//! Minimal codegen for self-hosting MVP

//! Direct Rust mapping with no optimization - as specified in self-hosting spec

#![allow(clippy::missing_errors_doc)]

use crate::frontend::ast::{Expr, ExprKind, Literal, Pattern, BinaryOp, UnaryOp};

use anyhow::Result;

/// Minimal code generator for self-hosting

pub struct MinimalCodeGen;

impl MinimalCodeGen {

    /// Generate Rust code directly from AST with no optimization

    pub fn gen_expr(expr: &Expr) -> Result<String> {

        match &expr.kind {

            ExprKind::Literal(lit) => Self::gen_literal(lit),

            ExprKind::Identifier(name) => Ok(name.clone()),

            ExprKind::Binary { left, op, right } => {

                let left_code = Self::gen_expr(left)?;

                let right_code = Self::gen_expr(right)?;

                let op_code = Self::gen_binary_op(*op);

                Ok(format!("({left_code} {op_code} {right_code})"))

            }

            ExprKind::Unary { op, operand } => {

                let operand_code = Self::gen_expr(operand)?;

                let op_code = Self::gen_unary_op(*op);

                Ok(format!("({op_code} {operand_code})"))

            }

            ExprKind::Let { name, value, body, .. } => {

                let value_code = Self::gen_expr(value)?;

                let body_code = Self::gen_expr(body)?;

                Ok(format!("{{ let {name} = {value_code}; {body_code} }}"))

            }

            ExprKind::Function { name, params, body, .. } => {

                let param_list = params.iter()

                    .map(|p| { let name = p.name(); format!("{name}: i32") }) // Simplified for MVP

                    .collect::<Vec<_>>()

                    .join(", ");

                let body_code = Self::gen_expr(body)?;

                Ok(format!("fn {name}({param_list}) {{ {body_code} }}"))

            }

            ExprKind::Lambda { params, body } => {

                let param_list = params.iter()

                    .map(crate::frontend::ast::Param::name)

                    .collect::<Vec<_>>()

                    .join(", ");

                let body_code = Self::gen_expr(body)?;

                Ok(format!("|{param_list}| {body_code}"))

            }

            ExprKind::Call { func, args } => {

                let func_code = Self::gen_expr(func)?;

                let arg_codes = args.iter()

                    .map(Self::gen_expr)

                    .collect::<Result<Vec<_>>>()?;

                Ok(format!("{func_code}({})", arg_codes.join(", ")))

            }

            ExprKind::If { condition, then_branch, else_branch } => {

                let cond_code = Self::gen_expr(condition)?;

                let then_code = Self::gen_expr(then_branch)?;

                if let Some(else_expr) = else_branch {

                    let else_code = Self::gen_expr(else_expr)?;

                    Ok(format!("if {cond_code} {{ {then_code} }} else {{ {else_code} }}"))

                } else {

                    Ok(format!("if {cond_code} {{ {then_code} }}"))

                }

            }

            ExprKind::Block(exprs) => {

                let mut code = String::new();

                code.push_str("{ ");

                for (i, expr) in exprs.iter().enumerate() {

                    let expr_code = Self::gen_expr(expr)?;

                    if i == exprs.len() - 1 {

                        // Last expression is the return value

                        code.push_str(&expr_code);

                    } else {

                        code.push_str(&format!("{expr_code}; "));

                    }

                }

                code.push_str(" }");

                Ok(code)

            }

            ExprKind::Match { expr, arms } => {

                let expr_code = Self::gen_expr(expr)?;

                let mut code = format!("match {expr_code} {{\n");

                for arm in arms {

                    let pattern_code = Self::gen_pattern(&arm.pattern)?;

                    let body_code = Self::gen_expr(&arm.body)?;

                    code.push_str(&format!("    {pattern_code} => {body_code},\n"));

                }

                code.push('}');

                Ok(code)

            }

            ExprKind::List(elements) => {

                let element_codes = elements.iter()

                    .map(Self::gen_expr)

                    .collect::<Result<Vec<_>>>()?;

                let elements = element_codes.join(", ");

                Ok(format!("vec![{elements}]"))

            }

            ExprKind::Struct { name, fields, .. } => {

                let field_list = fields.iter()

                    .map(|f| { let name = &f.name; format!("    {name}: String,") }) // Simplified for MVP

                    .collect::<Vec<_>>()

                    .join("\n");

                Ok(format!("struct {name} {{\n{field_list}\n}}"))

            }

            ExprKind::StructLiteral { name, fields } => {

                let field_codes = fields.iter()

                    .map(|f| {

                        let value_code = Self::gen_expr(&f.1)?;

                        let field_name = &f.0;

                        Ok(format!("{field_name}: {value_code}"))

                    })

                    .collect::<Result<Vec<_>>>()?;

                let fields = field_codes.join(", ");

                Ok(format!("{name} {{ {fields} }}"))

            }

            ExprKind::MethodCall { receiver, method, args } => {

                let receiver_code = Self::gen_expr(receiver)?;

                let arg_codes = args.iter()

                    .map(Self::gen_expr)

                    .collect::<Result<Vec<_>>>()?;

                let args = arg_codes.join(", ");

                Ok(format!("{receiver_code}.{method}({args})"))

            }

            ExprKind::Macro { name, args } => {

                let arg_codes = args.iter()

                    .map(Self::gen_expr)

                    .collect::<Result<Vec<_>>>()?;

                let args = arg_codes.join(", ");

                Ok(format!("{name}!({args})"))

            }

            ExprKind::QualifiedName { module, name } => {

                Ok(format!("{module}::{name}"))

            }

            ExprKind::StringInterpolation { parts } => {

                // Simplified string interpolation for MVP

                let mut result = String::from("format!(");

                let mut format_str = String::new();

                let mut args = Vec::new();

                for part in parts {

                    match part {

                        crate::frontend::ast::StringPart::Text(s) => {

                            format_str.push_str(s);

                        }

                        crate::frontend::ast::StringPart::Expr(expr) => {

                            format_str.push_str("{}");

                            args.push(Self::gen_expr(expr)?);

                        }

                        crate::frontend::ast::StringPart::ExprWithFormat { expr, format_spec } => {

                            format_str.push('{');

                            format_str.push_str(format_spec);

                            format_str.push('}');

                            args.push(Self::gen_expr(expr)?);

                        }

                    }

                }

                result.push_str(&format!("\"{format_str}\""));

                if !args.is_empty() {

                    result.push_str(", ");

                    result.push_str(&args.join(", "));

                }

                result.push(')');

                Ok(result)

            }

            _ => {

                // For self-hosting MVP, unsupported constructs generate compile errors

                // This ensures developers know what needs to be implemented

                Err(anyhow::anyhow!(

                    "Minimal codegen does not support {:?} - use full transpiler for complete language support", 

                    expr.kind

                ))

            }

        }

    }

    fn gen_literal(lit: &Literal) -> Result<String> {

        match lit {

            Literal::Integer(i) => Ok(i.to_string()),

            Literal::Float(f) => Ok(f.to_string()),

            Literal::String(s) => Ok(format!("\"{}\"", s.replace('"', "\\\""))),

            Literal::Bool(b) => Ok(b.to_string()),

            Literal::Char(c) => Ok(format!("'{c}'")),

            Literal::Unit => Ok("()".to_string()),

        }

    }

    fn gen_binary_op(op: BinaryOp) -> &'static str {

        match op {

            BinaryOp::Add => "+",

            BinaryOp::Subtract => "-", 

            BinaryOp::Multiply => "*",

            BinaryOp::Divide => "/",

            BinaryOp::Modulo => "%",

            BinaryOp::Equal => "==",

            BinaryOp::NotEqual => "!=",

            BinaryOp::Less => "<",

            BinaryOp::LessEqual => "<=",

            BinaryOp::Greater => ">",

            BinaryOp::GreaterEqual => ">=",

            BinaryOp::And => "&&",

            BinaryOp::Or => "||",

            BinaryOp::NullCoalesce => "??", // JavaScript-style null coalescing

            BinaryOp::BitwiseAnd => "&",

            BinaryOp::BitwiseOr => "|",

            BinaryOp::BitwiseXor => "^",

            BinaryOp::LeftShift => "<<",

            BinaryOp::Power => "pow", // Will need function call wrapper

        }

    }

    fn gen_unary_op(op: UnaryOp) -> &'static str {

        match op {

            UnaryOp::Not => "!",

            UnaryOp::Negate => "-",

            UnaryOp::BitwiseNot => "~",

            UnaryOp::Reference => "&",

        }

    }

    fn gen_pattern(pattern: &Pattern) -> Result<String> {

        match pattern {

            Pattern::Wildcard => Ok("_".to_string()),

            Pattern::Literal(lit) => Self::gen_literal(lit),

            Pattern::Identifier(name) => Ok(name.clone()),

            Pattern::List(patterns) => {

                let pattern_codes = patterns.iter()

                    .map(Self::gen_pattern)

                    .collect::<Result<Vec<_>>>()?;

                let patterns = pattern_codes.join(", ");

                Ok(format!("[{patterns}]"))

            }

            Pattern::Ok(inner) => {

                let inner_code = Self::gen_pattern(inner)?;

                Ok(format!("Ok({inner_code})"))

            }

            Pattern::Err(inner) => {

                let inner_code = Self::gen_pattern(inner)?;

                Ok(format!("Err({inner_code})"))

            }

            Pattern::Some(inner) => {

                let inner_code = Self::gen_pattern(inner)?;

                Ok(format!("Some({inner_code})"))

            }

            Pattern::None => Ok("None".to_string()),

            _ => Ok("_".to_string()), // Simplified for MVP

        }

    }

    // Type generation simplified for MVP - focus on minimal working compiler

    #[allow(dead_code)]

    fn gen_type(_ty: &crate::frontend::ast::Type) -> Result<String> {

        Ok("String".to_string()) // Simplified for self-hosting MVP

    }

    /// Generate complete Rust program for self-hosting

    pub fn gen_program(expr: &Expr) -> Result<String> {

        let main_code = Self::gen_expr(expr)?;

        Ok(format!(

            "use std::collections::HashMap;\n\n{main_code}"

        ))

    }

}

#[cfg(test)]

mod tests {

    use super::*;

    use crate::frontend::parser::Parser;

    fn gen_str(input: &str) -> Result<String> {

        let mut parser = Parser::new(input);

        let expr = parser.parse()?;

        MinimalCodeGen::gen_expr(&expr)

    }

    #[test]

    fn test_basic_expressions() {

        assert_eq!(gen_str("42").unwrap(), "42");

        assert_eq!(gen_str("true").unwrap(), "true");

        assert_eq!(gen_str("\"hello\"").unwrap(), "\"hello\"");

    }

    #[test] 

    fn test_binary_ops() {

        assert_eq!(gen_str("1 + 2").unwrap(), "(1 + 2)");

        assert_eq!(gen_str("x * y").unwrap(), "(x * y)");

    }

    #[test]

    fn test_function_def() {

        let result = gen_str("fun add(x: i32, y: i32) -> i32 { x + y }").unwrap();

        assert!(result.contains("fn add(x: i32, y: i32)"));

    }

    #[test]

    fn test_lambda() {

        assert_eq!(gen_str("|x| x + 1").unwrap(), "|x| (x + 1)");

    }

    #[test]

    fn test_list() {

        assert_eq!(gen_str("[1, 2, 3]").unwrap(), "vec![1, 2, 3]");

    }

}