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// Copyright 2011 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 template

import (

        "fmt"

        "io"

        "io/ioutil"

        "path/filepath"

        "sync"

        "text/template"

        "text/template/parse"

)

// Template is a specialized template.Template that produces a safe HTML

// document fragment.

type Template struct {

        escaped bool

        // We could embed the text/template field, but it's safer not to because

        // we need to keep our version of the name space and the underlying

        // template's in sync.

        text       *template.Template

        *nameSpace // common to all associated templates

}

// nameSpace is the data structure shared by all templates in an association.

type nameSpace struct {

        mu  sync.Mutex

        set map[string]*Template

}

// Execute applies a parsed template to the specified data object,

// writing the output to wr.

func (t *Template) Execute(wr io.Writer, data interface{}) (err error) {

        t.nameSpace.mu.Lock()

        if !t.escaped {

                if err = escapeTemplates(t, t.Name()); err != nil {

                        t.escaped = true

                }

        }

        t.nameSpace.mu.Unlock()

        if err != nil {

                return

        }

        return t.text.Execute(wr, data)

}

// ExecuteTemplate applies the template associated with t that has the given

// name to the specified data object and writes the output to wr.

func (t *Template) ExecuteTemplate(wr io.Writer, name string, data interface{}) error {

        tmpl, err := t.lookupAndEscapeTemplate(wr, name)

        if err != nil {

                return err

        }

        return tmpl.text.Execute(wr, data)

}

// lookupAndEscapeTemplate guarantees that the template with the given name

// is escaped, or returns an error if it cannot be. It returns the named

// template.

func (t *Template) lookupAndEscapeTemplate(wr io.Writer, name string) (tmpl *Template, err error) {

        t.nameSpace.mu.Lock()

        defer t.nameSpace.mu.Unlock()

        tmpl = t.set[name]

        if (tmpl == nil) != (t.text.Lookup(name) == nil) {

                panic("html/template internal error: template escaping out of sync")

        }

        if tmpl != nil && !tmpl.escaped {

                err = escapeTemplates(tmpl, name)

        }

        return tmpl, err

}

// Parse parses a string into a template. Nested template definitions

// will be associated with the top-level template t. Parse may be

// called multiple times to parse definitions of templates to associate

// with t. It is an error if a resulting template is non-empty (contains

// content other than template definitions) and would replace a

// non-empty template with the same name.  (In multiple calls to Parse

// with the same receiver template, only one call can contain text

// other than space, comments, and template definitions.)

func (t *Template) Parse(src string) (*Template, error) {

        t.nameSpace.mu.Lock()

        t.escaped = false

        t.nameSpace.mu.Unlock()

        ret, err := t.text.Parse(src)

        if err != nil {

                return nil, err

        }

        // In general, all the named templates might have changed underfoot.

        // Regardless, some new ones may have been defined.

        // The template.Template set has been updated; update ours.

        t.nameSpace.mu.Lock()

        defer t.nameSpace.mu.Unlock()

        for _, v := range ret.Templates() {

                name := v.Name()

                tmpl := t.set[name]

                if tmpl == nil {

                        tmpl = t.new(name)

                }

                tmpl.escaped = false

                tmpl.text = v

        }

        return t, nil

}

// AddParseTree is unimplemented.

func (t *Template) AddParseTree(name string, tree *parse.Tree) error {

        return fmt.Errorf("html/template: AddParseTree unimplemented")

}

// Clone is unimplemented.

func (t *Template) Clone(name string) error {

        return fmt.Errorf("html/template: Clone unimplemented")

}

// New allocates a new HTML template with the given name.

func New(name string) *Template {

        tmpl := &Template{

                false,

                template.New(name),

                &nameSpace{

                        set: make(map[string]*Template),

                },

        }

        tmpl.set[name] = tmpl

        return tmpl

}

// New allocates a new HTML template associated with the given one

// and with the same delimiters. The association, which is transitive,

// allows one template to invoke another with a {{template}} action.

func (t *Template) New(name string) *Template {

        t.nameSpace.mu.Lock()

        defer t.nameSpace.mu.Unlock()

        return t.new(name)

}

// new is the implementation of New, without the lock.

func (t *Template) new(name string) *Template {

        tmpl := &Template{

                false,

                t.text.New(name),

                t.nameSpace,

        }

        tmpl.set[name] = tmpl

        return tmpl

}

// Name returns the name of the template.

func (t *Template) Name() string {

        return t.text.Name()

}

// FuncMap is the type of the map defining the mapping from names to

// functions. Each function must have either a single return value, or two

// return values of which the second has type error. In that case, if the

// second (error) argument evaluates to non-nil during execution, execution

// terminates and Execute returns that error. FuncMap has the same base type

// as template.FuncMap, copied here so clients need not import "text/template".

type FuncMap map[string]interface{}

// Funcs adds the elements of the argument map to the template's function map.

// It panics if a value in the map is not a function with appropriate return

// type. However, it is legal to overwrite elements of the map. The return

// value is the template, so calls can be chained.

func (t *Template) Funcs(funcMap FuncMap) *Template {

        t.text.Funcs(template.FuncMap(funcMap))

        return t

}

// Delims sets the action delimiters to the specified strings, to be used in

// subsequent calls to Parse, ParseFiles, or ParseGlob. Nested template

// definitions will inherit the settings. An empty delimiter stands for the

// corresponding default: {{ or }}.

// The return value is the template, so calls can be chained.

func (t *Template) Delims(left, right string) *Template {

        t.text.Delims(left, right)

        return t

}

// Lookup returns the template with the given name that is associated with t,

// or nil if there is no such template.

func (t *Template) Lookup(name string) *Template {

        t.nameSpace.mu.Lock()

        defer t.nameSpace.mu.Unlock()

        return t.set[name]

}

// Must panics if err is non-nil in the same way as template.Must.

func Must(t *Template, err error) *Template {

        if err != nil {

                panic(err)

        }

        return t

}

// ParseFiles creates a new Template and parses the template definitions from

// the named files. The returned template's name will have the (base) name and

// (parsed) contents of the first file. There must be at least one file.

// If an error occurs, parsing stops and the returned *Template is nil.

func ParseFiles(filenames ...string) (*Template, error) {

        return parseFiles(nil, filenames...)

}

// ParseFiles parses the named files and associates the resulting templates with

// t. If an error occurs, parsing stops and the returned template is nil;

// otherwise it is t. There must be at least one file.

func (t *Template) ParseFiles(filenames ...string) (*Template, error) {

        return parseFiles(t, filenames...)

}

// parseFiles is the helper for the method and function. If the argument

// template is nil, it is created from the first file.

func parseFiles(t *Template, filenames ...string) (*Template, error) {

        if len(filenames) == 0 {

                // Not really a problem, but be consistent.

                return nil, fmt.Errorf("template: no files named in call to ParseFiles")

        }

        for _, filename := range filenames {

                b, err := ioutil.ReadFile(filename)

                if err != nil {

                        return nil, err

                }

                s := string(b)

                name := filepath.Base(filename)

                // First template becomes return value if not already defined,

                // and we use that one for subsequent New calls to associate

                // all the templates together. Also, if this file has the same name

                // as t, this file becomes the contents of t, so

                //  t, err := New(name).Funcs(xxx).ParseFiles(name)

                // works. Otherwise we create a new template associated with t.

                var tmpl *Template

                if t == nil {

                        t = New(name)

                }

                if name == t.Name() {

                        tmpl = t

                } else {

                        tmpl = t.New(name)

                }

                _, err = tmpl.Parse(s)

                if err != nil {

                        return nil, err

                }

        }

        return t, nil

}

// ParseGlob creates a new Template and parses the template definitions from the

// files identified by the pattern, which must match at least one file. The

// returned template will have the (base) name and (parsed) contents of the

// first file matched by the pattern. ParseGlob is equivalent to calling

// ParseFiles with the list of files matched by the pattern.

func ParseGlob(pattern string) (*Template, error) {

        return parseGlob(nil, pattern)

}

// ParseGlob parses the template definitions in the files identified by the

// pattern and associates the resulting templates with t. The pattern is

// processed by filepath.Glob and must match at least one file. ParseGlob is

// equivalent to calling t.ParseFiles with the list of files matched by the

// pattern.

func (t *Template) ParseGlob(pattern string) (*Template, error) {

        return parseGlob(t, pattern)

}

// parseGlob is the implementation of the function and method ParseGlob.

func parseGlob(t *Template, pattern string) (*Template, error) {

        filenames, err := filepath.Glob(pattern)

        if err != nil {

                return nil, err

        }

        if len(filenames) == 0 {

                return nil, fmt.Errorf("template: pattern matches no files: %#q", pattern)

        }

        return parseFiles(t, filenames...)

}