package api

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"io"
	"net/http"
	"slices"
	"strconv"
	"strings"
	"time"
	"unicode"

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

// The management API (/api/v1/bm) is what the console commands do, over
// HTTP: it runs behind golem15.user's shared API-token, scope, and permission
// middleware, not the students' jwt.auth.

// flag reads a boolean query parameter: 1 and true are on.
func flag(r *http.Request, name string) bool {
	v := r.URL.Query().Get(name)
	return v == "1" || v == "true"
}

func writeInvalid(w http.ResponseWriter, message string) {
	wire.WriteJSON(w, http.StatusUnprocessableEntity, map[string]any{"message": message})
}

// body reads the request body and answers 413 or 400 itself when it cannot.
func body(w http.ResponseWriter, r *http.Request) ([]byte, bool) {
	raw, err := io.ReadAll(r.Body)
	var tooLarge *http.MaxBytesError
	switch {
	case errors.As(err, &tooLarge):
		wire.WriteJSON(w, http.StatusRequestEntityTooLarge, map[string]any{"error": true, "message": "Request body too large."})
		return nil, false
	case err != nil:
		wire.WriteJSON(w, http.StatusBadRequest, map[string]any{"error": true, "message": "Unreadable request body."})
		return nil, false
	}
	return raw, true
}

type tokenJSON struct {
	ID        uint     `json:"id"`
	Name      string   `json:"name"`
	Scopes    []string `json:"scopes"`
	ExpiresAt *string  `json:"expires_at"`
}

// TokenInfo answers GET /me: the user and the token of the request, to
// check a token without changing anything.
func (h *Handlers) TokenInfo(w http.ResponseWriter, r *http.Request) {
	userID, ok := h.caller(w, r)
	if !ok {
		return
	}
	out := map[string]any{"user_id": userID}
	cred, _ := bouncer.Credential(r.Context())
	if t, ok := cred.(*usermodels.APIToken); ok {
		name := ""
		if t.Name != nil {
			name = *t.Name
		}
		tj := tokenJSON{ID: t.ID, Name: name, Scopes: wire.Slice(t.Scopes.Get())}
		if t.ExpiresAt != nil {
			s := models.FormatDateTime(*t.ExpiresAt)
			tj.ExpiresAt = &s
		}
		out["token"] = tj
	}
	writeData(w, out)
}

type seedCountsJSON struct {
	Created   int `json:"created"`
	Updated   int `json:"updated"`
	Unchanged int `json:"unchanged"`
	Deleted   int `json:"deleted"`
}

func newSeedCountsJSON(c classes.SeedCounts) seedCountsJSON {
	return seedCountsJSON{Created: c.Created, Updated: c.Updated, Unchanged: c.Unchanged, Deleted: c.Deleted}
}

// ApplySeed answers POST /seed?dry_run=&prune=: bm:seed over HTTP. The body
// is the seed document; the answer is the summary the command prints. A
// document that does not parse or validate is a 422 and writes nothing.
func (h *Handlers) ApplySeed(w http.ResponseWriter, r *http.Request) {
	raw, ok := body(w, r)
	if !ok {
		return
	}
	file, err := classes.ParseSeed(bytes.NewReader(raw))
	if err == nil {
		err = file.Validate()
	}
	if err != nil {
		writeInvalid(w, err.Error())
		return
	}
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	opts := classes.SeedOptions{DryRun: flag(r, "dry_run"), Prune: flag(r, "prune")}
	sum, err := classes.SeedWith(r.Context(), db, file, opts)
	if err != nil {
		writeOpaque500(w)
		return
	}
	writeData(w, map[string]any{
		"dry_run": opts.DryRun,
		"prune":   opts.Prune,
		"summary": map[string]seedCountsJSON{
			"meetings":       newSeedCountsJSON(sum.Meetings),
			"courses":        newSeedCountsJSON(sum.Courses),
			"class_sessions": newSeedCountsJSON(sum.ClassSessions),
			"deadlines":      newSeedCountsJSON(sum.Deadlines),
			"readings":       newSeedCountsJSON(sum.Readings),
		},
		"removed": wire.Slice(sum.Removed),
	})
}

// managedMaterialJSON is a material as the management API shows it: drafts
// too, so published_at may be null.
type managedMaterialJSON struct {
	ID          uint       `json:"id"`
	CourseID    *uint      `json:"course_id"`
	Course      *courseRef `json:"course"`
	Title       string     `json:"title"`
	Type        string     `json:"type"`
	Body        *string    `json:"body"`
	Source      *string    `json:"source"`
	URL         *string    `json:"url"`
	PublishedAt *string    `json:"published_at"`
	Tags        []tagJSON  `json:"tags"`
}

func newManagedMaterialJSON(m models.Material) managedMaterialJSON {
	out := managedMaterialJSON{
		ID: m.ID, CourseID: m.CourseID, Course: newCourseRef(m.Course), Title: m.Title, Type: m.Type,
		Body: m.Body, Source: m.Source, URL: m.URL, Tags: newTagsJSON(m.Tags),
	}
	if m.PublishedAt != nil {
		s := models.FormatDateTime(*m.PublishedAt)
		out.PublishedAt = &s
	}
	return out
}

// ManagedCourses answers GET /courses: every course, for the course_id of
// a material.
func (h *Handlers) ManagedCourses(w http.ResponseWriter, r *http.Request) {
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	var rows []models.Course
	if err := db.Order("semester, sort_order, name, id").Find(&rows).Error; err != nil {
		writeOpaque500(w)
		return
	}
	out := make([]courseJSON, 0, len(rows))
	for _, c := range rows {
		out = append(out, newCourseJSON(c))
	}
	writeData(w, out)
}

// ManagedMaterials answers GET /materials: every material, drafts
// included, newest first.
func (h *Handlers) ManagedMaterials(w http.ResponseWriter, r *http.Request) {
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	var rows []models.Material
	if err := preloadMaterial(db).Order("jz_bm_materials.id DESC").Find(&rows).Error; err != nil {
		writeOpaque500(w)
		return
	}
	out := make([]managedMaterialJSON, 0, len(rows))
	for _, m := range rows {
		out = append(out, newManagedMaterialJSON(m))
	}
	writeData(w, out)
}

// materialInput is the body of POST /materials and PUT /materials/{id}.
type materialInput struct {
	CourseID    *uint     `json:"course_id"`
	Title       string    `json:"title"`
	Type        string    `json:"type"`
	Body        *string   `json:"body"`
	Source      *string   `json:"source"`
	URL         *string   `json:"url"`
	PublishedAt *string   `json:"published_at"`
	Tags        *[]string `json:"tags"`
}

// materialDraft is a decoded and validated material body, ready to apply.
type materialDraft struct {
	in materialInput
	// hasPublishedAt tells a sent published_at (null included) from an
	// absent one.
	hasPublishedAt bool
	publishedAt    *time.Time
	tags           []models.Tag
}

// readMaterial decodes and validates the body of POST /materials and
// PUT /materials/{id}. It answers 400, 413, 422 or 500 itself and returns
// false then.
func (h *Handlers) readMaterial(w http.ResponseWriter, r *http.Request, db *gorm.DB) (materialDraft, bool) {
	var d materialDraft
	raw, ok := body(w, r)
	if !ok {
		return d, false
	}
	dec := json.NewDecoder(bytes.NewReader(raw))
	dec.DisallowUnknownFields()
	if err := dec.Decode(&d.in); err != nil {
		writeInvalid(w, "invalid JSON: "+err.Error())
		return d, false
	}
	var keys map[string]json.RawMessage
	_ = json.Unmarshal(raw, &keys)
	_, d.hasPublishedAt = keys["published_at"]

	in := &d.in
	in.Title = strings.TrimSpace(in.Title)
	errs := map[string][]string{}
	if in.Title == "" || len(in.Title) > 255 {
		errs["title"] = []string{"The title is required and may not be longer than 255 characters."}
	}
	if !slices.Contains(models.MaterialTypes, in.Type) {
		errs["type"] = []string{"The type must be one of: " + strings.Join(models.MaterialTypes, ", ") + "."}
	}
	if in.Source != nil && len(*in.Source) > 500 {
		errs["source"] = []string{"The source may not be longer than 500 characters."}
	}
	if in.URL != nil && len(*in.URL) > 2048 {
		errs["url"] = []string{"The url may not be longer than 2048 characters."}
	}
	if in.PublishedAt != nil {
		t, err := models.ParseDateTime(*in.PublishedAt)
		if err != nil {
			errs["published_at"] = []string{"The published_at is not a valid date and time."}
		}
		d.publishedAt = &t
	}
	if in.Tags != nil {
		for _, name := range *in.Tags {
			name = strings.TrimSpace(name)
			slug := slugify(name)
			if slug == "" || len(name) > 100 || len(slug) > 100 {
				errs["tags"] = []string{"Each tag must be a name of 1 to 100 characters."}
				break
			}
			if !slices.ContainsFunc(d.tags, func(t models.Tag) bool { return t.Slug == slug }) {
				d.tags = append(d.tags, models.Tag{Name: name, Slug: slug})
			}
		}
	}
	if in.CourseID != nil {
		var n int64
		if err := db.Model(&models.Course{}).Where("id = ?", *in.CourseID).Count(&n).Error; err != nil {
			writeOpaque500(w)
			return d, false
		}
		if n == 0 {
			errs["course_id"] = []string{"The selected course_id is invalid."}
		}
	}
	if len(errs) > 0 {
		writeValidation(w, errs)
		return d, false
	}
	return d, true
}

// identity scopes a query to the materials with the draft's title and
// course: the identity POST /materials upserts on.
func (d materialDraft) identity(q *gorm.DB) *gorm.DB {
	q = q.Where("title = ?", d.in.Title)
	if d.in.CourseID != nil {
		return q.Where("course_id = ?", *d.in.CourseID)
	}
	return q.Where("course_id IS NULL")
}

// apply writes the draft onto m inside tx. published_at: absent publishes
// a new material now and keeps an existing one as it is; null makes a
// draft; otherwise the sent time. tags: absent keeps them; otherwise the
// list replaces them, and unknown tags are created.
func (d materialDraft) apply(tx *gorm.DB, m *models.Material, created bool, now time.Time) error {
	in := d.in
	m.CourseID, m.Title, m.Type = in.CourseID, in.Title, in.Type
	m.Body, m.Source, m.URL = in.Body, in.Source, in.URL
	switch {
	case d.hasPublishedAt:
		m.PublishedAt = d.publishedAt
	case created:
		m.PublishedAt = &now
	}
	if err := tx.Omit("Course", "Tags").Save(m).Error; err != nil {
		return err
	}
	if in.Tags == nil {
		return nil
	}
	if err := tx.Where("material_id = ?", m.ID).Delete(&models.MaterialTag{}).Error; err != nil {
		return err
	}
	for _, t := range d.tags {
		var tag models.Tag
		res := tx.Where("slug = ?", t.Slug).Limit(1).Find(&tag)
		if res.Error != nil {
			return res.Error
		}
		if res.RowsAffected == 0 {
			tag = t
			if err := tx.Create(&tag).Error; err != nil {
				return err
			}
		}
		if err := tx.Create(&models.MaterialTag{MaterialID: m.ID, TagID: tag.ID}).Error; err != nil {
			return err
		}
	}
	return nil
}

// writeManaged answers with the material id, reloaded with its course and
// tags, plus any extra top-level keys.
func writeManaged(w http.ResponseWriter, db *gorm.DB, id uint, status int, extra map[string]any) {
	var out models.Material
	if err := preloadMaterial(db).First(&out, id).Error; err != nil {
		writeOpaque500(w)
		return
	}
	payload := map[string]any{"data": newManagedMaterialJSON(out)}
	for k, v := range extra {
		payload[k] = v
	}
	wire.WriteJSON(w, status, payload)
}

// UpsertMaterial answers POST /materials: it creates the material, or
// updates the one with the same title and course, so sending a document
// twice changes nothing. body, source and url are replaced as sent; see
// materialDraft.apply for published_at and tags. A renamed material is a
// new one here: PUT /materials/{id} renames.
func (h *Handlers) UpsertMaterial(w http.ResponseWriter, r *http.Request) {
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	d, ok := h.readMaterial(w, r, db)
	if !ok {
		return
	}
	var m models.Material
	created := false
	err := lagoon.Transaction(r.Context(), db, func(_ context.Context, tx *gorm.DB) error {
		res := d.identity(tx).Order("id").Limit(1).Find(&m)
		if res.Error != nil {
			return res.Error
		}
		created = res.RowsAffected == 0
		return d.apply(tx, &m, created, h.now())
	})
	if err != nil {
		writeOpaque500(w)
		return
	}
	status := http.StatusOK
	if created {
		status = http.StatusCreated
	}
	writeManaged(w, db, m.ID, status, map[string]any{"created": created})
}

// UpdateMaterial answers PUT /materials/{id}: the same body as POST, applied
// to that material, so a title or course can change. A title and course
// another material already has is a 422, because POST would then be
// ambiguous. An unknown id is a 404.
func (h *Handlers) UpdateMaterial(w http.ResponseWriter, r *http.Request) {
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	id, ok := surf.IntParam(r, "id")
	if !ok {
		writeNotFound(w)
		return
	}
	d, ok := h.readMaterial(w, r, db)
	if !ok {
		return
	}
	var m models.Material
	found, taken := false, false
	err := lagoon.Transaction(r.Context(), db, func(_ context.Context, tx *gorm.DB) error {
		res := tx.Where("id = ?", id).Limit(1).Find(&m)
		if res.Error != nil {
			return res.Error
		}
		if res.RowsAffected == 0 {
			return nil
		}
		found = true
		var n int64
		if err := d.identity(tx.Model(&models.Material{})).Where("id <> ?", m.ID).Count(&n).Error; err != nil {
			return err
		}
		if n > 0 {
			taken = true
			return nil
		}
		return d.apply(tx, &m, false, h.now())
	})
	switch {
	case err != nil:
		writeOpaque500(w)
	case !found:
		writeNotFound(w)
	case taken:
		writeValidation(w, map[string][]string{"title": {"Another material already has this title and course."}})
	default:
		writeManaged(w, db, m.ID, http.StatusOK, nil)
	}
}

// managedMaterialDetailJSON is GET /materials/{id}: the material with its
// public files.
type managedMaterialDetailJSON struct {
	managedMaterialJSON
	Files []fileJSON `json:"files"`
}

// ManagedMaterial answers GET /materials/{id}: one material, draft or not,
// with its public files.
func (h *Handlers) ManagedMaterial(w http.ResponseWriter, r *http.Request) {
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	id, ok := surf.IntParam(r, "id")
	if !ok {
		writeNotFound(w)
		return
	}
	var m models.Material
	res := preloadMaterial(db).Where("jz_bm_materials.id = ?", id).Limit(1).Find(&m)
	if res.Error != nil {
		writeOpaque500(w)
		return
	}
	if res.RowsAffected == 0 {
		writeNotFound(w)
		return
	}
	var files []attach.File
	err := db.Where("attachment_type = ? AND attachment_id = ? AND field = ?", m.MorphName(), strconv.FormatUint(uint64(m.ID), 10), models.MaterialFilesField).
		Order("sort_order, id").
		Find(&files).Error
	if err != nil {
		writeOpaque500(w)
		return
	}
	out := managedMaterialDetailJSON{managedMaterialJSON: newManagedMaterialJSON(m), Files: make([]fileJSON, 0, len(files))}
	for i := range files {
		f := &files[i]
		if !f.Public() {
			continue
		}
		out.Files = append(out.Files, fileJSON{ID: f.ID, URL: f.URL(), Name: f.FileName, Size: f.FileSize, Mime: f.ContentType})
	}
	writeData(w, out)
}

// DeleteMaterial answers DELETE /materials/{id}.
func (h *Handlers) DeleteMaterial(w http.ResponseWriter, r *http.Request) {
	db, ok := h.db(w, r)
	if !ok {
		return
	}
	id, ok := surf.IntParam(r, "id")
	if !ok {
		writeNotFound(w)
		return
	}
	res := db.Where("id = ?", id).Delete(&models.Material{})
	if res.Error != nil {
		writeOpaque500(w)
		return
	}
	if res.RowsAffected == 0 {
		writeNotFound(w)
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

// polish maps the Polish letters slugify cannot fold by case alone.
var polish = strings.NewReplacer("ą", "a", "ć", "c", "ę", "e", "ł", "l", "ń", "n", "ó", "o", "ś", "s", "ź", "z", "ż", "z")

// slugify turns a tag name into its slug: lower-case ASCII letters and
// digits, with a hyphen for every run of anything else.
func slugify(name string) string {
	var b strings.Builder
	hyphen := false
	for _, r := range polish.Replace(strings.ToLower(name)) {
		if r < unicode.MaxASCII && (unicode.IsLetter(r) || unicode.IsDigit(r)) {
			if hyphen && b.Len() > 0 {
				b.WriteByte('-')
			}
			hyphen = false
			b.WriteRune(r)
			continue
		}
		hyphen = true
	}
	return b.String()
}