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+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// The tabwriter package implements a write filter (tabwriter.Writer)
+// that translates tabbed columns in input into properly aligned text.
+//
+// The package is using the Elastic Tabstops algorithm described at
+// http://nickgravgaard.com/elastictabstops/index.html.
+//
+package tabwriter
+
+import (
+ "bytes"
+ "io"
+ "os"
+ "utf8"
+)
+
+
+// ----------------------------------------------------------------------------
+// Filter implementation
+
+// A cell represents a segment of text terminated by tabs or line breaks.
+// The text itself is stored in a separate buffer; cell only describes the
+// segment's size in bytes, its width in runes, and whether it's an htab
+// ('\t') terminated cell.
+//
+type cell struct {
+ size int // cell size in bytes
+ width int // cell width in runes
+ htab bool // true if the cell is terminated by an htab ('\t')
+}
+
+
+// A Writer is a filter that inserts padding around tab-delimited
+// columns in its input to align them in the output.
+//
+// The Writer treats incoming bytes as UTF-8 encoded text consisting
+// of cells terminated by (horizontal or vertical) tabs or line
+// breaks (newline or formfeed characters). Cells in adjacent lines
+// constitute a column. The Writer inserts padding as needed to
+// make all cells in a column have the same width, effectively
+// aligning the columns. It assumes that all characters have the
+// same width except for tabs for which a tabwidth must be specified.
+// Note that cells are tab-terminated, not tab-separated: trailing
+// non-tab text at the end of a line does not form a column cell.
+//
+// The Writer assumes that all Unicode code points have the same width;
+// this may not be true in some fonts.
+//
+// If DiscardEmptyColumns is set, empty columns that are terminated
+// entirely by vertical (or "soft") tabs are discarded. Columns
+// terminated by horizontal (or "hard") tabs are not affected by
+// this flag.
+//
+// If a Writer is configured to filter HTML, HTML tags and entities
+// are simply passed through. The widths of tags and entities are
+// assumed to be zero (tags) and one (entities) for formatting purposes.
+//
+// A segment of text may be escaped by bracketing it with Escape
+// characters. The tabwriter passes escaped text segments through
+// unchanged. In particular, it does not interpret any tabs or line
+// breaks within the segment. If the StripEscape flag is set, the
+// Escape characters are stripped from the output; otherwise they
+// are passed through as well. For the purpose of formatting, the
+// width of the escaped text is always computed excluding the Escape
+// characters.
+//
+// The formfeed character ('\f') acts like a newline but it also
+// terminates all columns in the current line (effectively calling
+// Flush). Cells in the next line start new columns. Unless found
+// inside an HTML tag or inside an escaped text segment, formfeed
+// characters appear as newlines in the output.
+//
+// The Writer must buffer input internally, because proper spacing
+// of one line may depend on the cells in future lines. Clients must
+// call Flush when done calling Write.
+//
+type Writer struct {
+ // configuration
+ output io.Writer
+ minwidth int
+ tabwidth int
+ padding int
+ padbytes [8]byte
+ flags uint
+
+ // current state
+ buf bytes.Buffer // collected text excluding tabs or line breaks
+ pos int // buffer position up to which cell.width of incomplete cell has been computed
+ cell cell // current incomplete cell; cell.width is up to buf[pos] excluding ignored sections
+ endChar byte // terminating char of escaped sequence (Escape for escapes, '>', ';' for HTML tags/entities, or 0)
+ lines [][]cell // list of lines; each line is a list of cells
+ widths []int // list of column widths in runes - re-used during formatting
+}
+
+
+func (b *Writer) addLine() { b.lines = append(b.lines, []cell{}) }
+
+
+// Reset the current state.
+func (b *Writer) reset() {
+ b.buf.Reset()
+ b.pos = 0
+ b.cell = cell{}
+ b.endChar = 0
+ b.lines = b.lines[0:0]
+ b.widths = b.widths[0:0]
+ b.addLine()
+}
+
+
+// Internal representation (current state):
+//
+// - all text written is appended to buf; tabs and line breaks are stripped away
+// - at any given time there is a (possibly empty) incomplete cell at the end
+// (the cell starts after a tab or line break)
+// - cell.size is the number of bytes belonging to the cell so far
+// - cell.width is text width in runes of that cell from the start of the cell to
+// position pos; html tags and entities are excluded from this width if html
+// filtering is enabled
+// - the sizes and widths of processed text are kept in the lines list
+// which contains a list of cells for each line
+// - the widths list is a temporary list with current widths used during
+// formatting; it is kept in Writer because it's re-used
+//
+// |<---------- size ---------->|
+// | |
+// |<- width ->|<- ignored ->| |
+// | | | |
+// [---processed---tab------------<tag>...</tag>...]
+// ^ ^ ^
+// | | |
+// buf start of incomplete cell pos
+
+
+// Formatting can be controlled with these flags.
+const (
+ // Ignore html tags and treat entities (starting with '&'
+ // and ending in ';') as single characters (width = 1).
+ FilterHTML uint = 1 << iota
+
+ // Strip Escape characters bracketing escaped text segments
+ // instead of passing them through unchanged with the text.
+ StripEscape
+
+ // Force right-alignment of cell content.
+ // Default is left-alignment.
+ AlignRight
+
+ // Handle empty columns as if they were not present in
+ // the input in the first place.
+ DiscardEmptyColumns
+
+ // Always use tabs for indentation columns (i.e., padding of
+ // leading empty cells on the left) independent of padchar.
+ TabIndent
+
+ // Print a vertical bar ('|') between columns (after formatting).
+ // Discarded colums appear as zero-width columns ("||").
+ Debug
+)
+
+
+// A Writer must be initialized with a call to Init. The first parameter (output)
+// specifies the filter output. The remaining parameters control the formatting:
+//
+// minwidth minimal cell width including any padding
+// tabwidth width of tab characters (equivalent number of spaces)
+// padding padding added to a cell before computing its width
+// padchar ASCII char used for padding
+// if padchar == '\t', the Writer will assume that the
+// width of a '\t' in the formatted output is tabwidth,
+// and cells are left-aligned independent of align_left
+// (for correct-looking results, tabwidth must correspond
+// to the tab width in the viewer displaying the result)
+// flags formatting control
+//
+// To format in tab-separated columns with a tab stop of 8:
+// b.Init(w, 8, 1, 8, '\t', 0);
+//
+// To format in space-separated columns with at least 4 spaces between columns:
+// b.Init(w, 0, 4, 8, ' ', 0);
+//
+func (b *Writer) Init(output io.Writer, minwidth, tabwidth, padding int, padchar byte, flags uint) *Writer {
+ if minwidth < 0 || tabwidth < 0 || padding < 0 {
+ panic("negative minwidth, tabwidth, or padding")
+ }
+ b.output = output
+ b.minwidth = minwidth
+ b.tabwidth = tabwidth
+ b.padding = padding
+ for i := range b.padbytes {
+ b.padbytes[i] = padchar
+ }
+ if padchar == '\t' {
+ // tab padding enforces left-alignment
+ flags &^= AlignRight
+ }
+ b.flags = flags
+
+ b.reset()
+
+ return b
+}
+
+
+// debugging support (keep code around)
+func (b *Writer) dump() {
+ pos := 0
+ for i, line := range b.lines {
+ print("(", i, ") ")
+ for _, c := range line {
+ print("[", string(b.buf.Bytes()[pos:pos+c.size]), "]")
+ pos += c.size
+ }
+ print("\n")
+ }
+ print("\n")
+}
+
+
+// local error wrapper so we can distinguish os.Errors we want to return
+// as errors from genuine panics (which we don't want to return as errors)
+type osError struct {
+ err os.Error
+}
+
+
+func (b *Writer) write0(buf []byte) {
+ n, err := b.output.Write(buf)
+ if n != len(buf) && err == nil {
+ err = os.EIO
+ }
+ if err != nil {
+ panic(osError{err})
+ }
+}
+
+
+func (b *Writer) writeN(src []byte, n int) {
+ for n > len(src) {
+ b.write0(src)
+ n -= len(src)
+ }
+ b.write0(src[0:n])
+}
+
+
+var (
+ newline = []byte{'\n'}
+ tabs = []byte("\t\t\t\t\t\t\t\t")
+)
+
+
+func (b *Writer) writePadding(textw, cellw int, useTabs bool) {
+ if b.padbytes[0] == '\t' || useTabs {
+ // padding is done with tabs
+ if b.tabwidth == 0 {
+ return // tabs have no width - can't do any padding
+ }
+ // make cellw the smallest multiple of b.tabwidth
+ cellw = (cellw + b.tabwidth - 1) / b.tabwidth * b.tabwidth
+ n := cellw - textw // amount of padding
+ if n < 0 {
+ panic("internal error")
+ }
+ b.writeN(tabs, (n+b.tabwidth-1)/b.tabwidth)
+ return
+ }
+
+ // padding is done with non-tab characters
+ b.writeN(b.padbytes[0:], cellw-textw)
+}
+
+
+var vbar = []byte{'|'}
+
+func (b *Writer) writeLines(pos0 int, line0, line1 int) (pos int) {
+ pos = pos0
+ for i := line0; i < line1; i++ {
+ line := b.lines[i]
+
+ // if TabIndent is set, use tabs to pad leading empty cells
+ useTabs := b.flags&TabIndent != 0
+
+ for j, c := range line {
+ if j > 0 && b.flags&Debug != 0 {
+ // indicate column break
+ b.write0(vbar)
+ }
+
+ if c.size == 0 {
+ // empty cell
+ if j < len(b.widths) {
+ b.writePadding(c.width, b.widths[j], useTabs)
+ }
+ } else {
+ // non-empty cell
+ useTabs = false
+ if b.flags&AlignRight == 0 { // align left
+ b.write0(b.buf.Bytes()[pos : pos+c.size])
+ pos += c.size
+ if j < len(b.widths) {
+ b.writePadding(c.width, b.widths[j], false)
+ }
+ } else { // align right
+ if j < len(b.widths) {
+ b.writePadding(c.width, b.widths[j], false)
+ }
+ b.write0(b.buf.Bytes()[pos : pos+c.size])
+ pos += c.size
+ }
+ }
+ }
+
+ if i+1 == len(b.lines) {
+ // last buffered line - we don't have a newline, so just write
+ // any outstanding buffered data
+ b.write0(b.buf.Bytes()[pos : pos+b.cell.size])
+ pos += b.cell.size
+ } else {
+ // not the last line - write newline
+ b.write0(newline)
+ }
+ }
+ return
+}
+
+
+// Format the text between line0 and line1 (excluding line1); pos
+// is the buffer position corresponding to the beginning of line0.
+// Returns the buffer position corresponding to the beginning of
+// line1 and an error, if any.
+//
+func (b *Writer) format(pos0 int, line0, line1 int) (pos int) {
+ pos = pos0
+ column := len(b.widths)
+ for this := line0; this < line1; this++ {
+ line := b.lines[this]
+
+ if column < len(line)-1 {
+ // cell exists in this column => this line
+ // has more cells than the previous line
+ // (the last cell per line is ignored because cells are
+ // tab-terminated; the last cell per line describes the
+ // text before the newline/formfeed and does not belong
+ // to a column)
+
+ // print unprinted lines until beginning of block
+ pos = b.writeLines(pos, line0, this)
+ line0 = this
+
+ // column block begin
+ width := b.minwidth // minimal column width
+ discardable := true // true if all cells in this column are empty and "soft"
+ for ; this < line1; this++ {
+ line = b.lines[this]
+ if column < len(line)-1 {
+ // cell exists in this column
+ c := line[column]
+ // update width
+ if w := c.width + b.padding; w > width {
+ width = w
+ }
+ // update discardable
+ if c.width > 0 || c.htab {
+ discardable = false
+ }
+ } else {
+ break
+ }
+ }
+ // column block end
+
+ // discard empty columns if necessary
+ if discardable && b.flags&DiscardEmptyColumns != 0 {
+ width = 0
+ }
+
+ // format and print all columns to the right of this column
+ // (we know the widths of this column and all columns to the left)
+ b.widths = append(b.widths, width) // push width
+ pos = b.format(pos, line0, this)
+ b.widths = b.widths[0 : len(b.widths)-1] // pop width
+ line0 = this
+ }
+ }
+
+ // print unprinted lines until end
+ return b.writeLines(pos, line0, line1)
+}
+
+
+// Append text to current cell.
+func (b *Writer) append(text []byte) {
+ b.buf.Write(text)
+ b.cell.size += len(text)
+}
+
+
+// Update the cell width.
+func (b *Writer) updateWidth() {
+ b.cell.width += utf8.RuneCount(b.buf.Bytes()[b.pos:b.buf.Len()])
+ b.pos = b.buf.Len()
+}
+
+
+// To escape a text segment, bracket it with Escape characters.
+// For instance, the tab in this string "Ignore this tab: \xff\t\xff"
+// does not terminate a cell and constitutes a single character of
+// width one for formatting purposes.
+//
+// The value 0xff was chosen because it cannot appear in a valid UTF-8 sequence.
+//
+const Escape = '\xff'
+
+
+// Start escaped mode.
+func (b *Writer) startEscape(ch byte) {
+ switch ch {
+ case Escape:
+ b.endChar = Escape
+ case '<':
+ b.endChar = '>'
+ case '&':
+ b.endChar = ';'
+ }
+}
+
+
+// Terminate escaped mode. If the escaped text was an HTML tag, its width
+// is assumed to be zero for formatting purposes; if it was an HTML entity,
+// its width is assumed to be one. In all other cases, the width is the
+// unicode width of the text.
+//
+func (b *Writer) endEscape() {
+ switch b.endChar {
+ case Escape:
+ b.updateWidth()
+ if b.flags&StripEscape == 0 {
+ b.cell.width -= 2 // don't count the Escape chars
+ }
+ case '>': // tag of zero width
+ case ';':
+ b.cell.width++ // entity, count as one rune
+ }
+ b.pos = b.buf.Len()
+ b.endChar = 0
+}
+
+
+// Terminate the current cell by adding it to the list of cells of the
+// current line. Returns the number of cells in that line.
+//
+func (b *Writer) terminateCell(htab bool) int {
+ b.cell.htab = htab
+ line := &b.lines[len(b.lines)-1]
+ *line = append(*line, b.cell)
+ b.cell = cell{}
+ return len(*line)
+}
+
+
+func handlePanic(err *os.Error) {
+ if e := recover(); e != nil {
+ *err = e.(osError).err // re-panics if it's not a local osError
+ }
+}
+
+
+// Flush should be called after the last call to Write to ensure
+// that any data buffered in the Writer is written to output. Any
+// incomplete escape sequence at the end is simply considered
+// complete for formatting purposes.
+//
+func (b *Writer) Flush() (err os.Error) {
+ defer b.reset() // even in the presence of errors
+ defer handlePanic(&err)
+
+ // add current cell if not empty
+ if b.cell.size > 0 {
+ if b.endChar != 0 {
+ // inside escape - terminate it even if incomplete
+ b.endEscape()
+ }
+ b.terminateCell(false)
+ }
+
+ // format contents of buffer
+ b.format(0, 0, len(b.lines))
+
+ return
+}
+
+
+var hbar = []byte("---\n")
+
+// Write writes buf to the writer b.
+// The only errors returned are ones encountered
+// while writing to the underlying output stream.
+//
+func (b *Writer) Write(buf []byte) (n int, err os.Error) {
+ defer handlePanic(&err)
+
+ // split text into cells
+ n = 0
+ for i, ch := range buf {
+ if b.endChar == 0 {
+ // outside escape
+ switch ch {
+ case '\t', '\v', '\n', '\f':
+ // end of cell
+ b.append(buf[n:i])
+ b.updateWidth()
+ n = i + 1 // ch consumed
+ ncells := b.terminateCell(ch == '\t')
+ if ch == '\n' || ch == '\f' {
+ // terminate line
+ b.addLine()
+ if ch == '\f' || ncells == 1 {
+ // A '\f' always forces a flush. Otherwise, if the previous
+ // line has only one cell which does not have an impact on
+ // the formatting of the following lines (the last cell per
+ // line is ignored by format()), thus we can flush the
+ // Writer contents.
+ if err = b.Flush(); err != nil {
+ return
+ }
+ if ch == '\f' && b.flags&Debug != 0 {
+ // indicate section break
+ b.write0(hbar)
+ }
+ }
+ }
+
+ case Escape:
+ // start of escaped sequence
+ b.append(buf[n:i])
+ b.updateWidth()
+ n = i
+ if b.flags&StripEscape != 0 {
+ n++ // strip Escape
+ }
+ b.startEscape(Escape)
+
+ case '<', '&':
+ // possibly an html tag/entity
+ if b.flags&FilterHTML != 0 {
+ // begin of tag/entity
+ b.append(buf[n:i])
+ b.updateWidth()
+ n = i
+ b.startEscape(ch)
+ }
+ }
+
+ } else {
+ // inside escape
+ if ch == b.endChar {
+ // end of tag/entity
+ j := i + 1
+ if ch == Escape && b.flags&StripEscape != 0 {
+ j = i // strip Escape
+ }
+ b.append(buf[n:j])
+ n = i + 1 // ch consumed
+ b.endEscape()
+ }
+ }
+ }
+
+ // append leftover text
+ b.append(buf[n:])
+ n = len(buf)
+ return
+}
+
+
+// NewWriter allocates and initializes a new tabwriter.Writer.
+// The parameters are the same as for the the Init function.
+//
+func NewWriter(output io.Writer, minwidth, tabwidth, padding int, padchar byte, flags uint) *Writer {
+ return new(Writer).Init(output, minwidth, tabwidth, padding, padchar, flags)
+}
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