// RUN: %verify "%s" --unicode-char:false ../Unicode/UnicodeStringsWithoutUnicodeChar.dfy
// RUN: %verify "%s" --unicode-char:true ../Unicode/UnicodeStringsWithUnicodeChar.dfy

/// ================================================
///  Serialization from Values.JSON to bytes (Spec)
/// ================================================
///
/// This is the high-level spec.  For the implementation, see
/// ``JSON.Serializer.dfy``.

include "../BoundedInts.dfy"
include "../NonlinearArithmetic/Logarithm.dfy"
include "../Collections/Sequences/Seq.dfy"
/// include one of these two files externally as well:
/// "../Unicode/UnicodeStringsWithoutUnicodeChar.dfy"
/// "../Unicode/UnicodeStringsWithUnicodeChar.dfy"

include "Values.dfy"
include "Errors.dfy"
include "Utils/Str.dfy"

module {:options "-functionSyntax:4"} JSON.Spec {
  import opened BoundedInts

  import opened Utils.Str
  import opened Values
  import opened Wrappers
  import opened Errors
  import opened UnicodeStrings
  import opened Logarithm

  import Seq

  type bytes = seq<uint8>
  type Result<+T> = SerializationResult<T>

  function EscapeUnicode(c: uint16): seq<uint16> {
    var sStr := Str.OfNat(c as nat, 16);
    Seq.MembershipImpliesIndexing(c => 0 <= c as int < 128, sStr);
    var s := ASCIIToUTF16(sStr);
    assert |s| <= 4 by {
      assert c as nat <= 0xFFFF;
      assert Log(16, c as nat) <= Log(16, 0xFFFF) by {
        LemmaLogIsOrdered(16, c as nat, 0xFFFF);
      }
      assert Log(16, 0xFFFF) == 3 by { reveal Log(); }
    }
    s + seq(4 - |s|, _ => ' ' as uint16)
  }

  function Escape(str: seq<uint16>, start: nat := 0): seq<uint16>
    decreases |str| - start
  {
    if start >= |str| then []
    else
      (match str[start]
       case 0x22 => ASCIIToUTF16("\\\"") // quotation mark
       case 0x5C => ASCIIToUTF16("\\\\")  // reverse solidus
       case 0x08 => ASCIIToUTF16("\\b")  // backspace
       case 0x0C => ASCIIToUTF16("\\f")  // form feed
       case 0x0A => ASCIIToUTF16("\\n")  // line feed
       case 0x0D => ASCIIToUTF16("\\r")  // carriage return
       case 0x09 => ASCIIToUTF16("\\t")  // tab
       case c =>
      if c < 0x001F then ASCIIToUTF16("\\u") + EscapeUnicode(c)
      else [str[start]])
      + Escape(str, start + 1)
  }

  function EscapeToUTF8(str: string, start: nat := 0): Result<bytes> {
    var utf16 :- ToUTF16Checked(str).ToResult'(SerializationError.InvalidUnicode);
    var escaped := Escape(utf16);
    var utf32 :- FromUTF16Checked(escaped).ToResult'(SerializationError.InvalidUnicode);
    ToUTF8Checked(utf32).ToResult'(SerializationError.InvalidUnicode)
  }

  // Can fail due to invalid UTF-16 sequences in a string when --unicode-char is off
  function String(str: string): Result<bytes> {
    var inBytes :- EscapeToUTF8(str);
    Success(ASCIIToUTF8("\"") + inBytes + ASCIIToUTF8("\""))
  }

  lemma OfIntOnlyASCII(n: int)
    ensures
      && var s := Str.OfInt(n);
      && forall i | 0 <= i < |s| :: 0 <= s[i] as int < 128
  {
    var s := Str.OfInt(n);
    forall i | 0 <= i < |s| ensures 0 <= s[i] as int < 128 {
      if i == 0 {
      } else {
        var isHexDigit := c => c in HEX_DIGITS;
        assert CharStrConversion.NumberStr(s, '-', isHexDigit);
        assert isHexDigit(s[i]);
      }
    }
  }

  function IntToBytes(n: int): bytes {
    var s := Str.OfInt(n);
    OfIntOnlyASCII(n);
    ASCIIToUTF8(s)
  }

  function Number(dec: Decimal): Result<bytes> {
    Success(IntToBytes(dec.n) +
            (if dec.e10 == 0 then []
            else ASCIIToUTF8("e") + IntToBytes(dec.e10)))
  }

  function KeyValue(kv: (string, JSON)): Result<bytes> {
    var key :- String(kv.0);
    var value :- JSON(kv.1);
    Success(key + ASCIIToUTF8(":") + value)
  }

  function Join(sep: bytes, items: seq<Result<bytes>>): Result<bytes> {
    if |items| == 0 then
      Success([])
    else
      var first :- items[0];
      if |items| == 1 then
        Success(first)
      else
        var rest :- Join(sep, items[1..]);
        Success(first + sep + rest)
  }

  function Object(obj: seq<(string, JSON)>): Result<bytes> {
    var middle :- Join(ASCIIToUTF8(","), seq(|obj|, i requires 0 <= i < |obj| => KeyValue(obj[i])));
    Success(ASCIIToUTF8("{") + middle + ASCIIToUTF8("}"))
  }

  function Array(arr: seq<JSON>): Result<bytes> {
    var middle :- Join(ASCIIToUTF8(","), seq(|arr|, i requires 0 <= i < |arr| => JSON(arr[i])));
    Success(ASCIIToUTF8("[") + middle + ASCIIToUTF8("]"))
  }

  function JSON(js: JSON): Result<bytes> {
    match js
    case Null => Success(ASCIIToUTF8("null"))
    case Bool(b) => Success(if b then ASCIIToUTF8("true") else ASCIIToUTF8("false"))
    case String(str) => String(str)
    case Number(dec) => Number(dec)
    case Object(obj) => Object(obj)
    case Array(arr) => Array(arr)
  }
}