--[[
    ECS World class
    @author : Eiyeron Fulmincendii

    Contains entities, components and system and orchestrates them.
]]--
local class = require("class")
local object = require("object")
local SystemFilter = require("SystemFilter")
local Entity = require("Entity")

ECSWorld = class(object)

function ECSWorld:init( )
    self.entities = {}
    self.components = {}
    self.system_filters = {}
end

--[[
    Search a filter that matches the required components.
]]--
function ECSWorld:searchFilter(required_components)
    -- TODO : inquire why it doesn't call a composant's metamethod.
    local component_list = table.sort(required_components)
    for i,l in ipairs(self.system_filters) do
        if l:compareComponentList(required_components) then
            return l
        end
    end
    return nil
end

--[[
    - system : system to register
    - ... : array of components to require
]]--
function ECSWorld:registerSystem(system_type, ...)
    local required_components = {...}
    local found_filter = self:searchFilter(required_components)
    if found_filter then
        found_filter:registerSystem(system_type)
    else
        local new_filter = SystemFilter:new(required_components)
        self.system_filters[#self.system_filters + 1] = new_filter
        self:searchAndRegisterEntitiesInNewSystemFilter(new_filter)
        new_filter:registerSystem(system_type)
    end
end

--[[
    On component attachment, register the holder entity to
    every filter that can handle it now.
]]
function ECSWorld:searchAndRegisterEntityInSystemFilter(entity)
    for i,system_filter in ipairs(self.system_filters) do
        if system_filter:checkEntityCompatibility(entity) and not system_filter:hasEntity(entity) then
            system_filter:registerEntry(entity)
        end
    end
end

--[[
    On SystemFilter creation, register every compatible entity.
]]
function ECSWorld:searchAndRegisterEntitiesInNewSystemFilter(new_filter)
    for i,entity in ipairs(self.entities) do
        if new_filter:checkEntityCompatibility(entity) and not new_filter:hasEntity(entity) then
            new_filter:registerEntry(entity)
        end
    end
end

--[[
    On Component detachment, prune the filters from the now-incompatible holder entity.
]]--
function ECSWorld:searchAndPruneEntityFromSystemFilter(entity)
    for i,system_filter in ipairs(self.system_filters) do
        if system_filter:hasEntity(entity) and not system_filter:checkEntityCompatibility(entity) then
            system_filter:unregisterEntry(entity)
        end
    end
end


--[[
    - Copies the entity into the ECSWorld's entities
    - Registers it in every SystemFilter already registered
]]
function ECSWorld:createEntity()
    local index = #self.entities + 1
    for i,entity_entry in ipairs(self.entities) do
        if entity_entry.__destroyed then
            index = i
            break
        end
    end
    local e = Entity:new(index, self)
    self.entities[index] = e
    return e
end

--[[
    Called by World itself to mark an entity as destroyed (to override it later if needed)
]]--
function ECSWorld:deleteEntity(entity)
    self:searchAndUnregisterEntitiesInSystemFilter(entity)
    entity.__destroyed = true
end

--[[
    Called by Systems via their Entity. Creates and attach a component to the holder
    entity.
]]--
function ECSWorld:attachComponentToEntity(entity, component_type, ...)
    -- Create on the fly the component list if the world doesn't have it for this component class.
    if not self.components[component_type] then self.components[component_type] = {} end
    self.components[component_type][entity.__eid] = component_type:new(...)
    self:searchAndRegisterEntityInSystemFilter(entity)
end

--[[
    Called by Systems via their Entity. Deletes and detaches the component from this entity.
]]--
function ECSWorld:detachComponentFromEntity(entity, component_type)
    -- TODO : better way to remove component
    self.components[component_type][entity.__eid] = nil
    self:searchAndPruneEntityFromSystemFilter(entity)
end

--[[
    Called by Systems via their Entity.
]]
function ECSWorld:entityGetComponent(entity, component_type)
    if not self.components[component_type] then return nil end
    return self.components[component_type][entity.__eid]
end

--[[
    Called by Systems via their Entity.
]]
function ECSWorld:entityHasComponent(entity, component_type)
    return self:entityGetComponent(entity, component_type) ~= nil
end

--[[
    Supposed to be called by the world owner. Calls every system and prunes marked for deletion entities
]]
function ECSWorld:update(dt)
    for i,system_filter in ipairs(self.system_filters) do
        system_filter:update(dt, self.entities)
    end
    -- Entity release. Done post-update.
    for i,entity in ipairs(self.entities) do
        if entity.__destroy_required == true then
            self:deleteEntity(entity)
        end
    end
end

return ECSWorld