package api

import (
	"net/http"
	"time"

	"git.golem15.com/golem15/summercms/modules/surf"
	"git.golem15.com/jakub/sm-bm-plugin/models"
	"gorm.io/gorm"
)

// readingRow is a reading joined with the caller's progress row.
type readingRow struct {
	models.Reading `gorm:"embedded"`
	ReadAt         *time.Time `gorm:"column:read_at"`
}

// listReadings returns the readings, optionally of one course, in course and
// reading order, each with the caller's read_at.
func listReadings(db *gorm.DB, userID, courseID uint) ([]readingJSON, error) {
	q := db.Table("jz_bm_readings AS r").
		Select("r.*, p.read_at").
		Joins("JOIN jz_bm_courses c ON c.id = r.course_id").
		Joins("LEFT JOIN jz_bm_reading_progress p ON p.reading_id = r.id AND p.user_id = ?", userID)
	if courseID != 0 {
		q = q.Where("r.course_id = ?", courseID)
	}
	var rows []readingRow
	if err := q.Order("c.semester, c.sort_order, c.name, r.course_id, r.sort_order, r.id").Scan(&rows).Error; err != nil {
		return nil, err
	}
	courses, err := coursesByID(db, readingCourseIDs(rows))
	if err != nil {
		return nil, err
	}
	out := make([]readingJSON, 0, len(rows))
	for _, row := range rows {
		item := readingJSON{
			ID:         row.ID,
			CourseID:   idOf(row.CourseID),
			Course:     newCourseRef(courses[idOf(row.CourseID)]),
			Title:      row.Title,
			Author:     row.Author,
			Source:     row.Source,
			URL:        row.URL,
			IsRequired: row.IsRequired,
			SortOrder:  row.SortOrder,
		}
		if row.ReadAt != nil {
			s := models.FormatDateTime(*row.ReadAt)
			item.ReadAt = &s
		}
		out = append(out, item)
	}
	return out, nil
}

func readingCourseIDs(rows []readingRow) []uint {
	seen := map[uint]bool{}
	var ids []uint
	for _, row := range rows {
		if id := idOf(row.CourseID); !seen[id] {
			seen[id] = true
			ids = append(ids, id)
		}
	}
	return ids
}

// coursesByID loads the given courses keyed by ID.
func coursesByID(db *gorm.DB, ids []uint) (map[uint]*models.Course, error) {
	out := map[uint]*models.Course{}
	if len(ids) == 0 {
		return out, nil
	}
	var rows []models.Course
	if err := db.Where("id IN ?", ids).Find(&rows).Error; err != nil {
		return nil, err
	}
	for i := range rows {
		out[rows[i].ID] = &rows[i]
	}
	return out, nil
}

// Readings answers GET /readings?course=ID: the reading lists with the
// caller's read state. An unknown course gives an empty list.
func (h *Handlers) Readings(w http.ResponseWriter, r *http.Request) {
	userID, ok := h.caller(w, r)
	if !ok {
		return
	}
	in := query(r, "course")
	if !h.validate(w, r, in, courseFilterRules) {
		return
	}
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	out, err := listReadings(db, userID, uintParam(in, "course"))
	if err != nil {
		writeOpaque500(w)
		return
	}
	writeData(w, out)
}

// progressJSON is the answer of the progress routes.
type progressJSON struct {
	ReadingID uint    `json:"reading_id"`
	ReadAt    *string `json:"read_at"`
}

// readingFor resolves {id} to an existing reading and answers 404 itself
// when there is none.
func readingFor(w http.ResponseWriter, r *http.Request, db *gorm.DB) (uint, bool) {
	id, ok := surf.IntParam(r, "id")
	if !ok {
		writeNotFound(w)
		return 0, false
	}
	var reading models.Reading
	res := db.Select("id").Where("id = ? AND course_id IS NOT NULL", id).Limit(1).Find(&reading)
	if res.Error != nil {
		writeOpaque500(w)
		return 0, false
	}
	if res.RowsAffected == 0 {
		writeNotFound(w)
		return 0, false
	}
	return reading.ID, true
}

// MarkRead answers PUT /readings/{id}/progress: it marks the reading read
// by the caller. Marking it again keeps the first read_at.
func (h *Handlers) MarkRead(w http.ResponseWriter, r *http.Request) {
	userID, ok := h.caller(w, r)
	if !ok {
		return
	}
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	readingID, ok := readingFor(w, r, db)
	if !ok {
		return
	}
	now := h.now().UTC()
	err := db.Exec(`INSERT INTO jz_bm_reading_progress (reading_id, user_id, read_at) VALUES (?, ?, ?)
ON CONFLICT (reading_id, user_id) DO NOTHING`, readingID, userID, now).Error
	if err != nil {
		writeOpaque500(w)
		return
	}
	var progress models.ReadingProgress
	if err := db.Where("reading_id = ? AND user_id = ?", readingID, userID).Take(&progress).Error; err != nil {
		writeOpaque500(w)
		return
	}
	readAt := models.FormatDateTime(progress.ReadAt)
	writeData(w, progressJSON{ReadingID: readingID, ReadAt: &readAt})
}

// UnmarkRead answers DELETE /readings/{id}/progress: it clears the caller's
// read mark. Clearing an unread reading is not an error.
func (h *Handlers) UnmarkRead(w http.ResponseWriter, r *http.Request) {
	userID, ok := h.caller(w, r)
	if !ok {
		return
	}
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	readingID, ok := readingFor(w, r, db)
	if !ok {
		return
	}
	if err := db.Where("reading_id = ? AND user_id = ?", readingID, userID).Delete(&models.ReadingProgress{}).Error; err != nil {
		writeOpaque500(w)
		return
	}
	writeData(w, progressJSON{ReadingID: readingID})
}