/*
Copyright IBM Corp. 2016 All Rights Reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

		 http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package couchdb

import (
	"encoding/hex"
	"fmt"
	"net/http"
	"regexp"
	"strconv"
	"strings"
	"time"

	"github.com/hyperledger/fabric/common/util"
)

var expectedDatabaseNamePattern = `[a-z][a-z0-9.$_()-]*`
var maxLength = 238

// To restrict the length of couchDB database name to the
// allowed length of 249 chars, the string length limit
// for chain/channel name, namespace/chaincode name, and
// collection name, which constitutes the database name,
// is defined.
var chainNameAllowedLength = 50
var namespaceNameAllowedLength = 50
var collectionNameAllowedLength = 50

//CreateCouchInstance creates a CouchDB instance
func CreateCouchInstance(couchDBConnectURL, id, pw string, maxRetries,
	maxRetriesOnStartup int, connectionTimeout time.Duration) (*CouchInstance, error) {

	couchConf, err := CreateConnectionDefinition(couchDBConnectURL,
		id, pw, maxRetries, maxRetriesOnStartup, connectionTimeout)
	if err != nil {
		logger.Errorf("Error during CouchDB CreateConnectionDefinition(): %s\n", err.Error())
		return nil, err
	}

	// Create the http client once
	// Clients and Transports are safe for concurrent use by multiple goroutines
	// and for efficiency should only be created once and re-used.
	client := &http.Client{Timeout: couchConf.RequestTimeout}

	transport := &http.Transport{Proxy: http.ProxyFromEnvironment}
	transport.DisableCompression = false
	client.Transport = transport

	//Create the CouchDB instance
	couchInstance := &CouchInstance{conf: *couchConf, client: client}

	connectInfo, retVal, verifyErr := couchInstance.VerifyCouchConfig()
	if verifyErr != nil {
		return nil, verifyErr
	}

	//return an error if the http return value is not 200
	if retVal.StatusCode != 200 {
		return nil, fmt.Errorf("CouchDB connection error, expecting return code of 200, received %v", retVal.StatusCode)
	}

	//check the CouchDB version number, return an error if the version is not at least 2.0.0
	errVersion := checkCouchDBVersion(connectInfo.Version)
	if errVersion != nil {
		return nil, errVersion
	}

	return couchInstance, nil
}

//checkCouchDBVersion verifies CouchDB is at least 2.0.0
func checkCouchDBVersion(version string) error {

	//split the version into parts
	majorVersion := strings.Split(version, ".")

	//check to see that the major version number is at least 2
	majorVersionInt, _ := strconv.Atoi(majorVersion[0])
	if majorVersionInt < 2 {
		return fmt.Errorf("CouchDB must be at least version 2.0.0.  Detected version %s", version)
	}

	return nil
}

//CreateCouchDatabase creates a CouchDB database object, as well as the underlying database if it does not exist
func CreateCouchDatabase(couchInstance CouchInstance, dbName string) (*CouchDatabase, error) {

	databaseName, err := mapAndValidateDatabaseName(dbName)
	if err != nil {
		logger.Errorf("Error during CouchDB CreateDatabaseIfNotExist() for dbName: %s  error: %s\n", dbName, err.Error())
		return nil, err
	}

	couchDBDatabase := CouchDatabase{CouchInstance: couchInstance, DBName: databaseName}

	// Create CouchDB database upon ledger startup, if it doesn't already exist
	_, err = couchDBDatabase.CreateDatabaseIfNotExist()
	if err != nil {
		logger.Errorf("Error during CouchDB CreateDatabaseIfNotExist() for dbName: %s  error: %s\n", dbName, err.Error())
		return nil, err
	}

	return &couchDBDatabase, nil
}

//CreateSystemDatabasesIfNotExist - creates the system databases if they do not exist
func CreateSystemDatabasesIfNotExist(couchInstance CouchInstance) error {

	dbName := "_users"
	systemCouchDBDatabase := CouchDatabase{CouchInstance: couchInstance, DBName: dbName}
	_, err := systemCouchDBDatabase.CreateDatabaseIfNotExist()
	if err != nil {
		logger.Errorf("Error during CouchDB CreateDatabaseIfNotExist() for system dbName: %s  error: %s\n", dbName, err.Error())
		return err
	}

	dbName = "_replicator"
	systemCouchDBDatabase = CouchDatabase{CouchInstance: couchInstance, DBName: dbName}
	_, err = systemCouchDBDatabase.CreateDatabaseIfNotExist()
	if err != nil {
		logger.Errorf("Error during CouchDB CreateDatabaseIfNotExist() for system dbName: %s  error: %s\n", dbName, err.Error())
		return err
	}

	dbName = "_global_changes"
	systemCouchDBDatabase = CouchDatabase{CouchInstance: couchInstance, DBName: dbName}
	_, err = systemCouchDBDatabase.CreateDatabaseIfNotExist()
	if err != nil {
		logger.Errorf("Error during CouchDB CreateDatabaseIfNotExist() for system dbName: %s  error: %s\n", dbName, err.Error())
		return err
	}

	return nil

}

// ConstructMetadataDBName truncates the db name to couchdb allowed length to
// construct the metadataDBName
func ConstructMetadataDBName(dbName string) string {
	if len(dbName) > maxLength {
		untruncatedDBName := dbName
		// Truncate the name if the length violates the allowed limit
		// As the passed dbName is same as chain/channel name, truncate using chainNameAllowedLength
		dbName = dbName[:chainNameAllowedLength]
		// For metadataDB (i.e., chain/channel DB), the dbName contains <first 50 chars
		// (i.e., chainNameAllowedLength) of chainName> + (SHA256 hash of actual chainName)
		dbName = dbName + "(" + hex.EncodeToString(util.ComputeSHA256([]byte(untruncatedDBName))) + ")"
		// 50 chars for dbName + 1 char for ( + 64 chars for sha256 + 1 char for ) = 116 chars
	}
	return dbName + "_"
}

// ConstructNamespaceDBName truncates db name to couchdb allowed length to
// construct the namespaceDBName
func ConstructNamespaceDBName(chainName, namespace string) string {
	// replace upper-case in namespace with a escape sequence '$' and the respective lower-case letter
	escapedNamespace := escapeUpperCase(namespace)
	namespaceDBName := chainName + "_" + escapedNamespace

	// For namespaceDBName of form 'chainName_namespace', on length limit violation, the truncated
	// namespaceDBName would contain <first 50 chars (i.e., chainNameAllowedLength) of chainName> + "_" +
	// <first 50 chars (i.e., namespaceNameAllowedLength) chars of namespace> +
	// (<SHA256 hash of [chainName_namespace]>)
	//
	// For namespaceDBName of form 'chainName_namespace$$collection', on length limit violation, the truncated
	// namespaceDBName would contain <first 50 chars (i.e., chainNameAllowedLength) of chainName> + "_" +
	// <first 50 chars (i.e., namespaceNameAllowedLength) of namespace> + "$$" + <first 50 chars
	// (i.e., collectionNameAllowedLength) of collection> + (<SHA256 hash of [chainName_namespace$$pcollection]>)

	if len(namespaceDBName) > maxLength {
		// Compute the hash of untruncated namespaceDBName that needs to be appended to
		// truncated namespaceDBName for maintaining uniqueness
		hashOfNamespaceDBName := hex.EncodeToString(util.ComputeSHA256([]byte(chainName + "_" + namespace)))

		// As truncated namespaceDBName is of form 'chainName_escapedNamespace', both chainName
		// and escapedNamespace need to be truncated to defined allowed length.
		if len(chainName) > chainNameAllowedLength {
			// Truncate chainName to chainNameAllowedLength
			chainName = chainName[0:chainNameAllowedLength]
		}
		// As escapedNamespace can be of either 'namespace' or 'namespace$$collectionName',
		// both 'namespace' and 'collectionName' need to be truncated to defined allowed length.
		// '$$' is used as joiner between namespace and collection name.
		// Split the escapedNamespace into escaped namespace and escaped collection name if exist.
		names := strings.Split(escapedNamespace, "$$")
		namespace := names[0]
		if len(namespace) > namespaceNameAllowedLength {
			// Truncate the namespace
			namespace = namespace[0:namespaceNameAllowedLength]
		}

		escapedNamespace = namespace

		// Check and truncate the length of collection name if exist
		if len(names) == 2 {
			collection := names[1]
			if len(collection) > collectionNameAllowedLength {
				// Truncate the escaped collection name
				collection = collection[0:collectionNameAllowedLength]
			}
			// Append truncated collection name to escapedNamespace
			escapedNamespace = escapedNamespace + "$$" + collection
		}
		// Construct and return the namespaceDBName
		// 50 chars for chainName + 1 char for '_' + 102 chars for escaped namespace + 1 char for '(' + 64 chars
		// for sha256 hash + 1 char for ')' = 219 chars
		return chainName + "_" + escapedNamespace + "(" + hashOfNamespaceDBName + ")"
	}
	return namespaceDBName
}

//mapAndValidateDatabaseName checks to see if the database name contains illegal characters
//CouchDB Rules: Only lowercase characters (a-z), digits (0-9), and any of the characters
//_, $, (, ), +, -, and / are allowed. Must begin with a letter.
//
//Restictions have already been applied to the database name from Orderer based on
//restrictions required by Kafka and couchDB (except a '.' char). The databaseName
// passed in here is expected to follow `[a-z][a-z0-9.$_-]*` pattern.
//
//This validation will simply check whether the database name matches the above pattern and will replace
// all occurence of '.' by '$'. This will not cause collisions in the transformed named
func mapAndValidateDatabaseName(databaseName string) (string, error) {
	// test Length
	if len(databaseName) <= 0 {
		return "", fmt.Errorf("Database name is illegal, cannot be empty")
	}
	if len(databaseName) > maxLength {
		return "", fmt.Errorf("Database name is illegal, cannot be longer than %d", maxLength)
	}
	re, err := regexp.Compile(expectedDatabaseNamePattern)
	if err != nil {
		return "", err
	}
	matched := re.FindString(databaseName)
	if len(matched) != len(databaseName) {
		return "", fmt.Errorf("databaseName '%s' does not matches pattern '%s'", databaseName, expectedDatabaseNamePattern)
	}
	// replace all '.' to '$'. The databaseName passed in will never contain an '$'.
	// So, this translation will not cause collisions
	databaseName = strings.Replace(databaseName, ".", "$", -1)
	return databaseName, nil
}

// escapeUpperCase replaces every upper case letter with a '$' and the respective
// lower-case letter
func escapeUpperCase(dbName string) string {
	re := regexp.MustCompile(`([A-Z])`)
	dbName = re.ReplaceAllString(dbName, "$$"+"$1")
	return strings.ToLower(dbName)
}