// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// This file implements various field and method lookup functions.

package types

// LookupFieldOrMethod looks up a field or method with given package and name
// in T and returns the corresponding *Var or *Func, an index sequence, and a
// bool indicating if there were any pointer indirections on the path to the
// field or method. If addressable is set, T is the type of an addressable
// variable (only matters for method lookups).
//
// The last index entry is the field or method index in the (possibly embedded)
// type where the entry was found, either:
//
//	1) the list of declared methods of a named type; or
//	2) the list of all methods (method set) of an interface type; or
//	3) the list of fields of a struct type.
//
// The earlier index entries are the indices of the embedded struct fields
// traversed to get to the found entry, starting at depth 0.
//
// If no entry is found, a nil object is returned. In this case, the returned
// index and indirect values have the following meaning:
//
//	- If index != nil, the index sequence points to an ambiguous entry
//	(the same name appeared more than once at the same embedding level).
//
//	- If indirect is set, a method with a pointer receiver type was found
//      but there was no pointer on the path from the actual receiver type to
//	the method's formal receiver base type, nor was the receiver addressable.
//
func ( Type,  bool,  *Package,  string) ( Object,  []int,  bool) {
	return (*Checker)(nil).lookupFieldOrMethod(, , , )
}

// Internal use of Checker.lookupFieldOrMethod: If the obj result is a method
// associated with a concrete (non-interface) type, the method's signature
// may not be fully set up. Call Checker.objDecl(obj, nil) before accessing
// the method's type.
// TODO(gri) Now that we provide the *Checker, we can probably remove this
// caveat by calling Checker.objDecl from lookupFieldOrMethod. Investigate.

// lookupFieldOrMethod is like the external version but completes interfaces
// as necessary.
func ( *Checker) ( Type,  bool,  *Package,  string) ( Object,  []int,  bool) {
	// Methods cannot be associated to a named pointer type
	// (spec: "The type denoted by T is called the receiver base type;
	// it must not be a pointer or interface type and it must be declared
	// in the same package as the method.").
	// Thus, if we have a named pointer type, proceed with the underlying
	// pointer type but discard the result if it is a method since we would
	// not have found it for T (see also issue 8590).
	if ,  := .(*Named);  != nil {
		if ,  := .underlying.(*Pointer);  != nil {
			, ,  = .rawLookupFieldOrMethod(, false, , )
			if ,  := .(*Func);  {
				return nil, nil, false
			}
			return
		}
	}

	return .rawLookupFieldOrMethod(, , , )
}

// TODO(gri) The named type consolidation and seen maps below must be
//           indexed by unique keys for a given type. Verify that named
//           types always have only one representation (even when imported
//           indirectly via different packages.)

// rawLookupFieldOrMethod should only be called by lookupFieldOrMethod and missingMethod.
func ( *Checker) ( Type,  bool,  *Package,  string) ( Object,  []int,  bool) {
	// WARNING: The code in this function is extremely subtle - do not modify casually!
	//          This function and NewMethodSet should be kept in sync.

	if  == "_" {
		return // blank fields/methods are never found
	}

	,  := deref()

	// *typ where typ is an interface has no methods.
	if  && IsInterface() {
		return
	}

	// Start with typ as single entry at shallowest depth.
	 := []embeddedType{{, nil, , false}}

	// Named types that we have seen already, allocated lazily.
	// Used to avoid endless searches in case of recursive types.
	// Since only Named types can be used for recursive types, we
	// only need to track those.
	// (If we ever allow type aliases to construct recursive types,
	// we must use type identity rather than pointer equality for
	// the map key comparison, as we do in consolidateMultiples.)
	var  map[*Named]bool

	// search current depth
	for len() > 0 {
		var  []embeddedType // embedded types found at current depth

		// look for (pkg, name) in all types at current depth
		for ,  := range  {
			 := .typ

			// If we have a named type, we may have associated methods.
			// Look for those first.
			if ,  := .(*Named);  != nil {
				if [] {
					// We have seen this type before, at a more shallow depth
					// (note that multiples of this type at the current depth
					// were consolidated before). The type at that depth shadows
					// this same type at the current depth, so we can ignore
					// this one.
					continue
				}
				if  == nil {
					 = make(map[*Named]bool)
				}
				[] = true

				// look for a matching attached method
				if ,  := lookupMethod(.methods, , );  != nil {
					// potential match
					// caution: method may not have a proper signature yet
					 = concat(.index, )
					if  != nil || .multiples {
						return nil, , false // collision
					}
					 = 
					 = .indirect
					continue // we can't have a matching field or interface method
				}

				// continue with underlying type
				 = .underlying
			}

			switch t := .(type) {
			case *Struct:
				// look for a matching field and collect embedded types
				for ,  := range .fields {
					if .sameId(, ) {
						assert(.typ != nil)
						 = concat(.index, )
						if  != nil || .multiples {
							return nil, , false // collision
						}
						 = 
						 = .indirect
						continue // we can't have a matching interface method
					}
					// Collect embedded struct fields for searching the next
					// lower depth, but only if we have not seen a match yet
					// (if we have a match it is either the desired field or
					// we have a name collision on the same depth; in either
					// case we don't need to look further).
					// Embedded fields are always of the form T or *T where
					// T is a type name. If e.typ appeared multiple times at
					// this depth, f.typ appears multiple times at the next
					// depth.
					if  == nil && .embedded {
						,  := deref(.typ)
						// TODO(gri) optimization: ignore types that can't
						// have fields or methods (only Named, Struct, and
						// Interface types need to be considered).
						 = append(, embeddedType{, concat(.index, ), .indirect || , .multiples})
					}
				}

			case *Interface:
				// look for a matching method
				// TODO(gri) t.allMethods is sorted - use binary search
				.completeInterface()
				if ,  := lookupMethod(.allMethods, , );  != nil {
					assert(.typ != nil)
					 = concat(.index, )
					if  != nil || .multiples {
						return nil, , false // collision
					}
					 = 
					 = .indirect
				}
			}
		}

		if  != nil {
			// found a potential match
			// spec: "A method call x.m() is valid if the method set of (the type of) x
			//        contains m and the argument list can be assigned to the parameter
			//        list of m. If x is addressable and &x's method set contains m, x.m()
			//        is shorthand for (&x).m()".
			if ,  := .(*Func);  != nil && ptrRecv() && ! && ! {
				return nil, nil, true // pointer/addressable receiver required
			}
			return
		}

		 = .consolidateMultiples()
	}

	return nil, nil, false // not found
}

// embeddedType represents an embedded type
type embeddedType struct {
	typ       Type
	index     []int // embedded field indices, starting with index at depth 0
	indirect  bool  // if set, there was a pointer indirection on the path to this field
	multiples bool  // if set, typ appears multiple times at this depth
}

// consolidateMultiples collects multiple list entries with the same type
// into a single entry marked as containing multiples. The result is the
// consolidated list.
func ( *Checker) ( []embeddedType) []embeddedType {
	if len() <= 1 {
		return  // at most one entry - nothing to do
	}

	 := 0                     // number of entries w/ unique type
	 := make(map[Type]int) // index at which type was previously seen
	for ,  := range  {
		if ,  := .lookupType(, .typ);  {
			[].multiples = true
			// ignore this entry
		} else {
			[.typ] = 
			[] = 
			++
		}
	}
	return [:]
}

func ( *Checker) ( map[Type]int,  Type) (int, bool) {
	// fast path: maybe the types are equal
	if ,  := [];  {
		return , true
	}

	for ,  := range  {
		if .identical(, ) {
			return , true
		}
	}

	return 0, false
}

// MissingMethod returns (nil, false) if V implements T, otherwise it
// returns a missing method required by T and whether it is missing or
// just has the wrong type.
//
// For non-interface types V, or if static is set, V implements T if all
// methods of T are present in V. Otherwise (V is an interface and static
// is not set), MissingMethod only checks that methods of T which are also
// present in V have matching types (e.g., for a type assertion x.(T) where
// x is of interface type V).
//
func ( Type,  *Interface,  bool) ( *Func,  bool) {
	,  := (*Checker)(nil).missingMethod(, , )
	return ,  != nil
}

// missingMethod is like MissingMethod but accepts a receiver.
// The receiver may be nil if missingMethod is invoked through
// an exported API call (such as MissingMethod), i.e., when all
// methods have been type-checked.
// If the type has the correctly named method, but with the wrong
// signature, the existing method is returned as well.
// To improve error messages, also report the wrong signature
// when the method exists on *V instead of V.
func ( *Checker) ( Type,  *Interface,  bool) (,  *Func) {
	.completeInterface()

	// fast path for common case
	if .Empty() {
		return
	}

	if ,  := .Underlying().(*Interface);  != nil {
		.completeInterface()
		// TODO(gri) allMethods is sorted - can do this more efficiently
		for ,  := range .allMethods {
			,  := lookupMethod(.allMethods, .pkg, .name)
			switch {
			case  == nil:
				if  {
					return , nil
				}
			case !.identical(.Type(), .typ):
				return , 
			}
		}
		return
	}

	// A concrete type implements T if it implements all methods of T.
	for ,  := range .allMethods {
		, ,  := .rawLookupFieldOrMethod(, false, .pkg, .name)

		// Check if *V implements this method of T.
		if  == nil {
			 := NewPointer()
			, _, _ = .rawLookupFieldOrMethod(, false, .pkg, .name)
			if  != nil {
				return , .(*Func)
			}
		}

		// we must have a method (not a field of matching function type)
		,  := .(*Func)
		if  == nil {
			return , nil
		}

		// methods may not have a fully set up signature yet
		if  != nil {
			.objDecl(, nil)
		}

		if !.identical(.typ, .typ) {
			return , 
		}
	}

	return
}

// assertableTo reports whether a value of type V can be asserted to have type T.
// It returns (nil, false) as affirmative answer. Otherwise it returns a missing
// method required by V and whether it is missing or just has the wrong type.
// The receiver may be nil if assertableTo is invoked through an exported API call
// (such as AssertableTo), i.e., when all methods have been type-checked.
func ( *Checker) ( *Interface,  Type) (,  *Func) {
	// no static check is required if T is an interface
	// spec: "If T is an interface type, x.(T) asserts that the
	//        dynamic type of x implements the interface T."
	if ,  := .Underlying().(*Interface);  && !strict {
		return
	}
	return .missingMethod(, , false)
}

// deref dereferences typ if it is a *Pointer and returns its base and true.
// Otherwise it returns (typ, false).
func deref( Type) (Type, bool) {
	if ,  := .(*Pointer);  != nil {
		return .base, true
	}
	return , false
}

// derefStructPtr dereferences typ if it is a (named or unnamed) pointer to a
// (named or unnamed) struct and returns its base. Otherwise it returns typ.
func derefStructPtr( Type) Type {
	if ,  := .Underlying().(*Pointer);  != nil {
		if ,  := .base.Underlying().(*Struct);  {
			return .base
		}
	}
	return 
}

// concat returns the result of concatenating list and i.
// The result does not share its underlying array with list.
func concat( []int,  int) []int {
	var  []int
	 = append(, ...)
	return append(, )
}

// fieldIndex returns the index for the field with matching package and name, or a value < 0.
func fieldIndex( []*Var,  *Package,  string) int {
	if  != "_" {
		for ,  := range  {
			if .sameId(, ) {
				return 
			}
		}
	}
	return -1
}

// lookupMethod returns the index of and method with matching package and name, or (-1, nil).
func lookupMethod( []*Func,  *Package,  string) (int, *Func) {
	if  != "_" {
		for ,  := range  {
			if .sameId(, ) {
				return , 
			}
		}
	}
	return -1, nil
}