--- /dev/null
+#!/bin/bash
+# usage:
+# expire-iso8601 <unit-in-seconds> <slop-in-seconds>
+# <min-interval-in-units> <extent-in-min-intervals>
+# [<min-interval-in-units> <extent-in-min-intervals> ...]
+#
+# eg
+# /home/ian/junk/expire-iso8601 86400 10000 1 14 7 4
+# uses units of 86400s (1 day) with a slop of 10ks;
+# it keeps daily copies (that is, dated no more than 86400+10000s apart)
+# for at least 1*14 days, ie the oldest will be at least 86400s*1*14-10000s
+# older than the very newest
+# and weekly copies (that is, dated no more than 7*86400+10000s apart)
+# for at least 7*4 days, ie the oldest will be at least 86400s*7*4-10000s
+# older than the very newest
+
+set -e
+
+fail () { echo >&2 "$*"; exit 2; }
+badusage () { fail "bad usage: $*"; }
+
+#-------------------- argument parsing --------------------
+
+[ $# -ge 4 ] || badusage 'too few arguments'
+
+unit=$1
+slop=$2
+shift;shift
+
+[ $(($# % 2)) = 0 ] || badusage 'odd keep arguments (need min/extent pairs)'
+argl="$*"
+
+alldigits () {
+ [ "x${1##*[^0-9]}" = "x$1" ] || badusage "$2 must be all digits"
+ [ x$1 ] || badusage "$2 must be nonempty"
+}
+
+while [ $# -gt 0 ]; do
+ min=$1; shift; extent=$1; shift
+ alldigits $min min
+ alldigits $extent extent
+done
+
+#-------------------- scanning the directory ----------
+
+# We build in $l a list of the relevant filenames and the time_t's
+# they represent. And, while we're at it, we find the most recent
+# such time_t ($ls) and its name ($ln).
+#
+# Each entry in $l is $time_t/$filename, and the list is
+# newline-separated for the benefit of sort(1).
+
+ls=0
+for cn in [0-9]*; do
+ echo $cn
+ case "$cn" in
+ ????-??-??)
+ conv="$cn";;
+ ????-??-??T[0-2][0-9]+[0-9][0-9][0-9][0-9]|\
+ ????-??-??T[0-2][0-9]:[0-6][0-9]+[0-9][0-9][0-9][0-9]|\
+ ????-??-??T[0-2][0-9]:[0-6][0-9]:[0-6][0-9]+[0-9][0-9][0-9][0-9])
+ conv="${cn%T*} ${cn#*T}";;
+ *)
+ echo >&2 "ignoring $cn"
+ continue;;
+ esac
+ cs=$(date -d "$conv" +%s)
+ if [ $cs -gt $ls ]; then
+ ls=$cs; ln=$cn
+ fi
+ l="$cs/$cn
+$l"
+done
+
+echo "newest $ln"
+
+#-------------------- main computation --------------------
+
+# We go through the items from most to least recent
+# ie in order of increasing age
+# ie in order of decreasing time_t
+# We constantly maintain records of this item (c) and the last two
+# (b and a).
+#
+# We then check to see if any of the specified minimum/extent pairs
+# mean we should keep c and b.
+#
+# We can delete c if b is older than every specified extent. b will
+# then be the latest version we keep and is old enough. (Note that if
+# the density isn't satisfied, the expected number of old items may
+# not be satisfied either; in the worst case, if b is very old, we
+# might end up with just two items left.)
+#
+# If we delete c then we just go on to the next c, which will
+# definitely be older, so will be deleted too (because b remains
+# unchanged): ie we then delete all the rest.
+#
+# If we don't delete c, we look at the gap between a and c. If this
+# gap is not too long (according to any of the minimum/extent pairs)
+# then it is OK to delete b. (A gap is too long if it's longer than a
+# relevant pair's minimum, but a pair isn't relevant if c is older
+# than the extent.) If we delete b then current c becomes the new b.
+#
+# If we don't delete either then b and c become the new a and b.
+
+- because b is clearly sufficient to
+# satisfy the
+# if we delete
+
+# {l,a,b,c}{s,n,a} = seconds, name of a,b,c where
+# c is one we're looking at now and
+# b is previous one
+# a is one before that
+# l is last (most recent)
+# where a, b, c have not been removed
+
+as=''
+an=''
+bs=''
+bn=''
+
+remove () {
+ echo "expire $1 (have $2)"
+}
+
+l=$(sort -nr <<END
+$l
+END
+)
+
+for ce in $l; do
+ cs=${ce%%/*}; cn=${ce#*/}
+ set $argl
+ c_mightneed=false
+ b_needfordensity=false
+ if test "$as"; then
+ ac_interval=$(( $as - $cs ))
+ fi
+ while [ $# != 0 ]; do
+ min=$(( $1 * $unit + $slop ))
+ extent=$(( $1 * $2 * $unit - $slop ))
+ # if b is as old as required by anything
+ # then c is definitely surplus
+ if ! [ "$bs" ] || \
+ [ $(($ls - $bs)) -le $extent ]; then
+ c_mightneed=true
+ fi
+ if ! test "$as" || \
+ [ $(($ls - $as)) -le $extent -a \
+ $ac_interval -gt $min ]; then
+ b_needfordensity=true
+ fi
+ shift;shift
+ done
+ if ! $c_mightneed; then
+ remove $cn "$bn"
+ continue
+ fi
+ if ! $b_needfordensity; then
+ remove $bn "$an $cn"
+ bn=$cn; bs=$cs
+ continue
+ fi
+ an=$bn; as=$bs
+ bn=$cn; bs=$cs
+done
+
+exit 0
~ian / chiark-utils.git / commitdiff