package main

import (
	htemplate "html/template"
	"io"
	"io/fs"
	"io/ioutil"
	"os"
	pathpkg "path"
	"path/filepath"
	"strings"
	"text/template"
)

// Template represents a template.
type Template interface {
	Execute(io.Writer, interface{}) error
}

// Templates contains site templates.
type Templates struct {
	tmpls map[string]Template
	funcs map[string]interface{}
}

// NewTemplates returns a new Templates with the default templates.
func NewTemplates() *Templates {
	t := &Templates{
		tmpls: map[string]Template{},
	}
	return t
}

// Funcs sets the functions available to newly created templates.
func (t *Templates) Funcs(funcs map[string]interface{}) {
	t.funcs = funcs
}

// LoadTemplate loads a template from the provided filenames.
func (t *Templates) LoadTemplate(name string, filenames ...string) error {
	if pathpkg.Ext(name) == ".html" {
		return t.loadHTMLTemplate(name, filenames...)
	}
	return t.loadTextTemplate(name, filenames...)
}

func (t *Templates) loadTextTemplate(name string, filenames ...string) error {
	tmpl := template.New(name).Funcs(t.funcs)
	for i := range filenames {
		b, err := ioutil.ReadFile(filenames[i])
		if err != nil {
			return err
		}
		if _, err := tmpl.Parse(string(b)); err != nil {
			return err
		}
	}
	t.tmpls[name] = tmpl
	return nil
}

func (t *Templates) loadHTMLTemplate(name string, filenames ...string) error {
	tmpl := htemplate.New(name).Funcs(t.funcs)
	for i := range filenames {
		b, err := ioutil.ReadFile(filenames[i])
		if err != nil {
			return err
		}
		if _, err := tmpl.Parse(string(b)); err != nil {
			return err
		}
	}
	t.tmpls[name] = tmpl
	return nil
}

// Load loads templates from the provided directory.
func (t *Templates) Load(dir string, exts []string) error {
	err := filepath.WalkDir(dir, func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if d.IsDir() {
			name := d.Name()
			if strings.HasPrefix(name, "_") && name != "_default" {
				return fs.SkipDir
			}

			// Load atom.xml template
			atom := pathpkg.Join(path, "atom.xml")
			if _, err := os.Stat(atom); err == nil {
				name := strings.TrimPrefix(atom, dir)
				t.LoadTemplate(name, atom)
			}

			// Load page templates
			for _, ext := range exts {
				for _, name := range []string{"index" + ext, "page" + ext} {
					filename := pathpkg.Join(path, name)
					if _, err := os.Stat(filename); err != nil {
						// Template does not exist
						continue
					}

					filenames := []string{filename}
					base := pathpkg.Join(path, "base"+ext)
					if _, err := os.Stat(base); err == nil {
						filenames = append(filenames, base)
					}

					name := strings.TrimPrefix(filename, dir)
					if err := t.LoadTemplate(name, filenames...); err != nil {
						return err
					}
				}
			}
		}
		return nil
	})
	if err != nil && !os.IsNotExist(err) {
		return err
	}

	// Load partial templates
	partials := pathpkg.Join(dir, "_partials")
	err = filepath.WalkDir(partials, func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if d.Type().IsRegular() {
			name := strings.TrimPrefix(path, dir)
			t.LoadTemplate(name, path)
		}
		return nil
	})
	if err != nil && !os.IsNotExist(err) {
		return err
	}
	return nil
}

// FindTemplate returns the template for the given path.
func (t *Templates) FindTemplate(path string, tmpl string) (Template, bool) {
	tmplPath := pathpkg.Join(path, tmpl)
	if t, ok := t.tmpls[tmplPath]; ok {
		return t, true
	}
	if t, ok := t.tmpls[pathpkg.Join("/_default", tmpl)]; ok {
		return t, true
	}
	// Failed to find template
	return nil, false
}

// FindPartial returns the partial template of the given name.
func (t *Templates) FindPartial(name string) (Template, bool) {
	if t, ok := t.tmpls[pathpkg.Join("/_partials", name)]; ok {
		return t, true
	}
	return nil, false
}