package domain

import (
	"fmt"
	"strings"
	"time"

	"orchestra/internal/review"
)

// Debt is the projected read model for accumulated cost: the defects,
// workarounds and operational burdens that real tasks keep paying for. It is
// derived from the event log rather than written by hand, so a claim in the
// ledger can always be checked against the events that produced it.
//
// Four classes, and no more. A fifth invented at runtime makes the priority
// model meaningless, because the thresholds in operations.CheckDebtEligibility
// are stated per class.
type DebtClass string

const (
	// DebtCorrectness is behaviour that is wrong or violates an invariant.
	DebtCorrectness DebtClass = "correctness"
	// DebtOperational works, but repeatedly costs time to diagnose, recover,
	// deploy, observe or operate.
	DebtOperational DebtClass = "operational"
	// DebtStructural is duplication or architecture demonstrably raising the
	// cost of future changes.
	DebtStructural DebtClass = "structural"
	// DebtPolish has no demonstrated cost yet, and never promotes itself.
	DebtPolish DebtClass = "polish"
)

func (c DebtClass) Valid() bool {
	switch c {
	case DebtCorrectness, DebtOperational, DebtStructural, DebtPolish:
		return true
	}
	return false
}

type DebtStatus string

const (
	DebtObserved  DebtStatus = "observed"
	DebtEligible  DebtStatus = "eligible"
	DebtScheduled DebtStatus = "scheduled"
	DebtRepaired  DebtStatus = "repaired"
	DebtWithdrawn DebtStatus = "withdrawn"
)

// ObservationKind names where one piece of evidence came from. It is the kind
// of the source fact, never an interpretation of it.
type ObservationKind string

const (
	ObservationBlockReason        ObservationKind = "block_reason"
	ObservationFailureClass       ObservationKind = "failure_class"
	ObservationReviewFinding      ObservationKind = "review_finding"
	ObservationPlanMismatch       ObservationKind = "plan_mismatch"
	ObservationDeferredFinding    ObservationKind = "deferred_finding"
	ObservationManualIntervention ObservationKind = "manual_intervention"
	ObservationWorkerFailure      ObservationKind = "worker_observation"
)

// SignatureVersion prefixes every signature this build produces. Normalization
// rules will change, and without a version a change silently regroups every
// historical observation, moving the recurrence counts that eligibility was
// already decided on. A v2 signature never matches a v1 one, so old evidence
// keeps the grouping it was counted under.
const SignatureVersion = "v1"

// DebtSignature is the mechanical dedup key. Every part is a typed fact, never
// prose, because exact signature match is the only path that attaches evidence
// without a human. An empty part becomes "-" so the arity never varies.
func DebtSignature(class DebtClass, reason, scope, component string) string {
	part := func(s string) string {
		s = strings.TrimSpace(strings.ToLower(s))
		s = strings.ReplaceAll(s, ":", "_")
		if s == "" {
			return "-"
		}
		return s
	}
	return strings.Join([]string{SignatureVersion, part(string(class)), part(reason), part(scope), part(component)}, ":")
}

// DebtComponent reduces a repository path to the unit that owns it. Two
// segments is the whole rule: it keeps internal/store distinct from
// internal/herdr without splitting one package across files.
func DebtComponent(path string) string {
	path = strings.TrimSpace(strings.Trim(path, "/"))
	if path == "" {
		return ""
	}
	parts := strings.Split(path, "/")
	if len(parts) == 1 {
		return parts[0]
	}
	return parts[0] + "/" + parts[1]
}

// DebtObservation is one piece of counted evidence. Provenance is required and
// is either an event id or, for history imported from a markdown ledger that
// predates this projection, an explicit legacy reference. Exactly one, because
// a fabricated event id would break the rule the ledger exists to enforce.
type DebtObservation struct {
	EventID   string          `json:"event_id,omitempty"`
	LegacyRef string          `json:"legacy_ref,omitempty"`
	TaskID    string          `json:"task_id,omitempty"`
	Kind      ObservationKind `json:"kind"`
	Signature string          `json:"signature"`
	Detail    string          `json:"detail,omitempty"`
	Paths     []string        `json:"paths,omitempty"`
	At        time.Time       `json:"at"`
}

func (o DebtObservation) Validate() error {
	if (o.EventID == "") == (o.LegacyRef == "") {
		return fmt.Errorf("observation needs exactly one of event_id and legacy_ref")
	}
	if o.Kind == "" {
		return fmt.Errorf("observation kind required")
	}
	if !strings.HasPrefix(o.Signature, SignatureVersion+":") {
		return fmt.Errorf("observation signature %q is not %s", o.Signature, SignatureVersion)
	}
	return nil
}

// DebtItem groups observations that share a signature. Every count the
// priority model needs is derived from Observations rather than stored, so a
// count can never drift from the log that justifies it.
type DebtItem struct {
	ID             string            `json:"id"`
	Class          DebtClass         `json:"class"`
	Status         DebtStatus        `json:"status"`
	Symptom        string            `json:"symptom"`
	Consequence    string            `json:"consequence,omitempty"`
	Severity       review.Severity   `json:"severity,omitempty"`
	Signatures     []string          `json:"signatures"`
	Paths          []string          `json:"paths,omitempty"`
	Observations   []DebtObservation `json:"observations"`
	IntroducedIn   string            `json:"introduced_in,omitempty"`
	RepairBoundary string            `json:"repair_boundary,omitempty"`
	RepairTask     string            `json:"repair_task,omitempty"`
	RepairCommit   string            `json:"repair_commit,omitempty"`
}

// Recurrence is how many times this shape has been seen.
func (d DebtItem) Recurrence() int { return len(d.Observations) }

// AffectedTasks is how broadly the shape has spread. Distinct tasks, because
// one task failing ten times is weaker evidence than ten tasks failing once.
func (d DebtItem) AffectedTasks() int {
	seen := map[string]bool{}
	for _, o := range d.Observations {
		if o.TaskID != "" {
			seen[o.TaskID] = true
		}
	}
	return len(seen)
}

// BlockedTasks counts distinct tasks this shape actually stopped.
func (d DebtItem) BlockedTasks() int {
	seen := map[string]bool{}
	for _, o := range d.Observations {
		if o.Kind == ObservationBlockReason && o.TaskID != "" {
			seen[o.TaskID] = true
		}
	}
	return len(seen)
}

// ManualInterventions counts recorded operator repairs. It reads zero on any
// log written before that recording exists, which is why the ledger reports it
// as an evidence gap rather than as an absence of operator cost.
func (d DebtItem) ManualInterventions() int {
	n := 0
	for _, o := range d.Observations {
		if o.Kind == ObservationManualIntervention {
			n++
		}
	}
	return n
}

// Components is the breadth of the shape across the tree.
func (d DebtItem) Components() []string {
	seen := map[string]bool{}
	out := []string{}
	for _, o := range d.Observations {
		for _, p := range o.Paths {
			if c := DebtComponent(p); c != "" && !seen[c] {
				seen[c] = true
				out = append(out, c)
			}
		}
	}
	return out
}

// Imported reports whether any evidence here came from a markdown ledger
// rather than from an event. A reader can then tell a counted fact from an
// imported claim without opening the observations.
func (d DebtItem) Imported() bool {
	for _, o := range d.Observations {
		if o.LegacyRef != "" {
			return true
		}
	}
	return false
}

// EvidenceGap is a debt signal the ledger knows it cannot see. Reporting the
// gap is the point: a ledger that silently omits what it cannot record reads
// as "no operator cost" when it means "operator cost is not recorded".
type EvidenceGap struct {
	Kind   ObservationKind `json:"kind"`
	Reason string          `json:"reason"`
	// Durable is false when no event type carries this evidence at all. It is
	// true when the log could carry it and this particular log does not.
	Durable bool `json:"durable"`
}

// DebtLedger is the whole read model: what history establishes, and what it
// cannot.
type DebtLedger struct {
	Items []DebtItem    `json:"items"`
	Gaps  []EvidenceGap `json:"gaps"`
	// Events is how many log entries the projection folded, so a caller can
	// tell an empty ledger from an unread log.
	Events int `json:"events"`
}

// DebtClassForBlockReason maps a typed block reason to a class. A reason that
// is a normal lifecycle stop rather than a cost returns false: waiting for a
// human decision is the system working, not debt.
func DebtClassForBlockReason(r BlockReason) (DebtClass, bool) {
	switch r {
	case BlockReasonLeaseFailure, BlockReasonWorkerOffline, BlockReasonLeaseExpired, BlockReasonSystem:
		return DebtOperational, true
	case BlockReasonHandoffValidation, BlockReasonPlanMismatch:
		return DebtCorrectness, true
	}
	return "", false
}

// DebtClassForFailureClass maps a worker failure class to a class. Only the
// classes a worker actually emits are listed; an unknown one is not guessed at.
func DebtClassForFailureClass(f string) (DebtClass, bool) {
	switch f {
	case "retry_limit", "launch_failed", "launch_transient", "launch_uncertain", "prompt_not_submitted", "lease_expired", "handoff_unanswered":
		return DebtOperational, true
	case "invalid_handoff":
		return DebtCorrectness, true
	}
	return "", false
}