Refactore all CRUD functions to a new core package.

This is a long pending refactor. All the DB, query, CRUD, and related
logic scattered across HTTP handlers are now moved into a central
`core` package with clean, abstracted methods, decoupling HTTP
handlers from executing direct DB queries and other business logic.

eg: `core.CreateList()`, `core.GetLists()` etc.

- Remove obsolete subscriber methods.
- Move optin hook queries to core.
- Move campaign methods to `core`.
- Move all campaign methods to `core`.
- Move public page functions to `core`.
- Move all template functions to `core`.
- Move media and settings function to `core`.
- Move handler middleware functions to `core`.
- Move all bounce functions to `core`.
- Move all dashboard functions to `core`.
- Fix GetLists() not honouring type
- Fix unwrapped JSON responses.
- Clean up obsolete pre-core util function.
- Replace SQL array null check with cardinality check.
- Fix missing validations in `core` queries.
- Remove superfluous deps on internal `subimporter`.
- Add dashboard functions to `core`.
- Fix broken domain ban check.
- Fix broken subscriber check middleware.
- Remove redundant error handling.
- Remove obsolete functions.
- Remove obsolete structs.
- Remove obsolete queries and DB functions.
- Document the `core` package.

models/queries.go

@@ -0,0 +1,141 @@
+package models
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+
+	"github.com/jmoiron/sqlx"
+	"github.com/lib/pq"
+)
+
+// Queries contains all prepared SQL queries.
+type Queries struct {
+	GetDashboardCharts *sqlx.Stmt `query:"get-dashboard-charts"`
+	GetDashboardCounts *sqlx.Stmt `query:"get-dashboard-counts"`
+
+	InsertSubscriber                *sqlx.Stmt `query:"insert-subscriber"`
+	UpsertSubscriber                *sqlx.Stmt `query:"upsert-subscriber"`
+	UpsertBlocklistSubscriber       *sqlx.Stmt `query:"upsert-blocklist-subscriber"`
+	GetSubscriber                   *sqlx.Stmt `query:"get-subscriber"`
+	GetSubscribersByEmails          *sqlx.Stmt `query:"get-subscribers-by-emails"`
+	GetSubscriberLists              *sqlx.Stmt `query:"get-subscriber-lists"`
+	GetSubscriberListsLazy          *sqlx.Stmt `query:"get-subscriber-lists-lazy"`
+	UpdateSubscriber                *sqlx.Stmt `query:"update-subscriber"`
+	BlocklistSubscribers            *sqlx.Stmt `query:"blocklist-subscribers"`
+	AddSubscribersToLists           *sqlx.Stmt `query:"add-subscribers-to-lists"`
+	DeleteSubscriptions             *sqlx.Stmt `query:"delete-subscriptions"`
+	ConfirmSubscriptionOptin        *sqlx.Stmt `query:"confirm-subscription-optin"`
+	UnsubscribeSubscribersFromLists *sqlx.Stmt `query:"unsubscribe-subscribers-from-lists"`
+	DeleteSubscribers               *sqlx.Stmt `query:"delete-subscribers"`
+	Unsubscribe                     *sqlx.Stmt `query:"unsubscribe"`
+	ExportSubscriberData            *sqlx.Stmt `query:"export-subscriber-data"`
+
+	// Non-prepared arbitrary subscriber queries.
+	QuerySubscribers                       string `query:"query-subscribers"`
+	QuerySubscribersCount                  string `query:"query-subscribers-count"`
+	QuerySubscribersForExport              string `query:"query-subscribers-for-export"`
+	QuerySubscribersTpl                    string `query:"query-subscribers-template"`
+	DeleteSubscribersByQuery               string `query:"delete-subscribers-by-query"`
+	AddSubscribersToListsByQuery           string `query:"add-subscribers-to-lists-by-query"`
+	BlocklistSubscribersByQuery            string `query:"blocklist-subscribers-by-query"`
+	DeleteSubscriptionsByQuery             string `query:"delete-subscriptions-by-query"`
+	UnsubscribeSubscribersFromListsByQuery string `query:"unsubscribe-subscribers-from-lists-by-query"`
+
+	CreateList      *sqlx.Stmt `query:"create-list"`
+	QueryLists      string     `query:"query-lists"`
+	GetLists        *sqlx.Stmt `query:"get-lists"`
+	GetListsByOptin *sqlx.Stmt `query:"get-lists-by-optin"`
+	UpdateList      *sqlx.Stmt `query:"update-list"`
+	UpdateListsDate *sqlx.Stmt `query:"update-lists-date"`
+	DeleteLists     *sqlx.Stmt `query:"delete-lists"`
+
+	CreateCampaign           *sqlx.Stmt `query:"create-campaign"`
+	QueryCampaigns           string     `query:"query-campaigns"`
+	GetCampaign              *sqlx.Stmt `query:"get-campaign"`
+	GetCampaignForPreview    *sqlx.Stmt `query:"get-campaign-for-preview"`
+	GetCampaignStats         *sqlx.Stmt `query:"get-campaign-stats"`
+	GetCampaignStatus        *sqlx.Stmt `query:"get-campaign-status"`
+	GetCampaignViewCounts    *sqlx.Stmt `query:"get-campaign-view-counts"`
+	GetCampaignClickCounts   *sqlx.Stmt `query:"get-campaign-click-counts"`
+	GetCampaignLinkCounts    *sqlx.Stmt `query:"get-campaign-link-counts"`
+	GetCampaignBounceCounts  *sqlx.Stmt `query:"get-campaign-bounce-counts"`
+	NextCampaigns            *sqlx.Stmt `query:"next-campaigns"`
+	NextCampaignSubscribers  *sqlx.Stmt `query:"next-campaign-subscribers"`
+	GetOneCampaignSubscriber *sqlx.Stmt `query:"get-one-campaign-subscriber"`
+	UpdateCampaign           *sqlx.Stmt `query:"update-campaign"`
+	UpdateCampaignStatus     *sqlx.Stmt `query:"update-campaign-status"`
+	UpdateCampaignCounts     *sqlx.Stmt `query:"update-campaign-counts"`
+	RegisterCampaignView     *sqlx.Stmt `query:"register-campaign-view"`
+	DeleteCampaign           *sqlx.Stmt `query:"delete-campaign"`
+
+	InsertMedia *sqlx.Stmt `query:"insert-media"`
+	GetAllMedia *sqlx.Stmt `query:"get-all-media"`
+	GetMedia    *sqlx.Stmt `query:"get-media"`
+	DeleteMedia *sqlx.Stmt `query:"delete-media"`
+
+	CreateTemplate     *sqlx.Stmt `query:"create-template"`
+	GetTemplates       *sqlx.Stmt `query:"get-templates"`
+	UpdateTemplate     *sqlx.Stmt `query:"update-template"`
+	SetDefaultTemplate *sqlx.Stmt `query:"set-default-template"`
+	DeleteTemplate     *sqlx.Stmt `query:"delete-template"`
+
+	CreateLink        *sqlx.Stmt `query:"create-link"`
+	RegisterLinkClick *sqlx.Stmt `query:"register-link-click"`
+
+	GetSettings    *sqlx.Stmt `query:"get-settings"`
+	UpdateSettings *sqlx.Stmt `query:"update-settings"`
+
+	// GetStats *sqlx.Stmt `query:"get-stats"`
+	RecordBounce              *sqlx.Stmt `query:"record-bounce"`
+	QueryBounces              string     `query:"query-bounces"`
+	DeleteBounces             *sqlx.Stmt `query:"delete-bounces"`
+	DeleteBouncesBySubscriber *sqlx.Stmt `query:"delete-bounces-by-subscriber"`
+}
+
+// CompileSubscriberQueryTpl takes an arbitrary WHERE expressions
+// to filter subscribers from the subscribers table and prepares a query
+// out of it using the raw `query-subscribers-template` query template.
+// While doing this, a readonly transaction is created and the query is
+// dry run on it to ensure that it is indeed readonly.
+func (q *Queries) CompileSubscriberQueryTpl(exp string, db *sqlx.DB) (string, error) {
+	tx, err := db.BeginTxx(context.Background(), &sql.TxOptions{ReadOnly: true})
+	if err != nil {
+		return "", err
+	}
+	defer tx.Rollback()
+
+	// Perform the dry run.
+	if exp != "" {
+		exp = " AND " + exp
+	}
+	stmt := fmt.Sprintf(q.QuerySubscribersTpl, exp)
+	if _, err := tx.Exec(stmt, true, pq.Int64Array{}); err != nil {
+		return "", err
+	}
+
+	return stmt, nil
+}
+
+// compileSubscriberQueryTpl takes an arbitrary WHERE expressions and a subscriber
+// query template that depends on the filter (eg: delete by query, blocklist by query etc.)
+// combines and executes them.
+func (q *Queries) ExecSubscriberQueryTpl(exp, tpl string, listIDs []int, db *sqlx.DB, args ...interface{}) error {
+	// Perform a dry run.
+	filterExp, err := q.CompileSubscriberQueryTpl(exp, db)
+	if err != nil {
+		return err
+	}
+
+	if len(listIDs) == 0 {
+		listIDs = []int{}
+	}
+
+	// First argument is the boolean indicating if the query is a dry run.
+	a := append([]interface{}{false, pq.Array(listIDs)}, args...)
+	if _, err := db.Exec(fmt.Sprintf(tpl, filterExp), a...); err != nil {
+		return err
+	}
+
+	return nil
+}