// Copyright 2017 Gerasimos Maropoulos, ΓΜ. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package view

import (
	"bytes"
	"fmt"
	"html/template"
	"io"
	"io/ioutil"
	"os"
	"path/filepath"
	"strings"
	"sync"
)

type (
	// HTMLEngine contains the html view engine structure.
	HTMLEngine struct {
		// files configuration
		directory string
		extension string
		assetFn   func(name string) ([]byte, error) // for embedded, in combination with directory & extension
		namesFn   func() []string                   // for embedded, in combination with directory & extension
		reload    bool                              // if true, each time the ExecuteWriter is called the templates will be reloaded.
		// parser configuration
		left        string
		right       string
		layout      string
		rmu         sync.RWMutex // locks for layoutFuncs and funcs
		layoutFuncs map[string]interface{}
		funcs       map[string]interface{}

		//
		middleware func(name string, contents string) (string, error)
		mu         sync.Mutex // locks for template files loader
		Templates  *template.Template
		//
	}
)

var _ Engine = &HTMLEngine{}

var emptyFuncs = template.FuncMap{
	"yield": func() (string, error) {
		return "", fmt.Errorf("yield was called, yet no layout defined")
	},
	"partial": func() (string, error) {
		return "", fmt.Errorf("block was called, yet no layout defined")
	},
	"partial_r": func() (string, error) {
		return "", fmt.Errorf("block was called, yet no layout defined")
	},
	"current": func() (string, error) {
		return "", nil
	}, "render": func() (string, error) {
		return "", nil
	},
}

// HTML creates and returns a new html view engine.
// The html engine used like the "html/template" standard go package
// but with a lot of extra features.
func HTML(directory, extension string) *HTMLEngine {
	s := &HTMLEngine{
		directory:   directory,
		extension:   extension,
		assetFn:     nil,
		namesFn:     nil,
		reload:      false,
		left:        "{{",
		right:       "}}",
		layout:      "",
		layoutFuncs: make(map[string]interface{}, 0),
		funcs:       make(map[string]interface{}, 0),
	}

	return s
}

// Ext returns the file extension which this view engine is responsible to render.
func (s *HTMLEngine) Ext() string {
	return s.extension
}

// Binary optionally, use it when template files are distributed
// inside the app executable (.go generated files).
//
// The assetFn and namesFn can come from the go-bindata library.
func (s *HTMLEngine) Binary(assetFn func(name string) ([]byte, error), namesFn func() []string) *HTMLEngine {
	s.assetFn, s.namesFn = assetFn, namesFn
	return s
}

// Reload if setted to true the templates are reloading on each render,
// use it when you're in development and you're boring of restarting
// the whole app when you edit a template file.
func (s *HTMLEngine) Reload(developmentMode bool) *HTMLEngine {
	s.reload = developmentMode
	return s
}

// 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 }}.
func (s *HTMLEngine) Delims(left, right string) *HTMLEngine {
	s.left, s.right = left, right
	return s
}

// Layout sets the layout template file which inside should use
// the {{ yield }} func to yield the main template file
// and optionally {{partial/partial_r/render}} to render other template files like headers and footers
//
// The 'tmplLayoutFile' is a relative path of the templates base directory,
// for the template file with its extension.
//
// Example: HTML("./templates", ".html").Layout("layouts/mainLayout.html")
//         // mainLayout.html is inside: "./templates/layouts/".
//
// Note: Layout can be changed for a specific call
// action with the option: "layout" on the Iris' context.Render function.
func (s *HTMLEngine) Layout(layoutFile string) *HTMLEngine {
	s.layout = layoutFile
	return s
}

// AddLayoutFunc adds the function to the template's layout-only function map.
// It is legal to overwrite elements of the default layout actions:
// - yield func() (template.HTML, error)
// - current  func() (string, error)
// - partial func(partialName string) (template.HTML, error)
// - partial_r func(partialName string) (template.HTML, error)
// - render func(fullPartialName string) (template.HTML, error).
func (s *HTMLEngine) AddLayoutFunc(funcName string, funcBody interface{}) *HTMLEngine {
	s.rmu.Lock()
	s.layoutFuncs[funcName] = funcBody
	s.rmu.Unlock()
	return s
}

// AddFunc adds the function to the template's function map.
// It is legal to overwrite elements of the default actions:
// - url func(routeName string, args ...string) string
// - urlpath func(routeName string, args ...string) string
// - render func(fullPartialName string) (template.HTML, error).
func (s *HTMLEngine) AddFunc(funcName string, funcBody interface{}) {
	s.rmu.Lock()
	s.funcs[funcName] = funcBody
	s.rmu.Unlock()
}

// Load parses the templates to the engine.
// It's alos responsible to add the necessary global functions.
//
// Returns an error if something bad happens, user is responsible to catch it.
func (s *HTMLEngine) Load() error {
	if s.assetFn != nil && s.namesFn != nil {
		// embedded
		return s.loadAssets()
	}

	// load from directory, make the dir absolute here too.
	dir, err := filepath.Abs(s.directory)
	if err != nil {
		return err
	}
	// change the directory field configuration, load happens after directory has been setted, so we will not have any problems here.
	s.directory = dir
	return s.loadDirectory()
}

// loadDirectory builds the templates from directory.
func (s *HTMLEngine) loadDirectory() error {
	dir, extension := s.directory, s.extension

	var templateErr error
	s.Templates = template.New(dir)
	s.Templates.Delims(s.left, s.right)

	filepath.Walk(dir, func(path string, info os.FileInfo, err error) error {
		if info == nil || info.IsDir() {

		} else {

			rel, err := filepath.Rel(dir, path)
			if err != nil {
				templateErr = err
				return err
			}

			ext := filepath.Ext(path)
			if ext == extension {

				buf, err := ioutil.ReadFile(path)
				if err != nil {
					templateErr = err
					return err
				}

				contents := string(buf)

				if err == nil {

					name := filepath.ToSlash(rel)
					tmpl := s.Templates.New(name)

					if s.middleware != nil {
						contents, err = s.middleware(name, contents)
					}
					if err != nil {
						templateErr = err
						return err
					}
					s.mu.Lock()
					// Add our funcmaps.
					if s.funcs != nil {
						tmpl.Funcs(s.funcs)
					}

					tmpl.Funcs(emptyFuncs).Parse(contents)
					s.mu.Unlock()
				}
			}

		}
		return nil
	})

	return templateErr
}

// loadAssets loads the templates by binary (go-bindata for embedded).
func (s *HTMLEngine) loadAssets() error {
	virtualDirectory, virtualExtension := s.directory, s.extension
	assetFn, namesFn := s.assetFn, s.namesFn

	var templateErr error
	s.Templates = template.New(virtualDirectory)
	s.Templates.Delims(s.left, s.right)
	names := namesFn()
	if len(virtualDirectory) > 0 {
		if virtualDirectory[0] == '.' { // first check for .wrong
			virtualDirectory = virtualDirectory[1:]
		}
		if virtualDirectory[0] == '/' || virtualDirectory[0] == os.PathSeparator { // second check for /something, (or ./something if we had dot on 0 it will be removed
			virtualDirectory = virtualDirectory[1:]
		}
	}

	for _, path := range names {
		if !strings.HasPrefix(path, virtualDirectory) {
			continue
		}
		ext := filepath.Ext(path)
		if ext == virtualExtension {

			rel, err := filepath.Rel(virtualDirectory, path)
			if err != nil {
				templateErr = err
				return err
			}

			buf, err := assetFn(path)
			if err != nil {
				templateErr = err
				return err
			}
			contents := string(buf)
			name := filepath.ToSlash(rel)
			tmpl := s.Templates.New(name)

			if s.middleware != nil {
				contents, err = s.middleware(name, contents)
			}
			if err != nil {
				templateErr = err
				return err
			}

			// Add our funcmaps.
			if s.funcs != nil {
				tmpl.Funcs(s.funcs)
			}

			tmpl.Funcs(emptyFuncs).Parse(contents)
		}
	}
	return templateErr
}

func (s *HTMLEngine) executeTemplateBuf(name string, binding interface{}) (*bytes.Buffer, error) {
	buf := new(bytes.Buffer)
	err := s.Templates.ExecuteTemplate(buf, name, binding)

	return buf, err
}

func (s *HTMLEngine) layoutFuncsFor(name string, binding interface{}) {
	funcs := template.FuncMap{
		"yield": func() (template.HTML, error) {
			buf, err := s.executeTemplateBuf(name, binding)
			// Return safe HTML here since we are rendering our own template.
			return template.HTML(buf.String()), err
		},
		"current": func() (string, error) {
			return name, nil
		},
		"partial": func(partialName string) (template.HTML, error) {
			fullPartialName := fmt.Sprintf("%s-%s", partialName, name)
			if s.Templates.Lookup(fullPartialName) != nil {
				buf, err := s.executeTemplateBuf(fullPartialName, binding)
				return template.HTML(buf.String()), err
			}
			return "", nil
		},
		//partial related to current page,
		//it would be easier for adding pages' style/script inline
		//for example when using partial_r '.script' in layout.html
		//templates/users/index.html would load templates/users/index.script.html
		"partial_r": func(partialName string) (template.HTML, error) {
			ext := filepath.Ext(name)
			root := name[:len(name)-len(ext)]
			fullPartialName := fmt.Sprintf("%s%s%s", root, partialName, ext)
			if s.Templates.Lookup(fullPartialName) != nil {
				buf, err := s.executeTemplateBuf(fullPartialName, binding)
				return template.HTML(buf.String()), err
			}
			return "", nil
		},
		"render": func(fullPartialName string) (template.HTML, error) {
			buf, err := s.executeTemplateBuf(fullPartialName, binding)
			return template.HTML(buf.String()), err
		},
	}
	s.rmu.RLock()
	for k, v := range s.layoutFuncs {
		funcs[k] = v
	}
	s.rmu.RUnlock()
	if tpl := s.Templates.Lookup(name); tpl != nil {
		tpl.Funcs(funcs)
	}
}

func (s *HTMLEngine) runtimeFuncsFor(name string, binding interface{}) {
	funcs := template.FuncMap{
		"render": func(fullPartialName string) (template.HTML, error) {
			buf, err := s.executeTemplateBuf(fullPartialName, binding)
			return template.HTML(buf.String()), err
		},
	}

	if tpl := s.Templates.Lookup(name); tpl != nil {
		tpl.Funcs(funcs)
	}
}

// ExecuteWriter executes a template and writes its result to the w writer.
func (s *HTMLEngine) ExecuteWriter(w io.Writer, name string, layout string, bindingData interface{}) error {
	// reload the templates if reload configuration field is true
	if s.reload {
		if err := s.Load(); err != nil {
			return err
		}
	}

	layout = getLayout(layout, s.layout)

	if layout != "" {
		s.layoutFuncsFor(name, bindingData)
		name = layout
	} else {
		s.runtimeFuncsFor(name, bindingData)
	}

	return s.Templates.ExecuteTemplate(w, name, bindingData)
}