package sitebuilder

import (
	"bytes"
	"fmt"
	"html/template"
	"io"
	"log"
	"os"
	"path/filepath"
	"sort"
	"strings"

	"github.com/yuin/goldmark"
	"github.com/yuin/goldmark/extension"
	"github.com/yuin/goldmark/parser"
	"github.com/yuin/goldmark/renderer/html"
	"lmika.dev/lmika/weiro/models"
)

type Builder struct {
	site       models.Site
	gmMarkdown goldmark.Markdown
	opts       Options
	tmpls      *template.Template
}

func New(site models.Site, opts Options) (*Builder, error) {
	tmpls, err := template.New("").
		Funcs(templateFns(site, opts)).
		ParseFS(opts.TemplatesFS, tmplNamePostSingle, tmplNamePostList, tmplNameLayoutMain)
	if err != nil {
		return nil, err
	}

	return &Builder{
		site:  site,
		opts:  opts,
		tmpls: tmpls,
		gmMarkdown: goldmark.New(
			goldmark.WithExtensions(extension.GFM),
			goldmark.WithParserOptions(
				parser.WithAutoHeadingID(),
			),
			goldmark.WithRendererOptions(
				html.WithHardWraps(),
				html.WithUnsafe(),
			),
		),
	}, nil
}

func (b *Builder) BuildSite(outDir string) error {
	buildCtx := buildContext{outDir: outDir}

	if err := os.RemoveAll(outDir); err != nil {
		return err
	}

	for _, post := range b.site.Posts {
		if err := b.writePost(buildCtx, post); err != nil {
			return err
		}
	}

	if err := b.renderPostList(buildCtx, b.site.Posts); err != nil {
		return err
	}

	return nil
}

func (b *Builder) renderPostList(ctx buildContext, postList []*models.Post) error {
	// TODO: paging
	postCopy := make([]*models.Post, len(postList))
	copy(postCopy, postList)

	sort.Slice(postCopy, func(i, j int) bool {
		return postCopy[i].Meta.Date.After(postCopy[j].Meta.Date)
	})

	pl := postListData{}
	for _, post := range postCopy {
		rp, err := b.renderPost(post)
		if err != nil {
			return err
		}
		pl.Posts = append(pl.Posts, rp)
	}

	return b.createAtPath(ctx, "", func(f io.Writer) error {
		return b.renderTemplate(f, tmplNamePostList, pl)
	})
}

func (b *Builder) renderPost(post *models.Post) (postSingleData, error) {
	postPath := post.Meta.Slug
	if b.opts.BasePosts != "" {
		postPath = filepath.Join(b.opts.BasePosts, strings.TrimPrefix(postPath, "/"))
	}

	var md bytes.Buffer
	if err := b.gmMarkdown.Convert([]byte(post.Content), &md); err != nil {
		return postSingleData{}, fmt.Errorf("failed to write post %s: %w", post.Meta.Slug, err)
	}

	return postSingleData{
		Path: postPath,
		Meta: post.Meta,
		HTML: template.HTML(md.String()),
	}, nil
}

func (b *Builder) writePost(ctx buildContext, post *models.Post) error {
	rp, err := b.renderPost(post)
	if err != nil {
		return err
	}

	return b.createAtPath(ctx, rp.Path, func(f io.Writer) error {
		return b.renderTemplate(f, tmplNamePostSingle, rp)
	})
}

func (b *Builder) createAtPath(ctx buildContext, path string, fn func(f io.Writer) error) error {
	outFile := filepath.Join(ctx.outDir, strings.TrimPrefix(path, "/"))
	if filepath.Ext(outFile) == "" {
		outFile = filepath.Join(outFile, "index.html")
	}
	log.Printf("Writing %s\n", outFile)

	// Render it within the template
	if err := os.MkdirAll(filepath.Dir(outFile), 0755); err != nil {
		return err
	}

	f, err := os.Create(outFile)
	if err != nil {
		return err
	}
	defer f.Close()

	return fn(f)
}

func (b *Builder) renderTemplate(w io.Writer, name string, data interface{}) error {
	var buf bytes.Buffer
	if err := b.tmpls.ExecuteTemplate(&buf, name, data); err != nil {
		return err
	}

	return b.tmpls.ExecuteTemplate(w, tmplNameLayoutMain, layoutData{
		Body: template.HTML(buf.String()),
	})
}

type buildContext struct {
	outDir string
}