util/promise.lua

   1 local promise_methods = {};
   2 local promise_mt = { __name = "promise", __index = promise_methods };
   3
   4 local xpcall = require "util.xpcall".xpcall;
   5
   6 function promise_mt:__tostring()
   7         return  "promise (" .. (self._state or "invalid") .. ")";
   8 end
   9
  10 local function is_promise(o)
  11         local mt = getmetatable(o);
  12         return mt == promise_mt;
  13 end
  14
  15 local function wrap_handler(f, resolve, reject, default)
  16         if not f then
  17                 return default;
  18         end
  19         return function (param)
  20                 local ok, ret = xpcall(f, debug.traceback, param);
  21                 if ok then
  22                         resolve(ret);
  23                 else
  24                         reject(ret);
  25                 end
  26                 return true;
  27         end;
  28 end
  29
  30 local function next_pending(self, on_fulfilled, on_rejected, resolve, reject)
  31         table.insert(self._pending_on_fulfilled, wrap_handler(on_fulfilled, resolve, reject, resolve));
  32         table.insert(self._pending_on_rejected, wrap_handler(on_rejected, resolve, reject, reject));
  33 end
  34
  35 local function next_fulfilled(promise, on_fulfilled, on_rejected, resolve, reject) -- luacheck: ignore 212/on_rejected
  36         wrap_handler(on_fulfilled, resolve, reject, resolve)(promise.value);
  37 end
  38
  39 local function next_rejected(promise, on_fulfilled, on_rejected, resolve, reject) -- luacheck: ignore 212/on_fulfilled
  40         wrap_handler(on_rejected, resolve, reject, reject)(promise.reason);
  41 end
  42
  43 local function promise_settle(promise, new_state, new_next, cbs, value)
  44         if promise._state ~= "pending" then
  45                 return;
  46         end
  47         promise._state = new_state;
  48         promise._next = new_next;
  49         for _, cb in ipairs(cbs) do
  50                 cb(value);
  51         end
  52         return true;
  53 end
  54
  55 local function new_resolve_functions(p)
  56         local resolved = false;
  57         local function _resolve(v)
  58                 if resolved then return; end
  59                 resolved = true;
  60                 if is_promise(v) then
  61                         v:next(new_resolve_functions(p));
  62                 elseif promise_settle(p, "fulfilled", next_fulfilled, p._pending_on_fulfilled, v) then
  63                         p.value = v;
  64                 end
  65
  66         end
  67         local function _reject(e)
  68                 if resolved then return; end
  69                 resolved = true;
  70                 if promise_settle(p, "rejected", next_rejected, p._pending_on_rejected, e) then
  71                         p.reason = e;
  72                 end
  73         end
  74         return _resolve, _reject;
  75 end
  76
  77 local function new(f)
  78         local p = setmetatable({ _state = "pending", _next = next_pending, _pending_on_fulfilled = {}, _pending_on_rejected = {} }, promise_mt);
  79         if f then
  80                 local resolve, reject = new_resolve_functions(p);
  81                 local ok, ret = pcall(f, resolve, reject);
  82                 if not ok and p._state == "pending" then
  83                         reject(ret);
  84                 end
  85         end
  86         return p;
  87 end
  88
  89 local function all(promises)
  90         return new(function (resolve, reject)
  91                 local count, total, results = 0, #promises, {};
  92                 for i = 1, total do
  93                         promises[i]:next(function (v)
  94                                 results[i] = v;
  95                                 count = count + 1;
  96                                 if count == total then
  97                                         resolve(results);
  98                                 end
  99                         end, reject);
 100                 end
 101         end);
 102 end
 103
 104 local function race(promises)
 105         return new(function (resolve, reject)
 106                 for i = 1, #promises do
 107                         promises[i]:next(resolve, reject);
 108                 end
 109         end);
 110 end
 111
 112 local function resolve(v)
 113         return new(function (_resolve)
 114                 _resolve(v);
 115         end);
 116 end
 117
 118 local function reject(v)
 119         return new(function (_, _reject)
 120                 _reject(v);
 121         end);
 122 end
 123
 124 local function try(f)
 125         return resolve():next(function () return f(); end);
 126 end
 127
 128 function promise_methods:next(on_fulfilled, on_rejected)
 129         return new(function (resolve, reject) --luacheck: ignore 431/resolve 431/reject
 130                 self:_next(on_fulfilled, on_rejected, resolve, reject);
 131         end);
 132 end
 133
 134 function promise_methods:catch(on_rejected)
 135         return self:next(nil, on_rejected);
 136 end
 137
 138 function promise_methods:finally(on_finally)
 139         local function _on_finally(value) on_finally(); return value; end
 140         local function _on_catch_finally(err) on_finally(); return reject(err); end
 141         return self:next(_on_finally, _on_catch_finally);
 142 end
 143
 144 return {
 145         new = new;
 146         resolve = resolve;
 147         reject = reject;
 148         all = all;
 149         race = race;
 150         try = try;
 151         is_promise = is_promise;
 152 }