package api

// Data plane for the public API gateway: /g/:slug/* proxies to the
// upstream_url of the matching api_services row. Callers authenticate with
// api_keys (X-API-Key or Authorization: Bearer), pass the rpm + monthly
// quota gates, and every request lands in usage_counters /
// metrics_timeseries / incident_events for the /admin/gateway analytics
// surfaces.

import (
	"context"
	"database/sql"
	"encoding/json"
	"net/http"
	"strings"
	"sync"
	"time"

	"containr/internal/database"
	"containr/internal/gateway"

	"github.com/gin-gonic/gin"
	"golang.org/x/crypto/bcrypt"
)

// jarvis: ceiling — a single shared transport; per-request timeouts come
// from api_services.request_timeout_ms on the request context.
var gatewayHTTPClient = &http.Client{
	Transport: &http.Transport{
		MaxIdleConns:        100,
		MaxIdleConnsPerHost: 10,
		IdleConnTimeout:     90 * time.Second,
	},
}

// gatewayRPM is a process-local per-minute counter map. Containr runs a
// single API process, so an in-memory bucket is sufficient — a multi-node
// control plane would need a Redis-backed limiter instead.
var gatewayRPM = struct {
	sync.Mutex
	buckets map[string]*rpmBucket
}{buckets: map[string]*rpmBucket{}}

type rpmBucket struct {
	window time.Time
	count  int
}

// gatewayRateAllow returns false when the bucket for the current minute has
// already reached limit. A limit <= 0 disables the check. `now` is injected
// so tests can freeze the window.
func gatewayRateAllow(bucketKey string, limit int, now time.Time) bool {
	if limit <= 0 {
		return true
	}
	window := now.Truncate(time.Minute)
	gatewayRPM.Lock()
	defer gatewayRPM.Unlock()
	b := gatewayRPM.buckets[bucketKey]
	if b == nil || !b.window.Equal(window) {
		b = &rpmBucket{window: window}
		gatewayRPM.buckets[bucketKey] = b
		// Best-effort sweep so the map cannot grow without bound.
		for k, old := range gatewayRPM.buckets {
			if old.window.Before(window.Add(-time.Minute)) {
				delete(gatewayRPM.buckets, k)
			}
		}
	}
	b.count++
	return b.count <= limit
}

type gatewayService struct {
	ID                 string
	UpstreamURL        string
	RoutePrefix        string
	UpstreamAuthHeader sql.NullString
	UpstreamAuthValue  sql.NullString
	Enabled            bool
	RPMLimit           sql.NullInt64
	MonthlyQuota       sql.NullInt64
	RequestTimeoutMS   int
}

type gatewayKey struct {
	ID                string
	Hash              string
	Enabled           bool
	RPMLimit          sql.NullInt64
	MonthlyQuota      sql.NullInt64
	AllowedServiceIDs string
}

// extractGatewayKey reads the caller's API key from X-API-Key first, then
// Authorization: Bearer.
func extractGatewayKey(c *gin.Context) string {
	if k := strings.TrimSpace(c.GetHeader("X-API-Key")); k != "" {
		return k
	}
	auth := strings.TrimSpace(c.GetHeader("Authorization"))
	if len(auth) > 7 && strings.EqualFold(auth[:7], "Bearer ") {
		return strings.TrimSpace(auth[7:])
	}
	return ""
}

// lookupGatewayService resolves the slug to an enabled service row.
func lookupGatewayService(ctx context.Context, db *database.DB, slug string) (*gatewayService, error) {
	var s gatewayService
	var enabled int
	err := db.QueryRowContext(ctx, `
		SELECT id, upstream_url, route_prefix, upstream_auth_header,
		       upstream_auth_value, enabled, rpm_limit, monthly_quota,
		       request_timeout_ms
		FROM api_services WHERE slug = $1
	`, slug).Scan(&s.ID, &s.UpstreamURL, &s.RoutePrefix,
		&s.UpstreamAuthHeader, &s.UpstreamAuthValue, &enabled,
		&s.RPMLimit, &s.MonthlyQuota, &s.RequestTimeoutMS)
	if err != nil {
		return nil, err
	}
	s.Enabled = enabled != 0
	return &s, nil
}

// authenticateGatewayKey resolves a presented key by its indexed prefix and
// bcrypt-verifies candidates. Returns nil when nothing matches.
func authenticateGatewayKey(ctx context.Context, db *database.DB, presented string) (*gatewayKey, error) {
	prefix := presented
	if len(prefix) > 8 {
		prefix = prefix[:8]
	}
	rows, err := db.QueryContext(ctx, `
		SELECT id, key_hash, enabled, rpm_limit, monthly_quota, allowed_service_ids
		FROM api_keys WHERE key_prefix = $1
	`, prefix)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	for rows.Next() {
		var k gatewayKey
		var enabled int
		if err := rows.Scan(&k.ID, &k.Hash, &enabled, &k.RPMLimit, &k.MonthlyQuota, &k.AllowedServiceIDs); err != nil {
			return nil, err
		}
		k.Enabled = enabled != 0
		if bcrypt.CompareHashAndPassword([]byte(k.Hash), []byte(presented)) == nil {
			return &k, nil
		}
	}
	return nil, rows.Err()
}

// keyAllowsService applies the allowed_service_ids JSON allowlist. An empty
// list means the key may call every service.
func keyAllowsService(k *gatewayKey, serviceID string) bool {
	var allowed []string
	if err := json.Unmarshal([]byte(k.AllowedServiceIDs), &allowed); err != nil || len(allowed) == 0 {
		return true
	}
	for _, id := range allowed {
		if id == serviceID {
			return true
		}
	}
	return false
}

// monthlyUsage sums a counter dimension for the current calendar month.
func monthlyUsage(ctx context.Context, db *database.DB, column, id, period string) (int, error) {
	var total int
	err := db.QueryRowContext(ctx, `
		SELECT COALESCE(SUM(request_count), 0) FROM usage_counters
		WHERE `+column+` = $1 AND period_month = $2
	`, id, period).Scan(&total)
	return total, err
}

// recordGatewayRequest persists usage, metrics, and failure incidents for a
// proxied call. Runs in the request path but is three small writes.
func recordGatewayRequest(ctx context.Context, db *database.DB, svc *gatewayService, k *gatewayKey, status int, period string) {
	_, _ = db.ExecContext(ctx, `
		INSERT INTO usage_counters (api_key_id, service_id, period_month, request_count, updated_at)
		VALUES ($1, $2, $3, 1, NOW())
		ON CONFLICT (api_key_id, service_id, period_month)
		DO UPDATE SET request_count = usage_counters.request_count + 1, updated_at = NOW()
	`, k.ID, svc.ID, period)
	_, _ = db.ExecContext(ctx, `
		UPDATE api_keys SET last_used_at = NOW() WHERE id = $1
	`, k.ID)
	labels, _ := json.Marshal(map[string]interface{}{
		"service_id": svc.ID,
		"key_id":     k.ID,
		"status":     status,
	})
	_, _ = db.ExecContext(ctx, `
		INSERT INTO metrics_timeseries (metric, value, labels_json, occurred_at)
		VALUES ('gateway_request', 1, $1, NOW())
	`, string(labels))
}

func recordGatewayIncident(ctx context.Context, db *database.DB, svcID string, keyID *string, code, msg, severity string, status int) {
	var kid interface{}
	if keyID != nil {
		kid = *keyID
	}
	_, _ = db.ExecContext(ctx, `
		INSERT INTO incident_events (service_id, api_key_id, code, message, severity, http_status, occurred_at)
		VALUES ($1, $2, $3, $4, $5, $6, NOW())
	`, svcID, kid, code, msg, severity, status)
}

// handleGatewayProxy is mounted at /g/:slug and /g/:slug/*path on the root
// router — outside /api/v1 so route_prefix stays clean.
func handleGatewayProxy(c *gin.Context) {
	db := c.MustGet("db").(*database.DB)
	ctx := c.Request.Context()
	slug := c.Param("slug")

	svc, err := lookupGatewayService(ctx, db, slug)
	if err == sql.ErrNoRows {
		respondError(c, http.StatusNotFound, "SERVICE_NOT_FOUND", "Gateway service not found")
		return
	}
	if err != nil {
		respondError(c, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to resolve gateway service")
		return
	}
	if !svc.Enabled {
		respondError(c, http.StatusServiceUnavailable, "SERVICE_DISABLED", "Gateway service is disabled")
		return
	}

	presented := extractGatewayKey(c)
	if presented == "" {
		recordGatewayIncident(ctx, db, svc.ID, nil, "MISSING_API_KEY", "Request without API key", "low", http.StatusUnauthorized)
		respondError(c, http.StatusUnauthorized, "API_KEY_REQUIRED", "An API key is required for this service")
		return
	}
	key, err := authenticateGatewayKey(ctx, db, presented)
	if err != nil {
		respondError(c, http.StatusInternalServerError, "INTERNAL_ERROR", "Failed to authenticate API key")
		return
	}
	// Disabled and unknown keys collapse to the same 401 — a disabled key
	// must not leak its existence.
	if key == nil || !key.Enabled {
		recordGatewayIncident(ctx, db, svc.ID, nil, "INVALID_API_KEY", "Request with invalid or disabled API key", "low", http.StatusUnauthorized)
		respondError(c, http.StatusUnauthorized, "INVALID_API_KEY", "Invalid API key")
		return
	}
	if !keyAllowsService(key, svc.ID) {
		recordGatewayIncident(ctx, db, svc.ID, &key.ID, "KEY_SCOPE_DENIED", "API key not allowed on this service", "medium", http.StatusForbidden)
		respondError(c, http.StatusForbidden, "KEY_SCOPE_DENIED", "API key is not permitted for this service")
		return
	}

	now := time.Now()
	if !gatewayRateAllow("key:"+key.ID, int(key.RPMLimit.Int64), now) ||
		!gatewayRateAllow("svc:"+svc.ID, int(svc.RPMLimit.Int64), now) {
		recordGatewayIncident(ctx, db, svc.ID, &key.ID, "RATE_LIMITED", "Per-minute rate limit exceeded", "medium", http.StatusTooManyRequests)
		respondError(c, http.StatusTooManyRequests, "RATE_LIMITED", "Rate limit exceeded")
		return
	}

	period := now.Format("2006-01")
	if key.MonthlyQuota.Valid && key.MonthlyQuota.Int64 > 0 {
		if used, err := monthlyUsage(ctx, db, "api_key_id", key.ID, period); err == nil && int64(used) >= key.MonthlyQuota.Int64 {
			respondError(c, http.StatusTooManyRequests, "QUOTA_EXCEEDED", "Monthly request quota exceeded")
			return
		}
	}
	if svc.MonthlyQuota.Valid && svc.MonthlyQuota.Int64 > 0 {
		if used, err := monthlyUsage(ctx, db, "service_id", svc.ID, period); err == nil && int64(used) >= svc.MonthlyQuota.Int64 {
			respondError(c, http.StatusTooManyRequests, "QUOTA_EXCEEDED", "Service monthly quota exceeded")
			return
		}
	}

	target, err := gateway.BuildTargetURL(svc.UpstreamURL, svc.RoutePrefix, c.Request.URL.Path, c.Request.URL.RawQuery)
	if err != nil {
		respondError(c, http.StatusBadGateway, "UPSTREAM_URL_INVALID", "Gateway upstream is misconfigured")
		return
	}
	headers := map[string]string{}
	if svc.UpstreamAuthHeader.Valid && svc.UpstreamAuthHeader.String != "" {
		headers[svc.UpstreamAuthHeader.String] = svc.UpstreamAuthValue.String
	}

	timeout := time.Duration(svc.RequestTimeoutMS) * time.Millisecond
	if timeout <= 0 {
		timeout = 8 * time.Second
	}
	reqCtx, cancel := context.WithTimeout(ctx, timeout)
	defer cancel()

	status, _, err := gateway.ProxyRequest(gatewayHTTPClient, c.Writer, c.Request.WithContext(reqCtx), target, headers)
	if err != nil {
		recordGatewayIncident(reqCtx, db, svc.ID, &key.ID, "UPSTREAM_ERROR", err.Error(), "high", http.StatusBadGateway)
		recordGatewayRequest(ctx, db, svc, key, http.StatusBadGateway, period)
		respondError(c, http.StatusBadGateway, "UPSTREAM_ERROR", "Upstream request failed")
		return
	}

	recordGatewayRequest(ctx, db, svc, key, status, period)
	if status >= 500 {
		recordGatewayIncident(ctx, db, svc.ID, &key.ID, "UPSTREAM_5XX", "Upstream returned "+http.StatusText(status), "high", status)
	}
}