#include <nix/expr/primops.hh>
#include <nix/expr/eval.hh>
#include <nix/expr/eval-inline.hh>
#include <nix/expr/nixexpr.hh>
#include <nix/expr/attr-set.hh>

using namespace nix;

static void prim_scope(EvalState & state, const PosIdx pos, Value ** args, Value & v)
{
    std::vector<Symbol> path;

    state.forceStringNoCtx(*args[0], pos, "'scope' path argument");
    auto s = std::string(args[0]->string_view());
    if (s.empty())
        state.error<TypeError>("'scope' requires a non-empty path")
            .atPos(pos)
            .debugThrow();
    size_t start = 0;
    while (start < s.size()) {
        auto dot = s.find('.', start);
        if (dot == std::string::npos) {
            path.push_back(state.symbols.create(s.substr(start)));
            break;
        }
        path.push_back(state.symbols.create(s.substr(start, dot - start)));
        start = dot + 1;
    }

    // Build nested attrset from inside out
    // Given path [a, b, c] and value v: { a = { b = { c = v; }; }; }
    Value * inner = args[1];
    for (auto it = path.rbegin(); it != path.rend(); ++it) {
        auto attrs = state.buildBindings(1);
        attrs.insert(*it, inner);
        Value * wrapper = state.allocValue();
        wrapper->mkAttrs(attrs.finish());
        inner = wrapper;
    }
    v = *inner;
}

static RegisterPrimOp rp({
    .name = "scope",
    .args = {"path", "value"},
    .doc = R"(
      Construct a nested attribute set from a dotted string path and a value.

      Example: `scope "a.b.c" 42` evaluates to `{ a = { b = { c = 42; }; }; }`.
    )",
    .fun = prim_scope,
});