hojicha-core 0.2.2

//! Zero-cost Event optimizations with inline storage
//!
//! This module provides performance-optimized event types that minimize allocations
//! and provide zero-cost abstractions for common event patterns.

use crate::event::{KeyEvent, MouseEvent};
use smallvec::SmallVec;
use std::mem;

/// Size threshold for inline message storage (in bytes)
const INLINE_SIZE: usize = 24;

/// Zero-cost event wrapper with inline storage for small messages
#[derive(Debug, Clone)]
pub enum OptimizedEvent<M> {
    /// A keyboard event - stored inline, no allocation
    Key(KeyEvent),
    /// A mouse event - stored inline, no allocation
    Mouse(MouseEvent),
    /// Terminal was resized - stored inline, no allocation
    Resize {
        /// Terminal width in columns
        width: u16,
        /// Terminal height in rows
        height: u16,
    },
    /// A tick event - stored inline, no allocation
    Tick,
    /// User-defined message with inline storage optimization
    User(InlineMessage<M>),
    /// Request to quit the program - stored inline, no allocation
    Quit,
    /// Terminal gained focus - stored inline, no allocation
    Focus,
    /// Terminal lost focus - stored inline, no allocation
    Blur,
    /// Program suspend request (Ctrl+Z) - stored inline, no allocation
    Suspend,
    /// Program resumed from suspend - stored inline, no allocation
    Resume,
    /// Bracketed paste event with COW string for efficiency
    Paste(std::borrow::Cow<'static, str>),
    /// Internal event to trigger external process execution - stored inline, no allocation
    #[doc(hidden)]
    ExecProcess,
}

/// Message storage that inlines small messages to avoid allocations
#[derive(Debug, Clone)]
pub enum InlineMessage<M> {
    /// Small message stored inline (no heap allocation)
    Inline(M),
    /// Large message stored on heap (only when necessary)
    Boxed(Box<M>),
}

impl<M> InlineMessage<M> {
    /// Create a new inline message, automatically choosing storage type
    #[inline(always)]
    pub fn new(msg: M) -> Self {
        if mem::size_of::<M>() <= INLINE_SIZE {
            Self::Inline(msg)
        } else {
            Self::Boxed(Box::new(msg))
        }
    }

    /// Get reference to the message
    #[inline(always)]
    pub fn get(&self) -> &M {
        match self {
            Self::Inline(msg) => msg,
            Self::Boxed(msg) => msg.as_ref(),
        }
    }

    /// Take the message out of storage
    #[inline(always)]
    pub fn into_inner(self) -> M {
        match self {
            Self::Inline(msg) => msg,
            Self::Boxed(msg) => *msg,
        }
    }

    /// Check if message is stored inline (zero allocation)
    #[inline(always)]
    pub fn is_inline(&self) -> bool {
        matches!(self, Self::Inline(_))
    }
}

impl<M> OptimizedEvent<M> {
    /// Create a new user event with automatic storage optimization
    #[inline(always)]
    pub fn user(msg: M) -> Self {
        Self::User(InlineMessage::new(msg))
    }

    /// Check if this is a key event
    #[inline(always)]
    pub const fn is_key(&self) -> bool {
        matches!(self, Self::Key(_))
    }

    /// Check if this is a specific key press
    #[inline(always)]
    pub fn is_key_press(&self, key: crate::event::Key) -> bool {
        matches!(self, Self::Key(k) if k.key == key)
    }

    /// Get the key event if this is a key event
    #[inline(always)]
    pub const fn as_key(&self) -> Option<&KeyEvent> {
        match self {
            Self::Key(k) => Some(k),
            _ => None,
        }
    }

    /// Check if this is a mouse event
    #[inline(always)]
    pub const fn is_mouse(&self) -> bool {
        matches!(self, Self::Mouse(_))
    }

    /// Get the mouse event if this is a mouse event
    #[inline(always)]
    pub const fn as_mouse(&self) -> Option<&MouseEvent> {
        match self {
            Self::Mouse(m) => Some(m),
            _ => None,
        }
    }

    /// Check if this is a user message
    #[inline(always)]
    pub const fn is_user(&self) -> bool {
        matches!(self, Self::User(_))
    }

    /// Get the user message if this is a user event
    #[inline(always)]
    pub fn as_user(&self) -> Option<&M> {
        match self {
            Self::User(msg) => Some(msg.get()),
            _ => None,
        }
    }

    /// Take the user message if this is a user event
    #[inline(always)]
    pub fn into_user(self) -> Option<M> {
        match self {
            Self::User(msg) => Some(msg.into_inner()),
            _ => None,
        }
    }

    /// Check if this is a quit event
    #[inline(always)]
    pub const fn is_quit(&self) -> bool {
        matches!(self, Self::Quit)
    }

    /// Check if this is a tick event
    #[inline(always)]
    pub const fn is_tick(&self) -> bool {
        matches!(self, Self::Tick)
    }

    /// Check if this is a resize event
    #[inline(always)]
    pub const fn is_resize(&self) -> bool {
        matches!(self, Self::Resize { .. })
    }

    /// Get resize dimensions if this is a resize event
    #[inline(always)]
    pub const fn as_resize(&self) -> Option<(u16, u16)> {
        match self {
            Self::Resize { width, height } => Some((*width, *height)),
            _ => None,
        }
    }
}

/// Event batch for efficient processing of multiple events
#[derive(Debug, Clone)]
pub struct EventBatch<M> {
    /// Events stored in a small vector to avoid allocations for small batches
    events: SmallVec<[OptimizedEvent<M>; 8]>,
}

impl<M> EventBatch<M> {
    /// Create a new empty event batch
    #[inline]
    pub fn new() -> Self {
        Self {
            events: SmallVec::new(),
        }
    }

    /// Create a new event batch with capacity
    #[inline]
    pub fn with_capacity(capacity: usize) -> Self {
        Self {
            events: SmallVec::with_capacity(capacity),
        }
    }

    /// Add an event to the batch
    #[inline]
    pub fn push(&mut self, event: OptimizedEvent<M>) {
        self.events.push(event);
    }

    /// Get the number of events in the batch
    #[inline]
    pub fn len(&self) -> usize {
        self.events.len()
    }

    /// Check if the batch is empty
    #[inline]
    pub fn is_empty(&self) -> bool {
        self.events.is_empty()
    }

    /// Iterate over events in the batch
    #[inline]
    pub fn iter(&self) -> std::slice::Iter<'_, OptimizedEvent<M>> {
        self.events.iter()
    }

    /// Drain all events from the batch
    #[inline]
    pub fn drain(&mut self) -> smallvec::Drain<'_, [OptimizedEvent<M>; 8]> {
        self.events.drain(..)
    }

    /// Clear the batch
    #[inline]
    pub fn clear(&mut self) {
        self.events.clear();
    }

    /// Check if batch is using inline storage (no heap allocations)
    #[inline]
    pub fn is_inline(&self) -> bool {
        !self.events.spilled()
    }
}

impl<M> Default for EventBatch<M> {
    #[inline]
    fn default() -> Self {
        Self::new()
    }
}

impl<M> IntoIterator for EventBatch<M> {
    type Item = OptimizedEvent<M>;
    type IntoIter = smallvec::IntoIter<[OptimizedEvent<M>; 8]>;

    #[inline]
    fn into_iter(self) -> Self::IntoIter {
        self.events.into_iter()
    }
}

/// Event coalescing for reducing redundant events
pub struct EventCoalescer<M> {
    /// Buffer for coalescing events
    buffer: SmallVec<[OptimizedEvent<M>; 16]>,
    /// Track last resize event to coalesce multiple resize events
    last_resize: Option<(u16, u16)>,
}

impl<M> EventCoalescer<M> {
    /// Create a new event coalescer
    #[inline]
    pub fn new() -> Self {
        Self {
            buffer: SmallVec::new(),
            last_resize: None,
        }
    }

    /// Add an event, coalescing with existing events where possible
    pub fn push(&mut self, event: OptimizedEvent<M>) {
        match event {
            // Coalesce resize events - only keep the latest
            OptimizedEvent::Resize { width, height } => {
                self.last_resize = Some((width, height));
            }
            // Coalesce tick events - only keep one tick per batch
            OptimizedEvent::Tick => {
                if !self.buffer.iter().any(|e| e.is_tick()) {
                    self.buffer.push(event);
                }
            }
            // Don't coalesce other events
            _ => {
                self.buffer.push(event);
            }
        }
    }

    /// Finish coalescing and return the batch
    pub fn finish(&mut self) -> EventBatch<M> {
        // Add the final resize event if any
        if let Some((width, height)) = self.last_resize.take() {
            self.buffer.push(OptimizedEvent::Resize { width, height });
        }

        let mut batch = EventBatch::with_capacity(self.buffer.len());
        batch.events.extend(self.buffer.drain(..));
        batch
    }

    /// Clear the coalescer
    #[inline]
    pub fn clear(&mut self) {
        self.buffer.clear();
        self.last_resize = None;
    }
}

impl<M> Default for EventCoalescer<M> {
    #[inline]
    fn default() -> Self {
        Self::new()
    }
}

/// Convert from the standard Event to OptimizedEvent
impl<M> From<crate::event::Event<M>> for OptimizedEvent<M> {
    #[inline]
    fn from(event: crate::event::Event<M>) -> Self {
        match event {
            crate::event::Event::Key(k) => Self::Key(k),
            crate::event::Event::Mouse(m) => Self::Mouse(m),
            crate::event::Event::Resize { width, height } => Self::Resize { width, height },
            crate::event::Event::Tick => Self::Tick,
            crate::event::Event::User(m) => Self::user(m),
            crate::event::Event::Quit => Self::Quit,
            crate::event::Event::Focus => Self::Focus,
            crate::event::Event::Blur => Self::Blur,
            crate::event::Event::Suspend => Self::Suspend,
            crate::event::Event::Resume => Self::Resume,
            crate::event::Event::Paste(text) => Self::Paste(text.into()),
            crate::event::Event::ExecProcess => Self::ExecProcess,
        }
    }
}

/// Convert from OptimizedEvent back to standard Event
impl<M> From<OptimizedEvent<M>> for crate::event::Event<M> {
    #[inline]
    fn from(event: OptimizedEvent<M>) -> Self {
        match event {
            OptimizedEvent::Key(k) => Self::Key(k),
            OptimizedEvent::Mouse(m) => Self::Mouse(m),
            OptimizedEvent::Resize { width, height } => Self::Resize { width, height },
            OptimizedEvent::Tick => Self::Tick,
            OptimizedEvent::User(m) => Self::User(m.into_inner()),
            OptimizedEvent::Quit => Self::Quit,
            OptimizedEvent::Focus => Self::Focus,
            OptimizedEvent::Blur => Self::Blur,
            OptimizedEvent::Suspend => Self::Suspend,
            OptimizedEvent::Resume => Self::Resume,
            OptimizedEvent::Paste(text) => Self::Paste(text.into_owned()),
            OptimizedEvent::ExecProcess => Self::ExecProcess,
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_inline_message_small() {
        let msg = 42u32;
        let inline_msg = InlineMessage::new(msg);
        assert!(inline_msg.is_inline());
        assert_eq!(*inline_msg.get(), 42);
    }

    #[test]
    fn test_inline_message_large() {
        // Create a large struct that exceeds INLINE_SIZE
        #[derive(Debug, PartialEq, Clone)]
        struct LargeStruct([u8; 32]); // This exceeds INLINE_SIZE of 24

        let msg = LargeStruct([0u8; 32]);
        let inline_msg = InlineMessage::new(msg.clone());
        // Large messages should be boxed
        assert!(!inline_msg.is_inline());
        assert_eq!(*inline_msg.get(), msg);
    }

    #[test]
    fn test_event_coalescing() {
        let mut coalescer: EventCoalescer<()> = EventCoalescer::new();

        // Add multiple resize events
        coalescer.push(OptimizedEvent::Resize {
            width: 80,
            height: 24,
        });
        coalescer.push(OptimizedEvent::Resize {
            width: 100,
            height: 30,
        });
        coalescer.push(OptimizedEvent::Resize {
            width: 120,
            height: 40,
        });

        // Add multiple ticks
        coalescer.push(OptimizedEvent::Tick);
        coalescer.push(OptimizedEvent::Tick);

        let batch = coalescer.finish();

        // Should have only one resize (the last one) and one tick
        assert_eq!(batch.len(), 2);

        let events: Vec<_> = batch.into_iter().collect();
        assert!(events.iter().any(|e| matches!(e, OptimizedEvent::Tick)));
        assert!(events.iter().any(|e| matches!(
            e,
            OptimizedEvent::Resize {
                width: 120,
                height: 40
            }
        )));
    }

    #[test]
    fn test_event_batch_inline_storage() {
        let mut batch = EventBatch::new();

        // Add a few events - should stay inline
        batch.push(OptimizedEvent::Tick);
        batch.push(OptimizedEvent::user(42u32));
        batch.push(OptimizedEvent::Quit);

        assert!(batch.is_inline()); // No heap allocation
        assert_eq!(batch.len(), 3);
    }

    #[test]
    fn test_zero_cost_event_checks() {
        let event = OptimizedEvent::user(String::from("test"));

        // These should all be constant time, no allocations
        assert!(event.is_user());
        assert!(!event.is_key());
        assert!(!event.is_mouse());
        assert_eq!(event.as_user().unwrap(), "test");
    }
}