package domain

import (
	"crypto/rand"
	"crypto/sha256"
	"encoding/base32"
	"encoding/binary"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"strings"
	"time"
)

var ErrConflict = errors.New("task version conflict")
var ErrNotFound = errors.New("task not found")
var ErrInvalid = errors.New("invalid event")

// ErrDuplicate is returned by Store.Append for a TaskCreated event whose
// (source, external_id) pair was already ingested. The caller already has a
// task for this content; nothing was appended.
var ErrDuplicate = errors.New("duplicate task ingestion")

// CurrentEventSchema is 3: schema 2 requires every event to declare its
// authorizing Surface; schema 3 adds lease fencing epochs. Older events stay
// readable so a deployment can recover its existing log before new writes
// are emitted (the store derives a non-renewable legacy epoch on replay).
const CurrentEventSchema = 3

type TaskState string

const (
	StateQueued    TaskState = "queued"
	StateLeased    TaskState = "leased"
	StateCompleted TaskState = "completed"
	StateFailed    TaskState = "failed"
	StateBlocked   TaskState = "blocked"
	// StateNeedsAttention records a recoverable fault without abandoning the
	// current fenced lease. The owning worker may still reconcile a late
	// completion, explicitly release it, or renew it while an operator
	// investigates; expiry remains the only automatic reclaim.
	StateNeedsAttention TaskState = "needs_attention"
	// StateInReview is a submitted change waiting on the human. It is not
	// completion: an agent never decides that a change shipped.
	StateInReview TaskState = "in_review"
)

// BlockReason is the machine-readable diagnosis for a TaskBlocked event.
// Blocker remains the operator-facing detail; this field lets projections
// group attention without repeatedly parsing prose at read time.
type BlockReason string

const (
	BlockReasonLeaseFailure      BlockReason = "lease_failure"
	BlockReasonWorkerOffline     BlockReason = "worker_offline"
	BlockReasonLeaseExpired      BlockReason = "lease_expired"
	BlockReasonApproval          BlockReason = "approval"
	BlockReasonHandoffValidation BlockReason = "handoff_validation"
	BlockReasonOperator          BlockReason = "operator_block"
	BlockReasonSystem            BlockReason = "system_error"
	// BlockReasonTrajectoryGate is a deliberate stop, not a fault: the plan is
	// sealed and Orchestra is waiting for the human to confirm the direction.
	BlockReasonTrajectoryGate BlockReason = "trajectory_gate"
	// BlockReasonHumanDecision is a bounded question the repository could not
	// answer. BlockReasonOperatorRequired is what a task becomes when it has
	// spent its question budget: an operator looks at it rather than the
	// agent asking again.
	BlockReasonHumanDecision    BlockReason = "human_decision"
	BlockReasonOperatorRequired BlockReason = "operator_required"
	BlockReasonUnknown          BlockReason = "unknown"
)

func (r BlockReason) Valid() bool {
	switch r {
	case BlockReasonLeaseFailure, BlockReasonWorkerOffline, BlockReasonLeaseExpired,
		BlockReasonApproval, BlockReasonHandoffValidation, BlockReasonOperator,
		BlockReasonSystem, BlockReasonUnknown, BlockReasonTrajectoryGate,
		BlockReasonHumanDecision, BlockReasonOperatorRequired:
		return true
	}
	return false
}

// InferBlockReason supplies a stable category for older events which only
// recorded a prose blocker. New producers should send block_reason directly.
func InferBlockReason(blocker string) BlockReason {
	v := strings.ToLower(blocker)
	switch {
	case strings.Contains(v, "handoff"):
		return BlockReasonHandoffValidation
	case strings.Contains(v, "approval") || strings.Contains(v, "permission"):
		return BlockReasonApproval
	case strings.Contains(v, "expired") && strings.Contains(v, "lease"):
		return BlockReasonLeaseExpired
	case strings.Contains(v, "worker") && (strings.Contains(v, "offline") || strings.Contains(v, "unreachable")):
		return BlockReasonWorkerOffline
	case strings.Contains(v, "lease") || strings.Contains(v, "agent.start") || strings.Contains(v, "pane"):
		return BlockReasonLeaseFailure
	default:
		return BlockReasonSystem
	}
}

type Estimate struct {
	Value      float64 `json:"value"`
	Who        string  `json:"who"`
	Confidence float64 `json:"confidence"`
}

// SessionEvidence is captured by the machine that owns a pane immediately
// before it drops its mapping. It is deliberately observation-only: it never
// claims that a pane is still live after the worker has closed it.
type SessionEvidence struct {
	PaneID     string    `json:"pane_id,omitempty"`
	HarnessID  string    `json:"harness_id,omitempty"`
	PaneState  string    `json:"pane_state,omitempty"`
	Source     string    `json:"source,omitempty"`
	CapturedAt time.Time `json:"captured_at,omitempty"`
	CheckedAt  time.Time `json:"checked_at,omitempty"`
}
type Lease struct {
	HarnessID string `json:"harness_id"`
	// Epoch is an opaque fencing token minted for every assignment. Versions
	// change for ordinary lifecycle events; an epoch changes only when
	// ownership changes, so an old pane can never become current again after
	// a release/re-lease cycle.
	Epoch string    `json:"epoch"`
	Until time.Time `json:"until"`
}
type Task struct {
	ID               string     `json:"id"`
	Source           string     `json:"source"`
	ExternalID       string     `json:"external_id"`
	Project          string     `json:"project"`
	Capability       []string   `json:"capability"`
	Parent           string     `json:"parent,omitempty"`
	InherentPriority int        `json:"inherent_priority"`
	Due              *time.Time `json:"due,omitempty"`
	Estimate         *Estimate  `json:"estimate,omitempty"`
	State            TaskState  `json:"state"`
	Lease            *Lease     `json:"lease,omitempty"`
	// HandoffRef survives the queued interval between TaskReleased and the
	// next router-owned TaskLeased event; it is the only artifact the worker
	// may use for local pickup validation.
	HandoffRef string `json:"handoff_ref,omitempty"`
	// ReleaseTransaction and ReleaseAnchor bind successor pickup to the exact
	// durable predecessor checkpoint. They survive queueing and re-lease.
	ReleaseTransaction string   `json:"release_transaction,omitempty"`
	ReleaseAnchor      string   `json:"release_anchor,omitempty"`
	PickupTransaction  string   `json:"pickup_transaction,omitempty"`
	PickupLeaseVersion int      `json:"pickup_lease_version,omitempty"`
	Version            int      `json:"version"`
	Title              string   `json:"title,omitempty"`
	Description        string   `json:"description,omitempty"`
	Acceptance         []string `json:"acceptance,omitempty"`
	QualityGate        string   `json:"quality_gate,omitempty"`
	// Block evidence is projected from TaskBlocked so terminal records remain
	// diagnosable after the live coordinator mapping is gone.
	Blocker     string          `json:"blocker,omitempty"`
	BlockReason BlockReason     `json:"block_reason,omitempty"`
	BlockedAt   time.Time       `json:"blocked_at,omitempty"`
	LastPaneID  string          `json:"last_pane_id,omitempty"`
	LastHarness string          `json:"last_harness_id,omitempty"`
	PaneState   string          `json:"pane_state,omitempty"` // open, closed, unreachable, unknown
	LastSession SessionEvidence `json:"last_session,omitempty"`
	// Recovery state is part of the durable projection, never process-local
	// router memory. This makes retry and operator diagnostics survive a
	// coordinator restart.
	Attempt        int       `json:"attempt,omitempty"`
	NextRetryAt    time.Time `json:"next_retry_at,omitempty"`
	FailureClass   string    `json:"failure_class,omitempty"`
	LifecyclePhase string    `json:"lifecycle_phase,omitempty"`
	// WorkPhase is the cognitive phase (frame/research/plan/implement/review),
	// orthogonal to State and LifecyclePhase. Empty means frame.
	WorkPhase WorkPhase `json:"work_phase,omitempty"`
	// DecisionRequest is the question this task is currently blocked on. It is
	// cleared when the task leaves the blocked state, because the answer then
	// stands on its own as a decision and the log still holds the question.
	DecisionRequest *DecisionRequest `json:"decision_request,omitempty"`
	// ReviewTargetSHA is the commit the current review phase was entered
	// against. A review of any other commit is not a review of this work.
	ReviewTargetSHA string `json:"review_target_sha,omitempty"`
	// Review is the last independent review, bound to the commit it was
	// performed against. A review is never a free-floating pass: when the code
	// moves, ResultSHA no longer matches and the review describes a tree that
	// does not exist any more.
	Review *ReviewRef `json:"review,omitempty"`
	// Submission is the durable record of the change handed to the human.
	Submission *SubmissionRef `json:"submission,omitempty"`
	// ResearchRef and PlanRef are the sealed artifacts of the phases already
	// finished. The next phase reads these, never the session that wrote them.
	ResearchRef string `json:"research_ref,omitempty"`
	PlanRef     string `json:"plan_ref,omitempty"`
	LastError   string `json:"last_error,omitempty"`
}

// ReviewRef binds a sealed review artifact to one commit.
type ReviewRef struct {
	ArtifactRef string `json:"artifact_ref"`
	ResultSHA   string `json:"result_sha"`
	// Blocking is the count of blocker and important findings, projected so a
	// completion check does not have to read the artifact to know the answer.
	Blocking int `json:"blocking"`
}

// EventReviewRecorded seals one independent review. Orchestra emits it; the
// reviewing session only supplies the findings.
const EventReviewRecorded = "ReviewRecorded"

// ReviewSatisfied reports whether this task holds an accepted review of the
// exact commit named. It is the mechanical half of completion eligibility.
func (t Task) ReviewSatisfied(resultSHA string) bool {
	return t.Review != nil && t.Review.ResultSHA == resultSHA && t.Review.Blocking == 0
}

type Event struct {
	SchemaVersion int             `json:"schema_version,omitempty"`
	Seq           uint64          `json:"seq"`
	ID            string          `json:"id"`
	Type          string          `json:"type"`
	TaskID        string          `json:"task_id"`
	Version       int             `json:"version"`
	At            time.Time       `json:"at"`
	Payload       json.RawMessage `json:"payload"`
	// Surface identifies the bus capability the emitter is authorized under
	// (see internal/authz). It is required on every event so authorization is
	// enforced once, at the store append boundary, regardless of whether the
	// emitter reached the store over HTTP, from the router, from a harness
	// adapter, or from a provider.
	Surface string `json:"surface"`
}

func Hash(v []byte) string { h := sha256.Sum256(v); return hex.EncodeToString(h[:]) }

// NewID returns a sortable, 128-bit ULID-like identifier using the canonical
// 48-bit millisecond timestamp plus 80 bits of cryptographic randomness.

var ulidEncoding = base32.NewEncoding("0123456789ABCDEFGHJKMNPQRSTVWXYZ").WithPadding(base32.NoPadding)

func NewID() string {
	b := make([]byte, 16)
	binary.BigEndian.PutUint64(b[:8], uint64(time.Now().UnixMilli())<<16)
	_, _ = rand.Read(b[6:])
	return ulidEncoding.EncodeToString(b)
}
func ValidateEvent(e Event) error {
	if e.SchemaVersion > CurrentEventSchema || e.Type == "" || e.TaskID == "" || len(e.Payload) == 0 || len(e.Payload) > 64*1024 {
		return ErrInvalid
	}
	if e.SchemaVersion >= 2 && strings.TrimSpace(e.Surface) == "" {
		return fmt.Errorf("%w: surface required", ErrInvalid)
	}
	allowed := map[string]bool{"TaskCreated": true, "TaskLeased": true, "TaskLeaseRenewed": true, "TaskReleased": true, "TaskLaunchAcknowledged": true, "TaskPickupValidated": true, "TaskCompleted": true, "TaskFailed": true, "TaskBlocked": true, "TaskNeedsAttention": true, "ApprovalRequested": true, "ApprovalGranted": true, "ApprovalDenied": true, "TaskAmended": true, "TaskCorrected": true, "QuotaReported": true, "StandupAdvisory": true, EventHumanDecisionRecorded: true, EventHumanDecisionSuperseded: true, EventWorkPhaseChanged: true, EventDeferredFindingRecorded: true, EventReviewRecorded: true, EventTaskSubmitted: true, EventTaskChangesRequested: true}
	if !allowed[e.Type] {
		return fmt.Errorf("%w: unknown type %q", ErrInvalid, e.Type)
	}
	var p map[string]any
	if err := json.Unmarshal(e.Payload, &p); err != nil {
		return fmt.Errorf("%w: payload is not JSON", ErrInvalid)
	}
	if p == nil {
		return fmt.Errorf("%w: payload must be an object", ErrInvalid)
	}
	if err := ValidatePayload(e.Type, p); err != nil {
		return err
	}
	if e.SchemaVersion >= 3 {
		switch e.Type {
		case "TaskLeased", "TaskLeaseRenewed", "TaskLaunchAcknowledged", "TaskPickupValidated":
			if v, ok := p["lease_epoch"].(string); !ok || strings.TrimSpace(v) == "" {
				return fmt.Errorf("%w: lease_epoch required", ErrInvalid)
			}
		}
	}
	return nil
}
func ValidateCreated(p map[string]any) error {
	for _, k := range []string{"source", "external_id", "project"} {
		if s, ok := p[k].(string); !ok || strings.TrimSpace(s) == "" {
			return fmt.Errorf("%w: %s required", ErrInvalid, k)
		}
	}
	return nil
}

func ValidatePayload(typ string, p map[string]any) error {
	requiredString := func(key string) error {
		v, ok := p[key].(string)
		if !ok || strings.TrimSpace(v) == "" {
			return fmt.Errorf("%w: %s required", ErrInvalid, key)
		}
		return nil
	}
	switch typ {
	case "TaskCreated":
		return ValidateCreated(p)
	case "TaskLeased":
		if err := requiredString("harness_id"); err != nil {
			return err
		}
		// Validation of a durable event must not depend on the current clock.
		// Comparing until_ns against time.Now() here made every lease event
		// fail validation once it expired, so replaying the log after a
		// restart refused the store's own history and the coordinator could
		// not start at all. Freshness is a lease question, answered by
		// Store.Lease and Store.ExpireLeases; well-formedness is this
		// function's question.
		until, untilOK := p["until_ns"].(float64)
		if ttl, ok := p["ttl"].(float64); ok {
			if ttl <= 0 {
				return fmt.Errorf("%w: ttl invalid", ErrInvalid)
			}
		} else if !untilOK || until <= 0 {
			return fmt.Errorf("%w: ttl required", ErrInvalid)
		}
		if v, ok := p["expected_version"].(float64); !ok || v < 0 || v != float64(int(v)) {
			return fmt.Errorf("%w: expected_version invalid", ErrInvalid)
		}
	case "TaskLeaseRenewed":
		if err := requiredString("harness_id"); err != nil {
			return err
		}
		// Time-independent for the same reason as TaskLeased above.
		until, ok := p["until_ns"].(float64)
		if !ok || until <= 0 {
			return fmt.Errorf("%w: until_ns required", ErrInvalid)
		}
		if v, ok := p["expected_version"].(float64); !ok || v < 0 || v != float64(int(v)) {
			return fmt.Errorf("%w: expected_version invalid", ErrInvalid)
		}
	case "TaskReleased":
		if err := requiredString("handoff_ref"); err != nil && p["reason"] == nil {
			return err
		}
	case "TaskPickupValidated":
		for _, key := range []string{"transaction_id", "handoff_ref", "anchor_sha", "harness_id"} {
			if err := requiredString(key); err != nil {
				return err
			}
		}
		if err := requiredHash(p, "handoff_ref"); err != nil {
			return err
		}
		if v, ok := p["anchor_sha"].(string); !ok || len(v) != 40 {
			return fmt.Errorf("%w: anchor_sha invalid", ErrInvalid)
		}
		if v, ok := p["lease_version"].(float64); !ok || v < 1 || v != float64(int(v)) {
			return fmt.Errorf("%w: lease_version invalid", ErrInvalid)
		}
		if _, ok := p["handoff_ref"]; ok {
			if err := requiredHash(p, "handoff_ref"); err != nil {
				return err
			}
			v, ok := p["anchor_sha"].(string)
			if !ok || len(v) != 40 || strings.TrimSpace(v) != v {
				return fmt.Errorf("%w: anchor_sha invalid", ErrInvalid)
			}
		}
	case "TaskCompleted":
		if err := requiredString("report_ref"); err != nil {
			return err
		}
		if err := requiredHash(p, "report_ref"); err != nil {
			return err
		}
		if receipt, ok := p["receipt"].(map[string]any); !ok || len(receipt) == 0 {
			return fmt.Errorf("%w: receipt required", ErrInvalid)
		}
		if v, ok := p["result_sha"]; ok {
			if s, ok := v.(string); !ok || len(s) != 40 {
				return fmt.Errorf("%w: result_sha invalid", ErrInvalid)
			}
			if err := requiredString("branch"); err != nil {
				return err
			}
			if err := requiredString("remote"); err != nil {
				return err
			}
		}
	case "TaskFailed":
		if err := requiredString("reason"); err != nil {
			return err
		}
	case "TaskLaunchAcknowledged":
		if err := requiredString("harness_id"); err != nil {
			return err
		}
	case "TaskBlocked", "TaskNeedsAttention":
		if err := requiredString("blocker"); err != nil {
			return err
		}
		if v, ok := p["block_reason"]; ok {
			s, ok := v.(string)
			if !ok || !BlockReason(s).Valid() {
				return fmt.Errorf("%w: block_reason invalid", ErrInvalid)
			}
		}
		if _, ok := p["handoff_ref"]; ok {
			if err := requiredHash(p, "handoff_ref"); err != nil {
				return err
			}
		}
		if v, ok := p["pane_state"]; ok && v != "open" && v != "closed" && v != "unreachable" && v != "unknown" {
			return fmt.Errorf("%w: pane_state invalid", ErrInvalid)
		}
		if v, ok := p["decision_request"]; ok {
			m, ok := v.(map[string]any)
			if !ok {
				return fmt.Errorf("%w: decision_request must be an object", ErrInvalid)
			}
			if err := decodeDecisionRequest(m).Validate(); err != nil {
				return err
			}
		}
	case "TaskAmended":
		if len(p) == 0 {
			return fmt.Errorf("%w: amendment cannot be empty", ErrInvalid)
		}
	case "TaskCorrected":
		// §3.1: "a wrong event is never edited; a compensating event is
		// appended and replay sees both." `corrects` names the event this one
		// reverses/repairs — existence against the log is checked in
		// Store.Append, where the log is visible; ValidatePayload only knows
		// shape.
		if err := requiredString("corrects"); err != nil {
			return err
		}
		if v, ok := p["state"]; ok {
			s, ok := v.(string)
			if !ok {
				return fmt.Errorf("%w: state must be a string", ErrInvalid)
			}
			switch TaskState(s) {
			case StateQueued, StateLeased, StateCompleted, StateFailed, StateBlocked, StateNeedsAttention, StateInReview:
			default:
				return fmt.Errorf("%w: state invalid", ErrInvalid)
			}
		}
		if v, ok := p["attempt"]; ok {
			n, ok := v.(float64)
			if !ok || n < 0 || n != float64(int(n)) {
				return fmt.Errorf("%w: attempt must be a non-negative whole number", ErrInvalid)
			}
		}
		if v, ok := p["next_retry_at"]; ok {
			s, ok := v.(string)
			if !ok {
				return fmt.Errorf("%w: next_retry_at must be a string", ErrInvalid)
			}
			if s != "" {
				if _, err := time.Parse(time.RFC3339, s); err != nil {
					return fmt.Errorf("%w: next_retry_at must be RFC3339 or empty", ErrInvalid)
				}
			}
		}
		if len(p) < 2 {
			return fmt.Errorf("%w: correction must change at least one field", ErrInvalid)
		}
	case "ApprovalRequested":
		for _, k := range []string{"subject_ref", "options"} {
			if _, ok := p[k]; !ok {
				return fmt.Errorf("%w: %s required", ErrInvalid, k)
			}
		}
	case "ApprovalGranted", "ApprovalDenied":
		if err := requiredString("subject_ref"); err != nil {
			return err
		}
	case "QuotaReported":
		if err := requiredString("harness_id"); err != nil {
			return err
		}
		if v, ok := p["consumed"].(float64); !ok || v < 0 {
			return fmt.Errorf("%w: consumed required", ErrInvalid)
		}
	case "StandupAdvisory":
		if _, ok := p["items"]; !ok {
			return fmt.Errorf("%w: items required", ErrInvalid)
		}
	case EventHumanDecisionRecorded:
		for _, k := range []string{"decision_id", "kind", "subject", "value"} {
			if err := requiredString(k); err != nil {
				return err
			}
		}
		if kind, _ := p["kind"].(string); !HumanDecisionKind(kind).Valid() {
			return fmt.Errorf("%w: kind invalid", ErrInvalid)
		}
		src, ok := p["source"].(map[string]any)
		if !ok {
			return fmt.Errorf("%w: source required", ErrInvalid)
		}
		if v, ok := src["provider"].(string); !ok || strings.TrimSpace(v) == "" {
			return fmt.Errorf("%w: source.provider required", ErrInvalid)
		}
		if v, ok := p["supersedes"]; ok {
			list, ok := v.([]any)
			if !ok {
				return fmt.Errorf("%w: supersedes must be an array", ErrInvalid)
			}
			for _, item := range list {
				if s, ok := item.(string); !ok || strings.TrimSpace(s) == "" {
					return fmt.Errorf("%w: supersedes entries must be decision ids", ErrInvalid)
				}
			}
		}
	case EventHumanDecisionSuperseded:
		if err := requiredString("decision_id"); err != nil {
			return err
		}
	case EventWorkPhaseChanged:
		return ValidateWorkPhaseChanged(p)
	case EventTaskSubmitted:
		return ValidateTaskSubmitted(p)
	case EventTaskChangesRequested:
		if v, ok := p["submitted_sha"].(string); !ok || len(v) != 40 {
			return fmt.Errorf("%w: submitted_sha invalid", ErrInvalid)
		}
		if v, ok := p["submission_event"].(string); !ok || strings.TrimSpace(v) == "" {
			return fmt.Errorf("%w: submission_event required", ErrInvalid)
		}
		ids, ok := p["decision_ids"].([]any)
		if !ok || len(ids) == 0 {
			return fmt.Errorf("%w: decision_ids required", ErrInvalid)
		}
		for _, id := range ids {
			if s, ok := id.(string); !ok || strings.TrimSpace(s) == "" {
				return fmt.Errorf("%w: decision_ids entries must be ids", ErrInvalid)
			}
		}
	case EventReviewRecorded:
		if err := requiredHash(p, "artifact_ref"); err != nil {
			return err
		}
		if v, ok := p["result_sha"].(string); !ok || len(v) != 40 {
			return fmt.Errorf("%w: result_sha invalid", ErrInvalid)
		}
		if v, ok := p["blocking"].(float64); !ok || v < 0 || v != float64(int(v)) {
			return fmt.Errorf("%w: blocking invalid", ErrInvalid)
		}
	case EventDeferredFindingRecorded:
		f := DeferredFinding{}
		f.Summary, _ = p["summary"].(string)
		f.Why, _ = p["why"].(string)
		return f.Validate()
	}
	return nil
}

func requiredHash(p map[string]any, key string) error {
	v, ok := p[key].(string)
	if !ok || len(v) != 64 {
		return fmt.Errorf("%w: %s must be sha256", ErrInvalid, key)
	}
	if _, err := hex.DecodeString(v); err != nil {
		return fmt.Errorf("%w: %s must be sha256", ErrInvalid, key)
	}
	return nil
}