#pragma once
///@file

#include "installables.hh"
#include "flake/flake.hh"

namespace nix {

struct PackageInfo;
struct SourceExprCommand;

namespace eval_cache { class EvalCache; class AttrCursor; }

struct App
{
    std::vector<DerivedPath> context;
    Path program;
    // FIXME: add args, sandbox settings, metadata, ...
};

struct UnresolvedApp
{
    App unresolved;
    App resolve(ref<Store> evalStore, ref<Store> store);
};

/**
 * Extra info about a \ref DerivedPath "derived path" that ultimately
 * come from a Nix language value.
 *
 * Invariant: every ExtraPathInfo gotten from an InstallableValue should
 * be possible to downcast to an ExtraPathInfoValue.
 */
struct ExtraPathInfoValue : ExtraPathInfo
{
    /**
     * Extra struct to get around C++ designated initializer limitations
     */
    struct Value {
        /**
         * An optional priority for use with "build envs". See Package
         */
        std::optional<NixInt> priority;

        /**
         * The attribute path associated with this value. The idea is
         * that an installable referring to a value typically refers to
         * a larger value, from which we project a smaller value out
         * with this.
         */
        std::string attrPath;

        /**
         * \todo merge with DerivedPath's 'outputs' field?
         */
        ExtendedOutputsSpec extendedOutputsSpec;
    };

    Value value;

    ExtraPathInfoValue(Value && v)
        : value(v)
    { }

    virtual ~ExtraPathInfoValue() = default;
};

/**
 * An Installable which corresponds a Nix language value, in addition to
 * a collection of \ref DerivedPath "derived paths".
 */
struct InstallableValue : Installable
{
    ref<EvalState> state;

    InstallableValue(ref<EvalState> state) : state(state) {}

    virtual ~InstallableValue() { }

    virtual std::pair<Value *, PosIdx> toValue(EvalState & state) = 0;

    /**
     * Get a cursor to each value this Installable could refer to.
     * However if none exists, throw exception instead of returning
     * empty vector.
     */
    virtual std::vector<ref<eval_cache::AttrCursor>>
    getCursors(EvalState & state);

    /**
     * Get the first and most preferred cursor this Installable could
     * refer to, or throw an exception if none exists.
     */
    virtual ref<eval_cache::AttrCursor>
    getCursor(EvalState & state);

    UnresolvedApp toApp(EvalState & state);

    static InstallableValue & require(Installable & installable);
    static ref<InstallableValue> require(ref<Installable> installable);

protected:

    /**
     * Handles either a plain path, or a string with a single string
     * context elem in the right format. The latter case is handled by
     * `EvalState::coerceToDerivedPath()`; see it for details.
     *
     * @param v Value that is hopefully a string or path per the above.
     *
     * @param pos Position of value to aid with diagnostics.
     *
     * @param errorCtx Arbitrary message for use in potential error message when something is wrong with `v`.
     *
     * @result A derived path (with empty info, for now) if the value
     * matched the above criteria.
     */
    std::optional<DerivedPathWithInfo> trySinglePathToDerivedPaths(Value & v, const PosIdx pos, std::string_view errorCtx);
};

}
