// SKC-LISP: Cranelift JIT Backend (Phase 3D-2)
// EmojiScript bytecode → Cranelift IR → x64/ARM64 native code

use cranelift::prelude::*;
use cranelift_jit::{JITBuilder, JITModule};
use cranelift_module::{Module, ModuleCompiledValues};
use std::collections::HashMap;

// ============================================================================
// EmojiScript Bytecode Opcodes
// ============================================================================

#[repr(u8)]
pub enum EmojiOpcode {
    // Stack operations
    Push32 = 0x01,      // Push 32-bit immediate
    Pop = 0x02,         // Pop stack
    Dup = 0x03,         // Duplicate top
    Swap = 0x04,        // Swap top 2

    // Arithmetic
    Add = 0x10,         // Add top 2
    Sub = 0x11,         // Subtract
    Mul = 0x12,         // Multiply
    Div = 0x13,         // Divide

    // Comparison & control
    Eq = 0x20,          // Equal
    Lt = 0x21,          // Less than
    Jmp = 0x30,         // Jump absolute
    JmpIf = 0x31,       // Jump if top != 0

    // Semantic passes
    Stream = 0x40,      // 🌊 Telemetry stream
    PolicyCheck = 0x41, // 🧠 Policy routing
    Seal = 0x42,        // 🔒 WORM seal
    ReadOnly = 0x43,    // 🔓 Capability downgrade

    // I/O & meta
    Print = 0x50,       // Print top
    Halt = 0xFF,        // Stop execution
}

// ============================================================================
// Cranelift IR Translation
// ============================================================================

pub struct EmojiScriptCompiler {
    builder_context: FunctionBuilderContext,
    jit: JITModule,
    signatures: HashMap<String, Signature>,
}

impl EmojiScriptCompiler {
    pub fn new() -> Result<Self, String> {
        let builder = JITBuilder::new(cranelift_module::default_libcall_names())
            .map_err(|e| format!("JIT builder failed: {:?}", e))?;

        let jit = JITModule::new(builder);

        Ok(Self {
            builder_context: FunctionBuilderContext::new(),
            jit,
            signatures: HashMap::new(),
        })
    }

    /// Parse emoji bytecode → EmojiOpcode sequence
    pub fn parse_bytecode(&self, bytecode: &[u8]) -> Result<Vec<EmojiOpcode>, String> {
        bytecode.iter()
            .filter_map(|&b| {
                match b {
                    0x01 | 0x02 | 0x03 | 0x04 |
                    0x10 | 0x11 | 0x12 | 0x13 |
                    0x20 | 0x21 | 0x30 | 0x31 |
                    0x40 | 0x41 | 0x42 | 0x43 |
                    0x50 | 0xFF => Some(Ok(unsafe { std::mem::transmute(b) })),
                    _ => Some(Err(format!("Unknown opcode: 0x{:02x}", b))),
                }
            })
            .collect()
    }

    /// Compile bytecode → Cranelift IR function
    pub fn compile_to_ir(&mut self, opcodes: &[EmojiOpcode]) -> Result<Function, String> {
        let mut sig = self.jit.make_signature();
        // Function signature: () → i64 (return top of stack)
        sig.returns.push(AbiParam::new(types::I64));

        let func_id = self.jit.declare_function("emojiscript_main", cranelift_module::Linkage::Local, &sig)
            .map_err(|e| format!("Function declaration failed: {:?}", e))?;

        let mut func = Function::with_name_and_sig(
            UserFunctionName::user(0, func_id.index() as u32),
            sig,
        );

        let mut builder = FunctionBuilder::new(&mut func, &mut self.builder_context);

        // Entry block
        let entry_block = builder.create_ebb();
        builder.append_ebb_params_for_function_params(entry_block);
        builder.switch_to_block(entry_block);
        builder.seal_block(entry_block);

        // Stack: simulated in local variables
        let mut stack_values: Vec<Value> = Vec::new();
        let stack_limit = 256;

        // Compile each opcode to IR
        for opcode in opcodes {
            match opcode {
                EmojiOpcode::Push32 => {
                    let imm = builder.ins().iconst(types::I64, 42); // Placeholder: real impl reads immediate
                    stack_values.push(imm);
                }

                EmojiOpcode::Pop => {
                    if !stack_values.is_empty() {
                        stack_values.pop();
                    }
                }

                EmojiOpcode::Dup => {
                    if let Some(&v) = stack_values.last() {
                        stack_values.push(v);
                    }
                }

                EmojiOpcode::Add => {
                    if stack_values.len() >= 2 {
                        let b = stack_values.pop().unwrap();
                        let a = stack_values.pop().unwrap();
                        let result = builder.ins().iadd(a, b);
                        stack_values.push(result);
                    }
                }

                EmojiOpcode::Sub => {
                    if stack_values.len() >= 2 {
                        let b = stack_values.pop().unwrap();
                        let a = stack_values.pop().unwrap();
                        let result = builder.ins().isub(a, b);
                        stack_values.push(result);
                    }
                }

                EmojiOpcode::Mul => {
                    if stack_values.len() >= 2 {
                        let b = stack_values.pop().unwrap();
                        let a = stack_values.pop().unwrap();
                        let result = builder.ins().imul(a, b);
                        stack_values.push(result);
                    }
                }

                EmojiOpcode::Eq => {
                    if stack_values.len() >= 2 {
                        let b = stack_values.pop().unwrap();
                        let a = stack_values.pop().unwrap();
                        let cmp = builder.ins().icmp(IntCC::Equal, a, b);
                        let result = builder.ins().bint(types::I64, cmp);
                        stack_values.push(result);
                    }
                }

                EmojiOpcode::Stream => {
                    // 🌊 Telemetry: emit event (placeholder: actual impl calls telemetry bus)
                    if let Some(&v) = stack_values.last() {
                        // Emit event with value
                    }
                }

                EmojiOpcode::PolicyCheck => {
                    // 🧠 Policy: route through registry (placeholder)
                    if let Some(&v) = stack_values.last() {
                        // Check policy
                    }
                }

                EmojiOpcode::Seal => {
                    // 🔒 WORM: hash and seal (placeholder)
                    if let Some(&v) = stack_values.last() {
                        // Blake3 hash + sign
                    }
                }

                EmojiOpcode::ReadOnly => {
                    // 🔓 Downgrade: reduce capabilities
                    if let Some(&v) = stack_values.last() {
                        let masked = builder.ins().band_imm(v, 0x7FFFFFFF);
                        stack_values.pop();
                        stack_values.push(masked);
                    }
                }

                EmojiOpcode::Halt => {
                    // Exit: return top of stack
                    if let Some(v) = stack_values.pop() {
                        builder.ins().return_(&[v]);
                    } else {
                        let zero = builder.ins().iconst(types::I64, 0);
                        builder.ins().return_(&[zero]);
                    }
                    return Ok(func);
                }

                _ => {}
            }
        }

        // Default return: top of stack or 0
        if let Some(v) = stack_values.pop() {
            builder.ins().return_(&[v]);
        } else {
            let zero = builder.ins().iconst(types::I64, 0);
            builder.ins().return_(&[zero]);
        }

        Ok(func)
    }

    /// Finalize + generate x64 or ARM64 native code
    pub fn finalize_to_native(&mut self, func: Function) -> Result<Vec<u8>, String> {
        // In production, this would use Cranelift's native backends
        // For now, return a placeholder bytecode
        Ok(vec![])
    }
}

// ============================================================================
// x86_64 Code Generation (Cranelift Backend)
// ============================================================================

pub struct X64CodeGenerator;

impl X64CodeGenerator {
    /// Generate x86_64 machine code from Cranelift IR
    pub fn generate(ir: &Function) -> Result<Vec<u8>, String> {
        // Placeholder: Real implementation uses Cranelift's x86_64 backend
        // Output: native x86_64 opcodes
        Ok(vec![])
    }
}

// ============================================================================
// ARM64 Code Generation (Cranelift Backend)
// ============================================================================

pub struct Arm64CodeGenerator;

impl Arm64CodeGenerator {
    /// Generate ARM64 machine code from Cranelift IR
    pub fn generate(ir: &Function) -> Result<Vec<u8>, String> {
        // Placeholder: Real implementation uses Cranelift's ARM64 backend
        // Output: native ARM64 opcodes
        Ok(vec![])
    }
}

// ============================================================================
// End-to-end Compilation: Bytecode → Native Code
// ============================================================================

pub fn compile_emojiscript_to_native(
    bytecode: &[u8],
    target: &str,  // "x86_64" or "aarch64"
) -> Result<Vec<u8>, String> {
    let mut compiler = EmojiScriptCompiler::new()?;

    // Step 1: Parse bytecode
    let opcodes = compiler.parse_bytecode(bytecode)?;

    // Step 2: Compile to Cranelift IR
    let ir_func = compiler.compile_to_ir(&opcodes)?;

    // Step 3: Generate native code based on target
    match target {
        "x86_64" => X64CodeGenerator::generate(&ir_func),
        "aarch64" => Arm64CodeGenerator::generate(&ir_func),
        _ => Err(format!("Unsupported target: {}", target)),
    }
}

// ============================================================================
// Tests
// ============================================================================

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

    #[test]
    fn test_parse_bytecode() {
        let compiler = EmojiScriptCompiler::new().unwrap();
        let bytecode = vec![0x01, 0x02, 0x03, 0xFF];
        let opcodes = compiler.parse_bytecode(&bytecode).unwrap();
        assert_eq!(opcodes.len(), 4);
    }

    #[test]
    fn test_compile_simple_program() {
        let bytecode = vec![
            EmojiOpcode::Push32 as u8,
            EmojiOpcode::Push32 as u8,
            EmojiOpcode::Add as u8,
            EmojiOpcode::Halt as u8,
        ];
        let result = compile_emojiscript_to_native(&bytecode, "x86_64");
        assert!(result.is_ok());
    }
}