package main

import (
	"encoding/json"
	"fmt"
	"html/template"
	"os"
	"path/filepath"
	"strings"
)

type Reference struct {
	Link ParsedLink
	Name string
}

type Refs map[string][]Reference

func processBackrefs(dirname string, page Page) error {
	filename := filepath.Join(dirname, "backrefs.json")
	refs := make(Refs)

	err := loadBackrefs(filename, refs)
	if err != nil {
		return fmt.Errorf("while loading backrefs: %w", err)
	}

	err = processBackrefsForPage(page, refs)
	if err != nil {
		return fmt.Errorf("while processing backrefs for %q: %w", page.Name, err)
	}

	if err = saveBackrefs(filename, refs); err != nil {
		return fmt.Errorf("while saving backrefs: %w", err)
	}
	return nil
}

func saveBackrefs(filename string, refs Refs) error {
	f, err := os.Create(filename)
	if err != nil {
		return err
	}
	defer f.Close()

	return json.NewEncoder(f).Encode(&refs)
}

func processBackrefsForPage(page Page, refs Refs) error {
	content := page.Content

	var listItems []struct {
		Id       string
		Indented int
		Text     string
	}

	var links []ParsedLink
	err := json.NewDecoder(strings.NewReader(content)).Decode(&listItems)
	if err == nil {
		for _, item := range listItems {
			foundLinks, err := ParseLinks(item.Id, item.Text)
			if err != nil {
				continue
			}
			links = append(links, foundLinks...)
		}
	} else {
		links, err = ParseLinks(page.Name, page.Content)
		if err != nil {
			return err
		}
	}

link:
	for _, link := range links {
		for i, ref := range refs[link.PageName] {
			if ref.Link.Id == link.Id {
				refs[link.PageName][i].Link = link
				continue link
			}
		}
		refs[link.PageName] = append(refs[link.PageName], Reference{link, page.Name})
	}

	return nil
}

func getBackrefs(fp *FilePages, p string) (map[string][]Backref, error) {
	refs := make(Refs)
	p = strings.Replace(p, " ", "_", -1)

	filename := filepath.Join(fp.dirname, "backrefs.json")
	err := loadBackrefs(filename, refs)
	if err != nil {
		return nil, err
	}

	result := make(map[string][]Backref)

	for _, ref := range refs[p] {
		title := strings.Replace(ref.Name, "_", " ", -1)
		if _, e := result[ref.Name]; !e {
			result[ref.Name] = nil
		}

		line := strings.TrimLeft(ref.Link.Line, " ")
		if line[0] == '*' && line[1] == ' ' {
			line = line[2:]
		}
		links := renderLinks(line)
		pageText := renderMarkdown2(links)

		removeBrackets := func(r rune) rune {
			if r == '[' || r == ']' || r == '*' {
				return -1
			}
			return r
		}

		result[ref.Name] = append(result[ref.Name], Backref{
			Name:     ref.Name,
			Title:    title,
			LineHTML: template.HTML(pageText),
			Line:     strings.Map(removeBrackets, ref.Link.Line),
		})
	}

	return result, nil
}

func loadBackrefs(filename string, refs Refs) error {
	f, err := os.Open(filename)
	if err != nil {
		return err
	}
	defer f.Close()
	err = json.NewDecoder(f).Decode(&refs)
	if err != nil {
		return err
	}
	return nil
}