use std::{collections::HashMap, str::FromStr};

use crate::{
    ast,
    builtin::Builtin,
    symbol_table::{DefId, SymbolSpec, SymbolTable},
};

mod test;
mod types;

pub use types::*;

pub fn reduce(ast: &ast::AST, symbol_table: &SymbolTable) -> ReducedIR {
    let reducer = Reducer::new(symbol_table);
    reducer.reduce(ast)
}

struct Reducer<'a> {
    symbol_table: &'a SymbolTable,
    functions: HashMap<DefId, FunctionDefinition>,
}

impl<'a> Reducer<'a> {
    fn new(symbol_table: &'a SymbolTable) -> Self {
        Self { symbol_table, functions: HashMap::new() }
    }

    fn reduce(mut self, ast: &ast::AST) -> ReducedIR {
        // First reduce all functions
        // TODO once this works, maybe rewrite it using the Visitor
        for statement in ast.statements.statements.iter() {
            self.top_level_statement(statement);
        }

        // Then compute the entrypoint statements (which may reference previously-computed
        // functions by ID)
        let mut entrypoint = vec![];
        for statement in ast.statements.statements.iter() {
            let ast::Statement { id: item_id, kind, .. } = statement;
            match &kind {
                ast::StatementKind::Expression(expr) => {
                    entrypoint.push(Statement::Expression(self.expression(expr)));
                }
                ast::StatementKind::Declaration(ast::Declaration::Binding {
                    name: _,
                    constant,
                    expr,
                    ..
                }) => {
                    let symbol = self.symbol_table.lookup_symbol(item_id).unwrap();
                    let def_id = symbol.def_id().unwrap();
                    entrypoint.push(Statement::Binding {
                        id: def_id,
                        constant: *constant,
                        expr: self.expression(expr),
                    });
                }
                _ => (),
            }
        }

        ReducedIR { functions: self.functions, entrypoint }
    }

    fn top_level_statement(&mut self, statement: &ast::Statement) {
        let ast::Statement { id: item_id, kind, .. } = statement;
        match kind {
            ast::StatementKind::Expression(_expr) => {
                //TODO expressions can in principle contain definitions, but I won't worry
                //about it now
            }
            ast::StatementKind::Declaration(decl) =>
                if let ast::Declaration::FuncDecl(_, statements) = decl {
                    self.insert_function_definition(item_id, statements);
                },
            ast::StatementKind::Import(..) => (),
            ast::StatementKind::Module(_modspec) => {
                //TODO handle modules
            }
        }
    }

    fn function_internal_statement(&mut self, statement: &ast::Statement) -> Option<Statement> {
        let ast::Statement { id: item_id, kind, .. } = statement;
        match kind {
            ast::StatementKind::Expression(expr) => Some(Statement::Expression(self.expression(expr))),
            ast::StatementKind::Declaration(decl) => match decl {
                ast::Declaration::FuncDecl(_, statements) => {
                    self.insert_function_definition(item_id, statements);
                    None
                }
                ast::Declaration::Binding { constant, expr, .. } => {
                    let symbol = self.symbol_table.lookup_symbol(item_id).unwrap();
                    let def_id = symbol.def_id().unwrap();
                    Some(Statement::Binding { id: def_id, constant: *constant, expr: self.expression(expr) })
                }

                _ => None,
            },
            _ => None,
        }
    }

    fn insert_function_definition(&mut self, item_id: &ast::ItemId, statements: &ast::Block) {
        let symbol = self.symbol_table.lookup_symbol(item_id).unwrap();
        let def_id = symbol.def_id().unwrap();
        let function_def = FunctionDefinition { body: self.function_internal_block(statements) };
        self.functions.insert(def_id, function_def);
    }

    fn expression(&mut self, expr: &ast::Expression) -> Expression {
        use crate::ast::ExpressionKind::*;

        match &expr.kind {
            NatLiteral(n) => Expression::Literal(Literal::Nat(*n)),
            FloatLiteral(f) => Expression::Literal(Literal::Float(*f)),
            StringLiteral(s) => Expression::Literal(Literal::StringLit(s.clone())),
            BoolLiteral(b) => Expression::Literal(Literal::Bool(*b)),
            BinExp(binop, lhs, rhs) => self.binop(binop, lhs, rhs),
            PrefixExp(op, arg) => self.prefix(op, arg),
            Value(qualified_name) => self.value(qualified_name),
            Call { f, arguments } => Expression::Call {
                f: Box::new(self.expression(f)),
                args: arguments.iter().map(|arg| self.invocation_argument(arg)).collect(),
            },
            TupleLiteral(exprs) => Expression::Tuple(exprs.iter().map(|e| self.expression(e)).collect()),
            IfExpression { discriminator, body } =>
                self.reduce_if_expression(discriminator.as_ref().map(|x| x.as_ref()), body),
            Lambda { params, body, .. } => Expression::Callable(Callable::Lambda {
                arity: params.len() as u8,
                body: self.function_internal_block(body),
            }),
            NamedStruct { name, fields } => {
                let symbol = self.symbol_table.lookup_symbol(&name.id).unwrap();
                let constructor = match symbol.spec() {
                    SymbolSpec::RecordConstructor { tag, members: _, type_id } =>
                        Expression::Callable(Callable::RecordConstructor { type_id, tag }),
                    e => return Expression::ReductionError(format!("Bad symbol for NamedStruct: {:?}", e)),
                };

                //TODO need to order the fields correctly, which needs symbol table information
                // Until this happens, NamedStructs won't work
                let mut ordered_args = vec![];
                for (_name, _type_id) in fields {
                    unimplemented!()
                }

                Expression::Call { f: Box::new(constructor), args: ordered_args }
            }
            Index { .. } => Expression::ReductionError("Index expr not implemented".to_string()),
            WhileExpression { .. } => Expression::ReductionError("While expr not implemented".to_string()),
            ForExpression { .. } => Expression::ReductionError("For expr not implemented".to_string()),
            ListLiteral { .. } => Expression::ReductionError("ListLiteral expr not implemented".to_string()),
        }
    }

    fn reduce_if_expression(
        &mut self,
        discriminator: Option<&ast::Expression>,
        body: &ast::IfExpressionBody,
    ) -> Expression {
        use ast::IfExpressionBody::*;

        let cond = Box::new(match discriminator {
            Some(expr) => self.expression(expr),
            None => return Expression::ReductionError("blank cond if-expr not supported".to_string()),
        });
        match body {
            SimpleConditional { then_case, else_case } => {
                let then_clause = self.function_internal_block(then_case);
                let else_clause = match else_case.as_ref() {
                    None => vec![],
                    Some(stmts) => self.function_internal_block(stmts),
                };
                Expression::Conditional { cond, then_clause, else_clause }
            }
            SimplePatternMatch { pattern, then_case, else_case } => {
                let alternatives = vec![
                    Alternative {
                        pattern: match pattern.reduce(self.symbol_table) {
                            Ok(p) => p,
                            Err(e) => return Expression::ReductionError(format!("Bad pattern: {:?}", e)),
                        },
                        item: self.function_internal_block(then_case),
                    },
                    Alternative {
                        pattern: Pattern::Ignored,
                        item: match else_case.as_ref() {
                            Some(else_case) => self.function_internal_block(else_case),
                            None => vec![],
                        },
                    },
                ];

                Expression::CaseMatch { cond, alternatives }
            }
            CondList(ref condition_arms) => {
                let mut alternatives = vec![];
                for arm in condition_arms {
                    match arm.condition {
                        ast::Condition::Expression(ref _expr) =>
                            return Expression::ReductionError("case-expression".to_string()),
                        ast::Condition::Pattern(ref pat) => {
                            let alt = Alternative {
                                pattern: match pat.reduce(self.symbol_table) {
                                    Ok(p) => p,
                                    Err(e) =>
                                        return Expression::ReductionError(format!("Bad pattern: {:?}", e)),
                                },
                                item: self.function_internal_block(&arm.body),
                            };
                            alternatives.push(alt);
                        }
                        ast::Condition::TruncatedOp(_, _) =>
                            return Expression::ReductionError("case-expression-trunc-op".to_string()),
                        ast::Condition::Else =>
                            return Expression::ReductionError("case-expression-else".to_string()),
                    }
                }
                Expression::CaseMatch { cond, alternatives }
            }
        }
    }

    fn invocation_argument(&mut self, invoc: &ast::InvocationArgument) -> Expression {
        use crate::ast::InvocationArgument::*;
        match invoc {
            Positional(ex) => self.expression(ex),
            Keyword { .. } => Expression::ReductionError("Keyword arguments not supported".to_string()),
            Ignored => Expression::ReductionError("Ignored arguments not supported".to_string()),
        }
    }

    fn function_internal_block(&mut self, block: &ast::Block) -> Vec<Statement> {
        block.statements.iter().filter_map(|stmt| self.function_internal_statement(stmt)).collect()
    }

    fn prefix(&mut self, prefix: &ast::PrefixOp, arg: &ast::Expression) -> Expression {
        let builtin: Option<Builtin> = TryFrom::try_from(prefix).ok();
        match builtin {
            Some(op) => Expression::Call {
                f: Box::new(Expression::Callable(Callable::Builtin(op))),
                args: vec![self.expression(arg)],
            },
            None => {
                //TODO need this for custom prefix ops
                Expression::ReductionError("User-defined prefix ops not supported".to_string())
            }
        }
    }

    fn binop(&mut self, binop: &ast::BinOp, lhs: &ast::Expression, rhs: &ast::Expression) -> Expression {
        use Expression::ReductionError;

        let operation = Builtin::from_str(binop.sigil()).ok();
        match operation {
            Some(Builtin::Assignment) => {
                let lval = match &lhs.kind {
                    ast::ExpressionKind::Value(qualified_name) => {
                        if let Some(symbol) = self.symbol_table.lookup_symbol(&qualified_name.id) {
                            symbol.def_id().unwrap()
                        } else {
                            return ReductionError(format!("Couldn't look up name: {:?}", qualified_name));
                        }
                    }
                    _ => return ReductionError("Trying to assign to a non-name".to_string()),
                };

                Expression::Assign { lval, rval: Box::new(self.expression(rhs)) }
            }
            Some(op) => Expression::Call {
                f: Box::new(Expression::Callable(Callable::Builtin(op))),
                args: vec![self.expression(lhs), self.expression(rhs)],
            },
            //TODO handle a user-defined operation
            None => ReductionError("User-defined operations not supported".to_string()),
        }
    }

    fn value(&mut self, qualified_name: &ast::QualifiedName) -> Expression {
        use SymbolSpec::*;

        let symbol = match self.symbol_table.lookup_symbol(&qualified_name.id) {
            Some(s) => s,
            None =>
                return Expression::ReductionError(format!("No symbol found for name: {:?}", qualified_name)),
        };

        let def_id = symbol.def_id();

        match symbol.spec() {
            Func => Expression::Lookup(Lookup::Function(def_id.unwrap())),
            GlobalBinding => Expression::Lookup(Lookup::GlobalVar(def_id.unwrap())),
            LocalVariable => Expression::Lookup(Lookup::LocalVar(def_id.unwrap())),
            FunctionParam(n) => Expression::Lookup(Lookup::Param(n)),
            DataConstructor { tag, type_id } =>
                Expression::Callable(Callable::DataConstructor { type_id, tag }),
            RecordConstructor { .. } => Expression::ReductionError(format!(
                "The symbol for value {:?} is unexpectdly a RecordConstructor",
                qualified_name
            )),
        }
    }
}

impl ast::Pattern {
    fn reduce(&self, symbol_table: &SymbolTable) -> Result<Pattern, PatternError> {
        Ok(match self {
            ast::Pattern::Ignored => Pattern::Ignored,
            ast::Pattern::TuplePattern(subpatterns) => {
                let items: Result<Vec<Pattern>, PatternError> =
                    subpatterns.iter().map(|pat| pat.reduce(symbol_table)).into_iter().collect();
                let items = items?;
                Pattern::Tuple { tag: None, subpatterns: items }
            }
            ast::Pattern::Literal(lit) => Pattern::Literal(match lit {
                ast::PatternLiteral::NumPattern { neg, num } => match (neg, num) {
                    (false, ast::ExpressionKind::NatLiteral(n)) => Literal::Nat(*n),
                    (false, ast::ExpressionKind::FloatLiteral(f)) => Literal::Float(*f),
                    (true, ast::ExpressionKind::NatLiteral(n)) => Literal::Int(-(*n as i64)),
                    (true, ast::ExpressionKind::FloatLiteral(f)) => Literal::Float(-f),
                    (_, e) =>
                        return Err(format!("Internal error, unexpected pattern literal: {:?}", e).into()),
                },
                ast::PatternLiteral::StringPattern(s) => Literal::StringLit(s.clone()),
                ast::PatternLiteral::BoolPattern(b) => Literal::Bool(*b),
            }),
            ast::Pattern::TupleStruct(name, subpatterns) => {
                let symbol = symbol_table.lookup_symbol(&name.id).unwrap();
                if let SymbolSpec::DataConstructor { tag, type_id: _ } = symbol.spec() {
                    let items: Result<Vec<Pattern>, PatternError> =
                        subpatterns.iter().map(|pat| pat.reduce(symbol_table)).into_iter().collect();
                    let items = items?;
                    Pattern::Tuple { tag: Some(tag), subpatterns: items }
                } else {
                    return Err(
                        "Internal error, trying to match something that's not a DataConstructor".into()
                    );
                }
            }
            ast::Pattern::VarOrName(name) => {
                let symbol = symbol_table.lookup_symbol(&name.id).unwrap();
                match symbol.spec() {
                    SymbolSpec::DataConstructor { tag, type_id: _ } =>
                        Pattern::Tuple { tag: Some(tag), subpatterns: vec![] },
                    SymbolSpec::LocalVariable => {
                        let def_id = symbol.def_id().unwrap();
                        Pattern::Binding(def_id)
                    }
                    spec => return Err(format!("Unexpected VarOrName symbol: {:?}", spec).into()),
                }
            }
            ast::Pattern::Record(name, _specified_members /*Vec<(Rc<String>, Pattern)>*/) => {
                let symbol = symbol_table.lookup_symbol(&name.id).unwrap();
                match symbol.spec() {
                    SymbolSpec::RecordConstructor { tag: _, members: _, type_id: _ } => unimplemented!(),
                    spec => return Err(format!("Unexpected Record pattern symbol: {:?}", spec).into()),
                }
            }
        })
    }
}