// This is Free Software under GNU Affero General Public License v >= 3.0
// without warranty, see README.md and license for details.
//
// SPDX-License-Identifier: AGPL-3.0-or-later
// License-Filename: LICENSES/AGPL-3.0.txt
//
// Copyright (C) 2021 by via donau
//   – Österreichische Wasserstraßen-Gesellschaft mbH
// Software engineering by Intevation GmbH
//
// Author(s):
//  * Sascha L. Teichmann <sascha.teichmann@intevation.de>

package imports

import (
	"bytes"
	"context"
	"database/sql"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"text/template"
	"time"

	"gemma.intevation.de/gemma/pkg/auth"
	"gemma.intevation.de/gemma/pkg/common"
	"gemma.intevation.de/gemma/pkg/config"
	"gemma.intevation.de/gemma/pkg/log"
	"gemma.intevation.de/gemma/pkg/misc"
	"gemma.intevation.de/gemma/pkg/models"
	"gemma.intevation.de/gemma/pkg/xlsx"

	"github.com/xuri/excelize/v2"
)

// Report is a job to generate a report and send emails to the
// receivers.
type Report struct {
	models.QueueConfigurationType
	Name models.SafePath `json:"name"`
}

// ReportJobKind is the unique name of this import job type.
const ReportJobKind JobKind = "report"

type reportJobCreator struct{}

const (
	selectReportUsersSQL = `
SELECT username, email_address
FROM users.list_users
WHERE report_reciever
ORDER BY country, username`

	selectCurrentUserSQL = `
SELECT current_user, email_address
FROM users.list_users
WHERE username = current_user`
)

var reportMailTmpl = template.Must(template.New("report-mail").
	Parse(`Dear {{ .Receiver }}

this is an automatically generated report from the Gemma system.
You got this mail because you are listed as a report receiver.
If you received it without consent please
contact {{ .Admin }} under {{ .AdminEmail }}.

Find attached {{ .Attachment }} containing the {{ .Report }} report from {{ .When }}.

Kind Regards`))

func init() { RegisterJobCreator(ReportJobKind, reportJobCreator{}) }

func (reportJobCreator) Description() string { return "report" }

func (reportJobCreator) AutoAccept() bool { return true }

func (reportJobCreator) Create() Job { return new(Report) }

func (reportJobCreator) Depends() [2][]string { return [2][]string{{}, {}} }

func (reportJobCreator) StageDone(context.Context, *sql.Tx, int64, Feedback) error {
	return nil
}

// RequiresRoles enforces to be a sys_admin to run this .
func (*Report) RequiresRoles() auth.Roles { return auth.Roles{"sys_admin"} }

// Description gives a short info about relevant facts of this import.
func (r *Report) Description([]string) (string, error) { return string(r.Name), nil }

// CleanUp is an empty implementation.
func (*Report) CleanUp() error { return nil }

// MarshalAttributes implements a DB marshaling of this job.
func (r *Report) MarshalAttributes(attrs common.Attributes) error {
	if err := r.QueueConfigurationType.MarshalAttributes(attrs); err != nil {
		return err
	}
	attrs.Set("name", string(r.Name))
	return nil
}

// UnmarshalAttributes implements a DB unmarshaling of this job.
func (r *Report) UnmarshalAttributes(attrs common.Attributes) error {
	if err := r.QueueConfigurationType.UnmarshalAttributes(attrs); err != nil {
		return err
	}
	name, found := attrs.Get("name")
	if !found {
		return errors.New("missing 'name' attribute")
	}
	r.Name = models.SafePath(name)
	if !r.Name.Valid() {
		return fmt.Errorf("'%s' is not a safe path", name)
	}
	return nil
}

func (r *Report) loadTemplate() (*excelize.File, *xlsx.Action, error) {
	path := config.ReportPath()
	if path == "" {
		return nil, nil, errors.New("no report dir configured")
	}

	if stat, err := os.Stat(path); err != nil {
		if os.IsNotExist(err) {
			return nil, nil, fmt.Errorf("report dir '%s' does not exists", path)
		}
		return nil, nil, err
	} else if !stat.Mode().IsDir() {
		return nil, nil, fmt.Errorf("report dir '%s' is not a directory", path)
	}

	xlsxFilename := filepath.Join(path, string(r.Name)+".xlsx")
	yamlFilename := filepath.Join(path, string(r.Name)+".yaml")

	for _, check := range []string{xlsxFilename, yamlFilename} {
		if _, err := os.Stat(check); err != nil {
			if os.IsNotExist(err) {
				return nil, nil, fmt.Errorf("'%s' does not exists", check)
			}
			return nil, nil, err
		}
	}

	template, err := excelize.OpenFile(xlsxFilename)
	if err != nil {
		return nil, nil, err
	}

	action, err := xlsx.ActionFromFile(yamlFilename)
	if err != nil {
		return nil, nil, err
	}

	return template, action, nil
}

// Do executes the actual report generation.
func (r *Report) Do(
	ctx context.Context,
	_ int64,
	conn *sql.Conn,
	feedback Feedback,
) (interface{}, error) {

	start := time.Now()

	feedback.Info("Generating report %s.", r.Name)

	template, action, err := r.loadTemplate()
	if err != nil {
		return nil, err
	}

	tx, err := conn.BeginTx(ctx, &sql.TxOptions{ReadOnly: true})
	if err != nil {
		return nil, err
	}
	defer tx.Rollback()

	// Fetch receivers
	var users []misc.EmailReceiver

	if err := func() error {
		rows, err := tx.QueryContext(ctx, selectReportUsersSQL)
		if err != nil {
			return err
		}
		defer rows.Close()

		for rows.Next() {
			var u misc.EmailReceiver
			if err := rows.Scan(&u.Name, &u.Address); err != nil {
				return err
			}
			users = append(users, u)
		}
		return rows.Err()
	}(); err != nil {
		return nil, err
	}

	if len(users) == 0 {
		feedback.Warn("No users found to send reports to.")
		return nil, nil
	}

	// Fetch admin who is responsible for the report.
	var admin misc.EmailReceiver
	if err := tx.QueryRowContext(
		ctx, selectCurrentUserSQL).Scan(&admin.Name, &admin.Address); err != nil {
		log.Errorf("cannot find sender: %v\n", err)
		return nil, fmt.Errorf("cannot find sender: %v", err)
	}

	// Generate the actual report.
	if err := action.Execute(ctx, tx, template); err != nil {
		log.Errorf("%v\n", err)
		return nil, fmt.Errorf("generating report failed: %v", err)
	}

	var buf bytes.Buffer
	if _, err := template.WriteTo(&buf); err != nil {
		log.Errorf("%v\n", err)
		return nil, fmt.Errorf("generating report failed: %v", err)
	}

	feedback.Info("Sending report to %d receiver(s).", len(users))

	now := start.UTC().Format("2006-01-02")

	attached := string(r.Name) + "-" + now + ".xlsx"

	body := func(u misc.EmailReceiver) (string, error) {
		fill := struct {
			Receiver   string
			Attachment string
			Report     string
			When       string
			Admin      string
			AdminEmail string
		}{
			Receiver:   u.Name,
			Attachment: attached,
			Report:     string(r.Name),
			When:       now,
			Admin:      admin.Name,
			AdminEmail: admin.Address,
		}
		var sb strings.Builder
		if err := reportMailTmpl.Execute(&sb, &fill); err != nil {
			return "", err
		}
		return sb.String(), nil
	}

	errorHandler := func(r misc.EmailReceiver, err error) error {
		// We do not terminate the sending of the emails if
		// sending failed. We only log it.
		feedback.Warn("Sending report to %s failed: %v", r.Name, err)
		return nil
	}

	if err := misc.SendMailToAll(
		users,
		"Report "+string(r.Name)+" from "+now,
		body,
		[]misc.EmailAttachment{{
			Name:    attached,
			Content: buf.Bytes(),
		}},
		errorHandler,
	); err != nil {
		return nil, err
	}

	feedback.Info("Generating and sending report took %v.",
		time.Since(start))

	return nil, nil
}