--
-- (C) 2017 - ntop.org
--
local ts_common = {}

-- ##############################################

ts_common.metrics = {}
ts_common.metrics.counter = "counter"
ts_common.metrics.gauge = "gauge"
ts_common.metrics.derivative = "derivative"

ts_common.aggregation = {}
ts_common.aggregation.mean = "mean"
ts_common.aggregation.max = "max"
ts_common.aggregation.min = "min"
ts_common.aggregation.last = "last"

-- ##############################################

-- Find the percentile of a list of values
-- N - A list of values.  N must be sorted.
-- P - A float value from 0.0 to 1.0
local function percentile(N, P)
    local n = math.floor(math.floor(P * #N + 0.5))
    return (N[n - 1])
end

function ts_common.ninetififthPercentile(serie)
    local nan_points = 0

    if #serie <= 1 then
        return serie[1]
    end

    local N = {}

    for i, val in ipairs(serie) do
        if val ~= val then
            nan_points = nan_points + 1
            -- Convert NaN to 0
            val = 0
        end

        N[i] = val
    end

    -- No points to calculate percentile, return NaN
    if nan_points == #serie then
        return 0/0
    end

    table.sort(N) -- <<== Sort first
    return (percentile(N, 0.95))
end

-- ##############################################

function ts_common.calculateMinMax(total_serie)
    local min_val, max_val
    local min_val_pt, max_val_pt
    local found = false

    min_val = 0/0
    max_val = 0/0
    min_val_pt = 1
    max_val_pt = 1

    for idx, val in pairs(total_serie) do
        -- Check if it's nan
        if val == val then
            if (found == false) then
                min_val = val
                max_val = val
                min_val_pt = idx - 1
                max_val_pt = idx - 1
                found = true
            end

            if (val < min_val) then
                min_val = val
                min_val_pt = idx - 1
            end

            if (val > max_val) then
                max_val = val
                max_val_pt = idx - 1
            end
        end
    end

    return {
        min_val = min_val,
        max_val = max_val,
        min_val_idx = min_val_pt,
        max_val_idx = max_val_pt
    }
end

-- ##############################################

function ts_common.calculateStatistics(total_serie, step, keep_total, data_type)
    local total
    local counter = 0
    local percentile = ts_common.ninetififthPercentile(total_serie) or 0

    for idx, val in pairs(total_serie) do
        -- not a NaN value
        if val == val then
            counter = counter + 1
            total = (total or 0) + val
        end
    end
    
    if not total then
        total = 0/0 -- NaN
    end

    -- Use counter for excluding nan values
    local avg = total / counter

    if data_type ~= ts_common.metrics.gauge then
        total = total * step
    else
        if not keep_total then
            -- no total for gauge values!
            total = nil
        end
    end

    -- tprint("num: "..#total_serie .. " / " .. "total: "..total .. " / step: "..step .. " / avg: "..avg)

    return {
        total = total,
        average = avg,
        ["95th_percentile"] = percentile
    }
end

-- ##############################################

-- NOTE: this corresponds to graph_utils interpolateSerie
-- This is approximate.
-- Aproximate means it doesn't adjust the step.
-- TODO: take as input and adjust the step as well.
function ts_common.upsampleSerie(serie, num_points)
    if num_points <= #serie then
        return serie
    end

    local res = {}
    local intervals = num_points / #serie;

    local lerp = function(v0, v1, t)
        return (1 - t) * v0 + t * v1
    end

    if #serie == 0 then
        return res
    end

    for i = 1, num_points do
        local index = (i - 1) / (intervals)
        local _, t = math.modf(index)
        local prev_i = math.floor(index)
        local next_i = math.min(math.ceil(index), #serie - 1)

        local v = lerp(serie[prev_i + 1], serie[next_i + 1], t)
        res[i] = v
    end

    return res
end

-- ##############################################

-- If a point value exceeds this value, it should be discarded as invalid
function ts_common.getMaxPointValue(schema, metric, tags)
    if tags.ifid ~= nil then
        if string.contains(metric, "bytes") then
            local ifspeed = getInterfaceSpeed(tonumber(tags.ifid))

            if ifspeed ~= nil then
                -- bit/s
                return ifspeed * 1000 * 1000
            end
        elseif string.contains(metric, "packets") then
            local ifspeed = getInterfaceSpeed(tonumber(tags.ifid))

            if ifspeed ~= nil then
                -- mbit/s
                local speed_mbps = ifspeed
                local max_pps_baseline = 14881 -- for 10 mbps

                return speed_mbps / 10 * max_pps_baseline
            end
        end
    end

    return math.huge
end

-- ##############################################

function ts_common.normalizeVal(v, max_val, options)
    -- it's undesirable to normalize and set a 0 when
    -- the number is greater than max value
    -- this was causing missing points in the charts
    -- with ZMQ interface which can actually exceed the nominal value

    if v ~= v then
        if not options.keep_nan then
            -- NaN value
            v = options.fill_value
        end
    elseif v < options.min_value then
        v = options.min_value
    end

    return v
end

-- ##############################################

function ts_common.calculateSampledTimeStep(raw_step, tstart, tend, options)
    local estimed_num_points = math.ceil((tend - tstart) / raw_step)
    local time_step = raw_step

    if estimed_num_points > options.max_num_points then
        -- downsample
        local num_samples = math.ceil(estimed_num_points / options.max_num_points)
        time_step = num_samples * raw_step
    end

    return time_step
end

-- ##############################################

function ts_common.fillSeries(schema, tstart, tend, time_step, fill_value)
    local count = math.ceil((tend - tstart) / time_step)
    local res = {}

    for idx, metric in ipairs(schema._metrics) do
        local data = {}

        for i = 1, count do
            data[i] = fill_value
            i = i + 1
        end

        res[idx] = {
            label = metric,
            data = data
        }
    end

    return res, count
end

-- ##############################################

function ts_common.serieWithTimestamp(serie, tstart, tstep)
    local data = {}
    local t = tstart

    for i, pt in ipairs(serie) do
        data[t] = pt
        t = t + tstep
    end

    return data
end

-- ##############################################

local last_error = nil
local last_error_msg = nil
ts_common.ERR_OPERATION_TOO_SLOW = "OPERATION_TOO_SLOW"

function ts_common.clearLastError()
    err = nil
end

function ts_common.setLastError(err, msg)
    last_error = err
    last_error_msg = msg
end

function ts_common.getLastError()
    return last_error
end

function ts_common.getLastErrorMessage()
    return last_error_msg
end

-- ##############################################

return ts_common
