Golang import linter skeleton

import.go

package importlint

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

// NB(prateek): http://goast.yuroyoro.net/ is enormously helpful.

// importDecl is the collection of importGroups contained in a single import block.
type importDecl struct {
	Groups []importGroup
}

// importGroup is a collection of imports that are not.
type importGroup struct {
	Imports []ImportSpec
}

type ImportSpec struct {
	Position token.Position
	Name     string
	Path     string
}

// Imports returns the file imports grouped by paragraph.
func Imports(fset *token.FileSet, f *ast.File) []importDecl {
	var importDecls []importDecl

	for _, decl := range f.Decls {
		genDecl, ok := decl.(*ast.GenDecl)
		if !ok || genDecl.Tok != token.IMPORT {
			break
		}

		var (
			importDecl importDecl
			group      importGroup
		)

		var lastLine int
		for _, spec := range genDecl.Specs {
			importSpec := spec.(*ast.ImportSpec)
			pos := importSpec.Path.ValuePos
			line := fset.Position(pos).Line
			if lastLine > 0 && pos > 0 && line-lastLine > 1 {
				importDecl.Groups = append(importDecl.Groups, group)
				group = importGroup{}
			}
			group.Imports = append(group.Imports, newImportSpec(importSpec, line))
			lastLine = line
		}
		importDecl.Groups = append(importDecl.Groups, group)
		importDecls = append(importDecls, importDecl)
	}

	return importDecls
}

func newImportSpec(is *ast.ImportSpec, line int) ImportSpec {
	var (
		name string
		path string
	)

	nameID := is.Name
	if nameID != nil {
		name = nameID.Name
	}

	pathLit := is.Path
	if pathLit != nil {
		path = pathLit.Value
	}

	return ImportSpec{
		Name: name,
		Path: path,
		Line: line,
	}
}