Atlassian Jira groovy using script runner behaviors

Need two jira script runner behaviors each performing separate tasks

Behavior 1:- Field automations:

We have three fields 1-Internal Severity 2- Technical Severity 3- Final severity, all are single select

when
IS =High and TS= Not Effective or Not Assessed or none, then FS = High and make FS read only
IS =High and TS= Partially Effective, then FS = should be made selectable and show options Moderate-High & Moderate
IS =High and TS= Effective, then FS = Low-Moderate, and make FS read only
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IS = Moderate-High and TS =Not Effective or Not Assessed or none, then FS= Moderate-High, and make FS read only
IS = Moderate-High and TS= Partially Effective, then FS = should be made selectable and show options Moderate-High & Moderate
IS = Moderate-High and TS= Effective, then FS = Low, and make FS read only
-----------------
IS =Moderate and TS =Not Effective or Not Assessed or none then FS= Moderate, and make FS read only
IS =Moderate and TS= Partially Effective, then FS = should be made selectable and show options Low-Moderate & Low
IS =Moderate and TS= Effective, then FS = Low, and make FS read only
--------------------------
IS=Low-Moderate and TS =Not Effective or Not Assessed or none then FS= Low-Moderate, and make FS read only
IS=Low-Moderate and TS= Partially Effective, then FS = Low, and make FS read only
IS=Low-Moderate and TS= Effective, then FS = Low, and make FS read only
------------------------
IS=Low and TS =Not Effective or Not Assessed or none then FS= Low and make FS read only
IS=Low and TS= Partially Effective, then FS = Low, and make FS read only
IS=Low and TS= Effective, then FS = Low, and make FS read only.


Behaviour 2:

We have three fields single select

Field 1- Instance Name: its option format------ Instance name (type:)(vendor:)
Field 2- Instance Name(Business unit): its option format---- Instance Name (BU: abc)
Field 3 - Business Unit : single select list

when Field 1 is selected, behaviour should look for Instance name(which is first part of the field option) and match it with instance name in field 2(which is first part of option) and populate filed 3 with matching BU from field 2, which is part 2 of the field 2 option (BU:abc) so that filed 3 will have option abc select