package nginx

import (
	"fmt"
	"io"
)

var (
	defaultPrefix = ""
	defaultIndent = "\t"
)

// Encoder implements parser.Encoder
type Encoder struct {
	writer io.Writer
	prefix []byte
	indent []byte
}

// SetIndent with the <prefix> that begins each line (default is emptys string)
// and the <indent> string repeated for each indentation level (default is tab '\t')
func (e *Encoder) SetIndent(prefix, indent string) {
	e.prefix = make([]byte, 0)
	e.prefix = append(e.prefix, []byte(prefix)...)

	e.indent = make([]byte, 0)
	e.indent = append(e.indent, []byte(indent)...)
}

// Encode is the main function of the parser.Encoder interface
func (e *Encoder) Encode(v interface{}) error {

	// default indentation
	if e.prefix == nil || e.indent == nil {
		e.SetIndent(defaultPrefix, defaultIndent)
	}

	// check 'v'
	vcast, ok := v.(*Line)
	if !ok {
		return ErrInvalidReceiver
	}

	// empty config
	if len(vcast.Lines) < 1 {
		return nil
	}

	// actual indentation level
	indent := 0

	// actual lines to write
	stack := make([]*Line, 0)

	// push nginx.Lines in reverse order
	for l := len(vcast.Lines) - 1; l >= 0; l-- {
		stack = append(stack, vcast.Lines[l])
	}

	for len(stack) > 0 {

		// pop stack
		line := stack[len(stack)-1]
		stack = stack[:len(stack)-1]

		// line representation
		repr := make([]byte, 0)

		if line == nil { // section end
			indent--
		}

		// 1. add indentation
		repr = append(repr, []byte(e.prefix)...)
		for i := 0; i < indent; i++ {
			repr = append(repr, []byte(e.indent)...)
		}

		// 2. section end
		if line == nil {
			repr = append(repr, []byte("}\n\n")...)
			// Note: new line after section for readability

			// 3. comments
		} else if line.Type == COMMENT {

			repr = append(repr, []byte(fmt.Sprintf("#%s\n", line.Components[0]))...)
		} else if line.Type == COLONCOMMENT {
			repr = append(repr, []byte(fmt.Sprintf(";%s\n", line.Components[0]))...)

			// 4.assignments
		} else if line.Type == ASSIGNMENT {
			repr = append(repr, []byte(fmt.Sprintf("%s\t\t%s;\n", line.Components[0], line.Components[1]))...)

			// 5. include
		} else if line.Type == INCLUDE {
			repr = append(repr, []byte(fmt.Sprintf("include %s;\n", line.Components[0]))...)

			// 6. section
		} else {
			// push to stack
			stack = append(stack, nil)

			// push children lines in reverse order
			if len(line.Lines) > 0 {
				for l := len(line.Lines) - 1; l >= 0; l-- {
					stack = append(stack, line.Lines[l])
				}
			}

			if len(line.Components) > 1 {
				repr = append(repr, []byte(fmt.Sprintf("%s %s {\n", line.Components[0], line.Components[1]))...)
			} else {
				repr = append(repr, []byte(fmt.Sprintf("%s {\n", line.Components[0]))...)
			}

			indent++

		}

		_, err := e.writer.Write(repr)
		if err != nil {
			return err
		}

	}

	return nil
}