use rustc_hash::FxHashSet as HashSet;

use crate::Emitter;
use crate::expressions::context::ExpressionContext;
use crate::expressions::emission::EmittedExpression;
use crate::expressions::staging::VariadicCombine;
use crate::names::go_name;
use crate::types::abi_transition::emit_fn_arg_shape_adapter;
use crate::types::coercion::{Coercion, CoercionDirection, OptionShape, classify_option_shape};
use syntax::ast::{Annotation, Expression};
use syntax::types::Type;

struct CalleeAnalysis<'a> {
    fn_param_types: Vec<Type>,
    generic_fn_param_types: Option<&'a [Type]>,
    pointer_indices: HashSet<usize>,
    is_go_call: bool,
    is_prelude_dispatch: bool,
}

struct CallArgsContext<'a> {
    fn_param_types: &'a [Type],
    generic_fn_param_types: Option<&'a [Type]>,
    pointer_indices: &'a HashSet<usize>,
    is_go_call: bool,
    /// Suppresses the Go-fn identity short-circuit on fn-typed params
    /// dispatching into prelude generic helpers (e.g. `OptionAndThen`).
    is_prelude_dispatch: bool,
    spread: Option<&'a Expression>,
    wrap_spread_to_any: bool,
    combine_variadic: Option<VariadicCombine>,
}

/// Escape-aware close-quote search; plain `find` would collide with `\"` inside the literal.
fn find_go_string_literal_close(s: &str) -> Option<usize> {
    let bytes = s.as_bytes();
    if bytes.first() != Some(&b'"') {
        return None;
    }
    let mut i = 1;
    while i < bytes.len() {
        match bytes[i] {
            b'\\' => i += 2,
            b'"' => return Some(i),
            _ => i += 1,
        }
    }
    None
}

/// Collapse redundant fmt wrappers:
/// - `fmt.Print{ln}(fmt.Sprintf(...))` → `fmt.Printf(..., "\n")`
/// - `fmt.Print{ln}(fmt.Sprint(x))` → `fmt.Print{ln}(x)`
fn collapse_fmt_print(
    function_string: &str,
    args: &[Expression],
    args_strings: &[String],
    call_str: String,
) -> String {
    if function_string != "fmt.Print" && function_string != "fmt.Println" {
        return call_str;
    }
    if args_strings.len() != 1 {
        return call_str;
    }
    let arg = &args_strings[0];

    if let Some(inner) = arg
        .strip_prefix("fmt.Sprintf(")
        .and_then(|s| s.strip_suffix(')'))
    {
        let suffix = if function_string == "fmt.Println" {
            "\\n"
        } else {
            ""
        };
        if suffix.is_empty() {
            return format!("fmt.Printf({})", inner);
        }
        if let Some(close_quote) = find_go_string_literal_close(inner) {
            let format_open = &inner[..close_quote];
            let close_and_rest = &inner[close_quote..];
            return format!("fmt.Printf({}{}{})", format_open, suffix, close_and_rest);
        }
        return call_str;
    }

    if let Some(arg_expression) = args.first()
        && let Expression::Call {
            expression: inner_callee,
            args: inner_args,
            spread,
            ..
        } = arg_expression.unwrap_parens()
        && spread.is_none()
        && inner_args.len() == 1
        && inner_callee.unwrap_parens().as_dotted_path().as_deref() == Some("fmt.Sprint")
        && let Some(inner) = arg
            .strip_prefix("fmt.Sprint(")
            .and_then(|s| s.strip_suffix(')'))
    {
        return format!("{}({})", function_string, inner);
    }

    call_str
}

impl<'a> Emitter<'a> {
    pub(super) fn emit_regular_call(
        &mut self,
        output: &mut String,
        call_expression: &Expression,
        call_ty: Option<&Type>,
        expression_ctx: ExpressionContext<'_>,
    ) -> String {
        let Expression::Call {
            expression: callee,
            args,
            type_args,
            spread,
            ..
        } = call_expression
        else {
            unreachable!("emit_regular_call requires a Call expression");
        };
        let function = callee.unwrap_parens();
        let spread = (**spread).as_ref();

        if let Some(go_name) = self.get_callee_go_name(function).map(str::to_string) {
            let stages: Vec<EmittedExpression> = args
                .iter()
                .map(|a| self.stage_operand(a, ExpressionContext::value()))
                .collect();
            let wrap_to_any = Self::spread_needs_any_wrap(function, spread);
            let combine = Self::variadic_combine_for(function, spread, 0);
            let args_strings =
                self.sequence_with_spread(output, stages, spread, wrap_to_any, "_arg", combine);
            return format!("{}({})", go_name, args_strings.join(", "));
        }

        let mut function_string = self.emit_operand(output, function, expression_ctx.callee());

        if function.deref_inner().is_some() {
            function_string = format!("({})", function_string);
        }

        let type_args_string = self.resolve_call_type_args(
            function,
            type_args,
            call_ty,
            &mut function_string,
            expression_ctx,
        );

        let analysis = self.analyze_callee(function);
        let args_ctx = CallArgsContext {
            fn_param_types: &analysis.fn_param_types,
            generic_fn_param_types: analysis.generic_fn_param_types,
            pointer_indices: &analysis.pointer_indices,
            is_go_call: analysis.is_go_call,
            is_prelude_dispatch: analysis.is_prelude_dispatch,
            spread,
            wrap_spread_to_any: Self::spread_needs_any_wrap(function, spread),
            combine_variadic: Self::variadic_combine_for(function, spread, 0),
        };
        let args_strings = self.emit_call_args(output, args, &args_ctx);

        let call_str = format!(
            "{}{}({})",
            function_string,
            type_args_string,
            args_strings.join(", ")
        );
        let call_str = collapse_fmt_print(&function_string, args, &args_strings, call_str);

        if let Some(wrapped) =
            self.wrap_go_array_return(output, function, &call_str, expression_ctx)
        {
            return wrapped;
        }
        call_str
    }

    fn analyze_callee(&mut self, function: &Expression) -> CalleeAnalysis<'a> {
        let pointer_indices = self.get_recursive_enum_pointer_indices(function);
        let fn_param_types: Vec<Type> = function
            .get_type()
            .unwrap_forall()
            .get_function_params()
            .map(<[Type]>::to_vec)
            .unwrap_or_default();
        let generic_fn_param_types = self.callee_generic_param_types(function);
        let (is_go_call, is_prelude_dispatch) = match function.unwrap_parens() {
            Expression::DotAccess { expression, .. } => {
                let is_prelude = matches!(
                    expression.get_type().strip_refs().unwrap_forall(),
                    Type::Nominal { id, .. } if id.starts_with("prelude.")
                );
                (Self::is_go_receiver(expression), is_prelude)
            }
            Expression::Identifier {
                qualified: Some(q), ..
            } if q.starts_with("prelude.") => (false, true),
            _ => (false, false),
        };
        CalleeAnalysis {
            fn_param_types,
            generic_fn_param_types,
            pointer_indices,
            is_go_call,
            is_prelude_dispatch,
        }
    }

    /// Callee's declared param types from its definition, before instantiation.
    fn callee_generic_param_types(&self, function: &Expression) -> Option<&'a [Type]> {
        let Expression::Identifier {
            qualified: Some(q), ..
        } = function.unwrap_parens()
        else {
            return None;
        };
        self.facts
            .definition(q.as_str())?
            .ty()
            .unwrap_forall()
            .get_function_params()
    }

    /// Materialize a Go array-returning call into a variable and reslice it,
    /// so the caller sees a `[]T` slice instead of a fixed-size array.
    /// Skipped in discarded-call contexts via raw-array-return context.
    fn wrap_go_array_return(
        &mut self,
        output: &mut String,
        function: &Expression,
        call_str: &str,
        ctx: ExpressionContext<'_>,
    ) -> Option<String> {
        if ctx.keeps_raw_go_array_return() {
            return None;
        }
        let Expression::DotAccess {
            expression: receiver_expression,
            member,
            ..
        } = function.unwrap_parens()
        else {
            return None;
        };
        if !Self::is_go_receiver(receiver_expression)
            || !self.has_go_array_return(receiver_expression, member)
        {
            return None;
        }
        let temp = self.hoist_tmp_value(output, "arr", call_str);
        Some(format!("{}[:]", temp))
    }

    fn resolve_call_type_args(
        &mut self,
        function: &Expression,
        type_args: &[Annotation],
        call_ty: Option<&Type>,
        function_string: &mut String,
        ctx: ExpressionContext<'_>,
    ) -> String {
        let mut type_args_string = self.format_type_args_from_annotations(type_args);

        let slot_ty = ctx.expected_slot_type();

        if type_args_string.is_empty()
            && let Some(inferred) = self.infer_return_only_type_args(function)
        {
            type_args_string = slot_ty
                .and_then(|t| self.prelude_container_type_args(t))
                .unwrap_or(inferred);
        }

        if type_args_string.is_empty() && Self::is_prelude_variant_constructor(function) {
            let candidate = call_ty
                .and_then(|t| self.prelude_container_type_args(t))
                .or_else(|| slot_ty.and_then(|t| self.prelude_container_type_args(t)));
            type_args_string = candidate.unwrap_or_default();
        }

        if !type_args_string.is_empty()
            && let Some(bracket_start) = function_string.find('[')
        {
            function_string.truncate(bracket_start);
        }

        type_args_string
    }

    fn emit_call_args(
        &mut self,
        output: &mut String,
        args: &[Expression],
        ctx: &CallArgsContext<'_>,
    ) -> Vec<String> {
        let mut stages: Vec<EmittedExpression> = args
            .iter()
            .enumerate()
            .map(|(i, arg)| {
                let mut setup = String::new();
                let value = self.emit_call_arg(&mut setup, arg, i, ctx);
                EmittedExpression::new(setup, value, arg)
            })
            .collect();

        if let Some(spread) = ctx.spread
            && let Some(adapter_stage) = self.try_emit_variadic_spread_adapter(spread, ctx)
        {
            stages.push(adapter_stage);
            let spread_idx = stages.len() - 1;
            let mut values = self.sequence(output, stages, "_arg");
            self.finalize_spread_stage(
                &mut values,
                spread_idx,
                ctx.wrap_spread_to_any,
                ctx.combine_variadic.as_ref().cloned(),
            );
            return values;
        }

        self.sequence_with_spread(
            output,
            stages,
            ctx.spread,
            ctx.wrap_spread_to_any,
            "_arg",
            ctx.combine_variadic.as_ref().cloned(),
        )
    }

    pub(crate) fn variadic_combine_for(
        function: &Expression,
        spread: Option<&Expression>,
        extra_leading: usize,
    ) -> Option<VariadicCombine> {
        spread?;
        let fn_ty = function.get_type();
        let unwrapped = fn_ty.unwrap_forall();
        let elem_ty = unwrapped.is_variadic()?;
        let fixed_in_signature = unwrapped.get_function_params()?.len().saturating_sub(1);
        Some(VariadicCombine {
            elem_ty,
            fixed_count: fixed_in_signature + extra_leading,
        })
    }

    fn spread_needs_any_wrap(function: &Expression, spread: Option<&Expression>) -> bool {
        let Some(spread_expr) = spread else {
            return false;
        };
        let Some(variadic_elem) = function.get_type().unwrap_forall().is_variadic() else {
            return false;
        };
        if !variadic_elem.is_unknown() {
            return false;
        }
        spread_expr
            .get_type()
            .inner()
            .is_some_and(|t| !t.is_unknown())
    }

    /// Classify and emit a single call argument.
    fn emit_call_arg(
        &mut self,
        output: &mut String,
        arg: &Expression,
        index: usize,
        ctx: &CallArgsContext<'_>,
    ) -> String {
        let effective_param_ty = self.effective_param_type(index, ctx.fn_param_types);
        let generic_param_ty = ctx
            .generic_fn_param_types
            .and_then(|params| self.effective_param_type(index, params));

        if ctx.is_go_call
            && let Some(result) = self.try_emit_callback_wrapper(output, arg, effective_param_ty)
        {
            return result;
        }

        if let Some(result) = self.try_adapt_lowered_fn_arg_shape(output, arg, generic_param_ty) {
            return result;
        }

        if let Some(result) = self.try_emit_nullable_coercion(output, arg, effective_param_ty) {
            return result;
        }

        if ctx.is_go_call
            && let Some(result) =
                self.try_emit_go_pointer_param_unwrap(output, arg, effective_param_ty)
        {
            return result;
        }

        if ctx.pointer_indices.contains(&index) {
            let value = self.emit_value(output, arg, ExpressionContext::value());
            if matches!(arg, Expression::Reference { .. }) || arg.get_type().is_ref() {
                return value;
            }
            let temp = self.hoist_tmp_value(output, "ptr", &value);
            return format!("&{}", temp);
        }

        let unwrapped_param_ty = effective_param_ty.map(|p| p.unwrap_forall());
        let suppress = ctx.is_prelude_dispatch
            && unwrapped_param_ty.is_some_and(|p| matches!(p, Type::Function { .. }));
        let flows_to_unknown = unwrapped_param_ty.is_some_and(|p| p.resolves_to_unknown());
        let arg_ctx = ExpressionContext::value()
            .with_forced_tagged_go_function(suppress)
            .with_unknown_argument_target(flows_to_unknown);
        let value = self.emit_composite_value(output, arg, arg_ctx);
        if suppress
            && let Some(tagged) =
                self.try_lower_arg_to_tagged(output, arg, &value, effective_param_ty)
        {
            return tagged;
        }
        match effective_param_ty {
            Some(target) => {
                let coercion =
                    Coercion::resolve(self, &arg.get_type(), target, CoercionDirection::Internal);
                coercion.apply(self, output, value)
            }
            None => value,
        }
    }

    fn effective_param_type<'p>(
        &self,
        index: usize,
        fn_param_types: &'p [Type],
    ) -> Option<&'p Type> {
        fn_param_types.get(index).or_else(|| {
            fn_param_types
                .last()
                .filter(|t| t.get_name() == Some("VarArgs"))
        })
    }

    /// Adapt a lowered-return fn arg when its shape disagrees with the
    /// callee's generic-param shape.
    fn try_adapt_lowered_fn_arg_shape(
        &mut self,
        output: &mut String,
        arg: &Expression,
        generic_param_ty: Option<&Type>,
    ) -> Option<String> {
        if Self::is_tagged_shape_fn_value(arg) {
            return None;
        }

        let raw_param_ty = generic_param_ty?;
        let variadic_inner = (raw_param_ty.get_name() == Some("VarArgs"))
            .then(|| raw_param_ty.inner())
            .flatten();
        let param_ty = variadic_inner.as_ref().unwrap_or(raw_param_ty);
        let param_fn = self
            .facts
            .resolve_to_function_type(param_ty.unwrap_forall())?;
        let param_ret = param_fn.get_function_ret()?;
        let param_shape = self.classify_direct_emission(param_ret);

        let arg_ty = arg.get_type();
        let arg_fn = self
            .facts
            .resolve_to_function_type(arg_ty.unwrap_forall())?;
        let arg_ret = arg_fn.get_function_ret()?;
        let arg_shape = self.classify_direct_emission(arg_ret)?;

        if param_shape.as_ref() == Some(&arg_shape) {
            return None;
        }

        let value = self.emit_value(output, arg, ExpressionContext::value());
        emit_fn_arg_shape_adapter(
            self,
            output,
            &value,
            &arg_fn,
            &arg_shape,
            param_shape.as_ref(),
        )
    }

    /// Adapt `slice...` spread into a generic `VarArgs<fn(…)>` when the
    /// slice's element fn-shape disagrees with the variadic's element.
    fn try_emit_variadic_spread_adapter(
        &mut self,
        spread: &Expression,
        ctx: &CallArgsContext<'_>,
    ) -> Option<EmittedExpression> {
        let generic_params = ctx.generic_fn_param_types?;
        let raw_variadic = generic_params.last()?;
        if raw_variadic.get_name() != Some("VarArgs") {
            return None;
        }
        let variadic_inner = raw_variadic.inner()?;
        let param_fn = self
            .facts
            .resolve_to_function_type(variadic_inner.unwrap_forall())?;
        let param_ret = param_fn.get_function_ret()?;
        let param_shape = self.classify_direct_emission(param_ret);

        let spread_ty = spread.get_type();
        let elem_ty = spread_ty.unwrap_forall().inner()?;
        let arg_fn = self
            .facts
            .resolve_to_function_type(elem_ty.unwrap_forall())?;
        let arg_ret = arg_fn.get_function_ret()?;
        let arg_shape = self.classify_direct_emission(arg_ret)?;

        if param_shape.as_ref() == Some(&arg_shape) {
            return None;
        }

        let mut setup = String::new();
        let src_value = self.emit_value(&mut setup, spread, ExpressionContext::value());
        let src_var = self.hoist_tmp_value(&mut setup, "src", &src_value);

        let target_elem_ret = match param_shape.as_ref() {
            Some(shape) => self.render_lowered_return_ty(shape, arg_ret),
            None => self.go_type_as_string(arg_ret),
        };
        let arg_fn_params = arg_fn.get_function_params().unwrap_or(&[]);
        let param_type_strs: Vec<String> = arg_fn_params
            .iter()
            .map(|p| self.go_type_as_string(p))
            .collect();
        let target_elem_ty = format!("func({}) {}", param_type_strs.join(", "), target_elem_ret);

        let adapted = self.fresh_var(Some("adapted"));
        self.declare(&adapted);
        let loop_cb = self.fresh_var(Some("cb"));

        let mut body = String::new();
        let closure = emit_fn_arg_shape_adapter(
            self,
            &mut body,
            &loop_cb,
            &arg_fn,
            &arg_shape,
            param_shape.as_ref(),
        )?;
        crate::write_line!(body, "{}[i] = {}", adapted, closure);

        crate::write_line!(
            setup,
            "{} := make([]{}, len({}))",
            adapted,
            target_elem_ty,
            src_var
        );
        crate::write_line!(
            setup,
            "for i, {} := range {} {{\n{}}}",
            loop_cb,
            src_var,
            body
        );

        Some(EmittedExpression::new(setup, adapted, spread))
    }

    fn try_emit_callback_wrapper(
        &mut self,
        output: &mut String,
        arg: &Expression,
        effective_param_ty: Option<&Type>,
    ) -> Option<String> {
        let param_fn_ty = effective_param_ty
            .and_then(|param_ty| {
                self.facts
                    .resolve_to_function_type(param_ty.unwrap_forall())
            })
            .filter(|fn_ty| {
                let Type::Function { return_type, .. } = fn_ty else {
                    return false;
                };
                return_type.is_result()
                    || return_type.is_option()
                    || return_type.tuple_arity().is_some_and(|a| a >= 2)
            })?;

        let arg_ty = arg.get_type();
        let arg_fn_ty = self.facts.resolve_to_function_type(arg_ty.unwrap_forall());
        if let Some(Type::Function {
            return_type: arg_ret,
            ..
        }) = arg_fn_ty.as_ref()
            && let Type::Function {
                return_type: param_ret,
                ..
            } = &param_fn_ty
            && self.classify_direct_emission(arg_ret).is_some()
            && self.classify_direct_emission(param_ret).is_some()
        {
            return Some(self.emit_value(output, arg, ExpressionContext::value()));
        }

        let value = self.emit_value(output, arg, ExpressionContext::value());
        Some(crate::types::abi_transition::emit_lisette_callback_wrapper(
            self,
            output,
            &value,
            &param_fn_ty,
        ))
    }

    /// Bridge a Lisette `Option<T>` argument to Go's nil-accepting form when
    /// the param and arg agree on an Option shape that Go expresses as `*T`:
    /// either both `Nullable` (`Option<Ref<T>>`) or both `PointerBridged`
    /// (`Option<scalar>` produced by bindgen's `nilable_param` config).
    fn try_emit_go_pointer_param_unwrap(
        &mut self,
        output: &mut String,
        arg: &Expression,
        effective_param_ty: Option<&Type>,
    ) -> Option<String> {
        let param_ty = effective_param_ty?;
        let arg_ty = arg.get_type();
        match (
            classify_option_shape(self, param_ty),
            classify_option_shape(self, &arg_ty),
        ) {
            (OptionShape::Nullable, OptionShape::Nullable)
            | (OptionShape::PointerBridged, OptionShape::PointerBridged) => {}
            _ => return None,
        }
        if arg.is_none_literal() {
            return Some("nil".to_string());
        }
        let value = self.emit_value(output, arg, ExpressionContext::value());
        let coercion = Coercion::resolve(self, &arg_ty, param_ty, CoercionDirection::ToGoBoundary);
        Some(coercion.apply(self, output, value))
    }

    fn try_emit_nullable_coercion(
        &mut self,
        output: &mut String,
        arg: &Expression,
        effective_param_ty: Option<&Type>,
    ) -> Option<String> {
        let param_ty = effective_param_ty?;
        let arg_ty = arg.get_type();
        let check_ty = if param_ty.get_name() == Some("VarArgs") {
            param_ty.inner().unwrap_or_else(|| param_ty.clone())
        } else {
            param_ty.clone()
        };

        if arg_ty.is_option() && check_ty.resolves_to_unknown() {
            if arg.is_none_literal() {
                return Some("nil".to_string());
            }
            let value = self.emit_value(output, arg, ExpressionContext::value());
            let coercion =
                Coercion::resolve(self, &arg_ty, &check_ty, CoercionDirection::ToGoBoundary);
            return Some(coercion.apply(self, output, value));
        }

        if !matches!(classify_option_shape(self, &arg_ty), OptionShape::Nullable) {
            return None;
        }
        let needs_coercion = self
            .facts
            .as_interface(&check_ty)
            .is_some_and(|id| go_name::is_go_import(&id));

        if !needs_coercion {
            return None;
        }

        Some(self.emit_unwrap_go_nullable_arg(output, arg, &arg_ty))
    }

    fn emit_unwrap_go_nullable_arg(
        &mut self,
        output: &mut String,
        arg: &Expression,
        arg_ty: &Type,
    ) -> String {
        if arg.is_none_literal() {
            return "nil".to_string();
        }
        let value = self.emit_value(output, arg, ExpressionContext::value());
        let coercion = Coercion::resolve(self, arg_ty, arg_ty, CoercionDirection::ToGoBoundary);
        coercion.apply(self, output, value)
    }
}
