package youtrack

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strings"
	"sync"
	"time"
)

const (
	defaultPageSize = 100
	maxPages        = 50
	issueFields     = "idReadable,summary,description,updated,customFields(id,name,$type,value(name,presentation,$type),possibleEvents(id,presentation,$type))"
)

// Issue is a minimal YouTrack issue used for sync.
type Issue struct {
	IDReadable  string
	Summary     string
	Description string
	State       string
	Updated     time.Time
}

// WorkItem is a YouTrack time-tracking work item.
type WorkItem struct {
	ID       string
	Date     time.Time
	Minutes  int
	Text     string
}

// Client talks to the YouTrack REST API.
type Client struct {
	BaseURL    string
	Token      string
	HTTPClient *http.Client

	mu            sync.Mutex
	projectIDByKey map[string]string
}

func (c *Client) http() *http.Client {
	if c.HTTPClient != nil {
		return c.HTTPClient
	}
	return http.DefaultClient
}

func (c *Client) base() string {
	return strings.TrimRight(strings.TrimSpace(c.BaseURL), "/")
}

func (c *Client) ensureAuth() error {
	if c.base() == "" {
		return fmt.Errorf("youtrack: base URL required")
	}
	if strings.TrimSpace(c.Token) == "" {
		return fmt.Errorf("youtrack: token required")
	}
	return nil
}

// ListIssues fetches issues matching query (paginated).
func (c *Client) ListIssues(ctx context.Context, query string) ([]Issue, error) {
	if err := c.ensureAuth(); err != nil {
		return nil, err
	}

	var all []Issue
	for page := 0; page < maxPages; page++ {
		skip := page * defaultPageSize
		u, err := url.Parse(c.base() + "/api/issues")
		if err != nil {
			return nil, fmt.Errorf("youtrack: parse url: %w", err)
		}
		q := u.Query()
		q.Set("query", query)
		q.Set("fields", issueFields)
		q.Set("$top", fmt.Sprintf("%d", defaultPageSize))
		q.Set("$skip", fmt.Sprintf("%d", skip))
		u.RawQuery = q.Encode()

		var raw []rawIssue
		if err := c.doJSON(ctx, http.MethodGet, u.String(), nil, &raw); err != nil {
			return nil, err
		}
		for _, r := range raw {
			all = append(all, r.toIssue())
		}
		if len(raw) < defaultPageSize {
			break
		}
	}
	return all, nil
}

// CreateIssue creates an issue in the project identified by shortName (e.g. PROJ).
func (c *Client) CreateIssue(ctx context.Context, projectKey, summary, description, state string) (Issue, error) {
	if err := c.ensureAuth(); err != nil {
		return Issue{}, err
	}
	projectKey = strings.TrimSpace(projectKey)
	if projectKey == "" {
		return Issue{}, fmt.Errorf("youtrack: project key required")
	}
	if strings.TrimSpace(summary) == "" {
		return Issue{}, fmt.Errorf("youtrack: summary required")
	}

	projectID, err := c.resolveProjectID(ctx, projectKey)
	if err != nil {
		return Issue{}, err
	}

	body := map[string]any{
		"project": map[string]string{"id": projectID},
		"summary": summary,
	}
	if description != "" {
		body["description"] = description
	}
	// Do not set State via customFields — project field types differ
	// (StateIssueCustomField vs StateMachineIssueCustomField). Use ApplyCommand.

	u := c.base() + "/api/issues?fields=" + url.QueryEscape(issueFields)
	var raw rawIssue
	if err := c.doJSON(ctx, http.MethodPost, u, body, &raw); err != nil {
		return Issue{}, err
	}
	iss := raw.toIssue()
	if state != "" && iss.IDReadable != "" {
		if err := c.SetState(ctx, iss.IDReadable, state); err != nil {
			// Title/description already created — don't fail the whole create on state.
			iss.State = iss.State // keep whatever default YouTrack assigned
			_ = err
		} else {
			iss.State = state
		}
	}
	return iss, nil
}

// UpdateIssue updates summary, description and optional State on an existing issue.
func (c *Client) UpdateIssue(ctx context.Context, idReadable, summary, description, state string) (Issue, error) {
	if err := c.ensureAuth(); err != nil {
		return Issue{}, err
	}
	idReadable = strings.TrimSpace(idReadable)
	if idReadable == "" {
		return Issue{}, fmt.Errorf("youtrack: issue id required")
	}

	body := map[string]any{
		"summary":     summary,
		"description": description,
	}

	u := fmt.Sprintf("%s/api/issues/%s?fields=%s",
		c.base(), url.PathEscape(idReadable), url.QueryEscape(issueFields))
	var raw rawIssue
	if err := c.doJSON(ctx, http.MethodPost, u, body, &raw); err != nil {
		return Issue{}, err
	}
	iss := raw.toIssue()
	if iss.IDReadable == "" {
		iss.IDReadable = idReadable
	}

	if state != "" {
		if err := c.SetState(ctx, idReadable, state); err != nil {
			// Summary/description already saved — state mapping is best-effort
			// (field names / state-machine transitions vary per project).
			_ = err
		} else {
			iss.State = state
		}
	}
	return iss, nil
}

// GetIssue loads a single issue by readable id.
func (c *Client) GetIssue(ctx context.Context, idReadable string) (Issue, error) {
	raw, err := c.getIssueRaw(ctx, idReadable)
	if err != nil {
		return Issue{}, err
	}
	return raw.toIssue(), nil
}

func (c *Client) getIssueRaw(ctx context.Context, idReadable string) (rawIssue, error) {
	if err := c.ensureAuth(); err != nil {
		return rawIssue{}, err
	}
	idReadable = strings.TrimSpace(idReadable)
	if idReadable == "" {
		return rawIssue{}, fmt.Errorf("youtrack: issue id required")
	}
	u := fmt.Sprintf("%s/api/issues/%s?fields=%s",
		c.base(), url.PathEscape(idReadable), url.QueryEscape(issueFields))
	var raw rawIssue
	if err := c.doJSON(ctx, http.MethodGet, u, nil, &raw); err != nil {
		return rawIssue{}, err
	}
	return raw, nil
}

// SetState sets the issue's state-like custom field to desiredState.
// Discovers the real field name/$type from the issue (works with renamed fields
// and StateMachineIssueCustomField).
func (c *Client) SetState(ctx context.Context, idReadable, desiredState string) error {
	desiredState = strings.TrimSpace(desiredState)
	if desiredState == "" {
		return nil
	}
	raw, err := c.getIssueRaw(ctx, idReadable)
	if err != nil {
		return err
	}
	sf := findStateField(raw.CustomFields)
	if sf == nil {
		return nil // project has no state-like field
	}
	current := parseStateValue(sf.Value)
	if strings.EqualFold(current, desiredState) {
		return nil
	}

	// State-machine fields must be updated via transition events.
	if strings.Contains(sf.Type, "StateMachine") {
		ev := matchStateEvent(sf.PossibleEvents, desiredState)
		if ev == nil {
			return fmt.Errorf("no transition toward %q on %s (available: %s)",
				desiredState, sf.Name, joinEventPresentations(sf.PossibleEvents))
		}
		body := map[string]any{
			"customFields": []map[string]any{{
				"id":    sf.ID,
				"name":  sf.Name,
				"$type": sf.Type,
				"event": map[string]any{
					"id":           ev.ID,
					"presentation": ev.Presentation,
					"$type":        typeOr(ev.Type, "Event"),
				},
			}},
		}
		u := fmt.Sprintf("%s/api/issues/%s", c.base(), url.PathEscape(idReadable))
		return c.doJSON(ctx, http.MethodPost, u, body, nil)
	}

	// Plain state / enum-like field: use the field's actual name and $type.
	body := map[string]any{
		"customFields": []map[string]any{{
			"id":    sf.ID,
			"name":  sf.Name,
			"$type": typeOr(sf.Type, "StateIssueCustomField"),
			"value": map[string]string{"name": desiredState},
		}},
	}
	u := fmt.Sprintf("%s/api/issues/%s", c.base(), url.PathEscape(idReadable))
	if err := c.doJSON(ctx, http.MethodPost, u, body, nil); err != nil {
		// Fallback: command with discovered field name (quoted for multi-word values).
		cmd := formatFieldCommand(sf.Name, desiredState)
		if cmdErr := c.ApplyCommand(ctx, idReadable, cmd); cmdErr != nil {
			return fmt.Errorf("%v (command %q also failed: %w)", err, cmd, cmdErr)
		}
	}
	return nil
}

// ApplyCommand runs a YouTrack command against one issue (e.g. `Status Fixed`).
func (c *Client) ApplyCommand(ctx context.Context, idReadable, command string) error {
	if err := c.ensureAuth(); err != nil {
		return err
	}
	idReadable = strings.TrimSpace(idReadable)
	command = strings.TrimSpace(command)
	if idReadable == "" || command == "" {
		return fmt.Errorf("youtrack: issue id and command required")
	}
	body := map[string]any{
		"query": command,
		"issues": []map[string]string{
			{"idReadable": idReadable},
		},
	}
	u := c.base() + "/api/commands"
	return c.doJSON(ctx, http.MethodPost, u, body, nil)
}

func formatFieldCommand(fieldName, value string) string {
	fieldName = strings.TrimSpace(fieldName)
	value = strings.TrimSpace(value)
	if strings.ContainsAny(value, " \t") {
		return fmt.Sprintf("%s %s", fieldName, quoteCommandValue(value))
	}
	return fieldName + " " + value
}

func quoteCommandValue(v string) string {
	return "{" + v + "}"
}

type stateEvent struct {
	ID           string
	Presentation string
	Type         string
}

func findStateField(fields []rawCustomField) *rawCustomField {
	var named *rawCustomField
	for i := range fields {
		cf := &fields[i]
		if strings.Contains(cf.Type, "State") {
			return cf
		}
		if strings.EqualFold(cf.Name, "State") || strings.EqualFold(cf.Name, "Status") {
			named = cf
		}
	}
	return named
}

func matchStateEvent(events []rawEvent, desired string) *rawEvent {
	if len(events) == 0 {
		return nil
	}
	desiredLower := strings.ToLower(strings.TrimSpace(desired))
	for i := range events {
		p := strings.ToLower(events[i].Presentation)
		id := strings.ToLower(events[i].ID)
		if p == desiredLower || id == desiredLower {
			return &events[i]
		}
	}
	// Fuzzy: match by status family keywords.
	keywords := stateKeywords(desiredLower)
	for i := range events {
		p := strings.ToLower(events[i].Presentation)
		id := strings.ToLower(events[i].ID)
		for _, kw := range keywords {
			if strings.Contains(p, kw) || strings.Contains(id, kw) {
				return &events[i]
			}
		}
	}
	return nil
}

func stateKeywords(desired string) []string {
	switch {
	case strings.Contains(desired, "progress"), desired == "wip":
		return []string{"progress", "start", "wip", "ongoing", "bearbeitung"}
	case strings.Contains(desired, "fix"), strings.Contains(desired, "done"),
		strings.Contains(desired, "complete"), strings.Contains(desired, "resolve"):
		return []string{"fix", "done", "complete", "resolve", "close", "erledigt", "fertig"}
	default:
		return []string{"open", "reopen", "submit", "offen", "neu"}
	}
}

func joinEventPresentations(events []rawEvent) string {
	parts := make([]string, 0, len(events))
	for _, e := range events {
		if e.Presentation != "" {
			parts = append(parts, e.Presentation)
		} else {
			parts = append(parts, e.ID)
		}
	}
	return strings.Join(parts, ", ")
}

func typeOr(v, fallback string) string {
	if strings.TrimSpace(v) == "" {
		return fallback
	}
	return v
}

func (c *Client) cacheProjectID(shortName, id string) {
	c.mu.Lock()
	defer c.mu.Unlock()
	if c.projectIDByKey == nil {
		c.projectIDByKey = map[string]string{}
	}
	c.projectIDByKey[shortName] = id
}

func (c *Client) resolveProjectID(ctx context.Context, shortName string) (string, error) {
	shortName = strings.TrimSpace(shortName)
	if shortName == "" {
		return "", fmt.Errorf("youtrack: project key required")
	}

	c.mu.Lock()
	if c.projectIDByKey == nil {
		c.projectIDByKey = map[string]string{}
	}
	if id, ok := c.projectIDByKey[shortName]; ok {
		c.mu.Unlock()
		return id, nil
	}
	c.mu.Unlock()

	// 1) Direct lookup — YouTrack accepts shortName as {projectID}.
	if id, err := c.fetchProjectByID(ctx, shortName); err == nil {
		c.cacheProjectID(shortName, id)
		return id, nil
	}

	// 2) List/filter — query is a free-text match on name/shortName (not "shortName: X").
	if id, err := c.findProjectInList(ctx, shortName); err == nil {
		c.cacheProjectID(shortName, id)
		return id, nil
	}

	// 3) Fallback without admin rights: read project id from an existing issue.
	if id, err := c.findProjectViaIssue(ctx, shortName); err == nil {
		c.cacheProjectID(shortName, id)
		return id, nil
	}

	return "", fmt.Errorf("youtrack: project %q not found", shortName)
}

func (c *Client) fetchProjectByID(ctx context.Context, projectID string) (string, error) {
	u := fmt.Sprintf("%s/api/admin/projects/%s?fields=%s",
		c.base(), url.PathEscape(projectID), url.QueryEscape("id,shortName"))
	var p struct {
		ID        string `json:"id"`
		ShortName string `json:"shortName"`
	}
	if err := c.doJSON(ctx, http.MethodGet, u, nil, &p); err != nil {
		return "", err
	}
	if p.ID == "" {
		return "", fmt.Errorf("empty project id")
	}
	return p.ID, nil
}

func (c *Client) findProjectInList(ctx context.Context, shortName string) (string, error) {
	u, err := url.Parse(c.base() + "/api/admin/projects")
	if err != nil {
		return "", err
	}
	q := u.Query()
	q.Set("fields", "id,shortName")
	q.Set("query", shortName)
	q.Set("$top", "100")
	u.RawQuery = q.Encode()

	var projects []struct {
		ID        string `json:"id"`
		ShortName string `json:"shortName"`
	}
	if err := c.doJSON(ctx, http.MethodGet, u.String(), nil, &projects); err != nil {
		return "", err
	}
	for _, p := range projects {
		if strings.EqualFold(p.ShortName, shortName) && p.ID != "" {
			return p.ID, nil
		}
	}
	// Unfiltered list as last admin attempt (small instances).
	u2, err := url.Parse(c.base() + "/api/admin/projects")
	if err != nil {
		return "", err
	}
	q2 := u2.Query()
	q2.Set("fields", "id,shortName")
	q2.Set("$top", "1000")
	u2.RawQuery = q2.Encode()
	if err := c.doJSON(ctx, http.MethodGet, u2.String(), nil, &projects); err != nil {
		return "", err
	}
	for _, p := range projects {
		if strings.EqualFold(p.ShortName, shortName) && p.ID != "" {
			return p.ID, nil
		}
	}
	return "", fmt.Errorf("not in project list")
}

func (c *Client) findProjectViaIssue(ctx context.Context, shortName string) (string, error) {
	u, err := url.Parse(c.base() + "/api/issues")
	if err != nil {
		return "", err
	}
	q := u.Query()
	q.Set("query", "project: "+shortName)
	q.Set("fields", "idReadable,project(id,shortName)")
	q.Set("$top", "1")
	u.RawQuery = q.Encode()

	var issues []struct {
		Project *struct {
			ID        string `json:"id"`
			ShortName string `json:"shortName"`
		} `json:"project"`
	}
	if err := c.doJSON(ctx, http.MethodGet, u.String(), nil, &issues); err != nil {
		return "", err
	}
	if len(issues) == 0 || issues[0].Project == nil || issues[0].Project.ID == "" {
		return "", fmt.Errorf("no issues in project %s to resolve id", shortName)
	}
	return issues[0].Project.ID, nil
}

// Project is a YouTrack project summary for the register/import UI.
type Project struct {
	ID        string
	ShortName string
	Name      string
}

// ListProjects lists admin-accessible projects (requires sufficient token scope).
func (c *Client) ListProjects(ctx context.Context) ([]Project, error) {
	if err := c.ensureAuth(); err != nil {
		return nil, err
	}
	var all []Project
	for page := 0; page < maxPages; page++ {
		skip := page * defaultPageSize
		u, err := url.Parse(c.base() + "/api/admin/projects")
		if err != nil {
			return nil, err
		}
		q := u.Query()
		q.Set("fields", "id,shortName,name")
		q.Set("$top", fmt.Sprintf("%d", defaultPageSize))
		q.Set("$skip", fmt.Sprintf("%d", skip))
		u.RawQuery = q.Encode()

		var raw []struct {
			ID        string `json:"id"`
			ShortName string `json:"shortName"`
			Name      string `json:"name"`
		}
		if err := c.doJSON(ctx, http.MethodGet, u.String(), nil, &raw); err != nil {
			return nil, err
		}
		for _, p := range raw {
			all = append(all, Project{ID: p.ID, ShortName: p.ShortName, Name: p.Name})
		}
		if len(raw) < defaultPageSize {
			break
		}
	}
	return all, nil
}

// IssueURL builds the browser URL for an issue.
func (c *Client) IssueURL(idReadable string) string {
	return c.base() + "/issue/" + idReadable
}

const workItemFields = "id,date,duration(minutes,presentation),text"

// ListWorkItems returns time-tracking work items for an issue.
func (c *Client) ListWorkItems(ctx context.Context, idReadable string) ([]WorkItem, error) {
	if err := c.ensureAuth(); err != nil {
		return nil, err
	}
	idReadable = strings.TrimSpace(idReadable)
	if idReadable == "" {
		return nil, fmt.Errorf("youtrack: issue id required")
	}
	u := fmt.Sprintf("%s/api/issues/%s/timeTracking/workItems?fields=%s&$top=%d",
		c.base(), url.PathEscape(idReadable), url.QueryEscape(workItemFields), defaultPageSize)
	var raw []rawWorkItem
	if err := c.doJSON(ctx, http.MethodGet, u, nil, &raw); err != nil {
		return nil, err
	}
	out := make([]WorkItem, 0, len(raw))
	for _, r := range raw {
		out = append(out, r.toWorkItem())
	}
	return out, nil
}

// CreateWorkItem adds a work item (duration in minutes) to an issue.
func (c *Client) CreateWorkItem(ctx context.Context, idReadable string, minutes int, date time.Time, text string) (WorkItem, error) {
	if err := c.ensureAuth(); err != nil {
		return WorkItem{}, err
	}
	idReadable = strings.TrimSpace(idReadable)
	if idReadable == "" {
		return WorkItem{}, fmt.Errorf("youtrack: issue id required")
	}
	if minutes < 1 {
		minutes = 1
	}
	body := map[string]any{
		"duration": map[string]any{"minutes": minutes},
	}
	if !date.IsZero() {
		// YouTrack expects epoch millis; time part is typically midnight UTC.
		midnight := time.Date(date.Year(), date.Month(), date.Day(), 0, 0, 0, 0, time.UTC)
		body["date"] = midnight.UnixMilli()
	}
	if strings.TrimSpace(text) != "" {
		body["text"] = text
	}
	u := fmt.Sprintf("%s/api/issues/%s/timeTracking/workItems?fields=%s",
		c.base(), url.PathEscape(idReadable), url.QueryEscape(workItemFields))
	var raw rawWorkItem
	if err := c.doJSON(ctx, http.MethodPost, u, body, &raw); err != nil {
		return WorkItem{}, err
	}
	return raw.toWorkItem(), nil
}

// DeleteWorkItem removes a work item from an issue.
func (c *Client) DeleteWorkItem(ctx context.Context, idReadable, workItemID string) error {
	if err := c.ensureAuth(); err != nil {
		return err
	}
	idReadable = strings.TrimSpace(idReadable)
	workItemID = strings.TrimSpace(workItemID)
	if idReadable == "" || workItemID == "" {
		return fmt.Errorf("youtrack: issue id and work item id required")
	}
	u := fmt.Sprintf("%s/api/issues/%s/timeTracking/workItems/%s",
		c.base(), url.PathEscape(idReadable), url.PathEscape(workItemID))
	return c.doJSON(ctx, http.MethodDelete, u, nil, nil)
}

type rawWorkItem struct {
	ID       string `json:"id"`
	Date     int64  `json:"date"`
	Text     string `json:"text"`
	Duration *struct {
		Minutes int `json:"minutes"`
	} `json:"duration"`
}

func (r rawWorkItem) toWorkItem() WorkItem {
	w := WorkItem{ID: r.ID, Text: r.Text}
	if r.Date > 0 {
		w.Date = time.UnixMilli(r.Date).UTC()
	}
	if r.Duration != nil {
		w.Minutes = r.Duration.Minutes
	}
	return w
}

func (c *Client) doJSON(ctx context.Context, method, rawURL string, body any, dest any) error {
	var rdr io.Reader
	if body != nil {
		data, err := json.Marshal(body)
		if err != nil {
			return fmt.Errorf("youtrack: marshal: %w", err)
		}
		rdr = bytes.NewReader(data)
	}
	req, err := http.NewRequestWithContext(ctx, method, rawURL, rdr)
	if err != nil {
		return err
	}
	req.Header.Set("Authorization", "Bearer "+c.Token)
	req.Header.Set("Accept", "application/json")
	if body != nil {
		req.Header.Set("Content-Type", "application/json")
	}

	resp, err := c.http().Do(req)
	if err != nil {
		return fmt.Errorf("youtrack: request: %w", err)
	}
	defer resp.Body.Close()

	respBody, err := io.ReadAll(resp.Body)
	if err != nil {
		return fmt.Errorf("youtrack: read body: %w", err)
	}
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return fmt.Errorf("youtrack: %s: %s", resp.Status, truncate(string(respBody), 300))
	}
	if dest == nil || len(respBody) == 0 {
		return nil
	}
	if err := json.Unmarshal(respBody, dest); err != nil {
		return fmt.Errorf("youtrack: decode: %w", err)
	}
	return nil
}

type rawIssue struct {
	IDReadable   string           `json:"idReadable"`
	Summary      string           `json:"summary"`
	Description  string           `json:"description"`
	Updated      int64            `json:"updated"`
	CustomFields []rawCustomField `json:"customFields"`
}

type rawCustomField struct {
	ID             string          `json:"id"`
	Name           string          `json:"name"`
	Type           string          `json:"$type"`
	Value          json.RawMessage `json:"value"`
	PossibleEvents []rawEvent      `json:"possibleEvents"`
}

type rawEvent struct {
	ID           string `json:"id"`
	Presentation string `json:"presentation"`
	Type         string `json:"$type"`
}

func (r rawIssue) toIssue() Issue {
	iss := Issue{
		IDReadable:  r.IDReadable,
		Summary:     r.Summary,
		Description: r.Description,
	}
	if r.Updated > 0 {
		iss.Updated = time.UnixMilli(r.Updated).UTC()
	}
	if sf := findStateField(r.CustomFields); sf != nil {
		iss.State = parseStateValue(sf.Value)
	}
	return iss
}

func parseStateValue(raw json.RawMessage) string {
	if len(raw) == 0 || string(raw) == "null" {
		return ""
	}
	var obj struct {
		Name         string `json:"name"`
		Presentation string `json:"presentation"`
	}
	if err := json.Unmarshal(raw, &obj); err == nil {
		if obj.Name != "" {
			return obj.Name
		}
		return obj.Presentation
	}
	var s string
	if err := json.Unmarshal(raw, &s); err == nil {
		return s
	}
	return ""
}

func truncate(s string, n int) string {
	if len(s) <= n {
		return s
	}
	return s[:n] + "…"
}