// Copyright 2020 The Tint Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "src/type_determiner.h"

#include <memory>

#include "spirv/unified1/GLSL.std.450.h"
#include "src/ast/array_accessor_expression.h"
#include "src/ast/as_expression.h"
#include "src/ast/assignment_statement.h"
#include "src/ast/binary_expression.h"
#include "src/ast/break_statement.h"
#include "src/ast/call_expression.h"
#include "src/ast/case_statement.h"
#include "src/ast/cast_expression.h"
#include "src/ast/continue_statement.h"
#include "src/ast/else_statement.h"
#include "src/ast/identifier_expression.h"
#include "src/ast/if_statement.h"
#include "src/ast/loop_statement.h"
#include "src/ast/member_accessor_expression.h"
#include "src/ast/return_statement.h"
#include "src/ast/scalar_constructor_expression.h"
#include "src/ast/switch_statement.h"
#include "src/ast/type/array_type.h"
#include "src/ast/type/bool_type.h"
#include "src/ast/type/f32_type.h"
#include "src/ast/type/matrix_type.h"
#include "src/ast/type/pointer_type.h"
#include "src/ast/type/struct_type.h"
#include "src/ast/type/vector_type.h"
#include "src/ast/type_constructor_expression.h"
#include "src/ast/unary_op_expression.h"
#include "src/ast/unless_statement.h"
#include "src/ast/variable_decl_statement.h"

namespace tint {
namespace {

bool IsDerivative(const std::string& name) {
  return name == "dpdx" || name == "dpdx_fine" || name == "dpdx_coarse" ||
         name == "dpdy" || name == "dpdy_fine" || name == "dpdy_coarse" ||
         name == "fwidth" || name == "fwidth_fine" || name == "fwidth_coarse";
}

bool IsFloatIntrinsic(const std::string& name) {
  return name == "is_finite" || name == "is_inf" || name == "is_nan" ||
         name == "is_normal";
}

bool IsIntrinsic(const std::string& name) {
  return IsDerivative(name) || name == "all" || name == "any" ||
         IsFloatIntrinsic(name) || name == "dot" || name == "outer_product";
}

}  // namespace

TypeDeterminer::TypeDeterminer(Context* ctx, ast::Module* mod)
    : ctx_(*ctx), mod_(mod) {}

TypeDeterminer::~TypeDeterminer() = default;

void TypeDeterminer::set_error(const Source& src, const std::string& msg) {
  error_ = "";
  if (src.line > 0) {
    error_ +=
        std::to_string(src.line) + ":" + std::to_string(src.column) + ": ";
  }
  error_ += msg;
}

bool TypeDeterminer::Determine() {
  for (const auto& var : mod_->global_variables()) {
    variable_stack_.set_global(var->name(), var.get());
  }

  for (const auto& func : mod_->functions()) {
    name_to_function_[func->name()] = func.get();
  }

  if (!DetermineFunctions(mod_->functions())) {
    return false;
  }
  return true;
}

bool TypeDeterminer::DetermineFunctions(const ast::FunctionList& funcs) {
  for (const auto& func : funcs) {
    if (!DetermineFunction(func.get())) {
      return false;
    }
  }
  return true;
}

bool TypeDeterminer::DetermineFunction(ast::Function* func) {
  variable_stack_.push_scope();
  if (!DetermineStatements(func->body())) {
    return false;
  }
  variable_stack_.pop_scope();

  return true;
}

bool TypeDeterminer::DetermineStatements(const ast::StatementList& stmts) {
  for (const auto& stmt : stmts) {
    if (!DetermineVariableStorageClass(stmt.get())) {
      return false;
    }

    if (!DetermineResultType(stmt.get())) {
      return false;
    }
  }
  return true;
}

bool TypeDeterminer::DetermineVariableStorageClass(ast::Statement* stmt) {
  if (!stmt->IsVariableDecl()) {
    return true;
  }

  auto* var = stmt->AsVariableDecl()->variable();
  // Nothing to do for const
  if (var->is_const()) {
    return true;
  }

  if (var->storage_class() == ast::StorageClass::kFunction) {
    return true;
  }

  if (var->storage_class() != ast::StorageClass::kNone) {
    set_error(stmt->source(),
              "function variable has a non-function storage class");
    return false;
  }

  var->set_storage_class(ast::StorageClass::kFunction);
  return true;
}

bool TypeDeterminer::DetermineResultType(ast::Statement* stmt) {
  if (stmt->IsAssign()) {
    auto* a = stmt->AsAssign();
    return DetermineResultType(a->lhs()) && DetermineResultType(a->rhs());
  }
  if (stmt->IsBreak()) {
    auto* b = stmt->AsBreak();
    return DetermineResultType(b->conditional());
  }
  if (stmt->IsCase()) {
    auto* c = stmt->AsCase();
    return DetermineStatements(c->body());
  }
  if (stmt->IsContinue()) {
    auto* c = stmt->AsContinue();
    return DetermineResultType(c->conditional());
  }
  if (stmt->IsElse()) {
    auto* e = stmt->AsElse();
    return DetermineResultType(e->condition()) &&
           DetermineStatements(e->body());
  }
  if (stmt->IsFallthrough()) {
    return true;
  }
  if (stmt->IsIf()) {
    auto* i = stmt->AsIf();
    if (!DetermineResultType(i->condition()) ||
        !DetermineStatements(i->body())) {
      return false;
    }

    for (const auto& else_stmt : i->else_statements()) {
      if (!DetermineResultType(else_stmt.get())) {
        return false;
      }
    }
    return true;
  }
  if (stmt->IsKill()) {
    return true;
  }
  if (stmt->IsLoop()) {
    auto* l = stmt->AsLoop();
    return DetermineStatements(l->body()) &&
           DetermineStatements(l->continuing());
  }
  if (stmt->IsReturn()) {
    auto* r = stmt->AsReturn();
    return DetermineResultType(r->value());
  }
  if (stmt->IsSwitch()) {
    auto* s = stmt->AsSwitch();
    if (!DetermineResultType(s->condition())) {
      return false;
    }
    for (const auto& case_stmt : s->body()) {
      if (!DetermineResultType(case_stmt.get())) {
        return false;
      }
    }
    return true;
  }
  if (stmt->IsUnless()) {
    auto* u = stmt->AsUnless();
    return DetermineResultType(u->condition()) &&
           DetermineStatements(u->body());
  }
  if (stmt->IsVariableDecl()) {
    auto* v = stmt->AsVariableDecl();
    variable_stack_.set(v->variable()->name(), v->variable());
    return DetermineResultType(v->variable()->constructor());
  }

  set_error(stmt->source(), "unknown statement type for type determination");
  return false;
}

bool TypeDeterminer::DetermineResultType(const ast::ExpressionList& list) {
  for (const auto& expr : list) {
    if (!DetermineResultType(expr.get())) {
      return false;
    }
  }
  return true;
}

bool TypeDeterminer::DetermineResultType(ast::Expression* expr) {
  // This is blindly called above, so in some cases the expression won't exist.
  if (!expr) {
    return true;
  }

  if (expr->IsArrayAccessor()) {
    return DetermineArrayAccessor(expr->AsArrayAccessor());
  }
  if (expr->IsAs()) {
    return DetermineAs(expr->AsAs());
  }
  if (expr->IsBinary()) {
    return DetermineBinary(expr->AsBinary());
  }
  if (expr->IsCall()) {
    return DetermineCall(expr->AsCall());
  }
  if (expr->IsCast()) {
    return DetermineCast(expr->AsCast());
  }
  if (expr->IsConstructor()) {
    return DetermineConstructor(expr->AsConstructor());
  }
  if (expr->IsIdentifier()) {
    return DetermineIdentifier(expr->AsIdentifier());
  }
  if (expr->IsMemberAccessor()) {
    return DetermineMemberAccessor(expr->AsMemberAccessor());
  }
  if (expr->IsUnaryOp()) {
    return DetermineUnaryOp(expr->AsUnaryOp());
  }

  set_error(expr->source(), "unknown expression for type determination");
  return false;
}

bool TypeDeterminer::DetermineArrayAccessor(
    ast::ArrayAccessorExpression* expr) {
  if (!DetermineResultType(expr->array())) {
    return false;
  }
  if (!DetermineResultType(expr->idx_expr())) {
    return false;
  }

  auto* res = expr->array()->result_type();
  auto* parent_type = res->UnwrapPtrIfNeeded();
  ast::type::Type* ret = nullptr;
  if (parent_type->IsArray()) {
    ret = parent_type->AsArray()->type();
  } else if (parent_type->IsVector()) {
    ret = parent_type->AsVector()->type();
  } else if (parent_type->IsMatrix()) {
    auto* m = parent_type->AsMatrix();
    ret = ctx_.type_mgr().Get(
        std::make_unique<ast::type::VectorType>(m->type(), m->rows()));
  } else {
    set_error(expr->source(), "invalid parent type in array accessor");
    return false;
  }

  // If we're extracting from a pointer, we return a pointer.
  if (res->IsPointer()) {
    ret = ctx_.type_mgr().Get(std::make_unique<ast::type::PointerType>(
        ret, res->AsPointer()->storage_class()));
  }
  expr->set_result_type(ret);

  return true;
}

bool TypeDeterminer::DetermineAs(ast::AsExpression* expr) {
  expr->set_result_type(expr->type());
  return true;
}

bool TypeDeterminer::DetermineCall(ast::CallExpression* expr) {
  if (!DetermineResultType(expr->params())) {
    return false;
  }

  // The expression has to be an identifier as you can't store function pointers
  // but, if it isn't we'll just use the normal result determination to be on
  // the safe side.
  if (expr->func()->IsIdentifier()) {
    auto* ident = expr->func()->AsIdentifier();

    if (IsIntrinsic(ident->name())) {
      if (!DetermineIntrinsic(ident->name(), expr))
        return false;

    } else if (ident->has_path()) {
      auto* imp = mod_->FindImportByName(ident->path());
      if (imp == nullptr) {
        set_error(expr->source(), "Unable to find import for " + ident->name());
        return false;
      }

      uint32_t ext_id = 0;
      auto* result_type = GetImportData(expr->source(), imp->path(),
                                        ident->name(), expr->params(), &ext_id);
      if (result_type == nullptr) {
        if (error_.empty()) {
          set_error(expr->source(),
                    "Unable to determine result type for GLSL expression " +
                        ident->name());
        }
        return false;
      }

      imp->AddMethodId(ident->name(), ext_id);
      expr->func()->set_result_type(result_type);
    } else {
      // An identifier with a single name is a function call, not an import
      // lookup which we can handle with the regular identifier lookup.
      if (!DetermineResultType(ident)) {
        return false;
      }
    }
  } else {
    if (!DetermineResultType(expr->func())) {
      return false;
    }
  }
  expr->set_result_type(expr->func()->result_type());
  return true;
}

bool TypeDeterminer::DetermineIntrinsic(const std::string& name,
                                        ast::CallExpression* expr) {
  if (IsDerivative(name)) {
    if (expr->params().size() != 1) {
      set_error(expr->source(), "incorrect number of parameters for " + name);
      return false;
    }

    // The result type must be the same as the type of the parameter.
    auto& param = expr->params()[0];
    if (!DetermineResultType(param.get())) {
      return false;
    }
    expr->func()->set_result_type(param->result_type()->UnwrapPtrIfNeeded());
    return true;
  }
  if (name == "any" || name == "all") {
    expr->func()->set_result_type(
        ctx_.type_mgr().Get(std::make_unique<ast::type::BoolType>()));
    return true;
  }
  if (IsFloatIntrinsic(name)) {
    if (expr->params().size() != 1) {
      set_error(expr->source(), "incorrect number of parameters for " + name);
      return false;
    }

    auto* bool_type =
        ctx_.type_mgr().Get(std::make_unique<ast::type::BoolType>());

    auto* param_type = expr->params()[0]->result_type()->UnwrapPtrIfNeeded();
    if (param_type->IsVector()) {
      expr->func()->set_result_type(
          ctx_.type_mgr().Get(std::make_unique<ast::type::VectorType>(
              bool_type, param_type->AsVector()->size())));
    } else {
      expr->func()->set_result_type(bool_type);
    }
    return true;
  }
  if (name == "dot") {
    expr->func()->set_result_type(
        ctx_.type_mgr().Get(std::make_unique<ast::type::F32Type>()));
    return true;
  }
  if (name == "outer_product") {
    if (expr->params().size() != 2) {
      set_error(expr->source(),
                "incorrect number of parameters for outer_product");
      return false;
    }

    auto* param0_type = expr->params()[0]->result_type()->UnwrapPtrIfNeeded();
    auto* param1_type = expr->params()[1]->result_type()->UnwrapPtrIfNeeded();
    if (!param0_type->IsVector() || !param1_type->IsVector()) {
      set_error(expr->source(), "invalid parameter type for outer_product");
      return false;
    }

    expr->func()->set_result_type(
        ctx_.type_mgr().Get(std::make_unique<ast::type::MatrixType>(
            ctx_.type_mgr().Get(std::make_unique<ast::type::F32Type>()),
            param0_type->AsVector()->size(), param1_type->AsVector()->size())));
    return true;
  }

  return false;
}

bool TypeDeterminer::DetermineCast(ast::CastExpression* expr) {
  if (!DetermineResultType(expr->expr())) {
    return false;
  }

  expr->set_result_type(expr->type());
  return true;
}

bool TypeDeterminer::DetermineConstructor(ast::ConstructorExpression* expr) {
  if (expr->IsTypeConstructor()) {
    auto* ty = expr->AsTypeConstructor();
    for (const auto& value : ty->values()) {
      if (!DetermineResultType(value.get())) {
        return false;
      }
    }
    expr->set_result_type(ty->type());
  } else {
    expr->set_result_type(expr->AsScalarConstructor()->literal()->type());
  }
  return true;
}

bool TypeDeterminer::DetermineIdentifier(ast::IdentifierExpression* expr) {
  if (expr->has_path()) {
    set_error(expr->source(),
              "determine identifier should not be called with imports");
    return false;
  }

  auto name = expr->name();
  ast::Variable* var;
  if (variable_stack_.get(name, &var)) {
    // A constant is the type, but a variable is always a pointer so synthesize
    // the pointer around the variable type.
    if (var->is_const()) {
      expr->set_result_type(var->type());
    } else {
      expr->set_result_type(
          ctx_.type_mgr().Get(std::make_unique<ast::type::PointerType>(
              var->type(), var->storage_class())));
    }
    return true;
  }

  auto iter = name_to_function_.find(name);
  if (iter != name_to_function_.end()) {
    expr->set_result_type(iter->second->return_type());
    return true;
  }

  return true;
}

bool TypeDeterminer::DetermineMemberAccessor(
    ast::MemberAccessorExpression* expr) {
  if (!DetermineResultType(expr->structure())) {
    return false;
  }

  auto* res = expr->structure()->result_type();
  auto* data_type = res->UnwrapPtrIfNeeded();

  while (data_type->IsAlias()) {
    data_type = data_type->AsAlias()->type();
  }

  ast::type::Type* ret = nullptr;
  if (data_type->IsStruct()) {
    auto* strct = data_type->AsStruct()->impl();
    auto name = expr->member()->name();

    for (const auto& member : strct->members()) {
      if (member->name() == name) {
        ret = member->type();
        break;
      }
    }

    if (ret == nullptr) {
      set_error(expr->source(), "struct member " + name + " not found");
      return false;
    }

    // If we're extracting from a pointer, we return a pointer.
    if (res->IsPointer()) {
      ret = ctx_.type_mgr().Get(std::make_unique<ast::type::PointerType>(
          ret, res->AsPointer()->storage_class()));
    }
  } else if (data_type->IsVector()) {
    auto* vec = data_type->AsVector();

    auto size = expr->member()->name().size();
    if (size == 1) {
      // A single element swizzle is just the type of the vector.
      ret = vec->type();
      // If we're extracting from a pointer, we return a pointer.
      if (res->IsPointer()) {
        ret = ctx_.type_mgr().Get(std::make_unique<ast::type::PointerType>(
            ret, res->AsPointer()->storage_class()));
      }
    } else {
      // The vector will have a number of components equal to the length of the
      // swizzle. This assumes the validator will check that the swizzle
      // is correct.
      ret = ctx_.type_mgr().Get(
          std::make_unique<ast::type::VectorType>(vec->type(), size));
    }
  } else {
    set_error(expr->source(),
              "invalid type " + data_type->type_name() + " in member accessor");
    return false;
  }

  expr->set_result_type(ret);

  return true;
}

bool TypeDeterminer::DetermineBinary(ast::BinaryExpression* expr) {
  if (!DetermineResultType(expr->lhs()) || !DetermineResultType(expr->rhs())) {
    return false;
  }

  // Result type matches first parameter type
  if (expr->IsAnd() || expr->IsOr() || expr->IsXor() || expr->IsShiftLeft() ||
      expr->IsShiftRight() || expr->IsShiftRightArith() || expr->IsAdd() ||
      expr->IsSubtract() || expr->IsDivide() || expr->IsModulo()) {
    expr->set_result_type(expr->lhs()->result_type()->UnwrapPtrIfNeeded());
    return true;
  }
  // Result type is a scalar or vector of boolean type
  if (expr->IsLogicalAnd() || expr->IsLogicalOr() || expr->IsEqual() ||
      expr->IsNotEqual() || expr->IsLessThan() || expr->IsGreaterThan() ||
      expr->IsLessThanEqual() || expr->IsGreaterThanEqual()) {
    auto* bool_type =
        ctx_.type_mgr().Get(std::make_unique<ast::type::BoolType>());
    auto* param_type = expr->lhs()->result_type()->UnwrapPtrIfNeeded();
    if (param_type->IsVector()) {
      expr->set_result_type(
          ctx_.type_mgr().Get(std::make_unique<ast::type::VectorType>(
              bool_type, param_type->AsVector()->size())));
    } else {
      expr->set_result_type(bool_type);
    }
    return true;
  }
  if (expr->IsMultiply()) {
    auto* lhs_type = expr->lhs()->result_type()->UnwrapPtrIfNeeded();
    auto* rhs_type = expr->rhs()->result_type()->UnwrapPtrIfNeeded();

    // Note, the ordering here matters. The later checks depend on the prior
    // checks having been done.
    if (lhs_type->IsMatrix() && rhs_type->IsMatrix()) {
      expr->set_result_type(
          ctx_.type_mgr().Get(std::make_unique<ast::type::MatrixType>(
              lhs_type->AsMatrix()->type(), lhs_type->AsMatrix()->rows(),
              rhs_type->AsMatrix()->columns())));

    } else if (lhs_type->IsMatrix() && rhs_type->IsVector()) {
      auto* mat = lhs_type->AsMatrix();
      expr->set_result_type(ctx_.type_mgr().Get(
          std::make_unique<ast::type::VectorType>(mat->type(), mat->rows())));
    } else if (lhs_type->IsVector() && rhs_type->IsMatrix()) {
      auto* mat = rhs_type->AsMatrix();
      expr->set_result_type(
          ctx_.type_mgr().Get(std::make_unique<ast::type::VectorType>(
              mat->type(), mat->columns())));
    } else if (lhs_type->IsMatrix()) {
      // matrix * scalar
      expr->set_result_type(lhs_type);
    } else if (rhs_type->IsMatrix()) {
      // scalar * matrix
      expr->set_result_type(rhs_type);
    } else if (lhs_type->IsVector() && rhs_type->IsVector()) {
      expr->set_result_type(lhs_type);
    } else if (lhs_type->IsVector()) {
      // Vector * scalar
      expr->set_result_type(lhs_type);
    } else if (rhs_type->IsVector()) {
      // Scalar * vector
      expr->set_result_type(rhs_type);
    } else {
      // Scalar * Scalar
      expr->set_result_type(lhs_type);
    }

    return true;
  }

  set_error(expr->source(), "Unknown binary expression");
  return false;
}

bool TypeDeterminer::DetermineUnaryOp(ast::UnaryOpExpression* expr) {
  // Result type matches the parameter type.
  if (!DetermineResultType(expr->expr())) {
    return false;
  }
  expr->set_result_type(expr->expr()->result_type()->UnwrapPtrIfNeeded());
  return true;
}

ast::type::Type* TypeDeterminer::GetImportData(
    const Source& source,
    const std::string& path,
    const std::string& name,
    const ast::ExpressionList& params,
    uint32_t* id) {
  if (path != "GLSL.std.450") {
    return nullptr;
  }

  // Most of these are floating-point general except the below which are only
  // FP16 and FP32. We only have FP32 at this point so the below works, if we
  // get FP64 support or otherwise we'll need to differentiate.
  //   * radians
  //   * degrees
  //   * sin, cos, tan
  //   * asin, acos, atan
  //   * sinh, cosh, tanh
  //   * asinh, acosh, atanh
  //   * exp, exp2
  //   * log, log2

  if (name == "round" || name == "roundeven" || name == "trunc" ||
      name == "fabs" || name == "fsign" || name == "floor" || name == "ceil" ||
      name == "fract" || name == "radians" || name == "degrees" ||
      name == "sin" || name == "cos" || name == "tan" || name == "asin" ||
      name == "acos" || name == "atan" || name == "sinh" || name == "cosh" ||
      name == "tanh" || name == "asinh" || name == "acosh" || name == "atanh" ||
      name == "exp" || name == "log" || name == "exp2" || name == "log2" ||
      name == "sqrt" || name == "inversesqrt" || name == "normalize" ||
      name == "length") {
    if (params.size() != 1) {
      set_error(source, "incorrect number of parameters for " + name +
                            ". Expected 1 got " +
                            std::to_string(params.size()));
      return nullptr;
    }

    auto* result_type = params[0]->result_type()->UnwrapPtrIfNeeded();
    if (!result_type->is_float_scalar_or_vector()) {
      set_error(source, "incorrect type for " + name +
                            ". Requires a float scalar or a float vector");
      return nullptr;
    }

    if (name == "round") {
      *id = GLSLstd450Round;
    } else if (name == "roundeven") {
      *id = GLSLstd450RoundEven;
    } else if (name == "trunc") {
      *id = GLSLstd450Trunc;
    } else if (name == "fabs") {
      *id = GLSLstd450FAbs;
    } else if (name == "fsign") {
      *id = GLSLstd450FSign;
    } else if (name == "floor") {
      *id = GLSLstd450Floor;
    } else if (name == "ceil") {
      *id = GLSLstd450Ceil;
    } else if (name == "fract") {
      *id = GLSLstd450Fract;
    } else if (name == "radians") {
      *id = GLSLstd450Radians;
    } else if (name == "degrees") {
      *id = GLSLstd450Degrees;
    } else if (name == "sin") {
      *id = GLSLstd450Sin;
    } else if (name == "cos") {
      *id = GLSLstd450Cos;
    } else if (name == "tan") {
      *id = GLSLstd450Tan;
    } else if (name == "asin") {
      *id = GLSLstd450Asin;
    } else if (name == "acos") {
      *id = GLSLstd450Acos;
    } else if (name == "atan") {
      *id = GLSLstd450Atan;
    } else if (name == "sinh") {
      *id = GLSLstd450Sinh;
    } else if (name == "cosh") {
      *id = GLSLstd450Cosh;
    } else if (name == "tanh") {
      *id = GLSLstd450Tanh;
    } else if (name == "asinh") {
      *id = GLSLstd450Asinh;
    } else if (name == "acosh") {
      *id = GLSLstd450Acosh;
    } else if (name == "atanh") {
      *id = GLSLstd450Atanh;
    } else if (name == "exp") {
      *id = GLSLstd450Exp;
    } else if (name == "log") {
      *id = GLSLstd450Log;
    } else if (name == "exp2") {
      *id = GLSLstd450Exp2;
    } else if (name == "log2") {
      *id = GLSLstd450Log2;
    } else if (name == "sqrt") {
      *id = GLSLstd450Sqrt;
    } else if (name == "inversesqrt") {
      *id = GLSLstd450InverseSqrt;
    } else if (name == "normalize") {
      *id = GLSLstd450Normalize;
    } else if (name == "length") {
      *id = GLSLstd450Length;

      // Length returns a scalar of the same type as the parameter.
      return result_type->is_float_scalar() ? result_type
                                            : result_type->AsVector()->type();
    }

    return result_type;
  } else if (name == "atan2" || name == "pow" || name == "fmin" ||
             name == "fmax" || name == "step" || name == "reflect" ||
             name == "nmin" || name == "nmax" || name == "distance") {
    if (params.size() != 2) {
      error_ = "incorrect number of parameters for " + name +
               ". Expected 2 got " + std::to_string(params.size());
      return nullptr;
    }

    auto* result_type_0 = params[0]->result_type()->UnwrapPtrIfNeeded();
    auto* result_type_1 = params[1]->result_type()->UnwrapPtrIfNeeded();
    if (!result_type_0->is_float_scalar_or_vector() ||
        !result_type_1->is_float_scalar_or_vector()) {
      error_ = "incorrect type for " + name +
               ". Requires float scalar or a float vector values";
      return nullptr;
    }
    if (result_type_0 != result_type_1) {
      error_ = "mismatched parameter types for " + name;
      return nullptr;
    }

    if (name == "atan2") {
      *id = GLSLstd450Atan2;
    } else if (name == "pow") {
      *id = GLSLstd450Pow;
    } else if (name == "fmin") {
      *id = GLSLstd450FMin;
    } else if (name == "fmax") {
      *id = GLSLstd450FMax;
    } else if (name == "step") {
      *id = GLSLstd450Step;
    } else if (name == "reflect") {
      *id = GLSLstd450Reflect;
    } else if (name == "nmin") {
      *id = GLSLstd450NMin;
    } else if (name == "nmax") {
      *id = GLSLstd450NMax;
    } else if (name == "distance") {
      *id = GLSLstd450Distance;

      // Distance returns a scalar of the same type as the parameter.
      return result_type_0->is_float_scalar()
                 ? result_type_0
                 : result_type_0->AsVector()->type();
    }

    return result_type_0;
  } else if (name == "fclamp" || name == "fmix" || name == "smoothstep" ||
             name == "fma" || name == "nclamp" || name == "faceforward") {
    if (params.size() != 3) {
      error_ = "incorrect number of parameters for " + name +
               ". Expected 3 got " + std::to_string(params.size());
      return nullptr;
    }

    auto* result_type_0 = params[0]->result_type()->UnwrapPtrIfNeeded();
    auto* result_type_1 = params[1]->result_type()->UnwrapPtrIfNeeded();
    auto* result_type_2 = params[2]->result_type()->UnwrapPtrIfNeeded();
    if (!result_type_0->is_float_scalar_or_vector() ||
        !result_type_1->is_float_scalar_or_vector() ||
        !result_type_2->is_float_scalar_or_vector()) {
      error_ = "incorrect type for " + name +
               ". Requires float scalar or a float vector values";
      return nullptr;
    }
    if (result_type_0 != result_type_1 || result_type_0 != result_type_2) {
      error_ = "mismatched parameter types for " + name;
      return nullptr;
    }

    if (name == "fclamp") {
      *id = GLSLstd450FClamp;
    } else if (name == "fmix") {
      *id = GLSLstd450FMix;
    } else if (name == "smoothstep") {
      *id = GLSLstd450SmoothStep;
    } else if (name == "fma") {
      *id = GLSLstd450Fma;
    } else if (name == "nclamp") {
      *id = GLSLstd450NClamp;
    } else if (name == "faceforward") {
      *id = GLSLstd450FaceForward;
    }

    return result_type_0;
  }

  return nullptr;
}

}  // namespace tint