package appview

import (
	"crypto/md5"
	"embed"
	"encoding/json"
	"fmt"
	"html/template"
	"io/fs"
	"net/http"
	"net/url"
	"strings"
	"time"

	"atcr.io/pkg/appview/licenses"
)

// BrandingOverrides allows consumers to customize the AppView's public assets,
// templates, CSS, and template functions. Pass nil for default atcr.io behavior.
type BrandingOverrides struct {
	// PublicFS overlays public/ assets (favicons, CSS, images, etc.).
	// Files in this FS take priority over the embedded defaults.
	PublicFS fs.FS

	// TemplatesFS overlays templates/ (nav-brand.html, hero.html, etc.).
	// Go's template.ParseFS replaces {{ define "name" }} blocks when
	// called twice with the same name, so consumer templates naturally
	// override defaults.
	TemplatesFS fs.FS

	// ExtraCSS is injected as a <style> block after the main stylesheet.
	// Useful for DaisyUI color variable overrides without build tooling.
	ExtraCSS string

	// ExtraFuncMap is merged into the template FuncMap.
	ExtraFuncMap template.FuncMap
}

// assetHashes stores MD5 hashes of embedded assets for cache busting
var assetHashes = make(map[string]string)

func init() {
	// Compute MD5 hash of embedded default assets at startup.
	// Consumers should call ComputeAssetHashes(overrides) to recompute
	// with their overlay FS before serving requests.
	computeAssetHashesFromFS(publicFS)
}

func computeAssetHashesFromFS(fsys fs.FS) {
	files := []string{"css/style.css", "js/bundle.min.js"}
	for _, f := range files {
		var data []byte
		var err error

		if rfs, ok := fsys.(fs.ReadFileFS); ok {
			data, err = rfs.ReadFile("public/" + f)
		} else {
			fh, openErr := fsys.Open("public/" + f)
			if openErr != nil {
				continue
			}
			defer fh.Close()
			stat, statErr := fh.Stat()
			if statErr != nil {
				continue
			}
			data = make([]byte, stat.Size())
			_, err = fh.(interface{ Read([]byte) (int, error) }).Read(data)
		}

		if err != nil {
			continue
		}
		assetHashes[f] = fmt.Sprintf("%x", md5.Sum(data))[:8]
	}
}

// ComputeAssetHashes recomputes cache-busting hashes using the overlay FS.
// Call this before serving requests if using BrandingOverrides.
func ComputeAssetHashes(overrides *BrandingOverrides) {
	fsys := resolvePublicFS(overrides)
	computeAssetHashesFromFS(fsys)
}

// AssetHash returns the cache-busting hash for an asset path
func AssetHash(path string) string {
	if hash, ok := assetHashes[path]; ok {
		return hash
	}
	return ""
}

// CacheMiddleware adds Cache-Control headers to static file responses
func CacheMiddleware(h http.Handler, maxAge int) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Cache-Control", fmt.Sprintf("public, max-age=%d", maxAge))
		h.ServeHTTP(w, r)
	})
}

//go:generate sh -c "command -v npm >/dev/null 2>&1 && cd ../.. && npm run build:appview || echo 'npm not found, skipping build'"

//go:embed templates/**/*.html
var templatesFS embed.FS

//go:embed public
var publicFS embed.FS

// resolvePublicFS returns an fs.FS that layers overrides on top of the embedded default.
func resolvePublicFS(overrides *BrandingOverrides) fs.FS {
	if overrides == nil || overrides.PublicFS == nil {
		return publicFS
	}
	return newOverlayFS(overrides.PublicFS, publicFS)
}

// resolveTemplatesFS returns an fs.FS that layers overrides on top of the embedded default.
func resolveTemplatesFS(overrides *BrandingOverrides) fs.FS {
	if overrides == nil || overrides.TemplatesFS == nil {
		return templatesFS
	}
	return newOverlayFS(overrides.TemplatesFS, templatesFS)
}

// Templates returns parsed templates with helper functions.
// Pass nil for default atcr.io behavior.
func Templates(overrides *BrandingOverrides) (*template.Template, error) {
	extraCSS := ""
	if overrides != nil {
		extraCSS = overrides.ExtraCSS
	}

	funcMap := template.FuncMap{
		"timeAgo": func(t time.Time) string {
			duration := time.Since(t)

			if duration < time.Minute {
				return "just now"
			} else if duration < time.Hour {
				mins := int(duration.Minutes())
				if mins == 1 {
					return "1 minute ago"
				}
				return fmt.Sprintf("%d minutes ago", mins)
			} else if duration < 24*time.Hour {
				hours := int(duration.Hours())
				if hours == 1 {
					return "1 hour ago"
				}
				return fmt.Sprintf("%d hours ago", hours)
			} else {
				days := int(duration.Hours() / 24)
				if days == 1 {
					return "1 day ago"
				}
				return fmt.Sprintf("%d days ago", days)
			}
		},

		"timeAgoShort": func(t time.Time) string {
			duration := time.Since(t)

			if duration < time.Minute {
				return "now"
			} else if duration < time.Hour {
				return fmt.Sprintf("%dm", int(duration.Minutes()))
			} else if duration < 24*time.Hour {
				return fmt.Sprintf("%dh", int(duration.Hours()))
			} else if duration < 365*24*time.Hour {
				return fmt.Sprintf("%dd", int(duration.Hours()/24))
			} else {
				return fmt.Sprintf("%dy", int(duration.Hours()/(24*365)))
			}
		},

		"humanizeBytes": func(bytes int64) string {
			const unit = 1024
			if bytes < unit {
				return fmt.Sprintf("%d B", bytes)
			}
			div, exp := int64(unit), 0
			for n := bytes / unit; n >= unit; n /= unit {
				div *= unit
				exp++
			}
			return fmt.Sprintf("%.1f %cB", float64(bytes)/float64(div), "KMGTPE"[exp])
		},

		"truncateDigest": func(digest string, length int) string {
			if len(digest) <= length {
				return digest
			}
			return digest[:length] + "..."
		},

		"firstChar": func(s string) string {
			if len(s) == 0 {
				return "?"
			}
			return string([]rune(s)[0])
		},

		"trimPrefix": func(prefix, s string) string {
			if len(s) >= len(prefix) && s[:len(prefix)] == prefix {
				return s[len(prefix):]
			}
			return s
		},

		"displayHoldDID": func(holdDID string) string {
			// did:web:hold01.atcr.io → hold01.atcr.io
			if strings.HasPrefix(holdDID, "did:web:") {
				return strings.TrimPrefix(holdDID, "did:web:")
			}
			// did:plc:opaque... → did:plc:opaque...xxxx (truncated)
			if len(holdDID) > 20 {
				return holdDID[:20] + "…"
			}
			return holdDID
		},

		"sanitizeID": func(s string) string {
			// Replace special CSS selector characters with dashes
			// e.g., "sha256:abc123" becomes "sha256-abc123"
			// e.g., "v0.0.2" becomes "v0-0-2"
			// e.g., "did:web:172.28.0.3%3A8080" becomes "did-web-172-28-0-3-3A8080"
			s = strings.ReplaceAll(s, ":", "-")
			s = strings.ReplaceAll(s, ".", "-")
			s = strings.ReplaceAll(s, "%", "-")
			return s
		},

		"parseLicenses": func(licensesStr string) []licenses.LicenseInfo {
			return licenses.ParseLicenses(licensesStr)
		},

		"derefTime": func(t *time.Time) time.Time {
			if t == nil {
				return time.Time{}
			}
			return *t
		},

		"sub": func(a, b int) int {
			return a - b
		},

		"sub64": func(a, b int64) int64 {
			return a - b
		},

		"absInt": func(n int) int {
			if n < 0 {
				return -n
			}
			return n
		},

		"humanizeByteDelta": func(bytes int64) string {
			prefix := "+"
			if bytes < 0 {
				prefix = "-"
				bytes = -bytes
			} else if bytes == 0 {
				return "no change"
			}
			const unit = 1024
			if bytes < unit {
				return fmt.Sprintf("%s%d B", prefix, bytes)
			}
			div, exp := int64(unit), 0
			for n := bytes / unit; n >= unit; n /= unit {
				div *= unit
				exp++
			}
			return fmt.Sprintf("%s%.1f %cB", prefix, float64(bytes)/float64(div), "KMGTPE"[exp])
		},

		"dict": func(values ...any) map[string]any {
			dict := make(map[string]any, len(values)/2)
			for i := 0; i < len(values); i += 2 {
				key, _ := values[i].(string)
				dict[key] = values[i+1]
			}
			return dict
		},

		"resizeImage": func(imgURL string, width int) string {
			if imgURL == "" {
				return ""
			}
			// Only apply Cloudflare Image Resizing to imgs.blue URLs
			parsed, err := url.Parse(imgURL)
			if err != nil || parsed.Host != "imgs.blue" {
				return imgURL
			}
			// Cloudflare uses /cdn-cgi/image/width=X/ path format
			parsed.Path = fmt.Sprintf("/cdn-cgi/image/width=%d,format=auto%s", width, parsed.Path)
			return parsed.String()
		},

		"assetHash": AssetHash,

		"formatDate": func(t time.Time) string {
			return t.Format("Jan 2, 2006")
		},

		"isZeroTime": func(t time.Time) bool {
			return t.IsZero() || t.Year() < 2000
		},

		// icon renders an SVG icon from the sprite sheet
		// Usage: {{ icon "star" "size-4 text-amber-400" }}
		// The name is the icon ID in icons.svg, classes are applied to the SVG element
		"icon": func(name, classes string) template.HTML {
			return template.HTML(fmt.Sprintf(
				`<svg class="icon %s" aria-hidden="true"><use href="/icons.svg#%s"></use></svg>`,
				template.HTMLEscapeString(classes),
				template.HTMLEscapeString(name),
			))
		},

		// jsonldScript renders a complete <script type="application/ld+json"> block.
		// Returns the whole block as template.HTML to avoid html/template's JS context
		// escaping that double-encodes JSON inside <script> tags.
		// See https://github.com/golang/go/issues/20886
		// Usage: {{ jsonldScript .SomeStruct }}
		"jsonldScript": func(v any) template.HTML {
			var jsonBytes []byte
			if s, ok := v.(string); ok {
				jsonBytes = []byte(s)
			} else {
				var err error
				jsonBytes, err = json.MarshalIndent(v, "    ", "    ")
				if err != nil {
					jsonBytes = []byte("{}")
				}
			}
			return template.HTML("<script type=\"application/ld+json\">\n    " + string(jsonBytes) + "\n    </script>")
		},

		// ociClientName returns the OCI client name, defaulting to "docker" if empty.
		// Usage: {{ ociClientName .OciClient }}
		"ociClientName": func(client string) string {
			if client == "" {
				return "docker"
			}
			return client
		},

		// pullPrefix returns the "<client> pull " prefix for a pull command, or an
		// empty string when the user has selected "none" (image reference only).
		// Usage: {{ pullPrefix .OciClient }}
		"pullPrefix": func(client string) string {
			if client == "none" {
				return ""
			}
			if client == "" {
				return "docker pull "
			}
			return client + " pull "
		},

		// extraCSS returns a <style> block with consumer CSS overrides, or empty string.
		"extraCSS": func() template.HTML {
			if extraCSS == "" {
				return ""
			}
			return template.HTML("<style>" + extraCSS + "</style>")
		},
	}

	// Merge extra func map from overrides
	if overrides != nil && overrides.ExtraFuncMap != nil {
		for k, v := range overrides.ExtraFuncMap {
			funcMap[k] = v
		}
	}

	tmpl := template.New("").Funcs(funcMap)

	// Parse default templates
	tfs := resolveTemplatesFS(overrides)
	tmpl, err := tmpl.ParseFS(tfs, "templates/**/*.html")
	if err != nil {
		return nil, err
	}

	return tmpl, nil
}

// PublicHandler returns HTTP handler for static files.
// Pass nil for default atcr.io behavior.
func PublicHandler(overrides *BrandingOverrides) http.Handler {
	fsys := resolvePublicFS(overrides)
	sub, err := fs.Sub(fsys, "public")
	if err != nil {
		panic(err)
	}
	return http.FileServer(http.FS(sub))
}

// PublicRootFiles returns list of root-level files in static directory (not subdirectories).
// Pass nil for default atcr.io behavior.
func PublicRootFiles(overrides *BrandingOverrides) ([]string, error) {
	fsys := resolvePublicFS(overrides)
	var entries []fs.DirEntry
	var err error

	if rdfs, ok := fsys.(fs.ReadDirFS); ok {
		entries, err = rdfs.ReadDir("public")
	} else {
		entries, err = fs.ReadDir(fsys, "public")
	}
	if err != nil {
		return nil, err
	}

	var files []string
	for _, entry := range entries {
		// Only include files, not directories
		if !entry.IsDir() {
			files = append(files, entry.Name())
		}
	}
	return files, nil
}

// PublicSubdir returns an http.Handler for a subdirectory within public/.
// Pass nil for default atcr.io behavior.
func PublicSubdir(name string, overrides *BrandingOverrides) http.Handler {
	fsys := resolvePublicFS(overrides)
	sub, err := fs.Sub(fsys, "public/"+name)
	if err != nil {
		panic(err)
	}
	return http.FileServer(http.FS(sub))
}