package main

import (
	"encoding/xml"
	"html/template"
	"image"
	imagedraw "image/draw"
	"image/jpeg"
	_ "image/png"
	"io"
	"log"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/BurntSushi/toml"
	xdraw "golang.org/x/image/draw"
)

const (
	thumbSize       = 600
	mediumMaxSize   = 1600
	defaultPageSize = 60
)

// PhotoMeta is the structure of a .toml sidecar file.
type PhotoMeta struct {
	Caption string `toml:"caption"`
	Date    string `toml:"date"` // YYYY-MM-DD
}

// Photo is the in-memory representation of one image.
type Photo struct {
	Slug    string
	File    string // relative path under public/, e.g. "images/foo.jpg"
	Thumb   string // relative path under public/, e.g. "thumbs/foo.jpg"
	Medium  string // relative path under public/, e.g. "medium/foo.jpg"
	Caption string
	Date    time.Time
}

// DayGroup is a run of photos sharing the same calendar day, for the timeline.
type DayGroup struct {
	day    string // "2006-01-02", grouping key (unexported: not for templates)
	Label  string // "14 June 2026"
	Count  int
	Photos []Photo
}

type Generator struct {
	contentDir  string
	outputDir   string
	baseURL     string
	author      string
	handle      string
	bio         string
	bioAlt      string
	fontsURL    string
	serifFamily string
	mlFamily    string
	pageSize    int
	mu          sync.Mutex
	tmpl        *template.Template
}

func NewGenerator(contentDir, outputDir, baseURL, author, handle, bio, bioAlt, fontsURL, serifFamily, mlFamily string, pageSize int) *Generator {
	tmpl := template.Must(template.ParseFS(assets, "templates/*.html"))
	if pageSize < 1 {
		pageSize = defaultPageSize
	}
	return &Generator{
		contentDir:  contentDir,
		outputDir:   outputDir,
		baseURL:     baseURL,
		author:      author,
		handle:      handle,
		bio:         bio,
		bioAlt:      bioAlt,
		fontsURL:    fontsURL,
		serifFamily: serifFamily,
		mlFamily:    mlFamily,
		pageSize:    pageSize,
		tmpl:        tmpl,
	}
}

func (g *Generator) initial() string {
	for _, r := range g.author {
		return strings.ToUpper(string(r))
	}
	return ""
}

// Build performs a full rebuild of the site. It is safe to call concurrently;
// concurrent calls are serialised by a mutex.
func (g *Generator) Build() error {
	g.mu.Lock()
	defer g.mu.Unlock()

	photos, err := g.loadPhotos()
	if err != nil {
		return err
	}

	for _, d := range []string{"images", "thumbs", "medium", "photo", "grid", "static"} {
		if err := os.MkdirAll(filepath.Join(g.outputDir, d), 0755); err != nil {
			return err
		}
	}

	for i := range photos {
		if err := g.processImage(&photos[i]); err != nil {
			log.Printf("processImage %s: %v", photos[i].Slug, err)
		}
	}

	if err := g.renderTimelinePages(photos); err != nil {
		return err
	}
	if err := g.renderGridPages(photos); err != nil {
		return err
	}
	for i := range photos {
		var newer, older *Photo
		if i > 0 {
			newer = &photos[i-1]
		}
		if i+1 < len(photos) {
			older = &photos[i+1]
		}
		if err := g.renderPhotoPage(photos[i], newer, older); err != nil {
			return err
		}
	}
	if err := g.renderFeed(photos); err != nil {
		return err
	}
	if err := g.copyStatic(); err != nil {
		return err
	}

	log.Printf("built: %d photos", len(photos))
	return nil
}

// loadPhotos scans the content directory and returns photos sorted newest first.
func (g *Generator) loadPhotos() ([]Photo, error) {
	entries, err := os.ReadDir(g.contentDir)
	if err != nil {
		return nil, err
	}

	var photos []Photo
	for _, e := range entries {
		if e.IsDir() {
			continue
		}
		name := e.Name()
		ext := strings.ToLower(filepath.Ext(name))
		if ext != ".jpg" && ext != ".jpeg" && ext != ".png" {
			continue
		}

		slug := strings.TrimSuffix(name, filepath.Ext(name))
		meta := PhotoMeta{
			Caption: slug,
			Date:    time.Now().Format("2006-01-02"),
		}

		tomlPath := filepath.Join(g.contentDir, slug+".toml")
		if _, err := os.Stat(tomlPath); err == nil {
			if _, err := toml.DecodeFile(tomlPath, &meta); err != nil {
				log.Printf("parsing %s: %v", tomlPath, err)
			}
		}

		date, err := time.Parse("2006-01-02", meta.Date)
		if err != nil {
			date = time.Now()
		}

		photos = append(photos, Photo{
			Slug:    slug,
			File:    "images/" + name,
			Thumb:   "thumbs/" + slug + ".jpg",
			Medium:  "medium/" + slug + ".jpg",
			Caption: meta.Caption,
			Date:    date,
		})
	}

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

// processImage copies the original to public/images/ and writes a square
// thumbnail to public/thumbs/ plus an aspect-preserved medium image to
// public/medium/. Outputs are skipped when already newer than the source.
func (g *Generator) processImage(p *Photo) error {
	src := filepath.Join(g.contentDir, filepath.Base(p.File))
	dstImg := filepath.Join(g.outputDir, p.File)
	dstThumb := filepath.Join(g.outputDir, p.Thumb)
	dstMedium := filepath.Join(g.outputDir, p.Medium)

	if !upToDate(src, dstImg) {
		if err := copyFile(src, dstImg); err != nil {
			return err
		}
	}
	if !upToDate(src, dstThumb) {
		if err := generateThumb(src, dstThumb, thumbSize); err != nil {
			return err
		}
	}
	if !upToDate(src, dstMedium) {
		if err := generateMedium(src, dstMedium, mediumMaxSize); err != nil {
			return err
		}
	}
	return nil
}

// upToDate reports whether dst exists and is at least as new as src.
func upToDate(src, dst string) bool {
	si, err := os.Stat(src)
	if err != nil {
		return false
	}
	di, err := os.Stat(dst)
	if err != nil {
		return false
	}
	return !di.ModTime().Before(si.ModTime())
}

// generateThumb reads src, centre-crops it to a square, scales it to size×size,
// and writes a JPEG to dst.
func generateThumb(src, dst string, size int) error {
	f, err := os.Open(src)
	if err != nil {
		return err
	}
	defer f.Close()

	img, _, err := image.Decode(f)
	if err != nil {
		return err
	}

	// Centre crop to square.
	b := img.Bounds()
	w, h := b.Dx(), b.Dy()
	crop := w
	if h < w {
		crop = h
	}
	x0 := (w - crop) / 2
	y0 := (h - crop) / 2
	cropped := image.NewRGBA(image.Rect(0, 0, crop, crop))
	imagedraw.Draw(cropped, cropped.Bounds(), img, image.Point{x0, y0}, imagedraw.Src)

	// Scale to thumbSize×thumbSize using Catmull-Rom for quality.
	thumb := image.NewRGBA(image.Rect(0, 0, size, size))
	xdraw.CatmullRom.Scale(thumb, thumb.Bounds(), cropped, cropped.Bounds(), xdraw.Over, nil)

	out, err := os.Create(dst)
	if err != nil {
		return err
	}
	defer out.Close()
	return jpeg.Encode(out, thumb, &jpeg.Options{Quality: 85})
}

// generateMedium reads src, resizes it so its longest side is at most maxDim
// while preserving aspect ratio, and writes a JPEG to dst.
func generateMedium(src, dst string, maxDim int) error {
	f, err := os.Open(src)
	if err != nil {
		return err
	}
	defer f.Close()

	img, _, err := image.Decode(f)
	if err != nil {
		return err
	}

	b := img.Bounds()
	w, h := b.Dx(), b.Dy()
	nw, nh := w, h
	if w > maxDim || h > maxDim {
		if w >= h {
			nw = maxDim
			nh = h * maxDim / w
		} else {
			nh = maxDim
			nw = w * maxDim / h
		}
	}

	resized := image.NewRGBA(image.Rect(0, 0, nw, nh))
	xdraw.CatmullRom.Scale(resized, resized.Bounds(), img, b, xdraw.Over, nil)

	out, err := os.Create(dst)
	if err != nil {
		return err
	}
	defer out.Close()
	return jpeg.Encode(out, resized, &jpeg.Options{Quality: 88})
}

// renderGridPages writes the paginated square-grid view under public/grid/:
// grid/index.html and grid/page/N/index.html, chunking photos into pageSize
// slices for progressive pagination. The grid is the secondary view; the
// timeline is the site root.
func (g *Generator) renderGridPages(photos []Photo) error {
	total := len(photos)
	totalPages := (total + g.pageSize - 1) / g.pageSize
	if totalPages == 0 {
		totalPages = 1
	}
	gridDir := filepath.Join(g.outputDir, "grid")

	for i := 0; i < totalPages; i++ {
		start := i * g.pageSize
		end := start + g.pageSize
		if end > total {
			end = total
		}
		slice := photos[start:end]

		dst := filepath.Join(gridDir, "index.html")
		if i > 0 {
			dir := filepath.Join(gridDir, "page", strconv.Itoa(i+1))
			if err := os.MkdirAll(dir, 0755); err != nil {
				return err
			}
			dst = filepath.Join(dir, "index.html")
		}

		prev := ""
		next := ""
		switch i {
		case 0:
			// no prev
		case 1:
			prev = "/grid/"
		default:
			prev = "/grid/page/" + strconv.Itoa(i) + "/"
		}
		if i+1 < totalPages {
			next = "/grid/page/" + strconv.Itoa(i+2) + "/"
		}

		data := map[string]any{
			"Photos":      slice,
			"Total":       total,
			"Page":        i + 1,
			"TotalPages":  totalPages,
			"PrevURL":     prev,
			"NextURL":     next,
			"BaseURL":     g.baseURL,
			"Year":        time.Now().Year(),
			"Author":      g.author,
			"Handle":      g.handle,
			"Bio":         g.bio,
			"BioAlt":      g.bioAlt,
			"Initial":     g.initial(),
			"FontsURL":    g.fontsURL,
			"SerifFamily": g.serifFamily,
			"MlFamily":    g.mlFamily,
		}
		if err := g.render("grid.html", dst, data); err != nil {
			return err
		}
	}
	return nil
}

// renderPhotoPage writes public/photo/<slug>/index.html.
func (g *Generator) renderPhotoPage(p Photo, newer, older *Photo) error {
	dir := filepath.Join(g.outputDir, "photo", p.Slug)
	if err := os.MkdirAll(dir, 0755); err != nil {
		return err
	}
	return g.render("photo.html", filepath.Join(dir, "index.html"), map[string]any{
		"Photo":       p,
		"Newer":       newer,
		"Older":       older,
		"BaseURL":     g.baseURL,
		"Year":        time.Now().Year(),
		"Author":      g.author,
		"Handle":      g.handle,
		"Initial":     g.initial(),
		"FontsURL":    g.fontsURL,
		"SerifFamily": g.serifFamily,
		"MlFamily":    g.mlFamily,
	})
}

// groupByDay collapses photos (already sorted newest first) into per-day runs,
// preserving order. Two photos land in the same group iff their dates share a
// calendar day.
func groupByDay(photos []Photo) []DayGroup {
	var groups []DayGroup
	for _, p := range photos {
		day := p.Date.Format("2006-01-02")
		if n := len(groups); n > 0 && groups[n-1].day == day {
			groups[n-1].Photos = append(groups[n-1].Photos, p)
			groups[n-1].Count++
			continue
		}
		groups = append(groups, DayGroup{
			day:    day,
			Label:  day, // ISO 2006-01-02
			Count:  1,
			Photos: []Photo{p},
		})
	}
	return groups
}

// chunkDayGroups packs day groups into pages, filling each page until it holds
// at least target photos, then starting a new one. A single day is never split
// across a page boundary, so page sizes vary slightly around target. Always
// returns at least one page (empty when there are no photos) so the site root
// renders.
func chunkDayGroups(groups []DayGroup, target int) [][]DayGroup {
	var pages [][]DayGroup
	var cur []DayGroup
	count := 0
	for _, grp := range groups {
		cur = append(cur, grp)
		count += grp.Count
		if count >= target {
			pages = append(pages, cur)
			cur, count = nil, 0
		}
	}
	if len(cur) > 0 {
		pages = append(pages, cur)
	}
	if len(pages) == 0 {
		pages = [][]DayGroup{nil}
	}
	return pages
}

// renderTimelinePages writes the day-grouped timeline as the site root:
// index.html and page/N/index.html. Photos are grouped by day, then packed
// into pages of roughly pageSize without splitting a day across pages.
func (g *Generator) renderTimelinePages(photos []Photo) error {
	pages := chunkDayGroups(groupByDay(photos), g.pageSize)
	totalPages := len(pages)

	for i, groups := range pages {
		dst := filepath.Join(g.outputDir, "index.html")
		if i > 0 {
			dir := filepath.Join(g.outputDir, "page", strconv.Itoa(i+1))
			if err := os.MkdirAll(dir, 0755); err != nil {
				return err
			}
			dst = filepath.Join(dir, "index.html")
		}

		prev := ""
		next := ""
		switch i {
		case 0:
			// no prev
		case 1:
			prev = "/"
		default:
			prev = "/page/" + strconv.Itoa(i) + "/"
		}
		if i+1 < totalPages {
			next = "/page/" + strconv.Itoa(i+2) + "/"
		}

		data := map[string]any{
			"Groups":      groups,
			"Total":       len(photos),
			"Page":        i + 1,
			"TotalPages":  totalPages,
			"PrevURL":     prev,
			"NextURL":     next,
			"BaseURL":     g.baseURL,
			"Year":        time.Now().Year(),
			"Author":      g.author,
			"Handle":      g.handle,
			"Bio":         g.bio,
			"BioAlt":      g.bioAlt,
			"Initial":     g.initial(),
			"FontsURL":    g.fontsURL,
			"SerifFamily": g.serifFamily,
			"MlFamily":    g.mlFamily,
		}
		if err := g.render("timeline.html", dst, data); err != nil {
			return err
		}
	}
	return nil
}

func (g *Generator) render(tmpl, dst string, data any) error {
	f, err := os.Create(dst)
	if err != nil {
		return err
	}
	defer f.Close()
	return g.tmpl.ExecuteTemplate(f, tmpl, data)
}

// Atom feed ---------------------------------------------------------------

type atomFeed struct {
	XMLName xml.Name    `xml:"feed"`
	Xmlns   string      `xml:"xmlns,attr"`
	Title   string      `xml:"title"`
	Link    atomLink    `xml:"link"`
	Updated string      `xml:"updated"`
	ID      string      `xml:"id"`
	Entries []atomEntry `xml:"entry"`
}

type atomLink struct {
	Href string `xml:"href,attr"`
	Rel  string `xml:"rel,attr,omitempty"`
}

type atomEntry struct {
	Title   string   `xml:"title"`
	Link    atomLink `xml:"link"`
	ID      string   `xml:"id"`
	Updated string   `xml:"updated"`
	Summary string   `xml:"summary"`
}

func (g *Generator) renderFeed(photos []Photo) error {
	feed := atomFeed{
		Xmlns: "http://www.w3.org/2005/Atom",
		Title: "Photo Gallery",
		Link:  atomLink{Href: g.baseURL + "/feed.xml", Rel: "self"},
		ID:    g.baseURL + "/",
	}
	if len(photos) > 0 {
		feed.Updated = photos[0].Date.Format(time.RFC3339)
	}
	for _, p := range photos {
		url := g.baseURL + "/photo/" + p.Slug + "/"
		feed.Entries = append(feed.Entries, atomEntry{
			Title:   p.Caption,
			Link:    atomLink{Href: url},
			ID:      url,
			Updated: p.Date.Format(time.RFC3339),
			Summary: p.Caption,
		})
	}

	f, err := os.Create(filepath.Join(g.outputDir, "feed.xml"))
	if err != nil {
		return err
	}
	defer f.Close()

	f.WriteString(xml.Header)
	enc := xml.NewEncoder(f)
	enc.Indent("", "  ")
	return enc.Encode(feed)
}

// copyStatic copies embedded static/ assets to public/static/.
func (g *Generator) copyStatic() error {
	entries, err := assets.ReadDir("static")
	if err != nil {
		return err
	}
	for _, e := range entries {
		data, err := assets.ReadFile("static/" + e.Name())
		if err != nil {
			return err
		}
		dst := filepath.Join(g.outputDir, "static", e.Name())
		if err := os.WriteFile(dst, data, 0644); err != nil {
			return err
		}
	}
	return nil
}

func copyFile(src, dst string) error {
	in, err := os.Open(src)
	if err != nil {
		return err
	}
	defer in.Close()
	out, err := os.Create(dst)
	if err != nil {
		return err
	}
	defer out.Close()
	_, err = io.Copy(out, in)
	return err
}