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


typedef struct {
    ngx_str_t  default_charset;
} ngx_http_charset_loc_conf_t;


static int ngx_http_charset_filter_init(ngx_cycle_t *cycle);
static void *ngx_http_charset_create_loc_conf(ngx_conf_t *cf);
static char *ngx_http_charset_merge_loc_conf(ngx_conf_t *cf,
                                             void *parent, void *child);


static ngx_command_t  ngx_http_charset_filter_commands[] = {

    {ngx_string("default_charset"),
     NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_TAKE1,
     ngx_conf_set_str_slot,
     NGX_HTTP_LOC_CONF_OFFSET,
     offsetof(ngx_http_charset_loc_conf_t, default_charset),
     NULL},

    ngx_null_command
};


static ngx_http_module_t  ngx_http_charset_filter_module_ctx = {
    NULL,                                  /* pre conf */

    NULL,                                  /* create main configuration */
    NULL,                                  /* init main configuration */

    NULL,                                  /* create server configuration */
    NULL,                                  /* merge server configuration */

    ngx_http_charset_create_loc_conf,      /* create location configuration */
    ngx_http_charset_merge_loc_conf        /* merge location configuration */
};


ngx_module_t  ngx_http_charset_filter_module = {
    NGX_MODULE,
    &ngx_http_charset_filter_module_ctx,   /* module context */
    ngx_http_charset_filter_commands,      /* module directives */
    NGX_HTTP_MODULE,                       /* module type */
    ngx_http_charset_filter_init,          /* init module */
    NULL                                   /* init child */
};


static ngx_http_output_header_filter_pt  ngx_http_next_header_filter;
#if 0
static ngx_http_output_body_filter_pt    ngx_http_next_body_filter;
#endif


static int ngx_http_charset_header_filter(ngx_http_request_t *r)
{
    ngx_http_charset_loc_conf_t  *lcf;

    lcf = ngx_http_get_module_loc_conf(r, ngx_http_charset_filter_module);

    if (lcf->default_charset.len == 0) {
        return ngx_http_next_header_filter(r);
    }

    if (r->headers_out.content_type == NULL
        || ngx_strncasecmp(r->headers_out.content_type->value.data,
                                                              "text/", 5) != 0
        || ngx_strstr(r->headers_out.content_type->value.data, "charset")
                                                                       != NULL
       )
    {
        return ngx_http_next_header_filter(r);
    }

    if (r->headers_out.status == NGX_HTTP_MOVED_PERMANENTLY
        && r->headers_out.status == NGX_HTTP_MOVED_TEMPORARILY)
    {

        /*
         * do not set charset for the redirect because NN 4.x uses this
         * charset instead of the next page charset
         */

        r->headers_out.charset.len = 0;

    } else if (r->headers_out.charset.len == 0) {
        r->headers_out.charset = lcf->default_charset;
    }

    return ngx_http_next_header_filter(r);
}


#if 0
static int ngx_http_charset_body_filter(ngx_http_request_t *r, ngx_chain_t *in)
{
    ngx_log_debug(r->connection->log, "CHARSET BODY");
    return ngx_http_next_body_filter(r, in);
}
#endif


static int ngx_http_charset_filter_init(ngx_cycle_t *cycle)
{
    ngx_http_next_header_filter = ngx_http_top_header_filter;
    ngx_http_top_header_filter = ngx_http_charset_header_filter;

#if 0
    ngx_http_next_body_filter = ngx_http_top_body_filter;
    ngx_http_top_body_filter = ngx_http_charset_body_filter;
#endif

    return NGX_OK;
}


static void *ngx_http_charset_create_loc_conf(ngx_conf_t *cf)
{
    ngx_http_charset_loc_conf_t  *lcf;

    ngx_test_null(lcf,
                  ngx_pcalloc(cf->pool, sizeof(ngx_http_charset_loc_conf_t)),
                  NGX_CONF_ERROR);

    return lcf;
}


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

    ngx_conf_merge_str_value(conf->default_charset,
                             prev->default_charset, "");

    return NGX_CONF_OK;
}