How to conditionally select array index to update based on value - json

Question

I have a json file as below, need to append the new name into .root.application.names, but if the name passed in has prefix (everything before -, in below example it's jr), then find the list with same prefix names already present, and update it, if there is only one names list or if there is no matching list, then update first list.
In the below example, if
$application == 'application1' and $name == <whatever>; just update first list under application1, as there is only one list under application1, nothing to choose from.
$application == 'application2' and if $name has no prefix delimiter "-" or unmatched prefix (say sr-allen); then update the first list under application2.names, because foo has no or unmatched prefix.
$application == 'application2' and say $name == jr-allen; then update the second list under application2, because $name has prefix "jr-" and there is a list with items matching this prefix.
{
"root": {
"application1": [
{
"names": [
"john"
],
"project": "generic"
}
],
"application2": [
{
"names": [
"peter",
"jack"
],
"project": "generic"
},
{
"names": [
"jr-sam",
"jr-mike",
"jr-rita"
],
"project": "junior-project"
}
]
}
}
I found how to update the list, not sure how to add these conditions, any help please?
jq '."root"."application2"[1].names[."root"."application2"[1].names| length] |= . + "jr-allen"' foo.json
Update:
good if I can do this with jq/walk, I am still trying as below, but couldn't get anywhere close.
prefix=$(echo ${name} | cut -d"-" -f1) # this gives the prefix, e.g: "jr"
jq -r --arg app "${application}" name "${name}" prefix "${prefix}"'
def walk(f):
. as $in
| if type == "object" then
reduce keys[] as $key
( {}; . + { ($key): ($in[$key] | walk(f)) } ) | f
elif type == "array" then map( walk(f) ) | f
else f
end;
walk( if type=="object" and ."$app" and (.names[]|startswith("$prefix")) ) then .names[]="$name" else . end )
' foo.json

Answer 1

It took me a while to have any confidence that I have understood the requirements, but I believe the following at least captures the essence of what you have in mind.
To make the solution easier to understand, we begin with a helper function, the name of which makes its purpose clear enough, at least given the context:
def updateFirstNamesArrayWithMatchingPrefix($prefix; $value):
(first( range(0; length) as $i
| if any(.[$i].names[]; startswith($prefix))
then $i else empty end) // 0) as $i
| .[$i].names += [$value] ;
.root |=
if .[$app] | length == 1
then .[$app][0].names += [ $name ]
elif .[$app] | length > 1
then
( $name | split("-")) as $components
| if $components|length==1 # no prefix
then .[$app][0].names += [ $name ]
else ($components[0] + "-" ) as $prefix
| .[$app] |= updateFirstNamesArrayWithMatchingPrefix($prefix; $name)
end
else .
end
Testing
The above passes the four tests originally proposed by
#Inian:
jq --arg app "application1" --arg name "foo" -f script.jq jsonFile
jq --arg app "application2" --arg name "jr-foo" -f script.jq jsonFile
jq --arg app "application2" --arg name "sr-foo" -f script.jq jsonFile
jq --arg app "application2" --arg name "foo" -f script.jq jsonFile
Herrings?
Based on my understanding of the problem, it seems to me that walk may be a bit of a red herring, but if not, I hope you'll be able to adapt the above to meet your actual requirements.

Answer 2

Your requirement is: If prefix exists in name, update the last array element, else the first one.
When the array has one element, like for application1, the last is the first also.
#!/bin/bash
application="$1"
name="$2"
json_file="file.json"
ind=0
# if name matches "-", set index to the last array element
[[ "$name" == *"-"* ]] && ind=-1
jq --arg app "$application" \
--arg name "$name" \
--argjson ind "$ind" \
'.root[$app][$ind].names += [$name]' "$json_file"
I believe above script is self-explanatory enough, --argjson used for having an unquoted index, += stands for |= . +.
Testing
Commands below produce the expected result.
bash test.sh application1 jr-John
bash test.sh application2 jr-John
bash test.sh application1 Mary
bash test.sh application2 Mary