#! /bin/bash

########################################################################
#
# File:    reg_search
# Author:  Janis Johnson <janis187@us.ibm.com>
# Date:    2002/12/15
#
# Search for a small time interval within a range of dates in which
# results for a test changed, using a binary search.  The functionality
# for getting sources, building the component to test, and running the
# test are in other scripts that are run from here.  Before the search
# begins, we verify that we get the expected behavior for the first and
# last dates.
#
# Define these in a file whose name is the argument to this script:
#   LOW_DATE:   Date string recognized by the date command (local time).
#   HIGH_DATE:  Date string recognized by the date command (local time).
#   REG_UPDATE: Pathname of script to update your source tree; returns
#               zero for success, nonzero for failure.
#   REG_BUILD:  Pathname of script to build enough of the product to run
#               the test; returns zero for success, nonzero for failure.
#   REG_TEST:   Pathname of script to run the test; returns 1 if we
#               should search later dates, 0 if we should search earlier
#               dates.
# Optional:
#   DELTA:      Search to an interval within this many seconds; default
#               is one hour (although 300 works well).
#   REG_FINISH  Pathname of script to call at the end with the two final
#               dates as arguments.
#   SKIP_LOW    If 1, skip verifying the low date of the range;
#               define this only if you're restarting and have already
#               tested the low date.
#   SKIP_HIGH   If 1, skip verifying the high date of the range;
#               define this only if you're restarting and have already
#               tested the high date.
#   FIRST_MID   Use this as the first midpoint, to avoid a midpoint that
#               is known not to build.
#   HAS_CHANGES Pathname of script to report whether the current date has
#               no differences from one of the ends of the current range
#               to skip unnecessary build and testing; default is "true".
#   VERBOSITY   Default is 0, to print only errors and final message.
#   DATE_IN_MSG If set to anything but 0, include the time and date in
#               messages.
#
#
#
# Copyright (c) 2002, 2003, 2005, 2009, 2010 Free Software Foundation, Inc.
#
# This file is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; see the file COPYING3.  If not see
# <http://www.gnu.org/licenses/>.
# 
########################################################################

########################################################################
# Functions
########################################################################

# Issue a message if its verbosity level is high enough.

msg() {
  test ${1} -gt ${VERBOSITY}  && return

  if [ "x${DATE_IN_MSG}" = "x" ]; then
    echo "${2}"
  else
    echo "`${DATE}`  ${2}"
  fi
}

# Issue an error message and exit with a non-zero status.  If there
# is a valid current range whose end points have been tested, report
# it so the user can start again from there.

error() {
  msg 0 "error: ${1}"
  test ${VALID_RANGE} -eq 1 && \
    echo "current range:"
    echo "LOW_DATE=\"${LATER_THAN}\""
    echo "HIGH_DATE=\"${EARLIER_THAN}\""
  exit 1
}

# Turn seconds since the epoch into a date we can use with source
# control tools and report to the user.

make_date() {
  MADE_DATE=`${DATE} -u +"%Y-%m-%d %H:%M %Z" --date "1970-01-01 ${1} seconds"` \
    || error "make_date: date command failed"
}

# Build the components to test using sources as of a particular date and
# run a test case.  Pass each of the scripts the date that we're
# testing; the first one needs it, the others can ignore it if they want.

process_date() {
  TEST_DATE="${1}"

  ${REG_UPDATE} "${TEST_DATE}" || error "source update failed for ${TEST_DATE}"

  # If we're already in a valid range, skip this date if there are no
  # differences from either end of the range and adjust LATER.

  if [ ${VALID_RANGE} = 1 ]; then
    ${HAS_CHANGES} "${TEST_DATE}" "${LATER_THAN}" "${EARLIER_THAN}"
    RET=$?
    case ${RET} in
    0) ;;
    1) LATER=1; return;;
    2) LATER=0; return;;
    *) error "process_date: unexpected return value from ${HAS_CHANGES}";;
    esac
  fi

  ${REG_BUILD} "${TEST_DATE}"  || error "build failed for ${TEST_DATE}"
  ${REG_TEST} "${TEST_DATE}"
  LATER=$?
}

# Perform a binary search on dates within the range specified by
# the arguments, bounded by the number of seconds in DELTA.

search_dates() {
  let LOW=$1
  let HIGH=$2
  let DIFF=HIGH-LOW

  # Get the date in the middle of the range; MID is in seconds since
  # the epoch, DATE is readable by humans and tools.  The user can
  # override the initial mid date if it is known to have problems,
  # e.g., if a build fails for that date.

  if [ ${FIRST_MID} -ne 0 ]; then
    let MID=${FIRST_MID}
  else
    let MID=LOW/2+HIGH/2
  fi

  while [ ${DIFF} -ge ${DELTA} ]; do
    make_date ${MID}
    TEST_DATE="${MADE_DATE}"

    # Test it.

    process_date "${TEST_DATE}"

    # Narrow the search based on the outcome of testing DATE.

    if [ ${LATER} -eq 1 ]; then
      msg 1 "search dates later than \"${TEST_DATE}\""
      LATER_THAN="${TEST_DATE}"
      let LOW=MID
    else
      msg 1 "search dates earlier than \"${TEST_DATE}\""
      EARLIER_THAN="${TEST_DATE}"
      let HIGH=MID
    fi

    let DIFF=HIGH-LOW
    let MID=LOW/2+HIGH/2
  done
}

########################################################################
# Main program (so to speak)
########################################################################

# If DATE isn't defined, use the default date command; the configuration
# file can override this.

if [ "x${DATE}" = "x" ]; then
  DATE=date
fi

# The error function uses this.

VALID_RANGE=0

# Process the configuration file.

if [ $# != 1 ]; then
  echo Usage: $0 config_file
  exit 1
fi

CONFIG=${1}
if [ ! -f ${CONFIG} ]; then
  error "configuration file ${CONFIG} does not exist"
fi

# OK, the config file exists.  Source it, make sure required parameters
# are defined and their files exist, and give default values to optional
# parameters.

. ${CONFIG}

test "x${REG_UPDATE}" = "x" && error "REG_UPDATE is not defined"
test "x${REG_BUILD}" = "x" && error "REG_BUILD is not defined"
test "x${REG_TEST}" = "x" && error "REG_TEST is not defined"
test -x ${REG_TEST} || error "REG_TEST is not an executable file"
test "x${SKIP_LOW}" = "x" && SKIP_LOW=0
test "x${SKIP_HIGH}" = "x" && SKIP_HIGH=0
test "x${DELTA}" = "x" && DELTA=3600
test "x${VERBOSITY}" = "x" && VERBOSITY=0
test "x${HAS_CHANGES}" = "x" && HAS_CHANGES=true
test "x${REG_FINISH}" = "x" && REG_FINISH=true

msg 2 "LOW_DATE   = ${LOW_DATE}"
msg 2 "HIGH_DATE  = ${HIGH_DATE}"
msg 2 "REG_UPDATE = ${REG_UPDATE}"
msg 2 "REG_BUILD  = ${REG_BUILD}"
msg 2 "REG_TEST   = ${REG_TEST}"
msg 2 "SKIP_LOW   = ${SKIP_LOW}"
msg 2 "SKIP_HIGH  = ${SKIP_HIGH}"
msg 2 "FIRST_MID  = ${FIRST_MID}"
msg 2 "VERBOSITY  = ${VERBOSITY}"
msg 2 "DELTA      = ${DELTA}"

# Verify that DELTA is at least two minutes.

test ${DELTA} -lt 120 && \
  error "DELTA is ${DELTA}, must be at least 120 (two minutes)"

# Change the dates into seconds since the epoch.  This uses an extension
# in GNU date.

LOW_DATE=`${DATE} +%s --date "${LOW_DATE}"` || \
  error "date command failed for \"${LOW_DATE}\""
HIGH_DATE=`${DATE} +%s --date "${HIGH_DATE}"` || \
  error "date command failed for \"${LOW_DATE}\""

# If FIRST_MID was defined, convert it and make sure it's in the range.

if [ "x${FIRST_MID}" != "x" ]; then
  FIRST_MID=`${DATE} +%s --date "${FIRST_MID}"` || \
    error "date command failed for \"${FIRST_MID}\""
  test ${FIRST_MID} -le ${LOW_DATE}  && \
    error "FIRST_MID date is earlier than LOW_DATE"
  test ${FIRST_MID} -ge ${HIGH_DATE} && \
    error "FIRST_MID is later than HIGH_DATE"
else
  FIRST_MID=0
fi 

# Keep track of the bounds of the range where the test behavior changes,
# using a human-readable version of each date.

make_date ${LOW_DATE}
LATER_THAN="${MADE_DATE}"
make_date ${HIGH_DATE}
EARLIER_THAN="${MADE_DATE}"

msg 2 "LATER_THAN   = ${LATER_THAN}"
msg 2 "EARLIER_THAN = ${EARLIER_THAN}"

# Verify that the range isn't backwards.

test ${LOW_DATE} -lt ${HIGH_DATE} || error "date range is backwards"

# Verify that the first and last date in the range get the results we
# expect.  If not, quit, because any of several things could be wrong.

if [ ${SKIP_LOW} -eq 0 ]; then
  process_date "${LATER_THAN}"
  test ${LATER} -ne 1 && \
    error "unexpected result for low date ${LATER_THAN}"
  msg 1 "result for low date is as expected"
fi

if [ ${SKIP_HIGH} -eq 0 ]; then
  process_date "${EARLIER_THAN}"
  test ${LATER} -ne 0 && \
    error "unexpected result for high date ${EARLIER_THAN}"
  msg 1 "result for high date is as expected"
fi

# Search within the range, now that we know that the end points are valid.

VALID_RANGE=1
search_dates ${LOW_DATE} ${HIGH_DATE}

# Report the range that's left to investigate.

echo "Continue search between ${LATER_THAN} and ${EARLIER_THAN}"

# Invoke the optional script to report additional information about
# changes between the two dates.

${REG_FINISH} "${LATER_THAN}" "${EARLIER_THAN}"