//
//  EXTScope.h
//  extobjc
//
//  Created by Justin Spahr-Summers on 2011-05-04.
//  Copyright (C) 2012 Justin Spahr-Summers.
//  Released under the MIT license.
//

#import "OBSmetamacros.h"

/**
  *\@onExit defines some code to be executed when the current scope exits. The
  *code must be enclosed in braces and terminated with a semicolon, and will be
  *executed regardless of how the scope is exited, including from exceptions,
  *\c goto, \c return, \c break, and \c continue.
 *
  *Provided code will go into a block to be executed later. Keep this in mind as
  *it pertains to memory management, restrictions on assignment, etc. Because
  *the code is used within a block, \c return is a legal (though perhaps
  *confusing) way to exit the cleanup block early.
 *
  *Multiple \@onExit statements in the same scope are executed in reverse
  *lexical order. This helps when pairing resource acquisition with \@onExit
  *statements, as it guarantees teardown in the opposite order of acquisition.
 *
  *@note This statement cannot be used within scopes defined without braces
  *(like a one line \c if). In practice, this is not an issue, since \@onExit is
  *a useless construct in such a case anyways.
 */
#define obs_onExit \
    try {} @finally {} \
    __strong obs_mtl_cleanupBlock_t obs_metamacro_concat(obs_mtl_exitBlock_, __LINE__) __attribute__((cleanup(obs_mtl_executeCleanupBlock), unused)) = ^

/**
  *Creates \c __weak shadow variables for each of the variables provided as
  *arguments, which can later be made strong again with #strongify.
 *
  *This is typically used to weakly reference variables in a block, but then
  *ensure that the variables stay alive during the actual execution of the block
  *(if they were live upon entry).
 *
  *See #strongify for an example of usage.
 */
#define obs_weakify(...) \
    try {} @finally {} \
    obs_metamacro_foreach_cxt(obs_mtl_weakify_,, __weak, __VA_ARGS__)

/**
  *Like #weakify, but uses \c __unsafe_unretained instead, for targets or
  *classes that do not support weak references.
 */
#define obs_unsafeify(...) \
    try {} @finally {} \
    obs_metamacro_foreach_cxt(obs_mtl_weakify_,, __unsafe_unretained, __VA_ARGS__)

/**
  *Strongly references each of the variables provided as arguments, which must
  *have previously been passed to #weakify.
 *
  *The strong references created will shadow the original variable names, such
  *that the original names can be used without issue (and a significantly
  *reduced risk of retain cycles) in the current scope.
 *
  *@code

    id foo = [[NSObject alloc] init];
    id bar = [[NSObject alloc] init];

    @weakify(foo, bar);

    // this block will not keep 'foo' or 'bar' alive
    BOOL (^matchesFooOrBar)(id) = ^ BOOL (id obj){
        // but now, upon entry, 'foo' and 'bar' will stay alive until the block has
        // finished executing
        @strongify(foo, bar);

        return [foo isEqual:obj] || [bar isEqual:obj];
    };

  *@endcode
 */
#define obs_strongify(...) \
    try {} @finally {} \
    _Pragma("clang diagnostic push") \
    _Pragma("clang diagnostic ignored \"-Wshadow\"") \
    obs_metamacro_foreach(obs_mtl_strongify_,, __VA_ARGS__) \
    _Pragma("clang diagnostic pop")

/** *implementation details follow ***/
typedef void (^obs_mtl_cleanupBlock_t)();

void obs_mtl_executeCleanupBlock (__strong obs_mtl_cleanupBlock_t *block);

#define obs_mtl_weakify_(INDEX, CONTEXT, VAR) \
    CONTEXT __typeof__(VAR) obs_metamacro_concat(VAR, _weak_) = (VAR);

#define obs_mtl_strongify_(INDEX, VAR) \
    __strong __typeof__(VAR) VAR = obs_metamacro_concat(VAR, _weak_);