package authguard

import (
	"database/sql"
	"encoding/json"
	"errors"
	"github.com/andrew/go-computer/internal/auth"
	"github.com/andrew/go-computer/internal/config"
	"github.com/andrew/go-computer/internal/db"
	"github.com/andrew/go-computer/internal/handlers"
	"log"
	"net/http"
	"time"
)

// errLastAdmin is the transactional refusal to remove the final
// administrator (review H-4). It is raised inside the locked transaction so
// the count and the update cannot be interleaved by a concurrent demotion.
var errLastAdmin = errors.New("at least one administrator must remain")

func HandleAdminListUsers(w http.ResponseWriter, r *http.Request) {
	// COALESCE(email,'') (review COR-8): NOT LIKE evaluates to NULL for the
	// NULL emails OIDC-sourced accounts can carry, which hid them from the
	// admin list entirely.
	v, e := db.Many(r.Context(), db.FromContext(r.Context()), `SELECT jsonb_build_object('id',u.id,'name',u.name,'email',u.email,'image',u.image,'role',u.role,'createdAt',u."createdAt",'_count',jsonb_build_object('bookmarks',(SELECT count(*) FROM "Bookmark" b WHERE b."ownerId"=u.id),'pages',(SELECT count(*) FROM "Page" p WHERE p."ownerId"=u.id),'tags',(SELECT count(*) FROM "Tag" t WHERE t."ownerId"=u.id))) FROM "User" u WHERE COALESCE(email,'') NOT LIKE '%@example.com' ORDER BY "createdAt"`)
	if e != nil {
		handlers.WriteJSON(w, 500, handlers.Error{Error: "Database unavailable"})
		return
	}
	handlers.WriteJSON(w, 200, v)
}
func HandleAdminPatchUser(w http.ResponseWriter, r *http.Request) {
	var b struct {
		UserID string `json:"userId"`
		Role   string `json:"role"`
	}
	if json.NewDecoder(http.MaxBytesReader(w, r.Body, 4096)).Decode(&b) != nil || (b.Role != "USER" && b.Role != "ADMIN") {
		handlers.WriteJSON(w, 400, handlers.Error{Error: "Invalid role"})
		return
	}
	s, _ := auth.SessionFromContext(r.Context())
	if b.UserID == s.RealID && b.Role != "ADMIN" {
		handlers.WriteJSON(w, 400, handlers.Error{Error: "You cannot demote yourself"})
		return
	}
	d := db.FromContext(r.Context())
	repo := db.NewUserRepo(d)
	target, e := repo.FindByID(r.Context(), b.UserID)
	if e != nil {
		handlers.WriteJSON(w, 404, handlers.Error{Error: "Not found"})
		return
	}
	// Review SEC-11/H-4: an installation must keep at least one administrator.
	// Self-demotion is already refused; this closes the "demote the last
	// other admin" path. The role re-read, count and update all run in ONE
	// transaction serialized by an advisory lock, so two admins demoting
	// each other concurrently can no longer both observe admins == 2 and
	// leave zero. The pre-transaction role read above only picks the audit
	// message; the decision uses the locked value.
	if b.Role == "USER" && target.Role == "ADMIN" {
		e = db.Transaction(r.Context(), d, func(tx *sql.Tx) error {
			if _, e := tx.ExecContext(r.Context(), `SELECT pg_advisory_xact_lock(927439)`); e != nil {
				return e
			}
			var current string
			if e := tx.QueryRowContext(r.Context(), `SELECT role FROM "User" WHERE id=$1`, b.UserID).Scan(&current); e != nil {
				return e
			}
			if current == "ADMIN" {
				var admins int
				if e := tx.QueryRowContext(r.Context(), `SELECT count(*) FROM "User" WHERE role='ADMIN' AND COALESCE(email,'') NOT LIKE '%@example.com'`).Scan(&admins); e != nil {
					return e
				}
				if admins <= 1 {
					return errLastAdmin
				}
			}
			_, e := tx.ExecContext(r.Context(), `UPDATE "User" SET role=$1,"updatedAt"=now() WHERE id=$2`, b.Role, b.UserID)
			return e
		})
	} else {
		e = repo.SetRole(r.Context(), b.UserID, b.Role)
	}
	if errors.Is(e, sql.ErrNoRows) {
		handlers.WriteJSON(w, 404, handlers.Error{Error: "Not found"})
		return
	}
	if errors.Is(e, errLastAdmin) {
		handlers.WriteJSON(w, 400, handlers.Error{Error: "At least one administrator must remain"})
		return
	}
	if e != nil {
		handlers.WriteJSON(w, 500, handlers.Error{Error: "Unable to change role"})
		return
	}
	// Review SEC-11: role changes are audited. Ids and roles only.
	log.Printf("audit: admin %s changed role of %s: %s -> %s", s.RealID, b.UserID, target.Role, b.Role)
	handlers.WriteJSON(w, 200, handlers.OK{OK: true})
}
func HandleAdminViewAs(w http.ResponseWriter, r *http.Request) {
	var b struct {
		UserID *string `json:"userId"`
	}
	if json.NewDecoder(http.MaxBytesReader(w, r.Body, 4096)).Decode(&b) != nil {
		handlers.WriteJSON(w, 400, handlers.Error{Error: "Invalid JSON"})
		return
	}
	s, _ := auth.SessionFromContext(r.Context())
	c := http.Cookie{Name: auth.ViewAsCookie, Path: "/", HttpOnly: true, SameSite: http.SameSiteLaxMode, Secure: config.Load().CookieSecure(), MaxAge: -1}
	if b.UserID != nil && *b.UserID != "" && *b.UserID != s.RealID {
		if _, e := db.NewUserRepo(db.FromContext(r.Context())).FindByID(r.Context(), *b.UserID); e != nil {
			handlers.WriteJSON(w, 404, handlers.Error{Error: "Not found"})
			return
		}
		c.Value = *b.UserID
		c.MaxAge = int((8 * time.Hour).Seconds())
	}
	http.SetCookie(w, &c)
	handlers.WriteJSON(w, 200, handlers.OK{OK: true})
}