// RFC 6749 authorization endpoint for MCP OAuth, ported from PHP
// OAuthAuthorizeController::authorize byte-for-byte including its
// validation order (08-CONTEXT.md D-02/D-04/D-05; canonical PHP source:
// OAuthAuthorizeController.php).
//
// D-02: query-only parsing (no body is ever read). The client and the exact
// registered redirect URI are validated before any redirect response is
// constructed (T-08-OPEN-REDIRECT): an unknown client or unregistered
// redirect is a local text/plain 400 with no Location header. Every later
// failure redirects to the now-trusted redirect_uri with an ordered
// error/error_description/iss[/state] query built through an RFC 3986
// encoder, never url.Values.Encode (08-RESEARCH.md Pattern 3/Pitfall 5).
package wristband

import (
	"fmt"
	"net/http"
	"strings"
)

// authorizeAllowedScopes mirrors PHP OAuthAuthorizeController::ALLOWED_SCOPES.
var authorizeAllowedScopes = map[string]bool{
	"read": true, "write": true, "ai": true, "offline_access": true,
}

// Authorize handles GET /oauth/mcp/authorize (D-09: raw route, no
// middleware). It validates the client and exact redirect before any
// redirect response, enforces S256 PKCE syntax, the client's scope ceiling,
// and the RFC 8707 resource check, then persists an opaque pending request
// and redirects to the app's /connect handoff.
func (s *Server) Authorize(w http.ResponseWriter, r *http.Request) {
	if s.backend == nil {
		w.WriteHeader(http.StatusInternalServerError)
		return
	}

	ctx := r.Context()
	q := r.URL.Query()

	clientID := q.Get("client_id")
	var client *ClientRecord
	if clientID != "" {
		err := s.backend.WithinTx(ctx, func(tx Tx) error {
			c, err := tx.ByClientID(ctx, clientID)
			if err != nil {
				return err
			}
			client = c
			return nil
		})
		if err != nil {
			w.WriteHeader(http.StatusInternalServerError)
			return
		}
	}
	if client == nil || client.RevokedAt != nil {
		writeAuthorizeLocalError(w, "Unknown client.")
		return
	}

	redirectURI := q.Get("redirect_uri")
	if redirectURI == "" || !stringSliceContains(client.RedirectURIs, redirectURI) {
		writeAuthorizeLocalError(w, "Unregistered redirect URI.")
		return
	}

	var state *string
	if v := q.Get("state"); v != "" {
		state = &v
	}

	if q.Get("response_type") != "code" {
		s.authorizeErrorRedirect(w, redirectURI, "unsupported_response_type", "response_type must be code", state)
		return
	}

	if q.Get("code_challenge_method") != "S256" {
		s.authorizeErrorRedirect(w, redirectURI, "invalid_request", "code_challenge_method must be S256", state)
		return
	}

	challenge := q.Get("code_challenge")
	if l := len(challenge); l < 43 || l > 128 {
		s.authorizeErrorRedirect(w, redirectURI, "invalid_request", "code_challenge is required", state)
		return
	}

	scopes, scopeErr := parseAuthorizeScopes(q.Get("scope"))
	if scopeErr != "" {
		s.authorizeErrorRedirect(w, redirectURI, "invalid_scope", scopeErr, state)
		return
	}

	// Phase 07.13 (D-10/D-11/D-12 in the PHP source comment): a nil ceiling
	// is a no-op; offline_access always survives truncation because it is
	// peeled into a boolean below, not a data scope; truncating here (not
	// rejecting) means an over-broad request silently narrows instead of
	// failing, except when nothing data-bearing survives.
	if client.ScopeCeiling != nil {
		kept := make([]string, 0, len(scopes))
		for _, sc := range scopes {
			if sc == "offline_access" || stringSliceContains(client.ScopeCeiling, sc) {
				kept = append(kept, sc)
			}
		}
		dataScopes := make([]string, 0, len(kept))
		for _, sc := range kept {
			if sc != "offline_access" {
				dataScopes = append(dataScopes, sc)
			}
		}
		if len(dataScopes) == 0 {
			s.authorizeErrorRedirect(w, redirectURI, "invalid_scope", "requested scope is outside this client's ceiling", state)
			return
		}
		scopes = kept
	}

	var resource *string
	if v := q.Get("resource"); v != "" {
		resource = &v
	}
	if resource != nil && *resource != s.opts.Resource {
		s.authorizeErrorRedirect(w, redirectURI, "invalid_target", "resource does not match this server", state)
		return
	}

	// createPendingRequest (PHP OAuthCodeManager): peel offline_access into
	// a boolean flag; the persisted scopes list never contains it.
	offline := false
	dataScopes := make([]string, 0, len(scopes))
	for _, sc := range scopes {
		if sc == "offline_access" {
			offline = true
			continue
		}
		dataScopes = append(dataScopes, sc)
	}

	requestID, err := s.randomBytes(32)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		return
	}

	rec := &AuthCodeRecord{
		RequestID:           &requestID,
		ClientID:            client.ClientID,
		RedirectURI:         redirectURI,
		Scopes:              dataScopes,
		CodeChallenge:       challenge,
		CodeChallengeMethod: "S256",
		Resource:            resource,
		State:               state,
		ExpiresAt:           s.now().Add(s.opts.PendingRequestTTL),
		OfflineAccess:       offline,
	}
	err = s.backend.WithinTx(ctx, func(tx Tx) error {
		return tx.CreatePending(ctx, rec)
	})
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		return
	}

	spa := s.opts.Issuer + "/connect?request=" + rfc3986Escape(requestID)
	// Laravel appends ", private" to every explicit Cache-Control this
	// endpoint sets (session-cookie default merge); recorded PHP traffic is
	// "no-store, private", never a bare "no-store" (D-04, live-recorded byte
	// contract, 08-09-PLAN.md Task 2).
	w.Header().Set("Cache-Control", "no-store, private")
	writeRedirectHTML(w, http.StatusFound, spa)
}

// writeAuthorizeLocalError writes the PHP localError() response: a bare
// text/plain 400 with no Location and no house envelope
// (T-08-OPEN-REDIRECT).
func writeAuthorizeLocalError(w http.ResponseWriter, message string) {
	w.Header().Set("Cache-Control", "no-store, private")
	w.Header().Set("Content-Type", "text/plain; charset=UTF-8")
	w.WriteHeader(http.StatusBadRequest)
	_, _ = w.Write([]byte(message))
}

// authorizeErrorRedirect ports OAuthAuthorizeController::errorRedirect: an
// ordered error/error_description/iss[/state] query appended to the
// already-trusted redirectURI via RFC 3986 encoding (D-04/Pattern 3).
func (s *Server) authorizeErrorRedirect(w http.ResponseWriter, redirectURI, errCode, description string, state *string) {
	pairs := [][2]string{
		{"error", errCode},
		{"error_description", description},
		{"iss", s.opts.Issuer},
	}
	if state != nil {
		pairs = append(pairs, [2]string{"state", *state})
	}
	w.Header().Set("Cache-Control", "no-store, private")
	writeRedirectHTML(w, http.StatusFound, appendOrderedQuery(redirectURI, pairs))
}

// parseAuthorizeScopes ports OAuthAuthorizeController::parseScopes. An
// absent or empty scope query value defaults to ["read"]; otherwise every
// whitespace-separated token must be one of authorizeAllowedScopes.
func parseAuthorizeScopes(raw string) ([]string, string) {
	parts := strings.Fields(strings.TrimSpace(raw))
	if len(parts) == 0 {
		return []string{"read"}, ""
	}
	for _, p := range parts {
		if !authorizeAllowedScopes[p] {
			return nil, "scope contains an unsupported value"
		}
	}
	return parts, ""
}

// stringSliceContains reports whether ss contains v.
func stringSliceContains(ss []string, v string) bool {
	for _, s := range ss {
		if s == v {
			return true
		}
	}
	return false
}

// rfc3986Escape percent-encodes s per RFC 3986 (PHP rawurlencode/
// PHP_QUERY_RFC3986): unreserved characters A-Z a-z 0-9 - _ . ~ pass
// through unescaped; everything else, including the space byte, becomes an
// uppercase %XX triplet. This intentionally differs from
// net/url.QueryEscape (form-style '+' for space, different reserved-char
// handling), which would corrupt the exact PHP redirect-byte contract
// (08-RESEARCH.md Pattern 3/Pitfall 5).
func rfc3986Escape(s string) string {
	var b strings.Builder
	b.Grow(len(s))
	for i := 0; i < len(s); i++ {
		c := s[i]
		if isRFC3986Unreserved(c) {
			b.WriteByte(c)
		} else {
			fmt.Fprintf(&b, "%%%02X", c)
		}
	}
	return b.String()
}

func isRFC3986Unreserved(c byte) bool {
	return (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') || (c >= '0' && c <= '9') ||
		c == '-' || c == '_' || c == '.' || c == '~'
}

// buildOrderedQuery RFC3986-encodes and joins pairs in the given order
// (never net/url.Values.Encode, which sorts keys and space-encodes as '+').
func buildOrderedQuery(pairs [][2]string) string {
	parts := make([]string, len(pairs))
	for i, p := range pairs {
		parts[i] = rfc3986Escape(p[0]) + "=" + rfc3986Escape(p[1])
	}
	return strings.Join(parts, "&")
}

// appendOrderedQuery ports OAuthAuthorizeController::appendQuery: appends an
// ordered RFC 3986 query to uri, using '&' when uri already carries a query
// string and '?' otherwise.
func appendOrderedQuery(uri string, pairs [][2]string) string {
	sep := "?"
	if strings.Contains(uri, "?") {
		sep = "&"
	}
	return uri + sep + buildOrderedQuery(pairs)
}