/*
 * Copyright (C) Igor Sysoev
 */


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


#define NGX_HTTP_REWRITE_COPY_MATCH  0
#define NGX_HTTP_REWRITE_COPY_SHORT  1
#define NGX_HTTP_REWRITE_COPY_LONG   2


typedef struct {
    ngx_int_t    op;
    size_t       len;
    uintptr_t    data;
} ngx_http_rewrite_op_t;


typedef struct {
    ngx_regex_t  *regex;
    ngx_uint_t    ncaptures;

    ngx_array_t   ops;
    ngx_uint_t    size;

    ngx_str_t     re_name;
    ngx_str_t     s_name;

    ngx_uint_t    status;
    unsigned      last:1;
} ngx_http_rewrite_rule_t;


typedef struct {
    ngx_array_t   rules;
    ngx_flag_t    log;
} ngx_http_rewrite_srv_conf_t;


typedef struct {
    ngx_str_t     redirect;
} ngx_http_rewrite_loc_conf_t;


static void *ngx_http_rewrite_create_srv_conf(ngx_conf_t *cf);
static char *ngx_http_rewrite_merge_srv_conf(ngx_conf_t *cf,
                                             void *parent, void *child);
static void *ngx_http_rewrite_create_loc_conf(ngx_conf_t *cf);
static char *ngx_http_rewrite_rule(ngx_conf_t *cf, ngx_command_t *cmd,
                                   void *conf);
static char *ngx_http_redirect(ngx_conf_t *cf, void *post, void *data);
static ngx_int_t ngx_http_rewrite_init(ngx_cycle_t *cycle);


static ngx_conf_post_handler_pt  ngx_http_redirect_p = ngx_http_redirect;


static ngx_command_t  ngx_http_rewrite_commands[] = {

    { ngx_string("rewrite"),
      NGX_HTTP_SRV_CONF|NGX_CONF_TAKE23,
      ngx_http_rewrite_rule,
      NGX_HTTP_SRV_CONF_OFFSET,
      0,
      NULL },

    { ngx_string("redirect"),
      NGX_HTTP_LOC_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_slot,
      NGX_HTTP_LOC_CONF_OFFSET,
      0,
      &ngx_http_redirect_p },

    { ngx_string("rewrite_log"),
      NGX_HTTP_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_flag_slot,
      NGX_HTTP_SRV_CONF_OFFSET,
      offsetof(ngx_http_rewrite_srv_conf_t, log),
      NULL },

      ngx_null_command
};


ngx_http_module_t  ngx_http_rewrite_module_ctx = {
    NULL,                                  /* pre conf */

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

    ngx_http_rewrite_create_srv_conf,      /* create server configuration */
    ngx_http_rewrite_merge_srv_conf,       /* merge server configuration */

    ngx_http_rewrite_create_loc_conf,      /* create location configration */
    NULL,                                  /* merge location configration */
};


ngx_module_t  ngx_http_rewrite_module = {
    NGX_MODULE,
    &ngx_http_rewrite_module_ctx,          /* module context */
    ngx_http_rewrite_commands,             /* module directives */
    NGX_HTTP_MODULE,                       /* module type */
    ngx_http_rewrite_init,                 /* init module */
    NULL                                   /* init child */
};


static ngx_int_t ngx_http_rewrite_handler(ngx_http_request_t *r)
{
    int                          *captures;
    u_char                       *p;
    size_t                        len;
    uintptr_t                     data;
    ngx_int_t                     rc;
    ngx_uint_t                    i, m, n;
    ngx_str_t                     uri;
    ngx_http_rewrite_op_t        *op;
    ngx_http_rewrite_rule_t      *rule;
    ngx_http_rewrite_srv_conf_t  *scf;

    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "http rewrite handler");

    scf = ngx_http_get_module_srv_conf(r, ngx_http_rewrite_module);

    rule = scf->rules.elts;
    for (i = 0; i < scf->rules.nelts; i++) {

        if (rule[i].ncaptures) {
            captures = ngx_palloc(r->pool, rule[i].ncaptures * sizeof(int));
            if (captures == NULL) {
                return NGX_HTTP_INTERNAL_SERVER_ERROR;
            }

        } else {
            captures = NULL;
        }

        rc = ngx_regex_exec(rule[i].regex, &r->uri,
                            captures, rule[i].ncaptures);

        if (rc == NGX_REGEX_NO_MATCHED) {
            if (scf->log) {
                ngx_log_error(NGX_LOG_NOTICE, r->connection->log, 0,
                              "\"%V\" does not match \"%V\"",
                              &rule[i].re_name, &r->uri);
            }

            continue;
        }

        if (rc < 0) {
            ngx_log_error(NGX_LOG_ALERT, r->connection->log, 0,
                          ngx_regex_exec_n
                          " failed: %d on \"%V\" using \"%V\"",
                          rc, &r->uri, &rule[i].re_name);
            return NGX_HTTP_INTERNAL_SERVER_ERROR;
        }

        if (scf->log) {
            ngx_log_error(NGX_LOG_NOTICE, r->connection->log, 0,
                          "\"%V\" matches \"%V\"",
                          &rule[i].re_name, &r->uri);
        }

        if (rule[i].status) {
            return rule[i].status;
        }

        uri.len = rule[i].size;

        for (n = 1; n < (ngx_uint_t) rc; n++) {
           uri.len += captures[2 * n + 1] - captures[2 * n];
        }

        if (!(uri.data = ngx_palloc(r->pool, uri.len))) {
            return NGX_HTTP_INTERNAL_SERVER_ERROR;
        }

        p = uri.data;

        op = rule[i].ops.elts;
        for (n = 0; n < rule[i].ops.nelts; n++) {
            if (op[n].op == NGX_HTTP_REWRITE_COPY_SHORT) {
                len = op[n].len;
                data = op[n].data;
                while (len--) {
                    *p++ = (char) (data & 0xff);
                    data >>= 8;
                }

            } else if (op[n].op == NGX_HTTP_REWRITE_COPY_LONG) {
                p = ngx_cpymem(p, (void *) op[n].data, op[n].len);

            } else { /* NGX_HTTP_REWRITE_COPY_MATCH */
                m = 2 * op[n].data;
                p = ngx_cpymem(p, &r->uri.data[captures[m]],
                               captures[m + 1] - captures[m]);
            }
        }

        uri.len = p - uri.data;

        if (scf->log) {
            ngx_log_error(NGX_LOG_NOTICE, r->connection->log, 0,
                          "rewritten uri: \"%V\"", &uri);
        }

        r->uri = uri;

        if (ngx_http_set_exten(r) != NGX_OK) {
            return NGX_HTTP_INTERNAL_SERVER_ERROR;
        }

        if (rule[i].last) {
            return NGX_DECLINED;
        }
    }

    return NGX_DECLINED;
}


static ngx_int_t ngx_http_redirect_handler(ngx_http_request_t *r)
{
    u_char                       *p;
    ngx_http_rewrite_loc_conf_t  *rlcf;

    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "http redirect handler");

    rlcf = ngx_http_get_module_loc_conf(r, ngx_http_rewrite_module);

    r->headers_out.location = ngx_list_push(&r->headers_out.headers);
    if (r->headers_out.location == NULL) {
        return NGX_HTTP_INTERNAL_SERVER_ERROR;
    }

    if (rlcf->redirect.data[0] != '/') {
        r->headers_out.location->key.len = sizeof("Location") - 1;
        r->headers_out.location->key.data = (u_char *) "Location";
    }

    r->headers_out.location->value.len =  rlcf->redirect.len
                                          + r->unparsed_uri.len;
    r->headers_out.location->value.data = ngx_palloc(r->pool,
                                           r->headers_out.location->value.len);

    if (r->headers_out.location->value.data == NULL) {
        return NGX_HTTP_INTERNAL_SERVER_ERROR;
    }

    p = ngx_cpymem(r->headers_out.location->value.data, rlcf->redirect.data,
                   rlcf->redirect.len);
    p = ngx_cpystrn(p, r->unparsed_uri.data + 1, r->unparsed_uri.len);

    return NGX_HTTP_MOVED_TEMPORARILY;
}


static void *ngx_http_rewrite_create_srv_conf(ngx_conf_t *cf)
{
    ngx_http_rewrite_srv_conf_t  *conf;

    if (!(conf = ngx_palloc(cf->pool, sizeof(ngx_http_rewrite_srv_conf_t)))) {
        return NGX_CONF_ERROR;
    }

    ngx_init_array(conf->rules, cf->pool, 5, sizeof(ngx_http_rewrite_rule_t),
                   NGX_CONF_ERROR);

    conf->log = NGX_CONF_UNSET;

    return conf;
}


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

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

    return NGX_CONF_OK;
}


static void *ngx_http_rewrite_create_loc_conf(ngx_conf_t *cf)
{
    ngx_http_rewrite_loc_conf_t  *conf;

    if (!(conf = ngx_pcalloc(cf->pool, sizeof(ngx_http_rewrite_loc_conf_t)))) {
        return NGX_CONF_ERROR;
    }

    return conf;
}


static char *ngx_http_rewrite_rule(ngx_conf_t *cf, ngx_command_t *cmd,
                                   void *conf)
{
    ngx_http_rewrite_srv_conf_t *scf = conf;

    u_char                   *data, *p;
    size_t                    len;
    ngx_str_t                *value, err;
    ngx_uint_t                i, n;
    ngx_http_rewrite_op_t    *op;
    ngx_http_rewrite_rule_t  *rule;
    u_char                    errstr[NGX_MAX_CONF_ERRSTR];

    if (!(rule = ngx_push_array(&scf->rules))) {
        return NGX_CONF_ERROR;
    }

    ngx_init_array(rule->ops, cf->pool, 5, sizeof(ngx_http_rewrite_op_t),
                   NGX_CONF_ERROR);

    rule->ncaptures = 0;
    rule->size = 0;
    rule->status = 0;
    rule->last = 0;

    value = cf->args->elts;

    /* STUB */ {
        err.len = NGX_MAX_CONF_ERRSTR;
        err.data = errstr;

        rule->regex = ngx_regex_compile(&value[1], 0, cf->pool, &err);
    
        if (rule->regex == NULL) {
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0, "%s", err.data);
            return NGX_CONF_ERROR;
        }
    
        rule->re_name = value[1];
        rule->s_name = value[2];

        if (ngx_strcasecmp(value[2].data, "forbidden:") == 0) {

            if (cf->args->nelts == 3) {
                rule->status = NGX_HTTP_FORBIDDEN;
                rule->last = 1;
                return NGX_CONF_OK;
            }

            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "invalid parameter \"%V\"", &value[3]);
            return NGX_CONF_ERROR;
        }

        for (i = 0; i < value[2].len; /* void */) {

            if (!(op = ngx_push_array(&rule->ops))) {
                return NGX_CONF_ERROR;
            }

            data = &value[2].data[i];

            if (value[2].data[i] == '$'
                && i < value[2].len
                && value[2].data[i + 1] >= '1'
                && value[2].data[i + 1] <= '9')
            {
                op->op = NGX_HTTP_REWRITE_COPY_MATCH; 
                op->data = value[2].data[++i] - '0';

                if (rule->ncaptures < op->data) {
                    rule->ncaptures = op->data;
                }

                i++;

            } else {
                i++;

                while (i < value[2].len && value[2].data[i] != '$') {
                    i++;
                }

                len = &value[2].data[i] - data;
                rule->size += len;

                if (len) {

                    op->len = len;

                    if (len <= sizeof(uintptr_t)) {
                        op->op = NGX_HTTP_REWRITE_COPY_SHORT; 
                        op->data = 0;

                        while (len--) {
                            op->data <<= 8;
                            op->data |= data[len];
                        }

                    } else {
                        op->op = NGX_HTTP_REWRITE_COPY_LONG;

                        if (!(p = ngx_palloc(cf->pool, len))) {
                            return NGX_CONF_ERROR;
                        }

                        ngx_memcpy(p, data, len);
                        op->data = (uintptr_t) p;
                    }
                }
            }
        }

        n = ngx_regex_capture_count(rule->regex);

        if (rule->ncaptures > n) {
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "pattern \"%V\" has less captures "
                               "than referrenced in substitution \"%V\"",
                               &value[1], &value[2]);
            return NGX_CONF_ERROR;
        }

        if (rule->ncaptures < n) {
            rule->ncaptures = n;
        }

        if (rule->ncaptures) {
            rule->ncaptures = (rule->ncaptures + 1) * 3;
        }

        if (cf->args->nelts > 3) {
            if (ngx_strcmp(value[3].data, "last") == 0) {
                rule->last = 1;

            } else {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                   "invalid parameter \"%V\"", &value[3]);
                return NGX_CONF_ERROR;
            }
        }
    }

    return NGX_CONF_OK;
}


static char *ngx_http_redirect(ngx_conf_t *cf, void *post, void *data)
{
    ngx_http_core_loc_conf_t  *clcf;

    clcf = ngx_http_conf_get_module_loc_conf(cf, ngx_http_core_module);
    clcf->handler = ngx_http_redirect_handler;

    return NGX_CONF_OK;
}


static ngx_int_t ngx_http_rewrite_init(ngx_cycle_t *cycle)
{
    ngx_http_handler_pt        *h;
    ngx_http_core_main_conf_t  *cmcf;

    cmcf = ngx_http_cycle_get_module_main_conf(cycle, ngx_http_core_module);

    h = ngx_push_array(&cmcf->phases[NGX_HTTP_REWRITE_PHASE].handlers);
    if (h == NULL) {
        return NGX_ERROR;
    }

    *h = ngx_http_rewrite_handler;

    return NGX_OK;
}