#!/usr/bin/env awk -f


function log10(n) {
    return log(n)/log(10.0)
}


function merge_meas(est_val, est_unc, meas_val, meas_unc) {

    # add sanity (staleness) check on previous estimate
    #z_est = (meas_val - est_val)/est_unc
    #z_meas = (meas_val - est_val)/meas_unc

    # Kalman filtering compares variances,
    # convert uncertainties to square units
    est_unc = (0.5*est_unc)^2.0
    meas_unc = (0.5*meas_unc)^2.0

    K = (est_unc)/((est_unc) + (meas_unc))
    est_val = est_val + K*(meas_val - est_val)
    est_unc = (est_unc*meas_unc)/(est_unc + meas_unc)

    # convert uncertainties back to original units
    est_unc = 2.0*sqrt(est_unc)
    meas_unc = 2.0*sqrt(meas_unc)

    return sprintf(OFMT OFS OFMT ORS, est_val, est_unc)

}


function sigfig(val, unc) {

    omag_val = log10(val)
    omag_unc = log10(unc)

    omag_high = sqrt((omag_val)^2.0 + (omag_unc)^2.0)
    omag_low = ((omag_val)^-1.0 + (omag_unc)^-1.0)^-1.0

    sfig_unc = sprintf("%.f", sqrt((omag_high - omag_low)^2.0 + 6.0^2.0))
    sfig_val = sprintf("%.f", sqrt(sfig_unc^2.0 + 9.0^2.0))

    ofmt_val = "%." sfig_val "g"
    ofmt_unc = "%." sfig_unc "g"

    return sprintf(ofmt_val OFS ofmt_unc, val, unc)

}


function unc_g(val) {

    # order of magnitude
    omag_val = log10(val)

    # trim punctuation from val
    sub("[eE].*$", "", val)
    gsub("[.+-]", "", val)
    omag_unc = sprintf("%d", omag_val - length(val) + 1.0)

    return sprintf("%g", 10.0^(omag_unc))

}


function ck_cptime() {

    t_sys_meas[1] = systime()
    t_sys_meas[2] = 1.0

    "sysctl kern.cp_time" | getline cptime_cmd
    close("sysctl kern.cp_time")

    split(merge_meas(t_sys_meas[1], t_sys_meas[2], systime(), 1.0), t_sys_meas)

    sub("^.*=", "", cptime_cmd)
    gsub(",", OFS, cptime_cmd)
    #split(cptime_cmd, cptime_arr, ",")

    return sprintf("%s", cptime_cmd)

}


function ck_time(unm) {

    if (unm ~ /FreeBSD/ || unm ~ /Linux/) {
        "date +%s.%N" | getline t
        close("date +%s.%N")
    }
    else {
        "date +%s" | getline t
        close("date +%s")
    }

    return t

}


function ck_uptime(unm) {

    # check uptime cmd
    "uptime" | getline t_up_cmd
    close("uptime")

    # evaluate measured uptime
    t_up_meas[1] = 0.0
    t_up_meas[2] = ck_time(unm)

    sub("^[ ]*[0-9]:[0-9]*[ ]", "", t_up_cmd)
    sub("^.* up ", "", t_up_cmd)
    sub(", load.*$", "", t_up_cmd)
    split(t_up_cmd, t_up_cmd_arr, ",")

    for (i in t_up_cmd_arr) {

        if (t_up_cmd_arr[i] ~ /day/) {
            split(t_up_cmd_arr[i], days)
            (days[1] + 0.0) ? t_up_meas[1] += 86400.0*(days[1] + 0.0) : t_up_meas[1] += 0.0
            (t_up_meas[2] + 0.0) > 86400.0 ? t_up_meas[2] = 86400.0 : t_up_meas[2] += 0.0
        }

        if (t_up_cmd_arr[i] ~ /hr/) {
            split(t_up_cmd_arr[i], hrs)
            (hrs[1] + 0.0) ? t_up_meas[1] += 3600.0*(hrs[1] + 0.0) : t_up_meas[1] += 0.0
            (t_up_meas[2] + 0.0) > 3600.0 ? t_up_meas[2] = 3600.0 : t_up_meas[2] += 0.0
        }

        if (t_up_cmd_arr[i] ~ /min/) {
            split(t_up_cmd_arr[i], mins)
            (mins[1] + 0.0) ? t_up_meas[1] += 60.0*(mins[1] + 0.0) : t_up_meas[1] += 0.0
            (t_up_meas[2] + 0.0) > 60.0 ? t_up_meas[2] = 60.0 : t_up_meas[2] += 0.0
        }

        if (t_up_cmd_arr[i] ~ /sec/) {
            split(t_up_cmd_arr[i], sec)
            (sec[1] + 0.0) ? t_up_meas[1] += sec[1] : t_up_meas[1] += 0.0
            (t_up_meas[2] + 0.0) > 1.0 ? t_up_meas[2] = 1.0 : t_up_meas[2] += 0.0
        }

        if (t_up_cmd_arr[i] ~ /:/) {
            split(t_up_cmd_arr[i], hrs_min, ":")
            t_up_meas[1] += 3600.0*(hrs_min[1] + 0.0)
            (t_up_meas[2] + 0.0) > 3600.0 ? t_up_meas[2] = 3600.0 : t_up_meas[2] += 0.0
            t_up_meas[1] += 60.0*(hrs_min[2] + 0.0)
            (t_up_meas[2] + 0.0) > 60.0 ? t_up_meas[2] = 60.0 : t_up_meas[2] += 0.0
        }

    }

    if (uname ~ /FreeBSD/ || uname ~ /Linux/) {
        split(ck_proc_uptime(uname), t_pu_meas)
        t_pu_meas[2] = unc_g(t_pu_meas[1])
        split(merge_meas(t_up_meas[1], t_up_meas[2], t_pu_meas[1], t_pu_meas[2]), t_up_meas)
    }

    return sigfig(t_up_meas[1], t_up_meas[2])

}


function ck_proc_uptime(unm) {

    proc_file = ""
    if (unm ~ /FreeBSD/) {
        proc_file = "/compat/linux/proc/uptime"
    }
    if (unm ~ /Linux/) {
        proc_file = "/proc/uptime"
    }

    getline proc_uptime < proc_file
    close(proc_file)

    return proc_uptime

}


BEGIN {

    OFMT="%f"
    pi = 4.0*atan2(1.0, 1.0)
    c0 = 299792458  # m/sec

    "uname" | getline uname
    close("uname")

    #print("_systime_", systime())
    #print("_boottime_", ck_boottime())
    #print( uname, ck_cptime() )


    ## check systime, check uptime, check systime again
    t_meas[1] = ck_time(uname)
    split(ck_uptime(uname), t_up_meas)
    t_meas[2] = ck_time(uname)

    ## convert to [val, unc] vector
    t_meas[2] -= t_meas[1]
    t_meas[1] += 0.5*t_meas[2]
    if ( t_meas[2] == 0.0 ) {
        t_meas[2] = unc_g(t_meas[1])
    }
    t_meas_str = sigfig(t_meas[1], t_meas[2])

    ## estimate dt
    #dt[1] = t_meas[1] - t_prev[1]
    #dt[2] = t_meas[2] + t_prev[2]

    print( t_meas_str, ck_cptime() )
}