package web

import (
	"context"
	"fmt"
	"html/template"
	"io/fs"
	"net/http"
	"path"
	"strings"
	"time"

	content "inventree/web"
)

// templateFuncs are available to every template (pages and fragments).
var templateFuncs = template.FuncMap{
	"dict": func(pairs ...any) (map[string]any, error) {
		if len(pairs)%2 != 0 {
			return nil, fmt.Errorf("dict: odd number of arguments")
		}
		m := make(map[string]any, len(pairs)/2)
		for i := 0; i < len(pairs); i += 2 {
			key, ok := pairs[i].(string)
			if !ok {
				return nil, fmt.Errorf("dict: key %v is not a string", pairs[i])
			}
			m[key] = pairs[i+1]
		}
		return m, nil
	},
	"add": func(a, b int) int { return a + b },
	"sub": func(a, b int) int { return a - b },
	"mul": func(a, b int) int { return a * b },
	"ceilDiv": func(a, b int) int {
		if b <= 0 {
			return 0
		}
		return (a + b - 1) / b
	},
	"seq": func(n int) []int {
		out := make([]int, n)
		for i := range out {
			out[i] = i
		}
		return out
	},
	"seqFrom1": func(n int) []int {
		out := make([]int, n)
		for i := range out {
			out[i] = i + 1
		}
		return out
	},
	"fmtDate": func(t time.Time) string {
		if t.IsZero() {
			return ""
		}
		return t.Format("2006-01-02 15:04")
	},
	"fmtDateShort": func(t time.Time) string {
		if t.IsZero() {
			return ""
		}
		return t.Format("Jan 2, 2006")
	},
	"iconOr": func(icon, fallback string) string {
		if icon == "" {
			return fallback
		}
		return icon
	},
	"hasPrefix": strings.HasPrefix,
	"lower":     strings.ToLower,
	"list":      func(items ...string) []string { return items },
	"deref": func(p *int64) int64 {
		if p == nil {
			return 0
		}
		return *p
	},
}

// templateSet bundles the shared fragment/partial template collection with
// one isolated template set per full page (see loadTemplates for why pages
// must be isolated from one another).
type templateSet struct {
	shared *template.Template            // layout.html + partials/*.html; used to render AJAX fragments directly
	pages  map[string]*template.Template // page name -> shared clone + that page's templates/pages/<name>.html
	login  *template.Template            // standalone minimal layout for the login screen
}

// loadTemplates parses layout.html and every partial once into a shared
// template set, then clones that set once per page in templates/pages/ so
// each page can define a block named "content" without colliding with the
// others (html/template templates sharing one *template.Template must have
// unique names, but isolated clones may reuse the same name freely).
func loadTemplates(a *App) (*templateSet, error) {
	// siteName is bound per-App (rather than living in the package-level
	// templateFuncs) since it needs a live DB read through a.Settings; it's
	// used by layout.html for the <title> and navbar brand text.
	appFuncs := template.FuncMap{
		"siteName": func() string {
			name, err := a.Settings.Get(context.Background(), "site_name", "inventree")
			if err != nil || name == "" {
				return "inventree"
			}
			return name
		},
	}

	shared := template.New("root").Funcs(templateFuncs).Funcs(appFuncs)

	shared, err := shared.ParseFS(content.TemplatesFS, "templates/layout.html")
	if err != nil {
		return nil, fmt.Errorf("parse layout: %w", err)
	}
	shared, err = parseGlob(shared, "templates/partials")
	if err != nil {
		return nil, fmt.Errorf("parse partials: %w", err)
	}

	pageFiles, err := fs.Glob(content.TemplatesFS, "templates/pages/*.html")
	if err != nil {
		return nil, err
	}

	pages := map[string]*template.Template{}
	for _, pf := range pageFiles {
		name := strings.TrimSuffix(path.Base(pf), ".html")
		clone, err := shared.Clone()
		if err != nil {
			return nil, fmt.Errorf("clone template set for %s: %w", name, err)
		}
		if _, err := clone.ParseFS(content.TemplatesFS, pf); err != nil {
			return nil, fmt.Errorf("parse page %s: %w", pf, err)
		}
		pages[name] = clone
	}

	login := template.New("login-root").Funcs(templateFuncs).Funcs(appFuncs)
	login, err = login.ParseFS(content.TemplatesFS, "templates/login.html")
	if err != nil {
		return nil, fmt.Errorf("parse login: %w", err)
	}

	return &templateSet{shared: shared, pages: pages, login: login}, nil
}

func parseGlob(t *template.Template, dir string) (*template.Template, error) {
	files, err := fs.Glob(content.TemplatesFS, dir+"/*.html")
	if err != nil {
		return nil, err
	}
	if len(files) == 0 {
		return t, nil
	}
	return t.ParseFS(content.TemplatesFS, files...)
}

// Render executes the named page's "layout" template (which pulls in that
// page's "content" block) into the response. Page "login" uses its own
// minimal "login" template instead.
func (a *App) Render(w http.ResponseWriter, status int, page string, data any) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")

	if page == "login" {
		w.WriteHeader(status)
		if err := a.templates.login.ExecuteTemplate(w, "login", data); err != nil {
			a.Log.Error("template render failed", "page", page, "error", err)
		}
		return
	}

	ts, ok := a.templates.pages[page]
	if !ok {
		writeErr(w, http.StatusInternalServerError, "template not found: "+page)
		return
	}
	w.WriteHeader(status)
	if err := ts.ExecuteTemplate(w, "layout", data); err != nil {
		a.Log.Error("template render failed", "page", page, "error", err)
	}
}

// RenderFragment executes a single named partial (defined under
// templates/partials/) with no layout wrapper, for AJAX responses.
func (a *App) RenderFragment(w http.ResponseWriter, status int, name string, data any) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.WriteHeader(status)
	if err := a.templates.shared.ExecuteTemplate(w, name, data); err != nil {
		a.Log.Error("fragment render failed", "name", name, "error", err)
	}
}