package api

import (
	"context"
	"net/http"
	"time"

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

// The checklists of the student API: each user's own lists (usually the
// preparation for one zjazd), never anyone else's; a checklist or item of
// another user answers 404 like a missing one. Bodies are JSON objects of
// columns, checked as on the management API (Fillable, Rules, existing
// foreign keys). An item with a reading shares its done mark with the
// reading list: marking it done marks the reading read, and a reading read
// in the reading list shows its items done.

// presentationsTable is the deck table of golem15.presentations, read by
// name without importing the plugin.
const presentationsTable = "golem15_presentations_presentations"

var checklistsRules = []lagoon.RequestRule{
	{Field: "meeting", Rules: lagoon.ParseRules("nullable|integer|min:1")},
}

// checklistProgress counts a checklist's items.
type checklistProgress struct {
	Total        int `json:"total"`
	Done         int `json:"done"`
	Percent      int `json:"percent"`
	MinutesTotal int `json:"minutes_total"`
	MinutesDone  int `json:"minutes_done"`
	MinutesLeft  int `json:"minutes_left"`
}

func (p *checklistProgress) add(item checklistItemJSON) {
	p.Total++
	minutes := 0
	if item.EstimateMinutes != nil {
		minutes = *item.EstimateMinutes
	}
	p.MinutesTotal += minutes
	if item.Done {
		p.Done++
		p.MinutesDone += minutes
	} else {
		p.MinutesLeft += minutes
	}
	p.Percent = p.Done * 100 / p.Total
}

// checklistMeetingRef is the short form of a checklist's zjazd.
type checklistMeetingRef struct {
	ID       uint   `json:"id"`
	Number   int    `json:"number"`
	StartsOn string `json:"starts_on"`
	EndsOn   string `json:"ends_on"`
}

// checklistJSON is a checklist with its progress, and its items on the
// detail route.
type checklistJSON struct {
	ID          uint                 `json:"id"`
	MeetingID   *uint                `json:"meeting_id"`
	Meeting     *checklistMeetingRef `json:"meeting"`
	Title       string               `json:"title"`
	Description *string              `json:"description"`
	SortOrder   int                  `json:"sort_order"`
	Progress    checklistProgress    `json:"progress"`
	Items       []checklistItemJSON  `json:"items,omitempty"`
	CreatedAt   string               `json:"created_at"`
	UpdatedAt   string               `json:"updated_at"`
}

type linkedReading struct {
	ID     uint    `json:"id"`
	Title  string  `json:"title"`
	Author *string `json:"author"`
}

type linkedDeadline struct {
	ID    uint   `json:"id"`
	Title string `json:"title"`
	DueAt string `json:"due_at"`
	Kind  string `json:"kind"`
}

type linkedMaterial struct {
	ID    uint   `json:"id"`
	Title string `json:"title"`
}

type linkedPresentation struct {
	Slug  string `json:"slug"`
	Title string `json:"title"`
}

// checklistItemJSON is one item with its done state and the rows it points
// at (null when unset or gone; presentation is null when the caller owns no
// deck with that slug).
type checklistItemJSON struct {
	ID               uint                `json:"id"`
	ChecklistID      uint                `json:"checklist_id"`
	Kind             string              `json:"kind"`
	Title            string              `json:"title"`
	Notes            *string             `json:"notes"`
	URL              *string             `json:"url"`
	CourseID         *uint               `json:"course_id"`
	Course           *courseRef          `json:"course"`
	ReadingID        *uint               `json:"reading_id"`
	Reading          *linkedReading      `json:"reading"`
	DeadlineID       *uint               `json:"deadline_id"`
	Deadline         *linkedDeadline     `json:"deadline"`
	MaterialID       *uint               `json:"material_id"`
	Material         *linkedMaterial     `json:"material"`
	PresentationSlug *string             `json:"presentation_slug"`
	Presentation     *linkedPresentation `json:"presentation"`
	DueAt            *string             `json:"due_at"`
	EstimateMinutes  *int                `json:"estimate_minutes"`
	SortOrder        int                 `json:"sort_order"`
	Done             bool                `json:"done"`
	DoneAt           *string             `json:"done_at"`
}

// checklistItemRow is an item with its effective done mark: the reading's
// read_at for an item with a reading, else its own done_at.
type checklistItemRow struct {
	models.ChecklistItem `gorm:"embedded"`
	DoneMark             *time.Time `gorm:"column:done_mark"`
}

func formatTime(t *time.Time) *string {
	if t == nil {
		return nil
	}
	s := models.FormatDateTime(*t)
	return &s
}

// loadChecklistItems returns the caller's items of the given checklists,
// keyed by checklist, in display order.
func loadChecklistItems(db *gorm.DB, userID uint, checklistIDs []uint) (map[uint][]checklistItemJSON, error) {
	out := map[uint][]checklistItemJSON{}
	if len(checklistIDs) == 0 {
		return out, nil
	}
	var rows []checklistItemRow
	err := db.Table("jz_bm_checklist_items AS i").
		Select("i.*, CASE WHEN i.reading_id IS NULL THEN i.done_at ELSE p.read_at END AS done_mark").
		Joins("JOIN jz_bm_checklists c ON c.id = i.checklist_id").
		Joins("LEFT JOIN jz_bm_reading_progress p ON p.reading_id = i.reading_id AND p.user_id = c.user_id").
		Where("c.user_id = ? AND i.checklist_id IN ?", userID, checklistIDs).
		Order("i.checklist_id, i.sort_order, i.id").
		Scan(&rows).Error
	if err != nil {
		return nil, err
	}
	var courseIDs, readingIDs, deadlineIDs, materialIDs []uint
	var slugs []string
	for _, row := range rows {
		if row.CourseID != nil {
			courseIDs = append(courseIDs, *row.CourseID)
		}
		if row.ReadingID != nil {
			readingIDs = append(readingIDs, *row.ReadingID)
		}
		if row.DeadlineID != nil {
			deadlineIDs = append(deadlineIDs, *row.DeadlineID)
		}
		if row.MaterialID != nil {
			materialIDs = append(materialIDs, *row.MaterialID)
		}
		if row.PresentationSlug != nil {
			slugs = append(slugs, *row.PresentationSlug)
		}
	}
	courses, err := coursesByID(db, courseIDs)
	if err != nil {
		return nil, err
	}
	readings := map[uint]*linkedReading{}
	if len(readingIDs) > 0 {
		var rs []models.Reading
		if err := db.Where("id IN ?", readingIDs).Find(&rs).Error; err != nil {
			return nil, err
		}
		for _, r := range rs {
			readings[r.ID] = &linkedReading{ID: r.ID, Title: r.Title, Author: r.Author}
		}
	}
	deadlines := map[uint]*linkedDeadline{}
	if len(deadlineIDs) > 0 {
		var ds []models.Deadline
		if err := db.Where("id IN ?", deadlineIDs).Find(&ds).Error; err != nil {
			return nil, err
		}
		for _, d := range ds {
			deadlines[d.ID] = &linkedDeadline{ID: d.ID, Title: d.Title, DueAt: models.FormatDateTime(d.DueAt), Kind: d.Kind}
		}
	}
	materials := map[uint]*linkedMaterial{}
	if len(materialIDs) > 0 {
		// Only published materials, as in the material list.
		var ms []models.Material
		if err := db.Select("id", "title").Where("id IN ? AND published_at IS NOT NULL", materialIDs).Find(&ms).Error; err != nil {
			return nil, err
		}
		for _, m := range ms {
			materials[m.ID] = &linkedMaterial{ID: m.ID, Title: m.Title}
		}
	}
	decks, err := ownedDecks(db, userID, slugs)
	if err != nil {
		return nil, err
	}
	for _, row := range rows {
		item := checklistItemJSON{
			ID:               row.ID,
			ChecklistID:      row.ChecklistID,
			Kind:             row.Kind,
			Title:            row.Title,
			Notes:            row.Notes,
			URL:              row.URL,
			CourseID:         row.CourseID,
			ReadingID:        row.ReadingID,
			DeadlineID:       row.DeadlineID,
			MaterialID:       row.MaterialID,
			PresentationSlug: row.PresentationSlug,
			DueAt:            formatTime(row.DueAt),
			EstimateMinutes:  row.EstimateMinutes,
			SortOrder:        row.SortOrder,
			Done:             row.DoneMark != nil,
			DoneAt:           formatTime(row.DoneMark),
		}
		if row.CourseID != nil {
			item.Course = newCourseRef(courses[*row.CourseID])
		}
		if row.ReadingID != nil {
			item.Reading = readings[*row.ReadingID]
		}
		if row.DeadlineID != nil {
			item.Deadline = deadlines[*row.DeadlineID]
		}
		if row.MaterialID != nil {
			item.Material = materials[*row.MaterialID]
		}
		if row.PresentationSlug != nil {
			item.Presentation = decks[*row.PresentationSlug]
		}
		out[row.ChecklistID] = append(out[row.ChecklistID], item)
	}
	return out, nil
}

// ownedDecks returns the caller's decks among slugs, keyed by slug. Without
// golem15.presentations installed there are none.
func ownedDecks(db *gorm.DB, userID uint, slugs []string) (map[string]*linkedPresentation, error) {
	out := map[string]*linkedPresentation{}
	if len(slugs) == 0 || !db.Migrator().HasTable(presentationsTable) {
		return out, nil
	}
	var rows []linkedPresentation
	err := db.Table(presentationsTable).Select("slug, title").
		Where("owner_user_id = ? AND slug IN ?", userID, slugs).Scan(&rows).Error
	if err != nil {
		return nil, err
	}
	for i := range rows {
		out[rows[i].Slug] = &rows[i]
	}
	return out, nil
}

// checklistsJSON builds the answer for the given checklists, with items
// when withItems.
func checklistsJSON(db *gorm.DB, userID uint, lists []models.Checklist, withItems bool) ([]checklistJSON, error) {
	ids := make([]uint, 0, len(lists))
	meetingIDs := []uint{}
	for _, c := range lists {
		ids = append(ids, c.ID)
		if c.MeetingID != nil {
			meetingIDs = append(meetingIDs, *c.MeetingID)
		}
	}
	items, err := loadChecklistItems(db, userID, ids)
	if err != nil {
		return nil, err
	}
	meetings := map[uint]*checklistMeetingRef{}
	if len(meetingIDs) > 0 {
		var ms []models.Meeting
		if err := db.Where("id IN ?", meetingIDs).Find(&ms).Error; err != nil {
			return nil, err
		}
		for _, m := range ms {
			meetings[m.ID] = &checklistMeetingRef{ID: m.ID, Number: m.Number, StartsOn: m.StartsOn.String(), EndsOn: m.EndsOn.String()}
		}
	}
	out := make([]checklistJSON, 0, len(lists))
	for _, c := range lists {
		item := checklistJSON{
			ID:          c.ID,
			MeetingID:   c.MeetingID,
			Title:       c.Title,
			Description: c.Description,
			SortOrder:   c.SortOrder,
			CreatedAt:   models.FormatDateTime(c.CreatedAt),
			UpdatedAt:   models.FormatDateTime(c.UpdatedAt),
		}
		if c.MeetingID != nil {
			item.Meeting = meetings[*c.MeetingID]
		}
		for _, it := range items[c.ID] {
			item.Progress.add(it)
		}
		if withItems {
			item.Items = items[c.ID]
			if item.Items == nil {
				item.Items = []checklistItemJSON{}
			}
		}
		out = append(out, item)
	}
	return out, nil
}

// Checklists answers GET /checklists?meeting=ID: the caller's checklists
// with their progress, without items.
func (h *Handlers) Checklists(w http.ResponseWriter, r *http.Request) {
	userID, ok := h.caller(w, r)
	if !ok {
		return
	}
	in := query(r, "meeting")
	if !h.validate(w, r, in, checklistsRules) {
		return
	}
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	q := db.Where("user_id = ?", userID)
	if id := uintParam(in, "meeting"); id != 0 {
		q = q.Where("meeting_id = ?", id)
	}
	var lists []models.Checklist
	if err := q.Order("sort_order, id").Find(&lists).Error; err != nil {
		writeOpaque500(w)
		return
	}
	out, err := checklistsJSON(db, userID, lists, false)
	if err != nil {
		writeOpaque500(w)
		return
	}
	writeData(w, out)
}

// checklistFor resolves {id} to one of the caller's checklists and answers
// 404 itself when there is none.
func checklistFor(w http.ResponseWriter, r *http.Request, db *gorm.DB, userID uint) (*models.Checklist, bool) {
	id, ok := surf.IntParam(r, "id")
	if !ok {
		writeNotFound(w)
		return nil, false
	}
	var c models.Checklist
	res := db.Where("id = ? AND user_id = ?", id, userID).Limit(1).Find(&c)
	if res.Error != nil {
		writeOpaque500(w)
		return nil, false
	}
	if res.RowsAffected == 0 {
		writeNotFound(w)
		return nil, false
	}
	return &c, true
}

// itemFor resolves {id} to an item of one of the caller's checklists and
// answers 404 itself when there is none.
func itemFor(w http.ResponseWriter, r *http.Request, db *gorm.DB, userID uint) (*models.ChecklistItem, bool) {
	id, ok := surf.IntParam(r, "id")
	if !ok {
		writeNotFound(w)
		return nil, false
	}
	var item models.ChecklistItem
	res := db.Table("jz_bm_checklist_items AS i").Select("i.*").
		Joins("JOIN jz_bm_checklists c ON c.id = i.checklist_id").
		Where("i.id = ? AND c.user_id = ?", id, userID).Limit(1).Find(&item)
	if res.Error != nil {
		writeOpaque500(w)
		return nil, false
	}
	if res.RowsAffected == 0 {
		writeNotFound(w)
		return nil, false
	}
	return &item, true
}

// writeChecklist answers one checklist with its items.
func writeChecklist(w http.ResponseWriter, db *gorm.DB, userID uint, c models.Checklist, status int) {
	out, err := checklistsJSON(db, userID, []models.Checklist{c}, true)
	if err != nil || len(out) != 1 {
		writeOpaque500(w)
		return
	}
	wire.WriteJSON(w, status, map[string]any{"data": out[0]})
}

// writeItem answers one item as the detail route shows it.
func writeItem(w http.ResponseWriter, db *gorm.DB, userID uint, item models.ChecklistItem, status int) {
	items, err := loadChecklistItems(db, userID, []uint{item.ChecklistID})
	if err != nil {
		writeOpaque500(w)
		return
	}
	for _, it := range items[item.ChecklistID] {
		if it.ID == item.ID {
			wire.WriteJSON(w, status, map[string]any{"data": it})
			return
		}
	}
	writeOpaque500(w)
}

// Checklist answers GET /checklists/{id}: one of the caller's checklists
// with its items.
func (h *Handlers) Checklist(w http.ResponseWriter, r *http.Request) {
	userID, ok := h.caller(w, r)
	if !ok {
		return
	}
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	c, ok := checklistFor(w, r, db, userID)
	if !ok {
		return
	}
	writeChecklist(w, db, userID, *c, http.StatusOK)
}

var checklistReferences = map[string]string{"meeting_id": "jz_bm_meetings"}

var itemReferences = map[string]string{
	"course_id":   "jz_bm_courses",
	"reading_id":  "jz_bm_readings",
	"deadline_id": "jz_bm_deadlines",
	"material_id": "jz_bm_materials",
}

// CreateChecklist answers POST /checklists: 201 with the new checklist.
func (h *Handlers) CreateChecklist(w http.ResponseWriter, r *http.Request) {
	userID, ok := h.caller(w, r)
	if !ok {
		return
	}
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	c := &models.Checklist{UserID: userID}
	if _, ok := h.fillRecord(w, r, db, c, c, checklistReferences, nil); !ok {
		return
	}
	if err := db.Create(c).Error; err != nil {
		writeOpaque500(w)
		return
	}
	writeChecklist(w, db, userID, *c, http.StatusCreated)
}

// UpdateChecklist answers PATCH /checklists/{id}: the sent columns change.
func (h *Handlers) UpdateChecklist(w http.ResponseWriter, r *http.Request) {
	userID, ok := h.caller(w, r)
	if !ok {
		return
	}
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	c, ok := checklistFor(w, r, db, userID)
	if !ok {
		return
	}
	if _, ok := h.fillRecord(w, r, db, c, c, checklistReferences, nil); !ok {
		return
	}
	if err := db.Save(c).Error; err != nil {
		writeOpaque500(w)
		return
	}
	writeChecklist(w, db, userID, *c, http.StatusOK)
}

// DeleteChecklist answers DELETE /checklists/{id}: 204; its items go with
// it. Reading marks stay.
func (h *Handlers) DeleteChecklist(w http.ResponseWriter, r *http.Request) {
	userID, ok := h.caller(w, r)
	if !ok {
		return
	}
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	c, ok := checklistFor(w, r, db, userID)
	if !ok {
		return
	}
	if err := db.Delete(c).Error; err != nil {
		writeOpaque500(w)
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

// checkItem adds the item checks the rules cannot make: the target
// checklist is the caller's, and a deck slug names one of the caller's
// decks.
func checkItem(db *gorm.DB, userID uint) func(map[string]any, map[string][]string) error {
	return func(check map[string]any, errs map[string][]string) error {
		if id, ok := check["checklist_id"].(uint); ok {
			var n int64
			if err := db.Model(&models.Checklist{}).Where("id = ? AND user_id = ?", id, userID).Count(&n).Error; err != nil {
				return err
			}
			if n == 0 {
				errs["checklist_id"] = append(errs["checklist_id"], "The selected checklist_id is invalid.")
			}
		}
		if slug, ok := check["presentation_slug"].(string); ok && slug != "" {
			decks, err := ownedDecks(db, userID, []string{slug})
			if err != nil {
				return err
			}
			if decks[slug] == nil {
				errs["presentation_slug"] = append(errs["presentation_slug"], "The selected presentation_slug is not one of your decks.")
			}
		}
		return nil
	}
}

// CreateChecklistItem answers POST /checklists/{id}/items: 201 with the new
// item, at the end of the list unless sort_order is sent. kind defaults to
// zadanie.
func (h *Handlers) CreateChecklistItem(w http.ResponseWriter, r *http.Request) {
	userID, ok := h.caller(w, r)
	if !ok {
		return
	}
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	c, ok := checklistFor(w, r, db, userID)
	if !ok {
		return
	}
	var last struct{ Max *int }
	if err := db.Model(&models.ChecklistItem{}).Select("MAX(sort_order) AS max").Where("checklist_id = ?", c.ID).Scan(&last).Error; err != nil {
		writeOpaque500(w)
		return
	}
	item := &models.ChecklistItem{ChecklistID: c.ID, Kind: "zadanie"}
	if last.Max != nil {
		item.SortOrder = *last.Max + 1
	}
	if _, ok := h.fillRecord(w, r, db, item, item, itemReferences, checkItem(db, userID)); !ok {
		return
	}
	if err := db.Create(item).Error; err != nil {
		writeOpaque500(w)
		return
	}
	writeItem(w, db, userID, *item, http.StatusCreated)
}

// UpdateChecklistItem answers PATCH /checklist-items/{id}: the sent columns
// change; checklist_id moves the item to another of the caller's lists.
func (h *Handlers) UpdateChecklistItem(w http.ResponseWriter, r *http.Request) {
	userID, ok := h.caller(w, r)
	if !ok {
		return
	}
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	item, ok := itemFor(w, r, db, userID)
	if !ok {
		return
	}
	if _, ok := h.fillRecord(w, r, db, item, item, itemReferences, checkItem(db, userID)); !ok {
		return
	}
	if err := db.Save(item).Error; err != nil {
		writeOpaque500(w)
		return
	}
	writeItem(w, db, userID, *item, http.StatusOK)
}

// DeleteChecklistItem answers DELETE /checklist-items/{id}: 204. A reading
// mark stays.
func (h *Handlers) DeleteChecklistItem(w http.ResponseWriter, r *http.Request) {
	userID, ok := h.caller(w, r)
	if !ok {
		return
	}
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	item, ok := itemFor(w, r, db, userID)
	if !ok {
		return
	}
	if err := db.Delete(item).Error; err != nil {
		writeOpaque500(w)
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

// MarkChecklistItemDone answers PUT /checklist-items/{id}/done. An item
// with a reading marks the reading read by the caller (the reading list
// shows it read); any other item gets done_at. Marking it again keeps the
// first mark.
func (h *Handlers) MarkChecklistItemDone(w http.ResponseWriter, r *http.Request) {
	h.setItemDone(w, r, true)
}

// UnmarkChecklistItemDone answers DELETE /checklist-items/{id}/done: it
// clears the mark, and for an item with a reading the caller's read mark.
func (h *Handlers) UnmarkChecklistItemDone(w http.ResponseWriter, r *http.Request) {
	h.setItemDone(w, r, false)
}

func (h *Handlers) setItemDone(w http.ResponseWriter, r *http.Request, done bool) {
	userID, ok := h.caller(w, r)
	if !ok {
		return
	}
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	item, ok := itemFor(w, r, db, userID)
	if !ok {
		return
	}
	now := h.now().UTC()
	err := lagoon.Transaction(r.Context(), db, func(_ context.Context, tx *gorm.DB) error {
		if item.ReadingID != nil {
			if done {
				return tx.Exec(`INSERT INTO jz_bm_reading_progress (reading_id, user_id, read_at) VALUES (?, ?, ?)
ON CONFLICT (reading_id, user_id) DO NOTHING`, *item.ReadingID, userID, now).Error
			}
			return tx.Where("reading_id = ? AND user_id = ?", *item.ReadingID, userID).Delete(&models.ReadingProgress{}).Error
		}
		q := tx.Model(&models.ChecklistItem{}).Where("id = ?", item.ID)
		if done {
			return q.Where("done_at IS NULL").Update("done_at", now).Error
		}
		return q.Update("done_at", nil).Error
	})
	if err != nil {
		writeOpaque500(w)
		return
	}
	writeItem(w, db, userID, *item, http.StatusOK)
}