--[[
Copyright (c) 2010-2013 Matthias Richter

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

Except as contained in this notice, the name(s) of the above copyright holders
shall not be used in advertising or otherwise to promote the sale, use or
other dealings in this Software without prior written authorization.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
]]--

local Timer = {}
Timer.__index = Timer

local function _nothing_() end

local function updateTimerHandle(handle)
        -- handle: {
        --   time = <number>,
        --   after = <function>,
        --   during = <function>,
        --   limit = <number>,
        --   count = <number>,
        --   paused = <boolean>
        -- }
        if handle.paused then return end

        handle.time = handle.time + DT
        if handle.during(math.max(handle.limit - handle.time, 0)) == false then
            handle.count = 0
        end

        while handle.time >= handle.limit and handle.count > 0 do
            if handle.after(handle.after) == false then
                handle.count = 0
                break
            end
            handle.time = handle.time - handle.limit
            handle.count = handle.count - 1

            -- Fix for infinite loop when waiting 0 seconds
            if handle.limit == 0 then
                break
            end
        end
end

function Timer:update()
    -- timers may create new timers, which leads to undefined behavior
    -- in pairs() - so we need to put them in a different table first
    local to_update = {}
    for handle in pairs(self.functions) do
        to_update[handle] = handle
    end

    for handle in pairs(to_update) do
        if self.functions[handle] then
            updateTimerHandle(handle)
            if handle.count == 0 then
                self.functions[handle] = nil
            end
        end
    end
end

function Timer:pause(handle)
    if handle then
        if self.functions[handle] then
            handle.paused = true
        end
    else
        for handle in pairs(self.functions) do
            handle.paused = true
        end
    end
end

function Timer:unpause(handle)
    if handle then
        if self.functions[handle] then
            handle.paused = false
        end
    else
        for handle in pairs(self.functions) do
            handle.paused = false
        end
    end
end

function Timer:during(delay, during, after)
    local handle = { time = 0, during = during, after = after or _nothing_, limit = delay, count = 1, paused = false }
    self.functions[handle] = true
    return handle
end

function Timer:after(delay, func)
    return self:during(delay, _nothing_, func)
end

function Timer:every(delay, after, count)
    local count = count or math.huge -- exploit below: math.huge - 1 = math.huge
    local handle = { time = 0, during = _nothing_, after = after, limit = delay, count = count, paused = false }
    self.functions[handle] = true
    return handle
end

function Timer:cancel(handle)
    if type(handle) == "table" and handle.handle then
        handle = handle.handle
    end
    self.functions[handle] = nil
end

function Timer:clear()
    self.functions = {}
end

function Timer:script(f)
    local container = { handle = nil }
    local thread = coroutine.create(f)
    local co = function (...)
        local ok, msg = coroutine.resume(thread, ...)
        if not ok then
            COROUTINE_TRACEBACK = debug.traceback(thread)
            error(msg)
        end
    end
    co(function(t)
        container.handle = self:after(t or 0, co)
        coroutine.yield()
    end)
    return container
end

Timer.tween = setmetatable({
    -- helper functions
    out = function(f) -- 'rotates' a function
        return function(s, ...) return 1 - f(1-s, ...) end
    end,
    chain = function(f1, f2) -- concatenates two functions
        return function(s, ...) return (s < .5 and f1(2*s, ...) or 1 + f2(2*s-1, ...)) * .5 end
    end,

    -- useful tweening functions
    linear = function(s) return s end,
    quad   = function(s) return s*s end,
    cubic  = function(s) return s*s*s end,
    quart  = function(s) return s*s*s*s end,
    quint  = function(s) return s*s*s*s*s end,
    sine   = function(s) return 1-math.cos(s*math.pi/2) end,
    expo   = function(s) return 2^(10*(s-1)) end,
    circ   = function(s) return 1 - math.sqrt(1-s*s) end,

    back = function(s,bounciness)
        bounciness = bounciness or 1.70158
        return s*s*((bounciness+1)*s - bounciness)
    end,

    bounce = function(s) -- magic numbers ahead
        local a,b = 7.5625, 1/2.75
        return math.min(a*s^2, a*(s-1.5*b)^2 + .75, a*(s-2.25*b)^2 + .9375, a*(s-2.625*b)^2 + .984375)
    end,

    elastic = function(s, amp, period)
        amp, period = amp and math.max(1, amp) or 1, period or .3
        return (-amp * math.sin(2*math.pi/period * (s-1) - math.asin(1/amp))) * 2^(10*(s-1))
    end,
}, {

-- register new tween
__call = function(tween, self, len, subject, target, method, after, ...)
    -- recursively collects fields that are defined in both subject and target into a flat list
    local function tween_collect_payload(subject, target, out)
        for k,v in pairs(target) do
            local ref = subject[k]
            assert(type(v) == type(ref), 'Type mismatch in field "'..tostring(k)..'".')
            if type(v) == 'table' then
                tween_collect_payload(ref, v, out)
            else
                local ok, delta = pcall(function() return (v-ref)*1 end)
                assert(ok, 'Field "'..tostring(k)..'" does not support arithmetic operations')
                out[#out+1] = {subject, k, delta}
            end
        end
        return out
    end

    method = tween[method or 'linear'] -- see __index
    local payload, t, args = tween_collect_payload(subject, target, {}), 0, {...}

    local last_s = 0
    return self:during(len, function()
        t = t + DT
        local s = method(math.min(1, t/len), unpack(args))
        local ds = s - last_s
        last_s = s
        for _, info in ipairs(payload) do
            local ref, key, delta = unpack(info)
            ref[key] = ref[key] + delta * ds
        end
    end, after)
end,

-- fetches function and generated compositions for method `key`
__index = function(tweens, key)
    if type(key) == 'function' then return key end

    assert(type(key) == 'string', 'Method must be function or string.')
    if rawget(tweens, key) then return rawget(tweens, key) end

    local function construct(pattern, f)
        local method = rawget(tweens, key:match(pattern))
        if method then return f(method) end
        return nil
    end

    local out, chain = rawget(tweens,'out'), rawget(tweens,'chain')
    return construct('^in%-([^-]+)$', function(...) return ... end)
           or construct('^out%-([^-]+)$', out)
           or construct('^in%-out%-([^-]+)$', function(f) return chain(f, out(f)) end)
           or construct('^out%-in%-([^-]+)$', function(f) return chain(out(f), f) end)
           or error('Unknown interpolation method: ' .. key)
end})

-- Timer instancing
function Timer.new()
    return setmetatable({functions = {}, tween = Timer.tween}, Timer)
end

-- default instance
local default = Timer.new()

-- module forwards calls to default instance
local module = {}
for k in pairs(Timer) do
    if k ~= "__index" then
        module[k] = function(...) return default[k](default, ...) end
    end
end
module.tween = setmetatable({}, {
    __index = Timer.tween,
    __newindex = function(k,v) Timer.tween[k] = v end,
    __call = function(t, ...) return default:tween(...) end,
})

return setmetatable(module, {__call = Timer.new})
