package codegen

import (
	"fmt"
	"maps"
	"slices"
	"strings"
	"text/template"

	log "dappco.re/go/core/log"
)

// wcTemplate is the Web Component class template.
// Uses closed Shadow DOM for isolation. Content is set via the shadow root's
// DOM API using trusted go-html codegen output (never user input).
var wcTemplate = template.Must(template.New("wc").Parse(`class {{.ClassName}} extends HTMLElement {
  #shadow;
  constructor() {
    super();
    this.#shadow = this.attachShadow({ mode: "closed" });
  }
  connectedCallback() {
    this.#shadow.textContent = "";
    const slot = this.getAttribute("data-slot") || "{{.Slot}}";
    this.dispatchEvent(new CustomEvent("wc-ready", { detail: { tag: "{{.Tag}}", slot } }));
  }
  render(html) {
    const tpl = document.createElement("template");
    tpl.insertAdjacentHTML("afterbegin", html);
    this.#shadow.textContent = "";
    this.#shadow.appendChild(tpl.content.cloneNode(true));
  }
}`))

// GenerateClass produces a JS class definition for a custom element.
func GenerateClass(tag, slot string) (string, error) {
	if !strings.Contains(tag, "-") {
		return "", log.E("codegen.GenerateClass", "custom element tag must contain a hyphen: "+tag, nil)
	}
	var b strings.Builder
	err := wcTemplate.Execute(&b, struct {
		ClassName, Tag, Slot string
	}{
		ClassName: TagToClassName(tag),
		Tag:       tag,
		Slot:      slot,
	})
	if err != nil {
		return "", log.E("codegen.GenerateClass", "template exec", err)
	}
	return b.String(), nil
}

// GenerateRegistration produces the customElements.define() call.
func GenerateRegistration(tag, className string) string {
	return fmt.Sprintf(`customElements.define("%s", %s);`, tag, className)
}

// TagToClassName converts a kebab-case tag to PascalCase class name.
func TagToClassName(tag string) string {
	var b strings.Builder
	for p := range strings.SplitSeq(tag, "-") {
		if len(p) > 0 {
			b.WriteString(strings.ToUpper(p[:1]))
			b.WriteString(p[1:])
		}
	}
	return b.String()
}

// GenerateBundle produces all WC class definitions and registrations
// for a set of HLCRF slot assignments.
func GenerateBundle(slots map[string]string) (string, error) {
	var b strings.Builder

	for _, entry := range sortedSlotEntries(slots) {
		cls, err := GenerateClass(entry.Tag, entry.Slot)
		if err != nil {
			return "", err
		}
		b.WriteString(cls)
		b.WriteByte('\n')
		b.WriteString(GenerateRegistration(entry.Tag, TagToClassName(entry.Tag)))
		b.WriteByte('\n')
	}
	return b.String(), nil
}

// GenerateTypeDefinitions produces a TypeScript declaration file for the
// generated custom elements.
func GenerateTypeDefinitions(slots map[string]string) (string, error) {
	entries := sortedSlotEntries(slots)
	var b strings.Builder

	for _, entry := range entries {
		className := TagToClassName(entry.Tag)
		b.WriteString("declare class ")
		b.WriteString(className)
		b.WriteString(" extends HTMLElement {\n")
		b.WriteString("  connectedCallback(): void;\n")
		b.WriteString("  render(html: string): void;\n")
		b.WriteString("}\n")
	}

	b.WriteString("\ndeclare global {\n")
	b.WriteString("  interface HTMLElementTagNameMap {\n")
	for _, entry := range entries {
		className := TagToClassName(entry.Tag)
		b.WriteString(`    "`)
		b.WriteString(entry.Tag)
		b.WriteString(`": `)
		b.WriteString(className)
		b.WriteString(";\n")
	}
	b.WriteString("  }\n")
	b.WriteString("}\n")
	b.WriteString("\nexport {};\n")

	return b.String(), nil
}

type slotEntry struct {
	Slot string
	Tag  string
}

func sortedSlotEntries(slots map[string]string) []slotEntry {
	keys := slices.Collect(maps.Keys(slots))
	slices.Sort(keys)

	seen := make(map[string]bool, len(keys))
	entries := make([]slotEntry, 0, len(keys))
	for _, slot := range keys {
		tag := slots[slot]
		if seen[tag] {
			continue
		}
		seen[tag] = true
		entries = append(entries, slotEntry{Slot: slot, Tag: tag})
	}
	return entries
}