Create session package

[Anthony-Jhoiro]

Session() will be the main function, it can be related to a "user".
It will be called by volume func and will execute Execute() func for each request in a group.

type Session struct {
All returned variables from a request
Global variables ? like token
}

func (s *Session) Create( rg Requestgroup) (error)

Add possibility to use "context" to pass variables (like token , or dataset)

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Edit by Anthony-Jhoiro 03/05/2020

Interfaces suggestions (explanations bellow) :

package session

type Context interface {
	// ResolveVariable returns the value of a variable, if the variable does 
	// not exists in the context, return an empty string and false or return 
	// the value and true
	ResolveVariable(variableName string) (string, bool)
}

type SessionExecutionTrace struct {}

type Session interface {
	// Get the context of the session
	GetContext() Context
	// Run executes each step of the session
	Run() (SessionExecutionTrace, error)
}

// ContextBuilder Help to build contexts in an abstract way
type ContextBuilder interface {
	// AddVariable adds a variable to the context
	AddVariable(key string, value string)
	// ConcatContext adds the information of a context into the new context
	ConcatContext(ctx Context)
	// Build Build the context
	Build() Context
}

It is important that the SessionContext should be immutable as a lot of async processes might use it and we do not want to avoid side effects.To pass variables between Session "steps" a new context should be created each time.

To make this operation easier, a ContextBuilder can be useful to group all of our methods and help provide immutable contexts.

It might be a good idea to split the session package into 2 smaller packages to handle the main session and the context separately but might be overkill.