package middleware

import (
	"context"
	"net/http"
	"os"
	"strings"
	"sync"
	"time"

	"github.com/gin-gonic/gin"
	"go.uber.org/zap"
	"gorm.io/gorm"
)

// maintenanceState carries the latest cached view of the platform-wide
// maintenance flag. It is refreshed lazily from `platform_settings` when a
// request comes in after the TTL has expired, so operators flipping the flag
// on one pod propagate to every other pod within a bounded window (10s).
type maintenanceState struct {
	mu        sync.RWMutex
	enabled   bool
	lastCheck time.Time
	db        *gorm.DB
	logger    *zap.Logger
	ttl       time.Duration
}

const defaultMaintenanceCacheTTL = 10 * time.Second

var (
	state             = &maintenanceState{ttl: defaultMaintenanceCacheTTL}
	maintenanceInitMu sync.Mutex
)

func init() {
	v := os.Getenv("MAINTENANCE_MODE")
	state.mu.Lock()
	state.enabled = v == "true" || v == "1"
	state.mu.Unlock()
}

// InitMaintenanceMode wires the DB pool so subsequent MaintenanceModeEnabled()
// calls refresh from `platform_settings.maintenance_mode` with a TTL cache.
// Safe to call more than once (last write wins). If db is nil the middleware
// falls back to the in-memory state seeded from MAINTENANCE_MODE.
func InitMaintenanceMode(db *gorm.DB, logger *zap.Logger) {
	maintenanceInitMu.Lock()
	defer maintenanceInitMu.Unlock()

	if logger == nil {
		logger = zap.NewNop()
	}
	state.mu.Lock()
	state.db = db
	state.logger = logger
	state.lastCheck = time.Time{} // force refresh on first call
	state.mu.Unlock()

	// Prime the cache so the very first request doesn't see a stale value.
	refreshFromDB(context.Background())
}

// refreshFromDB reads the current value from the DB and updates the cache.
// Never propagates errors to callers — a broken DB should not silently
// enable maintenance mode, so the previous cached value wins.
func refreshFromDB(ctx context.Context) {
	state.mu.RLock()
	db := state.db
	logger := state.logger
	state.mu.RUnlock()
	if db == nil {
		return
	}

	var row struct {
		ValueBool *bool `gorm:"column:value_bool"`
	}
	err := db.WithContext(ctx).
		Table("platform_settings").
		Select("value_bool").
		Where("key = ?", "maintenance_mode").
		Take(&row).Error

	state.mu.Lock()
	state.lastCheck = time.Now()
	state.mu.Unlock()

	if err != nil {
		if err != gorm.ErrRecordNotFound && logger != nil {
			logger.Warn("Failed to refresh maintenance flag from DB — keeping cached value",
				zap.Error(err),
			)
		}
		return
	}

	enabled := row.ValueBool != nil && *row.ValueBool
	state.mu.Lock()
	state.enabled = enabled
	state.mu.Unlock()
}

// MaintenanceModeEnabled returns the cached maintenance flag, refreshing from
// the DB if the TTL has expired and a DB pool has been wired.
func MaintenanceModeEnabled() bool {
	state.mu.RLock()
	enabled := state.enabled
	lastCheck := state.lastCheck
	hasDB := state.db != nil
	ttl := state.ttl
	state.mu.RUnlock()

	if hasDB && time.Since(lastCheck) > ttl {
		refreshFromDB(context.Background())
		state.mu.RLock()
		enabled = state.enabled
		state.mu.RUnlock()
	}
	return enabled
}

// SetMaintenanceMode sets the in-memory flag without touching the DB. It is
// kept for tests and for cases where a caller already owns the DB write — it
// does not persist the value across pods. Use PlatformSettings to change
// state across a deployment.
func SetMaintenanceMode(enabled bool) {
	state.mu.Lock()
	state.enabled = enabled
	state.lastCheck = time.Now().Add(state.ttl) // suppress the next DB refresh
	state.mu.Unlock()
}

// MaintenanceGin returns a Gin middleware for maintenance mode.
// Exempt paths: /health, /healthz, /readyz, /api/v1/health, /api/v1/admin, /swagger, /docs
func MaintenanceGin() gin.HandlerFunc {
	return func(c *gin.Context) {
		if !MaintenanceModeEnabled() {
			c.Next()
			return
		}
		path := c.Request.URL.Path
		if isMaintenanceExempt(path) {
			c.Next()
			return
		}
		c.AbortWithStatusJSON(http.StatusServiceUnavailable, gin.H{"error": "Platform is under maintenance"})
	}
}

func isMaintenanceExempt(path string) bool {
	path = strings.TrimSuffix(path, "/")
	exempts := []string{"/health", "/healthz", "/readyz", "/health/deep", "/metrics", "/swagger", "/docs", "/api/versions"}
	for _, exempt := range exempts {
		if path == exempt || strings.HasPrefix(path, exempt+"/") {
			return true
		}
	}
	if strings.Contains(path, "/api/v1/health") {
		return true
	}
	if strings.Contains(path, "/api/v1/admin") {
		return true
	}
	return false
}