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// multistep is a library for bulding up complex actions using individual,
// discrete steps.
package multistep
// A StepAction determines the next step to take regarding multi-step actions.
type StepAction uint
const (
ActionContinue StepAction = iota
ActionHalt
)
// This is the key set in the state bag when using the basic runner to
// signal that the step sequence was cancelled.
const StateCancelled = "cancelled"
// This is the key set in the state bag when a step halted the sequence.
const StateHalted = "halted"
// Step is a single step that is part of a potentially large sequence
// of other steps, responsible for performing some specific action.
type Step interface {
// Run is called to perform the action. The parameter is a "state bag"
// of untyped things. Please be very careful about type-checking the
// items in this bag.
//
// The return value determines whether multi-step sequences continue
// or should halt.
Run(StateBag) StepAction
// Cleanup is called in reverse order of the steps that have run
// and allow steps to clean up after themselves. Do not assume if this
// ran that the entire multi-step sequence completed successfully. This
// method can be ran in the face of errors and cancellations as well.
//
// The parameter is the same "state bag" as Run, and represents the
// state at the latest possible time prior to calling Cleanup.
Cleanup(StateBag)
}
// Runner is a thing that runs one or more steps.
type Runner interface {
// Run runs the steps with the given initial state.
Run(StateBag)
// Cancel cancels a potentially running stack of steps.
Cancel()
}
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