Linux: Appending values into files, to the end of particular lines, and at the bottom of the file if there is on "key" - bash

Question

I have one file, file1, that has values like so:
key1|value1|
key2|value2|
key3|value3|
I have another file, file2, that has key based values I would like to add to add to file1:
key2 value4
key3 value5
key4 value6
I would like to add values to file1 to lines where the "key" matches, and if there is no "key" in file1, simply adding the new key & value to the bottom:
key1|value1|
key2|value2|value4|
key3|value3|value5|
key4|value6|
It seems like this is something that could be done with 2 calls to awk, but I am not familiar enough with it. I'm also open to using bash or shell commands.
UPDATE
I found this to work
awk 'NR==FNR {a[$1]=$2; next} {print $1,$2,a[$1];delete a[$1]}END{for(k in a) print k,a[k]}' file2 file1

Answer 1

The only deviation from the desired output is that keys from file1 that are not in file2 are not known AOT, so they are printed at the end to keep things semi-online:
awk -v first=data1.txt -f script.awk data2.txt
BEGIN {
OLD=FS
FS="|"
while (getline < first)
table[$1] = $0
OFS=FS
FS=OLD
}
!($1 in table) {
queue[$1] = $0
}
$1 in table {
id=$1
gsub(FS, OFS)
sub(/[^|]*\|/, "")
print table[id] $0 OFS
delete table[id]
}
END {
for (id in table)
print table[id]
for (id in queue) {
gsub(FS, OFS, queue[id])
print queue[id] OFS
}
}
key2|value2|value4|
key3|value3|value5|
key1|value1|
key4|value6|

Answer 2

this is the LOL answer ... ha ha . I basically loop over both keeping track of them and sort ... silly'ish , probably not even something you would want to use bash for perhaps ..
declare -a checked
checked=()
file="/tmp/file.txt"
> "${file}"
while IFS= read -r line1 ;do
key1=$(echo $line1 | cut -d'|' -f1)
if ! grep -qi ${key1} "/tmp/file2.txt" ; then
echo "$line1" >> "${file}"
continue
fi
while IFS= read -r line2 ;do
key2=$(echo $line2 | cut -d' ' -f1)
if ! grep -qi ${key2} "/tmp/file1.txt" ; then
if ! [[ "${checked[#]}" =~ $key2 ]] ;then
echo "$(echo $line2| awk '{print $1"|"$2}')|" >> "${file}"
checked+=(${key2})
continue
fi
fi
if [[ "$key2" == "$key1" ]] ;then
echo "${line1}$(echo $line2 | cut -d' ' -f2-)|" >> "${file}"
continue
fi
done < "/tmp/file2.txt"
done < "/tmp/file1.txt"
sort -k2 -n ${file}
[[ -f "${file}" ]] && rm -f "${file}"
Output:
key1|value1|
key2|value2|value4|
key3|value3|value5|
key4|value6|