const c = @import("c.zig");

const Loop = @import("Loop.zig");
const errors = @import("error.zig");

/// Returns a struct that has all the shared handle functions for the
/// given handle type T. The type T must have a field named "handle".
/// This is expected to be used with usingnamespace to add the shared
/// handler functions to other handle types.
pub fn Handle(comptime T: type) type {
    // 1. T should be a struct
    // 2. First field should be the handle pointer

    return struct {
        // note: this has to be here: https://github.com/ziglang/zig/issues/11367
        const tInfo = @typeInfo(T).Struct;
        const HandleType = tInfo.fields[0].field_type;

        // Request handle to be closed. close_cb will be called asynchronously
        // after this call. This MUST be called on each handle before memory
        // is released. Moreover, the memory can only be released in close_cb
        // or after it has returned.
        //
        // Handles that wrap file descriptors are closed immediately but
        // close_cb will still be deferred to the next iteration of the event
        // loop. It gives you a chance to free up any resources associated with
        // the handle.
        //
        // In-progress requests, like uv_connect_t or uv_write_t, are cancelled
        // and have their callbacks called asynchronously with status=UV_ECANCELED.
        pub fn close(self: T, comptime cb: ?fn (*T) void) void {
            const cbParam = if (cb) |f|
                (struct {
                    pub fn callback(handle: [*c]c.uv_handle_t) callconv(.C) void {
                        // We get the raw handle, so we need to reconstruct
                        // the T. This is mutable because a lot of the libuv APIs
                        // are non-const but modifying it makes no sense.
                        var param: T = .{ .handle = @ptrCast(HandleType, handle) };
                        @call(.{ .modifier = .always_inline }, f, .{&param});
                    }
                }).callback
            else
                null;

            c.uv_close(@ptrCast(*c.uv_handle_t, self.handle), cbParam);
        }

        /// Loop returns the loop that this handle is a part of.
        pub fn loop(self: T) Loop {
            const handle = @ptrCast(*c.uv_handle_t, self.handle);
            return .{ .loop = c.uv_handle_get_loop(handle) };
        }

        /// Returns non-zero if the handle is active, zero if it’s inactive.
        /// Rule of thumb: if a handle of type uv_foo_t has a uv_foo_start()
        /// function, then it’s active from the moment that function is called.
        /// Likewise, uv_foo_stop() deactivates the handle again.
        pub fn isActive(self: T) !bool {
            const res = c.uv_is_active(@ptrCast(*c.uv_handle_t, self.handle));
            try errors.convertError(res);
            return res > 0;
        }

        /// Sets handle->data to data.
        pub fn setData(self: T, pointer: ?*anyopaque) void {
            c.uv_handle_set_data(
                @ptrCast(*c.uv_handle_t, self.handle),
                pointer,
            );
        }

        /// Returns handle->data.
        pub fn getData(self: T, comptime DT: type) ?*DT {
            return if (c.uv_handle_get_data(@ptrCast(*c.uv_handle_t, self.handle))) |ptr|
                @ptrCast(?*DT, @alignCast(@alignOf(DT), ptr))
            else
                null;
        }
    };
}