use std::sync::Arc;

use dashmap::DashMap;

use oxide_compiler::compiler::Compiler;
use oxide_compiler::module::CompiledModule;

use crate::{kernel_debug, kernel_info};

pub use oxide_compiler::compiler::structural_hash;

/// Shared compiled-module cache.
///
/// Concurrency model:
/// - Read-heavy after warmup: cache hits dominate steady-state execution.
/// - Backed by a fixed-shard `DashMap` so lookup contention stays predictable across
///   developer machines and CI hosts.
pub struct CodeForge {
    map: DashMap<u64, Arc<CompiledModule>>,
}

impl CodeForge {
    pub fn new() -> Self {
        Self {
            map: DashMap::with_shard_amount(16),
        }
    }

    pub fn get_or_compile(
        &self, program: &oxide_parser::Program, compiler: &Compiler,
    ) -> Result<Arc<CompiledModule>, String> {
        let hash = structural_hash(program);

        if let Some(module) = self.map.get(&hash) {
            kernel_info!("CodeForge hit hash={:#x}", hash);
            return Ok(Arc::clone(&module));
        }

        let module = compiler.compile(program)?;
        let module = Arc::new(module);
        kernel_debug!("CodeForge miss hash={:#x}", hash);

        Ok(Arc::clone(self.map.entry(hash).or_insert(module).value()))
    }
}

impl Default for CodeForge {
    fn default() -> Self {
        Self::new()
    }
}

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

    #[test]
    fn test_structural_hash_same_input() {
        let a1 = Allocator::default();
        let a2 = Allocator::default();
        let p1 = oxide_parser::parse(&a1, "1 + 2").expect("parse failed");
        let p2 = oxide_parser::parse(&a2, "1 + 2").expect("parse failed");
        assert_eq!(structural_hash(&p1), structural_hash(&p2));
    }

    #[test]
    fn test_structural_hash_same_structure() {
        let a1 = Allocator::default();
        let a2 = Allocator::default();
        let p1 = oxide_parser::parse(&a1, "var x = 1; var y = 2;").expect("parse failed");
        let p2 = oxide_parser::parse(&a2, "var a = 1; var b = 2;").expect("parse failed");
        assert_eq!(structural_hash(&p1), structural_hash(&p2));
    }

    #[test]
    fn test_structural_hash_different_ops() {
        let a1 = Allocator::default();
        let a2 = Allocator::default();
        let p1 = oxide_parser::parse(&a1, "1 + 2").expect("parse failed");
        let p2 = oxide_parser::parse(&a2, "1 - 2").expect("parse failed");
        assert_ne!(structural_hash(&p1), structural_hash(&p2));
    }

    #[test]
    fn test_cache_hit() {
        let forge = CodeForge::new();
        let compiler = Compiler::new();
        let allocator = Allocator::default();
        let program = oxide_parser::parse(&allocator, "1 + 2").expect("parse failed");

        let first = forge.get_or_compile(&program, &compiler).expect("first compile");
        let second = forge.get_or_compile(&program, &compiler).expect("second compile");

        assert_eq!((first.bytecode.len(), first.n_registers), (second.bytecode.len(), second.n_registers));
    }

    #[test]
    fn test_cache_miss_new_program() {
        let forge = CodeForge::new();
        let compiler = Compiler::new();

        let a1 = Allocator::default();
        let p1 = oxide_parser::parse(&a1, "1 + 2").expect("parse failed");
        let a2 = Allocator::default();
        let p2 = oxide_parser::parse(&a2, "3 * 4").expect("parse failed");

        let m1 = forge.get_or_compile(&p1, &compiler).expect("compile p1");
        let m2 = forge.get_or_compile(&p2, &compiler).expect("compile p2");

        assert_ne!(m1.bytecode, m2.bytecode);
    }
}