// Copyright 2015 Matthew Holt and The Caddy Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package templates

import (
	"bytes"
	"fmt"
	"html/template"
	"io"
	"net"
	"net/http"
	"path"
	"strings"
	"sync"

	"github.com/Masterminds/sprig"
	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
	"gopkg.in/russross/blackfriday.v2"
)

// templateContext is the templateContext with which HTTP templates are executed.
type templateContext struct {
	Root       http.FileSystem
	Req        *http.Request
	Args       []interface{} // defined by arguments to .Include
	RespHeader tplWrappedHeader

	config *Templates
}

// Include returns the contents of filename relative to the site root.
// Note that included files are NOT escaped, so you should only include
// trusted files. If it is not trusted, be sure to use escaping functions
// in your template.
func (c templateContext) Include(filename string, args ...interface{}) (template.HTML, error) {
	if c.Root == nil {
		return "", fmt.Errorf("root file system not specified")
	}

	file, err := c.Root.Open(filename)
	if err != nil {
		return "", err
	}
	defer file.Close()

	bodyBuf := bufPool.Get().(*bytes.Buffer)
	bodyBuf.Reset()
	defer bufPool.Put(bodyBuf)

	_, err = io.Copy(bodyBuf, file)
	if err != nil {
		return "", err
	}

	c.Args = args

	err = c.executeTemplateInBuffer(filename, bodyBuf)
	if err != nil {
		return "", err
	}

	return template.HTML(bodyBuf.String()), nil
}

// HTTPInclude returns the body of a virtual (lightweight) request
// to the given URI on the same server. Note that included bodies
// are NOT escaped, so you should only include trusted resources.
// If it is not trusted, be sure to use escaping functions yourself.
func (c templateContext) HTTPInclude(uri string) (template.HTML, error) {
	if c.Req.Header.Get(recursionPreventionHeader) == "1" {
		return "", fmt.Errorf("virtual include cycle")
	}

	buf := bufPool.Get().(*bytes.Buffer)
	buf.Reset()
	defer bufPool.Put(buf)

	virtReq, err := http.NewRequest("GET", uri, nil)
	if err != nil {
		return "", err
	}
	virtReq.Header.Set(recursionPreventionHeader, "1")

	vrw := &virtualResponseWriter{body: buf, header: make(http.Header)}
	server := c.Req.Context().Value(caddyhttp.ServerCtxKey).(http.Handler)

	server.ServeHTTP(vrw, virtReq)
	if vrw.status >= 400 {
		return "", fmt.Errorf("http %d", vrw.status)
	}

	err = c.executeTemplateInBuffer(uri, buf)
	if err != nil {
		return "", err
	}

	return template.HTML(buf.String()), nil
}

func (c templateContext) executeTemplateInBuffer(tplName string, buf *bytes.Buffer) error {
	tpl := template.New(tplName).Funcs(sprig.FuncMap())
	if len(c.config.Delimiters) == 2 {
		tpl.Delims(c.config.Delimiters[0], c.config.Delimiters[1])
	}

	parsedTpl, err := tpl.Parse(buf.String())
	if err != nil {
		return err
	}

	buf.Reset() // reuse buffer for output

	return parsedTpl.Execute(buf, c)
}

// Cookie gets the value of a cookie with name name.
func (c templateContext) Cookie(name string) string {
	cookies := c.Req.Cookies()
	for _, cookie := range cookies {
		if cookie.Name == name {
			return cookie.Value
		}
	}
	return ""
}

// Hostname gets the (remote) hostname of the client making the request.
// Performance warning: This involves a DNS lookup.
func (c templateContext) Hostname() string {
	ip := c.RemoteIP()

	hostnameList, err := net.LookupAddr(ip)
	if err != nil || len(hostnameList) == 0 {
		return c.Req.RemoteAddr
	}

	return hostnameList[0]
}

// RemoteIP gets the IP address of the client making the request.
func (c templateContext) RemoteIP() string {
	ip, _, err := net.SplitHostPort(c.Req.RemoteAddr)
	if err != nil {
		return c.Req.RemoteAddr
	}
	return ip
}

// Host returns the hostname portion of the Host header
// from the HTTP request.
func (c templateContext) Host() (string, error) {
	host, _, err := net.SplitHostPort(c.Req.Host)
	if err != nil {
		if !strings.Contains(c.Req.Host, ":") {
			// common with sites served on the default port 80
			return c.Req.Host, nil
		}
		return "", err
	}
	return host, nil
}

// StripHTML returns s without HTML tags. It is fairly naive
// but works with most valid HTML inputs.
func (c templateContext) StripHTML(s string) string {
	var buf bytes.Buffer
	var inTag, inQuotes bool
	var tagStart int
	for i, ch := range s {
		if inTag {
			if ch == '>' && !inQuotes {
				inTag = false
			} else if ch == '<' && !inQuotes {
				// false start
				buf.WriteString(s[tagStart:i])
				tagStart = i
			} else if ch == '"' {
				inQuotes = !inQuotes
			}
			continue
		}
		if ch == '<' {
			inTag = true
			tagStart = i
			continue
		}
		buf.WriteRune(ch)
	}
	if inTag {
		// false start
		buf.WriteString(s[tagStart:])
	}
	return buf.String()
}

// Markdown renders the markdown body as HTML. The resulting
// HTML is NOT escaped so that it can be rendered as HTML.
func (c templateContext) Markdown(body string) template.HTML {
	return template.HTML(blackfriday.Run([]byte(body)))
}

// ListFiles reads and returns a slice of names from the given
// directory relative to the root of c.
func (c templateContext) ListFiles(name string) ([]string, error) {
	if c.Root == nil {
		return nil, fmt.Errorf("root file system not specified")
	}

	dir, err := c.Root.Open(path.Clean(name))
	if err != nil {
		return nil, err
	}
	defer dir.Close()

	stat, err := dir.Stat()
	if err != nil {
		return nil, err
	}
	if !stat.IsDir() {
		return nil, fmt.Errorf("%v is not a directory", name)
	}

	dirInfo, err := dir.Readdir(0)
	if err != nil {
		return nil, err
	}

	names := make([]string, len(dirInfo))
	for i, fileInfo := range dirInfo {
		names[i] = fileInfo.Name()
	}

	return names, nil
}

// tplWrappedHeader wraps niladic functions so that they
// can be used in templates. (Template functions must
// return a value.)
type tplWrappedHeader struct{ http.Header }

// Add adds a header field value, appending val to
// existing values for that field. It returns an
// empty string.
func (h tplWrappedHeader) Add(field, val string) string {
	h.Header.Add(field, val)
	return ""
}

// Set sets a header field value, overwriting any
// other values for that field. It returns an
// empty string.
func (h tplWrappedHeader) Set(field, val string) string {
	h.Header.Set(field, val)
	return ""
}

// Del deletes a header field. It returns an empty string.
func (h tplWrappedHeader) Del(field string) string {
	h.Header.Del(field)
	return ""
}

var bufPool = sync.Pool{
	New: func() interface{} {
		return new(bytes.Buffer)
	},
}

const recursionPreventionHeader = "Caddy-Templates-Include"