package timeout

import (
	"time"

	"source.quilibrium.com/quilibrium/monorepo/consensus/models"
)

// Config contains the configuration parameters for a Truncated Exponential
// Backoff, as implemented by the `timeout.Controller`
//   - On timeout: increase timeout by multiplicative factor
//     `TimeoutAdjustmentFactor`. This results in exponentially growing timeout
//     duration on multiple subsequent timeouts.
//   - On progress: decrease timeout by multiplicative factor
//     `TimeoutAdjustmentFactor.
//
// Config is implemented such that it can be passed by value, while still
// supporting updates of `StateRateDelayMS` at runtime (all configs share the
// same memory holding `StateRateDelayMS`).
type Config struct {
	// MinReplicaTimeout is the minimum the timeout can decrease to [MILLISECONDS]
	MinReplicaTimeout float64
	// MaxReplicaTimeout is the maximum value the timeout can increase to
	// [MILLISECONDS]
	MaxReplicaTimeout float64
	// TimeoutAdjustmentFactor: MULTIPLICATIVE factor for increasing timeout when
	// rank change was triggered by a TC (unhappy path) or decreasing the timeout
	// on progress
	TimeoutAdjustmentFactor float64
	// HappyPathMaxRoundFailures is the number of rounds without progress where we
	// still consider being on hot path of execution. After exceeding this value
	// we will start increasing timeout values.
	HappyPathMaxRoundFailures uint64
	// MaxTimeoutStateRebroadcastInterval is the maximum value for timeout state
	// rebroadcast interval [MILLISECONDS]
	MaxTimeoutStateRebroadcastInterval float64
}

var DefaultConfig = NewDefaultConfig()

// NewDefaultConfig returns a default timeout configuration.
// We explicitly provide a method here, which demonstrates in-code how
// to compute standard values from some basic quantities.
func NewDefaultConfig() Config {
	// minReplicaTimeout is the lower bound on the replica's timeout value, this
	// is also the initial timeout with what replicas will start their execution.
	// If HotStuff is running at full speed, 1200ms should be enough. However, we
	// add some buffer. This value is for instant message delivery.
	minReplicaTimeout := 3 * time.Second
	maxReplicaTimeout := 1 * time.Minute
	timeoutAdjustmentFactorFactor := 1.2
	// after 6 successively failed rounds, the pacemaker leaves the hot path and
	// starts increasing timeouts (recovery mode)
	happyPathMaxRoundFailures := uint64(6)
	maxRebroadcastInterval := 5 * time.Second

	conf, err := NewConfig(
		minReplicaTimeout,
		maxReplicaTimeout,
		timeoutAdjustmentFactorFactor,
		happyPathMaxRoundFailures,
		maxRebroadcastInterval,
	)
	if err != nil {
		// we check in a unit test that this does not happen
		panic("Default config is not compliant with timeout Config requirements")
	}

	return conf
}

// NewConfig creates a new TimoutConfig.
//   - minReplicaTimeout: minimal timeout value for replica round [Milliseconds]
//     Consistency requirement: must be non-negative
//   - maxReplicaTimeout: maximal timeout value for replica round [Milliseconds]
//     Consistency requirement: must be non-negative and cannot be smaller than
//     minReplicaTimeout
//   - timeoutAdjustmentFactor: multiplicative factor for adjusting timeout
//     duration
//     Consistency requirement: must be strictly larger than 1
//   - happyPathMaxRoundFailures: number of successive failed rounds after which
//     we will start increasing timeouts
//   - stateRateDelay: a delay to delay the proposal broadcasting [Milliseconds]
//     Consistency requirement: must be non-negative
//
// Returns `models.ConfigurationError` is any of the consistency requirements is
// violated.
func NewConfig(
	minReplicaTimeout time.Duration,
	maxReplicaTimeout time.Duration,
	timeoutAdjustmentFactor float64,
	happyPathMaxRoundFailures uint64,
	maxRebroadcastInterval time.Duration,
) (Config, error) {
	if minReplicaTimeout <= 0 {
		return Config{}, models.NewConfigurationErrorf(
			"minReplicaTimeout must be a positive number[milliseconds]",
		)
	}
	if maxReplicaTimeout < minReplicaTimeout {
		return Config{}, models.NewConfigurationErrorf(
			"maxReplicaTimeout cannot be smaller than minReplicaTimeout",
		)
	}
	if timeoutAdjustmentFactor <= 1 {
		return Config{}, models.NewConfigurationErrorf(
			"timeoutAdjustmentFactor must be strictly bigger than 1",
		)
	}
	if maxRebroadcastInterval <= 0 {
		return Config{}, models.NewConfigurationErrorf(
			"maxRebroadcastInterval must be a positive number [milliseconds]",
		)
	}

	tc := Config{
		MinReplicaTimeout:                  float64(minReplicaTimeout.Milliseconds()),
		MaxReplicaTimeout:                  float64(maxReplicaTimeout.Milliseconds()),
		TimeoutAdjustmentFactor:            timeoutAdjustmentFactor,
		HappyPathMaxRoundFailures:          happyPathMaxRoundFailures,
		MaxTimeoutStateRebroadcastInterval: float64(maxRebroadcastInterval.Milliseconds()),
	}
	return tc, nil
}