diff --git a/.idea/php.xml b/.idea/php.xml
index d5e9721..f162a2c 100644
--- a/.idea/php.xml
+++ b/.idea/php.xml
@@ -56,6 +56,10 @@
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       <path value="$PROJECT_DIR$/vendor/vimeo/psalm" />
       <path value="$PROJECT_DIR$/vendor/webmozart/path-util" />
+      <path value="$PROJECT_DIR$/vendor/psr/http-message" />
+      <path value="$PROJECT_DIR$/vendor/dhii/collections-interface" />
+      <path value="$PROJECT_DIR$/vendor/dhii/data-key-value-aware-interface" />
+      <path value="$PROJECT_DIR$/vendor/dhii/data-identifiable-interface" />
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   </component>
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diff --git a/.idea/wordpress-interface.iml b/.idea/wordpress-interface.iml
index ea0aed4..4dc58d5 100644
--- a/.idea/wordpress-interface.iml
+++ b/.idea/wordpress-interface.iml
@@ -60,6 +60,10 @@
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       <excludeFolder url="file://$MODULE_DIR$/vendor/vimeo/psalm" />
       <excludeFolder url="file://$MODULE_DIR$/vendor/webmozart/path-util" />
+      <excludeFolder url="file://$MODULE_DIR$/vendor/psr/http-message" />
+      <excludeFolder url="file://$MODULE_DIR$/vendor/dhii/collections-interface" />
+      <excludeFolder url="file://$MODULE_DIR$/vendor/dhii/data-key-value-aware-interface" />
+      <excludeFolder url="file://$MODULE_DIR$/vendor/dhii/data-identifiable-interface" />
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diff --git a/composer.json b/composer.json
index 114136c..e3bb666 100644
--- a/composer.json
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@@ -12,7 +12,13 @@
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+    "dhii/data-key-value-aware-interface": "^0.2",
+    "dhii/data-identifiable-interface": "^0.1",
+    "dhii/collections-interface": "^0.3-alpha4",
+    "psr/http-message": "^1.0",
+    "psr/container": "^1.0 | ^2.0",
+    "symfony/polyfill-php80": "^1.19"
   },
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diff --git a/composer.lock b/composer.lock
index 8858861..661055b 100644
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+                "url": "https://github.com/Dhii/collections-interface.git",
+                "reference": "da334f75f6477ef7eecaf28df1d5253fe05684ee"
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+                "psr/container": "^1.0"
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+            "require-dev": {
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+                "slevomat/coding-standard": "^6.0",
+                "vimeo/psalm": "^3.11.7 | ^4.0"
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+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Dhii Team",
+                    "email": "development@dhii.co"
+                },
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+                    "name": "Anton Ukhanev",
+                    "email": "xedin.unknown@gmail.com"
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+                "source": "https://github.com/Dhii/collections-interface/tree/v0.3.0-alpha4"
+            },
+            "time": "2021-03-09T17:36:34+00:00"
+        },
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+            "version": "dev-develop",
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+                "type": "git",
+                "url": "https://github.com/Dhii/data-identifiable-interface.git",
+                "reference": "ee063fd2827d9de9e6f92c5abeb759c4f52f5558"
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+                "dhii/php-cs-fixer-config": "dev-php-5.3",
+                "phpunit/phpunit": "^4.8",
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+            "license": [
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+            "authors": [
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+                    "email": "development@dhii.co"
+                }
+            ],
+            "description": "Interfaces for objects that are identifiable.",
+            "support": {
+                "issues": "https://github.com/Dhii/data-identifiable-interface/issues",
+                "source": "https://github.com/Dhii/data-identifiable-interface/tree/v0.1.1-alpha1"
+            },
+            "time": "2018-05-10T15:15:49+00:00"
+        },
+        {
+            "name": "dhii/data-key-value-aware-interface",
+            "version": "dev-develop",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/Dhii/data-key-value-aware-interface.git",
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+            "require-dev": {
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+                "dhii/php-cs-fixer-config": "dev-php-5.3",
+                "dhii/stringable-interface": "^0.1",
+                "phpunit/phpunit": "4.*",
+                "ptrofimov/xpmock": "^1.1"
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+            "type": "library",
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+            "autoload": {
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+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Dhii Team",
+                    "email": "development@dhii.co"
+                }
+            ],
+            "description": "Interfaces that aim to increase interoperability of value objects",
+            "support": {
+                "issues": "https://github.com/Dhii/data-key-value-aware-interface/issues",
+                "source": "https://github.com/Dhii/data-key-value-aware-interface/tree/v0.2-alpha2"
+            },
+            "time": "2018-02-11T12:52:01+00:00"
+        },
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             "version": "0.2.x-dev",
@@ -221,6 +382,113 @@
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+            "version": "1.0.0",
+            "source": {
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+                "url": "https://github.com/php-fig/container.git",
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+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
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+            "authors": [
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+                    "name": "PHP-FIG",
+                    "homepage": "http://www.php-fig.org/"
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+            "description": "Common Container Interface (PHP FIG PSR-11)",
+            "homepage": "https://github.com/php-fig/container",
+            "keywords": [
+                "PSR-11",
+                "container",
+                "container-interface",
+                "container-interop",
+                "psr"
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+            "support": {
+                "issues": "https://github.com/php-fig/container/issues",
+                "source": "https://github.com/php-fig/container/tree/master"
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+            "time": "2017-02-14T16:28:37+00:00"
+        },
+        {
+            "name": "psr/http-message",
+            "version": "dev-master",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/php-fig/http-message.git",
+                "reference": "efd67d1dc14a7ef4fc4e518e7dee91c271d524e4"
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+                "reference": "efd67d1dc14a7ef4fc4e518e7dee91c271d524e4",
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+            "extra": {
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+                    "Psr\\Http\\Message\\": "src/"
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+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
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+            "authors": [
+                {
+                    "name": "PHP-FIG",
+                    "homepage": "http://www.php-fig.org/"
+                }
+            ],
+            "description": "Common interface for HTTP messages",
+            "homepage": "https://github.com/php-fig/http-message",
+            "keywords": [
+                "http",
+                "http-message",
+                "psr",
+                "psr-7",
+                "request",
+                "response"
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+            "support": {
+                "source": "https://github.com/php-fig/http-message/tree/master"
+            },
+            "time": "2019-08-29T13:16:46+00:00"
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@@ -403,12 +671,12 @@
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@@ -473,7 +741,7 @@
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@@ -633,16 +901,16 @@
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@@ -650,7 +918,8 @@
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+                "phpstan/phpstan": "^0.12.55",
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@@ -676,7 +945,7 @@
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+                "source": "https://github.com/composer/xdebug-handler/tree/2.0.0"
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@@ -692,7 +961,7 @@
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@@ -1527,16 +1796,16 @@
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+            "version": "0.5.4",
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@@ -1554,7 +1823,7 @@
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@@ -1571,9 +1840,9 @@
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-                "source": "https://github.com/phpstan/phpdoc-parser/tree/0.4.12"
+                "source": "https://github.com/phpstan/phpdoc-parser/tree/0.5.4"
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-            "time": "2021-02-28T14:30:10+00:00"
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@@ -1954,59 +2223,6 @@
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@@ -2782,7 +2998,7 @@
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@@ -2790,12 +3006,12 @@
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                 "url": "https://github.com/squizlabs/PHP_CodeSniffer.git",
-                "reference": "d02296fe420483999d2ad8cd8bdceb43014dc83e"
+                "reference": "342dbf2481b7a3c0b799fecd7b7c4def3c0408e3"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/squizlabs/PHP_CodeSniffer/zipball/d02296fe420483999d2ad8cd8bdceb43014dc83e",
-                "reference": "d02296fe420483999d2ad8cd8bdceb43014dc83e",
+                "url": "https://api.github.com/repos/squizlabs/PHP_CodeSniffer/zipball/342dbf2481b7a3c0b799fecd7b7c4def3c0408e3",
+                "reference": "342dbf2481b7a3c0b799fecd7b7c4def3c0408e3",
                 "shasum": ""
             },
             "require": {
@@ -2839,7 +3055,7 @@
                 "source": "https://github.com/squizlabs/PHP_CodeSniffer",
                 "wiki": "https://github.com/squizlabs/PHP_CodeSniffer/wiki"
             },
-            "time": "2021-03-05T07:46:22+00:00"
+            "time": "2021-04-16T04:22:12+00:00"
         },
         {
             "name": "symfony/console",
@@ -2847,12 +3063,12 @@
             "source": {
                 "type": "git",
                 "url": "https://github.com/symfony/console.git",
-                "reference": "c98349bda966c70d6c08b4cd8658377c94166492"
+                "reference": "36bbd079b69b94bcc9c9c9e1e37ca3b1e7971625"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/symfony/console/zipball/c98349bda966c70d6c08b4cd8658377c94166492",
-                "reference": "c98349bda966c70d6c08b4cd8658377c94166492",
+                "url": "https://api.github.com/repos/symfony/console/zipball/36bbd079b69b94bcc9c9c9e1e37ca3b1e7971625",
+                "reference": "36bbd079b69b94bcc9c9c9e1e37ca3b1e7971625",
                 "shasum": ""
             },
             "require": {
@@ -2928,7 +3144,7 @@
                     "type": "tidelift"
                 }
             ],
-            "time": "2021-02-22T18:44:15+00:00"
+            "time": "2021-04-16T17:32:19+00:00"
         },
         {
             "name": "symfony/polyfill-ctype",
@@ -3300,20 +3516,20 @@
             "source": {
                 "type": "git",
                 "url": "https://github.com/vimeo/psalm.git",
-                "reference": "96e0743892f3239f089b13eb978c33d743cfe904"
+                "reference": "ee778e9246ac33451a0f582d60a602288e687f98"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/vimeo/psalm/zipball/96e0743892f3239f089b13eb978c33d743cfe904",
-                "reference": "96e0743892f3239f089b13eb978c33d743cfe904",
+                "url": "https://api.github.com/repos/vimeo/psalm/zipball/ee778e9246ac33451a0f582d60a602288e687f98",
+                "reference": "ee778e9246ac33451a0f582d60a602288e687f98",
                 "shasum": ""
             },
             "require": {
-                "amphp/amp": "^2.1",
+                "amphp/amp": "^2.4.2",
                 "amphp/byte-stream": "^1.5",
                 "composer/package-versions-deprecated": "^1.8.0",
                 "composer/semver": "^1.4 || ^2.0 || ^3.0",
-                "composer/xdebug-handler": "^1.1",
+                "composer/xdebug-handler": "^1.1 || ^2.0",
                 "dnoegel/php-xdg-base-dir": "^0.1.1",
                 "ext-dom": "*",
                 "ext-json": "*",
@@ -3335,7 +3551,6 @@
                 "psalm/psalm": "self.version"
             },
             "require-dev": {
-                "amphp/amp": "^2.4.2",
                 "bamarni/composer-bin-plugin": "^1.2",
                 "brianium/paratest": "^4.0||^6.0",
                 "ext-curl": "*",
@@ -3348,6 +3563,7 @@
                 "slevomat/coding-standard": "^6.3.11",
                 "squizlabs/php_codesniffer": "^3.5",
                 "symfony/process": "^4.3",
+                "weirdan/phpunit-appveyor-reporter": "^1.0.0",
                 "weirdan/prophecy-shim": "^1.0 || ^2.0"
             },
             "suggest": {
@@ -3398,7 +3614,7 @@
                 "issues": "https://github.com/vimeo/psalm/issues",
                 "source": "https://github.com/vimeo/psalm/tree/master"
             },
-            "time": "2021-03-05T05:39:25+00:00"
+            "time": "2021-04-16T20:07:47+00:00"
         },
         {
             "name": "webmozart/assert",
diff --git a/src/Acl/CapableUserInterface.php b/src/Acl/CapableUserInterface.php
new file mode 100644
index 0000000..6c45117
--- /dev/null
+++ b/src/Acl/CapableUserInterface.php
@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\Acl;
+
+/**
+ * Represents a user who may have certain privileges.
+ */
+interface CapableUserInterface
+{
+    public function isAllowed(string $resourceKey, string $capability): bool;
+}
diff --git a/src/Acl/PrivilegeInterface.php b/src/Acl/PrivilegeInterface.php
new file mode 100644
index 0000000..d4a61e3
--- /dev/null
+++ b/src/Acl/PrivilegeInterface.php
@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\Acl;
+
+use Dhii\Data\KeyAwareInterface;
+use Stringable;
+
+/**
+ * Represents a role privilege.
+ */
+interface PrivilegeInterface extends KeyAwareInterface, Stringable
+{
+    public function getResource(): Stringable;
+
+    /**
+     * @param string $resourceKey The resource key, e.g. "posts".
+     * @return string[] A list of capabilities, e.g. "create" or "read".
+     */
+    public function getCapabilitiesForResource(string $resourceKey): array;
+}
diff --git a/src/Acl/RoleInterface.php b/src/Acl/RoleInterface.php
new file mode 100644
index 0000000..0754ca2
--- /dev/null
+++ b/src/Acl/RoleInterface.php
@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\Acl;
+
+use Dhii\Data\KeyAwareInterface;
+use Stringable;
+
+/**
+ * Represents a WordPress user role.
+ */
+interface RoleInterface extends KeyAwareInterface, Stringable
+{
+    /**
+     * @return iterable<string>
+     */
+    public function getPrivileges(): iterable;
+
+    public function isAllowed(string $resourceKey, string $capability): bool;
+}
diff --git a/src/Entity/EntityInterface.php b/src/Entity/EntityInterface.php
new file mode 100644
index 0000000..5c51f3c
--- /dev/null
+++ b/src/Entity/EntityInterface.php
@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\Entity;
+
+use Dhii\Collection\MapInterface;
+use Dhii\Data\IdAwareInterface;
+
+/**
+ * Represents a WordPress entity, a.k.a. "object".
+ */
+interface EntityInterface extends IdAwareInterface, MapInterface
+{
+    public function getEntityType(): string;
+
+    public function getAttributes(): MapInterface;
+
+    public function getQuery(): EntityQueryInterface;
+}
diff --git a/src/Entity/EntityQueryInterface.php b/src/Entity/EntityQueryInterface.php
new file mode 100644
index 0000000..3084726
--- /dev/null
+++ b/src/Entity/EntityQueryInterface.php
@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\Entity;
+
+use WpOop\WordPress\Meta\MetaQueryInterface;
+use WpOop\WordPress\Post\PostQueryInterface;
+use WpOop\WordPress\Query\QueryInterface;
+use WpOop\WordPress\Query\QueryResultInterface;
+use WpOop\WordPress\Taxonomy\TermQueryInterface;
+
+/**
+ * Represents a query for entities.
+ */
+interface EntityQueryInterface extends QueryInterface
+{
+    /**
+     * @return EntityQueryResultInterface
+     */
+    public function query(): QueryResultInterface;
+
+    /**
+     * @param iterable<int> $termIds
+     * @return static
+     */
+    public function withIdIn(iterable $termIds): TermQueryInterface;
+
+    /**
+     * @param iterable<int> $termIds
+     * @return static
+     */
+    public function withIdNotIn(iterable $termIds): TermQueryInterface;
+
+    /**
+     * @return static
+     */
+    public function withMeta(MetaQueryInterface $query): self;
+}
diff --git a/src/Entity/EntityQueryResultInterface.php b/src/Entity/EntityQueryResultInterface.php
new file mode 100644
index 0000000..b9d6666
--- /dev/null
+++ b/src/Entity/EntityQueryResultInterface.php
@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\Entity;
+
+use WpOop\WordPress\Query\QueryResultInterface;
+
+/**
+ * Represents a WordPress post query result.
+ *
+ * @extends Traversable<EntityInterface>
+ */
+interface EntityQueryResultInterface extends QueryResultInterface
+{
+    /**
+     * @return iterable<int>
+     */
+    public function getIds(): iterable;
+}
diff --git a/src/Meta/MetaInterface.php b/src/Meta/MetaInterface.php
new file mode 100644
index 0000000..8847cb5
--- /dev/null
+++ b/src/Meta/MetaInterface.php
@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\Meta;
+
+/**
+ * Represents a meta value.
+ */
+interface MetaInterface
+{
+
+}
diff --git a/src/Meta/MetaQueryInterface.php b/src/Meta/MetaQueryInterface.php
new file mode 100644
index 0000000..71187ae
--- /dev/null
+++ b/src/Meta/MetaQueryInterface.php
@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\Meta;
+
+
+use WpOop\WordPress\Query\ClauseQueryInterface;
+use WpOop\WordPress\Query\QueryConfiguratorInterface;
+
+/**
+ * @psalm-type FieldConfig = array{key: string, value: mixed, compare: string, type: string}
+ * @psalm-type MetaQueryConfig = array{relation: 'AND'|'OR', ...: FieldConfig|MetaQueryConfig}
+ */
+
+/**
+ * Represents a WordPress meta query.
+ */
+interface MetaQueryInterface extends ClauseQueryInterface
+{
+    /**
+     * @return static
+     */
+    public function withExists(string $key): self;
+
+    /**
+     * @param self $query The subquery query to add.
+     * @return static
+     */
+    public function withQuery(QueryConfiguratorInterface $query): QueryConfiguratorInterface;
+
+    /**
+     * @return array The configuration for {@see WP_Meta_Query}.
+     *               An array containing the `relation` key, as well as unlimited numeric keys each of which
+     *               contains a {@see FieldConfig}.
+     * @psalm-return MetaQueryConfig
+     */
+    public function getConfig(): array;
+}
diff --git a/src/Post/PostInterface.php b/src/Post/PostInterface.php
new file mode 100644
index 0000000..576ebf0
--- /dev/null
+++ b/src/Post/PostInterface.php
@@ -0,0 +1,107 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\Post;
+
+use DateTimeInterface;
+use Dhii\Data\KeyAwareInterface;
+use Dhii\Data\NameAwareInterface;
+use Dhii\Util\String\TitleAwareInterface;
+use Psr\Http\Message\UriInterface;
+use Stringable;
+use WpOop\WordPress\Entity\EntityInterface;
+use WpOop\WordPress\User\UserInterface;
+
+/**
+ * Represents a WordPress post.
+ */
+interface PostInterface extends EntityInterface, TitleAwareInterface, NameAwareInterface, KeyAwareInterface
+{
+    /**
+     * Signifies that a post has been published.
+     *
+     */
+    public const STATUS_PUBLISHED = 'published';
+    /**
+     * Signifies that a post has been scheduled to be published in the future.
+     *
+     */
+    public const STATUS_FUTURE = 'future';
+    /**
+     * Signifies that a post is incomplete.
+     *
+     */
+    public const STATUS_DRAFT = 'draft';
+    /**
+     * Signifies that a post is awaiting to be published.
+     *
+     */
+    public const STATUS_PENDING = 'pending';
+    /**
+     * Signifies that a post is not intended to be publicly viewable.
+     *
+     */
+    public const STATUS_PRIVATE = 'private';
+    /**
+     * Signifies that a post has been trashed.
+     *
+     */
+    public const STATUS_TRASH = 'trash';
+    /**
+     * Signifies that a post has been created automatically.
+     *
+     */
+    public const STATUS_AUTO_DRAFT = 'auto-draft';
+    /**
+     * Signifies that a post's status is determined by its parent post.
+     *
+     */
+    public const STATUS_INHERIT = 'inherit';
+
+    public function getId(): int;
+
+    public function getParentId(): int;
+
+    public function getKey(): string;
+
+    public function getAuthor(): UserInterface;
+
+    public function getCreatedAt(): DateTimeInterface;
+
+    public function getUpdatedAt(): DateTimeInterface;
+
+    public function getContent(): Stringable;
+
+    public function getTitle(): string;
+
+    public function getExcerpt(): string;
+
+    public function getStatus(): string;
+
+    public function getIsAllowComments(): bool;
+
+    public function getIsAllowedPing(): bool;
+
+    public function getPassword(): string;
+
+    public function getName(): string;
+
+    /**
+     * @return iterable<UriInterface>
+     */
+    public function getUrlsToPing(): iterable;
+
+    /**
+     * @return iterable<UriInterface>
+     */
+    public function getUrlsPinged(): iterable;
+
+    public function getGuid(): string;
+
+    public function getMenuOrder(): int;
+
+    public function getType(): string;
+
+    public function getMimeType(): string;
+}
diff --git a/src/Post/PostQueryInterface.php b/src/Post/PostQueryInterface.php
new file mode 100644
index 0000000..e039a22
--- /dev/null
+++ b/src/Post/PostQueryInterface.php
@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\Post;
+
+use WpOop\WordPress\Entity\EntityQueryInterface;
+use WpOop\WordPress\Entity\EntityQueryResultInterface;
+use WpOop\WordPress\Meta\MetaQueryInterface;
+use WpOop\WordPress\Query\QueryResultInterface;
+
+/**
+ * Represents a WordPress post query.
+ */
+interface PostQueryInterface extends EntityQueryInterface
+{
+    /**
+     * @return PostQueryResultInterface
+     */
+    public function query(): QueryResultInterface;
+
+    /**
+     * @param int[] $ids
+     * @return static
+     */
+    public function withAuthorIdIn(array $ids): self;
+
+    /**
+     * @param int[] $ids
+     * @return static
+     */
+    public function withAuthorIdNotIn(array $ids): self;
+}
diff --git a/src/Post/PostQueryResultInterface.php b/src/Post/PostQueryResultInterface.php
new file mode 100644
index 0000000..b484348
--- /dev/null
+++ b/src/Post/PostQueryResultInterface.php
@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\Post;
+
+use Traversable;
+use WpOop\WordPress\Entity\EntityQueryResultInterface;
+
+/**
+ * Represents a WordPress post query result.
+ *
+ * @extends Traversable<PostInterface>
+ */
+interface PostQueryResultInterface extends EntityQueryResultInterface
+{
+}
diff --git a/src/Query/ClauseQueryInterface.php b/src/Query/ClauseQueryInterface.php
new file mode 100644
index 0000000..4ebb387
--- /dev/null
+++ b/src/Query/ClauseQueryInterface.php
@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\Query;
+
+
+interface ClauseQueryInterface extends QueryConfiguratorInterface
+{
+    public function getJoinClause(): string;
+
+    public function getWhereClause(): string;
+}
diff --git a/src/Query/QueryConfiguratorInterface.php b/src/Query/QueryConfiguratorInterface.php
new file mode 100644
index 0000000..315ccbb
--- /dev/null
+++ b/src/Query/QueryConfiguratorInterface.php
@@ -0,0 +1,109 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\Query;
+
+use DateTimeInterface;
+use WpOop\WordPress\Meta\MetaQueryInterface;
+
+/**
+ * Represents a query that can be built.
+ */
+interface QueryConfiguratorInterface
+{
+    public const RELATION_TYPE_AND = 'AND';
+    public const RELATION_TYPE_OR = 'OR';
+
+    /**
+     * @return static
+     */
+    public function withLt(string $key, string $value): self;
+
+    /**
+     * @return static
+     */
+    public function withLtEq(string $key, string $value): self;
+
+    /**
+     * @return static
+     */
+    public function withGt(string $key, string $value): self;
+
+    /**
+     * @return static
+     */
+    public function withGtEq(string $key, string $value): self;
+
+    /**
+     * @return static
+     */
+    public function withEq(string $key, string $value): self;
+
+    /**
+     * @return static
+     */
+    public function withNotEq(string $key, string $value): self;
+
+    /**
+     * Like
+     *
+     * @return static
+     */
+    public function withApprox(string $key, string $value): self;
+
+    /**
+     * Not like
+     *
+     * @return static
+     */
+    public function withNotApprox(string $key, string $value): self;
+
+    /**
+     * @param iterable<string> $values
+     * @return static
+     */
+    public function withIn(string $key, iterable $values): self;
+
+    /**
+     * @param iterable<string> $values
+     * @return static
+     */
+    public function withNotIn(string $key, iterable $values): self;
+
+    /**
+     * @param numeric|string|DateTimeInterface $lowerBound
+     * @param numeric|string|DateTimeInterface $upperBound
+     * @return static
+     */
+    public function withBetween(string $key, $lowerBound, $upperBound): self;
+
+    /**
+     * @param numeric|string|DateTimeInterface $lowerBound
+     * @param numeric|string|DateTimeInterface $upperBound
+     * @return static
+     */
+    public function withNotBetween(string $key, $lowerBound,  $upperBound): self;
+
+    /**
+     * @return static
+     */
+    public function withRegexp(string $key, string $regexp): self;
+
+    /**
+     * @return static
+     */
+    public function withNotRegexp(string $key, string $regexp): self;
+
+    /**
+     * @param self $query The query to add a relationship with.
+     * @return static
+     */
+    public function withQuery(QueryConfiguratorInterface $query): self;
+
+    /**
+     * @param self::RELATION_TYPE_* $relation
+     * @return static
+     */
+    public function withRelation(string $relation): self;
+}
diff --git a/src/Query/QueryInterface.php b/src/Query/QueryInterface.php
new file mode 100644
index 0000000..a906f73
--- /dev/null
+++ b/src/Query/QueryInterface.php
@@ -0,0 +1,23 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\Query;
+
+/**
+ * Represents a generic query.
+ */
+interface QueryInterface
+{
+    public function query(): QueryResultInterface;
+
+    /**
+     * @return static
+     */
+    public function withLimit(int $limit): self;
+
+    /**
+     * @return static
+     */
+    public function withOffset(int $offset): self;
+}
diff --git a/src/Query/QueryResultInterface.php b/src/Query/QueryResultInterface.php
new file mode 100644
index 0000000..8e1dc6b
--- /dev/null
+++ b/src/Query/QueryResultInterface.php
@@ -0,0 +1,23 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\Query;
+
+use Dhii\Collection\CountableListInterface;
+use Dhii\Collection\MapInterface;
+use Traversable;
+
+/**
+ * Represents a generic query result.
+ *
+ * @extends Traversable<MapInterface>
+ */
+interface QueryResultInterface extends Traversable, CountableListInterface
+{
+    /**
+     * The total number of items found on all pages.
+     *
+     */
+    public function getTotalCount(): int;
+}
diff --git a/src/Query/RecordQueryConfiguratorInterface.php b/src/Query/RecordQueryConfiguratorInterface.php
new file mode 100644
index 0000000..bf07f8b
--- /dev/null
+++ b/src/Query/RecordQueryConfiguratorInterface.php
@@ -0,0 +1,23 @@
+<?php
+
+
+namespace WpOop\WordPress\Query;
+
+
+use WpOop\WordPress\Entity\EntityQueryResultInterface;
+
+/**
+ * A query for records
+ */
+interface RecordQueryConfiguratorInterface extends QueryConfiguratorInterface
+{
+
+    public function query(): EntityQueryResultInterface;
+
+    /**
+     * @return static
+     */
+    public function withLimit(int $limit): self;
+
+    public function withOffset(int $offset): self;
+}
diff --git a/src/Taxonomy/TaxonomyInterface.php b/src/Taxonomy/TaxonomyInterface.php
new file mode 100644
index 0000000..47d7b02
--- /dev/null
+++ b/src/Taxonomy/TaxonomyInterface.php
@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\Taxonomy;
+
+use Dhii\Util\String\DescriptionAwareInterface;
+use Dhii\Util\String\LabelAwareInterface;
+
+/**
+ * Represents a WordPress taxonomy.
+ */
+interface TaxonomyInterface extends LabelAwareInterface, DescriptionAwareInterface
+{
+    public function getKey(): string;
+
+    public function getLabel(): string;
+
+    public function getDescription(): string;
+
+    public function getIsPublic(): bool;
+
+    public function getIsHierarchical(): bool;
+
+    /**
+     * @return TermQueryInterface A term query set to retrieve terms for this taxonomy.
+     */
+    public function getTermQuery(): TermQueryInterface;
+}
diff --git a/src/Taxonomy/TermInterface.php b/src/Taxonomy/TermInterface.php
new file mode 100644
index 0000000..f90a98c
--- /dev/null
+++ b/src/Taxonomy/TermInterface.php
@@ -0,0 +1,25 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\Taxonomy;
+
+use Dhii\Data\KeyAwareInterface;
+use Dhii\Util\String\LabelAwareInterface;
+use WpOop\WordPress\Entity\EntityInterface;
+
+/**
+ * Represents a WordPress taxonomy term.
+ */
+interface TermInterface extends EntityInterface, LabelAwareInterface, KeyAwareInterface
+{
+    public function getId(): int;
+
+    public function getKey(): string;
+
+    public function getLabel(): string;
+
+    public function getDescription(): string;
+
+    public function getTaxonomy(): TaxonomyInterface;
+}
diff --git a/src/Taxonomy/TermQueryInterface.php b/src/Taxonomy/TermQueryInterface.php
new file mode 100644
index 0000000..77a3627
--- /dev/null
+++ b/src/Taxonomy/TermQueryInterface.php
@@ -0,0 +1,87 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\Taxonomy;
+
+use WpOop\WordPress\Meta\MetaQueryInterface;
+use WpOop\WordPress\Entity\EntityQueryInterface;
+use WpOop\WordPress\Query\QueryResultInterface;
+
+/**
+ * Represents a query for WordPress terms.
+ */
+interface TermQueryInterface extends EntityQueryInterface
+{
+    /**
+     * @return TermQueryResultInterface
+     */
+    public function query(): QueryResultInterface;
+
+    /**
+     * @return static
+     */
+    public function withEntityType(string $type): TermQueryInterface;
+
+    /**
+     * @param iterable<string> $taxonomyKeys
+     * @return static
+     */
+    public function withTaxonomyIn(iterable $taxonomyKeys): TermQueryInterface;
+
+    /**
+     * @param iterable<int> $objectIds
+     * @return static
+     */
+    public function withObjectIdIn(iterable $objectIds): TermQueryInterface;
+
+    /**
+     * @param iterable<int> $objectIds
+     * @return static
+     */
+    public function withObjectIdNotIn(iterable $objectIds): TermQueryInterface;
+
+    /**
+     * @param iterable<int> $termIds
+     * @return static
+     */
+    public function withIdNotInTreesOf(iterable $termIds): TermQueryInterface;
+
+    /**
+     * @param iterable<string> $keys
+     * @return static
+     */
+    public function withKeyIn(iterable $keys): TermQueryInterface;
+
+    /**
+     * @param iterable<string> $labels
+     * @return static
+     */
+    public function withLabelIn(iterable $labels): TermQueryInterface;
+
+    /**
+     * @return static
+     */
+    public function withIsHierarchical(bool $isHierarchical): TermQueryInterface;
+
+    /**
+     * @param string $keyOrLabelPart The part of the key or label that the terms have to match.
+     * @return static
+     */
+    public function withKeyOrLabelLike(string $keyOrLabelPart): TermQueryInterface;
+
+    /**
+     * @return static
+     */
+    public function withLabelLike(string $labelPart): TermQueryInterface;
+
+    /**
+     * @return static
+     */
+    public function withDescriptionLike(string $descriptionPart): TermQueryInterface;
+
+    /**
+     * @return static
+     */
+    public function withParentId(int $termId): TermQueryInterface;
+}
diff --git a/src/Taxonomy/TermQueryResultInterface.php b/src/Taxonomy/TermQueryResultInterface.php
new file mode 100644
index 0000000..7e2cd59
--- /dev/null
+++ b/src/Taxonomy/TermQueryResultInterface.php
@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\Taxonomy;
+
+use WpOop\WordPress\Entity\EntityQueryResultInterface;
+use Traversable;
+
+/**
+ * Represents a result of a WordPress term query.
+ *
+ * @extends Traversable<TermInterface>
+ */
+interface TermQueryResultInterface extends EntityQueryResultInterface
+{
+}
diff --git a/src/User/UserInterface.php b/src/User/UserInterface.php
new file mode 100644
index 0000000..b697e26
--- /dev/null
+++ b/src/User/UserInterface.php
@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\User;
+
+use DateTimeInterface;
+use Psr\Http\Message\UriInterface;
+use WpOop\WordPress\Acl\CapableUserInterface;
+use WpOop\WordPress\Acl\RoleInterface;
+use WpOop\WordPress\Entity\EntityInterface;
+
+/**
+ * Represents a WordPress user.
+ */
+interface UserInterface extends EntityInterface, CapableUserInterface
+{
+    public function getLogin(): int;
+
+    public function getPassword(): string;
+
+    public function getUsername(): string;
+
+    public function getEmail(): string;
+
+    public function getUrl(): UriInterface;
+
+    public function getCreatedAt(): DateTimeInterface;
+
+    public function getActivationKey(): string;
+
+    /**
+     * @return iterable<RoleInterface>
+     */
+    public function getRoles(): iterable;
+}
diff --git a/src/User/UserQueryInterface.php b/src/User/UserQueryInterface.php
new file mode 100644
index 0000000..c3c9de9
--- /dev/null
+++ b/src/User/UserQueryInterface.php
@@ -0,0 +1,32 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\User;
+
+use WpOop\WordPress\Entity\EntityQueryInterface;
+use WpOop\WordPress\Entity\EntityQueryResultInterface;
+use WpOop\WordPress\Query\QueryResultInterface;
+
+/**
+ * Represents a WordPress user query.
+ */
+interface UserQueryInterface extends EntityQueryInterface
+{
+    /**
+     * @return UserQueryResultInterface
+     */
+    public function query(): QueryResultInterface;
+
+    /**
+     * @param iterable<string> $roleKeys
+     * @return static
+     */
+    public function withRoleIn(iterable $roleKeys): self;
+
+    /**
+     * @param iterable<string> $roleKeys
+     * @return static
+     */
+    public function withRoleNotIn(iterable $roleKeys): self;
+}
diff --git a/src/User/UserQueryResultInterface.php b/src/User/UserQueryResultInterface.php
new file mode 100644
index 0000000..1cd2db3
--- /dev/null
+++ b/src/User/UserQueryResultInterface.php
@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace WpOop\WordPress\User;
+
+use WpOop\WordPress\Entity\EntityQueryResultInterface;
+use Traversable;
+
+/**
+ * Represents a user query result.
+ *
+ * @extends Traversable<UserInterface>
+ */
+interface UserQueryResultInterface extends EntityQueryResultInterface
+{
+
+}