// 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 <assert.h>
#include <stdio.h>
#include <string.h>

#include "erl_nif.h"
#include "erl_nif_compat.h"
#include "yajl/yajl_parse.h"
#include "yajl/yajl_parser.h"
#include "yajl/yajl_lex.h"

typedef struct {
    ERL_NIF_TERM head;
    ErlNifEnv* env;
} decode_ctx;

#define ENV(ctxarg) (((decode_ctx*)ctxarg)->env)

#define CONTINUE 1
#define CANCEL 0


static ERL_NIF_TERM
make_error(yajl_handle handle, ErlNifEnv* env)
{
    char* yajlError = (char*) yajl_get_error(handle, 0, NULL, 0);
    ERL_NIF_TERM errMsg;

    if(yajlError != NULL)
    {
        errMsg = enif_make_string(env, yajlError, ERL_NIF_LATIN1);
        yajl_free_error(handle, (unsigned char*) yajlError);
    }
    else
    {
        errMsg = enif_make_string(env, "unknown parse error", ERL_NIF_LATIN1);
    }

    return enif_make_tuple(env, 2,
        enif_make_atom(env, "error"),
        enif_make_tuple(env, 2,
            enif_make_uint(env, handle->bytesConsumed),
            errMsg
        )
    );
}


static void
add_to_head(void* vctx, ERL_NIF_TERM newhead)
{
    decode_ctx* ctx = (decode_ctx*)vctx;
    ctx->head = enif_make_list_cell(ctx->env, newhead, ctx->head);
}

static int
decode_null(void* ctx)
{
    add_to_head(ctx, enif_make_atom(ENV(ctx), "null"));
    return CONTINUE;
}

static int
decode_boolean(void* ctx, int val)
{
    add_to_head(ctx, enif_make_atom(ENV(ctx), val ? "true" : "false"));
    return CONTINUE;
}

static int
decode_number(void * ctx, const char * numberVal, unsigned int numberLen)
{
    // scan in the input to see if it's a float or int

    int numberType = 0; // 0 means integer, 1 means float
    unsigned int i;
    ErlNifBinary bin;
    int missingDot = 1;
    unsigned int expPos;

    for(i=0; i<numberLen; i++) {
        switch (numberVal[i]) {
        case '.':
            missingDot = 0;
            numberType = 1; // it's  a float
            goto loopend;
        case 'E':
        case 'e':
            expPos = i;
            numberType = 1; // it's  a float
            goto loopend;
        }
    }
loopend:
    if ((numberType == 1) && missingDot)
    {
        if(!enif_alloc_binary_compat(ENV(ctx), numberLen + 2, &bin))
        {
            return CANCEL;
        }
        memcpy(bin.data, numberVal, expPos);
        bin.data[expPos] = '.';
        bin.data[expPos + 1] = '0';
        memcpy(bin.data + expPos + 2, numberVal + expPos, numberLen - expPos);
    }
    else
    {
        if(!enif_alloc_binary_compat(ENV(ctx), numberLen, &bin))
        {
            return CANCEL;
        }
        memcpy(bin.data, numberVal, numberLen);
    }
    add_to_head(ctx, enif_make_tuple(ENV(ctx), 2,
                        enif_make_int(ENV(ctx), numberType),
                        enif_make_binary(ENV(ctx), &bin)));
    return CONTINUE;
}


static int
decode_string(void* ctx, const unsigned char* data, unsigned int size)
{
    ErlNifBinary bin;
    if(!enif_alloc_binary_compat(ENV(ctx), size, &bin))
    {
        return CANCEL;
    }
    memcpy(bin.data, data, size);
    add_to_head(ctx, enif_make_binary(ENV(ctx), &bin));
    return CONTINUE;
}

static int
decode_start_array(void* ctx)
{
    add_to_head(ctx, enif_make_int(ENV(ctx), 0));
    return CONTINUE;
}


static int
decode_end_array(void* ctx)
{
    add_to_head(ctx, enif_make_int(ENV(ctx), 1));
    return CONTINUE;
}


static int
decode_start_map(void* ctx)
{
    add_to_head(ctx, enif_make_int(ENV(ctx), 2));
    return CONTINUE;
}


static int
decode_end_map(void* ctx)
{
    add_to_head(ctx, enif_make_int(ENV(ctx), 3));
    return CONTINUE;
}


static int
decode_map_key(void* ctx, const unsigned char* data, unsigned int size)
{
    ErlNifBinary bin;
    if(!enif_alloc_binary_compat(ENV(ctx), size, &bin))
    {
       return CANCEL;
    }
    memcpy(bin.data, data, size);
    add_to_head(ctx, enif_make_tuple(ENV(ctx), 2,
                        enif_make_int(ENV(ctx), 3),
                        enif_make_binary(ENV(ctx), &bin)));
    return CONTINUE;
}

static yajl_callbacks
decoder_callbacks = {
    decode_null,
    decode_boolean,
    NULL,
    NULL,
    decode_number,
    decode_string,
    decode_start_map,
    decode_map_key,
    decode_end_map,
    decode_start_array,
    decode_end_array
};

static int
check_rest(unsigned char* data, unsigned int size, unsigned int used)
{
    unsigned int i = 0;
    for(i = used; i < size; i++)
    {
        switch(data[i])
        {
            case ' ':
            case '\t':
            case '\r':
            case '\n':
                continue;
            default:
                return CANCEL;
        }
    }

    return CONTINUE;
}

ERL_NIF_TERM
reverse_tokens(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
{
    decode_ctx ctx;
    yajl_parser_config conf = {0, 1}; // No comments, check utf8
    yajl_handle handle = yajl_alloc(&decoder_callbacks, &conf, NULL, &ctx);
    yajl_status status;
    unsigned int used;
    ErlNifBinary bin;
    ERL_NIF_TERM ret;

    ctx.env = env;
    ctx.head = enif_make_list_from_array(env, NULL, 0);

    if(!enif_inspect_iolist_as_binary(env, argv[0], &bin))
    {
        ret = enif_make_badarg(env);
        goto done;
    }

    status = yajl_parse(handle, bin.data, bin.size);
    used = handle->bytesConsumed;

    // Parsing something like "2.0" (without quotes) will
    // cause a spurious semi-error. We add the extra size
    // check so that "2008-20-10" doesn't pass.
    if(status == yajl_status_insufficient_data && used == bin.size)
    {
        status = yajl_parse_complete(handle);
    }

    if(status == yajl_status_ok && used != bin.size)
    {
        if(check_rest(bin.data, bin.size, used) == CANCEL)
        {
            ret = enif_make_tuple(env, 2,
                enif_make_atom(env, "error"),
                enif_make_atom(env, "garbage_after_value")
            );
            goto done;
        }
    }

    switch(status)
    {
        case yajl_status_ok:
            ret = enif_make_tuple(env, 2, enif_make_atom(env, "ok"), ctx.head);
            goto done;

        case yajl_status_error:
            ret = make_error(handle, env);
            goto done;

        case yajl_status_insufficient_data:
            ret = enif_make_tuple(env, 2,
                enif_make_atom(env, "error"),
                enif_make_atom(env, "insufficient_data")
            );
            goto done;

        case yajl_status_client_canceled:
        /* the only time we do this is when we can't allocate a binary. */
            ret = enif_make_tuple(env, 2,
                enif_make_atom(env, "error"),
                enif_make_atom(env, "insufficient_memory")
            );
            goto done;

        default:
            ret = enif_make_tuple(env, 2,
                enif_make_atom(env, "error"),
                enif_make_atom(env, "unknown")
            );
            goto done;
    }

done:
    if(handle != NULL) yajl_free(handle);
    return ret;
}