package pages

import (
	"fmt"
	"path"
	"path/filepath"
	"regexp"
	"sort"
	"strings"

	"github.com/osteele/gojekyll/helpers"
)

// PermalinkStyles defines built-in styles from https://jekyllrb.com/docs/permalinks/#builtinpermalinkstyles
var PermalinkStyles = map[string]string{
	"date":    "/:categories/:year/:month/:day/:title.html",
	"pretty":  "/:categories/:year/:month/:day/:title/",
	"ordinal": "/:categories/:year/:y_day/:title.html",
	"none":    "/:categories/:title.html",
}

// permalinkDateVariables maps Jekyll permalink template variable names
// to time.Format layout strings
var permalinkDateVariables = map[string]string{
	"month":      "01",
	"imonth":     "1",
	"day":        "02",
	"i_day":      "2",
	"hour":       "15",
	"minute":     "04",
	"second":     "05",
	"year":       "2006",
	"short_year": "06",
}

var templateVariableMatcher = regexp.MustCompile(`:\w+\b`)

// See https://jekyllrb.com/docs/permalinks/#template-variables
func (p *pageFields) permalinkTemplateVariables() map[string]string {
	var (
		collection string
		relpath    = strings.TrimPrefix(p.relpath, p.container.PathPrefix())
		root       = helpers.TrimExt(relpath)
		name       = filepath.Base(root)
		categories = p.categories()
	)
	sort.Strings(categories)
	// TODO recognize category; list
	vs := map[string]string{
		"categories": strings.Join(categories, "/"),
		"collection": collection,
		"name":       helpers.Slugify(name),
		"path":       "/" + root,
		"slug":       p.frontMatter.String("slug", helpers.Slugify(name)),
		"title":      p.frontMatter.String("slug", helpers.Slugify(name)),
		// The following isn't documented, but is evident
		"output_ext": p.OutputExt(),
		// TODO categories
	}
	for name, f := range permalinkDateVariables {
		vs[name] = p.modTime.Format(f)
	}
	return vs
}

func (p *pageFields) expandPermalink() (s string, err error) {
	pattern := p.frontMatter.String("permalink", p.container.DefaultPermalink())
	if p, found := PermalinkStyles[pattern]; found {
		pattern = p
	}
	templateVariables := p.permalinkTemplateVariables()
	// The ReplaceAllStringFunc callback signals errors via panic.
	// Turn them into return values.
	defer func() {
		if r := recover(); r != nil {
			if e, ok := r.(error); ok {
				err = e
			} else {
				panic(r)
			}
		}
	}()
	s = templateVariableMatcher.ReplaceAllStringFunc(pattern, func(m string) string {
		varname := m[1:]
		value, found := templateVariables[varname]
		if !found {
			panic(fmt.Errorf("unknown variable %q in permalink template %q", varname, pattern))
		}
		return value
	})
	return path.Clean(filepath.ToSlash(s)), nil
}

// The permalink is computed once instead of on demand, so that subsequent
// access needn't check for an error.
func (p *pageFields) initPermalink() (err error) {
	p.permalink, err = p.expandPermalink()
	return
}