#!/bin/bash
# Bash demo for manipulating files, entries and compute some averages
# (C) 2019 - F-Hauri.ch
# From my answer: https://stackoverflow.com/a/54416235/1765658

normalize() {          # Drop everything from string except suitable for base 64
    local result oLang=$LANG oLcAll=$LC_ALL
    LANG=C LC_ALL=C
    result=${1//[^A-Za-z0-9]}0000000000
    LANG=$oLang LC_ALL=$oLcAll
    printf -v $2 "${result:0:10}"
}
strU8DiffLen () {   # Compute difference between char length and number of bytes
    local bytlen oLang=$LANG oLcAll=$LC_ALL
    LANG=C LC_ALL=C
    bytlen=${#1}
    LANG=$oLang LC_ALL=$oLcAll
    return $(( bytlen - ${#1} ))
}

declare -A students
declare subjects=() sublen=0 stdlen=0 sortedstud=()
for file in subject/* ;do                               # read all subject files
    subj=${file##*/}
    subjects+=($subj)                                     # Add subject to array
    sublen=$(( ${#subj} > sublen ? ${#subj} : sublen )) # Max subject string len
    declare -A mark_$subj                   # Create subject's associative array

    while read student mark ;do
	stdlen=$(( ${#student} > $stdlen ? ${#student} : stdlen ))
        [ "$student" ] && {                                   # Skip empty lines
	    ((students[$student]++)) || {                # Count student's marks
		normalize $student nstud
		sortedstud[64#$nstud]+=$student\ 
	    }         # sortedstud built alphabetically sorted list of studients
	    printf -v mark_$subj[$student] "%d" $mark     # Store student's mark
	}
    done <$file
done

printf -v formatstr %${#subjects[@]}s;  # prepare format string for all subjects
formatstr="%-${stdlen}s %2s ${formatstr// / %${sublen}s}"

printf -v headline "$formatstr  Average" Student Qt "${subjects[@]}"
echo "$headline"                                               # print head line
echo "${headline//[^ ]/-}"                               # underscored head line

declare -Ai averages
for student in ${sortedstud[@]};do                  # Now one line by student...
    marks=()                                                       # Clear marks
    for subject in ${subjects[@]};do
        declare -n array=mark_$subject    # subject's associative array to array
	thismark=${array[$student]:-0}
	marks+=($thismark)                  # Add subject's mark to student line
	averages[$subject]+=$thismark                # add for subject's average
    done
    moy=${marks[*]}                                    # compute student average
    moy=000$(( (${moy// /+}) *1000/${#marks[@]} ))            # with two decimal
    
    # printout student's line
    strU8DiffLen $student
    printf "%-$[stdlen+$?]s ${formatstr#* }  %7.2f\n" $student \
	   ${students[$student]} ${marks[@]} ${moy:0:-3}.${moy:${#moy}-3}
done

echo "${headline//[^ ]/-}"                               # underscored head line
marks=()                                        # prepare subject's average line
declare -i oavg=0                                              # overall average
for subject in ${subjects[@]};do
    oavg+=${averages[$subject]}
    moy=000$(( ${averages[$subject]}000 / ${#students[@]} ))  # subj avg w 2 dec
    printf -v moy %.2f ${moy:0:-3}.${moy:${#moy}-3}
    marks+=($moy)               # add computed average to subjects averages line
done
moy=000$(( oavg * 1000 / ${#subjects[@]} / ${#students[@]} ))  # Overall average
printf "$formatstr  %7.2f\n" Avgs ${#students[@]} ${marks[@]} \
       ${moy:0:-3}.${moy:${#moy}-3}

### End of script
exit 0

### Quick building demo tree
cd /tmp
tar -zxvf <(
    base64 -d <<eof
H4sIAFUFUFwAA+3XXU6EMBQF4D6ziu7A/l2uLsBHE7eAYwUMghlKnNm9EKfEEHUyBpg4nu+lJJDQ
5HBK226KpqmuxJJUj4mGUTOpz2MktHXG9RdEWiitrWUhadFZHXRtyLZSiidflbsfnjt2/49qP/Jv
u4dnvwnLfAcn5K9JuT5/w0zIfw2T/F+yUMz+jiHg1Lnv87c09j9l0+dvU3JCqtln8oV/nv9dFkLh
36RWyW3l60zqm+S+KCspNSfnnhwsbtJ/X+dV2c68BBzvfzr2nw33/XeWUvR/DWP/WcYFgOICcI0F
4OJN+p/7Jt9mr8V+znec8P8/7P8cK4v+r2HsP8X6u1h/Qv0vX+x/6B59ff7znyFNw/5fGZz/AQAA
AAAAAAAAAAB+7R1PsalnACgAAA==
eof
)
cd school/

### Adding some subject
for newsub in biology history art chemistry;do
    while read student foo;do
	echo $student $(( (RANDOM%8)+12 ))
    done <subject/math >>subject/$newsub
done

### Adding some students
for newstud in Renée William Iñacio Theresa ;do
    for sub in subject/*;do
	echo $newstud  $(( (RANDOM%8)+12 )) >>$sub
    done
done

### Randomly delete 0 or 1 mark in all subject files
for file in subject/*;do
    ((val=1+(RANDOM%9)))
    ((val<8)) && sed ${val}d -i $file
done