//! Code for ray tracing pipelines

use crate::back::spv::{
    Block, BlockContext, Instruction, LocalType, LookupRaytracingFunction, Writer, WriterFlags,
};

impl Writer {
    fn write_trace_ray(
        &mut self,
        ir_module: &crate::Module,
        payload: crate::Handle<crate::GlobalVariable>,
    ) -> spirv::Word {
        if let Some(&word) = self
            .ray_tracing_functions
            .get(&LookupRaytracingFunction::TraceRay { payload })
        {
            return word;
        }

        let acceleration_structure_type_id =
            self.get_localtype_id(LocalType::AccelerationStructure);

        let ray_desc_type_id = self.get_handle_type_id(
            ir_module
                .special_types
                .ray_desc
                .expect("ray desc should be set if `traceRays` is called"),
        );

        let (func_id, mut function, arg_ids) = self.write_function_signature(
            &[acceleration_structure_type_id, ray_desc_type_id],
            self.void_type,
        );

        let acceleration_structure_id = arg_ids[0];
        let desc_id = arg_ids[1];
        let payload_id = self.global_variables[payload].access_id;

        let label_id = self.id_gen.next();
        let mut block = Block::new(label_id);

        let super::ExtractedRayDesc {
            ray_flags_id,
            cull_mask_id,
            tmin_id,
            tmax_id,
            ray_origin_id,
            ray_dir_id,
            valid_id,
        } = self.write_extract_ray_desc(&mut block, desc_id, self.trace_ray_argument_validation);

        let merge_label_id = self.id_gen.next();
        let merge_block = Block::new(merge_label_id);

        // NOTE: this block will be unreachable if trace ray validation is disabled.
        let invalid_label_id = self.id_gen.next();
        let mut invalid_block = Block::new(invalid_label_id);

        let valid_label_id = self.id_gen.next();
        let mut valid_block = Block::new(valid_label_id);

        match valid_id {
            Some(all_valid_id) => {
                block.body.push(Instruction::selection_merge(
                    merge_label_id,
                    spirv::SelectionControl::NONE,
                ));
                function.consume(
                    block,
                    Instruction::branch_conditional(all_valid_id, valid_label_id, invalid_label_id),
                );
            }
            None => {
                function.consume(block, Instruction::branch(valid_label_id));
            }
        }

        let zero = self.get_constant_scalar(crate::Literal::U32(0));

        valid_block.body.push(Instruction::trace_ray(
            acceleration_structure_id,
            ray_flags_id,
            cull_mask_id,
            zero,
            zero,
            zero,
            ray_origin_id,
            tmin_id,
            ray_dir_id,
            tmax_id,
            payload_id,
        ));

        function.consume(valid_block, Instruction::branch(merge_label_id));

        if self.flags.contains(WriterFlags::PRINT_ON_TRACE_RAYS_FAIL) {
            self.write_debug_printf(
                &mut invalid_block,
                "Naga ignored invalid arguments to traceRay with flags: %u t_min: %f t_max: %f origin: %v4f dir: %v4f",
                &[
                    ray_flags_id,
                    tmin_id,
                    tmax_id,
                    ray_origin_id,
                    ray_dir_id,
                ],
            );
        }

        function.consume(invalid_block, Instruction::branch(merge_label_id));

        function.consume(merge_block, Instruction::return_void());

        function.to_words(&mut self.logical_layout.function_definitions);

        self.ray_tracing_functions
            .insert(LookupRaytracingFunction::TraceRay { payload }, func_id);

        func_id
    }
}

impl BlockContext<'_> {
    pub(in super::super) fn write_ray_tracing_pipeline_function(
        &mut self,
        function: &crate::RayPipelineFunction,
        block: &mut Block,
    ) {
        match *function {
            crate::RayPipelineFunction::TraceRay {
                acceleration_structure,
                descriptor,
                payload,
            } => {
                // Checked for when validating the module in `validate_block_impl`.
                let crate::Expression::GlobalVariable(payload) =
                    self.ir_function.expressions[payload]
                else {
                    unreachable!()
                };

                let desc_id = self.cached[descriptor];
                let acc_struct_id = self.get_handle_id(acceleration_structure);

                let func = self.writer.write_trace_ray(self.ir_module, payload);

                let func_id = self.gen_id();
                block.body.push(Instruction::function_call(
                    self.writer.void_type,
                    func_id,
                    func,
                    &[acc_struct_id, desc_id],
                ));
            }
        }
    }
}