package api

import (
	"errors"
	"net/http"
	"regexp"
	"time"

	"messenger/internal/auth"
	"messenger/internal/store"
)

var usernameRe = regexp.MustCompile(`^[a-z0-9_]{3,32}$`)

type userJSON struct {
	ID          int64     `json:"id"`
	Username    string    `json:"username"`
	DisplayName string    `json:"display_name"`
	Avatar      string    `json:"avatar"`
	CreatedAt   time.Time `json:"created_at"`
}

func toUserJSON(u *store.User) userJSON {
	return userJSON{
		ID:          u.ID,
		Username:    u.Username,
		DisplayName: u.DisplayName,
		Avatar:      u.Avatar,
		CreatedAt:   u.CreatedAt,
	}
}

type credentialsRequest struct {
	Username    string `json:"username"`
	DisplayName string `json:"display_name"`
	Password    string `json:"password"`
}

func (h *apiHandler) register(w http.ResponseWriter, r *http.Request) {
	var req credentialsRequest
	if !decodeJSON(w, r, &req) {
		return
	}
	if !usernameRe.MatchString(req.Username) {
		writeError(w, http.StatusBadRequest, "username must be 3-32 chars of [a-z0-9_]")
		return
	}
	if req.DisplayName == "" || len(req.DisplayName) > 64 {
		writeError(w, http.StatusBadRequest, "display_name must be 1-64 chars")
		return
	}
	if len(req.Password) == 0 || len(req.Password) > 128 {
		writeError(w, http.StatusBadRequest, "password must be 1-128 chars")
		return
	}

	hash, err := auth.HashPassword(req.Password)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	user, err := h.store.CreateUser(r.Context(), req.Username, req.DisplayName, hash)
	if err != nil {
		if errors.Is(err, store.ErrDuplicate) {
			writeError(w, http.StatusConflict, "username already taken")
			return
		}
		writeError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	h.issueSession(w, r, user.ID)
	writeJSON(w, http.StatusCreated, toUserJSON(user))
}

func (h *apiHandler) login(w http.ResponseWriter, r *http.Request) {
	var req credentialsRequest
	if !decodeJSON(w, r, &req) {
		return
	}
	user, err := h.store.GetUserByUsername(r.Context(), req.Username)
	if err != nil {
		if errors.Is(err, store.ErrNotFound) {
			writeError(w, http.StatusUnauthorized, "invalid credentials")
			return
		}
		writeError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	ok, err := auth.VerifyPassword(user.PasswordHash, req.Password)
	if err != nil || !ok {
		writeError(w, http.StatusUnauthorized, "invalid credentials")
		return
	}
	h.issueSession(w, r, user.ID)
	writeJSON(w, http.StatusOK, toUserJSON(user))
}

func (h *apiHandler) refresh(w http.ResponseWriter, r *http.Request) {
	cookie, err := r.Cookie(refreshCookieName)
	if err != nil {
		writeError(w, http.StatusUnauthorized, "missing refresh token")
		return
	}
	session, err := h.store.GetSessionByRefreshHash(r.Context(), auth.HashRefreshToken(cookie.Value))
	if err != nil {
		writeError(w, http.StatusUnauthorized, "invalid refresh token")
		return
	}
	if session.RevokedAt != nil {
		writeError(w, http.StatusUnauthorized, "session revoked")
		return
	}
	if time.Now().After(session.ExpiresAt) {
		writeError(w, http.StatusUnauthorized, "session expired")
		return
	}

	// Rotation: revoke the used session and issue a fresh pair.
	if err := h.store.RevokeSession(r.Context(), session.ID); err != nil {
		writeError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	h.issueSession(w, r, session.UserID)
	writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
}

func (h *apiHandler) logout(w http.ResponseWriter, r *http.Request) {
	if cookie, err := r.Cookie(refreshCookieName); err == nil {
		session, err := h.store.GetSessionByRefreshHash(r.Context(), auth.HashRefreshToken(cookie.Value))
		if err == nil {
			_ = h.store.RevokeSession(r.Context(), session.ID)
		}
	}
	clearAuthCookies(w)
	writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
}

func (h *apiHandler) me(w http.ResponseWriter, r *http.Request) {
	userID, ok := userIDFrom(r.Context())
	if !ok {
		writeError(w, http.StatusUnauthorized, "unauthenticated")
		return
	}
	user, err := h.store.GetUserByID(r.Context(), userID)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	writeJSON(w, http.StatusOK, toUserJSON(user))
}

func (h *apiHandler) issueSession(w http.ResponseWriter, r *http.Request, userID int64) {
	access, err := h.tokens.IssueAccessToken(userID, accessTTL)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	rawRefresh, refreshHash, err := auth.GenerateRefreshToken()
	if err != nil {
		writeError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	_, err = h.store.CreateSession(r.Context(), userID, refreshHash, r.UserAgent(), r.RemoteAddr, time.Now().Add(refreshTTL))
	if err != nil {
		writeError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	setAuthCookies(w, access, rawRefresh, h.secure)
}