package main

import (
	"encoding/json"
	"fmt"
	"net/http"
	"os"
	"path/filepath"
	"sort"
	"strings"

	"git.k6n.net/mats/go-cart-actor/pkg/order"
)

// emailTemplateInfo is the metadata returned by the list endpoint.
type emailTemplateInfo struct {
	Name     string `json:"name"`
	Embedded bool   `json:"embedded,omitempty"`
}

// emailTemplateHandler serves CRUD operations for email templates stored in the
// ORDER_EMAIL_TEMPLATES directory. Embedded templates are read-only; on-disk
// copies override them and can be edited via PUT.
type emailTemplateHandler struct {
	dir string // the on-disk templates directory, from ORDER_EMAIL_TEMPLATES env
}

func newEmailTemplateHandler(dir string) *emailTemplateHandler {
	if dir == "" {
		dir = "data/order-email-templates"
	}
	return &emailTemplateHandler{dir: dir}
}

// list returns all known email templates (embedded + on-disk) with their source.
func (h *emailTemplateHandler) list(w http.ResponseWriter, r *http.Request) {
	embedded := knownEmbeddedTemplates()
	onDisk := h.listOnDisk()

	seen := map[string]bool{}
	var infos []emailTemplateInfo

	// List on-disk first (they take precedence).
	for _, name := range onDisk {
		infos = append(infos, emailTemplateInfo{Name: name})
		seen[name] = true
	}
	// Then add embedded templates not overridden by disk.
	for _, name := range embedded {
		if !seen[name] {
			infos = append(infos, emailTemplateInfo{Name: name, Embedded: true})
			seen[name] = true
		}
	}

	if infos == nil {
		infos = []emailTemplateInfo{}
	}
	writeJSON(w, http.StatusOK, infos)
}

// get returns the template content for the given name.
func (h *emailTemplateHandler) get(w http.ResponseWriter, r *http.Request) {
	name := r.PathValue("name")
	if name == "" {
		writeErr(w, http.StatusBadRequest, fmt.Errorf("template name is required"))
		return
	}
	store, err := order.LoadEmailTemplates(h.dir)
	if err != nil {
		writeErr(w, http.StatusInternalServerError, fmt.Errorf("load templates: %w", err))
		return
	}
	tmpl, err := store.Get(name)
	if err != nil {
		writeErr(w, http.StatusNotFound, fmt.Errorf("template %q not found", name))
		return
	}
	writeJSON(w, http.StatusOK, tmpl)
}

// save persists a template to the on-disk directory. Returns the saved template.
func (h *emailTemplateHandler) save(w http.ResponseWriter, r *http.Request) {
	name := r.PathValue("name")
	if name == "" || !validEmailTemplateName(name) {
		writeErr(w, http.StatusBadRequest, fmt.Errorf("invalid template name %q", name))
		return
	}
	var tmpl order.EmailTemplate
	if err := json.NewDecoder(r.Body).Decode(&tmpl); err != nil {
		writeErr(w, http.StatusBadRequest, fmt.Errorf("invalid template body: %w", err))
		return
	}
	if err := tmpl.Validate(name); err != nil {
		writeErr(w, http.StatusBadRequest, err)
		return
	}
	if err := os.MkdirAll(h.dir, 0o755); err != nil {
		writeErr(w, http.StatusInternalServerError, fmt.Errorf("create templates dir: %w", err))
		return
	}
	data, err := json.MarshalIndent(tmpl, "", "  ")
	if err != nil {
		writeErr(w, http.StatusInternalServerError, fmt.Errorf("marshal template: %w", err))
		return
	}
	path := filepath.Join(h.dir, name+".json")
	if err := os.WriteFile(path, append(data, '\n'), 0o644); err != nil {
		writeErr(w, http.StatusInternalServerError, fmt.Errorf("write template: %w", err))
		return
	}
	writeJSON(w, http.StatusOK, tmpl)
}

// delete removes an on-disk template. Embedded templates cannot be deleted.
func (h *emailTemplateHandler) delete(w http.ResponseWriter, r *http.Request) {
	name := r.PathValue("name")
	if name == "" {
		writeErr(w, http.StatusBadRequest, fmt.Errorf("template name is required"))
		return
	}
	// Check if it's embedded (read-only).
	if isEmbeddedTemplate(name) {
		writeErr(w, http.StatusForbidden, fmt.Errorf("template %q is built-in and cannot be deleted; save an override instead", name))
		return
	}
	path := filepath.Join(h.dir, name+".json")
	if err := os.Remove(path); err != nil {
		if os.IsNotExist(err) {
			writeErr(w, http.StatusNotFound, fmt.Errorf("template %q not found on disk", name))
			return
		}
		writeErr(w, http.StatusInternalServerError, fmt.Errorf("delete template: %w", err))
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

// preview renders a template with sample data and returns the result.
func (h *emailTemplateHandler) preview(w http.ResponseWriter, r *http.Request) {
	name := r.PathValue("name")
	if name == "" {
		writeErr(w, http.StatusBadRequest, fmt.Errorf("template name is required"))
		return
	}
	store, err := order.LoadEmailTemplates(h.dir)
	if err != nil {
		writeErr(w, http.StatusInternalServerError, fmt.Errorf("load templates: %w", err))
		return
	}
	tmpl, err := store.Get(name)
	if err != nil {
		writeErr(w, http.StatusNotFound, fmt.Errorf("template %q not found", name))
		return
	}

	// Build sample data for preview.
	sampleData := order.SampleTemplateData()
	subject, _ := order.RenderTextTemplate("preview-subject", tmpl.Subject, sampleData)
	textBody, _ := order.RenderTextTemplate("preview-text", tmpl.Text, sampleData)
	htmlBody, _ := order.RenderOptionalHTMLTemplate("preview-html", tmpl.HTML, sampleData)

	writeJSON(w, http.StatusOK, map[string]string{
		"subject": subject,
		"text":    textBody,
		"html":    htmlBody,
	})
}

// listOnDisk returns template names from the on-disk directory.
func (h *emailTemplateHandler) listOnDisk() []string {
	matches, err := filepath.Glob(filepath.Join(h.dir, "*.json"))
	if err != nil {
		return nil
	}
	var names []string
	for _, m := range matches {
		name := strings.TrimSuffix(filepath.Base(m), ".json")
		if validEmailTemplateName(name) {
			names = append(names, name)
		}
	}
	sort.Strings(names)
	return names
}

// knownEmbeddedTemplates returns the names of templates embedded in the binary.
// This must be kept in sync with the files in pkg/order/email_templates/.
func knownEmbeddedTemplates() []string {
	return []string{
		"fulfillment-shipped",
		"order-confirmation",
		"payment-receipt",
		"shipment-delivered",
		"return-confirmed",
		"refund-issued",
	}
}

// isEmbeddedTemplate reports whether name matches one of the embedded templates.
func isEmbeddedTemplate(name string) bool {
	for _, e := range knownEmbeddedTemplates() {
		if e == name {
			return true
		}
	}
	return false
}

// validEmailTemplateName validates a template name (alphanumeric + hyphens).
func validEmailTemplateName(s string) bool {
	if s == "" || len(s) > 64 {
		return false
	}
	for _, r := range s {
		if !(r == '-' || (r >= 'a' && r <= 'z') || (r >= '0' && r <= '9')) {
			return false
		}
	}
	return true
}