// Package sabnzbd is a client for the SABnzbd HTTP API.
package sabnzbd

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

// Client talks to a SABnzbd instance.
type Client struct {
	baseURL string
	apiKey  string
	http    *http.Client
}

// NewClient returns a client for the instance at baseURL.
func NewClient(baseURL, apiKey string) *Client {
	return &Client{
		baseURL: strings.TrimRight(baseURL, "/"),
		apiKey:  apiKey,
		http:    &http.Client{Timeout: 30 * time.Second},
	}
}

// Number is a float that SABnzbd sends either as a JSON number or as a string ("0.48").
type Number float64

// UnmarshalJSON accepts numbers, numeric strings, empty strings and null.
func (n *Number) UnmarshalJSON(b []byte) error {
	s := strings.Trim(string(b), `"`)
	if s == "" || s == "null" {
		*n = 0
		return nil
	}
	f, err := strconv.ParseFloat(s, 64)
	if err != nil {
		return fmt.Errorf("parsing number %q: %w", s, err)
	}
	*n = Number(f)
	return nil
}

// Slot is a job in the download queue.
type Slot struct {
	ID         string `json:"nzo_id"`
	Name       string `json:"filename"`
	Category   string `json:"cat"`
	Status     string `json:"status"` // Downloading, Queued, Paused, Fetching, ...
	Priority   string `json:"priority"`
	Size       string `json:"size"`
	SizeLeft   string `json:"sizeleft"`
	MB         Number `json:"mb"`
	MBLeft     Number `json:"mbleft"`
	Percentage Number `json:"percentage"`
	TimeLeft   string `json:"timeleft"`
}

// Queue is the current download queue.
type Queue struct {
	Status     string `json:"status"` // Downloading, Idle, Paused
	Paused     bool   `json:"paused"`
	KBPerSec   Number `json:"kbpersec"`
	SpeedLimit Number `json:"speedlimit_abs"` // bytes/s, 0 = unlimited
	Size       string `json:"size"`
	SizeLeft   string `json:"sizeleft"`
	TimeLeft   string `json:"timeleft"`
	TotalSlots int    `json:"noofslots_total"`
	Slots      []Slot `json:"slots"`
}

// HistorySlot is a finished (or post-processing) job.
type HistorySlot struct {
	ID          string `json:"nzo_id"`
	Name        string `json:"name"`
	Category    string `json:"category"`
	Status      string `json:"status"` // Completed, Failed, Extracting, ...
	Size        string `json:"size"`
	FailMessage string `json:"fail_message"`
	Completed   int64  `json:"completed"` // unix time
}

// Failed reports whether the job failed.
func (h HistorySlot) Failed() bool { return h.Status == "Failed" }

// Version returns the SABnzbd version string.
func (c *Client) Version(ctx context.Context) (string, error) {
	var r struct {
		Version string `json:"version"`
	}
	err := c.call(ctx, url.Values{"mode": {"version"}}, &r)
	return r.Version, err
}

// Queue fetches the download queue.
func (c *Client) Queue(ctx context.Context) (Queue, error) {
	var r struct {
		Queue Queue `json:"queue"`
	}
	err := c.call(ctx, url.Values{"mode": {"queue"}}, &r)
	return r.Queue, err
}

// History fetches the most recent limit history entries.
func (c *Client) History(ctx context.Context, limit int) ([]HistorySlot, error) {
	var r struct {
		History struct {
			Slots []HistorySlot `json:"slots"`
		} `json:"history"`
	}
	err := c.call(ctx, url.Values{"mode": {"history"}, "limit": {strconv.Itoa(limit)}}, &r)
	return r.History.Slots, err
}

// Pause pauses the whole queue.
func (c *Client) Pause(ctx context.Context) error {
	return c.call(ctx, url.Values{"mode": {"pause"}}, nil)
}

// Resume resumes the whole queue.
func (c *Client) Resume(ctx context.Context) error {
	return c.call(ctx, url.Values{"mode": {"resume"}}, nil)
}

// DeleteJob removes a job from the queue, optionally deleting its files.
func (c *Client) DeleteJob(ctx context.Context, id string, deleteFiles bool) error {
	return c.call(ctx, url.Values{
		"mode": {"queue"}, "name": {"delete"}, "value": {id}, "del_files": {boolParam(deleteFiles)},
	}, nil)
}

// DeleteHistory removes a history entry, optionally deleting its files.
func (c *Client) DeleteHistory(ctx context.Context, id string, deleteFiles bool) error {
	return c.call(ctx, url.Values{
		"mode": {"history"}, "name": {"delete"}, "value": {id}, "del_files": {boolParam(deleteFiles)},
	}, nil)
}

// Retry re-queues a failed job from the history.
func (c *Client) Retry(ctx context.Context, id string) error {
	return c.call(ctx, url.Values{"mode": {"retry"}, "value": {id}}, nil)
}

func boolParam(b bool) string {
	if b {
		return "1"
	}
	return "0"
}

// call performs an API request. SABnzbd reports failures with HTTP 200 and
// {"status": false, "error": "..."}, which is turned into an error here.
func (c *Client) call(ctx context.Context, params url.Values, out any) error {
	params.Set("output", "json")
	params.Set("apikey", c.apiKey)

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, c.baseURL+"/api?"+params.Encode(), nil)
	if err != nil {
		return stripURL(err)
	}
	resp, err := c.http.Do(req)
	if err != nil {
		return stripURL(err)
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(io.LimitReader(resp.Body, 16<<20))
	if err != nil {
		return stripURL(err)
	}
	if resp.StatusCode < 200 || resp.StatusCode > 299 {
		return fmt.Errorf("HTTP %d: %s", resp.StatusCode, snippet(body))
	}

	var failure struct {
		Status any    `json:"status"`
		Error  string `json:"error"`
	}
	if err := json.Unmarshal(body, &failure); err != nil {
		// e.g. the plain-text "Access denied - Hostname verification failed"
		return fmt.Errorf("unexpected response: %s", snippet(body))
	}
	if failure.Error != "" {
		return errors.New(failure.Error)
	}
	if ok, isBool := failure.Status.(bool); isBool && !ok {
		return errors.New("request failed")
	}
	if out == nil {
		return nil
	}
	if err := json.Unmarshal(body, out); err != nil {
		return fmt.Errorf("decoding response: %w", err)
	}
	return nil
}

func snippet(b []byte) string {
	return strings.TrimSpace(string(b[:min(len(b), 200)]))
}

// stripURL drops the request URL from transport errors: it contains the API key.
func stripURL(err error) error {
	var ue *url.Error
	if errors.As(err, &ue) {
		return fmt.Errorf("%s: %w", ue.Op, ue.Err)
	}
	return err
}