package loadgen

import (
	"errors"
	"fmt"
	"math"
	"time"
)

var ErrInvalidAcceptanceCriteria = errors.New("invalid load generator acceptance criteria")

// AcceptanceCriteria describes optional report gates. The explicit enforcement
// flags keep a zero-error requirement distinct from an omitted requirement.
type AcceptanceCriteria struct {
	EnforceFailureRate bool
	MaxFailureRate     float64
	EnforceP99Latency  bool
	MaxP99Latency      time.Duration
}

// AcceptanceResult is a machine-readable evaluation of one bounded workload.
// It carries no target, proxy, client, credential, or request identifier data.
type AcceptanceResult struct {
	Passed      bool     `json:"passed"`
	FailureRate float64  `json:"failureRate"`
	Violations  []string `json:"violations,omitempty"`
}

// EvaluateAcceptance applies the requested thresholds to a completed report.
// A report without completed requests cannot prove any requested threshold.
func EvaluateAcceptance(report Report, criteria AcceptanceCriteria) (AcceptanceResult, error) {
	if criteria.EnforceFailureRate && (math.IsNaN(criteria.MaxFailureRate) || math.IsInf(criteria.MaxFailureRate, 0) ||
		criteria.MaxFailureRate < 0 || criteria.MaxFailureRate > 1) {
		return AcceptanceResult{}, ErrInvalidAcceptanceCriteria
	}
	if criteria.EnforceP99Latency && criteria.MaxP99Latency <= 0 {
		return AcceptanceResult{}, ErrInvalidAcceptanceCriteria
	}

	result := AcceptanceResult{Passed: true}
	if !criteria.EnforceFailureRate && !criteria.EnforceP99Latency {
		return result, nil
	}
	if report.Completed == 0 {
		result.Passed = false
		result.Violations = []string{"no completed requests were measured"}
		return result, nil
	}

	result.FailureRate = float64(report.Failed) / float64(report.Completed)
	if criteria.EnforceFailureRate && result.FailureRate > criteria.MaxFailureRate {
		result.Passed = false
		result.Violations = append(result.Violations,
			fmt.Sprintf("failure rate %.6f exceeded limit %.6f", result.FailureRate, criteria.MaxFailureRate))
	}
	if criteria.EnforceP99Latency {
		if report.Latency.Samples == 0 {
			result.Passed = false
			result.Violations = append(result.Violations, "no latency samples were measured")
		} else if report.Latency.P99UpperBound > criteria.MaxP99Latency {
			result.Passed = false
			result.Violations = append(result.Violations,
				fmt.Sprintf("p99 latency %s exceeded limit %s", report.Latency.P99UpperBound, criteria.MaxP99Latency))
		}
	}
	return result, nil
}