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|
local scroller = {}
local range_calculators = {
ascending = function(max_results, num_results)
return 0, math.min(max_results, num_results)
end,
descending = function(max_results, num_results)
return math.max(max_results - num_results, 0), max_results
end,
}
local scroll_calculators = {
cycle = function(range_fn)
return function(max_results, num_results, row)
local start, finish = range_fn(max_results, num_results)
if row >= finish then
return start
elseif row < start then
return (finish - 1 < 0) and finish or finish - 1
end
return row
end
end,
limit = function(range_fn)
return function(max_results, num_results, row)
local start, finish = range_fn(max_results, num_results)
if row >= finish and finish > 0 then
return finish - 1
elseif row < start then
return start
end
return row
end
end,
}
scroller.create = function(scroll_strategy, sorting_strategy)
local range_fn = range_calculators[sorting_strategy]
if not range_fn then
error(debug.traceback("Unknown sorting strategy: " .. sorting_strategy))
end
local scroll_fn = scroll_calculators[scroll_strategy]
if not scroll_fn then
error(debug.traceback("Unknown scroll strategy: " .. (scroll_strategy or "")))
end
local calculator = scroll_fn(range_fn)
return function(max_results, num_results, row)
local result = calculator(max_results, num_results, row)
if result < 0 then
error(
string.format(
"Must never return a negative row: { result = %s, args = { %s %s %s } }",
result,
max_results,
num_results,
row
)
)
end
if result > max_results then
error(
string.format(
"Must never exceed max results: { result = %s, args = { %s %s %s } }",
result,
max_results,
num_results,
row
)
)
end
return result
end
end
scroller.top = function(sorting_strategy, max_results, num_results)
if sorting_strategy == "ascending" then
return 0
end
return (num_results > max_results) and 0 or (max_results - num_results)
end
scroller.middle = function(sorting_strategy, max_results, num_results)
local mid_pos
if sorting_strategy == "ascending" then
mid_pos = math.floor(num_results / 2)
else
mid_pos = math.floor(max_results - num_results / 2)
end
return (num_results < max_results) and mid_pos or math.floor(max_results / 2)
end
scroller.bottom = function(sorting_strategy, max_results, num_results)
if sorting_strategy == "ascending" then
return math.min(max_results, num_results) - 1
end
return max_results - 1
end
scroller.better = function(sorting_strategy)
if sorting_strategy == "ascending" then
return -1
else
return 1
end
end
scroller.worse = function(sorting_strategy)
return -(scroller.better(sorting_strategy))
end
return scroller
|
