liquid/render/context.go

package render

import (
	"bytes"
	"io"
	"io/ioutil"
	"os"
	"strings"

	"github.com/danog/liquid/expressions"
)

// Context provides the rendering context for a tag renderer.
type Context interface {
	// Get retrieves the value of a variable from the current lexical environment.
	Get(name string) interface{}
	// Errorf creates a SourceError, that includes the source location.
	// Use this to distinguish errors in the template from implementation errors
	// in the template engine.
	Errorf(format string, a ...interface{}) Error
	// Evaluate evaluates a compiled expression within the current lexical context.
	Evaluate(expressions.Expression) (interface{}, error)
	// EvaluateString compiles and evaluates a string expression such as “x”, “x < 10", or “a.b | split | first | default: 10”, within the current lexical context.
	EvaluateString(string) (interface{}, error)
	// ExpandTagArg renders the current tag argument string as a Liquid template.
	// It enables the implementation of tags such as Jekyll's "{% include {{ page.my_variable }} %}" andjekyll-avatar's  "{% avatar {{page.author}} %}".
	ExpandTagArg() (string, error)
	// InnerString is the rendered content of the current block.
	// It's used in the implementation of the Liquid "capture" tag and the Jekyll "highlght" tag.
	InnerString() (string, error)
	// RenderBlock is used in the implementation of the built-in control flow tags.
	// It's not guaranteed stable.
	RenderBlock(io.Writer, *BlockNode) error
	// RenderChildren is used in the implementation of the built-in control flow tags.
	// It's not guaranteed stable.
	RenderChildren(io.Writer) Error
	// RenderFile parses and renders a template. It's used in the implementation of the {% include %} tag.
	// RenderFile does not cache the compiled template.
	RenderFile(string, map[string]interface{}) (string, error)
	// Set updates the value of a variable in the current lexical environment.
	// It's used in the implementation of the {% assign %} and {% capture %} tags.
	Set(name string, value interface{})
	// SourceFile retrieves the value set by template.SetSourcePath.
	// It's used in the implementation of the {% include %} tag.
	SourceFile() string
	// TagArgs returns the text of the current tag, not including its name.
	// For example, the arguments to {% my_tag a b c %} would be “a b c”.
	TagArgs() string
	// TagName returns the name of the current tag; for example "my_tag" for {% my_tag a b c %}.
	TagName() string
	// WrapError creates a new error that records the source location from the current context.
	WrapError(err error) Error
}

type rendererContext struct {
	ctx  nodeContext
	node *TagNode
	cn   *BlockNode
}

func (c rendererContext) Errorf(format string, a ...interface{}) Error {
	return renderErrorf(c.node, format, a...)
}

func (c rendererContext) WrapError(err error) Error {
	return wrapRenderError(err, c.node)
}

func (c rendererContext) Evaluate(expr expressions.Expression) (out interface{}, err error) {
	return c.ctx.Evaluate(expr)
}

// EvaluateString evaluates an expression within the template context.
func (c rendererContext) EvaluateString(source string) (out interface{}, err error) {
	return expressions.EvaluateString(source, expressions.NewContext(c.ctx.bindings, c.ctx.config.Config.Config))
}

// Get gets a variable value within an evaluation context.
func (c rendererContext) Get(name string) interface{} {
	return c.ctx.bindings[name]
}

func (c rendererContext) ExpandTagArg() (string, error) {
	args := c.TagArgs()
	if strings.Contains(args, "{{") {
		root, err := c.ctx.config.Compile(args, c.node.SourceLoc)
		if err != nil {
			return "", err
		}
		buf := new(bytes.Buffer)
		err = Render(root, buf, c.ctx.bindings, c.ctx.config)
		if err != nil {
			return "", err
		}
		return buf.String(), nil
	}
	return args, nil
}

// RenderBlock renders a node.
func (c rendererContext) RenderBlock(w io.Writer, b *BlockNode) error {
	return c.ctx.RenderSequence(w, b.Body)
}

// RenderChildren renders the current node's children.
func (c rendererContext) RenderChildren(w io.Writer) Error {
	if c.cn == nil {
		return nil
	}
	return c.ctx.RenderSequence(w, c.cn.Body)
}

func (c rendererContext) RenderFile(filename string, b map[string]interface{}) (string, error) {
	source, err := ioutil.ReadFile(filename)
	if err != nil && os.IsNotExist(err) {
		// Is it cached?
		if cval, ok := c.ctx.config.Cache[filename]; ok {
			source = cval
		} else {
			return "", err
		}
	} else if err != nil {
		return "", err
	}
	root, err := c.ctx.config.Compile(string(source), c.node.SourceLoc)
	if err != nil {
		return "", err
	}
	bindings := map[string]interface{}{}
	for k, v := range c.ctx.bindings {
		bindings[k] = v
	}
	for k, v := range b {
		bindings[k] = v
	}
	buf := new(bytes.Buffer)
	if err := Render(root, buf, bindings, c.ctx.config); err != nil {
		return "", err
	}
	return buf.String(), nil
}

// InnerString renders the children to a string.
func (c rendererContext) InnerString() (string, error) {
	buf := new(bytes.Buffer)
	if err := c.RenderChildren(buf); err != nil {
		return "", err
	}
	return buf.String(), nil
}

// Set sets a variable value from an evaluation context.
func (c rendererContext) Set(name string, value interface{}) {
	c.ctx.bindings[name] = value
}

func (c rendererContext) SourceFile() string {
	return c.node.SourceLoc.Pathname
}

func (c rendererContext) TagArgs() string {
	switch {
	case c.node != nil:
		return c.node.Token.Args
	case c.cn != nil:
		return c.cn.Token.Args
	default:
		return ""
	}
}

func (c rendererContext) TagName() string {
	switch {
	case c.node != nil:
		return c.node.Token.Name
	case c.cn != nil:
		return c.cn.Token.Name
	default:
		return ""
	}
}