package scaffold

import (
	"bytes"
	"fmt"
	"image"
	"image/color"
	"image/jpeg"
	"os"
	"path"
	"strings"
)

// Demo writes a site root that exercises every feature the engine has, and returns what it wrote.
//
// A generator rather than stored files: nothing in this repository is content (ADR-0011), so the prose here is
// composed on the spot and is deliberately filler. It exists to be *served* — anything the engine can do that
// this cannot express is a gap in the engine.
//
// Refuses a directory that already holds content, because a demo that overwrites somebody's site is worse than
// no demo.
func Demo(siteDir string) ([]string, error) {
	root, err := os.OpenRoot(siteDir)
	if err != nil {
		return nil, fmt.Errorf("open %s: %w", siteDir, err)
	}
	defer root.Close()
	if _, err := root.Stat("content"); err == nil {
		return nil, fmt.Errorf("%s already has content; point this at an empty directory", siteDir)
	}

	written := []string{}
	for _, f := range demoFiles() {
		if err := mkdirAll(root, path.Dir(f.name)); err != nil {
			return written, err
		}
		file, err := root.OpenFile(f.name, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0o644)
		if err != nil {
			return written, fmt.Errorf("create %s: %w", f.name, err)
		}
		_, err = file.Write(f.body)
		file.Close()
		if err != nil {
			return written, fmt.Errorf("write %s: %w", f.name, err)
		}
		written = append(written, f.name)
	}
	return written, nil
}

// file is one thing the demo writes.
type file struct {
	name string
	body []byte
}

// demoFiles is the whole demo, in one list so what it covers can be read at a glance.
//
// Every feature appears at least once: two languages with a fallback, a series with ordered chapters, a gallery,
// a figure, an include, tags crossing sections, a slug with an alias keeping the old URL, an undated page, a
// draft, extras, a template override, static files, and a site declaration.
func demoFiles() []file {
	files := []file{{"site.yaml", []byte("base: http://localhost:8080\ntitle: A Khosra Demo\n")}}
	files = append(files, demoPosts()...)
	files = append(files, demoSeries()...)
	files = append(files, demoGallery()...)
	files = append(files, demoWriting()...)
	return append(files, demoSiteFurniture()...)
}

// demoPosts covers languages, the fallback chain, a rename with an alias, and a draft.
func demoPosts() []file {
	return []file{

		// A post in both languages: the Bengali variant proves chrome, dates and digits localise.
		{"content/posts/first-light/index.en.md", post("First Light", "2026-03-01", []string{"monsoon", "beginnings"},
			"The first demo post. Its Bengali twin sits beside it, so the language links in the footer go somewhere.\n\n"+
				"Quotes become \"curly\", dashes -- like this -- become dashes, and an ellipsis... arrives as one character.\n")},
		{"content/posts/first-light/index.bn.md", post("প্রথম আলো", "2026-03-01", []string{"monsoon"},
			"এই লেখাটি বাংলায়। তারিখ, সংখ্যা আর পৃষ্ঠার নাম বাংলায় দেখা যাবে।\n")},

		// English only: asking for it in Bengali falls back, and the canonical link says so.
		{"content/posts/only-english.en.md", post("Only in English", "2026-02-14", []string{"beginnings"},
			"There is no Bengali version of this one. Ask for `/bn/posts/only-english/` and the engine serves this,\n"+
				"with a canonical link naming the variant it actually gave you.\n")},

		// A slug override with an alias, so the old address keeps working.
		{"content/posts/renamed-thing/index.en.md", []byte("---\ntitle: This Was Renamed\ndate: 2026-02-01\n" +
			"slug: a-better-name\naliases: [posts/renamed-thing]\n---\n" +
			"Served at `/posts/a-better-name/`. The path this file implies redirects here instead of breaking.\n")},

		// A draft: not served at all until -dev on.
		{"content/posts/unfinished.en.md", []byte("---\ntitle: Unfinished\ndate: 2026-04-01\ndraft: true\n---\n" +
			"Invisible without `-dev on`, and so is anything beside it.\n")},
	}
}

// demoSeries covers a landing page with ordered chapters: prev/next, first/last, and an archive.
func demoSeries() []file {
	return []file{
		// A series: landing page plus ordered chapters, driving prev/next/first/last and an archive.
		{"content/comics/the-long-monsoon/_index.en.md", []byte("---\ntitle: The Long Monsoon\ndate: 2026-03-01\n" +
			"tags: [monsoon]\n---\nA series in three parts. This page lists them in reading order.\n")},
		{"content/comics/the-long-monsoon/first-rain.en.md", []byte("---\ntitle: First Rain\ndate: 2026-03-02\n" +
			"order: 10\n---\nChapter one. `order: 10` puts it first, and inserting a chapter later needs no renaming.\n")},
		{"content/comics/the-long-monsoon/the-flood/index.en.md", []byte("---\ntitle: The Flood\ndate: 2026-03-09\n" +
			"order: 20\n---\nChapter two, a directory bundle so it can own a picture.\n\n" +
			"{{< figure src=\"water.jpg\" alt=\"A wall of grey water\" caption=\"Day three\" >}}\n")},
		{"content/comics/the-long-monsoon/the-flood/water.jpg", photo(1800, 90, 110, 160)},
		{"content/comics/the-long-monsoon/aftermath.en.md", []byte("---\ntitle: Aftermath\ndate: 2026-03-16\n" +
			"order: 30\ntags: [monsoon]\n---\nChapter three. The gaps between 10, 20 and 30 leave room to insert.\n")},
	}
}

// demoGallery covers pictures beside a bundle: enumeration, resampling and a srcset.
func demoGallery() []file {
	return []file{
		// A gallery: every picture beside the bundle, sized and offered as a srcset.
		{"content/art/monsoon-studies/index.en.md", []byte("---\ntitle: Monsoon Studies\ndate: 2026-03-20\n" +
			"tags: [monsoon]\n---\nThree studies. The gallery below is every picture in this directory.\n\n" +
			"{{< gallery >}}\n")},
		{"content/art/monsoon-studies/10-grey.jpg", photo(1600, 120, 130, 150)},
		{"content/art/monsoon-studies/20-green.jpg", photo(1600, 80, 150, 90)},
		{"content/art/monsoon-studies/30-blue.jpg", photo(1600, 70, 110, 190)},
	}
}

// demoWriting covers an include and extras: a fragment with no URL, and supporting files that do have one.
func demoWriting() []file {
	return []file{
		// An include, and extras: supporting files published as artefacts of the process.
		{"content/writing/notes-on-water/index.en.md", []byte("---\ntitle: Notes on Water\ndate: 2026-03-25\n" +
			"tags: [monsoon, beginnings]\n---\nThe finished piece, assembled from a part beside it.\n\n" +
			"{{< include file=\"_method.md\" >}}\n")},
		{"content/writing/notes-on-water/_method.md", []byte("## Method\n\nAn underscore keeps this out of the " +
			"scan, so it has no URL of its own and never appears in a listing.\n")},
		{"content/writing/notes-on-water/extras/gauge.log", []byte("day one: 2m\nday two: 3m\nday three: 3m again\n")},
		{"content/writing/notes-on-water/extras/research.md", []byte("## Research\n\nRendered as Markdown inside " +
			"the extras listing, *emphasis and all*.\n")},
		{"content/writing/notes-on-water/extras/scan.jpg", photo(900, 160, 140, 100)},
	}
}

// demoSiteFurniture covers what surrounds the content: an undated page, a template override, static files.
func demoSiteFurniture() []file {
	return []file{
		// An undated page: reachable, and correctly absent from every feed.
		{"content/pages/about.en.md", []byte("---\ntitle: About This Demo\n---\n" +
			"No date, so this page is not a feed item — which is how the engine decides what belongs in a feed.\n\n" +
			"Everything here was generated by `khosra demo`. Edit any file while the server runs and the change\n" +
			"appears within a couple of seconds.\n")},

		// A template override: the same block the embedded theme defines, replaced.
		{"templates/list.html", []byte(`{{define "main" -}}` + "\n" +
			`<h1>{{.Title}}</h1>` + "\n" +
			`<p><em>This listing comes from the site's own template, not the embedded one.</em></p>` + "\n" +
			`{{- range .Items}}` + "\n" +
			`<article class="entry"><h2><a href="{{.URL}}">{{if .Title}}{{.Title}}{{else}}{{.Key}}{{end}}</a></h2>` + "\n" +
			`{{- if not .Date.IsZero}}<p><time datetime="{{.Date.Format "2006-01-02"}}">{{day $.Lang .Date}}</time></p>{{end}}` + "\n" +
			`</article>` + "\n" +
			`{{- end}}` + "\n" +
			`{{- if or .PrevURL .NextURL}}` + "\n" +
			`<nav class="pagination">` + "\n" +
			`{{- if .PrevURL}}<a rel="prev" href="{{.PrevURL}}">{{t .Lang "newer"}}</a>{{end}}` + "\n" +
			`<span>{{t .Lang "page-of" (num .Lang .Page) (num .Lang .Pages)}}</span>` + "\n" +
			`{{- if .NextURL}}<a rel="next" href="{{.NextURL}}">{{t .Lang "older"}}</a>{{end}}` + "\n" +
			`</nav>{{end}}` + "\n" +
			`{{- end}}` + "\n")},

		{"static/robots-note.txt", []byte("Anything under static/ is served verbatim at /static/.\n")},
	}
}

// post builds a bundle with the fields most posts carry.
func post(title, date string, tags []string, body string) []byte {
	var out bytes.Buffer
	fmt.Fprintf(&out, "---\ntitle: %s\ndate: %s\n", title, date)
	if len(tags) > 0 {
		fmt.Fprintf(&out, "tags: [%s]\n", strings.Join(tags, ", "))
	}
	fmt.Fprintf(&out, "---\n%s", body)
	return out.Bytes()
}

// photo is a real JPEG wide enough to earn derivatives, so the demo exercises resampling rather than describing
// it. A gradient, because a placeholder should look like a placeholder.
func photo(width int, r, g, b uint8) []byte {
	img := image.NewRGBA(image.Rect(0, 0, width, width*2/3))
	for x := range width {
		for y := range width * 2 / 3 {
			shade := uint8((x + y) / 12 % 90)
			img.Set(x, y, color.RGBA{r + shade, g + shade, b - shade/2, 255})
		}
	}
	var out bytes.Buffer
	if err := jpeg.Encode(&out, img, &jpeg.Options{Quality: 80}); err != nil {
		return nil
	}
	return out.Bytes()
}