// Copyright 2009 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.

// Package doc extracts source code documentation from a Go AST.
//
// This is a temporary copy of go/doc from Go 1.14 standard library
// for testing of and validation of CL 204830 (golang.org/cl/204830).
// Go 1.14 has been released, so go/doc can be used in its place as
// soon as Go 1.14 is used for deployment.
//
// This package shouldn't be modified unless it's a part of a plan to
// make an upstream change in go/doc package in the standard library.
package doc

import (
	"fmt"
	"go/ast"
	"go/token"
	"strings"

	"golang.org/x/mod/module"
)

// Package is the documentation for an entire package.
type Package struct {
	Doc        string
	Name       string
	ImportPath string
	Imports    []string
	Filenames  []string
	Notes      map[string][]*Note

	// Deprecated: For backward compatibility Bugs is still populated,
	// but all new code should use Notes instead.
	Bugs []string

	// declarations
	Consts []*Value
	Types  []*Type
	Vars   []*Value
	Funcs  []*Func

	// Examples is a sorted list of examples associated with
	// the package. Examples are extracted from _test.go files
	// provided to NewFromFiles.
	Examples []*Example
}

// Value is the documentation for a (possibly grouped) var or const declaration.
type Value struct {
	Doc          string
	Names        []string // var or const names in declaration order
	Decl         *ast.GenDecl
	IsDeprecated bool

	order int
}

// Type is the documentation for a type declaration.
type Type struct {
	Doc  string
	Name string
	Decl *ast.GenDecl

	// associated declarations
	Consts  []*Value // sorted list of constants of (mostly) this type
	Vars    []*Value // sorted list of variables of (mostly) this type
	Funcs   []*Func  // sorted list of functions returning this type
	Methods []*Func  // sorted list of methods (including embedded ones) of this type

	// Examples is a sorted list of examples associated with
	// this type. Examples are extracted from _test.go files
	// provided to NewFromFiles.
	Examples []*Example

	IsDeprecated bool
}

// Func is the documentation for a func declaration.
type Func struct {
	Doc  string
	Name string
	Decl *ast.FuncDecl

	// methods
	// (for functions, these fields have the respective zero value)
	Recv  string // actual   receiver "T" or "*T"
	Orig  string // original receiver "T" or "*T"
	Level int    // embedding level; 0 means not embedded

	// Examples is a sorted list of examples associated with this
	// function or method. Examples are extracted from _test.go files
	// provided to NewFromFiles.
	Examples []*Example

	IsDeprecated bool
}

// A Note represents a marked comment starting with "MARKER(uid): note body".
// Any note with a marker of 2 or more upper case [A-Z] letters and a uid of
// at least one character is recognized. The ":" following the uid is optional.
// Notes are collected in the Package.Notes map indexed by the notes marker.
type Note struct {
	Pos, End token.Pos // position range of the comment containing the marker
	UID      string    // uid found with the marker
	Body     string    // note body text
}

// Mode values control the operation of New and NewFromFiles.
type Mode int

const (
	// AllDecls says to extract documentation for all package-level
	// declarations, not just exported ones.
	AllDecls Mode = 1 << iota

	// AllMethods says to show all embedded methods, not just the ones of
	// invisible (unexported) anonymous fields.
	AllMethods

	// PreserveAST says to leave the AST unmodified. Originally, pieces of
	// the AST such as function bodies were nil-ed out to save memory in
	// godoc, but not all programs want that behavior.
	PreserveAST
)

// New computes the package documentation for the given package AST.
// New takes ownership of the AST pkg and may edit or overwrite it.
// To have the Examples fields populated, use NewFromFiles and include
// the package's _test.go files.
//
func New(pkg *ast.Package, importPath string, mode Mode) *Package {
	var r reader
	r.readPackage(pkg, mode)
	r.computeMethodSets()
	r.cleanupTypes()
	return &Package{
		Doc:        r.doc,
		Name:       pkg.Name,
		ImportPath: importPath,
		Imports:    sortedKeys(r.imports),
		Filenames:  r.filenames,
		Notes:      r.notes,
		Bugs:       noteBodies(r.notes["BUG"]),
		Consts:     sortedValues(r.values, token.CONST),
		Types:      sortedTypes(r.types, mode&AllMethods != 0),
		Vars:       sortedValues(r.values, token.VAR),
		Funcs:      sortedFuncs(r.funcs, true),
	}
}

// NewFromFiles computes documentation for a package.
//
// The package is specified by a list of *ast.Files and corresponding
// file set, which must not be nil. NewFromFiles does not skip files
// based on build constraints, so it is the caller's responsibility to
// provide only the files that are matched by the build context.
// The import path of the package is specified by importPath.
//
// Examples found in _test.go files are associated with the corresponding
// type, function, method, or the package, based on their name.
// If the example has a suffix in its name, it is set in the
// Example.Suffix field. Examples with malformed names are skipped.
//
// Optionally, a single extra argument of type Mode can be provided to
// control low-level aspects of the documentation extraction behavior.
//
// NewFromFiles takes ownership of the AST files and may edit them,
// unless the PreserveAST Mode bit is on.
//
func NewFromFiles(fset *token.FileSet, files []*ast.File, importPath string, opts ...interface{}) (*Package, error) {
	// Check for invalid API usage.
	if fset == nil {
		panic(fmt.Errorf("doc.NewFromFiles: no token.FileSet provided (fset == nil)"))
	}
	var mode Mode
	switch len(opts) { // There can only be 0 or 1 options, so a simple switch works for now.
	case 0:
		// Nothing to do.
	case 1:
		m, ok := opts[0].(Mode)
		if !ok {
			panic(fmt.Errorf("doc.NewFromFiles: option argument type must be doc.Mode"))
		}
		mode = m
	default:
		panic(fmt.Errorf("doc.NewFromFiles: there must not be more than 1 option argument"))
	}

	// Collect .go and _test.go files.
	var (
		goFiles     = make(map[string]*ast.File)
		testGoFiles []*ast.File
	)
	for i := range files {
		f := fset.File(files[i].Pos())
		if f == nil {
			return nil, fmt.Errorf("file files[%d] is not found in the provided file set", i)
		}
		switch name := f.Name(); {
		case strings.HasSuffix(name, ".go") && !strings.HasSuffix(name, "_test.go"):
			goFiles[name] = files[i]
		case strings.HasSuffix(name, "_test.go"):
			testGoFiles = append(testGoFiles, files[i])
		default:
			return nil, fmt.Errorf("file files[%d] filename %q does not have a .go extension", i, name)
		}
	}

	// TODO(dmitshur,gri): A relatively high level call to ast.NewPackage with a simpleImporter
	// ast.Importer implementation is made below. It might be possible to short-circuit and simplify.

	// Compute package documentation.
	pkg, _ := ast.NewPackage(fset, goFiles, simpleImporter, nil) // Ignore errors that can happen due to unresolved identifiers.
	p := New(pkg, importPath, mode)
	classifyExamples(p, Examples(fset, testGoFiles...))
	return p, nil
}

// simpleImporter returns a (dummy) package object named by the last path
// component of the provided package path (as is the convention for packages).
// This is sufficient to resolve package identifiers without doing an actual
// import. It never returns an error.
func simpleImporter(imports map[string]*ast.Object, path string) (*ast.Object, error) {
	pkg := imports[path]
	if pkg == nil {
		pkg = ast.NewObj(ast.Pkg, packageName(path))
		pkg.Data = ast.NewScope(nil) // required by ast.NewPackage for dot-import
		imports[path] = pkg
	}
	return pkg, nil
}

// packageName returns the last path component of the provided package,
// stripping the major version component, if any.
func packageName(path string) string {
	pathPrefix, _, _ := module.SplitPathVersion(path)
	// Note that strings.LastIndex returns -1 if there is no "/".
	return pathPrefix[strings.LastIndex(pathPrefix, "/")+1:]
}