pub use crate::arch::ProcessContext;
use core::{mem, slice};
use xous::{CtxID, MemoryAddress, MemoryRange, MemorySize, PID, SID, Message};

pub struct SenderID {
    pub sidx: usize,
    pub tidx: usize,
}

impl SenderID {
    pub fn from_usize(src: usize) -> Result<SenderID, xous::Error> {
        Ok(SenderID {
            sidx: src >> 16,
            tidx: src & 0xffff,
        })
    }
}

/// Internal representation of a queued message for a server. This should be
/// exactly 8 words / 32 bytes, yielding 128 queued messages per server
#[repr(usize)]
#[derive(PartialEq, Debug)]
enum QueuedMessage {
    Empty,
    ScalarMessage(
        usize, /* sender PID/CtxID */
        usize, /* sender base address */
        usize, /* id */
        usize, /* arg1 */
        usize, /* arg2 */
        usize, /* arg3 */
        usize, /* arg4 */
    ),
    MemoryMessageSend(
        usize, /* sender PID/CtxID */
        usize, /* reserved */
        usize, /* id */
        usize, /* buf */
        usize, /* buf_size */
        usize, /* offset */
        usize, /* valid */
    ),
    MemoryMessageROLend(
        usize, /* sender PID/CtxID */
        usize, /* sender base address */
        usize, /* id */
        usize, /* buf */
        usize, /* buf_size */
        usize, /* offset */
        usize, /* valid */
    ),
    MemoryMessageRWLend(
        usize, /* sender PID/CtxID */
        usize, /* sender base address */
        usize, /* id */
        usize, /* buf */
        usize, /* buf_size */
        usize, /* offset */
        usize, /* valid */
    ),

    /// When a message is taken that needs to be returned -- such as an ROLend
    /// or RWLend -- the slot is replaced with a WaitingResponse token and its
    /// index is returned as the message sender.  This is used to unblock the
    /// sending process.
    WaitingResponse(
        usize, /* sender PID/CtxID */
        usize, /* Client base address */
        usize, /* Server base address */
        usize, /* Range size */
    ),
}

/// A pointer to resolve a server ID to a particular process
#[derive(PartialEq)]
pub struct Server {
    /// A randomly-generated ID
    pub sid: SID,

    /// The process that owns this server
    pub pid: PID,

    /// An index into the queue
    queue_head: usize,

    queue_tail: usize,

    /// Where data will appear
    queue: &'static mut [QueuedMessage],

    /// The `context mask` is a bitfield of contexts that are able to handle
    /// this message. If there are no available contexts, then messages will
    /// need to be queued.
    ready_contexts: CtxID,
}

impl Server {
    pub fn init(
        new: &mut Option<Server>,
        pid: PID,
        sid: SID,
        queue_addr: *mut usize,
        queue_size: usize,
    ) -> Result<(), xous::Error> {
        if new != &None {
            return Err(xous::Error::MemoryInUse);
        }

        let queue = unsafe {
            slice::from_raw_parts_mut(
                queue_addr as *mut QueuedMessage,
                queue_size / mem::size_of::<QueuedMessage>(),
            )
        };

        *new = Some(Server {
            sid,
            pid,
            queue_head: 0,
            queue_tail: 0,
            queue,
            ready_contexts: 0,
        });
        Ok(())
    }

    pub fn print_queue(&self) {
        println!("    Q Queue Head: {}", self.queue_head);
        println!("    Q Queue Tail: {}", self.queue_tail);
        for (_idx, _entry) in self.queue.iter().enumerate() {
            if _entry != &QueuedMessage::Empty {
                println!("    Q  entry[{}]: {:?}", _idx, _entry);
            }
        }
    }

    /// Convert a `QueuedMesage::WaitingResponse` into `QueuedMessage::Empty`
    /// and return the pair.  Advance the tail.  Note that the `idx` could be
    /// somewhere other than the tail, but as long as it points to a valid
    /// message that's waiting a response, that's acceptable.
    pub fn take_waiting_message(
        &mut self,
        idx: usize,
    ) -> Result<Option<(PID, CtxID, MemoryAddress, MemoryAddress, MemorySize)>, xous::Error> {
        if idx > self.queue.len() {
            return Err(xous::Error::BadAddress);
        }
        let (pid_ctx, server_addr, client_addr, len) = match self.queue[idx] {
            QueuedMessage::WaitingResponse(pid_ctx, server_addr, client_addr, len) => {
                (pid_ctx, server_addr, client_addr, len)
            }
            _ => return Err(xous::Error::BadAddress),
        };
        self.queue[idx] = QueuedMessage::Empty;
        self.queue_tail += 1;
        if self.queue_tail >= self.queue.len() {
            self.queue_tail = 0;
        }

        let pid = ((pid_ctx >> 16) & 0xff) as PID;
        let ctx = (pid_ctx & 0xffff) as CtxID;
        let server_addr = match MemoryAddress::new(server_addr) {
            Some(o) => o,
            None => return Ok(None)
        };
        let client_addr = MemoryAddress::new(client_addr).expect("client memory address was 0, but server address was not");
        let len = MemorySize::new(len).expect("memory length was 0, but address was not None");
        Ok(Some((pid, ctx, server_addr, client_addr, len)))
    }

    /// Remove a message from the server's queue and replace it with
    /// QueuedMessage::WaitingResponse.
    pub fn take_next_message(&mut self, server_idx: usize) -> Option<xous::MessageEnvelope> {
        let result = match self.queue[self.queue_tail] {
            QueuedMessage::Empty => return None,
            QueuedMessage::WaitingResponse(_, _, _, _) => return None,
            QueuedMessage::MemoryMessageROLend(
                pid_ctx,
                client_addr,
                id,
                buf,
                buf_size,
                offset,
                valid,
            ) => (
                xous::MessageEnvelope {
                    sender: self.queue_tail | (server_idx << 16),
                    message: xous::Message::ImmutableBorrow(xous::MemoryMessage {
                        id,
                        buf: MemoryRange::new(buf, buf_size),
                        offset: MemorySize::new(offset),
                        valid: MemorySize::new(valid),
                    }),
                },
                pid_ctx,
                buf,
                client_addr,
                buf_size,
            ),
            QueuedMessage::MemoryMessageRWLend(
                pid_ctx,
                client_addr,
                id,
                buf,
                buf_size,
                offset,
                valid,
            ) => (
                xous::MessageEnvelope {
                    sender: self.queue_tail | (server_idx << 16),
                    message: xous::Message::MutableBorrow(xous::MemoryMessage {
                        id,
                        buf: MemoryRange::new(buf, buf_size),
                        offset: MemorySize::new(offset),
                        valid: MemorySize::new(valid),
                    }),
                },
                pid_ctx,
                buf,
                client_addr,
                buf_size,
            ),
            QueuedMessage::MemoryMessageSend(
                pid_ctx,
                _reserved,
                id,
                buf,
                buf_size,
                offset,
                valid,
            ) => (
                xous::MessageEnvelope {
                    sender: self.queue_tail | (server_idx << 16),
                    message: xous::Message::Move(xous::MemoryMessage {
                        id,
                        buf: MemoryRange::new(buf, buf_size),
                        offset: MemorySize::new(offset),
                        valid: MemorySize::new(valid),
                    }),
                },
                pid_ctx,
                0,
                0,
                0,
            ),
            QueuedMessage::ScalarMessage(pid_ctx, _reserved, id, arg1, arg2, arg3, arg4) => (
                xous::MessageEnvelope {
                    sender: self.queue_tail | (server_idx << 16),
                    message: xous::Message::Scalar(xous::ScalarMessage {
                        id,
                        arg1,
                        arg2,
                        arg3,
                        arg4,
                    }),
                },
                pid_ctx,
                0,
                0,
                0,
            ),
        };
        self.queue[self.queue_tail] =
            QueuedMessage::WaitingResponse(result.1, result.2, result.3, result.4);
        Some(result.0)
    }

    /// Add the given message to this server's queue.
    ///
    /// # Errors
    ///
    /// * **ServerQueueFull**: The server queue cannot accept any more messages
    pub fn queue_message(
        &mut self,
        pid: PID,
        context: CtxID,
        message: xous::Message,
        original_address: Option<MemoryAddress>,
    ) -> core::result::Result<usize, xous::Error> {
        if self.queue[self.queue_head] != QueuedMessage::Empty {
            return Err(xous::Error::ServerQueueFull);
        }

        self.queue[self.queue_head] = match message {
            xous::Message::Scalar(msg) => QueuedMessage::ScalarMessage(
                pid as usize | (context << 16),
                original_address.map(|x| x.get()).unwrap_or(0),
                msg.id,
                msg.arg1,
                msg.arg2,
                msg.arg3,
                msg.arg4,
            ),
            xous::Message::Move(msg) => QueuedMessage::MemoryMessageSend(
                pid as usize | (context << 16),
                original_address.map(|x| x.get()).unwrap_or(0),
                msg.id,
                msg.buf.addr.get(),
                msg.buf.size.get(),
                msg.offset.map(|x| x.get()).unwrap_or(0) as usize,
                msg.valid.map(|x| x.get()).unwrap_or(0) as usize,
            ),
            xous::Message::MutableBorrow(msg) => QueuedMessage::MemoryMessageRWLend(
                pid as usize | (context << 16),
                original_address.map(|x| x.get()).unwrap_or(0),
                msg.id,
                msg.buf.addr.get(),
                msg.buf.size.get(),
                msg.offset.map(|x| x.get()).unwrap_or(0) as usize,
                msg.valid.map(|x| x.get()).unwrap_or(0) as usize,
            ),
            xous::Message::ImmutableBorrow(msg) => QueuedMessage::MemoryMessageROLend(
                pid as usize | (context << 16),
                original_address.map(|x| x.get()).unwrap_or(0),
                msg.id,
                msg.buf.addr.get(),
                msg.buf.size.get(),
                msg.offset.map(|x| x.get()).unwrap_or(0) as usize,
                msg.valid.map(|x| x.get()).unwrap_or(0) as usize,
            ),
        };

        let idx = self.queue_head;
        self.queue_head += 1;
        if self.queue_head >= self.queue.len() {
            self.queue_head = 0;
        }
        Ok(idx)
    }

    pub fn queue_address(
        &mut self,
        pid: PID,
        context: CtxID,
        message: &Message,
        client_address: Option<MemoryAddress>,
    ) -> core::result::Result<usize, xous::Error> {
        if self.queue[self.queue_head] != QueuedMessage::Empty {
            return Err(xous::Error::ServerQueueFull);
        }
        let (server_address, len) = match message {
            xous::Message::Scalar(_) | xous::Message::Move(_) => (0, 0),
            xous::Message::MutableBorrow(msg) | xous::Message::ImmutableBorrow(msg) => {
                (msg.buf.addr.get(), msg.buf.size.get())
            }
        };

        self.queue[self.queue_head] = QueuedMessage::WaitingResponse(
            pid as usize | (context << 16),
            server_address,
            client_address.map(|x| x.get()).unwrap_or(0),
            len,
        );
        let idx = self.queue_head;
        self.queue_head += 1;
        if self.queue_head >= self.queue.len() {
            self.queue_head = 0;
        }
        Ok(idx)
    }
    // assert!(
    //     mem::size_of::<QueuedMessage>() == 32,
    //     "QueuedMessage was supposed to be 32 bytes, but instead was {} bytes",
    //     mem::size_of::<QueuedMessage>()
    // );

    /// Return a context ID that is available and blocking.  If no such context
    /// ID exists, or if this server isn't actually ready to receive packets,
    /// return None.
    pub fn take_available_context(&mut self) -> Option<CtxID> {
        if self.ready_contexts == 0 {
            return None;
        }
        let mut test_ctx_mask = 1;
        let mut ctx_number = 0;
        loop {
            // If the context mask matches this context number, remove it
            // and return the index.
            if self.ready_contexts & test_ctx_mask == test_ctx_mask {
                self.ready_contexts = self.ready_contexts & !test_ctx_mask;
                return Some(ctx_number);
            }
            // Advance to the next slot.
            test_ctx_mask = test_ctx_mask.rotate_left(1);
            ctx_number = ctx_number + 1;
            if test_ctx_mask == 1 {
                panic!("didn't find a free context, even though there should be one");
            }
        }
    }

    /// Add the given context to the list of ready and waiting contexts.
    pub fn park_context(&mut self, context: CtxID) {
        self.ready_contexts |= 1 << context;
    }
}