#include "traceback.hpp"

#define TRACEBACK_LEVELS1 12
#define TRACEBACK_LEVELS2 10


// Call this with the error message on top of the stack.
static void traceback_general(lua_State *L, lua_State *L1, int baselevel) {
    int top = lua_gettop(L);

    // Convert message to a string
    if (!lua_tostring(L, top)) {
        luaL_callmeta(L, top, "__tostring");
        // If callmeta didn't produce exactly one string, clear the stack
        // and push "unknown error"
        if ((lua_gettop(L) == top + 1) && (lua_tostring(L, -1))) {
            lua_remove(L, top);
        } else {
            lua_settop(L, top - 1);
            lua_pushstring(L, "unknown error");
        }
    }

    // Append the traceback.
    lua_Debug ar;
    int level = baselevel;
    int firstpart = 1;
    while (lua_getstack(L1, level++, &ar)) {
        if (level > TRACEBACK_LEVELS1 && firstpart) {
            /* no more than `LEVELS2' more levels? */
            if (!lua_getstack(L1, level + TRACEBACK_LEVELS2, &ar))
                level--; /* keep going */
            else {
                lua_pushliteral(L, "\n\t...");                 /* too many levels */
                while (lua_getstack(L1, level + TRACEBACK_LEVELS2, &ar)) /* find last levels */
                    level++;
            }
            firstpart = 0;
            continue;
        }
        lua_getinfo(L1, "Snl", &ar);
        if ((ar.currentline > 0) || (*ar.namewhat != 0) || (*ar.what != 'C')) {
            lua_pushliteral(L, "\n\t");
            lua_pushfstring(L, "%s:", ar.short_src);
            if (ar.currentline > 0)
                lua_pushfstring(L, "%d:", ar.currentline);
            if (*ar.namewhat != '\0') /* is there a name? */
                lua_pushfstring(L, " in function " LUA_QS, ar.name);
            else {
                if (*ar.what == 'm') /* main? */
                    lua_pushfstring(L, " in main chunk");
                else if (*ar.what == 'C' || *ar.what == 't')
                    lua_pushliteral(L, " ?"); /* C function or tail call */
                else
                    lua_pushfstring(L, " in function <%s:%d>",
                                    ar.short_src, ar.linedefined);
            }
            if (1 + lua_gettop(L) - top > 5) {
                lua_concat(L, 1 + lua_gettop(L) - top);
            }
        }
    }
    lua_pushstring(L, "\n");
    if (1 + lua_gettop(L) - top > 1) {
        lua_concat(L, 1 + lua_gettop(L) - top);
    }
}

int traceback_handler(lua_State *L) {
    traceback_general(L, L, 1);
    return 1;
}

void traceback_coroutine(lua_State *L, lua_State *CO) {
    lua_xmove(CO, L, 1);
    traceback_general(L, CO, 0);
}

int traceback_pcall(lua_State *L, int narg, int nret) {
    int status;
    int base = lua_gettop(L) - narg; /* function index */
    lua_pushcfunction(L, traceback_handler); /* push traceback function */
    lua_insert(L, base);             /* put it under chunk and args */
    status = lua_pcall(L, narg, nret, base);
    lua_remove(L, base); /* remove traceback function */
    return status;
}