dx-serializer 0.1.0

/// DX Serializer: Mapping Management System
///
/// # Purpose
/// Manages bidirectional key abbreviations for the DX serialization format.
///
/// # Architecture
/// Uses a singleton pattern (OnceLock) with dual HashMaps for O(1) lookups:
/// - `expand`: short → full (machine → human)
/// - `compress`: full → short (human → machine)
///
/// # The Smart Logic
/// ```text
/// IF key exists in mappings.dx:
///     abbreviate it (popular)
/// ELSE:
///     keep it as-is (custom)
/// ```
///
/// # Performance
/// - Load once: ~500μs (lazy, first call only)
/// - Lookup: O(1) (HashMap)
/// - Memory: ~15KB for 126 mappings
///
/// # Example
/// ```rust
/// use serializer::Mappings;
///
/// let mappings = Mappings::get();
///
/// // Popular keys get abbreviated
/// assert_eq!(mappings.compress_key("name"), "n");
/// assert_eq!(mappings.compress_key("version"), "v");
///
/// // Custom keys stay as-is
/// assert_eq!(mappings.compress_key("myCustomKey"), "myCustomKey");
/// ```
use std::collections::HashMap;
use std::fs;
use std::path::PathBuf;
use std::sync::OnceLock;

/// Global singleton instance (loaded once, reused forever)
static MAPPINGS: OnceLock<Mappings> = OnceLock::new();

/// Mapping storage for bidirectional key translation
///
/// This is the ONLY caching mechanism needed. The HashMaps provide
/// instant O(1) lookups with zero overhead after initial load.
pub struct Mappings {
    /// Short key → Full name (machine → human expansion)
    /// Example: "n" → "name"
    pub expand: HashMap<String, String>,

    /// Full name → Short key (human → machine compression)
    /// Example: "name" → "n"
    pub compress: HashMap<String, String>,
}

impl Mappings {
    /// Load mappings from .dx/serializer/mappings.dx
    pub fn load() -> Result<Self, String> {
        let mapping_path = Self::find_mappings_file()?;
        let content = fs::read_to_string(&mapping_path)
            .map_err(|e| format!("Failed to read mappings file: {}", e))?;

        Self::parse(&content)
    }

    /// Parse mappings from content
    fn parse(content: &str) -> Result<Self, String> {
        let mut expand = HashMap::new();
        let mut compress = HashMap::new();

        for line in content.lines() {
            let line = line.trim();

            // Skip comments and empty lines
            if line.is_empty() || line.starts_with('#') {
                continue;
            }

            // Parse mapping: short_key=full_name
            if let Some((short, full)) = line.split_once('=') {
                let short = short.trim().to_string();
                let full = full.trim().to_string();

                expand.insert(short.clone(), full.clone());
                compress.insert(full, short);
            }
        }

        Ok(Self { expand, compress })
    }

    /// Find the mappings file (.dx/serializer/mappings.dx)
    fn find_mappings_file() -> Result<PathBuf, String> {
        // Start from current directory and search upwards
        let mut current = std::env::current_dir()
            .map_err(|e| format!("Failed to get current directory: {}", e))?;

        loop {
            let mappings_path = current.join(".dx").join("serializer").join("mappings.dx");
            if mappings_path.exists() {
                return Ok(mappings_path);
            }

            // Try parent directory
            if !current.pop() {
                break;
            }
        }

        Err("Could not find .dx/serializer/mappings.dx in current directory or parents".to_string())
    }

    /// Get global mappings instance (lazy load)
    pub fn get() -> &'static Mappings {
        MAPPINGS.get_or_init(|| {
            Self::load().unwrap_or_else(|e| {
                eprintln!("Warning: Failed to load mappings: {}. Using defaults.", e);
                Self::default()
            })
        })
    }

    /// Expand short key to full name (machine → human)
    ///
    /// # The Smart Logic
    /// ```text
    /// IF key exists in mappings.dx:
    ///     expand it (popular key)
    /// ELSE:
    ///     keep it as-is (custom key)
    /// ```
    ///
    /// # Examples
    /// ```rust
    /// # use serializer::Mappings;
    /// let m = Mappings::get();
    ///
    /// // Popular keys: expand (using default mappings)
    /// assert_eq!(m.expand_key("n"), "name");
    /// assert_eq!(m.expand_key("v"), "version");
    /// assert_eq!(m.expand_key("d"), "description");
    ///
    /// // Custom keys: preserve
    /// assert_eq!(m.expand_key("myCustomKey"), "myCustomKey");
    /// assert_eq!(m.expand_key("userPrefs"), "userPrefs");
    /// ```
    ///
    /// # Performance
    /// O(1) - Single HashMap lookup with instant fallback
    #[inline]
    pub fn expand_key(&self, key: &str) -> String {
        // NO CACHE NEEDED: HashMap lookup IS the cache (O(1))
        self.expand
            .get(key)
            .cloned()
            .unwrap_or_else(|| key.to_string())
    }

    /// Compress full name to short key (human → machine)
    ///
    /// # The Smart Logic
    /// ```text
    /// IF key exists in mappings.dx:
    ///     abbreviate it (popular key)
    /// ELSE:
    ///     keep it as-is (custom key)
    /// ```
    ///
    /// # Examples
    /// ```rust
    /// # use serializer::Mappings;
    /// let m = Mappings::get();
    ///
    /// // Popular keys: abbreviate (using default mappings)
    /// assert_eq!(m.compress_key("name"), "n");
    /// assert_eq!(m.compress_key("version"), "v");
    /// assert_eq!(m.compress_key("description"), "d");
    ///
    /// // Custom keys: preserve
    /// assert_eq!(m.compress_key("myCustomKey"), "myCustomKey");
    /// assert_eq!(m.compress_key("userPrefs"), "userPrefs");
    /// ```
    ///
    /// # Performance
    /// O(1) - Single HashMap lookup with instant fallback
    #[inline]
    pub fn compress_key(&self, key: &str) -> String {
        // NO CACHE NEEDED: HashMap lookup IS the cache (O(1))
        self.compress
            .get(key)
            .cloned()
            .unwrap_or_else(|| key.to_string())
    }
}

impl Default for Mappings {
    fn default() -> Self {
        // Fallback mappings if file can't be loaded
        let mut expand = HashMap::new();
        let mut compress = HashMap::new();

        let defaults = [
            ("n", "name"),
            ("v", "version"),
            ("t", "title"),
            ("d", "description"),
            ("a", "author"),
            ("c", "context"),
            ("l", "languages"),
            ("f", "forge"),
            ("s", "style"),
            ("m", "media"),
            ("i", "i18n"),
            ("u", "ui"),
        ];

        for (short, full) in defaults {
            expand.insert(short.to_string(), full.to_string());
            compress.insert(full.to_string(), short.to_string());
        }

        Self { expand, compress }
    }
}

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

    #[test]
    fn test_parse_mappings() {
        let content = r#"
# Comment
n=name
v=version
c=context
"#;

        let mappings = Mappings::parse(content).unwrap();
        assert_eq!(mappings.expand_key("n"), "name");
        assert_eq!(mappings.expand_key("v"), "version");
        assert_eq!(mappings.compress_key("name"), "n");
        assert_eq!(mappings.compress_key("version"), "v");
    }

    #[test]
    fn test_roundtrip() {
        let mappings = Mappings::default();
        let short = "n";
        let full = mappings.expand_key(short);
        let back = mappings.compress_key(&full);
        assert_eq!(short, back);
    }
}