#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_http.h>


static ngx_http_output_header_filter_pt  ngx_http_next_header_filter;

static ngx_int_t ngx_http_key_header_filter(ngx_http_request_t*);

static ngx_int_t ngx_http_key_header_init(ngx_conf_t*);
static void* ngx_http_key_header_create_conf(ngx_conf_t*);
static char* ngx_http_key_header_merge_loc_conf(ngx_conf_t*, void* parent, void* child);

typedef struct
{
    ngx_flag_t enabled;
}
ngx_http_key_header_loc_conf_t; 



static ngx_command_t
ngx_http_key_header_filter_commands[] =
{
   {
     ngx_string("send_cache_key"),
     NGX_HTTP_MAIN_CONF | NGX_HTTP_SRV_CONF | NGX_HTTP_LOC_CONF | NGX_CONF_FLAG, 
     ngx_conf_set_flag_slot,
     NGX_HTTP_LOC_CONF_OFFSET, 
     offsetof(ngx_http_key_header_loc_conf_t, enabled),
     NULL
   },
      
   ngx_null_command
};



static ngx_http_module_t 
ngx_http_key_header_filter_module_ctx =
{
    NULL,                              /* Pre config */
    ngx_http_key_header_init,          /* Post config */
    NULL,                              /* Create main config */
    NULL,                              /* Init main config */
    NULL,                              /* Create server config */
    NULL,                              /* Merge server config */
    ngx_http_key_header_create_conf,   /* Create loc config */
    ngx_http_key_header_merge_loc_conf /* Merge loc config */
};



static ngx_int_t
ngx_http_key_header_init(ngx_conf_t*)
{
    ngx_http_next_header_filter = ngx_http_top_header_filter;
    ngx_http_top_header_filter = ngx_http_key_header_filter;
    return NGX_OK;
}


static void*
ngx_http_key_header_create_conf(ngx_conf_t *cf) 
{
    ngx_http_key_header_loc_conf_t *conf;
    conf = ngx_pcalloc(cf->pool, sizeof(ngx_http_key_header_loc_conf_t));
    if(conf == NULL) {
        return NGX_CONF_ERROR;
    }

    conf->enabled = NGX_CONF_UNSET;
    return conf;
}


static char*
ngx_http_key_header_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child) 
{
    ngx_http_key_header_loc_conf_t *prev = parent;
    ngx_http_key_header_loc_conf_t *conf = child;

    ngx_conf_merge_value(conf->enabled, prev->enabled, 0);

    return NGX_CONF_OK;
}

ngx_module_t ngx_http_key_header_module =
{
    NGX_MODULE_V1,
    &ngx_http_key_header_filter_module_ctx,     /* module context */
    ngx_http_key_header_filter_commands,        /* module directives */
    NGX_HTTP_MODULE,                            /* module type */
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NGX_MODULE_V1_PADDING
};

static ngx_int_t
ngx_http_key_header_filter(ngx_http_request_t *r )
{
    if(r->loc_conf != NULL) {
        ngx_http_key_header_loc_conf_t *conf = ngx_http_get_module_loc_conf(r, ngx_http_key_header_module);
        if(conf->enabled) {
            ngx_table_elt_t *h;
            h = ngx_list_push(&r->headers_out.headers);
            if(h == NULL) {
                return NGX_ERROR;
            }
            
            u_char hexKey[2 * NGX_HTTP_CACHE_KEY_LEN + 1];
            ngx_hex_dump(hexKey, r->cache->key, NGX_HTTP_CACHE_KEY_LEN);

            h->hash = 1;
            ngx_str_set(&h->key, "X-Cache-Key");
            ngx_str_set(&h->value, hexKey);
        }
    }
    return ngx_http_next_header_filter(r);   
}