')
                ->indent()
                ->write('$value = null;')
                ->outdent()
            ->write('} else {')
                ->indent()
                ->write('%s = [];', $merged)
                ->write('foreach ($value as %s) {', $val)
                    ->indent()
                    ->write('if (is_array(%s) && array_key_exists(0, %s)) {', $val, $val)
                        ->indent()
                        ->write('%s = array_merge(%s, %s);', $merged, $merged, $val)
                        ->outdent()
                    ->write('} elseif (%s !== []) {', $val)
                        ->indent()
                        ->write('%s[] = %s;', $merged, $val)
                        ->outdent()
                    ->write('}')
                    ->outdent()
                ->write('}')
                ->write('$value = %s;', $merged)
                ->outdent()
            ->write('}');

        return $this;
    }

    private function visit_projection(array $node)
    {
        $val = $this->makeVar('val');
        $collected = $this->makeVar('collected');
        $this->write('// Visiting projection node')
            ->dispatch($node['children'][0])
            ->write('');

        if (!isset($node['from'])) {
            $this->write('if (!is_array($value) && !($value instanceof \stdClass)) { $value = null; }');
        } elseif ($node['from'] == 'object') {
            $this->write('if (!Utils::isObject($value)) { $value = null; }');
        } elseif ($node['from'] == 'array') {
            $this->write('if (!Utils::isArray($value)) { $value = null; }');
        }

        $this->write('if ($value !== null) {')
            ->indent()
            ->write('%s = [];', $collected)
            ->write('foreach ((array) $value as %s) {', $val)
                ->indent()
                ->write('$value = %s;', $val)
                ->dispatch($node['children'][1])
                ->write('if ($value !== null) {')
                    ->indent()
                    ->write('%s[] = $value;', $collected)
                    ->outdent()
                ->write('}')
                ->outdent()
            ->write('}')
            ->write('$value = %s;', $collected)
            ->outdent()
        ->write('}');

        return $this;
    }

    private function visit_condition(array $node)
    {
        $value = $this->makeVar('beforeCondition');
        return $this
            ->write('%s = $value;', $value)
            ->write('// Visiting condition node')
            ->dispatch($node['children'][0])
            ->write('// Checking result of condition node')
            ->write('if (Utils::isTruthy($value)) {')
                ->indent()
                ->write('$value = %s;', $value)
                ->dispatch($node['children'][1])
                ->outdent()
            ->write('} else {')
                ->indent()
                ->write('$value = null;')
                ->outdent()
            ->write('}');
    }

    private function visit_comparator(array $node)
    {
        $value = $this->makeVar('val');
        $a = $this->makeVar('left');
        $b = $this->makeVar('right');

        $this
            ->write('// Visiting comparator node')
            ->write('%s = $value;', $value)
            ->dispatch($node['children'][0])
            ->write('%s = $value;', $a)
            ->write('$value = %s;', $value)
            ->dispatch($node['children'][1])
            ->write('%s = $value;', $b);

        if ($node['value'] == '==') {
            $this->write('$value = Utils::isEqual(%s, %s);', $a, $b);
        } elseif ($node['value'] == '!=') {
            $this->write('$value = !Utils::isEqual(%s, %s);', $a, $b);
        } else {
            $this->write(
                '$value = (is_int(%s) || is_float(%s)) && (is_int(%s) || is_float(%s)) && %s %s %s;',
                $a, $a, $b, $b, $a, $node['value'], $b
            );
        }

        return $this;
    }

    /** @internal */
    public function __call($method, $args)
    {
        throw new \RuntimeException(
            sprintf('Invalid node encountered: %s', json_encode($args[0]))
        );
    }
}
