/*
 *
 * Copyright 2016 gRPC authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

#include "src/core/ext/transport/chttp2/transport/bin_decoder.h"
#include <grpc/support/alloc.h>
#include <grpc/support/log.h>
#include "src/core/lib/slice/slice_internal.h"
#include "src/core/lib/slice/slice_string_helpers.h"
#include "src/core/lib/support/string.h"

static uint8_t decode_table[] = {
    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,
    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,
    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,
    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 62,   0x40, 0x40, 0x40, 63,
    52,   53,   54,   55,   56,   57,   58,   59,   60,   61,   0x40, 0x40,
    0x40, 0x40, 0x40, 0x40, 0x40, 0,    1,    2,    3,    4,    5,    6,
    7,    8,    9,    10,   11,   12,   13,   14,   15,   16,   17,   18,
    19,   20,   21,   22,   23,   24,   25,   0x40, 0x40, 0x40, 0x40, 0x40,
    0x40, 26,   27,   28,   29,   30,   31,   32,   33,   34,   35,   36,
    37,   38,   39,   40,   41,   42,   43,   44,   45,   46,   47,   48,
    49,   50,   51,   0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,
    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,
    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,
    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,
    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,
    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,
    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,
    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,
    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,
    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,
    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,
    0x40, 0x40, 0x40, 0x40};

static const uint8_t tail_xtra[4] = {0, 0, 1, 2};

static bool input_is_valid(uint8_t* input_ptr, size_t length) {
  size_t i;

  for (i = 0; i < length; ++i) {
    if ((decode_table[input_ptr[i]] & 0xC0) != 0) {
      gpr_log(GPR_ERROR,
              "Base64 decoding failed, invalid character '%c' in base64 "
              "input.\n",
              (char)(*input_ptr));
      return false;
    }
  }
  return true;
}

#define COMPOSE_OUTPUT_BYTE_0(input_ptr)        \
  (uint8_t)((decode_table[input_ptr[0]] << 2) | \
            (decode_table[input_ptr[1]] >> 4))

#define COMPOSE_OUTPUT_BYTE_1(input_ptr)        \
  (uint8_t)((decode_table[input_ptr[1]] << 4) | \
            (decode_table[input_ptr[2]] >> 2))

#define COMPOSE_OUTPUT_BYTE_2(input_ptr) \
  (uint8_t)((decode_table[input_ptr[2]] << 6) | decode_table[input_ptr[3]])

bool grpc_base64_decode_partial(struct grpc_base64_decode_context* ctx) {
  size_t input_tail;

  if (ctx->input_cur > ctx->input_end || ctx->output_cur > ctx->output_end) {
    return false;
  }

  // Process a block of 4 input characters and 3 output bytes
  while (ctx->input_end >= ctx->input_cur + 4 &&
         ctx->output_end >= ctx->output_cur + 3) {
    if (!input_is_valid(ctx->input_cur, 4)) return false;
    ctx->output_cur[0] = COMPOSE_OUTPUT_BYTE_0(ctx->input_cur);
    ctx->output_cur[1] = COMPOSE_OUTPUT_BYTE_1(ctx->input_cur);
    ctx->output_cur[2] = COMPOSE_OUTPUT_BYTE_2(ctx->input_cur);
    ctx->output_cur += 3;
    ctx->input_cur += 4;
  }

  // Process the tail of input data
  input_tail = (size_t)(ctx->input_end - ctx->input_cur);
  if (input_tail == 4) {
    // Process the input data with pad chars
    if (ctx->input_cur[3] == '=') {
      if (ctx->input_cur[2] == '=' && ctx->output_end >= ctx->output_cur + 1) {
        if (!input_is_valid(ctx->input_cur, 2)) return false;
        *(ctx->output_cur++) = COMPOSE_OUTPUT_BYTE_0(ctx->input_cur);
        ctx->input_cur += 4;
      } else if (ctx->output_end >= ctx->output_cur + 2) {
        if (!input_is_valid(ctx->input_cur, 3)) return false;
        *(ctx->output_cur++) = COMPOSE_OUTPUT_BYTE_0(ctx->input_cur);
        *(ctx->output_cur++) = COMPOSE_OUTPUT_BYTE_1(ctx->input_cur);
        ;
        ctx->input_cur += 4;
      }
    }

  } else if (ctx->contains_tail && input_tail > 1) {
    // Process the input data without pad chars, but constains_tail is set
    if (ctx->output_end >= ctx->output_cur + tail_xtra[input_tail]) {
      if (!input_is_valid(ctx->input_cur, input_tail)) return false;
      switch (input_tail) {
        case 3:
          ctx->output_cur[1] = COMPOSE_OUTPUT_BYTE_1(ctx->input_cur);
        /* fallthrough */
        case 2:
          ctx->output_cur[0] = COMPOSE_OUTPUT_BYTE_0(ctx->input_cur);
      }
      ctx->output_cur += tail_xtra[input_tail];
      ctx->input_cur += input_tail;
    }
  }

  return true;
}

grpc_slice grpc_chttp2_base64_decode(grpc_exec_ctx* exec_ctx,
                                     grpc_slice input) {
  size_t input_length = GRPC_SLICE_LENGTH(input);
  size_t output_length = input_length / 4 * 3;
  struct grpc_base64_decode_context ctx;
  grpc_slice output;

  if (input_length % 4 != 0) {
    gpr_log(GPR_ERROR,
            "Base64 decoding failed, input of "
            "grpc_chttp2_base64_decode has a length of %d, which is not a "
            "multiple of 4.\n",
            (int)input_length);
    return grpc_empty_slice();
  }

  if (input_length > 0) {
    uint8_t* input_end = GRPC_SLICE_END_PTR(input);
    if (*(--input_end) == '=') {
      output_length--;
      if (*(--input_end) == '=') {
        output_length--;
      }
    }
  }
  output = GRPC_SLICE_MALLOC(output_length);

  ctx.input_cur = GRPC_SLICE_START_PTR(input);
  ctx.input_end = GRPC_SLICE_END_PTR(input);
  ctx.output_cur = GRPC_SLICE_START_PTR(output);
  ctx.output_end = GRPC_SLICE_END_PTR(output);
  ctx.contains_tail = false;

  if (!grpc_base64_decode_partial(&ctx)) {
    char* s = grpc_slice_to_c_string(input);
    gpr_log(GPR_ERROR, "Base64 decoding failed, input string:\n%s\n", s);
    gpr_free(s);
    grpc_slice_unref_internal(exec_ctx, output);
    return grpc_empty_slice();
  }
  GPR_ASSERT(ctx.output_cur == GRPC_SLICE_END_PTR(output));
  GPR_ASSERT(ctx.input_cur == GRPC_SLICE_END_PTR(input));
  return output;
}

grpc_slice grpc_chttp2_base64_decode_with_length(grpc_exec_ctx* exec_ctx,
                                                 grpc_slice input,
                                                 size_t output_length) {
  size_t input_length = GRPC_SLICE_LENGTH(input);
  grpc_slice output = GRPC_SLICE_MALLOC(output_length);
  struct grpc_base64_decode_context ctx;

  // The length of a base64 string cannot be 4 * n + 1
  if (input_length % 4 == 1) {
    gpr_log(GPR_ERROR,
            "Base64 decoding failed, input of "
            "grpc_chttp2_base64_decode_with_length has a length of %d, which "
            "has a tail of 1 byte.\n",
            (int)input_length);
    grpc_slice_unref_internal(exec_ctx, output);
    return grpc_empty_slice();
  }

  if (output_length > input_length / 4 * 3 + tail_xtra[input_length % 4]) {
    gpr_log(GPR_ERROR,
            "Base64 decoding failed, output_length %d is longer "
            "than the max possible output length %d.\n",
            (int)output_length,
            (int)(input_length / 4 * 3 + tail_xtra[input_length % 4]));
    grpc_slice_unref_internal(exec_ctx, output);
    return grpc_empty_slice();
  }

  ctx.input_cur = GRPC_SLICE_START_PTR(input);
  ctx.input_end = GRPC_SLICE_END_PTR(input);
  ctx.output_cur = GRPC_SLICE_START_PTR(output);
  ctx.output_end = GRPC_SLICE_END_PTR(output);
  ctx.contains_tail = true;

  if (!grpc_base64_decode_partial(&ctx)) {
    char* s = grpc_slice_to_c_string(input);
    gpr_log(GPR_ERROR, "Base64 decoding failed, input string:\n%s\n", s);
    gpr_free(s);
    grpc_slice_unref_internal(exec_ctx, output);
    return grpc_empty_slice();
  }
  GPR_ASSERT(ctx.output_cur == GRPC_SLICE_END_PTR(output));
  GPR_ASSERT(ctx.input_cur <= GRPC_SLICE_END_PTR(input));
  return output;
}