//! Setting the default audio endpoint.
//!
//! Windows exposes no public API for this. `IPolicyConfig` is undocumented, but it is
//! what every audio switcher has used since Vista. If a Windows update ever breaks this
//! tool, this is the file it breaks in.

#![allow(non_snake_case)]

use core::ffi::c_void;

use windows::core::{interface, IUnknown, IUnknown_Vtbl, Result, GUID, HRESULT, PCWSTR};
use windows::Win32::Media::Audio::ERole;
use windows::Win32::System::Com::{CoCreateInstance, CLSCTX_ALL};

/// `CPolicyConfigClient`.
const CLSID_POLICY_CONFIG_CLIENT: GUID = GUID::from_u128(0x870af99c_171d_4f9e_af0d_e63df40c2bc9);

/// Only `SetDefaultEndpoint` is ever called, but every method preceding it in the vtable
/// has to be declared so the slot indices line up. The signatures of the unused ones are
/// irrelevant; their *order* is not — get it wrong and we call the wrong method.
#[interface("f8679f50-850a-41cf-9c72-430f290290c8")]
unsafe trait IPolicyConfig: IUnknown {
    unsafe fn GetMixFormat(&self, id: PCWSTR, format: *mut *mut c_void) -> HRESULT;
    unsafe fn GetDeviceFormat(&self, id: PCWSTR, def: i32, format: *mut *mut c_void) -> HRESULT;
    unsafe fn ResetDeviceFormat(&self, id: PCWSTR) -> HRESULT;
    unsafe fn SetDeviceFormat(&self, id: PCWSTR, end: *mut c_void, mix: *mut c_void) -> HRESULT;
    unsafe fn GetProcessingPeriod(
        &self,
        id: PCWSTR,
        def: i32,
        default_period: *mut i64,
        min_period: *mut i64,
    ) -> HRESULT;
    unsafe fn SetProcessingPeriod(&self, id: PCWSTR, period: *mut i64) -> HRESULT;
    unsafe fn GetShareMode(&self, id: PCWSTR, mode: *mut c_void) -> HRESULT;
    unsafe fn SetShareMode(&self, id: PCWSTR, mode: *mut c_void) -> HRESULT;
    unsafe fn GetPropertyValue(&self, id: PCWSTR, key: *const c_void, value: *mut c_void) -> HRESULT;
    unsafe fn SetPropertyValue(&self, id: PCWSTR, key: *const c_void, value: *mut c_void) -> HRESULT;
    unsafe fn SetDefaultEndpoint(&self, id: PCWSTR, role: ERole) -> HRESULT;
    unsafe fn SetEndpointVisibility(&self, id: PCWSTR, visible: i32) -> HRESULT;
}

/// Make `device_id` the default render endpoint for each of `roles`.
///
/// Roles are applied in order and the first failure aborts — a half-applied switch is
/// more confusing than a clean error.
pub fn set_default(device_id: &str, roles: &[ERole]) -> Result<()> {
    let wide: Vec<u16> = device_id.encode_utf16().chain(core::iter::once(0)).collect();

    unsafe {
        let policy: IPolicyConfig =
            CoCreateInstance(&CLSID_POLICY_CONFIG_CLIENT, None, CLSCTX_ALL)?;

        for role in roles {
            policy.SetDefaultEndpoint(PCWSTR(wide.as_ptr()), *role).ok()?;
        }
    }

    Ok(())
}