#lang racket/base
(require racket/contract/base
         racket/port
         racket/file
         file/gunzip
         "private/strip-prefix.rkt")

(provide
 (struct-out exn:fail:unzip:no-such-entry)

 (contract-out
  [unzip (((or/c path-string? input-port?))
          ((bytes? boolean? input-port? . -> . any))
         . ->* . any)]

  [make-filesystem-entry-reader (() (#:dest 
                                     (or/c #f path-string?)
                                     #:strip-count
                                     exact-nonnegative-integer?
                                     #:exists
                                     (or/c 'skip
                                           'error 'replace 'truncate 'truncate/replace 'append 'update
                                           'can-update 'must-truncate))
                                 . ->* .
                                 (bytes? boolean? input-port? . -> . any))]

  [read-zip-directory ((or/c path-string? input-port?) . -> . zip-directory?)]
  [zip-directory? (any/c . -> . boolean?)]
  [zip-directory-entries (zip-directory? . -> . (listof bytes?))]
  [zip-directory-contains? (zip-directory? (or/c path-string? bytes?) . -> . boolean?)]
  [zip-directory-includes-directory? (zip-directory? (or/c path-string? input-port?) . -> . boolean?)]
  [unzip-entry (((or/c path-string? input-port?) zip-directory? bytes?)
                ((bytes? boolean? input-port? . -> . any))
                . ->* .
                any)]

  [path->zip-path ((or/c string? path?) . -> . bytes?)]))

;; ===========================================================================
;; CONSTANTS
;; ===========================================================================

(define *local-file-header*                      #x04034b50)
(define *archive-extra-record*                   #x08064b50)
(define *central-file-header*                    #x02014b50)
(define *digital-signature*                      #x05054b50)
(define *zip64-end-of-central-directory-record*  #x06064b50)
(define *zip64-end-of-central-directory-locator* #x07064b50)
(define *end-of-central-directory-record*        #x06054b50)

;; ===========================================================================
;; DATATYPES AND UTILITIES
;; ===========================================================================

(define-struct (exn:fail:unzip:no-such-entry exn:fail) (entry)
  #:guard (lambda (msg cm entry who)
            (unless (bytes? entry)
              (raise-argument-error who "bytes?" entry))
            (values msg cm entry)))

;; (alistof bytes zip-entry)
(define-struct zip-directory (contents))

;; nat * boolean
(define-struct zip-entry (offset dir?))

(define (raise-unzip-error message)
  (error 'unzip "~a" message))
  
(define (raise-entry-not-found entry)
  (raise
   (make-exn:fail:unzip:no-such-entry
    (string->immutable-string
     (format "unzip: entry not found: \"~a\"" (bytes->string/latin-1 entry)))
    (current-continuation-marks)
    entry)))

;; zip-directory-entries : zip-directory -> (listof bytes)
(define (zip-directory-entries zipdir)
  (map car (zip-directory-contents zipdir)))

;; zip-directory-lookup : bytes zip-directory -> (option zip-entry)
(define (zip-directory-lookup entry zipdir)
  (let loop ([contents (zip-directory-contents zipdir)])
    (cond
     [(null? contents) #f]
     [(or (bytes=? entry (caar contents))
          (bytes=? (bytes-append entry #"/") (caar contents)))
      (cdar contents)]
     [else (loop (cdr contents))])))

;; zip-directory-contains? : zip-directory (union string path bytes) -> boolean
(define (zip-directory-contains? zipdir entry)
  (if (bytes? entry)
      (and (zip-directory-lookup entry zipdir) #t)
      (zip-directory-contains? zipdir (path->zip-path entry))))

;; matches-directory? : bytes bytes -> boolean
(define (bytes-prefix? dirname entry-name)
  (let ([dirname-len (bytes-length dirname)]
        [entry-name-len (bytes-length entry-name)])
    (and (>= entry-name-len dirname-len)
         (bytes=? (subbytes entry-name 0 dirname-len) dirname))))

;; zip-directory-includes-directory? : zip-directory (union string path bytes) -> boolean
(define (zip-directory-includes-directory? zipdir dirname)
  (if (bytes? dirname)
      (ormap (lambda (pair)
               (bytes-prefix? dirname (car pair)))
             (zip-directory-contents zipdir))
      (zip-directory-includes-directory? zipdir (path->zip-path dirname))))

;; path->zip-path : (union path string) -> bytes
(define (path->zip-path p)
  (let ([p (simplify-path p #f)])
    (if (path? p)
        (bytes->zip-bytes (path->bytes p))
        (bytes->zip-bytes (string->bytes/latin-1 p)))))

(define (bytes->zip-bytes b)
  (case (system-path-convention-type)
    [(windows) (regexp-replace* #rx#"\\\\" b #"/")]
    [else b]))

;; ===========================================================================
;; UNZIPPING ENGINE
;; ===========================================================================

(define *slash-byte* (char->integer #\/))

(define (directory-entry? name)
  (= (bytes-ref name (sub1 (bytes-length name))) *slash-byte*))

(define (read-integer count signed? in big-endian?)
  (define bstr (read-bytes count in))
  (unless (and (bytes? bstr) (= count (bytes-length bstr)))
    (error 'unzip "unexpected EOF"))
  (integer-bytes->integer bstr signed? big-endian?))

(define (peek-integer count signed? in big-endian?)
  (define bstr (peek-bytes count 0 in))
  (unless (and (bytes? bstr) (= count (bytes-length bstr)))
    (error 'unzip "unexpected EOF"))
  (integer-bytes->integer bstr signed? big-endian?))

(define (make-filter-input-port inflate orig-in)
  (define-values (in out) (make-pipe 4096))
  (values
   in
   (thread (lambda () 
             (inflate orig-in out)
             (close-output-port out)))))

(define (skip-bytes amt in)
  (read-bytes amt in)
  (void))

;; unzip-one-entry : input-port (bytes boolean input-port -> a) -> a
(define (unzip-one-entry in read-entry)
  (let ([read-int (lambda (count) (read-integer count #f in #f))])
    (let* ([signature            (read-int 4)]
           [version              (read-bytes 2 in)]
           [bits                 (read-int 2)]
           [compression          (read-int 2)]
           [time                 (read-int 2)]
           [date                 (read-int 2)]
           [crc-32               (read-int 4)]
           [compressed           (read-int 4)]
           [uncompressed         (read-int 4)]
           [filename-length      (read-int 2)]
           [extra-length         (read-int 2)]
           [filename             (read-bytes filename-length in)]
           [extra                (read-bytes extra-length in)])
      (let* ([mark (file-position in)]
             [dir? (directory-entry? filename)]
             ;; appnote VI-J : if bit 3 is set, the fields crc-32,
             ;; compressed size, and uncompressed size are set to
             ;; zero in the local header
             [in0 (if (bitwise-bit-set? bits 3)
                      in
                      (make-limited-input-port in compressed #f))])
        (dynamic-wind
            void
            (lambda ()
              (define-values (in t)
                (if (zero? compression)
                    (values in0 #f)
                    (make-filter-input-port inflate in0)))

              (read-entry filename dir? in)

              (when t (kill-thread t)))
            (lambda ()
              ;; appnote VI-C : if bit 3 is set, then the file data
              ;; is immediately followed by a data descriptor
              (if (bitwise-bit-set? bits 3)
                  (skip-bytes 12 in)
                  (file-position in (+ mark compressed))))))
      (void))))

;; find-central-directory : input-port nat -> nat nat nat
(define (find-central-directory in size)
  (let loop ([pos (- size 18)])
    (unless (positive? pos)
      (raise-unzip-error "no central directory"))
    (file-position in pos)
    (let* ([read-int (lambda (count) (read-integer count #f in #f))]
           [signature (read-int 4)])
      (if (= signature *end-of-central-directory-record*)
          (let ([disk-number       (read-int 2)]
                [directory-disk    (read-int 2)]
                [disk-entries      (read-int 2)]
                [entry-count       (read-int 2)]
                [directory-length  (read-int 4)]
                [directory-offset  (read-int 4)]
                [comment-length    (read-int 2)])
            (if (= (- size (file-position in)) comment-length)
                (values directory-offset directory-length entry-count)
                (loop (sub1 pos))))
          (loop (sub1 pos))))))

;; read-central-directory : input-port nat -> (alistof bytes zip-entry)
(define (read-central-directory in size)
  (let-values ([(offset length count) (find-central-directory in size)])
    (file-position in offset)
    (build-list count
                (lambda (i)
                  (let* ([read-int (lambda (count)
                                     (read-integer count #f in #f))]
                         [signature (read-int 4)])
                    (unless (= signature *central-file-header*)
                      (raise-unzip-error
                       (format "bad central file header signature: ~a"
                               signature)))
                    (let ([version             (read-int 2)]
                          [required            (read-int 2)]
                          [bits                (read-int 2)]
                          [compression         (read-int 2)]
                          [time                (read-int 2)]
                          [date                (read-int 2)]
                          [crc-32              (read-int 4)]
                          [compressed          (read-int 4)]
                          [uncompressed        (read-int 4)]
                          [filename-length     (read-int 2)]
                          [extra-length        (read-int 2)]
                          [comment-length      (read-int 2)]
                          [disk-number         (read-int 2)]
                          [internal-attributes (read-int 2)]
                          [external-attributes (read-int 4)]
                          [relative-offset     (read-int 4)])
                      (let* ([filename (read-bytes filename-length in)]
                             [dir? (directory-entry? filename)])
                        (skip-bytes (+ extra-length comment-length) in)
                        (cons filename (make-zip-entry relative-offset dir?)))))))))

;; ===========================================================================
;; FRONT END
;; ===========================================================================

(define (call-with-input in proc)
  ((if (input-port? in)
       (lambda (in f) (f in))
       call-with-input-file*)
   in
   proc))

;; unzip : [(or/c path-string? input-port) (bytes boolean input-port -> any)] -> any
(define unzip
  (lambda (in [read-entry (make-filesystem-entry-reader)])
    (call-with-input
     in
     (lambda (in)
       (when (= (peek-integer 4 #f in #f) *local-file-header*)
         (unzip-one-entry in read-entry)
         (unzip in read-entry))))))

(define (input-size in)
  (file-position in eof)
  (begin0
   (file-position in)
   (file-position in 0)))

;; read-zip-directory : (union string path) -> zip-directory
(define (read-zip-directory in)
  (make-zip-directory
   (call-with-input
    in
    (lambda (in)
      (read-central-directory in
                              (input-size in))))))

;; unzip-entry : (union string path) zip-directory bytes [(bytes boolean input-port -> a)] -> a
(define unzip-entry
  (lambda (in dir entry-name [read-entry (make-filesystem-entry-reader)])
    (cond
     [(zip-directory-lookup entry-name dir)
      => (lambda (entry)
           (call-with-input
            in
            (lambda (in)
              (file-position in (zip-entry-offset entry))
              (unzip-one-entry in read-entry))))]
     [else (raise-entry-not-found entry-name)])))

;; ===========================================================================
;; ENTRY PARSERS
;; ===========================================================================

;; make-filesystem-entry-reader : [output-flag] -> (bytes boolean input-port -> any)
(define make-filesystem-entry-reader
  (lambda (#:dest [dest-dir #f] #:strip-count [strip-count 0] #:exists [flag 'error])
    (lambda (name dir? in)
      (let* ([base-path (strip-prefix (bytes->path name) strip-count)]
             [path (and base-path
                        (if dest-dir
                            (build-path dest-dir base-path)
                            base-path))])
        (when path
          (if dir?
              (unless (directory-exists? path)
                (make-directory* path))
              (let ([parent (dirname path)])
                (unless (directory-exists? parent)
                  (make-directory* parent))
                (unless (and (eq? flag 'skip)
                             (file-exists? path))
                  (with-output-to-file path
                    #:exists flag
                    (lambda ()
                      (copy-port in (current-output-port))))))))))))

(define (dirname p)
  (define-values (base name dir?) (split-path p))
  (if (path? base)
      base
      (current-directory)))
