use crate::compiler::ast::AstNode;
use crate::compiler::lexer::Token;

pub struct Transpiler;

impl Transpiler {
    pub fn new() -> Self {
        Self
    }

    pub fn transpile(&self, ast: &AstNode) -> Result<String, String> {
        let mut output = String::new();
        
        output.push_str("// Auto-generated by MQL-Rust Transpiler\n");
        output.push_str("use crate::engine::backtester::{Backtester, OrderType};\n\n");
        
        self.visit_node(ast, &mut output)?;
        
        Ok(output)
    }

    fn visit_node(&self, node: &AstNode, out: &mut String) -> Result<(), String> {
        match node {
            AstNode::Program(nodes) => {
                for n in nodes {
                    self.visit_node(n, out)?;
                    out.push('\n');
                }
            }
            AstNode::VarDecl { var_type, is_input, name, init_value } => {
                // Convert input variables to public struct fields (for UI configuration) or global consts
                let type_str = self.mql_to_rust_type(var_type)?;
                if *is_input {
                    // For now, hardcode inputs as consts to simplify the transpiler proof-of-concept
                    out.push_str(&format!("pub const {}: {} = ", name.to_uppercase(), type_str));
                } else {
                    out.push_str(&format!("let mut {}: {} = ", name, type_str));
                }
                
                if let Some(val) = init_value {
                    self.visit_node(val, out)?;
                } else {
                    out.push_str("Default::default()");
                }
                out.push_str(";\n");
            }
            AstNode::FunctionDecl { return_type, name, params, body } => {
                let ret_str = self.mql_to_rust_type(return_type)?;
                
                // Special handling for MQL5 entry points
                if name == "OnInit" || name == "OnDeinit" || name == "OnTick" || name == "OnTimer" {
                    // Passing the backtester context
                    out.push_str(&format!("pub fn mql_{}(bt_ctx: &mut Backtester", name));
                } else {
                    out.push_str(&format!("fn {}(", name));
                }

                // Add params explicitly handling
                if !params.is_empty() {
                    if name.starts_with("On") { out.push_str(", "); } // Add comma if context was added
                    for (i, p) in params.iter().enumerate() {
                        if let AstNode::VarDecl { var_type, name: p_name, .. } = p {
                            let p_type = self.mql_to_rust_type(var_type)?;
                            out.push_str(&format!("{}: &{}", p_name, p_type));
                            if i < params.len() - 1 { out.push_str(", "); }
                        }
                    }
                }
                
                out.push_str(")");
                if *return_type != Token::Void {
                    out.push_str(&format!(" -> {}", ret_str));
                }
                out.push_str(" ");
                self.visit_node(body, out)?;
            }
            AstNode::Block(nodes) => {
                out.push_str("{\n");
                for n in nodes {
                    self.visit_node(n, out)?;
                    out.push('\n');
                }
                out.push_str("}\n");
            }
            AstNode::ExpressionStatement(expr) => {
                self.visit_node(expr, out)?;
                out.push_str(";");
            }
            AstNode::ReturnStatement(opt_expr) => {
                out.push_str("return ");
                if let Some(expr) = opt_expr {
                    self.visit_node(expr, out)?;
                }
                out.push_str(";");
            }
            AstNode::IfStatement { condition, then_branch, else_branch } => {
                out.push_str("if ");
                self.visit_node(condition, out)?;
                out.push_str(" ");
                self.visit_node(then_branch, out)?;
                if let Some(e) = else_branch {
                    out.push_str(" else ");
                    self.visit_node(e, out)?;
                }
            }
            AstNode::BinaryOp { left, op, right } => {
                self.visit_node(left, out)?;
                let op_str = match op {
                    Token::Plus => " + ",
                    Token::Minus => " - ",
                    Token::Star => " * ",
                    Token::Slash => " / ",
                    Token::Assign => " = ",
                    Token::Equals => " == ",
                    Token::NotEquals => " != ",
                    Token::GreaterEq => " >= ",
                    Token::LessEq => " <= ",
                    Token::Greater => " > ",
                    Token::Less => " < ",
                    Token::And => " && ",
                    Token::Or => " || ",
                    _ => return Err(format!("Unsupported binary operator {:?}", op)),
                };
                out.push_str(op_str);
                self.visit_node(right, out)?;
            }
            AstNode::UnaryOp { op, expr } => {
                let op_str = match op {
                    Token::Not => "!",
                    Token::Minus => "-",
                    _ => return Err(format!("Unsupported unary operator {:?}", op)),
                };
                out.push_str(op_str);
                self.visit_node(expr, out)?;
            }
            AstNode::FunctionCall { name, args } => {
                // If it's a built in order function, route to the context
                if name == "OrderSend" { // Simulating simpler logic
                    out.push_str("bt_ctx.market_order(");
                } else {
                    out.push_str(&format!("{}(", name));
                }
                
                for (i, arg) in args.iter().enumerate() {
                    self.visit_node(arg, out)?;
                    if i < args.len() - 1 { out.push_str(", "); }
                }
                out.push_str(")");
            }
            AstNode::OrderSendCall { symbol, cmd, volume, price, sl, tp } => {
                // Specialized mapping for trading commands
                let cmd_str = if *cmd == Token::Identifier("ORDER_TYPE_BUY".to_string()) {
                    "OrderType::Buy"
                } else {
                    "OrderType::Sell"
                };
                out.push_str(&format!(
                    "bt_ctx.market_order(\"{}\", {}, {}, Some({}), Some({}), \"Time_Sim\".to_string())",
                    symbol, cmd_str, volume, sl, tp
                ));
            }
            AstNode::Identifier(id) => {
                out.push_str(id);
            }
            AstNode::Literal(tok) => {
                match tok {
                    Token::IntLiteral(i) => out.push_str(&i.to_string()),
                    Token::DoubleLiteral(d) => out.push_str(&format!("{:.5}", d)),
                    Token::BoolLiteral(b) => out.push_str(if *b { "true" } else { "false" }),
                    Token::StringLiteral(s) => out.push_str(&format!("\"{}\"", s)),
                    _ => return Err(format!("Unexpected literal token {:?}", tok)),
                }
            }
            _ => return Err("Unsupported AST Node".to_string()),
        }
        Ok(())
    }

    fn mql_to_rust_type(&self, mql_type: &Token) -> Result<&'static str, String> {
        match mql_type {
            Token::Int => Ok("i64"),
            Token::Double => Ok("f64"),
            Token::Bool => Ok("bool"),
            Token::String => Ok("String"),
            Token::Void => Ok("()"),
            Token::MqlTick => Ok("crate::data::parser::Tick"),
            Token::MqlRates => Ok("crate::data::parser::Ohlcv"),
            _ => Err(format!("Unknown or unmapped MQL5 type: {:?}", mql_type)),
        }
    }
}