// Copyright 2024 The ChromiumOS Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

//! Dbus monitor for polling signal from powerd to update power properties.

use std::error::Error;
use std::os::unix::io::RawFd;

use base::AsRawDescriptor;
use base::RawDescriptor;
use base::ReadNotifier;
use dbus::ffidisp::BusType;
use dbus::ffidisp::Connection;
use dbus::ffidisp::ConnectionItem;
use dbus::ffidisp::WatchEvent;
use protobuf::Message;
use remain::sorted;
use thiserror::Error;

use crate::powerd::POWER_INTERFACE_NAME;
use crate::protos::power_supply_properties::PowerSupplyProperties;
use crate::BatteryData;
use crate::PowerData;
use crate::PowerMonitor;

// Signal name from power_manager/dbus_constants.h.
const POLL_SIGNAL_NAME: &str = "PowerSupplyPoll";

#[sorted]
#[derive(Error, Debug)]
pub enum DBusMonitorError {
    #[error("failed to convert protobuf message: {0}")]
    ConvertProtobuf(protobuf::Error),
    #[error("failed to add D-Bus match rule: {0}")]
    DBusAddMatch(dbus::Error),
    #[error("failed to connect to D-Bus: {0}")]
    DBusConnect(dbus::Error),
    #[error("failed to read D-Bus message: {0}")]
    DBusRead(dbus::arg::TypeMismatchError),
    #[error("multiple D-Bus fds")]
    MultipleDBusFd,
    #[error("no D-Bus fd")]
    NoDBusFd,
}

pub struct DBusMonitor {
    connection: Connection,
    connection_fd: RawFd,
    previous_data: Option<BatteryData>,
}

impl DBusMonitor {
    /// Connects and configures a new D-Bus connection to listen for powerd's PowerSupplyPoll
    /// signal.
    pub fn connect() -> std::result::Result<Box<dyn PowerMonitor>, Box<dyn Error>> {
        let connection =
            Connection::get_private(BusType::System).map_err(DBusMonitorError::DBusConnect)?;
        connection
            .add_match(&format!(
                "interface='{}',member='{}'",
                POWER_INTERFACE_NAME, POLL_SIGNAL_NAME
            ))
            .map_err(DBusMonitorError::DBusAddMatch)?;
        // Get the D-Bus connection's fd for async I/O. This should always return a single fd.
        let fds: Vec<RawFd> = connection
            .watch_fds()
            .into_iter()
            .filter(|w| w.readable())
            .map(|w| w.fd())
            .collect();
        if fds.is_empty() {
            return Err(DBusMonitorError::NoDBusFd.into());
        }
        if fds.len() > 1 {
            return Err(DBusMonitorError::MultipleDBusFd.into());
        }
        Ok(Box::new(Self {
            connection,
            connection_fd: fds[0],
            previous_data: None,
        }))
    }
}

fn denoise_value(new_val: u32, prev_val: u32, margin: f64) -> u32 {
    if new_val.abs_diff(prev_val) as f64 / prev_val.min(new_val).max(1) as f64 >= margin {
        new_val
    } else {
        prev_val
    }
}

impl PowerMonitor for DBusMonitor {
    /// Returns the newest pending `PowerData` message, if any.
    /// Callers should poll `PowerMonitor` to determine when messages are available.
    fn read_message(&mut self) -> std::result::Result<Option<PowerData>, Box<dyn Error>> {
        // Select the newest available power message before converting to protobuf.
        let newest_message: Option<dbus::Message> = self
            .connection
            .watch_handle(
                self.connection_fd,
                WatchEvent::Readable as std::os::raw::c_uint,
            )
            .fold(None, |last, item| match item {
                ConnectionItem::Signal(message) => {
                    // Ignore non-matching signals: although match rules are configured, some system
                    // signals can still get through, eg. NameAcquired.
                    let interface = match message.interface() {
                        Some(i) => i,
                        None => {
                            return last;
                        }
                    };

                    if &*interface != POWER_INTERFACE_NAME {
                        return last;
                    }

                    let member = match message.member() {
                        Some(m) => m,
                        None => {
                            return last;
                        }
                    };

                    if &*member != POLL_SIGNAL_NAME {
                        return last;
                    }

                    Some(message)
                }
                _ => last,
            });

        let previous_data = self.previous_data.take();
        match newest_message {
            Some(message) => {
                let data_bytes: Vec<u8> = message.read1().map_err(DBusMonitorError::DBusRead)?;
                let mut props = PowerSupplyProperties::new();
                props
                    .merge_from_bytes(&data_bytes)
                    .map_err(DBusMonitorError::ConvertProtobuf)?;
                let mut data: PowerData = props.into();
                if let (Some(new_data), Some(previous)) = (data.battery.as_mut(), previous_data) {
                    // The raw information from powerd signals isn't really that useful to
                    // the guest. Voltage/current are volatile values, so the .0333 hZ
                    // snapshot provided by powerd isn't particularly meaningful. We do
                    // need to provide *something*, but we might as well make it less noisy
                    // to avoid having the guest try to process mostly useless information.
                    // charge_counter is potentially useful to the guest, but it doesn't
                    // need to be higher precision than battery.percent.
                    new_data.voltage = denoise_value(new_data.voltage, previous.voltage, 0.1);
                    new_data.current = denoise_value(new_data.current, previous.current, 0.1);
                    new_data.charge_counter =
                        denoise_value(new_data.charge_counter, previous.charge_counter, 0.01);
                }
                self.previous_data = data.battery;
                Ok(Some(data))
            }
            None => Ok(None),
        }
    }
}

impl AsRawDescriptor for DBusMonitor {
    fn as_raw_descriptor(&self) -> RawDescriptor {
        self.connection_fd
    }
}

impl ReadNotifier for DBusMonitor {
    fn get_read_notifier(&self) -> &dyn AsRawDescriptor {
        self
    }
}