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Modern emails for Go

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# 🌸 myrtle
Myrtle is a composable, strongly typed email content builder for Go.

| Default | Terminal |
| --- | --- |
| ![Security example (default)](https://raw.githubusercontent.com/gzuidhof/myrtle/main/example/screenshot/default--security.png) | ![Security example (terminal)](https://raw.githubusercontent.com/gzuidhof/myrtle/main/example/screenshot/terminal--security.png) |

## Features

- Fluent builder pattern for email content.
- Strongly typed library of blocks.
- Modern built-in themes: `default`, `flat`, `terminal`, `editorial`.
- Built-in advanced blocks such as tables, charts, grids.
- High-impact blocks: timelines, standout stats rows, badges, attachments.
- Dual rendering APIs:
  - `HTML()` for final HTML output.
  - `Text()` for plain-text fallback output.
- Customizable and extensible: bring your own theme, styles or custom blocks.
- Left-to-right and right-to-left direction support (e.g. for Arabic/Hebrew).
- Renders OK in Outlook Classic and other notoriously difficult email clients.
- Dependency-free aside from [`goldmark`](https://github.com/yuin/goldmark) for Markdown rendering.

## Installation

```bash
go get github.com/gzuidhof/myrtle
```

## Quick start (security email)

```go
package main

import (
  "github.com/gzuidhof/myrtle"
  defaulttheme "github.com/gzuidhof/myrtle/theme/default"
)

func main() {
  email := myrtle.NewBuilder(defaulttheme.New()).
    WithPreheader("Use this one-time code to sign in").
    AddHeading("Your verification code").
    AddText("Use the code below to complete your sign-in. This code expires in 10 minutes.").
    AddVerificationCode("Verification code", "493817").
    AddKeyValue("Request details", []myrtle.KeyValuePair{
      {Key: "IP", Value: "203.0.113.5"},
      {Key: "Location", Value: "Amsterdam, NL"},
    }).
    AddText("If you did not request this code, secure your account immediately.").
    AddButton("Review account", "https://example.com/account/security").
    Build()

html, err := email.HTML()
  if err != nil {
    panic(err)
  }

md, err := email.Text()
  if err != nil {
    panic(err)
  }

// Use your favorite e-mail sending library to send the email with the generated HTML and text content.
  // ...

_ = html
  _ = md
}
```

Make use of auto-complete/Intellisense in your IDE to explore the rich library of blocks and customization options.

## Expandable snippets

<details>
<summary>Custom block (basic)</summary>

```go
package main

import (
  "fmt"

"github.com/gzuidhof/myrtle"
  "github.com/gzuidhof/myrtle/theme"
  defaulttheme "github.com/gzuidhof/myrtle/theme/default"
)

type DeploymentStatus struct {
  Service string
  Version string
  Status  string
}

func main() {
 block := myrtle.NewCustomBlock(
 theme.BlockKind("deployment_status"),
 DeploymentStatus{Service: "billing-api", Version: "v1.42.0", Status: "healthy"},
 func(v DeploymentStatus, values theme.Values) (string, error) {
 _ = values
 return fmt.Sprintf("%s on <code>%s</code>: %s", v.Service, v.Version, v.Status), nil
 },
 func(v DeploymentStatus, context myrtle.RenderContext) (string, error) {
 _ = context
 return fmt.Sprintf("%s on %s: %s", v.Service, v.Version, v.Status), nil
 },
 )

email := myrtle.NewBuilder(defaulttheme.New()).
    AddHeading("Deployment update").
    Add(block).
    Build()

_, _ = email.HTML()
  _, _ = email.Text()
}
```

</details>

<details>
<summary>Style tweaks (basic)</summary>

```go
package main

import (
  "github.com/gzuidhof/myrtle"
  "github.com/gzuidhof/myrtle/theme"
  defaulttheme "github.com/gzuidhof/myrtle/theme/default"
)

func main() {
  styles := theme.DefaultDarkModeStyles()
  styles.ColorPrimary = "#22d3ee"
  styles.MaxWidthMain = "640px"
  styles.MainContentBodyTopSpacing = "0"

email := myrtle.NewBuilder(
    defaulttheme.New(),
    myrtle.WithStyles(styles),
  ).
    WithPreheader("Theme overrides example").
    AddHeading("Style tweaks").
    AddText("This message uses a dark preset with a few token overrides.").
    AddButton("Open dashboard", "https://example.com/dashboard").
    Build()

_, _ = email.HTML()
  _, _ = email.Text()
}
```

</details>

<details>
<summary>Concurrent rendering with shared header/footer/theme/styles</summary>

```go
package main

import (
  "sync"

"github.com/gzuidhof/myrtle"
  "github.com/gzuidhof/myrtle/theme"
  defaulttheme "github.com/gzuidhof/myrtle/theme/default"
)

type RenderedEmail struct {
  To   string
  HTML string
  Text string
  Err  error
}

func main() {
  // Shared theme/styles/header/footer used to build one baseline builder.
  sharedStyles := theme.Styles{
    ColorPrimary: "#2563eb",
    MaxWidthMain: "640px",
  }

sharedHeader := myrtle.NewGroup().
    AddImage("https://example.com/logo.png", "Myrtle", myrtle.ImageWidth(120), myrtle.ImageAlign(myrtle.ImageAlignmentCenter)).
    AddText("Security updates", myrtle.TextAlign(myrtle.TextAlignCenter), myrtle.TextWeight(myrtle.TextWeightSemibold))

sharedFooter := myrtle.NewGroup().
    AddLegal(
      "Myrtle Inc.",
      "Dam Square 1, 1012 JS Amsterdam, Netherlands",
      "https://example.com/preferences",
      "https://example.com/unsubscribe",
    )

baseBuilder := myrtle.NewBuilder(defaulttheme.New(), myrtle.WithStyles(sharedStyles)).
    WithHeader(sharedHeader).
    WithFooter(sharedFooter).
    WithPreheader("Important account security update")

recipients := []string{"ana@example.com", "bo@example.com", "cy@example.com"}
  results := make([]RenderedEmail, len(recipients))

var wg sync.WaitGroup
  for i, to := range recipients {
    wg.Add(1)
    go func(i int, to string) {
      defer wg.Done()

// Clone the baseline builder and apply recipient-specific content.
      email := baseBuilder.Clone().
        AddHeading("Account alert").
        AddText("We detected a sign-in from a new location.").
        AddKeyValue("Recipient", []myrtle.KeyValuePair{{Key: "Email", Value: to}}).
        AddButton("Review activity", "https://example.com/security").
        Build()

html, err := email.HTML()
      if err != nil {
        results[i] = RenderedEmail{To: to, Err: err}
        return
      }

text, err := email.Text()
      results[i] = RenderedEmail{To: to, HTML: html, Text: text, Err: err}
    }(i, to)
  }
  wg.Wait()

_ = results
}
```

</details>

## Examples

- [example/weekly_operations_brief.go](example/high_impact.go)
- [example/account_deletion_confirmation.go](example/account_deletion_confirmation.go)
- [example/security.go](example/security.go)
- [example/monster.go](example/monster.go)

### Rendered examples

#### Weekly operations brief

| Default | Flat |
| --- | --- |
| ![Weekly operations brief (default)](https://raw.githubusercontent.com/gzuidhof/myrtle/main/example/screenshot/default--weekly-operations-brief.png) | ![Weekly operations brief (flat)](https://raw.githubusercontent.com/gzuidhof/myrtle/main/example/screenshot/flat--weekly-operations-brief.png) |
| Terminal | Editorial |
| ![Weekly operations brief (terminal)](https://raw.githubusercontent.com/gzuidhof/myrtle/main/example/screenshot/terminal--weekly-operations-brief.png) | ![Weekly operations brief (editorial)](https://raw.githubusercontent.com/gzuidhof/myrtle/main/example/screenshot/editorial--weekly-operations-brief.png) |

#### Account deletion confirmation

| Default | Flat |
| --- | --- |
| ![Account deletion confirmation (default)](https://raw.githubusercontent.com/gzuidhof/myrtle/main/example/screenshot/default--account-deletion-confirmation.png) | ![Account deletion confirmation (flat)](https://raw.githubusercontent.com/gzuidhof/myrtle/main/example/screenshot/flat--account-deletion-confirmation.png) |
| Terminal | Editorial |
| ![Account deletion confirmation (terminal)](https://raw.githubusercontent.com/gzuidhof/myrtle/main/example/screenshot/terminal--account-deletion-confirmation.png) | ![Account deletion confirmation (editorial)](https://raw.githubusercontent.com/gzuidhof/myrtle/main/example/screenshot/editorial--account-deletion-confirmation.png) |

#### Security confirmation

| Default | Flat |
| --- | --- |
| ![Security confirmation (default)](https://raw.githubusercontent.com/gzuidhof/myrtle/main/example/screenshot/default--security.png) | ![Security confirmation (flat)](https://raw.githubusercontent.com/gzuidhof/myrtle/main/example/screenshot/flat--security.png) |
| Terminal | Editorial |
| ![Security confirmation (terminal)](https://raw.githubusercontent.com/gzuidhof/myrtle/main/example/screenshot/terminal--security.png) | ![Security confirmation (editorial)](https://raw.githubusercontent.com/gzuidhof/myrtle/main/example/screenshot/editorial--security.png) |

#### Monster

The monster example is a fun showcase of many blocks and styles together. It intentionally has a lot of content to demonstrate how the builder and themes handle it.

- [example/screenshot/default--monster.png](example/screenshot/default--monster.png)

## Example server

The [example/server](example/server) package serves a directory of all example emails and block previews.

Clone this repository and run the server to preview example emails in the browser at `http://localhost:8380/`.

```bash
go run ./example/server/cmd
```

![Example server preview](https://raw.githubusercontent.com/gzuidhof/myrtle/main/example/screenshot/example-server.png)

## Development
The code for this repository is repetitive and verbose, I recommend you use AI-assisted code generation to speed up development. Writing inlined CSS manually is particularly painful.

This library is not stable yet, your layouts will likely shift a bit with future releases.

## License
Myrtle is licensed under the MIT License. See [LICENSE](LICENSE) for more information.

> Myrtle she wrote.

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