---- A Set class.
-- @class module
-- @name pl.Set

--[[
module ('pl.Set')
]]
local tablex = require 'pl.tablex'
local utils = require 'pl.utils'
local stdmt = utils.stdmt
local tmakeset,deepcompare,merge,keys,difference,tupdate = tablex.makeset,tablex.deepcompare,tablex.merge,tablex.keys,tablex.difference,tablex.update
local Map = stdmt.Map
local Set = stdmt.Set
local List = stdmt.List
local class = require 'pl.class'

-- the Set class --------------------
class(Map,nil,Set)

local function makeset (t)
    return setmetatable(t,Set)
end

--- create a set. <br>
-- @param t may be a Set, Map or list-like table.
-- @class function
-- @name Set
function Set:_init (t)
    local mt = getmetatable(t)
    if mt == Set or mt == Map then
        for k in pairs(t) do self[k] = true end
    else
        for _,v in ipairs(t) do self[v] = true end
    end
end

function Set:__tostring ()
    return '['..self:keys():join ','..']'
end

--- add a value to a set.
-- @param key a value
function Set:set (key)
    self[key] = true
end

--- remove a value from a set.
-- @param key a value
function Set:unset (key)
    self[key] = nil
end

--- get a list of the values in a set.
-- @class function
-- @name Set:values
Set.values = Map.keys

--- map a function over the values of a set.
-- @param fn a function
-- @param ... extra arguments to pass to the function.
-- @return a new set
function Set:map (fn,...)
    fn = utils.function_arg(1,fn)
    local res = {}
    for k in pairs(self) do
        res[fn(k,...)] = true
    end
    return makeset(res)
end

--- union of two sets (also +).
-- @param set another set
-- @return a new set
function Set:union (set)
    return merge(self,set,true)
end
Set.__add = Set.union

--- intersection of two sets (also *).
-- @param set another set
-- @return a new set
function Set:intersection (set)
    return merge(self,set,false)
end
Set.__mul = Set.intersection

--- new set with elements in the set that are not in the other (also -).
-- @param set another set
-- @return a new set
function Set:difference (set)
    return difference(self,set,false)
end
Set.__sub = Set.difference

-- a new set with elements in _either_ the set _or_ other but not both (also ^).
-- @param set another set
-- @return a new set
function Set:symmetric_difference (set)
    return difference(self,set,true)
end
Set.__pow = Set.symmetric_difference

--- is the first set a subset of the second?.
-- @return true or false
function Set:issubset (set)
    for k in pairs(self) do
        if not set[k] then return false end
    end
    return true
end
Set.__lt = Set.subset

--- is the set empty?.
-- @return true or false
function Set:issempty ()
    return next(self) == nil
end

--- are the sets disjoint? (no elements in common).
-- Uses naive definition, i.e. that intersection is empty
-- @param set another set
-- @return true or false
function Set:isdisjoint (set)
    return self:intersection(set):isempty()
end

return Set