// Package asv provides encoding and decoding for ASCII separated values.
package asv

import "io"
import "bufio"
import "strings"
import "strconv"

// Collection is composed of Files.
type Collection []File
// File is an element of a Collection, and is composed of Groups.
type File []Group
// Groups is an element of a File, and is composed of Records.
type Group []Record
// Record is an element of a Group, and is composed of Units.
type Record []Unit
// Unit is an element of a record.
type Unit string

func (collection Collection) String () string {
	builder := strings.Builder { }
	builder.WriteString("Collection { ")
	for index, file := range collection {
		if index > 0 { builder.WriteString(", ") }
		builder.WriteString(file.String())
	}
	builder.WriteString(" }")
	return builder.String()
}

func (file File) String () string {
	builder := strings.Builder { }
	builder.WriteString("File { ")
	for index, group := range file {
		if index > 0 { builder.WriteString(", ") }
		builder.WriteString(group.String())
	}
	builder.WriteString(" }")
	return builder.String()
}

func (group Group) String () string {
	builder := strings.Builder { }
	builder.WriteString("Group { ")
	for index, record := range group {
		if index > 0 { builder.WriteString(", ") }
		builder.WriteString(record.String())
	}
	builder.WriteString(" }")
	return builder.String()
}

func (record Record) String () string {
	builder := strings.Builder { }
	builder.WriteString("Record { ")
	for index, unit := range record {
		if index > 0 { builder.WriteString(", ") }
		builder.WriteString(strconv.Quote(string(unit)))
	}
	builder.WriteString(" }")
	return builder.String()
}

const (
	Escape          rune = '\x1B'
	FileSeparator   rune = '\x1C'
	GroupSeparator  rune = '\x1D'
	RecordSeparator rune = '\x1E'
	UnitSeparator   rune = '\x1F'
)

// IsSeparator returns true if the given rune is a separator.
func IsSeparator (r rune) bool {
	return r >= FileSeparator && r <= UnitSeparator
}

// Decoder decodes ASV values.
type Decoder struct {
	reader *bufio.Reader
}

// NewDecoder creates a new Decoder that reads from the specified io.Reader.
func NewDecoder (reader io.Reader) *Decoder {
	return &Decoder {
		reader: bufio.NewReader(reader),
	}
}

// ReadCollection reads files until EOF and returns them in a collection. This
// function will return nil instead of io.EOF.
func (this *Decoder) ReadCollection () (collection Collection, err error) {
	for {
		file, _, err := this.ReadFile()
		collection = append(collection, file)
		if err == io.EOF { return collection, nil}
		if err != nil    { return collection, err }
	}
}

// ReadFile reads groups until a separator higher than or equal to FileSeparator
// is encountered, or an EOF is encountered. The function will then return the
// resulting File, as well as the separator that caused it to terminate. On EOF,
// it will return 0 for next and io.EOF for err.
func (this *Decoder) ReadFile () (file File, next rune, err error) {
	for {
		group, next, err := this.ReadGroup()
		file = append(file, group)
		if err != nil { return file, 0, err }
		if next <= FileSeparator {
			return file, next, nil
		}
	}
}

// ReadGroup reads records until a separator higher than or equal to
// GroupSeparator is encountered, or an EOF is encountered. The function will
// then return the resulting Group, as well as the separator that caused it to
// terminate. On EOF, it will return 0 for next and io.EOF for err.
func (this *Decoder) ReadGroup () (group Group, next rune, err error) {
	for {
		record, next, err := this.ReadRecord()
		group = append(group, record)
		if err != nil { return group, 0, err }
		if next <= GroupSeparator {
			return group, next, nil
		}
	}
}

// ReadRecord reads units until a separator higher than or equal to
// RecordSeparator is encountered, or an EOF is encountered. The function will
// then return the resulting Record, as well as the separator that caused it to
// terminate. On EOF, it will return 0 for next and io.EOF for err.
func (this *Decoder) ReadRecord () (record Record, next rune, err error) {
	for {
		unit, next, err := this.ReadUnit()
		record = append(record, unit)
		if err != nil { return record, 0, err }
		if next <= RecordSeparator {
			return record, next, nil
		}
	}
}

// ReadUnit reads characters until a separator higher than or equal to
// UnitSeparator is encountered, or an EOF is encountered. The function will
// then return the resulting Unit, as well as the separator that caused it to
// terminate. On EOF, it will return 0 for next and io.EOF for err.
//
// If Escape is encountered before any character, that character will be
// included in the unit's string literally, minus the Escape.
func (this *Decoder) ReadUnit () (unit Unit, next rune, err error) {
	esc := false
	str := strings.Builder { }
	for {
		char, _, err := this.reader.ReadRune()
		if err != nil { return Unit(str.String()), 0, err }

		switch {
		case esc:
			esc = false
			str.WriteRune(char)
		case char == Escape:
			esc = true
		case IsSeparator(char):
			return Unit(str.String()), char, nil
		default:
			str.WriteRune(char)
		}
	}
}

// Encoder encodes ASV values. It keeps track of the last entity that was
// written, and inserts separators where necessary. After all data has been
// written, the client should call the Flush method to guarantee all data has
// been forwarded to the underlying io.Writer.
type Encoder struct {
	writer     *bufio.Writer
	lastEntity rune
}

// WriteCollection writes a collection to the underlying io.Writer.
func (this *Encoder) WriteCollection (collection Collection) (n int, err error) {
	for _, file := range collection {
		nn, err := this.WriteFile(file)
		n += nn
		if err != nil { return n, err }
	}
	return n, nil
}

// WriteFile writes a file to the underlying io.Writer.
func (this *Encoder) WriteFile (file File) (n int, err error) {
	nn, err := this.begin(FileSeparator)
	n += nn
	if err != nil { return n, err }
	defer this.end(FileSeparator)
	
	for _, group := range file {
		nn, err := this.WriteGroup(group)
		n += nn
		if err != nil { return n, err }
	}
	return n, nil
}

// WriteGroup writes a group to the underlying io.Writer.
func (this *Encoder) WriteGroup (group Group) (n int, err error) {
	nn, err := this.begin(GroupSeparator)
	n += nn
	if err != nil { return n, err }
	defer this.end(GroupSeparator)
	
	for _, record := range group {
		nn, err := this.WriteRecord(record)
		n += nn
		if err != nil { return n, err }
	}
	return n, nil
}

// WriteRecord writes a record to the underlying io.Writer.
func (this *Encoder) WriteRecord (record Record) (n int, err error) {
	nn, err := this.begin(RecordSeparator)
	n += nn
	if err != nil { return n, err }
	defer this.end(RecordSeparator)
	
	for _, unit := range record {
		nn, err := this.WriteUnit(unit)
		n += nn
		if err != nil { return n, err }
	}
	return n, nil
}

// WriteUnit writes a unit to the underlying io.Writer. All separators, as well
// as Escape, are prepended with an Escape.
func (this *Encoder) WriteUnit (unit Unit) (n int, err error) {
	nn, err := this.begin(UnitSeparator)
	n += nn
	if err != nil { return n, err }
	defer this.end(UnitSeparator)
	
	for _, char := range unit {
		if IsSeparator(char) || char == Escape {
			nn, _ := this.writer.WriteRune(Escape)
			n += nn
		}
		
		nn, err := this.writer.WriteRune(char)
		n += nn
		if err != nil { return n, err }
	}
	return n, nil
}

func (this *Encoder) begin (separator rune) (n int, err error) {
	if this.lastEntity == UnitSeparator {
		nn, err := this.writer.WriteRune(separator)
		n += nn
		if err != nil { return n, err }
	}
	return n, nil
}

func (this *Encoder) end (separator rune) {
	this.lastEntity = separator
}

// Flush writes any buffered data to the underlying io.Writer.
func (this *Encoder) Flush () error {
	return this.writer.Flush()
}