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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.

package os

import (
        "errors"
        "io"
        "syscall"
)

func (file *File) readdir(n int) (fi []FileInfo, err error) {
        // If this file has no dirinfo, create one.
        if file.dirinfo == nil {
                file.dirinfo = new(dirInfo)
        }
        d := file.dirinfo
        size := n
        if size <= 0 {
                size = 100
                n = -1
        }
        result := make([]FileInfo, 0, size) // Empty with room to grow.
        for n != 0 {
                // Refill the buffer if necessary
                if d.bufp >= d.nbuf {
                        d.bufp = 0
                        var e error
                        d.nbuf, e = file.Read(d.buf[:])
                        if e != nil && e != io.EOF {
                                return result, &PathError{"readdir", file.name, e}
                        }
                        if e == io.EOF {
                                break
                        }
                        if d.nbuf < syscall.STATFIXLEN {
                                return result, &PathError{"readdir", file.name, Eshortstat}
                        }
                }

                // Get a record from buffer
                m, _ := gbit16(d.buf[d.bufp:])
                m += 2
                if m < syscall.STATFIXLEN {
                        return result, &PathError{"readdir", file.name, Eshortstat}
                }
                dir, e := UnmarshalDir(d.buf[d.bufp : d.bufp+int(m)])
                if e != nil {
                        return result, &PathError{"readdir", file.name, e}
                }
                result = append(result, fileInfoFromStat(dir))

                d.bufp += int(m)
                n--
        }

        if n >= 0 && len(result) == 0 {
                return result, io.EOF
        }
        return result, nil
}

func (file *File) readdirnames(n int) (names []string, err error) {
        fi, err := file.Readdir(n)
        names = make([]string, len(fi))
        for i := range fi {
                names[i] = fi[i].Name()
        }
        return
}

type Dir struct {
        // system-modified data
        Type uint16 // server type
        Dev  uint32 // server subtype
        // file data
        Qid    Qid    // unique id from server
        Mode   uint32 // permissions
        Atime  uint32 // last read time
        Mtime  uint32 // last write time
        Length uint64 // file length
        Name   string // last element of path
        Uid    string // owner name
        Gid    string // group name
        Muid   string // last modifier name
}

type Qid struct {
        Path uint64 // the file server's unique identification for the file
        Vers uint32 // version number for given Path
        Type uint8  // the type of the file (syscall.QTDIR for example)
}

var nullDir = Dir{
        ^uint16(0),
        ^uint32(0),
        Qid{^uint64(0), ^uint32(0), ^uint8(0)},
        ^uint32(0),
        ^uint32(0),
        ^uint32(0),
        ^uint64(0),
        "",
        "",
        "",
        "",
}

// Null assigns members of d with special "don't care" values indicating
// they should not be written by syscall.Wstat. 
func (d *Dir) Null() {
        *d = nullDir
}

// pdir appends a 9P Stat message based on the contents of Dir d to a byte slice b.
func pdir(b []byte, d *Dir) []byte {
        n := len(b)
        b = pbit16(b, 0) // length, filled in later     
        b = pbit16(b, d.Type)
        b = pbit32(b, d.Dev)
        b = pqid(b, d.Qid)
        b = pbit32(b, d.Mode)
        b = pbit32(b, d.Atime)
        b = pbit32(b, d.Mtime)
        b = pbit64(b, d.Length)
        b = pstring(b, d.Name)
        b = pstring(b, d.Uid)
        b = pstring(b, d.Gid)
        b = pstring(b, d.Muid)
        pbit16(b[0:n], uint16(len(b)-(n+2)))
        return b
}

// UnmarshalDir reads a 9P Stat message from a 9P protocol message stored in b,
// returning the corresponding Dir struct.
func UnmarshalDir(b []byte) (d *Dir, err error) {
        n := uint16(0)
        n, b = gbit16(b)

        if int(n) != len(b) {
                return nil, Ebadstat
        }

        d = new(Dir)
        d.Type, b = gbit16(b)
        d.Dev, b = gbit32(b)
        d.Qid, b = gqid(b)
        d.Mode, b = gbit32(b)
        d.Atime, b = gbit32(b)
        d.Mtime, b = gbit32(b)
        d.Length, b = gbit64(b)
        d.Name, b = gstring(b)
        d.Uid, b = gstring(b)
        d.Gid, b = gstring(b)
        d.Muid, b = gstring(b)

        if len(b) != 0 {
                return nil, Ebadstat
        }

        return d, nil
}

// gqid reads the qid part of a 9P Stat message from a 9P protocol message stored in b,
// returning the corresponding Qid struct and the remaining slice of b.
func gqid(b []byte) (Qid, []byte) {
        var q Qid
        q.Path, b = gbit64(b)
        q.Vers, b = gbit32(b)
        q.Type, b = gbit8(b)
        return q, b
}

// pqid appends a Qid struct q to a 9P message b.
func pqid(b []byte, q Qid) []byte {
        b = pbit64(b, q.Path)
        b = pbit32(b, q.Vers)
        b = pbit8(b, q.Type)
        return b
}

// gbit8 reads a byte-sized numeric value from a 9P protocol message stored in b,
// returning the value and the remaining slice of b.
func gbit8(b []byte) (uint8, []byte) {
        return uint8(b[0]), b[1:]
}

// gbit16 reads a 16-bit numeric value from a 9P protocol message stored in b,
// returning the value and the remaining slice of b.
func gbit16(b []byte) (uint16, []byte) {
        return uint16(b[0]) | uint16(b[1])<<8, b[2:]
}

// gbit32 reads a 32-bit numeric value from a 9P protocol message stored in b,
// returning the value and the remaining slice of b.
func gbit32(b []byte) (uint32, []byte) {
        return uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24, b[4:]
}

// gbit64 reads a 64-bit numeric value from a 9P protocol message stored in b,
// returning the value and the remaining slice of b.
func gbit64(b []byte) (uint64, []byte) {
        lo, b := gbit32(b)
        hi, b := gbit32(b)
        return uint64(hi)<<32 | uint64(lo), b
}

// gstring reads a string from a 9P protocol message stored in b,
// returning the value as a Go string and the remaining slice of b.
func gstring(b []byte) (string, []byte) {
        n, b := gbit16(b)
        return string(b[0:n]), b[n:]
}

// pbit8 appends a byte-sized numeric value x to a 9P message b.
func pbit8(b []byte, x uint8) []byte {
        n := len(b)
        if n+1 > cap(b) {
                nb := make([]byte, n, 100+2*cap(b))
                copy(nb, b)
                b = nb
        }
        b = b[0 : n+1]
        b[n] = x
        return b
}

// pbit16 appends a 16-bit numeric value x to a 9P message b.
func pbit16(b []byte, x uint16) []byte {
        n := len(b)
        if n+2 > cap(b) {
                nb := make([]byte, n, 100+2*cap(b))
                copy(nb, b)
                b = nb
        }
        b = b[0 : n+2]
        b[n] = byte(x)
        b[n+1] = byte(x >> 8)
        return b
}

// pbit32 appends a 32-bit numeric value x to a 9P message b.
func pbit32(b []byte, x uint32) []byte {
        n := len(b)
        if n+4 > cap(b) {
                nb := make([]byte, n, 100+2*cap(b))
                copy(nb, b)
                b = nb
        }
        b = b[0 : n+4]
        b[n] = byte(x)
        b[n+1] = byte(x >> 8)
        b[n+2] = byte(x >> 16)
        b[n+3] = byte(x >> 24)
        return b
}

// pbit64 appends a 64-bit numeric value x to a 9P message b.
func pbit64(b []byte, x uint64) []byte {
        b = pbit32(b, uint32(x))
        b = pbit32(b, uint32(x>>32))
        return b
}

// pstring appends a Go string s to a 9P message b.
func pstring(b []byte, s string) []byte {
        if len(s) >= 1<<16 {
                panic(errors.New("string too long"))
        }
        b = pbit16(b, uint16(len(s)))
        b = append(b, s...)
        return b
}