// Copyright 2025 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT

package devtest

import (
	"errors"
	"io/fs"
	"net/http"
	"regexp"
	"strings"

	"gitea.dev/modules/setting"
	"gitea.dev/modules/templates"
	"gitea.dev/modules/util"
	"gitea.dev/services/context"
	"gitea.dev/services/mailer"

	"go.yaml.in/yaml/v4"
)

var mailDarkSchemeQuery = regexp.MustCompile(`@media\s*\(\s*prefers-color-scheme\s*:\s*dark\s*\)`)

func mailPreviewMockData(tmplName string) (map[string]any, error) {
	mockData := map[string]any{}
	mockDataContent, err := templates.AssetFS().ReadFile(tmplName + ".devtest.yml")
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			return mockData, nil
		}
		return nil, err
	}
	return mockData, yaml.Unmarshal(mockDataContent, &mockData)
}

func MailPreviewRender(ctx *context.Context) {
	tmplName := ctx.PathParam("*")
	mockData, err := mailPreviewMockData(tmplName)
	if err != nil {
		http.Error(ctx.Resp, "Failed to parse mock data: "+err.Error(), http.StatusInternalServerError)
		return
	}
	mockData["locale"] = ctx.Locale
	var mailBody strings.Builder
	if err := mailer.LoadedTemplates().BodyTemplates.ExecuteTemplate(&mailBody, tmplName, mockData); err != nil {
		http.Error(ctx.Resp, err.Error(), http.StatusInternalServerError)
		return
	}
	body := mailBody.String()
	// emulate mail clients, which resolve "cid:" URIs to the mail's inline attachments
	body = strings.ReplaceAll(body, `src="cid:`, `src="`+setting.AppSubURL+`/devtest/mail-preview-embed/`)
	previewStyle := "body {padding: 12px 16px}"
	// a page can force "color-scheme" on an embedded document but never "prefers-color-scheme"
	if scheme := ctx.FormString("scheme"); scheme == "light" || scheme == "dark" {
		body = mailDarkSchemeQuery.ReplaceAllString(body, util.Iif(scheme == "dark", "@media all", "@media not all"))
		previewStyle += "\n:root {color-scheme: " + scheme + "}"
	}
	body = strings.Replace(body, "</head>", "<style>"+previewStyle+"</style></head>", 1)
	// fragment templates like "mail/base/head" would be sniffed as text/plain otherwise
	ctx.Resp.Header().Set("Content-Type", "text/html; charset=utf-8")
	_, _ = ctx.Resp.Write([]byte(body))
}

func MailPreviewEmbed(ctx *context.Context) {
	content, err := mailer.LoadMailIcon(ctx.PathParam("*"))
	if err != nil {
		ctx.NotFound(err)
		return
	}
	ctx.Resp.Header().Set("Content-Type", "image/png")
	_, _ = ctx.Resp.Write(content)
}

func prepareMailPreviewRender(ctx *context.Context, tmplName string) {
	subject := "(default subject)"
	if mockData, err := mailPreviewMockData(tmplName); err == nil {
		if mockSubject, ok := mockData["Subject"].(string); ok {
			subject = util.IfZero(mockSubject, subject)
		}
	}
	tmplSubject := mailer.LoadedTemplates().SubjectTemplates.Lookup(tmplName)
	// FIXME: MAIL-TEMPLATE-SUBJECT: only "issue" related messages support using subject from templates
	if tmplSubject != nil {
		var buf strings.Builder
		err := tmplSubject.Execute(&buf, nil)
		if err != nil {
			subject = "ERROR: " + err.Error()
		} else {
			subject = util.IfZero(buf.String(), subject)
		}
	}
	ctx.Data["RenderMailSubject"] = subject
	ctx.Data["RenderMailTemplateName"] = tmplName
}

func MailPreview(ctx *context.Context) {
	ctx.Data["MailTemplateNames"] = mailer.LoadedTemplates().TemplateNames
	tmplName := ctx.FormString("tmpl")
	if tmplName != "" {
		prepareMailPreviewRender(ctx, tmplName)
	}
	ctx.HTML(http.StatusOK, "devtest/mail-preview")
}