package operations

import (
	"fmt"

	"orchestra/internal/domain"
)

// DebtCheck is why a debt item may or may not become work. Reasons are listed
// rather than summarised, for the same reason SubmissionCheck lists them: "not
// eligible" alone sends an operator reading code.
type DebtCheck struct {
	Eligible bool     `json:"eligible"`
	Reasons  []string `json:"reasons,omitempty"`
}

// CheckDebtEligibility is the whole promotion rule, as one pure function of a
// projected item. It decides only whether a maintenance task may be created.
// It never creates one, and it never changes what that task must then pass:
// classification as debt changes what gets scheduled, never what gets checked.
//
// The thresholds differ by class on purpose. Correctness and operational debt
// have already cost something measurable. Structural debt needs evidence that
// it is causing repeated work rather than merely offending taste. Polish never
// promotes itself, or the ledger becomes a permanent cleanup generator.
func CheckDebtEligibility(item domain.DebtItem) DebtCheck {
	recurrence, tasks := item.Recurrence(), item.AffectedTasks()
	blocked, manual := item.BlockedTasks(), item.ManualInterventions()
	switch item.Class {
	case domain.DebtCorrectness:
		if recurrence >= 1 {
			return DebtCheck{true, []string{fmt.Sprintf("correctness debt is eligible on first confirmed observation, and has %d", recurrence)}}
		}
		return DebtCheck{false, []string{"no confirmed observation"}}
	case domain.DebtOperational:
		var why []string
		if manual >= 1 {
			why = append(why, fmt.Sprintf("%d manual intervention(s) recorded", manual))
		}
		if recurrence >= 3 && tasks >= 2 {
			why = append(why, fmt.Sprintf("recurred %d times across %d tasks", recurrence, tasks))
		}
		if len(why) > 0 {
			return DebtCheck{true, why}
		}
		// Reasons state facts about this item and nothing about the
		// architecture around it. The second line here used to say manual
		// interventions were recorded by no event type, which was true when it
		// was written and false the moment OperatorInterventionRecorded
		// landed. A decision that is right for a reason that has become a lie
		// cannot be audited, and why a count is zero is not this function's
		// business: no intervention happened, none was recorded, or none was
		// migrated all read the same from here.
		return DebtCheck{false, []string{
			fmt.Sprintf("breadth threshold not met: %d occurrences across %d tasks, needs 3 across 2", recurrence, tasks),
			fmt.Sprintf("manual intervention threshold not met: %d recorded, needs 1", manual),
		}}
	case domain.DebtStructural:
		if recurrence >= 3 {
			return DebtCheck{true, []string{fmt.Sprintf("%d review findings in this component", recurrence)}}
		}
		if blocked >= 2 {
			return DebtCheck{true, []string{fmt.Sprintf("blocked %d distinct tasks in this component", blocked)}}
		}
		return DebtCheck{false, []string{
			fmt.Sprintf("needs 3 review findings or 2 blocked tasks in one component; has %d findings and %d blocked", recurrence, blocked),
		}}
	case domain.DebtPolish:
		return DebtCheck{false, []string{"polish never promotes itself, an operator promotes it explicitly"}}
	}
	return DebtCheck{false, []string{"unknown debt class " + string(item.Class)}}
}

// EligibleDebt filters a projected ledger to what policy would allow to become
// work. It returns the check alongside each item so the reasons stay visible.
func EligibleDebt(ledger domain.DebtLedger) []DebtCandidate {
	out := []DebtCandidate{}
	for _, item := range ledger.Items {
		if check := CheckDebtEligibility(item); check.Eligible {
			out = append(out, DebtCandidate{Item: item, Check: check})
		}
	}
	return out
}

type DebtCandidate struct {
	Item  domain.DebtItem `json:"item"`
	Check DebtCheck       `json:"check"`
}