package httpapi

import (
	"context"
	"encoding/base64"
	"encoding/json"
	"net/http"
	"strings"
)

// User is the authenticated principal carried on the request context. Identity
// comes from oauth2-proxy (Keycloak) in production; spin matches it to a Member
// row by email to resolve rank/role/admin within the app.
type User struct {
	ID           string   `json:"id"`
	Name         string   `json:"name"`
	Email        string   `json:"email"`
	Role         string   `json:"role"`
	Groups       []string `json:"groups,omitempty"`
	IsSuperAdmin bool     `json:"isSuperAdmin"`
}

type ctxKey string

const userKey ctxKey = "user"

// devUser is the fixed identity injected when DEV_AUTH is enabled (local dev).
var devUser = User{ID: "u-admin", Name: "관리자", Email: "theorose49@gmail.com", Role: "관리자", Groups: []string{"admin"}}

// authMiddleware injects the authenticated user into the request context.
//
//   - DEV_AUTH=true  → a fixed mock identity (local development).
//   - DEV_AUTH=false → the identity forwarded by oauth2-proxy after a successful
//     Keycloak login (X-Forwarded-* / X-Auth-Request-* headers + token claims).
//     The backend trusts these headers because it is only reachable behind the
//     proxy; requests without them are rejected.
func authMiddleware(devAuth bool, adminGroups []string) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			var u User
			if devAuth {
				u = devUser
				// Local dev runs as a super-admin so every screen is reachable.
				// Append ?as=user to any request to simulate a non-admin member.
				u.IsSuperAdmin = r.URL.Query().Get("as") != "user"
				if !u.IsSuperAdmin {
					u = User{ID: "u-member", Name: "김주임", Email: "member@special-partners.com", Role: "주임", Groups: []string{"user"}}
				}
			} else {
				var ok bool
				u, ok = userFromProxyHeaders(r)
				if !ok {
					writeError(w, http.StatusUnauthorized, "not authenticated (oauth2-proxy headers missing)")
					return
				}
				u.IsSuperAdmin = groupsIntersect(u.Groups, adminGroups)
			}
			ctx := context.WithValue(r.Context(), userKey, u)
			next.ServeHTTP(w, r.WithContext(ctx))
		})
	}
}

// groupsIntersect reports whether any of the user's groups is in adminGroups
// (case-insensitive).
func groupsIntersect(groups, adminGroups []string) bool {
	for _, g := range groups {
		for _, a := range adminGroups {
			if strings.EqualFold(strings.TrimSpace(g), strings.TrimSpace(a)) {
				return true
			}
		}
	}
	return false
}

// userFromProxyHeaders builds the principal from the headers oauth2-proxy
// injects. It prefers the X-Forwarded-* headers (--pass-user-headers), falls
// back to X-Auth-Request-* (--set-xauthrequest), and enriches the display name
// and role from the forwarded access-token claims when available.
func userFromProxyHeaders(r *http.Request) (User, bool) {
	hdr := func(keys ...string) string {
		for _, k := range keys {
			if v := strings.TrimSpace(r.Header.Get(k)); v != "" {
				return v
			}
		}
		return ""
	}

	email := hdr("X-Forwarded-Email", "X-Auth-Request-Email")
	username := hdr("X-Forwarded-Preferred-Username", "X-Auth-Request-Preferred-Username",
		"X-Forwarded-User", "X-Auth-Request-User")
	groups := splitGroups(hdr("X-Forwarded-Groups", "X-Auth-Request-Groups"))

	claims := decodeTokenClaims(r)
	if username == "" {
		username = firstNonEmpty(claims.PreferredUsername, claims.Sub)
	}
	if email == "" {
		email = claims.Email
	}
	if len(groups) == 0 {
		groups = splitGroups(strings.Join(claims.Groups, ","))
	}

	// No identifying header at all → request did not come through oauth2-proxy.
	if username == "" && email == "" {
		return User{}, false
	}

	return User{
		ID:     firstNonEmpty(email, username, claims.Sub),
		Name:   firstNonEmpty(claims.Name, username, email),
		Email:  email,
		Role:   deriveRole(groups, claims.RealmAccess.Roles),
		Groups: groups,
	}, true
}

// oidcClaims is the subset of Keycloak token claims we read.
type oidcClaims struct {
	Sub               string   `json:"sub"`
	Name              string   `json:"name"`
	PreferredUsername string   `json:"preferred_username"`
	Email             string   `json:"email"`
	Groups            []string `json:"groups"`
	RealmAccess       struct {
		Roles []string `json:"roles"`
	} `json:"realm_access"`
}

// decodeTokenClaims reads the forwarded access token and decodes its JWT payload
// WITHOUT signature verification — oauth2-proxy already validated it upstream and
// the backend is only reachable behind the proxy. Returns zero claims if absent.
func decodeTokenClaims(r *http.Request) oidcClaims {
	var c oidcClaims
	tok := firstNonEmpty(
		r.Header.Get("X-Forwarded-Access-Token"),
		r.Header.Get("X-Auth-Request-Access-Token"),
	)
	if tok == "" {
		if a := r.Header.Get("Authorization"); strings.HasPrefix(a, "Bearer ") {
			tok = strings.TrimSpace(strings.TrimPrefix(a, "Bearer "))
		}
	}
	if tok == "" {
		return c
	}
	parts := strings.Split(tok, ".")
	if len(parts) < 2 {
		return c
	}
	payload, err := base64.RawURLEncoding.DecodeString(parts[1])
	if err != nil {
		if payload, err = base64.URLEncoding.DecodeString(parts[1]); err != nil {
			return c
		}
	}
	_ = json.Unmarshal(payload, &c)
	return c
}

var ignoredRealmRoles = map[string]bool{"offline_access": true, "uma_authorization": true}

// deriveRole picks a human-readable role for display: the first Keycloak group,
// else the first non-default realm role, else "구성원".
func deriveRole(groups, realmRoles []string) string {
	for _, g := range groups {
		if g != "" {
			return g
		}
	}
	for _, role := range realmRoles {
		if role == "" || ignoredRealmRoles[role] || strings.HasPrefix(role, "default-roles") {
			continue
		}
		return role
	}
	return "구성원"
}

func splitGroups(raw string) []string {
	var out []string
	for _, g := range strings.Split(raw, ",") {
		g = strings.TrimPrefix(strings.TrimSpace(g), "/")
		if g != "" {
			out = append(out, g)
		}
	}
	return out
}

func firstNonEmpty(vals ...string) string {
	for _, v := range vals {
		if strings.TrimSpace(v) != "" {
			return v
		}
	}
	return ""
}

// currentUser returns the authenticated user from context.
func currentUser(ctx context.Context) User {
	if u, ok := ctx.Value(userKey).(User); ok {
		return u
	}
	return devUser
}