package bnp

import (
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strings"
)

// Presentation members: a root preview.png plus an optional screenshots/ dir.
// Neither ships behavior — the registry ingests them at publish into the
// plugin's managed gallery (spec 2026-07-05-registry-presentation-reviews).
// The .so-era source archives carried preview.png implicitly; the .bnp
// packers dropped it, which silently wiped previews on republish — these
// entries restore that and add the multi-screenshot surface.
const (
	filePreview    = "preview.png"
	dirScreenshots = "screenshots"
	// maxScreenshotBytes caps one presentation image (registry gallery cap).
	maxScreenshotBytes = 8 << 20
	// maxScreenshotFiles caps the screenshots/ dir (registry gallery cap).
	maxScreenshotFiles = 12
)

// screenshotExtOK reports whether a filename carries an accepted gallery
// image extension.
func screenshotExtOK(name string) bool {
	switch strings.ToLower(filepath.Ext(name)) {
	case ".png", ".jpg", ".jpeg", ".webp":
		return true
	}
	return false
}

// validateScreenshotsDir checks the optional screenshots/ dir: accepted
// extensions only, ≤ maxScreenshotBytes per file, ≤ maxScreenshotFiles total,
// no subdirectories or irregular files. Returns the file count (0 when the
// dir is absent).
func validateScreenshotsDir(dir string) (int, error) {
	root := filepath.Join(dir, dirScreenshots)
	info, err := os.Stat(root)
	if os.IsNotExist(err) {
		return 0, nil
	}
	if err != nil {
		return 0, fmt.Errorf("stat %s/: %w", dirScreenshots, err)
	}
	if !info.IsDir() {
		return 0, fmt.Errorf("%s exists but is not a directory", dirScreenshots)
	}
	entries, err := os.ReadDir(root)
	if err != nil {
		return 0, fmt.Errorf("read %s/: %w", dirScreenshots, err)
	}
	count := 0
	for _, e := range entries {
		if e.IsDir() {
			return 0, fmt.Errorf("%s/%s: subdirectories are not allowed in screenshots/", dirScreenshots, e.Name())
		}
		fi, err := e.Info()
		if err != nil {
			return 0, fmt.Errorf("%s/%s: %w", dirScreenshots, e.Name(), err)
		}
		if !fi.Mode().IsRegular() {
			return 0, fmt.Errorf("%s/%s: not a regular file", dirScreenshots, e.Name())
		}
		if !screenshotExtOK(e.Name()) {
			return 0, fmt.Errorf("%s/%s: unsupported image type (allowed: .png .jpg .jpeg .webp)", dirScreenshots, e.Name())
		}
		if fi.Size() > maxScreenshotBytes {
			return 0, fmt.Errorf("%s/%s: %d bytes exceeds the %d MB per-image cap", dirScreenshots, e.Name(), fi.Size(), maxScreenshotBytes>>20)
		}
		count++
	}
	if count > maxScreenshotFiles {
		return 0, fmt.Errorf("%s/ holds %d images; the gallery cap is %d", dirScreenshots, count, maxScreenshotFiles)
	}
	return count, nil
}

// presentationEntries validates and returns pack entries for the optional
// root preview.png and screenshots/ dir. Both are optional; absence is not an
// error.
func presentationEntries(dir string) (entries []packEntry, previewIncluded bool, screenshotCount int, err error) {
	previewPath := filepath.Join(dir, filePreview)
	if fi, statErr := os.Stat(previewPath); statErr == nil {
		if !fi.Mode().IsRegular() {
			return nil, false, 0, fmt.Errorf("%s is not a regular file", filePreview)
		}
		if fi.Size() > maxScreenshotBytes {
			return nil, false, 0, fmt.Errorf("%s: %d bytes exceeds the %d MB per-image cap", filePreview, fi.Size(), maxScreenshotBytes>>20)
		}
		entries = append(entries, packEntry{ArtifactPath: filePreview, Source: previewPath})
		previewIncluded = true
	}

	screenshotCount, err = validateScreenshotsDir(dir)
	if err != nil {
		return nil, false, 0, err
	}
	if screenshotCount > 0 {
		root := filepath.Join(dir, dirScreenshots)
		files, readErr := os.ReadDir(root)
		if readErr != nil {
			return nil, false, 0, fmt.Errorf("read %s/: %w", dirScreenshots, readErr)
		}
		names := make([]string, 0, len(files))
		for _, f := range files {
			names = append(names, f.Name())
		}
		sort.Strings(names)
		for _, name := range names {
			entries = append(entries, packEntry{
				ArtifactPath: dirScreenshots + "/" + name,
				Source:       filepath.Join(root, name),
			})
		}
	}
	return entries, previewIncluded, screenshotCount, nil
}