package services

// ApprovalService implements the 4-Augen-Prüfung workflow on
// paliad.deadlines and paliad.appointments (t-paliad-138).
//
// Architecture: write-then-approve (m's Q5 choice). The mutation lands on
// the entity row immediately; the entity carries approval_status='pending'
// + pending_request_id until an approver flips it to 'approved'. Delete is
// the one stage-then-write exception — we mark the row pending instead of
// hard-deleting, then hard-delete on approve / restore on reject.
//
// Submission entry points (Submit{Create,Update,Complete,Delete}) are
// invoked by DeadlineService / AppointmentService inside their existing
// transactions. They:
//   1. Look up the policy for (project, entity_type, lifecycle_event).
//   2. If no policy → no-op (entity stays approval_status='approved').
//   3. If policy → run a deadlock check (qualified approver != requester
//      must exist), insert an approval_requests row, mark the entity
//      pending, emit a *_approval_requested project_events row.
//
// Decision entry points (Approve / Reject / Revoke) run their own tx and:
//   - Approve: validate canApprove(caller, request); flip the entity back
//     to approved (or hard-delete for delete-lifecycle); emit
//     *_approval_approved.
//   - Reject: validate canApprove; revert the entity from pre_image (or
//     hard-delete a pending-create); emit *_approval_rejected.
//   - Revoke: validate caller == requester; same revert as Reject; emit
//     *_approval_revoked.
//
// Self-approval is blocked at three layers:
//   1. canApprove() returns ErrSelfApproval when caller == requester.
//   2. The DB CHECK constraint approval_requests_no_self_approval refuses
//      decided_by == requested_by writes.
//   3. The deadlock-check excludes the requester from the qualified-approver
//      pool, so the deadlock path can't be silently bypassed.

import (
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"strings"
	"time"

	"github.com/google/uuid"
	"github.com/jmoiron/sqlx"

	"mgit.msbls.de/m/paliad/internal/models"
)

// ApprovalService is the workflow orchestrator. It holds no entity-specific
// knowledge — DeadlineService / AppointmentService call its Submit*
// methods, and the Approve / Reject / Revoke paths run direct SQL on the
// entity tables to keep the dependency graph acyclic.
type ApprovalService struct {
	db    *sqlx.DB
	users *UserService
}

// NewApprovalService wires the service.
func NewApprovalService(db *sqlx.DB, users *UserService) *ApprovalService {
	return &ApprovalService{db: db, users: users}
}

// LookupPolicy returns the approval policy for the given tuple, or nil if
// none exists. Read inside the same tx as Submit* so policy reads see
// whatever the calling tx may have already written.
func (s *ApprovalService) LookupPolicy(ctx context.Context, tx *sqlx.Tx, projectID uuid.UUID, entityType, lifecycleEvent string) (*models.ApprovalPolicy, error) {
	var p models.ApprovalPolicy
	q := `SELECT id, project_id, entity_type, lifecycle_event, required_role,
	             created_at, updated_at, created_by
	        FROM paliad.approval_policies
	       WHERE project_id = $1 AND entity_type = $2 AND lifecycle_event = $3`
	row := txOrDB(tx, s.db).QueryRowxContext(ctx, q, projectID, entityType, lifecycleEvent)
	if err := row.StructScan(&p); err != nil {
		if errors.Is(err, sql.ErrNoRows) {
			return nil, nil
		}
		return nil, fmt.Errorf("lookup approval policy: %w", err)
	}
	return &p, nil
}

// hasQualifiedApprover counts users on the project's team-membership path
// (direct OR ancestor) whose (profession, responsibility) tuple meets the
// strict-ladder threshold, plus any global_admin user, plus any partner-
// unit-derived member where the attachment grants authority (t-paliad-139).
// Excludes requesterID.
//
// Returns true if at least one such user exists. The path-walk JOIN matches
// the visibility predicate so an ancestor partner qualifies for a
// descendant's approval, just like they have visibility.
//
// t-paliad-148: peer authority requires BOTH a profession with sufficient
// level AND a responsibility ∈ {lead, member} that opens the gate.
// observer/external rows are excluded even if the user's profession would
// otherwise qualify — that's the point of the project-level gate.
func (s *ApprovalService) hasQualifiedApprover(ctx context.Context, tx *sqlx.Tx, projectID, requesterID uuid.UUID, requiredRole string) (bool, error) {
	q := `WITH path AS (
	        SELECT string_to_array(p.path, '.')::uuid[] AS ids
	          FROM paliad.projects p WHERE p.id = $1
	      )
	      SELECT EXISTS (
	          SELECT 1 FROM paliad.project_teams pt
	            JOIN paliad.users u ON u.id = pt.user_id
	            JOIN path ON pt.project_id = ANY(path.ids)
	           WHERE pt.user_id <> $2
	             AND pt.responsibility IN ('lead', 'member')
	             AND paliad.approval_role_level(u.profession) >= paliad.approval_role_level($3)
	          UNION ALL
	          SELECT 1 FROM paliad.users u
	           WHERE u.global_role = 'global_admin' AND u.id <> $2
	          UNION ALL
	          SELECT 1 FROM paliad.project_partner_units ppu
	            JOIN paliad.partner_unit_members pum ON pum.partner_unit_id = ppu.partner_unit_id
	            JOIN path ON ppu.project_id = ANY(path.ids)
	           WHERE pum.user_id <> $2
	             AND ppu.derive_grants_authority = true
	             AND pum.unit_role = ANY(ppu.derive_unit_roles)
	             AND paliad.approval_role_level(
	                     paliad.approval_role_from_unit_role(pum.unit_role)
	                 ) >= paliad.approval_role_level($3)
	          LIMIT 1
	      ) AS ok`
	var ok bool
	if err := txOrDB(tx, s.db).GetContext(ctx, &ok, q, projectID, requesterID, requiredRole); err != nil {
		return false, fmt.Errorf("deadlock check: %w", err)
	}
	return ok, nil
}

// SubmitCreate is invoked by Deadline/AppointmentService inside their
// create-tx, after the entity row has been INSERTed but before the
// commit. If a (project, entity_type, 'create') policy applies, it inserts
// the approval_requests row, marks the entity pending, and emits the
// *_approval_requested audit event.
//
// payload is the just-inserted entity's field values (used as audit echo).
//
// Returns the new request ID if pending, nil if no policy applied.
func (s *ApprovalService) SubmitCreate(ctx context.Context, tx *sqlx.Tx, projectID, entityID, requesterID uuid.UUID, entityType string, payload map[string]any) (*uuid.UUID, error) {
	return s.submit(ctx, tx, projectID, entityID, requesterID, entityType, LifecycleCreate, nil, payload)
}

// SubmitUpdate is invoked after the entity row has been UPDATEd. preImage
// carries the date-bearing fields that were just overwritten (per Q4
// allowlist) so a rejection can restore them. payload echoes the new values.
func (s *ApprovalService) SubmitUpdate(ctx context.Context, tx *sqlx.Tx, projectID, entityID, requesterID uuid.UUID, entityType string, preImage, payload map[string]any) (*uuid.UUID, error) {
	if len(preImage) == 0 {
		// Nothing in the date-bearing allowlist actually changed — bypass
		// the approval flow entirely (the underlying UPDATE was cosmetic).
		return nil, nil
	}
	return s.submit(ctx, tx, projectID, entityID, requesterID, entityType, LifecycleUpdate, preImage, payload)
}

// SubmitComplete is invoked after status was flipped to 'completed'
// (deadline) or completed_at was set (appointment). preImage stores the
// pre-completion state so a rejection can revert.
func (s *ApprovalService) SubmitComplete(ctx context.Context, tx *sqlx.Tx, projectID, entityID, requesterID uuid.UUID, entityType string, preImage, payload map[string]any) (*uuid.UUID, error) {
	return s.submit(ctx, tx, projectID, entityID, requesterID, entityType, LifecycleComplete, preImage, payload)
}

// SubmitDelete is invoked WITHOUT a prior delete on the entity (delete is
// the stage-then-write exception). The entity row stays alive with
// approval_status='pending'; on approve we hard-delete, on reject we just
// clear the pending markers.
//
// preImage stores the full row state so the inbox can render
// "About to delete: Frist X (due 2026-05-12)".
func (s *ApprovalService) SubmitDelete(ctx context.Context, tx *sqlx.Tx, projectID, entityID, requesterID uuid.UUID, entityType string, preImage map[string]any) (*uuid.UUID, error) {
	return s.submit(ctx, tx, projectID, entityID, requesterID, entityType, LifecycleDelete, preImage, nil)
}

// submit is the shared lifecycle-handling kernel.
func (s *ApprovalService) submit(ctx context.Context, tx *sqlx.Tx, projectID, entityID, requesterID uuid.UUID, entityType, lifecycle string, preImage, payload map[string]any) (*uuid.UUID, error) {
	policy, err := s.LookupPolicy(ctx, tx, projectID, entityType, lifecycle)
	if err != nil {
		return nil, err
	}
	if policy == nil {
		// No policy applies — entity stays approval_status='approved'. No-op.
		return nil, nil
	}

	// Deadlock check: somebody other than the requester must be qualified
	// to approve, either via project team membership or as global_admin.
	ok, err := s.hasQualifiedApprover(ctx, tx, projectID, requesterID, policy.RequiredRole)
	if err != nil {
		return nil, err
	}
	if !ok {
		return nil, fmt.Errorf("%w: required role %q", ErrNoQualifiedApprover, policy.RequiredRole)
	}

	// Concurrent-pending guard: the entity table has a CHECK / NOT NULL
	// guard against double-pending — but we surface a clean error rather
	// than letting the UPDATE silently fail. The guard relies on
	// approval_status='approved' being the precondition for a fresh
	// pending state.
	currentStatus, err := s.entityApprovalStatus(ctx, tx, entityType, entityID)
	if err != nil {
		return nil, err
	}
	if currentStatus == ApprovalStatusPending {
		return nil, ErrConcurrentPending
	}

	requestID := uuid.New()
	preImageJSON, err := marshalJSONOrNull(preImage)
	if err != nil {
		return nil, fmt.Errorf("marshal pre_image: %w", err)
	}
	payloadJSON, err := marshalJSONOrNull(payload)
	if err != nil {
		return nil, fmt.Errorf("marshal payload: %w", err)
	}

	insertReqSQL := `INSERT INTO paliad.approval_requests
	    (id, project_id, entity_type, entity_id, lifecycle_event,
	     pre_image, payload, requested_by, required_role, status)
	  VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, 'pending')`
	if _, err := tx.ExecContext(ctx, insertReqSQL,
		requestID, projectID, entityType, entityID, lifecycle,
		preImageJSON, payloadJSON, requesterID, policy.RequiredRole); err != nil {
		return nil, fmt.Errorf("insert approval_request: %w", err)
	}

	// Mark the entity row pending. The WHERE approval_status='approved'
	// (or 'legacy') guard makes the UPDATE atomic vs concurrent pending.
	updateEntitySQL := fmt.Sprintf(`UPDATE paliad.%s
	    SET approval_status = 'pending', pending_request_id = $1, updated_at = now()
	  WHERE id = $2 AND approval_status IN ('approved','legacy')`,
		entityTableName(entityType))
	res, err := tx.ExecContext(ctx, updateEntitySQL, requestID, entityID)
	if err != nil {
		return nil, fmt.Errorf("mark entity pending: %w", err)
	}
	rows, _ := res.RowsAffected()
	if rows != 1 {
		// Either the entity vanished or another tx flipped it pending.
		return nil, ErrConcurrentPending
	}

	// Audit emit.
	eventType := approvalEventType(entityType, "requested")
	descPtr := approvalDescription("requested", policy.RequiredRole, lifecycle)
	meta := map[string]any{
		"approval_request_id": requestID.String(),
		"lifecycle_event":     lifecycle,
		"required_role":       policy.RequiredRole,
		entityType + "_id":    entityID.String(),
	}
	if err := insertProjectEventWithMeta(ctx, tx, projectID, requesterID, eventType, eventType, descPtr, meta); err != nil {
		return nil, err
	}
	return &requestID, nil
}

// Approve flips a pending request to 'approved' and applies the lifecycle
// to the entity. Runs in its own transaction.
func (s *ApprovalService) Approve(ctx context.Context, requestID, callerID uuid.UUID, note string) error {
	return s.decide(ctx, requestID, callerID, RequestStatusApproved, note)
}

// Reject flips a pending request to 'rejected' and reverts the entity from
// pre_image. Runs in its own transaction.
func (s *ApprovalService) Reject(ctx context.Context, requestID, callerID uuid.UUID, note string) error {
	return s.decide(ctx, requestID, callerID, RequestStatusRejected, note)
}

// Revoke is invoked by the requester to undo their own pending submission
// before any approver acts on it. The entity reverts as if the request had
// been rejected, but the request status is 'revoked'. Runs in its own tx.
func (s *ApprovalService) Revoke(ctx context.Context, requestID, callerID uuid.UUID) error {
	return s.decide(ctx, requestID, callerID, RequestStatusRevoked, "")
}

// decide is the shared kernel for Approve / Reject / Revoke. The decision
// kind is derived from the (caller, request) relationship and the requested
// final status:
//   - RequestStatusApproved: caller must NOT be requester; admin override or peer.
//   - RequestStatusRejected: same authorization rules as Approve.
//   - RequestStatusRevoked:  caller MUST be requester.
func (s *ApprovalService) decide(ctx context.Context, requestID, callerID uuid.UUID, finalStatus, note string) error {
	tx, err := s.db.BeginTxx(ctx, nil)
	if err != nil {
		return fmt.Errorf("begin tx: %w", err)
	}
	defer tx.Rollback()

	req, err := s.getRequestForUpdate(ctx, tx, requestID)
	if err != nil {
		return err
	}
	if req.Status != RequestStatusPending {
		return fmt.Errorf("%w: status=%s", ErrRequestNotPending, req.Status)
	}

	var decisionKind string
	switch finalStatus {
	case RequestStatusApproved, RequestStatusRejected:
		kind, err := s.canApprove(ctx, tx, callerID, req)
		if err != nil {
			return err
		}
		decisionKind = kind
	case RequestStatusRevoked:
		if callerID != req.RequestedBy {
			return ErrNotApprover
		}
		decisionKind = DecisionKindPeer // unused for revoke but keeps non-NULL audit
	default:
		return fmt.Errorf("invalid final status %q", finalStatus)
	}

	// Apply the lifecycle outcome to the entity.
	switch finalStatus {
	case RequestStatusApproved:
		if err := s.applyApproved(ctx, tx, req, callerID); err != nil {
			return err
		}
	case RequestStatusRejected, RequestStatusRevoked:
		if err := s.applyRevert(ctx, tx, req); err != nil {
			return err
		}
	}

	// Update the request row.
	now := time.Now().UTC()
	var trimmedNote *string
	if n := strings.TrimSpace(note); n != "" {
		trimmedNote = &n
	}
	updateReqSQL := `UPDATE paliad.approval_requests
	    SET status = $1, decided_by = $2, decided_at = $3, decision_kind = $4,
	        decision_note = $5, updated_at = $3
	  WHERE id = $6`
	// For revoke, decided_by stays NULL (the requester didn't "decide" to
	// approve, they pulled the request) — but a CHECK (decided_by != requested_by)
	// would block decided_by=requester anyway. NULL is correct.
	var decidedBy any
	var decisionKindArg any
	if finalStatus != RequestStatusRevoked {
		decidedBy = callerID
		decisionKindArg = decisionKind
	} else {
		decidedBy = nil
		decisionKindArg = nil
	}
	if _, err := tx.ExecContext(ctx, updateReqSQL,
		finalStatus, decidedBy, now, decisionKindArg, trimmedNote, requestID); err != nil {
		return fmt.Errorf("update approval_request: %w", err)
	}

	// Audit emit.
	var verlaufKind string
	switch finalStatus {
	case RequestStatusApproved:
		verlaufKind = "approved"
	case RequestStatusRejected:
		verlaufKind = "rejected"
	case RequestStatusRevoked:
		verlaufKind = "revoked"
	}
	eventType := approvalEventType(req.EntityType, verlaufKind)
	descPtr := approvalDescription(verlaufKind, req.RequiredRole, req.LifecycleEvent)
	meta := map[string]any{
		"approval_request_id": req.ID.String(),
		"lifecycle_event":     req.LifecycleEvent,
		req.EntityType + "_id": req.EntityID.String(),
	}
	if finalStatus != RequestStatusRevoked {
		meta["decision_kind"] = decisionKind
	}
	if trimmedNote != nil {
		meta["decision_note"] = *trimmedNote
	}
	if err := insertProjectEventWithMeta(ctx, tx, req.ProjectID, callerID, eventType, eventType, descPtr, meta); err != nil {
		return err
	}
	return tx.Commit()
}

// canApprove enforces the strict-ladder gate plus the no-self-approval
// rule. Returns the decision_kind ('peer' | 'admin_override' |
// 'derived_peer') the caller should record, or an error.
//
// Resolution order (t-paliad-139 §4.2):
//  1. Self-approval is hard-blocked.
//  2. global_admin always wins ('admin_override').
//  3. Direct or ancestor project_teams membership with sufficient role
//     ('peer').
//  4. Partner-unit-derived membership with derive_grants_authority=true
//     and a unit_role that maps (via approval_role_from_unit_role) to a
//     project_role with sufficient level ('derived_peer').
func (s *ApprovalService) canApprove(ctx context.Context, tx *sqlx.Tx, callerID uuid.UUID, req *models.ApprovalRequest) (string, error) {
	if callerID == req.RequestedBy {
		return "", ErrSelfApproval
	}
	user, err := s.users.GetByID(ctx, callerID)
	if err != nil {
		return "", err
	}
	if user == nil {
		return "", ErrNotApprover
	}
	if user.GlobalRole == "global_admin" {
		return DecisionKindAdminOverride, nil
	}
	// Path-walk: check direct OR ancestor team membership with a
	// responsibility that opens the gate (lead/member) AND a profession
	// whose level meets the threshold (t-paliad-148 tuple-with-gate).
	q := `SELECT EXISTS (
	    SELECT 1 FROM paliad.project_teams pt
	      JOIN paliad.users u ON u.id = pt.user_id
	     WHERE pt.user_id = $1
	       AND pt.project_id = ANY(string_to_array(
	           (SELECT path FROM paliad.projects WHERE id = $2), '.')::uuid[])
	       AND pt.responsibility IN ('lead', 'member')
	       AND paliad.approval_role_level(u.profession) >= paliad.approval_role_level($3)
	)`
	var ok bool
	if err := tx.GetContext(ctx, &ok, q, callerID, req.ProjectID, req.RequiredRole); err != nil {
		return "", fmt.Errorf("authorization check: %w", err)
	}
	if ok {
		return DecisionKindPeer, nil
	}
	// t-paliad-139 derivation branch: check authority-granting partner-unit
	// attachments on the project's path.
	qDerived := `SELECT EXISTS (
	    SELECT 1 FROM paliad.project_partner_units ppu
	      JOIN paliad.partner_unit_members pum ON pum.partner_unit_id = ppu.partner_unit_id
	     WHERE pum.user_id = $1
	       AND ppu.project_id = ANY(string_to_array(
	           (SELECT path FROM paliad.projects WHERE id = $2), '.')::uuid[])
	       AND ppu.derive_grants_authority = true
	       AND pum.unit_role = ANY(ppu.derive_unit_roles)
	       AND paliad.approval_role_level(
	               paliad.approval_role_from_unit_role(pum.unit_role)
	           ) >= paliad.approval_role_level($3)
	)`
	var derivedOK bool
	if err := tx.GetContext(ctx, &derivedOK, qDerived, callerID, req.ProjectID, req.RequiredRole); err != nil {
		return "", fmt.Errorf("derived authorization check: %w", err)
	}
	if derivedOK {
		return DecisionKindDerivedPeer, nil
	}
	return "", ErrNotApprover
}

// applyApproved finalises the lifecycle on the entity row.
func (s *ApprovalService) applyApproved(ctx context.Context, tx *sqlx.Tx, req *models.ApprovalRequest, approverID uuid.UUID) error {
	table := entityTableName(req.EntityType)
	now := time.Now().UTC()

	if req.LifecycleEvent == LifecycleDelete {
		// Hard-delete the entity. The approval_requests.entity_id reference
		// is a polymorphic uuid (no FK) so it survives the row going away.
		// pending_request_id on the entity has ON DELETE SET NULL but the
		// entity is the one being deleted, not the request — so this is
		// just a plain DELETE.
		if _, err := tx.ExecContext(ctx,
			fmt.Sprintf(`DELETE FROM paliad.%s WHERE id = $1`, table),
			req.EntityID); err != nil {
			return fmt.Errorf("delete on approve: %w", err)
		}
		return nil
	}

	// Non-delete approve = clear pending markers, set approved_by/at.
	q := fmt.Sprintf(`UPDATE paliad.%s
	    SET approval_status = 'approved',
	        pending_request_id = NULL,
	        approved_by = $1,
	        approved_at = $2,
	        updated_at = $2
	  WHERE id = $3`, table)
	if _, err := tx.ExecContext(ctx, q, approverID, now, req.EntityID); err != nil {
		return fmt.Errorf("clear pending on approve: %w", err)
	}
	return nil
}

// applyRevert undoes the in-flight change on the entity row, restoring it
// from the request's pre_image jsonb. Used by both Reject and Revoke.
func (s *ApprovalService) applyRevert(ctx context.Context, tx *sqlx.Tx, req *models.ApprovalRequest) error {
	table := entityTableName(req.EntityType)

	switch req.LifecycleEvent {
	case LifecycleCreate:
		// The entity should never have existed. Hard-delete.
		if _, err := tx.ExecContext(ctx,
			fmt.Sprintf(`DELETE FROM paliad.%s WHERE id = $1`, table),
			req.EntityID); err != nil {
			return fmt.Errorf("delete on reject-create: %w", err)
		}
		return nil

	case LifecycleDelete:
		// We never deleted the entity (delete is stage-then-write); just
		// clear the pending markers so the row is fully alive again.
		q := fmt.Sprintf(`UPDATE paliad.%s
		    SET approval_status = CASE WHEN approval_status = 'pending'
		                                THEN 'approved' ELSE approval_status END,
		        pending_request_id = NULL,
		        updated_at = now()
		  WHERE id = $1`, table)
		if _, err := tx.ExecContext(ctx, q, req.EntityID); err != nil {
			return fmt.Errorf("clear pending on reject-delete: %w", err)
		}
		return nil

	case LifecycleUpdate, LifecycleComplete:
		// Restore pre_image fields, clear pending markers.
		preImage := map[string]any{}
		if len(req.PreImage) > 0 {
			if err := json.Unmarshal(req.PreImage, &preImage); err != nil {
				return fmt.Errorf("unmarshal pre_image: %w", err)
			}
		}
		setClauses, args, err := buildRevertSetClauses(req.EntityType, preImage)
		if err != nil {
			return err
		}
		// Always clear pending markers + revert approval_status.
		setClauses = append(setClauses,
			"approval_status = 'approved'",
			"pending_request_id = NULL",
			"updated_at = now()")
		args = append(args, req.EntityID)
		q := fmt.Sprintf(`UPDATE paliad.%s SET %s WHERE id = $%d`,
			table, strings.Join(setClauses, ", "), len(args))
		if _, err := tx.ExecContext(ctx, q, args...); err != nil {
			return fmt.Errorf("revert entity from pre_image: %w", err)
		}
		return nil

	default:
		return fmt.Errorf("%w: lifecycle %q", ErrUnknownEntityType, req.LifecycleEvent)
	}
}

// buildRevertSetClauses translates pre_image jsonb keys into SQL SET
// fragments. Only the date-bearing allowlist (Q4) is honoured; unknown
// keys are silently dropped to defend against malformed pre_image rows
// (defence-in-depth: callers should already be sending only allowlisted
// fields, but a hostile UPDATE on the request row shouldn't let arbitrary
// fields be reverted).
func buildRevertSetClauses(entityType string, preImage map[string]any) ([]string, []any, error) {
	var setClauses []string
	var args []any

	add := func(col string, val any) {
		args = append(args, val)
		setClauses = append(setClauses, fmt.Sprintf("%s = $%d", col, len(args)))
	}

	switch entityType {
	case EntityTypeDeadline:
		for _, col := range []string{"due_date", "original_due_date", "warning_date"} {
			if v, ok := preImage[col]; ok {
				add(col, v)
			}
		}
		// Complete-revert restores status='pending' + completed_at NULL.
		// We detect this branch by the presence of a status key; lifecycle
		// is the formal source but pre_image is what the caller stored.
		if v, ok := preImage["status"]; ok {
			add("status", v)
		}
		if _, ok := preImage["completed_at"]; ok {
			// Always NULL on revert — completion didn't really happen.
			args = append(args, nil)
			setClauses = append(setClauses, fmt.Sprintf("completed_at = $%d", len(args)))
		}

	case EntityTypeAppointment:
		for _, col := range []string{"start_at", "end_at"} {
			if v, ok := preImage[col]; ok {
				add(col, v)
			}
		}
		if _, ok := preImage["completed_at"]; ok {
			args = append(args, nil)
			setClauses = append(setClauses, fmt.Sprintf("completed_at = $%d", len(args)))
		}

	default:
		return nil, nil, fmt.Errorf("%w: %q", ErrUnknownEntityType, entityType)
	}

	if len(setClauses) == 0 {
		return nil, nil, fmt.Errorf("%w: empty pre_image for %s", ErrUnknownEntityType, entityType)
	}
	return setClauses, args, nil
}

// getRequestForUpdate locks an approval_requests row inside the tx for
// decision processing.
func (s *ApprovalService) getRequestForUpdate(ctx context.Context, tx *sqlx.Tx, requestID uuid.UUID) (*models.ApprovalRequest, error) {
	var req models.ApprovalRequest
	q := `SELECT id, project_id, entity_type, entity_id, lifecycle_event,
	             pre_image, payload, requested_by, requested_at, required_role,
	             status, decided_by, decided_at, decision_kind, decision_note,
	             created_at, updated_at
	        FROM paliad.approval_requests
	       WHERE id = $1
	         FOR UPDATE`
	if err := tx.GetContext(ctx, &req, q, requestID); err != nil {
		if errors.Is(err, sql.ErrNoRows) {
			return nil, ErrRequestNotPending
		}
		return nil, fmt.Errorf("load request: %w", err)
	}
	return &req, nil
}

// entityApprovalStatus reads the current approval_status on the entity
// row. Returns "" if the row doesn't exist.
func (s *ApprovalService) entityApprovalStatus(ctx context.Context, tx *sqlx.Tx, entityType string, entityID uuid.UUID) (string, error) {
	q := fmt.Sprintf(`SELECT approval_status FROM paliad.%s WHERE id = $1`,
		entityTableName(entityType))
	var status string
	if err := txOrDB(tx, s.db).GetContext(ctx, &status, q, entityID); err != nil {
		if errors.Is(err, sql.ErrNoRows) {
			return "", nil
		}
		return "", fmt.Errorf("read approval_status: %w", err)
	}
	return status, nil
}

// entityTableName resolves the SQL table name for a given entity_type.
// Internal helper — entityType comes from server-side constants, not user
// input, so a panic on an unknown value is a programming error.
func entityTableName(entityType string) string {
	switch entityType {
	case EntityTypeDeadline:
		return "deadlines"
	case EntityTypeAppointment:
		return "appointments"
	default:
		panic(fmt.Sprintf("approval: unknown entity_type %q", entityType))
	}
}

// approvalEventType returns the project_events.event_type value for a
// given (entity, lifecycle-step) pair. Step is one of "requested" |
// "approved" | "rejected" | "revoked".
func approvalEventType(entityType, step string) string {
	return entityType + "_approval_" + step
}

// approvalDescription returns the short audit description string. Frontend
// renders the localized version via translateEvent; this is the raw audit
// row's description column, used as a fallback and for /admin/audit-log.
func approvalDescription(step, requiredRole, lifecycle string) *string {
	d := fmt.Sprintf("%s — %s/%s", step, lifecycle, requiredRole)
	return &d
}

// txOrDB returns the tx if non-nil, else the db. Lets read helpers run
// either inside a calling tx (for consistency with concurrent writes) or
// standalone for List endpoints.
func txOrDB(tx *sqlx.Tx, db *sqlx.DB) sqlxQueryer {
	if tx != nil {
		return tx
	}
	return db
}

// sqlxQueryer is the minimal subset of *sqlx.DB / *sqlx.Tx we need.
// Defined here to avoid adding a public abstraction across the package.
type sqlxQueryer interface {
	GetContext(ctx context.Context, dest any, query string, args ...any) error
	SelectContext(ctx context.Context, dest any, query string, args ...any) error
	QueryRowxContext(ctx context.Context, query string, args ...any) *sqlx.Row
}

// marshalJSONOrNull returns []byte("null") JSON-RawMessage style for
// nil/empty maps so callers can pass it directly to a jsonb column without
// branching at every call site.
func marshalJSONOrNull(m map[string]any) ([]byte, error) {
	if len(m) == 0 {
		return nil, nil
	}
	return json.Marshal(m)
}

// ============================================================================
// Read paths — inbox + policy CRUD.
// ============================================================================

// ApprovalRequestView is the inbox-friendly projection of an approval
// request: the bare ApprovalRequest plus the contextual labels the inbox
// needs to render a row without further fetches.
type ApprovalRequestView struct {
	models.ApprovalRequest
	ProjectTitle    string  `db:"project_title"     json:"project_title"`
	EntityTitle     *string `db:"entity_title"      json:"entity_title,omitempty"`
	RequesterName   string  `db:"requester_name"    json:"requester_name"`
	RequesterEmail  string  `db:"requester_email"   json:"requester_email"`
	DeciderName     *string `db:"decider_name"      json:"decider_name,omitempty"`
	DeciderEmail    *string `db:"decider_email"     json:"decider_email,omitempty"`
}

const approvalRequestViewColumns = `
    ar.id, ar.project_id, ar.entity_type, ar.entity_id, ar.lifecycle_event,
    ar.pre_image, ar.payload, ar.requested_by, ar.requested_at, ar.required_role,
    ar.status, ar.decided_by, ar.decided_at, ar.decision_kind, ar.decision_note,
    ar.created_at, ar.updated_at,
    p.title AS project_title,
    CASE WHEN ar.entity_type = 'deadline'    THEN d.title
         WHEN ar.entity_type = 'appointment' THEN a.title
         END AS entity_title,
    COALESCE(ru.display_name, ru.email) AS requester_name,
    ru.email                            AS requester_email,
    du.display_name                     AS decider_name,
    du.email                            AS decider_email`

const approvalRequestViewJoins = `
    paliad.approval_requests ar
    JOIN paliad.projects p ON p.id = ar.project_id
    JOIN paliad.users    ru ON ru.id = ar.requested_by
    LEFT JOIN paliad.users du ON du.id = ar.decided_by
    LEFT JOIN paliad.deadlines    d ON ar.entity_type = 'deadline'    AND d.id = ar.entity_id
    LEFT JOIN paliad.appointments a ON ar.entity_type = 'appointment' AND a.id = ar.entity_id`

// InboxFilter narrows the inbox listings.
type InboxFilter struct {
	Status     string  // "" → no filter; otherwise one of RequestStatus*
	ProjectID  *uuid.UUID
	EntityType string  // "" → both
	Limit      int     // 0 → 100
}

// ListPendingForApprover returns approval requests where the caller is
// qualified to approve and is not the requester.
func (s *ApprovalService) ListPendingForApprover(ctx context.Context, callerID uuid.UUID, filter InboxFilter) ([]ApprovalRequestView, error) {
	limit := filter.Limit
	if limit <= 0 || limit > 200 {
		limit = 100
	}
	conds := []string{
		"ar.status = 'pending'",
		"ar.requested_by <> $1",
		// Eligibility (any one branch suffices):
		//  - caller is global_admin, OR
		//  - caller has direct/ancestor project_teams membership with
		//    responsibility ∈ {lead, member} AND profession at or above
		//    the threshold (t-paliad-148 tuple-with-gate), OR
		//  - caller is a partner-unit-derived member with derive_grants_authority=true
		//    on an attachment in the project's path, and the unit_role maps to a
		//    profession at or above the threshold (t-paliad-139).
		`(EXISTS (SELECT 1 FROM paliad.users u WHERE u.id = $1 AND u.global_role = 'global_admin')
		  OR EXISTS (
		      SELECT 1 FROM paliad.project_teams pt
		        JOIN paliad.users u ON u.id = pt.user_id
		       WHERE pt.user_id = $1
		         AND pt.project_id = ANY(string_to_array(p.path, '.')::uuid[])
		         AND pt.responsibility IN ('lead', 'member')
		         AND paliad.approval_role_level(u.profession) >= paliad.approval_role_level(ar.required_role)
		  )
		  OR EXISTS (
		      SELECT 1 FROM paliad.project_partner_units ppu
		        JOIN paliad.partner_unit_members pum ON pum.partner_unit_id = ppu.partner_unit_id
		       WHERE pum.user_id = $1
		         AND ppu.project_id = ANY(string_to_array(p.path, '.')::uuid[])
		         AND ppu.derive_grants_authority = true
		         AND pum.unit_role = ANY(ppu.derive_unit_roles)
		         AND paliad.approval_role_level(
		                 paliad.approval_role_from_unit_role(pum.unit_role)
		             ) >= paliad.approval_role_level(ar.required_role)
		  ))`,
	}
	args := []any{callerID}
	if filter.ProjectID != nil {
		args = append(args, *filter.ProjectID)
		conds = append(conds, fmt.Sprintf("ar.project_id = $%d", len(args)))
	}
	if filter.EntityType != "" {
		args = append(args, filter.EntityType)
		conds = append(conds, fmt.Sprintf("ar.entity_type = $%d", len(args)))
	}
	args = append(args, limit)

	q := fmt.Sprintf(`SELECT %s FROM %s WHERE %s ORDER BY ar.requested_at ASC LIMIT $%d`,
		approvalRequestViewColumns, approvalRequestViewJoins,
		strings.Join(conds, " AND "), len(args))

	var out []ApprovalRequestView
	if err := s.db.SelectContext(ctx, &out, q, args...); err != nil {
		return nil, fmt.Errorf("list pending for approver: %w", err)
	}
	return out, nil
}

// ListSubmittedByUser returns approval requests authored by the caller.
// Status filter optional.
func (s *ApprovalService) ListSubmittedByUser(ctx context.Context, callerID uuid.UUID, filter InboxFilter) ([]ApprovalRequestView, error) {
	limit := filter.Limit
	if limit <= 0 || limit > 200 {
		limit = 100
	}
	conds := []string{"ar.requested_by = $1"}
	args := []any{callerID}
	if filter.Status != "" {
		args = append(args, filter.Status)
		conds = append(conds, fmt.Sprintf("ar.status = $%d", len(args)))
	}
	if filter.ProjectID != nil {
		args = append(args, *filter.ProjectID)
		conds = append(conds, fmt.Sprintf("ar.project_id = $%d", len(args)))
	}
	if filter.EntityType != "" {
		args = append(args, filter.EntityType)
		conds = append(conds, fmt.Sprintf("ar.entity_type = $%d", len(args)))
	}
	args = append(args, limit)

	q := fmt.Sprintf(`SELECT %s FROM %s WHERE %s ORDER BY ar.requested_at DESC LIMIT $%d`,
		approvalRequestViewColumns, approvalRequestViewJoins,
		strings.Join(conds, " AND "), len(args))

	var out []ApprovalRequestView
	if err := s.db.SelectContext(ctx, &out, q, args...); err != nil {
		return nil, fmt.Errorf("list submitted by user: %w", err)
	}
	return out, nil
}

// GetRequest returns one approval request hydrated for the inbox detail
// view. Visibility is gated upstream by the handler (anyone with project
// access can see the request).
func (s *ApprovalService) GetRequest(ctx context.Context, requestID uuid.UUID) (*ApprovalRequestView, error) {
	q := fmt.Sprintf(`SELECT %s FROM %s WHERE ar.id = $1`,
		approvalRequestViewColumns, approvalRequestViewJoins)
	var v ApprovalRequestView
	if err := s.db.GetContext(ctx, &v, q, requestID); err != nil {
		if errors.Is(err, sql.ErrNoRows) {
			return nil, nil
		}
		return nil, fmt.Errorf("get approval request: %w", err)
	}
	return &v, nil
}

// PendingCountForUser returns how many requests await this user's approval.
// Cheap query for the sidebar bell badge.
//
// Eligibility mirrors ListPendingForApprover: global_admin OR direct/
// ancestor project_teams membership with responsibility ∈ {lead, member}
// AND profession meeting the threshold (t-paliad-148) OR partner-unit-
// derived authority (t-paliad-139).
func (s *ApprovalService) PendingCountForUser(ctx context.Context, callerID uuid.UUID) (int, error) {
	q := `SELECT COUNT(*)
	        FROM paliad.approval_requests ar
	        JOIN paliad.projects p ON p.id = ar.project_id
	       WHERE ar.status = 'pending'
	         AND ar.requested_by <> $1
	         AND (EXISTS (SELECT 1 FROM paliad.users u WHERE u.id = $1 AND u.global_role = 'global_admin')
	              OR EXISTS (
	                  SELECT 1 FROM paliad.project_teams pt
	                    JOIN paliad.users u ON u.id = pt.user_id
	                   WHERE pt.user_id = $1
	                     AND pt.project_id = ANY(string_to_array(p.path, '.')::uuid[])
	                     AND pt.responsibility IN ('lead', 'member')
	                     AND paliad.approval_role_level(u.profession) >= paliad.approval_role_level(ar.required_role)
	              )
	              OR EXISTS (
	                  SELECT 1 FROM paliad.project_partner_units ppu
	                    JOIN paliad.partner_unit_members pum ON pum.partner_unit_id = ppu.partner_unit_id
	                   WHERE pum.user_id = $1
	                     AND ppu.project_id = ANY(string_to_array(p.path, '.')::uuid[])
	                     AND ppu.derive_grants_authority = true
	                     AND pum.unit_role = ANY(ppu.derive_unit_roles)
	                     AND paliad.approval_role_level(
	                             paliad.approval_role_from_unit_role(pum.unit_role)
	                         ) >= paliad.approval_role_level(ar.required_role)
	              ))`
	var n int
	if err := s.db.GetContext(ctx, &n, q, callerID); err != nil {
		return 0, fmt.Errorf("pending count: %w", err)
	}
	return n, nil
}

// ============================================================================
// Policy CRUD — paliad.approval_policies.
// ============================================================================

// ListPolicies returns the (up to 8) policy rows for a project. Caller
// must already have project visibility.
func (s *ApprovalService) ListPolicies(ctx context.Context, projectID uuid.UUID) ([]models.ApprovalPolicy, error) {
	q := `SELECT id, project_id, entity_type, lifecycle_event, required_role,
	             created_at, updated_at, created_by
	        FROM paliad.approval_policies
	       WHERE project_id = $1
	    ORDER BY entity_type, lifecycle_event`
	var out []models.ApprovalPolicy
	if err := s.db.SelectContext(ctx, &out, q, projectID); err != nil {
		return nil, fmt.Errorf("list approval policies: %w", err)
	}
	return out, nil
}

// UpsertPolicy creates or replaces a single (project, entity, lifecycle)
// policy row. Caller must be global_admin (gate enforced at handler).
func (s *ApprovalService) UpsertPolicy(ctx context.Context, projectID, callerID uuid.UUID, entityType, lifecycle, requiredRole string) (*models.ApprovalPolicy, error) {
	if !IsValidRequiredRole(requiredRole) {
		return nil, fmt.Errorf("%w: required_role %q", ErrInvalidInput, requiredRole)
	}
	if entityType != EntityTypeDeadline && entityType != EntityTypeAppointment {
		return nil, fmt.Errorf("%w: entity_type %q", ErrInvalidInput, entityType)
	}
	switch lifecycle {
	case LifecycleCreate, LifecycleUpdate, LifecycleComplete, LifecycleDelete:
	default:
		return nil, fmt.Errorf("%w: lifecycle_event %q", ErrInvalidInput, lifecycle)
	}

	q := `INSERT INTO paliad.approval_policies
	        (project_id, entity_type, lifecycle_event, required_role, created_by)
	      VALUES ($1, $2, $3, $4, $5)
	      ON CONFLICT (project_id, entity_type, lifecycle_event)
	        DO UPDATE SET required_role = EXCLUDED.required_role,
	                      updated_at = now()
	      RETURNING id, project_id, entity_type, lifecycle_event, required_role,
	                created_at, updated_at, created_by`
	var p models.ApprovalPolicy
	if err := s.db.GetContext(ctx, &p, q, projectID, entityType, lifecycle, requiredRole, callerID); err != nil {
		return nil, fmt.Errorf("upsert approval policy: %w", err)
	}
	return &p, nil
}

// DeletePolicy removes a single (project, entity, lifecycle) policy row,
// reverting that lifecycle event back to the no-approval-needed default.
func (s *ApprovalService) DeletePolicy(ctx context.Context, projectID uuid.UUID, entityType, lifecycle string) error {
	q := `DELETE FROM paliad.approval_policies
	       WHERE project_id = $1 AND entity_type = $2 AND lifecycle_event = $3`
	if _, err := s.db.ExecContext(ctx, q, projectID, entityType, lifecycle); err != nil {
		return fmt.Errorf("delete approval policy: %w", err)
	}
	return nil
}