cabret/README.md

# Cabret

Cabret is a yaml based static site generator, ideally with the same features as Hugo but with a simpler model. Here is a simple example of a _Cabretfile.yaml_

## Build

```bash shell
$ go build -v -o ./bin/cabret ./cmd/cabret
```

## Introduction

```yaml
build:
  - pipeline:
      - source: index.html
      - use: layout
        path: layouts/base.html
      - target: dist/index.html
  - pipeline:
      - source: posts/{{ .Id }}.md
      - plugin: markdown
      - use: layout
        path: layouts/base.html
      - target: dist/posts/{{ .Id }}/index.html
```

Cabret is based on the idea of a data pipeline. Along a pipeline flows **a list** of `Content` items that are just items with a data, mime type and metadata.

```go
type Content struct {
    Type      string
    Metadata  map[string]any
    Data      []byte          
}
```

The `Type` is the _mime type_ of the `Data`. The `Metadata` can be whatever the user wants and operations can populate it with special fields as they please. In some cases its useful to have `Data` be `nil`, when that happens the `Type` should be `cabret.MetadataOnly` (just the string `"metadata-only"`)

## Operations

Each pipeline is a list of operations, the first field in an operation should be one of `source`, `use` or `target`.

- `source: <path pattern>`

    A **path pattern** is a "glob pattern" with captures, some examples are

    ```
    posts/{id}.md 
    {{folders}}/{year}-{month}-{day}.json
    ``` 

    the only difference is that `{{...}}` captures can match slashes so can be used to match more than one "path part", while `{...}` can only match non slash characters.

    Load files matching the given pattern and populates the field `.Metadata.MatchResult` with the captures.

    Other supported forms are

    ```yaml
    use: source
    path: <path pattern>
    ```

    ```yaml
    use: source
    paths: 
      - <path pattern1>
      ...
      - <path patternN>
    ```

- `target: <path template>`

    A **path template** can contains `{...}` interpolations, the key inside the braces will be replaced using the `.Metadata.MatchResult` map. Double braces can also be used and are evaluated using Go `text/template` with context the whole item metadata.

    For each incoming item this will render the given path template with the item metadata and write the content to disk.

- `use: <operation>`

    This will apply the provided operations to the incoming items, for now available operations are

    - **Template** is a list operation that will concatenate all incoming items and render them using the specified template engine

        ```yaml
        use: template
        engine: <name>
        ```

        for now `engine` can be one of

        - `html` &mdash; golang html template engine

        - `text` &mdash; golang text template engine

        - (_TODO_) `handlebars` &mdash; the famous Handlebars template engine 

    - **Layout** is an item operation that works like the previous one as it will use a template engine to render the content of the output item. The main difference is that this will pass the previous item content in the template context in the `.Content` field.

        ```yaml
        use: layout
        path: <glob pattern>
        ```

        ```yaml
        use: layout
        paths: 
          - <glob pattern 1>
          ...
          - <glob pattern N>
        ```

        This operation will automatically choose between the go html or text template engines based on the first file name extension, _TODO: make this configurable like the `template` operation_)

        The template context is the incoming item metadata as well its data passed in the `.Content` variable.

        This is useful for wrapping partial html pages into full documents.

    - **Markdown** doesn't need any other options (TODO: add some options to configure _goldmark_)

        ```yaml
        use: markdown
        ```

        This will render each incoming item using goldmark with some reasonable default options.

        By default this will also read YAML frontmatter.

    - **Frontmatter** as the previous one but just reads frontmatter.

        ```yaml
        use: frontmatter
        ```

    - **Categorize** can be used in the following forms

        ```yaml
        use: categorize
        key: <key>
        bind: <variable> # optional
        ```

        This will categorize all items based on the provided key, for example if key is `tags` then the incoming list of posts will be converted in a list of empty contents with a `Category` field telling the item's category and an `Items` field containing a list of posts with that tag.

        By default the output item category is placed into `Category` but this can be changed with the `bind` option.

    - **Chunk** can be used to paginate some items

        ```yaml
        use: chunk
        size: <number>
        ```

        This operation will group the incoming items in chunk with the provided size (except for the last one that can end up holding less items). The output items hold no data but have the following structure

        ```go
        Metadata: {
          Page: <Page Number>
          TotalPages: <Total Page Count>
          Items: <Chunk>
        }
        ```

    - **Slice** extract a sub range of items

        ```yaml
        use: slice
        from: <start> # inclusive, defaults to 0
        to: <end>     # exclusive, defaults to len(Items)
        ```

        Does what you expect to the incoming list of items.

    - **Program** is an item operation that will run a specified program passing the current item as stdin. The program output is then processed and becomes the new item data.

        ```yaml
        use: program
        io: <stdin/stdout format> # optional, defaults to "raw"
        command: <shell command>  # required
        ```

        The io format specifies how the current item is passed to the given program

        - `raw` &mdash; will just pass the item `.Data` raw as stdin to the specified command.
        
        - `json` &mdash; will encode the whole item (also including type and metadata) as json ad pass that string as stdin to the specified command.

        _TODO: Make the shell command be a go text/template string, for passing metadata directly thorough the command string._

    - (_TODO_) **Sort** sorts the incoming items using the provided key and direction (by default is ascending)

        ```yaml
        use: sort
        direction: <ascending or descending>
        key: <key to use for sorting>
        ```

## Architecture

- `cabret.go` &mdash; all abstract types and functions 

- `path/` &mdash; handles path patterns and templates

- `config/` &mdash; contains config structure definitions and handles loading from YAML

- `cmd/cabret/` &mdash; module that puts it all together in a CLI application

- `operation/` &mdash; module containing all operations

    - `operation/template/` &mdash; a small module that abstract the concept of a template, used by the layout operation.

- `runner/` &mdash; a module that depends on `config`, `parse` and `operations` and evaluates operations.

- `parse/` &mdash; handles the conversion of pipelines and lists of operations to core types.