--[[**
	ensures value is a table and all keys pass keyCheck and all values pass valueCheck

	@param keyCheck The function to use to check the keys
	@param valueCheck The function to use to check the values

	@returns A function that will return true iff the condition is passed
**--]]
function t.map(keyCheck, valueCheck)
	assert(t.callback(keyCheck), t.callback(valueCheck))
	local keyChecker = t.keys(keyCheck)
	local valueChecker = t.values(valueCheck)

	return function(value)
		local keySuccess, keyErr = keyChecker(value)
		if not keySuccess then
			return false, keyErr or ""
		end

		local valueSuccess, valueErr = valueChecker(value)
		if not valueSuccess then
			return false, valueErr or ""
		end

		return true
	end
end

do
	local arrayKeysCheck = t.keys(t.integer)
	--[[**
		ensures value is an array and all values of the array match check

		@param check The check to compare all values with

		@returns A function that will return true iff the condition is passed
	**--]]
	function t.array(check)
		assert(t.callback(check))
		local valuesCheck = t.values(check)

		return function(value)
			local keySuccess, keyErrMsg = arrayKeysCheck(value)
			if keySuccess == false then
				return false, string.format("[array] %s", keyErrMsg or "")
			end

			-- # is unreliable for sparse arrays
			-- Count upwards using ipairs to avoid false positives from the behavior of #
			local arraySize = 0

			for _ in ipairs(value) do
				arraySize = arraySize + 1
			end

			for key in pairs(value) do
				if key < 1 or key > arraySize then
					return false, string.format("[array] key %s must be sequential", tostring(key))
				end
			end

			local valueSuccess, valueErrMsg = valuesCheck(value)
			if not valueSuccess then
				return false, string.format("[array] %s", valueErrMsg or "")
			end

			return true
		end
	end
end

do
	local callbackArray = t.array(t.callback)
	--[[**
		creates a union type

		@param ... The checks to union

		@returns A function that will return true iff the condition is passed
	**--]]
	function t.union(...)
		local checks = {...}
		assert(callbackArray(checks))

		return function(value)
			for _, check in ipairs(checks) do
				if check(value) then
					return true
				end
			end

			return false, "bad type for union"
		end
	end

	--[[**
		Alias for t.union
	**--]]
	t.some = t.union

	--[[**
		creates an intersection type

		@param ... The checks to intersect

		@returns A function that will return true iff the condition is passed
	**--]]
	function t.intersection(...)
		local checks = {...}
		assert(callbackArray(checks))

		return function(value)
			for _, check in ipairs(checks) do
				local success, errMsg = check(value)
				if not success then
					return false, errMsg or ""
				end
			end

			return true
		end
	end

	--[[**
		Alias for t.intersection
	**--]]
	t.every = t.intersection
end

do
	local checkInterface = t.map(t.any, t.callback)
	--[[**
		ensures value matches given interface definition

		@param checkTable The interface definition

		@returns A function that will return true iff the condition is passed
	**--]]
	function t.interface(checkTable)
		assert(checkInterface(checkTable))
		return function(value)
			local tableSuccess, tableErrMsg = t.table(value)
			if tableSuccess == false then
				return false, tableErrMsg or ""
			end

			for key, check in pairs(checkTable) do
				local success, errMsg = check(value[key])
				if success == false then
					return false, string.format("[interface] bad value for %s:\n\t%s", tostring(key), errMsg or "")
				end
			end

			return true
		end
	end

	--[[**
		ensures value matches given interface definition strictly

		@param checkTable The interface definition

		@returns A function that will return true iff the condition is passed
	**--]]
	function t.strictInterface(checkTable)
		assert(checkInterface(checkTable))
		return function(value)
			local tableSuccess, tableErrMsg = t.table(value)
			if tableSuccess == false then
				return false, tableErrMsg or ""
			end

			for key, check in pairs(checkTable) do
				local success, errMsg = check(value[key])
				if success == false then
					return false, string.format("[interface] bad value for %s:\n\t%s", tostring(key), errMsg or "")
				end
			end

			for key in pairs(value) do
				if not checkTable[key] then
					return false, string.format("[interface] unexpected field %q", tostring(key))
				end
			end

			return true
		end
	end
end