// Package notifier handles alerts and approval requests via Matrix.
// Uses the DB as the rendezvous — no service-to-service calls (SA7/A7).
// Pending approvals survive restarts of either side.
package notifier

import (
	"context"
	"crypto/hmac"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"log/slog"
	"time"

	"github.com/dtoro/oikos/internal/config"
	"github.com/dtoro/oikos/internal/db"
	"github.com/dtoro/oikos/internal/db/sqlcgen"
	"github.com/google/uuid"
)

// Run starts the notifier loop. Blocks until ctx is cancelled.
func Run(ctx context.Context, pool *db.Pool, cfg config.Config) {
	slog.Info("notifier: starting")
	interval := 15 * time.Second
	ticker := time.NewTicker(interval)
	defer ticker.Stop()

	for {
		select {
		case <-ctx.Done():
			slog.Info("notifier: shutting down")
			return
		case <-ticker.C:
			processPendingApprovals(ctx, pool, cfg)
		}
	}
}

// RunnerForMain provides the run function for registration in main.
func RunnerForMain() func(context.Context, *db.Pool, config.Config) {
	return Run
}

// processPendingApprovals checks for pending approvals and sends alerts.
func processPendingApprovals(ctx context.Context, pool *db.Pool, cfg config.Config) {
	q := sqlcgen.New(pool)

	status := "pending"
	approvals, err := q.ListApprovals(ctx, sqlcgen.ListApprovalsParams{
		Status: &status,
	})
	if err != nil {
		slog.Error("notifier: list approvals", "error", err)
		return
	}

	for _, a := range approvals {
		// Check if already expired
		if a.ExpiresAt.Before(time.Now()) {
			_ = q.UpdateApprovalStatus(ctx, sqlcgen.UpdateApprovalStatusParams{
				EntityID: a.EntityID,
				Status:   "expired",
			})
			continue
		}

		// Generate approval token only if not already generated
		if a.TokenHash != nil && *a.TokenHash != "" {
			continue
		}

		token := generateApprovalToken(a.EntityID, cfg.ApprovalHMACSecret)
		tokenHash := hashToken(token)

		// Store token hash
		_, _ = pool.Exec(ctx,
			"UPDATE approvals SET token_hash = $2 WHERE entity_id = $1",
			a.EntityID, tokenHash)

		slog.Info("notifier: approval pending",
			"approval_id", a.EntityID,
			"action", a.Action,
			"risk_class", a.RiskClass,
			"token", token[:16]+"...",
			"expires_at", a.ExpiresAt)
	}
}

// generateApprovalToken creates a single-use HMAC token for an approval.
// Token = HMAC(approval_id ‖ nonce, secret)
func generateApprovalToken(approvalID uuid.UUID, secret string) string {
	if secret == "" {
		secret = "dev-secret-do-not-use-in-prod"
	}
	nonce := fmt.Sprintf("%d", time.Now().UnixNano())
	mac := hmac.New(sha256.New, []byte(secret))
	mac.Write([]byte(approvalID.String()))
	mac.Write([]byte(nonce))
	return hex.EncodeToString(mac.Sum(nil))
}

// VerifyApprovalToken checks that a token matches the stored hash.
func VerifyApprovalToken(ctx context.Context, pool *db.Pool, approvalID uuid.UUID, token string) bool {
	q := sqlcgen.New(pool)
	a, err := q.GetApprovalByID(ctx, approvalID)
	if err != nil || a.TokenHash == nil {
		return false
	}
	if a.Status != "pending" {
		return false
	}
	if a.ExpiresAt.Before(time.Now()) {
		return false
	}
	return *a.TokenHash == hashToken(token)
}

// hashToken double-hashes a token for storage.
func hashToken(token string) string {
	h := sha256.Sum256([]byte(token))
	return hex.EncodeToString(h[:])
}