use crate::context::InferenceContext;
use crate::inference_core::resolve_call;
use crate::magic_methods::*;
use crate::primitives::*;
use crate::typedef::{Type, TypeEnum::*};
use rustpython_parser::ast::{
    Comparison, Comprehension, ComprehensionKind, Expression, ExpressionType, Operator,
    UnaryOperator,
};
use std::convert::TryInto;

type ParserResult = Result<Option<Type>, String>;

pub fn infer_expr<'b: 'a, 'a>(
    ctx: &mut InferenceContext<'a>,
    expr: &'b Expression,
) -> ParserResult {
    match &expr.node {
        ExpressionType::Number { value } => infer_constant(ctx, value),
        ExpressionType::Identifier { name } => infer_identifier(ctx, name),
        ExpressionType::List { elements } => infer_list(ctx, elements),
        ExpressionType::Tuple { elements } => infer_tuple(ctx, elements),
        ExpressionType::Attribute { value, name } => infer_attribute(ctx, value, name),
        ExpressionType::BoolOp { values, .. } => infer_bool_ops(ctx, values),
        ExpressionType::Binop { a, b, op } => infer_bin_ops(ctx, op, a, b),
        ExpressionType::Unop { op, a } => infer_unary_ops(ctx, op, a),
        ExpressionType::Compare { vals, ops } => infer_compare(ctx, vals, ops),
        ExpressionType::Call {
            args,
            function,
            keywords,
        } => {
            if !keywords.is_empty() {
                Err("keyword is not supported".into())
            } else {
                infer_call(ctx, &args, &function)
            }
        }
        ExpressionType::Subscript { a, b } => infer_subscript(ctx, a, b),
        ExpressionType::IfExpression { test, body, orelse } => {
            infer_if_expr(ctx, &test, &body, orelse)
        }
        ExpressionType::Comprehension { kind, generators } => match kind.as_ref() {
            ComprehensionKind::List { element } => {
                if generators.len() == 1 {
                    infer_list_comprehension(ctx, element, &generators[0])
                } else {
                    Err("only 1 generator statement is supported".into())
                }
            }
            _ => Err("only list comprehension is supported".into()),
        },
        ExpressionType::True | ExpressionType::False => Ok(Some(ctx.get_primitive(BOOL_TYPE))),
        _ => Err("not supported".into()),
    }
}

fn infer_constant(
    ctx: &mut InferenceContext,
    value: &rustpython_parser::ast::Number,
) -> ParserResult {
    use rustpython_parser::ast::Number;
    match value {
        Number::Integer { value } => {
            let int32: Result<i32, _> = value.try_into();
            if int32.is_ok() {
                Ok(Some(ctx.get_primitive(INT32_TYPE)))
            } else {
                let int64: Result<i64, _> = value.try_into();
                if int64.is_ok() {
                    Ok(Some(ctx.get_primitive(INT64_TYPE)))
                } else {
                    Err("integer out of range".into())
                }
            }
        }
        Number::Float { .. } => Ok(Some(ctx.get_primitive(FLOAT_TYPE))),
        _ => Err("not supported".into()),
    }
}

fn infer_identifier(ctx: &mut InferenceContext, name: &str) -> ParserResult {
    Ok(Some(ctx.resolve(name)?))
}

fn infer_list<'b: 'a, 'a>(
    ctx: &mut InferenceContext<'a>,
    elements: &'b [Expression],
) -> ParserResult {
    if elements.is_empty() {
        return Ok(Some(ParametricType(LIST_TYPE, vec![BotType.into()]).into()));
    }

    let mut types = elements.iter().map(|v| infer_expr(ctx, v));

    let head = types.next().unwrap()?;
    if head.is_none() {
        return Err("list elements must have some type".into());
    }
    for v in types {
        if v? != head {
            return Err("inhomogeneous list is not allowed".into());
        }
    }
    Ok(Some(ParametricType(LIST_TYPE, vec![head.unwrap()]).into()))
}

fn infer_tuple<'b: 'a, 'a>(
    ctx: &mut InferenceContext<'a>,
    elements: &'b [Expression],
) -> ParserResult {
    let types: Result<Option<Vec<_>>, String> =
        elements.iter().map(|v| infer_expr(ctx, v)).collect();
    if let Some(t) = types? {
        Ok(Some(ParametricType(TUPLE_TYPE, t).into()))
    } else {
        Err("tuple elements must have some type".into())
    }
}

fn infer_attribute<'a>(
    ctx: &mut InferenceContext<'a>,
    value: &'a Expression,
    name: &str,
) -> ParserResult {
    let value = infer_expr(ctx, value)?.ok_or_else(|| "no value".to_string())?;
    if let TypeVariable(id) = value.as_ref() {
        let v = ctx.get_variable_def(*id);
        if v.bound.is_empty() {
            return Err("no fields on unbounded type variable".into());
        }
        let ty = v.bound[0].get_base(ctx).and_then(|v| v.fields.get(name));
        if ty.is_none() {
            return Err("unknown field".into());
        }
        for x in v.bound[1..].iter() {
            let ty1 = x.get_base(ctx).and_then(|v| v.fields.get(name));
            if ty1 != ty {
                return Err("unknown field (type mismatch between variants)".into());
            }
        }
        return Ok(Some(ty.unwrap().clone()));
    }

    match value.get_base(ctx) {
        Some(b) => match b.fields.get(name) {
            Some(t) => Ok(Some(t.clone())),
            None => Err("no such field".into()),
        },
        None => Err("this object has no fields".into()),
    }
}

fn infer_bool_ops<'a>(ctx: &mut InferenceContext<'a>, values: &'a [Expression]) -> ParserResult {
    assert_eq!(values.len(), 2);
    let left = infer_expr(ctx, &values[0])?.ok_or_else(|| "no value".to_string())?;
    let right = infer_expr(ctx, &values[1])?.ok_or_else(|| "no value".to_string())?;

    let b = ctx.get_primitive(BOOL_TYPE);
    if left == b && right == b {
        Ok(Some(b))
    } else {
        Err("bool operands must be bool".into())
    }
}

fn infer_bin_ops<'b: 'a, 'a>(
    ctx: &mut InferenceContext<'a>,
    op: &Operator,
    left: &'b Expression,
    right: &'b Expression,
) -> ParserResult {
    let left = infer_expr(ctx, left)?.ok_or_else(|| "no value".to_string())?;
    let right = infer_expr(ctx, right)?.ok_or_else(|| "no value".to_string())?;
    let fun = binop_name(op);
    resolve_call(ctx, Some(left), fun, &[right])
}

fn infer_unary_ops<'b: 'a, 'a>(
    ctx: &mut InferenceContext<'a>,
    op: &UnaryOperator,
    obj: &'b Expression,
) -> ParserResult {
    let ty = infer_expr(ctx, obj)?.ok_or_else(|| "no value".to_string())?;
    if let UnaryOperator::Not = op {
        if ty == ctx.get_primitive(BOOL_TYPE) {
            Ok(Some(ty))
        } else {
            Err("logical not must be applied to bool".into())
        }
    } else {
        resolve_call(ctx, Some(ty), unaryop_name(op), &[])
    }
}

fn infer_compare<'b: 'a, 'a>(
    ctx: &mut InferenceContext<'a>,
    vals: &'b [Expression],
    ops: &'b [Comparison],
) -> ParserResult {
    let types: Result<Option<Vec<_>>, _> = vals.iter().map(|v| infer_expr(ctx, v)).collect();
    let types = types?;
    if types.is_none() {
        return Err("comparison operands must have type".into());
    }
    let types = types.unwrap();
    let boolean = ctx.get_primitive(BOOL_TYPE);
    let left = &types[..types.len() - 1];
    let right = &types[1..];

    for ((a, b), op) in left.iter().zip(right.iter()).zip(ops.iter()) {
        let fun = comparison_name(op).ok_or_else(|| "unsupported comparison".to_string())?;
        let ty = resolve_call(ctx, Some(a.clone()), fun, &[b.clone()])?;
        if ty.is_none() || ty.unwrap() != boolean {
            return Err("comparison result must be boolean".into());
        }
    }
    Ok(Some(boolean))
}

fn infer_call<'b: 'a, 'a>(
    ctx: &mut InferenceContext<'a>,
    args: &'b [Expression],
    function: &'b Expression,
) -> ParserResult {
    let types: Result<Option<Vec<_>>, _> = args.iter().map(|v| infer_expr(ctx, v)).collect();
    let types = types?;
    if types.is_none() {
        return Err("function params must have type".into());
    }

    let (obj, fun) = match &function.node {
        ExpressionType::Identifier { name } => (None, name),
        ExpressionType::Attribute { value, name } => (
            Some(infer_expr(ctx, &value)?.ok_or_else(|| "no value".to_string())?),
            name,
        ),
        _ => return Err("not supported".into()),
    };
    resolve_call(ctx, obj, fun.as_str(), &types.unwrap())
}

fn infer_subscript<'b: 'a, 'a>(
    ctx: &mut InferenceContext<'a>,
    a: &'b Expression,
    b: &'b Expression,
) -> ParserResult {
    let a = infer_expr(ctx, a)?.ok_or_else(|| "no value".to_string())?;
    let t = if let ParametricType(LIST_TYPE, ls) = a.as_ref() {
        ls[0].clone()
    } else {
        return Err("subscript is not supported for types other than list".into());
    };

    match &b.node {
        ExpressionType::Slice { elements } => {
            let int32 = ctx.get_primitive(INT32_TYPE);
            let types: Result<Option<Vec<_>>, _> = elements
                .iter()
                .map(|v| {
                    if let ExpressionType::None = v.node {
                        Ok(Some(int32.clone()))
                    } else {
                        infer_expr(ctx, v)
                    }
                })
                .collect();
            let types = types?.ok_or_else(|| "slice must have type".to_string())?;
            if types.iter().all(|v| v == &int32) {
                Ok(Some(a))
            } else {
                Err("slice must be int32 type".into())
            }
        }
        _ => {
            let b = infer_expr(ctx, b)?.ok_or_else(|| "no value".to_string())?;
            if b == ctx.get_primitive(INT32_TYPE) {
                Ok(Some(t))
            } else {
                Err("index must be either slice or int32".into())
            }
        }
    }
}

fn infer_if_expr<'b: 'a, 'a>(
    ctx: &mut InferenceContext<'a>,
    test: &'b Expression,
    body: &'b Expression,
    orelse: &'b Expression,
) -> ParserResult {
    let test = infer_expr(ctx, test)?.ok_or_else(|| "no value".to_string())?;
    if test != ctx.get_primitive(BOOL_TYPE) {
        return Err("test should be bool".into());
    }

    let body = infer_expr(ctx, body)?;
    let orelse = infer_expr(ctx, orelse)?;
    if body.as_ref() == orelse.as_ref() {
        Ok(body)
    } else {
        Err("divergent type".into())
    }
}

fn infer_simple_binding<'a: 'b, 'b>(
    ctx: &mut InferenceContext<'b>,
    name: &'a Expression,
    ty: Type,
) -> Result<(), String> {
    match &name.node {
        ExpressionType::Identifier { name } => {
            if name == "_" {
                Ok(())
            } else if ctx.defined(name.as_str()) {
                Err("duplicated naming".into())
            } else {
                ctx.assign(name.as_str(), ty)?;
                Ok(())
            }
        }
        ExpressionType::Tuple { elements } => {
            if let ParametricType(TUPLE_TYPE, ls) = ty.as_ref() {
                if elements.len() == ls.len() {
                    for (a, b) in elements.iter().zip(ls.iter()) {
                        infer_simple_binding(ctx, a, b.clone())?;
                    }
                    Ok(())
                } else {
                    Err("different length".into())
                }
            } else {
                Err("not supported".into())
            }
        }
        _ => Err("not supported".into()),
    }
}

fn infer_list_comprehension<'b: 'a, 'a>(
    ctx: &mut InferenceContext<'a>,
    element: &'b Expression,
    comprehension: &'b Comprehension,
) -> ParserResult {
    if comprehension.is_async {
        return Err("async is not supported".into());
    }

    let iter = infer_expr(ctx, &comprehension.iter)?.ok_or_else(|| "no value".to_string())?;
    if let ParametricType(LIST_TYPE, ls) = iter.as_ref() {
        ctx.with_scope(|ctx| {
            infer_simple_binding(ctx, &comprehension.target, ls[0].clone())?;

            let boolean = ctx.get_primitive(BOOL_TYPE);
            for test in comprehension.ifs.iter() {
                let result =
                    infer_expr(ctx, test)?.ok_or_else(|| "no value in test".to_string())?;
                if result != boolean {
                    return Err("test must be bool".into());
                }
            }
            let result = infer_expr(ctx, element)?.ok_or_else(|| "no value")?;
            Ok(Some(ParametricType(LIST_TYPE, vec![result]).into()))
        })
        .1
    } else {
        Err("iteration is supported for list only".into())
    }
}