package source

import (
	"fmt"
	"go/ast"
	"go/token"
	"go/types"
)

// indexExprAtPos returns the index of the expression containing pos.
func indexExprAtPos(pos token.Pos, args []ast.Expr) int {
	for i, expr := range args {
		if expr.Pos() <= pos && pos <= expr.End() {
			return i
		}
	}
	return len(args)
}

func exprAtPos(pos token.Pos, args []ast.Expr) ast.Expr {
	for _, expr := range args {
		if expr.Pos() <= pos && pos <= expr.End() {
			return expr
		}
	}
	return nil
}

// fieldSelections returns the set of fields that can
// be selected from a value of type T.
func fieldSelections(T types.Type) (fields []*types.Var) {
	// TODO(adonovan): this algorithm doesn't exclude ambiguous
	// selections that match more than one field/method.
	// types.NewSelectionSet should do that for us.

	seen := make(map[types.Type]bool) // for termination on recursive types
	var visit func(T types.Type)
	visit = func(T types.Type) {
		if !seen[T] {
			seen[T] = true
			if T, ok := deref(T).Underlying().(*types.Struct); ok {
				for i := 0; i < T.NumFields(); i++ {
					f := T.Field(i)
					fields = append(fields, f)
					if f.Anonymous() {
						visit(f.Type())
					}
				}
			}
		}
	}
	visit(T)

	return fields
}

// resolveInvalid traverses the node of the AST that defines the scope
// containing the declaration of obj, and attempts to find a user-friendly
// name for its invalid type. The resulting Object and its Type are fake.
func resolveInvalid(obj types.Object, node ast.Node, info *types.Info) types.Object {
	// Construct a fake type for the object and return a fake object with this type.
	formatResult := func(expr ast.Expr) types.Object {
		var typename string
		switch t := expr.(type) {
		case *ast.SelectorExpr:
			typename = fmt.Sprintf("%s.%s", t.X, t.Sel)
		case *ast.Ident:
			typename = t.String()
		default:
			return nil
		}
		typ := types.NewNamed(types.NewTypeName(token.NoPos, obj.Pkg(), typename, nil), nil, nil)
		return types.NewVar(obj.Pos(), obj.Pkg(), obj.Name(), typ)
	}
	var resultExpr ast.Expr
	ast.Inspect(node, func(node ast.Node) bool {
		switch n := node.(type) {
		case *ast.ValueSpec:
			for _, name := range n.Names {
				if info.Defs[name] == obj {
					resultExpr = n.Type
				}
			}
			return false
		case *ast.Field: // This case handles parameters and results of a FuncDecl or FuncLit.
			for _, name := range n.Names {
				if info.Defs[name] == obj {
					resultExpr = n.Type
				}
			}
			return false
		// TODO(rstambler): Handle range statements.
		default:
			return true
		}
	})
	return formatResult(resultExpr)
}

func isPointer(T types.Type) bool {
	_, ok := T.(*types.Pointer)
	return ok
}

// deref returns a pointer's element type; otherwise it returns typ.
func deref(typ types.Type) types.Type {
	if p, ok := typ.Underlying().(*types.Pointer); ok {
		return p.Elem()
	}
	return typ
}