#======================================================================

#                    T I M E _ L A G . P L 

#                    doc: Fri Dec 17 21:59:07 2010

#                    dlm: Sun Jun 26 20:47:09 2011

#                    (c) 2010 A.M. Thurnherr

#                    uE-Info: 17 80 NIL 0 0 72 2 2 4 NIL ofnI

#======================================================================

# HISTORY:

#	Dec 17, 2010: - created

#	Dec 18, 2010: - adapted for multi-pass lagging

#	Dec 20: 2010: - added code to adjust start and end of profile ens

#				    based on extent of CTD profile and guestimated time

#				    ofset

#	Jun 26, 2010: - added heuristic to chose between weighted-mean and

#					unambiguously best offsets

#				  - turned -3 criterion into warning when 3 lags are consecutive

# TODO:

#	- better seabed code (from LADCPproc)

#	- intermediate-step timelagging guess

#	- flip aliased ensembles

sub mad_w($$$)									# mean absolute deviation

{

	my($fe,$le,$so) = @_;						# first/last LADCP ens, CTD scan offset

	my($sad) = my($n) = 0;

	for (my($e)=$fe; $e<=$le; $e++) {

		my($s) = int(($LADCP{ENSEMBLE}[$e]->{ELAPSED} + $CTD{TIME_LAG} - $CTD{ELAPSED}[0]) / $CTD{DT} + 0.5);

		die("assertion failed\n" .

			"\ttest: abs($LADCP{ENSEMBLE}[$e]->{ELAPSED} + $CTD{TIME_LAG} - $CTD{ELAPSED}[$s]) <= $CTD{DT}/2\n" .

			"\te = $e, s = $s, ensemble = $LADCP{ENSEMBLE}[$e]->{NUMBER}"

		) unless (abs($LADCP{ENSEMBLE}[$e]->{ELAPSED} + $CTD{TIME_LAG} - $CTD{ELAPSED}[$s]) <= $CTD{DT}/2);

		my($dw) = $LADCP{ENSEMBLE}[$e]->{REFLR_W} - $CTD{W}[$s+$so];

		next unless (abs($dw) <= $opt_m);

		$sad += abs($dw);

		$n++;

	}

	return ($n>0) ? $sad/$n : 9e99;				# n == 0, e.g. in bottom gap

}

sub bestLag($$$$)								# find best lag in window

{

	my($fe,$le,$ww,$soi) = @_;					# first/last LADCP ens, window width, scan-offset increment

	my($bestso) = 0;							# error at first-guess offset

	my($bestmad) = mad_w($fe,$le,0);

	for (my($dso) = 1; $dso <= int($ww/2/$CTD{DT} + 0.5); $dso+=$soi) {

		my($mad) = mad_w($fe,$le,-$dso);

		$bestmad=$mad,$bestso=-$dso if ($mad < $bestmad);

		$mad = mad_w($fe,$le,$dso);

		$bestmad=$mad,$bestso=$dso if ($mad < $bestmad);

	}

	return ($bestso,$bestmad);

}

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

# carry out lag correlations and keep tally of the results

#	- fist and last 10% of LADCP profile ignored

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

sub calc_lag($$$)

{

	my($n_windows,$w_size,$scan_increment) = @_;

RETRY:

	progress("Calculating $n_windows time-lags from ${w_size}s-long windows at %dHz resolution...\n",

		int(1/$scan_increment/$CTD{DT}+0.5));

	my($approx_CTD_profile_start_ens) =

		$firstGoodEns + int(($CTD{ELAPSED}[0] - $CTD{TIME_LAG}) / $LADCP{MEAN_DT});

	my($approx_CTD_profile_end_ens) =

		$firstGoodEns + int(($CTD{ELAPSED}[$#{$CTD{ELAPSED}}] + $CTD{ELAPSED}[0] - $CTD{TIME_LAG}) / $LADCP{MEAN_DT});

	my($approx_joint_profile_start_ens) = max($firstGoodEns,$approx_CTD_profile_start_ens);

	my($approx_joint_profile_end_ens) 	= min($lastGoodEns,$approx_CTD_profile_end_ens);

	debugmsg("profile start: $firstGoodEns -> $approx_joint_profile_start_ens\n");

	debugmsg("profile end  : $lastGoodEns -> $approx_joint_profile_end_ens\n");

	my($skip_ens) = int(($approx_joint_profile_end_ens - $approx_joint_profile_start_ens) / 10 + 0.5);

	my(%nBest);

	for (my($wi)=0; $wi<$n_windows; $wi++) {

		my($fe) = $approx_joint_profile_start_ens + $skip_ens + $wi*int(($approx_joint_profile_end_ens-$approx_joint_profile_start_ens-2*$skip_ens)/$n_windows+0.5);

		my($so,$mad) = bestLag($fe,$fe+int($w_size/$LADCP{MEAN_DT}+0.5),$w_size,$scan_increment);

		debugmsg("%.1f cm/s mad(w) at %3d scans offset\n",100*$mad,$so);

		$nBest{$so}++;

	}

	my(@best_lag);

	foreach my $i (keys(%nBest)) {

		$best_lag[0] = $i if ($nBest{$i} > $nBest{$best_lag[0]});

	}

	foreach my $i (keys(%nBest)) {

		next if ($i == $best_lag[0]);

		$best_lag[1] = $i if ($nBest{$i} > $nBest{$best_lag[1]});

	}

	foreach my $i (keys(%nBest)) {

		next if ($i == $best_lag[0] || $i == $best_lag[1]);

		$best_lag[2] = $i if ($nBest{$i} > $nBest{$best_lag[2]});

	}

	progress("\t3 most popular offsets: %d (%d%%), %d (%d%%), %d (%d%%)\n",

		$best_lag[0],int(($nBest{$best_lag[0]}/$n_windows)*100+0.5),

		$best_lag[1],int(($nBest{$best_lag[1]}/$n_windows)*100+0.5),

		$best_lag[2],int(($nBest{$best_lag[2]}/$n_windows)*100+0.5));

	if ($nBest{$best_lag[0]}+$nBest{$best_lag[1]}+$nBest{$best_lag[2]} <= 6) {

		warning(0,"cannot determine valid lag => trying again with doubled window size\n");

		undef(%nBest);

		$w_size *= 2;

		goto RETRY;

	}

	unless ($nBest{$best_lag[0]}+$nBest{$best_lag[1]}+$nBest{$best_lag[2]} >= $opt_3*$n_windows) {

		if (max(@best_lag)-min(@best_lag) > 2) {

			croak(sprintf("$0: cannot determine a valid lag; top 3 tags account for %d%% of total (use -3 to relax criterion)\n",

				int(100*($nBest{$best_lag[0]}+$nBest{$best_lag[1]}+$nBest{$best_lag[2]})/$n_windows+0.5)))

		} else {

			warning(1,"top 3 tags account for only %d%% of total\n",

				int(100*($nBest{$best_lag[0]}+$nBest{$best_lag[1]}+$nBest{$best_lag[2]})/$n_windows+0.5));

		}

	}

	my($bmo);

	if (max(@best_lag)-min(@best_lag) > 5 || $nBest{$best_lag[0]}/$n_windows >= 0.5) {

		$bmo = $best_lag[0];

		progress("\tunambiguously best offset = %d scans\n",$bmo);

	} else {

		$bmo = ($nBest{$best_lag[0]}*$best_lag[0] +

				$nBest{$best_lag[1]}*$best_lag[1] +

				$nBest{$best_lag[2]}*$best_lag[2]) / ($nBest{$best_lag[0]} +

													  $nBest{$best_lag[1]} +

													  $nBest{$best_lag[2]});

		progress("\tweighted-mean offset = %.1f scans\n",$bmo);

	}

	if ($bmo > 0.9*$w_size/2/$CTD{DT}) {

		warning(0,"lag too close to the edge of the window --- trying again after adjusting the guestimated offset\n");

		$CTD{TIME_LAG} += $w_size/2;

		undef(%nBest);

		goto RETRY;

	}

	if (-$bmo > 0.9*$w_size/2/$CTD{DT}) {

		warning(0,"lag too close to the edge of the window --- trying again after adjusting the guestimated offset\n");

		$CTD{TIME_LAG} -= $w_size/2;

		undef(%nBest);

		goto RETRY;

	}

	return $CTD{TIME_LAG}+$bmo*$CTD{DT};

}

1;