package cabana

import (
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"io/fs"
	"path"
	"regexp"
	"strings"

	"git.golem15.com/golem15/summercms/modules/boardwalk"
	"git.golem15.com/golem15/summercms/modules/pact"
)

// widgetTagPattern is a valid custom-element name restricted to lowercase
// ASCII: a letter, then at least one hyphenated segment.
var widgetTagPattern = regexp.MustCompile(`^[a-z][a-z0-9]*(-[a-z0-9]+)+$`)

// reservedWidgetTags are the hyphenated names the HTML specification reserves;
// customElements.define refuses them.
var reservedWidgetTags = map[string]bool{
	"annotation-xml": true, "color-profile": true, "font-face": true, "font-face-src": true,
	"font-face-uri": true, "font-face-format": true, "font-face-name": true, "missing-glyph": true,
}

// assetSegment is one segment of the plugin ID in an asset URL.
var assetSegment = regexp.MustCompile(`^[A-Za-z0-9_-]+$`)

// pluginAsset is one declared controller JS or CSS file, read from the
// plugin's embedded tree and hashed at boot. The asset route serves only
// these exact keys (D-13, D-15, D-16).
type pluginAsset struct {
	// key is vendor/plugin/<path after assets/>, the URL tail under
	// {prefix}/assets/.
	key         string
	body        []byte
	contentType string
	// etag is the quoted hex sha256 of body; version is its first 12 hex
	// characters, used as the ?v= cache buster.
	etag    string
	version string
}

// builtinToolbarActions are the toolbar actions the framework implements
// itself (D-14); a controller may not register an action with these names.
var builtinToolbarActions = map[string]bool{"create": true, "delete": true}

// widgetTagPrefix is the custom-element prefix a plugin's widgets must use:
// the plugin ID lowercased with dots and underscores turned into hyphens,
// plus a trailing hyphen (acme.conform -> "acme-conform-"). It keeps two
// plugins from defining the same element.
func widgetTagPrefix(pluginID string) string {
	return strings.NewReplacer(".", "-", "_", "-").Replace(strings.ToLower(pluginID)) + "-"
}

// compileExtension validates a controller's runtime admin extension points
// after its list and form are compiled and its writable fields are bound: the
// registered actions and every `type: widget` field. Every failure stops boot.
func compileExtension(pluginID string, cc *CompiledController, fsys fs.FS) error {
	if cc == nil || cc.Controller == nil {
		return nil
	}
	id := cc.Controller.ID()
	actions, err := compileActions(cc.Controller)
	if err != nil {
		return fmt.Errorf("cabana: admin controller %s/%s: %w", pluginID, id, err)
	}
	cc.Actions = actions
	if err := compileClientAssets(pluginID, cc, fsys); err != nil {
		return err
	}
	if err := compilePartials(pluginID, cc, fsys); err != nil {
		return err
	}
	if cc.Form == nil {
		return nil
	}
	file := cc.Form.fieldsPath
	if file == "" {
		file = "fields.yaml"
	}
	fields := map[string]FormField{}
	for _, field := range cc.Form.Fields {
		fields[field.Name] = field
	}
	writable := map[string]bool{}
	for _, field := range cc.Writable {
		writable[field.Name] = true
	}
	prefix := widgetTagPrefix(pluginID)
	for i := range cc.Form.Fields {
		field := &cc.Form.Fields[i]
		if field.Type != "widget" {
			continue
		}
		if err := checkWidgetTag(field.Widget, prefix); err != nil {
			return bootErr(pluginID, id, file, fmt.Errorf("field %s: %w", field.Name, err))
		}
		action, ok := actions[field.Action]
		if !ok {
			return bootErr(pluginID, id, file, fmt.Errorf("field %s: action %s is not registered by the controller (pact.HasAdminActions)", field.Name, field.Action))
		}
		for _, key := range field.Fill {
			target, exists := fields[key]
			if !exists {
				return bootErr(pluginID, id, file, fmt.Errorf("field %s: fill %s is not a field of this form", field.Name, key))
			}
			if !scalarFormField(target.Type) || !writable[key] {
				return bootErr(pluginID, id, file, fmt.Errorf("field %s: fill %s is not a writable scalar field", field.Name, key))
			}
		}
		field.ActionLabel = action.Label
		if len(cc.scripts) == 0 {
			return bootErr(pluginID, id, file, fmt.Errorf("field %s: a widget needs the controller to declare its JS through pact.AdminClientAssets", field.Name))
		}
	}
	return nil
}

// compilePartials reads and parses every partial the controller declares:
// config_list.yaml headerPartial and each `type: partial` field's path, both
// resolving to {ConfigDir}/_{name}.htm. A missing or unparsable template, or a
// controller without pact.AdminPartialData, fails boot (D-11).
func compilePartials(pluginID string, cc *CompiledController, fsys fs.FS) error {
	id := cc.Controller.ID()
	var names []string
	formNames := map[string]bool{}
	if cc.List != nil && cc.List.HeaderPartial != "" {
		names = append(names, cc.List.HeaderPartial)
	}
	if cc.Form != nil {
		for _, field := range cc.Form.Fields {
			if field.Type == "partial" {
				names = append(names, field.Path)
				formNames[field.Path] = true
			}
		}
	}
	if len(names) == 0 {
		return nil
	}
	dir := strings.Trim(path.Clean(cc.Controller.ConfigDir()), "/")
	if dir == "." || strings.HasPrefix(dir, "..") {
		return bootErr(pluginID, id, cc.Controller.ConfigDir(), fmt.Errorf("config directory escapes the plugin"))
	}
	partials := map[string]*compiledPartial{}
	for _, name := range names {
		if _, done := partials[name]; done {
			continue
		}
		file := path.Join(dir, "_"+name+".htm")
		if provider, ok := cc.Controller.(pact.AdminPartialData); !ok || provider == nil {
			return bootErr(pluginID, id, file, fmt.Errorf("partial %s needs the controller to implement pact.AdminPartialData", name))
		}
		src, err := readAsset(fsys, file)
		if err != nil {
			return bootErr(pluginID, id, file, fmt.Errorf("partial %s: template is not in the plugin's embedded files: %w", name, err))
		}
		compiled, err := parsePartial(name, src)
		if err != nil {
			return bootErr(pluginID, id, file, fmt.Errorf("partial %s: %w", name, err))
		}
		partials[name] = compiled
	}
	cc.partials, cc.formPartials = partials, formNames
	return nil
}

// compileClientAssets reads and hashes the files a controller declares
// through pact.AdminClientAssets. Each path must be clean, live under
// assets/, carry a JS (.js, .mjs) or CSS (.css) extension and exist in the
// plugin's embedded tree; there is no disk override.
func compileClientAssets(pluginID string, cc *CompiledController, fsys fs.FS) error {
	src, ok := cc.Controller.(pact.AdminClientAssets)
	if !ok || src == nil {
		return nil
	}
	id := cc.Controller.ID()
	vendor, plugin, found := strings.Cut(pluginID, ".")
	if !found || !assetSegment.MatchString(vendor) || !assetSegment.MatchString(plugin) {
		return fmt.Errorf("cabana: admin controller %s/%s: plugin ID must be vendor.plugin to serve admin assets", pluginID, id)
	}
	read := func(files []string, exts ...string) ([]*pluginAsset, error) {
		out := make([]*pluginAsset, 0, len(files))
		seen := map[string]bool{}
		for _, name := range files {
			if err := checkAssetPath(name, exts); err != nil {
				return nil, bootErr(pluginID, id, name, err)
			}
			if seen[name] {
				return nil, bootErr(pluginID, id, name, fmt.Errorf("asset declared twice"))
			}
			seen[name] = true
			body, err := fs.ReadFile(fsys, name)
			if err != nil {
				return nil, bootErr(pluginID, id, name, fmt.Errorf("asset is not in the plugin's embedded files: %w", err))
			}
			sum := sha256.Sum256(body)
			digest := hex.EncodeToString(sum[:])
			out = append(out, &pluginAsset{
				key:         vendor + "/" + plugin + "/" + strings.TrimPrefix(name, "assets/"),
				body:        body,
				contentType: boardwalk.ContentType(name),
				etag:        `"` + digest + `"`,
				version:     digest[:12],
			})
		}
		return out, nil
	}
	scripts, err := read(src.AdminJS(), ".js", ".mjs")
	if err != nil {
		return err
	}
	styles, err := read(src.AdminCSS(), ".css")
	if err != nil {
		return err
	}
	cc.scripts, cc.styles = scripts, styles
	return nil
}

func checkAssetPath(name string, exts []string) error {
	if name != path.Clean(name) || !strings.HasPrefix(name, "assets/") || len(name) == len("assets/") {
		return fmt.Errorf("asset path must be a clean path under assets/")
	}
	for _, segment := range strings.Split(name, "/") {
		if segment == ".." || segment == "" {
			return fmt.Errorf("asset path must be a clean path under assets/")
		}
	}
	ext := strings.ToLower(path.Ext(name))
	for _, want := range exts {
		if ext == want {
			return nil
		}
	}
	return fmt.Errorf("asset must end in %s", strings.Join(exts, " or "))
}

func checkWidgetTag(tag, prefix string) error {
	if !widgetTagPattern.MatchString(tag) {
		return fmt.Errorf("widget %q is not a valid custom-element name (lowercase, with a hyphen)", tag)
	}
	if reservedWidgetTags[tag] {
		return fmt.Errorf("widget %q is a reserved element name", tag)
	}
	if !strings.HasPrefix(tag, prefix) {
		return fmt.Errorf("widget %q must start with the plugin prefix %q", tag, prefix)
	}
	return nil
}

// compileActions collects a controller's registered actions into the single
// action namespace (assumption-delta decision: create and delete are reserved).
func compileActions(ctl pact.AdminController) (map[string]pact.AdminAction, error) {
	out := map[string]pact.AdminAction{}
	src, ok := ctl.(pact.HasAdminActions)
	if !ok || src == nil {
		return out, nil
	}
	for _, action := range src.AdminActions() {
		if !identifier(action.Name) {
			return nil, fmt.Errorf("action name %q is not an identifier", action.Name)
		}
		if builtinToolbarActions[action.Name] {
			return nil, fmt.Errorf("action %s uses a reserved built-in name (create, delete)", action.Name)
		}
		if _, dup := out[action.Name]; dup {
			return nil, fmt.Errorf("duplicate action %s", action.Name)
		}
		if action.Run == nil {
			return nil, fmt.Errorf("action %s has no Run function", action.Name)
		}
		out[action.Name] = action
	}
	return out, nil
}