// SPDX-License-Identifier: AGPL-3.0-or-later

// Package render provides HTML template rendering with layout support.
package render

import (
	"fmt"
	"html/template"
	"io"
	"io/fs"
	"log/slog"
	"net/http"
	"os"
	"path/filepath"
	"strings"

	"kode.naiv.no/olemd/favoritter/internal/config"
	"kode.naiv.no/olemd/favoritter/internal/middleware"
	"kode.naiv.no/olemd/favoritter/internal/model"
	"kode.naiv.no/olemd/favoritter/internal/store"
	"kode.naiv.no/olemd/favoritter/web"
)

// Renderer parses and executes HTML templates.
type Renderer struct {
	templates map[string]*template.Template
	cfg       *config.Config
}

// PageData holds data passed to page templates.
type PageData struct {
	Title       string
	User        *model.User
	CSRFToken   string
	BasePath    string
	SiteName    string
	Flash       string
	FlashType   string // "success", "error", "info"
	ExternalURL string
	Data        any
}

// New creates a Renderer, parsing all templates from the embedded filesystem.
func New(cfg *config.Config) (*Renderer, error) {
	r := &Renderer{
		cfg: cfg,
	}

	if err := r.parseTemplates(); err != nil {
		return nil, err
	}

	return r, nil
}

func (r *Renderer) parseTemplates() error {
	r.templates = make(map[string]*template.Template)

	var templateFS fs.FS
	if r.cfg.DevMode {
		// In dev mode, read templates from disk for live reload.
		templateFS = os.DirFS(filepath.Join("web", "templates"))
	} else {
		sub, err := fs.Sub(web.TemplatesFS, "templates")
		if err != nil {
			return fmt.Errorf("sub templates fs: %w", err)
		}
		templateFS = sub
	}

	funcMap := r.templateFuncs()

	// Parse the base layout.
	baseLayout, err := template.New("base.html").Funcs(funcMap).ParseFS(templateFS, "layouts/base.html")
	if err != nil {
		return fmt.Errorf("parse base layout: %w", err)
	}

	// Parse each page template with the base layout.
	pages, err := fs.Glob(templateFS, "pages/*.html")
	if err != nil {
		return fmt.Errorf("glob pages: %w", err)
	}

	for _, page := range pages {
		name := strings.TrimPrefix(page, "pages/")
		name = strings.TrimSuffix(name, ".html")

		t, err := baseLayout.Clone()
		if err != nil {
			return fmt.Errorf("clone base for %s: %w", name, err)
		}

		_, err = t.ParseFS(templateFS, page)
		if err != nil {
			return fmt.Errorf("parse page %s: %w", name, err)
		}

		r.templates[name] = t
	}

	// Parse partial templates (for HTMX responses).
	partials, err := fs.Glob(templateFS, "partials/*.html")
	if err != nil {
		return fmt.Errorf("glob partials: %w", err)
	}

	for _, partial := range partials {
		name := "partial:" + strings.TrimPrefix(partial, "partials/")
		name = strings.TrimSuffix(name, ".html")

		t, err := template.New(filepath.Base(partial)).Funcs(funcMap).ParseFS(templateFS, partial)
		if err != nil {
			return fmt.Errorf("parse partial %s: %w", name, err)
		}

		r.templates[name] = t
	}

	slog.Info("templates loaded", "pages", len(pages), "partials", len(partials))
	return nil
}

// Page renders a full page with the base layout.
func (r *Renderer) Page(w http.ResponseWriter, req *http.Request, name string, data PageData) {
	if r.cfg.DevMode {
		// Reparse templates on every request in dev mode.
		if err := r.parseTemplates(); err != nil {
			slog.Error("template reparse failed", "error", err)
			http.Error(w, "Template error", http.StatusInternalServerError)
			return
		}
	}

	// Populate common data from context.
	data.User = middleware.UserFromContext(req.Context())
	data.CSRFToken = middleware.CSRFTokenFromContext(req.Context())
	data.BasePath = r.cfg.BasePath
	data.SiteName = r.cfg.SiteName
	data.ExternalURL = r.cfg.ExternalURL

	t, ok := r.templates[name]
	if !ok {
		slog.Error("template not found", "name", name)
		http.Error(w, "Template not found", http.StatusInternalServerError)
		return
	}

	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	if err := t.ExecuteTemplate(w, "base.html", data); err != nil {
		slog.Error("template execute failed", "name", name, "error", err)
	}
}

// Error renders an error page with the given HTTP status code.
func (r *Renderer) Error(w http.ResponseWriter, req *http.Request, code int, message string) {
	data := PageData{
		Title: message,
		Data: map[string]any{
			"Code":    code,
			"Message": message,
		},
	}

	// Populate common fields from context (same as Page does).
	data.User = middleware.UserFromContext(req.Context())
	data.CSRFToken = middleware.CSRFTokenFromContext(req.Context())
	data.BasePath = r.cfg.BasePath
	data.SiteName = r.cfg.SiteName
	data.ExternalURL = r.cfg.ExternalURL

	t, ok := r.templates["error"]
	if !ok {
		http.Error(w, message, code)
		return
	}

	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.WriteHeader(code)
	if err := t.ExecuteTemplate(w, "base.html", data); err != nil {
		slog.Error("error template execute failed", "error", err)
	}
}

// Partial renders a partial template (for HTMX responses).
func (r *Renderer) Partial(w io.Writer, name string, data any) error {
	key := "partial:" + name
	t, ok := r.templates[key]
	if !ok {
		return fmt.Errorf("partial template %q not found", name)
	}
	return t.Execute(w, data)
}

func (r *Renderer) templateFuncs() template.FuncMap {
	return template.FuncMap{
		// basePath returns the configured base path for URL construction.
		"basePath": func() string {
			return r.cfg.BasePath
		},
		// externalURL returns the configured external URL.
		"externalURL": func() string {
			return r.cfg.ExternalURL
		},
		// truncate truncates a string to n runes (not bytes) to avoid
		// splitting multi-byte UTF-8 characters (Norwegian æøå etc.).
		"truncate": func(n int, s string) string {
			runes := []rune(s)
			if len(runes) <= n {
				return s
			}
			return string(runes[:n]) + "..."
		},
		// join joins strings with a separator.
		"join": strings.Join,
		// contains checks if a string contains a substring.
		"contains": strings.Contains,
		// add returns a + b.
		"add": func(a, b int) int { return a + b },
		// subtract returns a - b.
		"subtract": func(a, b int) int { return a - b },
		// maxTags returns the maximum number of tags per fave.
		"maxTags": func() int { return store.MaxTagsPerFave },
	}
}