Add indexer doc about AeFinder introduction and how to set up an AeFinder plugin

docs-sphinx/index.rst

@@ -24,6 +24,7 @@ Welcome to AElf's official documentation!
    Running a side chain <tutorials/cross-chain/index>
    Running AElf on the cloud <tutorials/cloud/index>
    Smart Contract Developing Demos <tutorials/smart-contract-demos/index>
+   Building an indexer plugin <tutorials/indexer/index>
 
 
 .. toctree::

docs-sphinx/tutorials/indexer/aelf-indexer-introduction.rst

@@ -0,0 +1,84 @@
+Introduction
+============
+
+"Indexing" refers to the process of synchronizing block data from AElf blockchain 
+nodes to a locally centralized ElasticSearch environment for storage.
+
+This system then provides various data interfaces. Whether you are a dApp 
+developer looking to build exciting applications on the AElf blockchain or just 
+curious about how the AElf node's scanning system operates, this document is suitable 
+for you.
+
+Overall Workflow
+----------------
+
+The overall workflow of the indexer, starting from the AElf nodes, pushing block 
+data to the DApp, getting the desired on-chain data.
+
+.. image:: indexer-overall.png
+   :alt: Overall Workflow
+
+1. AElf Node Push
+~~~~~~~~~~~~~~~~~
+
+The AElf Indexer enhances functionality for AElf nodes, enabling automatic asynchronous 
+or synchronous transmission of historical or latest block information to the RabbitMQ 
+message queue. The AElf Indexer's storage module then receives and processes the 
+relevant block data.
+
+2. Indexer Storage
+~~~~~~~~~~~~~~~~~~
+
+Upon receiving block data from RabbitMQ, the Indexer storage module identifies and 
+processes the data, identifying any forked blocks. During this process, some auxiliary 
+data is stored in MongoDB, but ultimately, all block data (excluding forks) is stored 
+in Elasticsearch. The data is organized into different indices based on the structures 
+of Block, Transaction, and Logevent.
+
+3. Indexer Subscription and Push
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+**Subscription:**
+Consumers of the AElf Indexer can initiate subscriptions for block-related information 
+through the subscription API. Currently, subscriptions primarily support block height, 
+block transactions, and block transaction event dimensions, especially subscribing based 
+on transaction events, which is applicable in various scenarios. After making a subscription 
+API request with a client ID, a subscription version is returned, which is noted and later 
+written into the client interface plugin developed subsequently.
+
+**Push:**
+Upon receiving a subscription request, the AElf Indexer subscription and push module 
+fetches data from Elasticsearch based on the subscription requirements and streams 
+the data to the Kafka message queue.
+
+4. Indexer Client
+~~~~~~~~~~~~~~~~~
+
+The Indexer client receives subscribed block data from Kafka and passes it to the 
+interface plugin for processing. Interface plugins are developed separately and 
+handle various transactions and events within blocks, storing the processed result 
+set in a specific Elasticsearch index. Based on requirements, GraphQL interfaces are 
+defined, utilizing Elasticsearch as a data source to develop business logic and expose 
+the data externally.
+
+5. DApp Integration
+~~~~~~~~~~~~~~~~~~~~
+
+Within the DApp, desired data can be requested by directly calling the GraphQL interface 
+exposed by the AElf Indexer client interface plugin, based on the client ID.
+
+Why Indexer Is Needed
+----------------------
+
+The role of the Indexer in the AElf blockchain is crucial. It synchronizes block 
+information from AElf nodes to a local ElasticSearch environment, providing developers 
+with convenient and efficient data access interfaces. By enabling real-time or historical 
+data asynchronous or synchronous transmission, the Indexer enhances the functionality of 
+AElf nodes, allowing them to handle block information more flexibly. Moreover, it offers 
+robust data querying and subscription mechanisms. This mechanism enables decentralized 
+application (DApp) developers to easily subscribe to and retrieve relevant information 
+about specific blocks, transactions, or events, facilitating the development of applications 
+on the AElf blockchain. With the Indexer, developers can establish indexes, query, and analyze 
+blockchain data more effortlessly, improving DApp development efficiency and providing 
+convenience for broader blockchain data utilization.
+