package api

import (
	"context"
	"encoding/base64"
	"encoding/hex"
	"encoding/json"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"github.com/johanj/clavitor/edition"
	"github.com/johanj/clavitor/lib"
)

// base64Decode handles both standard and url-safe base64 (with or without padding).
func base64Decode(s string) ([]byte, error) {
	s = strings.TrimRight(s, "=")
	b, err := base64.RawURLEncoding.DecodeString(s)
	if err != nil {
		b, err = base64.RawStdEncoding.DecodeString(s)
	}
	return b, err
}

func base64UrlEncode(b []byte) string {
	return base64.RawURLEncoding.EncodeToString(b)
}

type contextKey string

const (
	ctxActor    contextKey = "actor"
	ctxAgent    contextKey = "agent"
	ctxDB       contextKey = "db"
	ctxVaultKey contextKey = "vault_key"
)

func ActorFromContext(ctx context.Context) string {
	v, ok := ctx.Value(ctxActor).(string)
	if !ok {
		return lib.ActorWeb
	}
	return v
}

func AgentFromContext(ctx context.Context) *lib.AgentData {
	v, _ := ctx.Value(ctxAgent).(*lib.AgentData)
	return v
}

func DBFromContext(ctx context.Context) *lib.DB {
	v, _ := ctx.Value(ctxDB).(*lib.DB)
	return v
}

func VaultKeyFromContext(ctx context.Context) []byte {
	v, _ := ctx.Value(ctxVaultKey).([]byte)
	return v
}

// IsAgentRequest returns true if the request was made with a cvt_ agent token.
func IsAgentRequest(r *http.Request) bool {
	return AgentFromContext(r.Context()) != nil
}

// L1Middleware extracts L1 from Bearer token and opens the vault DB.
// Supports two token formats:
//   - cvt_ prefix: CVT wire token (type 0x00) — extract L0 for routing, L1 for encryption, agent_id for scope lookup
//   - raw base64: legacy L1 bearer (8 bytes) — vault owner, full access
func L1Middleware(dataDir string) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			auth := r.Header.Get("Authorization")

			// No auth = unauthenticated request (registration, login, etc.)
			// We CANNOT open a random vault via wildcard - in hosted mode there are many vaults.
			// The request must either provide a bearer token or target a specific vault via L0.
			if auth == "" || !strings.HasPrefix(auth, "Bearer ") {
				next.ServeHTTP(w, r)
				return
			}

			bearerVal := strings.TrimPrefix(auth, "Bearer ")

			if strings.HasPrefix(bearerVal, "cvt_") {
				// --- CVT wire token ---
				l0, l1Raw, agentID, err := lib.ParseWireToken(bearerVal)
				if err != nil {
					ErrorResponse(w, http.StatusUnauthorized, "invalid_token", "Invalid CVT token")
					return
				}

				l1Key := lib.NormalizeKey(l1Raw)
				vaultPrefix := base64UrlEncode(l0)
				dbPath := filepath.Join(dataDir, "clavitor-"+vaultPrefix)

				db, err := lib.OpenDB(dbPath)
				if err != nil {
					ErrorResponse(w, http.StatusNotFound, "vault_not_found", "Vault not found")
					return
				}
				defer db.Close()

				// Look up agent by agent_id via blind index
				agentIDHex := hex.EncodeToString(agentID)
				agent, err := lib.AgentLookup(db, l1Key, agentIDHex)
				if err != nil {
					// Community: Log to stderr. Commercial: Also POSTs to telemetry endpoint.
					// This indicates DB corruption, decryption failure, or disk issues.
					edition.Current.AlertOperator(r.Context(), "auth_system_error",
						"Agent lookup failed (DB/decryption error)", map[string]any{"error": err.Error()})
					ErrorResponse(w, http.StatusInternalServerError, "system_error", "Authentication system error - contact support")
					return
				}
				if agent == nil {
					ErrorResponse(w, http.StatusUnauthorized, "unknown_agent", "Invalid or revoked token")
					return
				}

				clientIP := realIP(r)

				// IP whitelist: first contact fills it, subsequent requests checked
				if agent.AllowedIPs == "" {
					// First contact — record the IP
					//
					// SECURITY NOTE: There is a theoretical race condition here.
					// If two parallel requests from different IPs arrive simultaneously
					// for the same agent's first contact, both could pass the empty check
					// before either writes to the database.
					//
					// This was reviewed and accepted because:
					// 1. Requires a stolen agent token (already a compromise scenario)
					// 2. Requires two agents with the same token racing first contact
					// 3. The "loser" simply won't be auto-whitelisted (one IP wins)
					// 4. Cannot be reproduced in testing; practically impossible to trigger
					// 5. Per-vault SQLite isolation limits blast radius
					//
					// The fix would require plaintext allowed_ips column + atomic conditional
					// update. Not worth the complexity for this edge case.
					agent.AllowedIPs = clientIP
					if err := lib.AgentUpdateAllowedIPs(db, l1Key, agent); err != nil {
						log.Printf("agent %s: failed to record first-contact IP: %v", agent.Name, err)
						ErrorResponse(w, http.StatusInternalServerError, "ip_record_failed", "Failed to record agent IP")
						return
					}
					log.Printf("agent %s: first contact from %s, IP recorded", agent.Name, clientIP)
				} else if !lib.AgentIPAllowed(agent, clientIP) {
					log.Printf("agent %s: blocked IP %s (allowed: %s)", agent.Name, clientIP, agent.AllowedIPs)
					ErrorResponse(w, http.StatusForbidden, "ip_blocked", "IP not allowed for this agent")
					return
				}

				// Locked agents are refused immediately, before any handler runs.
				// This is the second-strike state — the owner has to PRF-unlock
				// before this agent can do anything again.
				if agent.Locked {
					lib.AuditLog(db, &lib.AuditEvent{
						Action: "agent_locked_request_refused",
						Actor:  lib.ActorAgent,
						Title:  agent.Name,
						IPAddr: clientIP,
					})
					ErrorResponse(w, http.StatusLocked, "agent_locked",
						"Agent is locked. Owner unlock required.")
					return
				}

				// Per-agent rate limiting (unique-entries quota) is enforced in
				// handlers that read a specific entry — GetEntry, MatchURL,
				// HandleListAlternates — via agentReadEntry(). Middleware
				// doesn't know which entry the agent is asking for here.

				ctx := context.WithValue(r.Context(), ctxDB, db)
				ctx = context.WithValue(ctx, ctxVaultKey, l1Key)
				ctx = context.WithValue(ctx, ctxActor, lib.ActorAgent)
				ctx = context.WithValue(ctx, ctxAgent, agent)
				next.ServeHTTP(w, r.WithContext(ctx))

			} else {
				// --- Legacy L1 bearer (web UI / extension) ---
				l1Raw, err := base64Decode(bearerVal)
				if err != nil || len(l1Raw) != 8 {
					ErrorResponse(w, http.StatusUnauthorized, "invalid_l1", "Invalid L1 key in Bearer")
					return
				}

				l1Key := lib.NormalizeKey(l1Raw)
				vaultPrefix := base64UrlEncode(l1Raw[:4])
				dbPath := filepath.Join(dataDir, "clavitor-"+vaultPrefix)

				var db *lib.DB
				if _, err := os.Stat(dbPath); err == nil {
					db, err = lib.OpenDB(dbPath)
					if err != nil {
						ErrorResponse(w, http.StatusInternalServerError, "db_error", "Failed to open vault")
						return
					}
				}
				if db == nil {
					ErrorResponse(w, http.StatusNotFound, "vault_not_found", "Vault not found")
					return
				}
				defer db.Close()

				ctx := context.WithValue(r.Context(), ctxDB, db)
				ctx = context.WithValue(ctx, ctxVaultKey, l1Key)
				ctx = context.WithValue(ctx, ctxActor, lib.ActorWeb)
				next.ServeHTTP(w, r.WithContext(ctx))
			}
		})
	}
}

// LoggingMiddleware logs HTTP requests.
func LoggingMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()
		wrapped := &statusWriter{ResponseWriter: w, status: 200}
		next.ServeHTTP(wrapped, r)
		log.Printf("%s %s %d %s", r.Method, r.URL.Path, wrapped.status, time.Since(start))
	})
}

type statusWriter struct {
	http.ResponseWriter
	status int
}

func (w *statusWriter) WriteHeader(code int) {
	w.status = code
	w.ResponseWriter.WriteHeader(code)
}

// RateLimitMiddleware implements per-(IP, method, path) rate limiting.
//
// The bucket key is the *request identity*, not just the source IP. Same
// endpoint from the same IP shares a counter; different endpoints get
// independent counters. This means:
//
//   - SPA loading 8 different endpoints on first paint: 8 buckets at count 1,
//     none blocked.
//   - Brute-forcer hammering /api/auth/login/complete with different bodies:
//     one bucket, blocked at requestsPerMinute attempts. Body is intentionally
//     NOT part of the key — if it were, varying the body would bypass the
//     limiter and brute-force protection would be gone.
//   - Polling the same endpoint every few seconds: shares a bucket, counts up.
//     Blocked at requestsPerMinute, which is what we want.
func RateLimitMiddleware(requestsPerMinute int) func(http.Handler) http.Handler {
	var mu sync.Mutex
	buckets := make(map[string]*rateLimitEntry)

	go func() {
		for {
			time.Sleep(time.Minute)
			mu.Lock()
			now := time.Now()
			for k, entry := range buckets {
				if now.Sub(entry.windowStart) > time.Minute {
					delete(buckets, k)
				}
			}
			mu.Unlock()
		}
	}()

	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			// Owner-only bulk endpoints are exempt from the global rate limit.
			// /api/entries/batch refuses agents at the handler entry
			// (CreateEntryBatch returns 403 for any cvt_-token request), so this
			// path is owner-only by handler enforcement. The harvester defense
			// for agent-reachable paths lives in the per-agent unique-entries
			// quota (agentReadEntry), not here. Throttling the import flow
			// would only DOS the legitimate import — no defense gained.
			if r.URL.Path == "/api/entries/batch" {
				next.ServeHTTP(w, r)
				return
			}

			key := realIP(r) + "|" + r.Method + "|" + r.URL.Path
			mu.Lock()
			entry, exists := buckets[key]
			now := time.Now()
			if !exists || now.Sub(entry.windowStart) > time.Minute {
				entry = &rateLimitEntry{windowStart: now, count: 0}
				buckets[key] = entry
			}
			entry.count++
			count := entry.count
			mu.Unlock()

			if count > requestsPerMinute {
				ErrorResponse(w, http.StatusTooManyRequests, "rate_limited", "Too many requests")
				return
			}
			next.ServeHTTP(w, r)
		})
	}
}

type rateLimitEntry struct {
	windowStart time.Time
	count       int
}

// Per-agent rate limiter — tracks UNIQUE entry IDs read per minute / per hour.
//
// Repeated reads of the same credential do NOT count: an agent legitimately
// re-fetching the same credential to log into the same site many times stays
// at unique-count = 1. The limit fires only when the agent starts touching
// many *different* credentials, which is the harvesting pattern we care about.
//
// Two windows run independently:
//   - RateLimit     → unique entries per rolling minute
//   - RateLimitHour → unique entries per rolling hour
//
// A limit of 0 means unlimited for that window.
var agentRateLimiter = newAgentLimiter()

type agentLimiterEntry struct {
	minuteWindowStart time.Time
	minuteEntries     map[string]struct{}
	hourWindowStart   time.Time
	hourEntries       map[string]struct{}
}

type agentLimiter struct {
	mu     sync.Mutex
	agents map[string]*agentLimiterEntry
}

func newAgentLimiter() *agentLimiter {
	al := &agentLimiter{agents: make(map[string]*agentLimiterEntry)}
	go func() {
		for {
			time.Sleep(5 * time.Minute)
			al.mu.Lock()
			now := time.Now()
			for id, e := range al.agents {
				// Drop agents whose hour window has expired (no recent activity).
				if now.Sub(e.hourWindowStart) > time.Hour {
					delete(al.agents, id)
				}
			}
			al.mu.Unlock()
		}
	}()
	return al
}

// LimitResult signals which window (if any) blocked an agent read.
type LimitResult int

const (
	LimitAllowed        LimitResult = iota
	LimitMinuteHit                  // Minute-window cap reached. Soft throttle, no strike.
	LimitHourHit                    // Hour-window cap reached. Strike — caller must persist.
)

// agentReadEntry enforces the per-agent unique-entries quota when an agent
// fetches a credential. Call immediately after the AgentCanAccess scope check.
//
// On hour-limit hit, applies the strike-and-lock policy:
//   - First strike (or > 2h since last strike): record the strike, throttle.
//   - Second strike within 2h: lock the agent, persist Locked=true, audit-log.
//
// Both persistence and audit happen in here so the call sites stay one-liners.
//
// Returns true if the read may proceed; false if blocked. No-op for nil agent
// (vault owner / web UI) and for agents with both limits set to 0 (unlimited).
func agentReadEntry(agent *lib.AgentData, entryID string, db *lib.DB, vk []byte) bool {
	if agent == nil {
		return true
	}
	if agent.Locked {
		// Belt-and-suspenders. L1Middleware blocks locked agents at the top
		// before any handler runs, but if that check is ever bypassed this
		// catches it at the per-entry layer.
		return false
	}
	if agent.RateLimit == 0 && agent.RateLimitHour == 0 {
		return true
	}

	result := agentRateLimiter.checkEntry(agent.AgentID, entryID, agent.RateLimit, agent.RateLimitHour)
	switch result {
	case LimitAllowed:
		return true
	case LimitMinuteHit:
		return false // soft throttle, no strike
	case LimitHourHit:
		// Strike-and-lock policy.
		now := time.Now().Unix()
		const strikeWindowSeconds = 2 * 60 * 60 // 2 hours
		secondStrike := agent.LastStrikeAt > 0 && (now-agent.LastStrikeAt) < strikeWindowSeconds

		if secondStrike {
			// Lock the agent. Persist + audit + update in-memory state.
			if err := lib.AgentLockWithStrike(db, vk, agent.EntryID, now); err != nil {
				log.Printf("agent %s: failed to persist lock: %v", agent.Name, err)
			}
			lib.AuditLog(db, &lib.AuditEvent{
				Action: "agent_locked", Actor: lib.ActorAgent,
				Title: agent.Name,
			})
			log.Printf("agent %s: LOCKED after second hour-limit strike (last strike %ds ago)",
				agent.Name, now-agent.LastStrikeAt)
			agent.Locked = true
			agent.LastStrikeAt = now
		} else {
			// First strike. Record timestamp; don't lock.
			if err := lib.AgentRecordStrike(db, vk, agent.EntryID, now); err != nil {
				log.Printf("agent %s: failed to persist strike: %v", agent.Name, err)
			}
			lib.AuditLog(db, &lib.AuditEvent{
				Action: "agent_strike", Actor: lib.ActorAgent,
				Title: agent.Name,
			})
			log.Printf("agent %s: hour-limit strike recorded", agent.Name)
			agent.LastStrikeAt = now
		}
		return false
	}
	return false
}

// checkEntry records the agent's intent to read entryID and returns:
//   - LimitAllowed       — entry recorded, read allowed
//   - LimitMinuteHit     — minute-window cap exceeded; entry NOT added to either set
//   - LimitHourHit       — hour-window cap exceeded; entry NOT added to either set
//
// Repeated calls with the same entryID inside an active window are free:
// the entry is already in the set, len(set) does not grow, the call returns
// LimitAllowed.
func (al *agentLimiter) checkEntry(agentID, entryID string, maxPerMinute, maxPerHour int) LimitResult {
	al.mu.Lock()
	defer al.mu.Unlock()

	now := time.Now()
	e, exists := al.agents[agentID]
	if !exists {
		e = &agentLimiterEntry{
			minuteWindowStart: now,
			minuteEntries:     make(map[string]struct{}),
			hourWindowStart:   now,
			hourEntries:       make(map[string]struct{}),
		}
		al.agents[agentID] = e
	}

	// Roll the windows if they have expired.
	if now.Sub(e.minuteWindowStart) > time.Minute {
		e.minuteWindowStart = now
		e.minuteEntries = make(map[string]struct{})
	}
	if now.Sub(e.hourWindowStart) > time.Hour {
		e.hourWindowStart = now
		e.hourEntries = make(map[string]struct{})
	}

	_, alreadyMinute := e.minuteEntries[entryID]
	_, alreadyHour := e.hourEntries[entryID]

	// Hour limit takes precedence — it's the strike trigger.
	if maxPerHour > 0 && !alreadyHour && len(e.hourEntries) >= maxPerHour {
		return LimitHourHit
	}
	if maxPerMinute > 0 && !alreadyMinute && len(e.minuteEntries) >= maxPerMinute {
		return LimitMinuteHit
	}

	e.minuteEntries[entryID] = struct{}{}
	e.hourEntries[entryID] = struct{}{}
	return LimitAllowed
}

// allowEntry is a thin compatibility wrapper around checkEntry for callers
// that only need a yes/no answer (currently the unit tests).
func (al *agentLimiter) allowEntry(agentID, entryID string, maxPerMinute, maxPerHour int) bool {
	return al.checkEntry(agentID, entryID, maxPerMinute, maxPerHour) == LimitAllowed
}

// CORSMiddleware handles CORS headers.
func CORSMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		origin := r.Header.Get("Origin")
		if origin != "" && (strings.Contains(origin, "localhost") || strings.Contains(origin, "127.0.0.1")) {
			w.Header().Set("Access-Control-Allow-Origin", origin)
			w.Header().Set("Vary", "Origin")
		}
		w.Header().Set("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS")
		w.Header().Set("Access-Control-Allow-Headers", "Authorization, Content-Type")
		w.Header().Set("Access-Control-Max-Age", "86400")
		if r.Method == "OPTIONS" {
			w.WriteHeader(http.StatusNoContent)
			return
		}
		next.ServeHTTP(w, r)
	})
}

// SecurityHeadersMiddleware adds security headers.
func SecurityHeadersMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("X-Frame-Options", "DENY")
		w.Header().Set("X-Content-Type-Options", "nosniff")
		w.Header().Set("X-XSS-Protection", "1; mode=block")
		w.Header().Set("Referrer-Policy", "strict-origin-when-cross-origin")
		// CSP: removed unused tailwindcss, tightened img-src to self+data only
		w.Header().Set("Content-Security-Policy", "default-src 'self'; script-src 'self' 'unsafe-inline'; style-src 'self' 'unsafe-inline' https://fonts.googleapis.com; font-src 'self' data: https://fonts.gstatic.com; img-src 'self' data:; connect-src 'self' localhost 127.0.0.1 https://clavitor.ai")
		next.ServeHTTP(w, r)
	})
}

// MaxBodySizeMiddleware limits request body size and rejects binary content.
// Allows 64KB max for markdown notes. Rejects binary data (images, executables, etc).
func MaxBodySizeMiddleware(maxBytes int64) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			// Security: Reject binary content types
			contentType := r.Header.Get("Content-Type")
			if isBinaryContentType(contentType) {
				ErrorResponse(w, http.StatusUnsupportedMediaType, "binary_not_allowed",
					"Binary content not allowed. Only text/markdown data accepted.")
				return
			}
			r.Body = http.MaxBytesReader(w, r.Body, maxBytes)
			next.ServeHTTP(w, r)
		})
	}
}

// isBinaryContentType detects common binary content types.
func isBinaryContentType(ct string) bool {
	ct = strings.ToLower(ct)
	binaryTypes := []string{
		"image/", "audio/", "video/", "application/pdf",
		"application/zip", "application/gzip", "application/octet-stream",
		"application/x-executable", "application/x-dosexec",
		"multipart/form-data", // usually file uploads
	}
	for _, bt := range binaryTypes {
		if strings.Contains(ct, bt) {
			return true
		}
	}
	return false
}

// ErrorResponse sends a JSON error response.
func ErrorResponse(w http.ResponseWriter, status int, code, message string) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	json.NewEncoder(w).Encode(map[string]string{"error": message, "code": code})
}

// JSONResponse sends a JSON success response.
func JSONResponse(w http.ResponseWriter, status int, data any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	json.NewEncoder(w).Encode(data)
}

func realIP(r *http.Request) string {
	if xff := r.Header.Get("X-Forwarded-For"); xff != "" {
		parts := strings.SplitN(xff, ",", 2)
		return strings.TrimSpace(parts[0])
	}
	if xri := r.Header.Get("X-Real-IP"); xri != "" {
		return xri
	}
	addr := r.RemoteAddr
	if idx := strings.LastIndex(addr, ":"); idx != -1 {
		return addr[:idx]
	}
	return addr
}