package store

import (
	"bytes"
	"context"
	"crypto/sha256"
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"strings"
	"time"

	"github.com/oklog/ulid/v2"

	"yovision/bell/internal/alert"
)

func (p *Postgres) AlertReady(ctx context.Context) error {
	var version int64
	if err := p.db.QueryRowContext(ctx, `SELECT COALESCE(MAX(version),0) FROM bell.schema_migrations`).Scan(&version); err != nil || version < 6 {
		return errors.New("postgres Bell schema migration v6 is required for alerts")
	}
	for _, table := range []string{"rule_versions", "event_rule_sweeps", "rule_evaluations", "alerts", "alert_events", "alert_transitions", "alert_command_receipts"} {
		var selectAllowed, insertAllowed, updateAllowed, deleteAllowed, truncateAllowed bool
		if err := p.db.QueryRowContext(ctx, `SELECT
			has_table_privilege(current_user,$1,'SELECT'), has_table_privilege(current_user,$1,'INSERT'),
			has_table_privilege(current_user,$1,'UPDATE'), has_table_privilege(current_user,$1,'DELETE'),
			has_table_privilege(current_user,$1,'TRUNCATE')`, "bell."+table).Scan(
			&selectAllowed, &insertAllowed, &updateAllowed, &deleteAllowed, &truncateAllowed,
		); err != nil || !selectAllowed || !insertAllowed || updateAllowed || deleteAllowed || truncateAllowed {
			return fmt.Errorf("Bell runtime alert privileges violate append-only boundary for %s", table)
		}
	}
	return nil
}

func (p *Postgres) PublishRule(ctx context.Context, rule alert.RuleSpec) (bool, error) {
	if err := rule.Validate(); err != nil {
		return false, err
	}
	digest, err := rule.Digest()
	if err != nil {
		return false, err
	}
	tx, err := p.db.BeginTx(ctx, nil)
	if err != nil {
		return false, errors.New("begin Bell rule publish")
	}
	defer tx.Rollback()
	if _, err := tx.ExecContext(ctx, `SELECT pg_advisory_xact_lock(hashtextextended($1,0))`, fmt.Sprintf("rule:%d:%s", rule.TenantID, rule.RuleKey)); err != nil {
		return false, errors.New("lock Bell rule key")
	}
	var existing string
	err = tx.QueryRowContext(ctx, `SELECT id FROM bell.rule_versions WHERE tenant_id=$1 AND rule_key=$2 AND config_hash=$3`, rule.TenantID, rule.RuleKey, digest[:]).Scan(&existing)
	if err == nil {
		return false, tx.Commit()
	}
	if !errors.Is(err, sql.ErrNoRows) {
		return false, errors.New("read Bell rule version")
	}
	var version int
	if err := tx.QueryRowContext(ctx, `SELECT COALESCE(MAX(version),0)+1 FROM bell.rule_versions WHERE tenant_id=$1 AND rule_key=$2`, rule.TenantID, rule.RuleKey).Scan(&version); err != nil {
		return false, errors.New("allocate Bell rule version")
	}
	if _, err := tx.ExecContext(ctx, `INSERT INTO bell.rule_versions(
		id,tenant_id,site_id,rule_key,version,display_name,event_kind,minimum_severity,enabled,effective_from,config_hash
	) VALUES($1,$2,$3,$4,$5,$6,$7,$8,$9,$10,$11)`, newPrefixedID("ruv_"), rule.TenantID, rule.SiteID,
		rule.RuleKey, version, rule.DisplayName, rule.EventKind, rule.MinimumSeverity, rule.Enabled, rule.EffectiveFrom, digest[:]); err != nil {
		return false, fmt.Errorf("insert Bell rule version: %w", err)
	}
	if err := tx.Commit(); err != nil {
		return false, errors.New("commit Bell rule version")
	}
	return true, nil
}

func (p *Postgres) EvaluateNext(ctx context.Context) (bool, error) {
	tx, err := p.db.BeginTx(ctx, nil)
	if err != nil {
		return false, errors.New("begin Bell rule evaluation")
	}
	defer tx.Rollback()
	var eventID, kind, severity string
	var tenantID, siteID, deviceID int64
	var occurredAt time.Time
	err = tx.QueryRowContext(ctx, `SELECT e.id,e.tenant_id,e.site_id,e.device_id,e.kind,e.severity,e.occurred_at
		FROM bell.events e WHERE NOT EXISTS(SELECT 1 FROM bell.event_rule_sweeps s WHERE s.event_id=e.id)
		ORDER BY e.created_at,e.id LIMIT 1`).Scan(&eventID, &tenantID, &siteID, &deviceID, &kind, &severity, &occurredAt)
	if errors.Is(err, sql.ErrNoRows) {
		return false, nil
	}
	if err != nil {
		return false, errors.New("select Bell event for rules")
	}
	if _, err := tx.ExecContext(ctx, `SELECT pg_advisory_xact_lock(hashtextextended($1,0))`, "event-rule:"+eventID); err != nil {
		return false, errors.New("lock Bell event evaluation")
	}
	result, err := tx.ExecContext(ctx, `INSERT INTO bell.event_rule_sweeps(event_id) VALUES($1) ON CONFLICT DO NOTHING`, eventID)
	if err != nil {
		return false, errors.New("claim Bell event evaluation")
	}
	rowsAffected, _ := result.RowsAffected()
	if rowsAffected == 0 {
		return false, tx.Commit()
	}
	rows, err := tx.QueryContext(ctx, `SELECT id,rule_key,version,display_name,event_kind,minimum_severity,enabled
		FROM (SELECT DISTINCT ON (rule_key) id,rule_key,version,display_name,event_kind,minimum_severity,enabled,effective_from
		      FROM bell.rule_versions WHERE tenant_id=$1 AND effective_from <= $3 AND (site_id IS NULL OR site_id=$2)
		      ORDER BY rule_key,version DESC,effective_from DESC) latest ORDER BY rule_key`, tenantID, siteID, occurredAt)
	if err != nil {
		return false, errors.New("read effective Bell rules")
	}
	defer rows.Close()
	type effectiveRule struct {
		id, key, name, kind, minimum string
		version                      int
		enabled                      bool
	}
	rules := make([]effectiveRule, 0)
	for rows.Next() {
		var rule effectiveRule
		if err := rows.Scan(&rule.id, &rule.key, &rule.version, &rule.name, &rule.kind, &rule.minimum, &rule.enabled); err != nil {
			return false, errors.New("scan effective Bell rule")
		}
		rules = append(rules, rule)
	}
	if err := rows.Err(); err != nil {
		return false, errors.New("iterate effective Bell rules")
	}
	if err := rows.Close(); err != nil {
		return false, errors.New("close effective Bell rules")
	}
	eventRank, _ := alert.SeverityRank(severity)
	for _, rule := range rules {
		matched, reason := true, "matched"
		minimumRank, _ := alert.SeverityRank(rule.minimum)
		switch {
		case !rule.enabled:
			matched, reason = false, "disabled"
		case rule.kind != kind:
			matched, reason = false, "event_kind"
		case eventRank < minimumRank:
			matched, reason = false, "severity"
		}
		value := "no_match"
		if matched {
			value = "matched"
		}
		evaluationID := newPrefixedID("eva_")
		if _, err := tx.ExecContext(ctx, `INSERT INTO bell.rule_evaluations(id,event_id,rule_version_id,result,reason) VALUES($1,$2,$3,$4,$5)`, evaluationID, eventID, rule.id, value, reason); err != nil {
			return false, fmt.Errorf("append Bell rule evaluation: %w", err)
		}
		if !matched {
			continue
		}
		alertID := newPrefixedID("alt_")
		if _, err := tx.ExecContext(ctx, `INSERT INTO bell.alerts(id,tenant_id,site_id,rule_evaluation_id,rule_version_id,severity,title) VALUES($1,$2,$3,$4,$5,$6,$7)`, alertID, tenantID, siteID, evaluationID, rule.id, severity, rule.name); err != nil {
			return false, errors.New("create Bell alert")
		}
		if _, err := tx.ExecContext(ctx, `INSERT INTO bell.alert_events(alert_id,event_id) VALUES($1,$2)`, alertID, eventID); err != nil {
			return false, errors.New("link Bell alert event")
		}
		if _, err := tx.ExecContext(ctx, `INSERT INTO bell.alert_transitions(id,alert_id,sequence,from_state,to_state,actor_ref) VALUES($1,$2,1,NULL,'open','system:rule-worker')`, newPrefixedID("trn_"), alertID); err != nil {
			return false, errors.New("open Bell alert")
		}
		_ = deviceID
	}
	if err := tx.Commit(); err != nil {
		return false, errors.New("commit Bell rule evaluation")
	}
	return true, nil
}

func (p *Postgres) ListAlerts(ctx context.Context, tenantID, siteID int64, state string, limit int, cursor string) (alert.Page, error) {
	if limit < 1 || limit > alert.MaxPageSize {
		return alert.Page{}, errors.New("invalid alert page size")
	}
	if state != "" && state != "open" && state != "acknowledged" && state != "closed" {
		return alert.Page{}, errors.New("invalid alert state")
	}
	rows, err := p.db.QueryContext(ctx, `SELECT a.id,a.severity,a.title,t.to_state,r.rule_key,r.version,a.created_at
		FROM bell.alerts a JOIN bell.rule_versions r ON r.id=a.rule_version_id
		JOIN LATERAL(SELECT to_state FROM bell.alert_transitions WHERE alert_id=a.id ORDER BY sequence DESC LIMIT 1)t ON true
		WHERE a.tenant_id=$1 AND a.site_id=$2 AND ($3='' OR t.to_state=$3)
		  AND ($4='' OR (a.created_at,a.id) < (SELECT c.created_at,c.id FROM bell.alerts c WHERE c.id=$4 AND c.tenant_id=$1 AND c.site_id=$2))
		ORDER BY a.created_at DESC,a.id DESC LIMIT $5`, tenantID, siteID, state, cursor, limit+1)
	if err != nil {
		return alert.Page{}, errors.New("list Bell alerts")
	}
	defer rows.Close()
	page := alert.Page{Items: make([]alert.Summary, 0, limit)}
	for rows.Next() {
		var item alert.Summary
		if err := rows.Scan(&item.ID, &item.Severity, &item.Title, &item.State, &item.RuleKey, &item.RuleVersion, &item.CreatedAt); err != nil {
			return alert.Page{}, errors.New("scan Bell alert list")
		}
		page.Items = append(page.Items, item)
	}
	if err := rows.Err(); err != nil {
		return alert.Page{}, errors.New("iterate Bell alert list")
	}
	if len(page.Items) > limit {
		cursor := page.Items[limit-1].ID
		page.NextCursor = &cursor
		page.Items = page.Items[:limit]
	}
	return page, nil
}

func (p *Postgres) GetAlert(ctx context.Context, tenantID, siteID int64, alertID string) (alert.Detail, error) {
	var detail alert.Detail
	err := p.db.QueryRowContext(ctx, `SELECT a.id,a.severity,a.title,t.to_state,r.rule_key,r.version,a.created_at
		FROM bell.alerts a JOIN bell.rule_versions r ON r.id=a.rule_version_id
		JOIN LATERAL(SELECT to_state FROM bell.alert_transitions WHERE alert_id=a.id ORDER BY sequence DESC LIMIT 1)t ON true
		WHERE a.tenant_id=$1 AND a.site_id=$2 AND a.id=$3`, tenantID, siteID, alertID).Scan(
		&detail.ID, &detail.Severity, &detail.Title, &detail.State, &detail.RuleKey, &detail.RuleVersion, &detail.CreatedAt)
	if errors.Is(err, sql.ErrNoRows) {
		return alert.Detail{}, alert.ErrNotFound
	}
	if err != nil {
		return alert.Detail{}, errors.New("read Bell alert")
	}
	detail.EvidenceStatus = "not_enabled"
	detail.DeliveryStatus = "not_enabled"
	detail.Events = []alert.EventRef{}
	detail.Transitions = []alert.Transition{}
	rows, err := p.db.QueryContext(ctx, `SELECT e.id,e.device_id,e.kind,e.severity,e.occurred_at FROM bell.alert_events ae JOIN bell.events e ON e.id=ae.event_id WHERE ae.alert_id=$1 ORDER BY e.occurred_at,e.id`, alertID)
	if err != nil {
		return alert.Detail{}, errors.New("read Bell alert events")
	}
	for rows.Next() {
		var value alert.EventRef
		if err := rows.Scan(&value.ID, &value.DeviceID, &value.Kind, &value.Severity, &value.OccurredAt); err != nil {
			rows.Close()
			return alert.Detail{}, errors.New("scan Bell alert event")
		}
		detail.Events = append(detail.Events, value)
	}
	if err := rows.Close(); err != nil {
		return alert.Detail{}, errors.New("close Bell alert events")
	}
	rows, err = p.db.QueryContext(ctx, `SELECT sequence,from_state,to_state,actor_ref,note,occurred_at FROM bell.alert_transitions WHERE alert_id=$1 ORDER BY sequence`, alertID)
	if err != nil {
		return alert.Detail{}, errors.New("read Bell alert transitions")
	}
	defer rows.Close()
	for rows.Next() {
		var value alert.Transition
		if err := rows.Scan(&value.Sequence, &value.FromState, &value.ToState, &value.ActorRef, &value.Note, &value.OccurredAt); err != nil {
			return alert.Detail{}, errors.New("scan Bell alert transition")
		}
		detail.Transitions = append(detail.Transitions, value)
	}
	return detail, rows.Err()
}

func (p *Postgres) Command(ctx context.Context, tenantID, siteID int64, alertID, command, key, actorRef string, note *string) (int, alert.CommandResponse, error) {
	if (command != "ack" && command != "close") || tenantID < 1 || siteID < 1 || !alert.ValidIdempotencyKey(key) || !alert.ValidActorRef(actorRef) {
		return 0, alert.CommandResponse{}, errors.New("invalid Bell alert command")
	}
	if note != nil && len([]rune(*note)) > 500 {
		return 0, alert.CommandResponse{}, errors.New("Bell alert command note is too long")
	}
	digest := sha256.Sum256([]byte(strings.Join([]string{alertID, command, actorRef, valueOrEmpty(note)}, "\x00")))
	tx, err := p.db.BeginTx(ctx, nil)
	if err != nil {
		return 0, alert.CommandResponse{}, errors.New("begin Bell alert command")
	}
	defer tx.Rollback()
	if _, err := tx.ExecContext(ctx, `SELECT pg_advisory_xact_lock(hashtextextended($1,0))`, fmt.Sprintf("alert-key:%d:%s", tenantID, key)); err != nil {
		return 0, alert.CommandResponse{}, errors.New("lock Bell alert command key")
	}
	var storedHash, storedBody []byte
	var storedStatus int
	err = tx.QueryRowContext(ctx, `SELECT command_hash,response_status,response_body::text FROM bell.alert_command_receipts WHERE tenant_id=$1 AND idempotency_key=$2`, tenantID, key).Scan(&storedHash, &storedStatus, &storedBody)
	if err == nil {
		if !bytes.Equal(storedHash, digest[:]) {
			return 0, alert.CommandResponse{}, alert.ErrIdempotencyConflict
		}
		var response alert.CommandResponse
		if err := json.Unmarshal(storedBody, &response); err != nil {
			return 0, alert.CommandResponse{}, errors.New("decode Bell alert command receipt")
		}
		return storedStatus, response, tx.Commit()
	}
	if !errors.Is(err, sql.ErrNoRows) {
		return 0, alert.CommandResponse{}, errors.New("read Bell alert command receipt")
	}
	if _, err := tx.ExecContext(ctx, `SELECT pg_advisory_xact_lock(hashtextextended($1,0))`, "alert:"+alertID); err != nil {
		return 0, alert.CommandResponse{}, errors.New("lock Bell alert")
	}
	var current, currentActor string
	var currentTime time.Time
	var sequence int
	err = tx.QueryRowContext(ctx, `SELECT t.to_state,t.actor_ref,t.occurred_at,t.sequence FROM bell.alerts a
		JOIN LATERAL(SELECT to_state,actor_ref,occurred_at,sequence FROM bell.alert_transitions WHERE alert_id=a.id ORDER BY sequence DESC LIMIT 1)t ON true
		WHERE a.id=$1 AND a.tenant_id=$2 AND a.site_id=$3`, alertID, tenantID, siteID).Scan(&current, &currentActor, &currentTime, &sequence)
	if errors.Is(err, sql.ErrNoRows) {
		return 0, alert.CommandResponse{}, alert.ErrNotFound
	}
	if err != nil {
		return 0, alert.CommandResponse{}, errors.New("read Bell alert state")
	}
	status := 200
	response := alert.CommandResponse{AlertID: alertID, State: current, ActorRef: currentActor, OccurredAt: currentTime}
	allowed := (command == "ack" && current == "open") || (command == "close" && current == "acknowledged")
	if !allowed {
		status = 409
		switch {
		case command == "ack" && (current == "acknowledged" || current == "closed"):
			response.Code = "already_acknowledged"
			_ = tx.QueryRowContext(ctx, `SELECT actor_ref,occurred_at FROM bell.alert_transitions WHERE alert_id=$1 AND to_state='acknowledged' ORDER BY sequence LIMIT 1`, alertID).Scan(&response.ActorRef, &response.OccurredAt)
		case command == "close" && current == "open":
			response.Code = "acknowledgement_required"
		case command == "close" && current == "closed":
			response.Code = "already_closed"
		default:
			response.Code = "invalid_state"
		}
	} else {
		next := "acknowledged"
		if command == "close" {
			next = "closed"
		}
		response.State = next
		response.ActorRef = ""
		response.OccurredAt = time.Time{}
		if err := tx.QueryRowContext(ctx, `INSERT INTO bell.alert_transitions(id,alert_id,sequence,from_state,to_state,actor_ref,note)
			VALUES($1,$2,$3,$4,$5,$6,$7) RETURNING actor_ref,occurred_at`,
			newPrefixedID("trn_"), alertID, sequence+1, current, next, actorRef, note).Scan(&response.ActorRef, &response.OccurredAt); err != nil {
			return 0, alert.CommandResponse{}, errors.New("append Bell alert transition")
		}
	}
	body, err := json.Marshal(response)
	if err != nil {
		return 0, alert.CommandResponse{}, errors.New("encode Bell alert command response")
	}
	if _, err := tx.ExecContext(ctx, `INSERT INTO bell.alert_command_receipts(tenant_id,idempotency_key,command_hash,response_status,response_body) VALUES($1,$2,$3,$4,$5::jsonb)`, tenantID, key, digest[:], status, body); err != nil {
		return 0, alert.CommandResponse{}, errors.New("append Bell alert command receipt")
	}
	if err := tx.Commit(); err != nil {
		return 0, alert.CommandResponse{}, errors.New("commit Bell alert command")
	}
	return status, response, nil
}

func newPrefixedID(prefix string) string { return prefix + ulid.Make().String() }

func valueOrEmpty(value *string) string {
	if value == nil {
		return ""
	}
	return *value
}