package handler

import (
	"context"
	"errors"
	"net/http"
	"strings"
	"time"

	"codeberg.org/VARASYS/ZDDC/zddc/internal/auth"
	"codeberg.org/VARASYS/ZDDC/zddc/internal/config"
	"codeberg.org/VARASYS/ZDDC/zddc/internal/policy"
	"log/slog"
)

type contextKey string

// EmailKey is the context key for the authenticated user's email.
const EmailKey contextKey = "email"

// DeciderKey is the context key for the request's policy decider.
// Set by ACLMiddleware so handlers deep in the stack can issue policy
// queries without taking the decider as an explicit parameter. Although
// the decider is an app-wide singleton (not per-request state), routing
// it through context keeps the call-site signatures stable across the
// "swap internal evaluator for external OPA" plumbing change.
const DeciderKey contextKey = "policy-decider"

// ACLMiddleware extracts the user email and stores it (along with the
// policy decider) in the request context. It does NOT enforce ACL
// itself — each handler performs its own ACL check via
// policy.AllowFromChain.
//
// Two email sources, in order:
//
//  1. `Authorization: Bearer <token>` — if present, the token is
//     validated against the supplied auth.Store. On success, the
//     request runs as the token-file's email. On failure (invalid /
//     expired / no validator configured), the middleware short-circuits
//     with 401 — silently falling back to header-based auth would let
//     a misconfigured client masquerade as anonymous.
//  2. Otherwise, the email is read from cfg.EmailHeader, exactly as
//     before. This is the upstream-auth-proxy path (oauth2-proxy,
//     Caddy auth, etc.) that injects the header on validated requests.
//
// `tokens` may be nil — deployments without the token system simply
// reject any Bearer attempts with 401. This keeps Bearer-vs-no-Bearer
// trust paths decoupled from the operator's choice to issue tokens.
func ACLMiddleware(cfg config.Config, decider policy.Decider, tokens *auth.Store, next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		var email string
		if bearer := bearerToken(r); bearer != "" {
			if tokens == nil {
				http.Error(w, "Unauthorized", http.StatusUnauthorized)
				return
			}
			tok, err := tokens.Validate(bearer)
			if err != nil {
				if !errors.Is(err, auth.ErrInvalidToken) {
					slog.Warn("token validation error", "err", err)
				}
				http.Error(w, "Unauthorized", http.StatusUnauthorized)
				return
			}
			email = tok.Email
		} else {
			email = r.Header.Get(cfg.EmailHeader)
		}
		// DEBUG-level header dump for diagnosing proxy / SSO header
		// passthrough. Off by default (LogLevel info); enable with
		// ZDDC_LOG_LEVEL=debug. Logs the configured header name, the
		// observed value at that name, and the full request header
		// map so an operator can see exactly what reached the binary.
		// Note: at debug level this also captures auth tokens, cookies,
		// and anything else upstream proxies forward — only enable in
		// trusted environments.
		slog.Debug("request headers",
			"configured", cfg.EmailHeader,
			"observed", email,
			"headers", r.Header)
		ctx := context.WithValue(r.Context(), EmailKey, email)
		if decider != nil {
			ctx = context.WithValue(ctx, DeciderKey, decider)
		}
		next.ServeHTTP(w, r.WithContext(ctx))
	})
}

// bearerToken returns the token value from the Authorization header
// (case-insensitive on the "Bearer" scheme per RFC 6750), or the empty
// string when no Bearer credential is present.
func bearerToken(r *http.Request) string {
	v := r.Header.Get("Authorization")
	if v == "" {
		return ""
	}
	const prefix = "bearer "
	if len(v) <= len(prefix) || !strings.EqualFold(v[:len(prefix)], prefix) {
		return ""
	}
	return strings.TrimSpace(v[len(prefix):])
}

// EmailFromContext extracts the user email from the request context.
func EmailFromContext(r *http.Request) string {
	if v, ok := r.Context().Value(EmailKey).(string); ok {
		return v
	}
	return ""
}

// WithEmail returns a context carrying email under EmailKey. Test seam
// for handlers that look up the authenticated user via EmailFromContext;
// production traffic gets the same value injected by ACLMiddleware.
func WithEmail(ctx context.Context, email string) context.Context {
	return context.WithValue(ctx, EmailKey, email)
}

// DeciderFromContext extracts the policy decider from the request
// context. Returns the internal decider as a fallback if none was
// installed — this matches the "no OPA configured" semantics and
// keeps test setups that don't install ACLMiddleware functional.
func DeciderFromContext(r *http.Request) policy.Decider {
	if v, ok := r.Context().Value(DeciderKey).(policy.Decider); ok {
		return v
	}
	return &policy.InternalDecider{}
}

// responseWriter wraps http.ResponseWriter to capture status code and bytes written.
type responseWriter struct {
	http.ResponseWriter
	status int
	bytes  int
	wrote  bool
}

// WriteHeader records the status code and writes it to the underlying ResponseWriter.
func (rw *responseWriter) WriteHeader(code int) {
	rw.status = code
	rw.wrote = true
	rw.ResponseWriter.WriteHeader(code)
}

// Write records the bytes written and writes to the underlying ResponseWriter.
func (rw *responseWriter) Write(b []byte) (int, error) {
	n, err := rw.ResponseWriter.Write(b)
	rw.bytes += n
	return n, err
}

// HSTSMiddleware sets the Strict-Transport-Security response header,
// instructing browsers to refuse plain-HTTP connections to this host
// for the next year (NIST SP 800-52 Rev. 2 § 4.4.6, also DoD STIG
// expectation; OWASP recommendation max-age >= 1 year). Use ONLY when
// zddc-server is itself terminating TLS — when an upstream proxy
// terminates, that proxy should set HSTS instead.
//
// includeSubDomains is set; preload is not (preload requires
// pre-submitting the domain to the browser-vendor list — out of
// scope for this server, and operators who want it can override
// upstream).
//
// max-age = 31536000 = 365 days.
func HSTSMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Strict-Transport-Security", "max-age=31536000; includeSubDomains")
		next.ServeHTTP(w, r)
	})
}

// AccessLogMiddleware logs a structured line per HTTP request after the
// response is written.
//
// Always emits to slog.Default() (stderr) so server-lifecycle logs and
// access logs share an output stream by default.
//
// If `auditLogger` is non-nil, the same structured fields are also written
// to it. The intended caller wires up auditLogger with a JSON handler
// pointing at a rotating file (see cmd/zddc-server's setupAccessAuditLog),
// so an operator gets a persisted audit trail on disk in addition to the
// stderr stream — useful when stderr is not journald-captured (e.g.
// container logging where the orchestrator drops stderr after restarts).
func AccessLogMiddleware(auditLogger *slog.Logger, next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// Capture request start time
		start := time.Now()

		// Snapshot the as-typed URL path before downstream handlers may
		// rewrite it (case-insensitive canonicalization). The audit
		// stream records what the client actually sent, not the
		// resolved canonical form.
		requestedPath := r.URL.Path

		// Wrap the ResponseWriter
		wrapped := &responseWriter{ResponseWriter: w, status: 200}

		// Serve the request
		next.ServeHTTP(wrapped, r)

		// Calculate duration
		durationMs := int(time.Since(start).Milliseconds())

		// Get email from context
		email := EmailFromContext(r)
		if email == "" {
			email = "anonymous"
		}

		args := []any{
			"ts", start.Format(time.RFC3339),
			"email", email,
			"method", r.Method,
			"path", requestedPath,
			"status", wrapped.status,
			"bytes", wrapped.bytes,
			"duration_ms", durationMs,
		}
		if r.URL.Path != requestedPath {
			args = append(args, "resolved_path", r.URL.Path)
		}

		// Stderr stream (existing behavior).
		slog.Info("access", args...)

		// Audit file (when configured). Same fields, separate handler so
		// the file can be JSON-formatted regardless of stderr's handler.
		if auditLogger != nil {
			auditLogger.Info("access", args...)
		}
	})
}
