package analyzer

import (
	"flag"
	"go/ast"

	"golang.org/x/tools/go/analysis"
	"golang.org/x/tools/go/analysis/passes/inspect"
	"golang.org/x/tools/go/ast/inspector"
)

var Analyzer = &analysis.Analyzer{
	Name:     "explicitreturn",
	Doc:      "Enforces explicit return statements",
	Flags:    flag.FlagSet{},
	Run:      run,
	Requires: []*analysis.Analyzer{inspect.Analyzer},
}

func run(pass *analysis.Pass) (interface{}, error) {
	inspector := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)

	// only filter function defintions
	nodeFilter := []ast.Node{
		(*ast.FuncDecl)(nil),
		(*ast.FuncLit)(nil),
	}

	inspector.Preorder(nodeFilter, func(node ast.Node) {
		var funcBody *ast.BlockStmt

		switch n := node.(type) {
		case *ast.FuncLit:
			funcBody = n.Body
			for _, statement := range funcBody.List {
				s, ok := statement.(*ast.ReturnStmt)
				if ok && s.Results == nil {
					pass.Reportf(s.Pos(), "implicit return found for anonymous function")
				}
			}
		case *ast.FuncDecl:
			funcBody = n.Body
			for _, statement := range funcBody.List {
				s, ok := statement.(*ast.ReturnStmt)
				if ok && s.Results == nil {
					pass.Reportf(s.Return, "implicit return found in function %s", n.Name)
				}
			}
		default:
			return
		}
	})

	return nil, nil
}