--- Makes working with events in Factorio a lot more simple.
-- <p>By default, Factorio allows you to register **only one handler** to an event.
-- <p>This module lets you easily register **multiple handlers** to an event.
-- <p>Using this module is as simple as replacing @{LuaBootstrap.on_event|script.on_event} with @{Event.register}.
-- <blockquote>
-- Due to the way that Factorio's event system works, it is not recommended to intermingle `script.on_event` and `Event.register` in a mod.
-- <br>This module hooks into Factorio's event system, and using `script.on_event` for the same event will change which events are registered.
-- </blockquote>
-- <blockquote>
-- This module does not have many of the multiplayer protections that `script.on_event` does.
-- <br>Due to this, great care should be taken when registering events conditionally.
-- </blockquote>
-- @module Event
-- @usage local Event = require('stdlib/event/event')

--Holds the event registry
local event_registry = {}

local Event = {
    _module_name = 'Event',
    core_events = {
        init = 'on_init',
        load = 'on_load',
        configuration_changed = 'on_configuration_changed',
        init_and_config = {'on_init', 'on_configuration_changed'}
    },
    custom_events = {}, -- Holds custom event ids
    protected_mode = false,
    force_crc = false,
    stop_processing = {} -- just has to be unique
}
setmetatable(Event, {__index = require('stdlib/core')})

local Is = require('stdlib/utils/is')

local bootstrap_register = {
    on_init = function()
        Event.dispatch({name = 'on_init'})
    end,
    on_load = function()
        Event.dispatch({name = 'on_load', tick = -1})
    end,
    on_configuration_changed = function(event)
        event.name = 'on_configuration_changed'
        Event.dispatch(event)
    end
}

local function valid_id(id)
    return (Is.Number(id) or Is.String(id)), 'Invalid Event Id, Must be string/int/defines.events, Passed in: ' .. type(id)
end

--- Registers a handler for the given events.
-- If a `nil` handler is passed, remove the given events and stop listening to them.
-- <p>Events dispatch in the order they are registered.
-- <p>An *event ID* can be obtained via @{defines.events},
-- @{LuaBootstrap.generate_event_name|script.generate_event_name} which is in <span class="types">@{int}</span>,
-- and can be a custom input name which is in <span class="types">@{string}</span>.
-- <p>The `event_id` parameter takes in either a single, multiple, or mixture of @{defines.events}, @{int}, and @{string}.
-- @usage
-- -- Create an event that prints the current tick every tick.
-- Event.register(defines.events.on_tick, function(event) print event.tick end)
-- -- Create an event that prints the new ID of a train.
-- Event.register(Trains.on_train_id_changed, function(event) print(event.new_id) end)
-- -- Function call chaining
-- Event.register(event1, handler1).register(event2, handler2)
-- @param event_id (<span class="types">@{defines.events}, @{int}, @{string}, or {@{defines.events}, @{int}, @{string},...}</span>)
-- @tparam function handler the function to call when the given events are triggered
-- @tparam[opt=nil] function matcher a function whose return determines if the handler is executed. event and pattern are passed into this
-- @tparam[opt=nil] mixed pattern an invariant that can be used in the matcher function, passed as the second parameter to your matcher
-- @return (<span class="types">@{Event}</span>) Event module object allowing for call chaining
function Event.register(event_id, handler, matcher, pattern)
    Is.Assert(event_id, 'missing event_id argument')
    Is.Assert(Is.Function(handler), 'handler function is missing, use Event.remove to un register events')
    Is.Assert(Is.Nil(matcher) or Is.Function(matcher), 'matcher must be a function when present')

    --Recursively handle event id tables
    if Is.Table(event_id) then
        for _, id in pairs(event_id) do
            Event.register(id, handler)
        end
        return Event
    end

    Is.Assert(valid_id(event_id))

    -- If the event_id has never been registered before make sure we call the correct script action to register
    -- our Event handler with factorio
    if not event_registry[event_id] then
        event_registry[event_id] = {}

        if Is.String(event_id) then
            --String event ids will either be Bootstrap events or custom input events
            if bootstrap_register[event_id] then
                script[event_id](bootstrap_register[event_id])
            else
                script.on_event(event_id, Event.dispatch)
            end
        elseif event_id >= 0 then
            --Positive values will be defines.events
            script.on_event(event_id, Event.dispatch)
        elseif event_id < 0 then
            --Use negative values to register on_nth_tick
            script.on_nth_tick(math.abs(event_id), Event.dispatch)
        end
    end

    local registry = event_registry[event_id]

    --If handler is already registered for this event: remove it for re-insertion at the end.
    if #registry > 0 then
        for i, registered in ipairs(registry) do
            if registered.handler == handler and registered.pattern == pattern and registered.matcher == matcher then
                table.remove(registry, i)
                log('Same handler already registered for event ' .. event_id .. ' at position ' .. i .. ', moving it to the bottom')
                break
            end
        end
    end

    --Finally insert the handler
    table.insert(registry, {handler = handler, matcher = matcher, pattern = pattern})
    return Event
end

--- Removes a handler from the given events.
-- <p>When the last handler for an event is removed, stop listening to that event.
-- <p>An *event ID* can be obtained via @{defines.events},
-- @{LuaBootstrap.generate_event_name|script.generate_event_name} which is in <span class="types">@{int}</span>,
-- and can be a custom input name which is in <span class="types">@{string}</span>.
-- <p>The `event_id` parameter takes in either a single, multiple, or mixture of @{defines.events}, @{int}, and @{string}.
-- @param event_id (<span class="types">@{defines.events}, @{int}, @{string}, or {@{defines.events}, @{int}, @{string},...}</span>)
-- @tparam[opt] function handler the handler to remove, if not present remove all registered handlers for the event_id
-- @tparam[opt] function matcher
-- @tparam[opt] mixed pattern
-- @return (<span class="types">@{Event}</span>) Event module object allowing for call chaining
function Event.remove(event_id, handler, matcher, pattern)
    Is.Assert(event_id, 'missing event_id argument')

    -- Handle recursion here
    if Is.Table(event_id) then
        for _, id in pairs(event_id) do
            Event.remove(id, handler)
        end
        return Event
    end

    Is.Assert(valid_id(event_id))

    local registry = event_registry[event_id]
    if registry then
        local found_something = false
        for i = #registry, 1, -1 do
            local registered = registry[i]
            if handler then -- handler, possibly matcher, possibly pattern
                if handler == registered.handler then
                    if not matcher and not pattern then
                        table.remove(registry, i)
                        found_something = true
                    elseif matcher then
                        if matcher == registered.matcher then
                            if not pattern then
                                table.remove(registry, i)
                                found_something = true
                            elseif pattern and pattern == registered.pattern then
                                table.remove(registry, i)
                                found_something = true
                            end
                        end
                    elseif pattern and pattern == registered.pattern then
                        table.remove(registry, i)
                        found_something = true
                    end
                end
            elseif matcher then -- no handler, matcher, possibly pattern
                if matcher == registered.matcher then
                    if not pattern then
                        table.remove(registry, i)
                        found_something = true
                    elseif pattern and pattern == registered.pattern then
                        table.remove(registry, i)
                        found_something = true
                    end
                end
            elseif pattern then -- no handler, no matcher, pattern
                if pattern == registered.pattern then
                    table.remove(registry, i)
                    found_something = true
                end
            else -- no handler, matcher, or pattern
                table.remove(registry, i)
                found_something = true
            end
        end

        if found_something and table.size(registry) == 0 then
            -- Clear the registry data and un subscribe if there are no registered handlers left
            event_registry[event_id] = nil

            if Is.String(event_id) then
                -- String event ids will either be Bootstrap events or custom input events
                if bootstrap_register[event_id] then
                    script[event_id](nil)
                else
                    script.on_event(event_id, nil)
                end
            elseif event_id >= 0 then
                -- Positive values will be defines.events
                script.on_event(event_id, nil)
            elseif event_id < 0 then
                -- Use negative values to remove on_nth_tick
                script.on_nth_tick(math.abs(event_id), nil)
            end
        elseif not found_something then
            log('Attempt to deregister already non-registered listener from event: ' .. event_id)
        end
    else
        log('Attempt to deregister already non-registered listener from event: ' .. event_id)
    end
    return Event
end

-- A dispatch helper function
--
-- Call any matcher and, as applicable, the event handler, in protected mode.  Errors are
-- caught and logged to stdout but event processing proceeds thereafter; errors are suppressed.
local function run_protected(registered, event)
    local success, err
    if registered.matcher then
        success, err = pcall(registered.matcher, event, registered.pattern)
        if success and err then
            success, err = pcall(registered.handler, event)
        end
    else
        success, err = pcall(registered.handler, event)
    end

    -- If the handler errors lets make sure someone notices
    if not success then
        if not Event.log_and_print(err) then
            -- no players received the message, force a real error so someone notices
            error(err)
        end
    end

    -- force a crc check if option is enabled. This is a debug option and will hamper performance if enabled
    if (Event.force_crc or event.force_crc) and game then
        log('CRC check called for event [' .. event.name .. ']')
        game.force_crc()
    end

    return success and err or nil
end

--- The user should create a table in this format, for a table that will be passed into @{Event.dispatch}.
-- <p>In general, the user should create an event data table that is in a similar format as the one that Factorio returns.
--> The event data table **MUST** have either `name` or `input_name`.
-- @tfield[opt] int|defines.events name unique event ID generated with @{LuaBootstrap.generate_event_name|script.generate_event_name} ***OR*** @{defines.events}
-- @tfield[opt] string input_name custom input name of an event
-- @field[opt] ... any # of additional fields with extra data, which are passed into the handler registered to an event that this table represents
-- @usage
-- -- below code is from Trains module.
-- -- old_id & new_id are additional fields passed into the handler that's registered to Trains.on_train_id_changed event.
-- local event_data = {
-- old_id = renaming.old_id,
-- new_id = renaming.new_id,
-- name = Trains.on_train_id_changed
-- }
-- Event.dispatch(event_data)
-- @table event_data

--- Calls the handlers that are registered to the given event.
-- <p>Abort calling remaining handlers if any one of them has invalid userdata.
-- <p>Handlers are dispatched in the order they were created.
-- @param event (<span class="types">@{event_data}</span>) the event data table
-- @see https://forums.factorio.com/viewtopic.php?t=32039#p202158 Invalid Event Objects
function Event.dispatch(event)
    Is.Assert.Table(event, 'missing event table')
    --get the registered handlers from name, input_name, or nth_tick in that priority.
    local registry
    if event.name then
        registry = event_registry[event.name]
    elseif event.input_name then
        registry = event_registry[event.input_name]
    elseif event.nth_tick then
        registry = event_registry[-event.nth_tick]
    end

    if registry then
        -- protected_mode runs the handler and matcher in pcall, additionaly forcing a crc can only be
        -- accomplished in protected_mode
        local protected = Event.protected_mode or event.protected_mode

        --add the tick if it is not present, this only affects calling Event.dispatch manually
        --doing the check up here as it will faster than checking every iteration for a constant value
        event.tick = event.tick or game and game.tick or 0

        for _, registered in ipairs(registry) do
            -- Check for userdata and stop processing this and further handlers if not valid
            -- This is the same behavior as factorio events.
            -- This is done inside the loop as other events can modify the event.
            for _, val in pairs(event) do
                if Is.Object(val) and not val.valid then
                    return
                end
            end

            if protected then
                if run_protected(registered, event) == Event.stop_processing then
                    return
                end
            elseif registered.matcher then
                if registered.matcher(event, registered.pattern) then
                    if registered.handler(event) == Event.stop_processing then
                        return
                    end
                end
            else
                if registered.handler(event) == Event.stop_processing then
                    return
                end
            end
        end
    end
end

--- Retrieve or Generate an event_name and store it in Event.custom_events
-- @tparam string event_name the custom name for your event.
-- @treturn int the id associated with the event.
-- @usage
-- Event.register(Event.generate_event_name("my_custom_event"), handler)
function Event.generate_event_name(event_name)
    Is.Assert.String(event_name, 'event_name must be a string.')

    local id
    if Is.Number(Event.custom_events[event_name]) then
        id = Event.custom_events[event_name]
    else
        id = script.generate_event_name()
        Event.custom[event_name] = id
    end
    return id
end

-- TODO complete stub
function Event.raise_event(...)
    script.raise_event(...)
end

function Event.get_event_handler(event_id)
    Is.Assert(valid_id(event_id))
    return {
        script = (tonumber(event_id) or 0 >= 0 or Is.String(event_id)) and script.get_event_handler(event_id),
        handlers = event_registry[event_id]
    }
end

--- Retrieve the event_registry
-- @treturn table event_registry
function Event.get_registry()
    return event_registry
end

function Event.dump(reg_type)
    local init, config, load, events, nth = 0, 0, 0, 0, 0
    for id, registry in pairs(event_registry) do
        if tonumber(id) then
            if id < 0 then
                nth = nth + #registry
            else
                events = events + #registry
            end
        else
            if id == "on_init" then
                init = init + #registry
            elseif id == "on_configuration_changed" then
                config = config + #registry
            elseif id == "load" then
                load = load + #registry
            else
                events = events + #registry
            end
        end
    end
    local all = {
        core = init + load + config,
        init = init,
        config = config,
        load = load,
        events = events,
        nth = nth,
        all = init + config + load + events + nth
    }
    return reg_type and all[reg_type] or all
end

--- Filters events related to entity_type.
-- DEPRECATED
-- @tparam string event_parameter The event parameter to look inside to find the entity type
-- @tparam string entity_type The entity type to filter events for
-- @tparam callable matcher The matcher to invoke if the filter passes. The object defined in the event parameter is passed
function Event.filter_entity(event_parameter, entity_type, matcher)
    return function(evt)
        if (evt[event_parameter].type == entity_type) then
            matcher(evt[event_parameter])
        end
    end
end

return Event