package api

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"net/url"
	"strconv"
	"strings"
	"time"
)

// SessionCookie is the cookie terdut-server's web UI signs in with.
const SessionCookie = "terdut_session"

// Client talks to terdut-server as the user who signed in. Login trades a
// username and password for a session, the same one the web UI holds, and every
// request after it carries that session's cookie.
//
// The cookie is attached by hand rather than through a cookie jar: the server
// marks it Secure behind https, and a jar drops a Secure cookie it is handed
// over plain http, which would make a local server unusable for no reason. There
// is nothing else a jar would do here — the token is opaque and does not change
// while the session lives.
type Client struct {
	baseURL    string
	httpClient *http.Client
	session    string
}

func NewClient(baseURL string) *Client {
	return &Client{
		baseURL: strings.TrimRight(baseURL, "/"),
		httpClient: &http.Client{
			Timeout: 10 * time.Second,
		},
	}
}

// SetSession resumes a session from a token saved earlier.
func (c *Client) SetSession(token string) { c.session = token }

// HasSession reports whether there is a session to try. It says nothing about
// whether the server still honours it.
func (c *Client) HasSession() bool { return c.session != "" }

// Login signs in and returns the session token, which the client also keeps and
// sends from then on. The server answers a wrong password, an unknown user and
// an account with no password all with the same 401, so the caller cannot tell
// them apart. Too many failures come back as 429.
func (c *Client) Login(username, password string) (string, error) {
	body := struct {
		Username string `json:"username"`
		Password string `json:"password"`
	}{Username: username, Password: password}
	req, err := c.newRequestWithBody(http.MethodPost, "/api/login", body)
	if err != nil {
		return "", err
	}
	// A stale session must not ride along on the request that replaces it.
	req.Header.Del("Cookie")

	resp, err := c.httpClient.Do(req)
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()
	if resp.StatusCode >= 400 {
		return "", statusError(resp)
	}
	for _, ck := range resp.Cookies() {
		if ck.Name == SessionCookie && ck.Value != "" {
			c.session = ck.Value
			return ck.Value, nil
		}
	}
	return "", fmt.Errorf("server signed us in but sent no %s cookie", SessionCookie)
}

// AuthConfig asks how the server can be signed in to. It is unauthenticated, so
// it works before anybody has signed in.
func (c *Client) AuthConfig() (AuthConfig, error) {
	var cfg AuthConfig
	req, err := http.NewRequest(http.MethodGet, c.baseURL+"/api/auth/config", nil)
	if err != nil {
		return cfg, err
	}
	req.Header.Set("Accept", "application/json")
	err = c.do(req, &cfg)
	return cfg, err
}

// The ways a device login poll can end other than with a session.
var (
	// ErrDevicePending means nobody has approved yet: poll again after the
	// interval.
	ErrDevicePending = errors.New("waiting for approval")

	// ErrDeviceSlowDown means the server was polled faster than it asked. It is
	// not a failure; poll again, a little slower.
	ErrDeviceSlowDown = errors.New("polling too fast")

	// ErrDeviceExpired means the person took too long, or the server forgot the
	// login. ErrDeviceDenied means they refused it.
	ErrDeviceExpired = errors.New("the sign-in expired")
	ErrDeviceDenied  = errors.New("the sign-in was refused")
)

// StartDeviceLogin asks the server to begin a device login.
func (c *Client) StartDeviceLogin() (*DeviceLogin, error) {
	req, err := c.newRequestWithBody(http.MethodPost, "/api/oidc/device", struct{}{})
	if err != nil {
		return nil, err
	}
	req.Header.Del("Cookie")
	var d DeviceLogin
	if err := c.do(req, &d); err != nil {
		return nil, err
	}
	if d.DeviceCode == "" || d.UserCode == "" || d.VerificationURL == "" {
		return nil, errors.New("server started a sign-in but sent no code")
	}
	return &d, nil
}

// PollDeviceLogin asks whether the person has approved. On approval it returns
// the session token, which the client also keeps; until then it returns one of
// the ErrDevice* errors.
func (c *Client) PollDeviceLogin(deviceCode string) (string, error) {
	req, err := c.newRequestWithBody(http.MethodPost, "/api/oidc/device/token",
		struct {
			DeviceCode string `json:"device_code"`
		}{deviceCode})
	if err != nil {
		return "", err
	}
	req.Header.Del("Cookie")

	resp, err := c.httpClient.Do(req)
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()

	switch resp.StatusCode {
	case http.StatusAccepted:
		return "", ErrDevicePending
	case http.StatusTooManyRequests:
		return "", ErrDeviceSlowDown
	case http.StatusGone:
		var e struct {
			Error string `json:"error"`
		}
		_ = json.NewDecoder(resp.Body).Decode(&e)
		if e.Error == "denied" {
			return "", ErrDeviceDenied
		}
		return "", ErrDeviceExpired
	}
	if resp.StatusCode >= 400 {
		return "", statusError(resp)
	}
	for _, ck := range resp.Cookies() {
		if ck.Name == SessionCookie && ck.Value != "" {
			c.session = ck.Value
			return ck.Value, nil
		}
	}
	return "", fmt.Errorf("server signed us in but sent no %s cookie", SessionCookie)
}

// Logout ends the session on the server and forgets it here.
func (c *Client) Logout() error {
	req, err := c.newRequest(http.MethodPost, "/api/logout")
	if err != nil {
		return err
	}
	err = c.do(req, nil)
	c.session = ""
	return err
}

// authorize puts the session on a request.
func (c *Client) authorize(req *http.Request) {
	req.Header.Set("Accept", "application/json")
	if c.session != "" {
		req.AddCookie(&http.Cookie{Name: SessionCookie, Value: c.session})
	}
}

func (c *Client) newRequest(method, path string) (*http.Request, error) {
	req, err := http.NewRequest(method, c.baseURL+path, nil)
	if err != nil {
		return nil, err
	}
	c.authorize(req)
	return req, nil
}

// StatusError is a response the server answered with a 4xx or 5xx. Message is
// the server's own {"error": ...} text, empty when the body carried none.
type StatusError struct {
	Code    int
	Message string
}

func (e *StatusError) Error() string {
	if e.Message != "" {
		return fmt.Sprintf("server returned %d: %s", e.Code, e.Message)
	}
	return fmt.Sprintf("server returned %d", e.Code)
}

// IsUnauthorized reports whether err is the server refusing the session: it
// expired, was ended elsewhere, or belongs to an account since disabled.
func IsUnauthorized(err error) bool {
	var se *StatusError
	return errors.As(err, &se) && se.Code == http.StatusUnauthorized
}

func statusError(resp *http.Response) error {
	var e struct {
		Error string `json:"error"`
	}
	_ = json.NewDecoder(resp.Body).Decode(&e)
	return &StatusError{Code: resp.StatusCode, Message: e.Error}
}

func (c *Client) do(req *http.Request, out any) error {
	resp, err := c.httpClient.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()

	if resp.StatusCode >= 400 {
		return statusError(resp)
	}

	if out != nil {
		return json.NewDecoder(resp.Body).Decode(out)
	}
	return nil
}

// ListAlerts fetches alerts. teamID limits them to one team; 0 means every team
// the caller belongs to. status may be "firing", "resolved", or "" for all.
// Set archived=true to fetch only archived alerts; false returns only non-archived.
//
// Alerts are read-only on the server — there is nothing to acknowledge or
// archive here. This is the raw feed, useful for checking what Alertmanager is
// actually sending; the work queue is ListIncidents.
func (c *Client) ListAlerts(teamID int64, status string, archived bool, limit int) ([]Alert, error) {
	q := url.Values{}
	if teamID > 0 {
		q.Set("team_id", strconv.FormatInt(teamID, 10))
	}
	if status != "" {
		q.Set("status", status)
	}
	if archived {
		q.Set("archived", "true")
	}
	if limit > 0 {
		q.Set("limit", strconv.Itoa(limit))
	}
	path := "/api/alerts"
	if len(q) > 0 {
		path += "?" + q.Encode()
	}

	req, err := c.newRequest(http.MethodGet, path)
	if err != nil {
		return nil, err
	}
	var alerts []Alert
	return alerts, c.do(req, &alerts)
}

// GetAlertStats fetches aggregate alert counts.
func (c *Client) GetAlertStats() (*AlertStats, error) {
	req, err := c.newRequest(http.MethodGet, "/api/stats/alerts")
	if err != nil {
		return nil, err
	}
	var stats AlertStats
	return &stats, c.do(req, &stats)
}

func (c *Client) newRequestWithBody(method, path string, body any) (*http.Request, error) {
	data, err := json.Marshal(body)
	if err != nil {
		return nil, err
	}
	req, err := http.NewRequest(method, c.baseURL+path, bytes.NewReader(data))
	if err != nil {
		return nil, err
	}
	c.authorize(req)
	req.Header.Set("Content-Type", "application/json")
	return req, nil
}

func (c *Client) GetAlert(id int64) (*Alert, error) {
	req, err := c.newRequest(http.MethodGet, fmt.Sprintf("/api/alerts/%d", id))
	if err != nil {
		return nil, err
	}
	var alert Alert
	return &alert, c.do(req, &alert)
}

// ── Incidents ──────────────────────────────────────────────────────────────

// ListIncidents fetches the work queue. teamID limits it to one team; 0 means
// every team the caller belongs to. status may be "triggered",
// "acknowledged", "resolved", or "" for the server default of open incidents
// only. archived and snoozed each switch the list to that set rather than
// adding to it, matching the server's filters.
func (c *Client) ListIncidents(teamID int64, status string, archived, snoozed bool, limit int) ([]Incident, error) {
	q := url.Values{}
	if teamID > 0 {
		q.Set("team_id", strconv.FormatInt(teamID, 10))
	}
	if status != "" {
		q.Set("status", status)
	}
	if archived {
		q.Set("archived", "true")
	}
	if snoozed {
		q.Set("snoozed", "true")
	}
	if limit > 0 {
		q.Set("limit", strconv.Itoa(limit))
	}
	path := "/api/incidents"
	if len(q) > 0 {
		path += "?" + q.Encode()
	}

	req, err := c.newRequest(http.MethodGet, path)
	if err != nil {
		return nil, err
	}
	var incidents []Incident
	return incidents, c.do(req, &incidents)
}

// GetIncident returns one incident with its member alerts inline.
func (c *Client) GetIncident(id int64) (*Incident, error) {
	req, err := c.newRequest(http.MethodGet, fmt.Sprintf("/api/incidents/%d", id))
	if err != nil {
		return nil, err
	}
	var incident Incident
	return &incident, c.do(req, &incident)
}

func (c *Client) GetIncidentTimeline(id int64) ([]IncidentEvent, error) {
	req, err := c.newRequest(http.MethodGet, fmt.Sprintf("/api/incidents/%d/timeline", id))
	if err != nil {
		return nil, err
	}
	var events []IncidentEvent
	return events, c.do(req, &events)
}

// GetSimilarIncidents lists earlier resolved incidents that look like this one
// and have notes. Servers before the similar-incidents endpoint answer 404; the
// caller treats any error as "nothing to show".
func (c *Client) GetSimilarIncidents(id int64) ([]SimilarIncident, error) {
	req, err := c.newRequest(http.MethodGet, fmt.Sprintf("/api/incidents/%d/similar", id))
	if err != nil {
		return nil, err
	}
	var similar []SimilarIncident
	return similar, c.do(req, &similar)
}

func (c *Client) AcknowledgeIncident(id int64) (*Incident, error) {
	req, err := c.newRequest(http.MethodPost, fmt.Sprintf("/api/incidents/%d/acknowledge", id))
	if err != nil {
		return nil, err
	}
	var incident Incident
	return &incident, c.do(req, &incident)
}

func (c *Client) UnacknowledgeIncident(id int64) error {
	req, err := c.newRequest(http.MethodDelete, fmt.Sprintf("/api/incidents/%d/acknowledge", id))
	if err != nil {
		return err
	}
	return c.do(req, nil)
}

// ResolveIncident closes an incident by hand. This is terminal on the server: a
// later occurrence in the same group opens a new incident rather than reopening
// this one, and if the alert underneath never stops firing the incident stays
// closed. Use SnoozeIncident for "not now".
func (c *Client) ResolveIncident(id int64) (*Incident, error) {
	req, err := c.newRequest(http.MethodPost, fmt.Sprintf("/api/incidents/%d/resolve", id))
	if err != nil {
		return nil, err
	}
	var incident Incident
	return &incident, c.do(req, &incident)
}

func (c *Client) AssignIncident(id, userID int64) (*Incident, error) {
	body := struct {
		UserID int64 `json:"user_id"`
	}{UserID: userID}
	req, err := c.newRequestWithBody(http.MethodPost, fmt.Sprintf("/api/incidents/%d/assign", id), body)
	if err != nil {
		return nil, err
	}
	var incident Incident
	return &incident, c.do(req, &incident)
}

// SnoozeIncident hides an incident from the default queue for a duration,
// without closing it.
func (c *Client) SnoozeIncident(id int64, duration string) (*Incident, error) {
	body := struct {
		Duration string `json:"duration"`
	}{Duration: duration}
	req, err := c.newRequestWithBody(http.MethodPost, fmt.Sprintf("/api/incidents/%d/snooze", id), body)
	if err != nil {
		return nil, err
	}
	var incident Incident
	return &incident, c.do(req, &incident)
}

func (c *Client) UnsnoozeIncident(id int64) error {
	req, err := c.newRequest(http.MethodDelete, fmt.Sprintf("/api/incidents/%d/snooze", id))
	if err != nil {
		return err
	}
	return c.do(req, nil)
}

func (c *Client) ArchiveIncident(id int64) (*Incident, error) {
	req, err := c.newRequest(http.MethodPost, fmt.Sprintf("/api/incidents/%d/archive", id))
	if err != nil {
		return nil, err
	}
	var incident Incident
	return &incident, c.do(req, &incident)
}

func (c *Client) UnarchiveIncident(id int64) error {
	req, err := c.newRequest(http.MethodDelete, fmt.Sprintf("/api/incidents/%d/archive", id))
	if err != nil {
		return err
	}
	return c.do(req, nil)
}

// AddNote appends a note to the incident's timeline. pinned files it as the
// resolution note: what fixed the incident, shown on similar ones later.
func (c *Client) AddNote(incidentID int64, content string, pinned bool) (*IncidentEvent, error) {
	req, err := c.newRequestWithBody(http.MethodPost,
		fmt.Sprintf("/api/incidents/%d/notes", incidentID), map[string]any{"content": content, "pinned": pinned})
	if err != nil {
		return nil, err
	}
	var event IncidentEvent
	return &event, c.do(req, &event)
}

// DeleteNote removes one of your own notes. Only notes are deletable — the rest
// of the timeline is a record of what happened.
func (c *Client) DeleteNote(incidentID, eventID int64) error {
	req, err := c.newRequest(http.MethodDelete,
		fmt.Sprintf("/api/incidents/%d/notes/%d", incidentID, eventID))
	if err != nil {
		return err
	}
	return c.do(req, nil)
}

func (c *Client) GetIncidentStats() (*IncidentStats, error) {
	req, err := c.newRequest(http.MethodGet, "/api/stats/incidents")
	if err != nil {
		return nil, err
	}
	var stats IncidentStats
	return &stats, c.do(req, &stats)
}

// ── Statistics ─────────────────────────────────────────────────────────────

func (c *Client) GetTopAlerts(limit int) ([]TopAlert, error) {
	req, err := c.newRequest(http.MethodGet, fmt.Sprintf("/api/stats/alerts/top?limit=%d", limit))
	if err != nil {
		return nil, err
	}
	var result []TopAlert
	return result, c.do(req, &result)
}

func (c *Client) GetStatsByHour() ([]HourStat, error) {
	req, err := c.newRequest(http.MethodGet, "/api/stats/alerts/by-hour")
	if err != nil {
		return nil, err
	}
	var result []HourStat
	return result, c.do(req, &result)
}

func (c *Client) GetStatsByDay() ([]DayStat, error) {
	req, err := c.newRequest(http.MethodGet, "/api/stats/alerts/by-day")
	if err != nil {
		return nil, err
	}
	var result []DayStat
	return result, c.do(req, &result)
}

// ── Teams ──────────────────────────────────────────────────────────────────

// ListTeams returns the teams the caller belongs to, with the caller's role in
// each. Everything else the server returns is scoped to these. A server that
// predates teams (v0.12) answers 404, which is how the TUI spots one.
func (c *Client) ListTeams() ([]Team, error) {
	req, err := c.newRequest(http.MethodGet, "/api/teams")
	if err != nil {
		return nil, err
	}
	var teams []Team
	return teams, c.do(req, &teams)
}

// ListTeamMembers returns who belongs to a team. A schedule can only be given to
// its own members, so this is the assignee list for one.
func (c *Client) ListTeamMembers(teamID int64) ([]TeamMember, error) {
	req, err := c.newRequest(http.MethodGet, fmt.Sprintf("/api/teams/%d/members", teamID))
	if err != nil {
		return nil, err
	}
	var members []TeamMember
	return members, c.do(req, &members)
}

// ── Schedule ───────────────────────────────────────────────────────────────

// GetSchedule returns a team's on-call entries between two YYYY-MM-DD dates.
func (c *Client) GetSchedule(teamID int64, from, to string) ([]ScheduleEntry, error) {
	q := url.Values{"from": {from}, "to": {to}}
	req, err := c.newRequest(http.MethodGet, fmt.Sprintf("/api/teams/%d/schedule?%s", teamID, q.Encode()))
	if err != nil {
		return nil, err
	}
	var entries []ScheduleEntry
	return entries, c.do(req, &entries)
}

// GetCurrentOnCall returns today's on-call entries, one per team that has
// somebody scheduled. It is empty, not an error, when nobody is.
func (c *Client) GetCurrentOnCall() ([]ScheduleEntry, error) {
	req, err := c.newRequest(http.MethodGet, "/api/schedule/current")
	if err != nil {
		return nil, err
	}
	var entries []ScheduleEntry
	return entries, c.do(req, &entries)
}

// AssignSchedule puts one team member on call for the given dates. Only a team
// owner or an administrator may.
//
// The server holds one person per day and refuses a date somebody already has,
// so replace is what takes a shift off its current holder. It is all-or-nothing
// either way: a week of free and taken days moves as a unit, or not at all.
func (c *Client) AssignSchedule(teamID, userID int64, dates []string, replace bool) ([]ScheduleEntry, error) {
	body := struct {
		UserID  int64    `json:"user_id"`
		Dates   []string `json:"dates"`
		Replace bool     `json:"replace,omitempty"`
	}{UserID: userID, Dates: dates, Replace: replace}
	req, err := c.newRequestWithBody(http.MethodPost, fmt.Sprintf("/api/teams/%d/schedule", teamID), body)
	if err != nil {
		return nil, err
	}
	var entries []ScheduleEntry
	return entries, c.do(req, &entries)
}

func (c *Client) DeleteScheduleEntry(teamID, id int64) error {
	req, err := c.newRequest(http.MethodDelete, fmt.Sprintf("/api/teams/%d/schedule/%d", teamID, id))
	if err != nil {
		return err
	}
	return c.do(req, nil)
}

// ── Users ──────────────────────────────────────────────────────────────────

func (c *Client) ListUsers() ([]User, error) {
	req, err := c.newRequest(http.MethodGet, "/api/users")
	if err != nil {
		return nil, err
	}
	var users []User
	return users, c.do(req, &users)
}

func (c *Client) CreateUser(username, email string) (*User, error) {
	body := struct {
		Username string `json:"username"`
		Email    string `json:"email"`
	}{Username: username, Email: email}
	req, err := c.newRequestWithBody(http.MethodPost, "/api/users", body)
	if err != nil {
		return nil, err
	}
	var user User
	return &user, c.do(req, &user)
}

// SetUserNotifyTarget points a user's push notifications at an ntfy topic.
//
// An empty topic clears it: the server stores NULL, and that user's incidents
// page the shared fallback topic instead — which carries no Acknowledge button,
// because anyone subscribed to it could otherwise acknowledge as somebody else.
func (c *Client) SetUserNotifyTarget(userID int64, topic string) (*User, error) {
	body := struct {
		NtfyTopic string `json:"ntfy_topic"`
	}{NtfyTopic: topic}
	req, err := c.newRequestWithBody(http.MethodPut, fmt.Sprintf("/api/users/%d/notify", userID), body)
	if err != nil {
		return nil, err
	}
	var user User
	return &user, c.do(req, &user)
}

func (c *Client) DeleteUser(id int64) error {
	req, err := c.newRequest(http.MethodDelete, fmt.Sprintf("/api/users/%d", id))
	if err != nil {
		return err
	}
	return c.do(req, nil)
}

func (c *Client) CreateAPIKey(userID int64, name string) (*APIKey, error) {
	body := struct {
		Name string `json:"name"`
	}{Name: name}
	req, err := c.newRequestWithBody(http.MethodPost, fmt.Sprintf("/api/users/%d/api-keys", userID), body)
	if err != nil {
		return nil, err
	}
	var key APIKey
	return &key, c.do(req, &key)
}

func (c *Client) DeleteAPIKey(userID, keyID int64) error {
	req, err := c.newRequest(http.MethodDelete, fmt.Sprintf("/api/users/%d/api-keys/%d", userID, keyID))
	if err != nil {
		return err
	}
	return c.do(req, nil)
}

// Me returns the user the API key belongs to, and whether they have a web UI
// password.
func (c *Client) Me() (*Me, error) {
	req, err := c.newRequest(http.MethodGet, "/api/me")
	if err != nil {
		return nil, err
	}
	var me Me
	return &me, c.do(req, &me)
}

// SetPassword sets a user's web UI password. current is only checked by the
// server when a user changes their own existing password; pass "" otherwise.
func (c *Client) SetPassword(userID int64, password, current string) error {
	body := struct {
		Password        string `json:"password"`
		CurrentPassword string `json:"current_password,omitempty"`
	}{Password: password, CurrentPassword: current}
	req, err := c.newRequestWithBody(http.MethodPut, fmt.Sprintf("/api/users/%d/password", userID), body)
	if err != nil {
		return err
	}
	return c.do(req, nil)
}

// HealthCheck calls GET /healthz, which is unauthenticated and does no database
// check, so it says the process is up, not that the API key works.
func (c *Client) HealthCheck() error {
	req, err := http.NewRequest(http.MethodGet, c.baseURL+"/healthz", nil)
	if err != nil {
		return err
	}
	resp, err := c.httpClient.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("health check failed: %s", resp.Status)
	}
	return nil
}