// Package templates implements template execution for files to be
// dynamically rendered for the client.
package templates

import (
	"bytes"
	"mime"
	"net/http"
	"os"
	"path"
	"path/filepath"
	"sync"
	"text/template"

	"github.com/mholt/caddy/caddyhttp/httpserver"
)

// ServeHTTP implements the httpserver.Handler interface.
func (t Templates) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
	for _, rule := range t.Rules {
		if !httpserver.Path(r.URL.Path).Matches(rule.Path) {
			continue
		}

		// Check for index files
		fpath := r.URL.Path
		if idx, ok := httpserver.IndexFile(t.FileSys, fpath, rule.IndexFiles); ok {
			fpath = idx
		}

		// Check the extension
		reqExt := path.Ext(fpath)

		for _, ext := range rule.Extensions {
			if reqExt == ext {
				// Create execution context
				ctx := httpserver.NewContextWithHeader(w.Header())
				ctx.Root = t.FileSys
				ctx.Req = r
				ctx.URL = r.URL

				// New template
				templateName := filepath.Base(fpath)
				tpl := template.New(templateName)

				// Set delims
				if rule.Delims != [2]string{} {
					tpl.Delims(rule.Delims[0], rule.Delims[1])
				}

				// Add custom functions
				tpl.Funcs(httpserver.TemplateFuncs)

				// Build the template
				templatePath := filepath.Join(t.Root, fpath)
				tpl, err := tpl.ParseFiles(templatePath)
				if err != nil {
					if os.IsNotExist(err) {
						return http.StatusNotFound, nil
					} else if os.IsPermission(err) {
						return http.StatusForbidden, nil
					}
					return http.StatusInternalServerError, err
				}

				// Execute it
				buf := t.BufPool.Get().(*bytes.Buffer)
				buf.Reset()
				defer t.BufPool.Put(buf)
				err = tpl.Execute(buf, ctx)
				if err != nil {
					return http.StatusInternalServerError, err
				}

				// If Content-Type isn't set here, http.ResponseWriter.Write
				// will set it according to response body. But other middleware
				// such as gzip can modify response body, then Content-Type
				// detected by http.ResponseWriter.Write is wrong.
				ctype := mime.TypeByExtension(ext)
				if ctype == "" {
					ctype = http.DetectContentType(buf.Bytes())
				}
				w.Header().Set("Content-Type", ctype)

				templateInfo, err := os.Stat(templatePath)
				if err == nil {
					// add the Last-Modified header if we were able to read the stamp
					httpserver.SetLastModifiedHeader(w, templateInfo.ModTime())
				}
				buf.WriteTo(w)

				return http.StatusOK, nil
			}
		}
	}

	return t.Next.ServeHTTP(w, r)
}

// Templates is middleware to render templated files as the HTTP response.
type Templates struct {
	Next    httpserver.Handler
	Rules   []Rule
	Root    string
	FileSys http.FileSystem
	BufPool *sync.Pool // docs: "A Pool must not be copied after first use."
}

// Rule represents a template rule. A template will only execute
// with this rule if the request path matches the Path specified
// and requests a resource with one of the extensions specified.
type Rule struct {
	Path       string
	Extensions []string
	IndexFiles []string
	Delims     [2]string
}