In the task you have to write console application for managing users list. It should accept there types of operation: add list findById remove Users list should be stored in the json file. When you start your application and tries to perform some operations, existing file should be used or new one should be created if it does not exist. Example of the json file (users.json): [{id: "1", email: «[email protected]», age: 31}, {id: "2", email: «[email protected]», age: 41}] In the main.go file you can find a function called Perform(args Arguments, writer io.Writer) error. You have to call this function from the main function and pass arguments from the console and os.Stdout stream. Perform function body you have to write by yourself :). Arguments - is a map[string]string with the following fields: id, item, operation and fileName. Create a separate type for the arguments map: type Arguments map[string]string to prevent duplication of map[string]string. Unit tests use Arguments type also. Arguments should be passed via console flags: ./main.go -operation «add» -item ‘{«id»: "1", «email»: «[email protected]», «age»: 23}’ -fileName «users.json» -operation, -itemand -fileName are console flags. To parse them and build map you can take a Look at «flag» package: https://golang.org/pkg/flag/. Pay attention that -fileName flag should be provided every time with the name of file where you store users!

Application has to retrieve list from the users.json file and print it to the io.Writer stream. Use writer from the argument of Perform function to print the result! It is important for passing unit tests. It can be smth like writer.Write(bytes) File content: [{«id»: "1", «email»: «[email protected]», «age»: 23}] Command: ./main -operation «list» -fileName «users.json» (main is bult go application. Binary file after go build command) Output to the console: [{«id»: "1", «email»: «[email protected]», «age»: 23}] If file is empty then nothing should be printed to the console. Errors:

1. If -operation flag is missing, then error -operation flag has to be specified» has to be returned from Perform function. Package errors can be used for creating errors (https://golang.org/pkg/errors/).
2. If —fileName flag is missing, then error «-fileName flag has to be specified» has to be returned from Perform function.
3. If operation can not be handled, for example «abc» operation, then «Operation abcd not allowed!» error has to be return from the Perform function All cases are covered by unit tests. If you want to be sure your solution works correct, just start go test -v command in the root of the repo

For adding new item to the array inside users.json file, application should provide the following cmd command: ./main -operation «add» -item «{«id»: "1", «email»: «[email protected]», «age»: 23}» -fileName «users.json» -item - valid json object with the id, email and age fields Errors:

1. All errors about operation and fileName flags mentioned above
2. If -item flag is not provided Perform function should return error «-item flag has to be specified»

Application should allow removing user with the following command: ./main -operation «remove» -id "2" -fileName «users.json» If user with id "2", for example, does not exist, Perform functions should print message to the io.Writer «Item with id 2 not found». If user with specified id exists, it should be removed from the users.json file. Errors:

1. All errors about operation and fileName flags mentioned above
2. If -id flag is not provided error «-id flag has to be specified» should be returned from Perform function

Application should allow finding user by id with the following command: ./main -operation «findById» -id "1" -fileName «users.json» If user with specified id does not exist in the users.json file, then empty string has to be written to the io.Writer If user exists, then json object should be written in io.Writer Errors:

1. All errors about operation and fileName flags mentioned above
2. If -id flag is not provided error «-id flag has to be specified» should be returned from Perform function All cases of the task are covered by unit tests, So, you can check your solution during the implementation.

1. For opening and creating file use os package and OpenFile function https://golang.org/pkg/os/
2. To simply read file use ioutil package and ReadAll function https://golang.org/pkg/io/ioutil/
3. To convert json string to the object use encoding/json package and Unmarshal function: https://golang.org/pkg/encoding/json/
4. To convert json array or object to string use json package and Marshal function.
5. Go does not have throw operator and try catch statement. Instead, it has multi return and allows returning error from a function: func () (User, error) {} Take a look: https://medium.com/@hussachai/error-handling-in-go-a-quick-opinionated-guide-9199dd7c7f76
6. If you receive error in Perform function, just call panic function for exiting the execution and printing error

Note that flags and operations names should be the same as mentioned above or unit tests will never pass.