package preview

import (
	"context"
	"encoding/base64"
	"encoding/json"
	"fmt"
	"html/template"
	"os"
	"path/filepath"
	"regexp"
	"sort"
	"strings"
	texttmpl "text/template"

	"gitea-mail-templates/tools/builder"
	"gitea-mail-templates/tools/config"
	"gitea-mail-templates/tools/upstream"
)

type PreviewResult struct {
	Rendered  map[string]map[string]map[string]string
	Registry  map[string]map[string]string
	Params    map[string]map[string]string
	Languages []string
	Themes    []string
	Upstream  string
	Commit    string
	Logo      []byte
	Fallback  map[string][]string
	Warnings  map[string]map[string][]string
}

func DiscoverThemes(dir string) ([]string, error) { return builder.Discover(dir) }

// AlignConfig discovers all entrypoints from the snapshot. Metadata is a fixture
// catalog, not a second list of templates. Uncovered new mail types fail closed.
func AlignConfig(s *upstream.Snapshot, cfg *config.TemplatesConfig) error {
	found := map[string]bool{}
	for _, p := range s.Entrypoints() {
		id := upstream.TemplateID(p)
		if found[id] {
			return fmt.Errorf("duplicate entrypoint ID %s", id)
		}
		found[id] = true
		fixture, ok := cfg.Templates[id]
		if !ok {
			return fmt.Errorf("new upstream mail type %s needs a preview fixture", p)
		}
		fixture.Path = strings.Split(p, "/")
		cfg.Templates[id] = fixture
	}
	for id := range cfg.Templates {
		if !found[id] {
			return fmt.Errorf("stale fixture %s is absent from upstream snapshot", id)
		}
	}
	return nil
}

// RenderAll builds installable overrides and renders every official language.
func RenderAll(themesDir string, cfg *config.TemplatesConfig, filter map[string]bool) (*PreviewResult, error) {
	root := filepath.Dir(themesDir)
	s, err := upstream.Prepare(context.Background(), root)
	if err != nil {
		return nil, err
	}
	if err := AlignConfig(s, cfg); err != nil {
		return nil, err
	}
	packages, err := builder.BuildAll(themesDir, s, filter)
	if err != nil {
		return nil, err
	}
	if err := builder.Write(filepath.Join(root, "build", "themes"), s, packages); err != nil {
		return nil, err
	}
	// Include framework-added labels/controls, not only stock mail keys.
	reference := *s
	reference.Templates = map[string][]byte{}
	for name, b := range s.Templates {
		reference.Templates[name] = b
	}
	for _, p := range packages {
		for name, b := range p.Files {
			reference.Templates[name] = b
		}
	}
	missing, err := upstream.MissingKeys(&reference)
	if err != nil {
		return nil, err
	}
	result := &PreviewResult{Rendered: map[string]map[string]map[string]string{}, Registry: config.Registry(cfg), Params: map[string]map[string]string{}, Languages: s.Languages(), Upstream: s.Lock.Tag, Fallback: missing, Warnings: map[string]map[string][]string{}}
	for id, t := range cfg.Templates {
		result.Params[id] = config.FlattenParams(t.Params)
	}
	for name := range packages {
		result.Themes = append(result.Themes, name)
	}
	sort.Strings(result.Themes)
	result.Commit = s.Lock.Commit
	result.Logo = s.Files["public/assets/img/favicon.png"]
	for _, lang := range result.Languages {
		result.Rendered[lang] = map[string]map[string]string{}
		result.Warnings[lang] = map[string][]string{}
		for _, name := range result.Themes {
			templates := builder.EffectiveTemplates(s, packages[name])
			result.Rendered[lang][name] = map[string]string{}
			for id, fixture := range cfg.Templates {
				mail, err := RenderMail(s, templates, strings.Join(fixture.Path, "/"), fixture.Params, lang)
				if err != nil {
					return nil, fmt.Errorf("%s/%s/%s: %w", lang, name, id, err)
				}
				result.Rendered[lang][name][id] = mail.HTML
				if len(mail.Warnings) > 0 {
					result.Warnings[lang][id] = mail.Warnings
				}
			}
		}
	}
	return result, nil
}

type Mail struct {
	Subject  string
	HTML     string
	Warnings []string
}

var subjectSplit = regexp.MustCompile(`(?m)^-{3,}\s*$`)

// RenderMail parses subjects with text/template, bodies with html/template, and
// registers shared partials under Gitea's mail/... names.
func RenderMail(s *upstream.Snapshot, files map[string][]byte, entry string, params map[string]any, lang string) (Mail, error) {
	var result Mail
	catalog, ok := s.Locales[lang]
	if !ok {
		return result, fmt.Errorf("unknown preview language %s", lang)
	}
	data := CloneParams(params)
	var problems []error
	data["locale"] = Locale{Lang: lang, Catalog: catalog, English: s.Locales["en-US"], Problems: &problems, Warnings: &result.Warnings}
	markSafeHTML(data)
	root := template.New("").Funcs(TemplateFuncs).Option("missingkey=error")
	var entrySubject string
	names := make([]string, 0, len(files))
	for p := range files {
		names = append(names, p)
	}
	sort.Strings(names)
	for _, p := range names {
		source := string(files[p])
		subject, body := splitMail(source)
		if p == entry {
			entrySubject = subject
		}
		if _, err := root.New(builder.TemplateName(p)).Parse(body); err != nil {
			return result, fmt.Errorf("%s: %w", p, err)
		}
	}
	if entrySubject != "" {
		// Gitea's subject environment is intentionally smaller than the body map.
		sub, err := texttmpl.New("subject").Funcs(texttmpl.FuncMap{"AppName": TemplateFuncs["AppName"], "AppDomain": TemplateFuncs["AppDomain"], "dict": Dict}).Option("missingkey=error").Parse(entrySubject)
		if err != nil {
			return result, err
		}
		var buf strings.Builder
		if err := sub.Execute(&buf, data); err != nil {
			return result, err
		}
		result.Subject = strings.Join(strings.Fields(buf.String()), " ")
		runes := []rune(result.Subject)
		if len(runes) > 256 {
			result.Subject = string(runes[:256])
		}
	}
	if result.Subject == "" {
		if subject, ok := data["FallbackSubject"].(string); ok {
			result.Subject = subject
		} else if subject, ok := data["Subject"].(string); ok {
			result.Subject = subject
		}
	}
	data["Subject"] = result.Subject
	var buf strings.Builder
	if err := root.ExecuteTemplate(&buf, builder.TemplateName(entry), data); err != nil {
		return result, err
	}
	if len(problems) > 0 {
		return result, problems[0]
	}
	result.HTML = buf.String()
	return result, nil
}

func splitMail(source string) (string, string) {
	loc := subjectSplit.FindStringIndex(source)
	if loc == nil {
		return "", source
	}
	return source[:loc[0]], source[loc[1]:]
}

// CloneParams prevents safe-HTML conversions or branch fixtures from mutating
// another language's input data.
func CloneParams(params map[string]any) map[string]any {
	result := map[string]any{}
	for k, v := range params {
		switch v := v.(type) {
		case map[string]any:
			result[k] = CloneParams(v)
		case []any:
			values := make([]any, len(v))
			for i, item := range v {
				if m, ok := item.(map[string]any); ok {
					values[i] = CloneParams(m)
				} else {
					values[i] = item
				}
			}
			result[k] = values
		default:
			result[k] = v
		}
	}
	return result
}

// The small manifest is always loaded first; each catalog's rendered data is a
// classic script so static preview also works without fetch on file://.
func WriteRenderedJS(result *PreviewResult, output string) error {
	dir := filepath.Dir(output)
	dataDir := filepath.Join(dir, "rendered")
	if err := os.MkdirAll(dataDir, 0755); err != nil {
		return err
	}
	manifest := map[string]any{"schema": 1, "upstream": result.Upstream, "languages": result.Languages, "themes": result.Themes, "registry": result.Registry, "params": result.Params, "fallback": result.Fallback, "warnings": result.Warnings}
	manifest["logo"] = "data:image/png;base64," + base64.StdEncoding.EncodeToString(result.Logo)
	manifest["upstream_commit"] = result.Commit
	data, err := json.Marshal(manifest)
	if err != nil {
		return err
	}
	// Payloads are written before the manifest, so a failed render never publishes
	// a manifest that advertises missing files.
	for _, lang := range result.Languages {
		payload, err := json.Marshal(result.Rendered[lang])
		if err != nil {
			return err
		}
		key, _ := json.Marshal(lang)
		script := "window.__MAIL_PREVIEW_DATA__ = window.__MAIL_PREVIEW_DATA__ || {};\nwindow.__MAIL_PREVIEW_DATA__[" + string(key) + "] = " + string(payload) + ";\n"
		if err := os.WriteFile(filepath.Join(dataDir, lang+".js"), []byte(script), 0644); err != nil {
			return err
		}
	}
	script := "// Generated by tools; do not edit.\nwindow.__MAIL_PREVIEW__ = " + string(data) + ";\n"
	return os.WriteFile(output, []byte(script), 0644)
}

func PrintDetailedSummary(result *PreviewResult, _ string, _ *config.TemplatesConfig) {
	fmt.Printf("[PASS] %s: %d themes × %d mail types × %d languages\n", result.Upstream, len(result.Themes), len(result.Registry), len(result.Languages))
	for _, lang := range result.Languages {
		for _, warnings := range result.Warnings[lang] {
			for _, warning := range warnings {
				fmt.Println(warning)
			}
		}
		if keys := result.Fallback[lang]; len(keys) > 0 {
			fmt.Printf("[FALLBACK] %s -> en-US: %s\n", lang, strings.Join(keys, ", "))
		}
	}
}

func markSafeHTML(data map[string]any) {
	for k, v := range data {
		switch v := v.(type) {
		case string:
			if k == "RenderedNote" || k == "Body" || k == "RenderedContent" {
				data[k] = template.HTML(v)
			}
		case map[string]any:
			markSafeHTML(v)
		case []any:
			for _, item := range v {
				if m, ok := item.(map[string]any); ok {
					markSafeHTML(m)
				}
			}
		}
	}
}