(** SPDX-License-Identifier: MPL-2.0 *)
(* SPDX-FileCopyrightText: 2026 Jonathan D.A. Jewell *)

(** GPU Backend Implementation (Stub)
    
    Placeholder for GPU compute backend.
    Will generate WebGPU, Vulkan, Metal, CUDA, or OpenCL code.
*)

open Ast
open Architecture

(** GPU Backend Context *)
type context = {
  config : gpu_config;
  capabilities : capability list;
}

(** GPU Backend Implementation *)
module Gpu_backend : PROCESSOR_BACKEND = struct
  type context = context
  
  let create_context () : context = {
    config = {
      api = `WebGPU;
      device_type = `Discrete;
      enable_compute = true;
      enable_graphics = false;
      max_workgroups = (1024, 1024, 64);
      shader_model = "wgsl";
    };
    capabilities = [
      BasicArithmetic;
      MemoryManagement;
      ControlFlow;
      FunctionCalls;
      SIMDOperations;
      HardwareAcceleration;
    ];
  }
  
  let get_capabilities (ctx : context) : capability list = ctx.capabilities
  
  let supports_feature (ctx : context) (feature : string) : bool =
    match feature with
    | "simd" -> true
    | "hardware_acceleration" -> true
    | "parallel_compute" -> true
    | "gpu_memory" -> true
    | _ -> false
  
  let emit_prologue (ctx : context) : string =
    match ctx.config.api with
    | `WebGPU -> 
        "@compute @workgroup_size(64, 1, 1)\n"
        ^ "fn main(@builtin(global_invocation_id) global_id : vec3<u32>) {\n"
    | `Vulkan -> 
        "#version 450\n"
        ^ "layout(local_size_x = 64) in;\n"
        ^ "void main() {\n"
    | _ -> ""
  
  let emit_epilogue (ctx : context) : string =
    match ctx.config.api with
    | `WebGPU -> "}\n"
    | `Vulkan -> "}\n"
    | _ -> ""
  
  let emit_function (ctx : context) (fd : fn_decl) : string =
    let prologue = emit_prologue ctx in
    let body = emit_expression ctx fd.fd_body in
    let epilogue = emit_epilogue ctx in
    Printf.sprintf "%s%s%s" prologue body epilogue
  
  let emit_expression (ctx : context) (expr : expr) : string =
    match expr with
    | ExprLit (LitInt (n, _)) -> 
        begin match ctx.config.api with
        | `WebGPU -> Printf.sprintf "  let x = %du;\n" n
        | `Vulkan -> Printf.sprintf "  uint x = %u;\n" n
        | _ -> ""
        end
    | ExprBinary (left, OpAdd, right) -> 
        let left_code = emit_expression ctx left in
        let right_code = emit_expression ctx right in
        begin match ctx.config.api with
        | `WebGPU -> Printf.sprintf "%s%s  let result = x + y;\n" left_code right_code
        | `Vulkan -> Printf.sprintf "%s%s  uint result = x + y;\n" left_code right_code
        | _ -> ""
        end
    | _ -> "  // TODO: GPU expression emission\n"
  
  let emit_statement (ctx : context) (stmt : stmt) : string =
    match stmt with
    | StmtLet sl -> emit_expression ctx sl.sl_value
    | StmtExpr e -> emit_expression ctx e
    | _ -> "  // TODO: GPU statement emission\n"
  
  let generate_code (ctx : context) (program : program) : string =
    let prologue = emit_prologue ctx in
    let function_code = String.concat "\n" (List.map (emit_function ctx) program.top_levels) in
    let epilogue = emit_epilogue ctx in
    prologue ^ "\n" ^ function_code ^ "\n" ^ epilogue
  
  (* Optimization passes *)
  let run_optimizations (ctx : context) (program : program) : program = program
  let inline_functions (ctx : context) (program : program) : program = program
  let constant_folding (ctx : context) (program : program) : program = program
  let dead_code_elimination (ctx : context) (program : program) : program = program
end