// Command satgen refreshes internal/sat/birds.json from the public databases.
//
// A one-shot generator, run by hand, NOT part of the build — the same
// arrangement as cmd/cntygen. Satellites are switched between modes and new
// ones fly, and the shipped frequency plan should be re-cut every few releases
// rather than typed from memory.
//
//	go run ./cmd/satgen
//
// It reads three sources and joins them on the NORAD catalog number:
//
//   - Celestrak's amateur group and PE0SAT's mirror, for WHICH satellites
//     OpsLog can get elements for. There is no point shipping a frequency plan
//     for a bird whose TLE never arrives.
//   - SatNOGS DB, for the transmitters. It is the maintained, machine-readable
//     transponder database; AMSAT's chart is authoritative but is a web page.
//
// It NEVER destroys a curated entry. The hand-written plans carry things
// SatNOGS does not reliably hold — a CTCSS tone, a readable label, the QO-100
// passband as operators actually describe it — so an existing bird is kept
// verbatim and only has its NORAD number filled in. New satellites are appended.
// Read the diff before committing it: this is a starting point for an operator,
// and a wrong uplink is worse than a missing one.
package main

import (
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"regexp"
	"sort"
	"strconv"
	"strings"
	"time"

	"hamlog/internal/sat"
)

const (
	birdsPath   = "internal/sat/birds.json"
	satnogsTX   = "https://db.satnogs.org/api/transmitters/?format=json"
	satnogsSats = "https://db.satnogs.org/api/satellites/?format=json"
)

// satellite is the subset of a SatNOGS satellite record we use. Its whole
// purpose is the decay date: a frequency plan for a spacecraft that burned up
// two years ago is a row in the operator's list that will never do anything.
type satellite struct {
	NORAD   int    `json:"norad_cat_id"`
	Name    string `json:"name"`
	Names   string `json:"names"` // other designations, comma or newline separated
	Status  string `json:"status"`
	Decayed string `json:"decayed"`
}

// tleFeeds are the element sources OpsLog itself reads (see internal/sat/tle.go).
var tleFeeds = []string{
	"https://celestrak.org/NORAD/elements/gp.php?GROUP=amateur&FORMAT=tle",
	"http://tle.pe0sat.nl/kepler/amateur.txt",
}

// transmitter is the subset of a SatNOGS DB record we use.
type transmitter struct {
	Description  string `json:"description"`
	Alive        bool   `json:"alive"`
	Type         string `json:"type"` // Transmitter | Transponder | Transceiver
	UplinkLow    int64  `json:"uplink_low"`
	UplinkHigh   int64  `json:"uplink_high"`
	DownlinkLow  int64  `json:"downlink_low"`
	DownlinkHigh int64  `json:"downlink_high"`
	Mode         string `json:"mode"`
	Invert       bool   `json:"invert"`
	NORAD        int    `json:"norad_cat_id"`
	Status       string `json:"status"`
}

func main() {
	feed, err := loadFeeds()
	if err != nil {
		die(err)
	}
	fmt.Printf("elements: %d satellites across %d feeds\n", len(feed), len(tleFeeds))

	txs, err := loadTransmitters()
	if err != nil {
		die(err)
	}
	fmt.Printf("satnogs: %d transmitters\n", len(txs))

	cat, err := loadSatellites()
	if err != nil {
		die(err)
	}
	fmt.Printf("satnogs: %d catalogued satellites\n", len(cat))

	birds, err := loadBirds()
	if err != nil {
		die(err)
	}
	fmt.Printf("existing plan: %d satellites\n", len(birds))

	// 0. Drop what has come down. SatNOGS carries the re-entry date, so this is
	//    a documented fact rather than a judgement about which of the missing
	//    satellites are missing for good — the first-generation Tevel
	//    constellation alone had left eight rows that could never do anything.
	kept := birds[:0]
	for _, b := range birds {
		if s, ok := decayed(b, cat); ok {
			fmt.Printf("  - %s re-entered %s — removed\n", b.Name, strings.TrimSuffix(s.Decayed, "T00:00:00Z"))
			continue
		}
		kept = append(kept, b)
	}
	birds = kept

	// 1. Give every curated entry its catalog number, so the join stops
	//    depending on how three different parties spell the same satellite.
	covered := map[int]bool{}
	for i := range birds {
		if birds[i].NORAD == 0 {
			if n, ok := noradFor(birds[i], feed); ok {
				birds[i].NORAD = n
				fmt.Printf("  + NORAD %5d for %s\n", n, birds[i].Name)
			} else {
				fmt.Printf("  ! no elements found for %s — left without a catalog number\n", birds[i].Name)
			}
		}
		if birds[i].NORAD != 0 {
			covered[birds[i].NORAD] = true
		}
	}

	// 2. Append the satellites we can track and have a usable uplink for.
	byNORAD := map[int][]transmitter{}
	for _, t := range txs {
		if !usable(t) || feed[t.NORAD] == "" || covered[t.NORAD] {
			continue
		}
		byNORAD[t.NORAD] = append(byNORAD[t.NORAD], t)
	}
	added := 0
	for n, list := range byNORAD {
		b := sat.Bird{Name: displayName(feed[n]), NORAD: n}
		if alias := strings.TrimSpace(feed[n]); alias != "" && alias != b.Name {
			b.Aliases = []string{alias}
		}
		for _, t := range list {
			b.Transponders = append(b.Transponders, toTransponder(t))
		}
		sort.Slice(b.Transponders, func(i, j int) bool {
			return b.Transponders[i].DownLo < b.Transponders[j].DownLo
		})
		birds = append(birds, b)
		added++
		fmt.Printf("  NEW %5d %-24s %d transponder(s)\n", n, b.Name, len(b.Transponders))
	}

	sort.SliceStable(birds, func(i, j int) bool { return birds[i].Name < birds[j].Name })
	out, err := json.MarshalIndent(birds, "", "  ")
	if err != nil {
		die(err)
	}
	if err := os.WriteFile(birdsPath, append(out, '\n'), 0o644); err != nil {
		die(err)
	}
	fmt.Printf("\nwrote %s — %d satellites (%d new)\n", birdsPath, len(birds), added)
}

// usable decides whether a SatNOGS transmitter is something an operator can
// work through.
//
// The database holds every emission a satellite makes, and most of them are not
// a contact: a telemetry beacon with a command uplink is listed exactly like an
// FM repeater, and shipping the command channel as a transponder would invite
// somebody to transmit on it. So both ends must exist, and anything that
// describes itself as telemetry or control is refused unless it also calls
// itself a repeater, a transponder or a digipeater.
func usable(t transmitter) bool {
	if !t.Alive || t.Status != "active" {
		return false
	}
	if t.UplinkLow <= 0 || t.DownlinkLow <= 0 {
		return false
	}
	d := strings.ToLower(t.Description)
	isWorkable := strings.Contains(d, "repeater") || strings.Contains(d, "transponder") ||
		strings.Contains(d, "digipeater") || strings.Contains(d, "aprs") ||
		strings.Contains(d, "voice") || strings.Contains(d, "sstv") || strings.Contains(d, "dstar")
	if isWorkable {
		return true
	}
	for _, bad := range []string{"telemetry", "command", "control", "dtmf", "beacon", "tlm"} {
		if strings.Contains(d, bad) {
			return false
		}
	}
	// An ANALOG emission with both ends is a contact by construction: nobody
	// puts an FM or SSB uplink on a satellite for housekeeping. This is what
	// catches the plainly-described repeaters — AO-27 says only "Mode V/U FM",
	// and rejecting it for not using the word "repeater" would have dropped one
	// of the best-known FM birds there is.
	if m := adifMode(t.Mode); m == "FM" || m == "SSB" || m == "CW" {
		return true
	}
	// A digital emission has to say what it is. A GMSK uplink is a command
	// channel far more often than it is a digipeater, and shipping the wrong one
	// invites an operator to transmit on a control frequency.
	return t.Type == "Transponder" || (t.UplinkHigh > t.UplinkLow && t.DownlinkHigh > t.DownlinkLow)
}

// ctcssRe pulls a tone out of prose. SatNOGS has no field for it, and it is not
// optional: an FM uplink without the right tone opens nothing at all.
var ctcssRe = regexp.MustCompile(`(?i)(?:ctcss|pl)[^0-9]{0,4}(\d{2,3}(?:\.\d)?)|(\d{2,3}(?:\.\d)?)\s*(?:hz)?\s*(?:ctcss|pl)\b`)

func toTransponder(t transmitter) sat.Transponder {
	tp := sat.Transponder{
		Label:     cleanLabel(t.Description),
		Mode:      adifMode(t.Mode),
		DownLo:    t.DownlinkLow,
		DownHi:    t.DownlinkHigh,
		UpLo:      t.UplinkLow,
		UpHi:      t.UplinkHigh,
		Inverting: t.Invert,
	}
	// A "high" equal to the "low" is SatNOGS saying "a channel", not a one-hertz
	// passband; Transponder.Linear() must not be fooled into interpolating.
	if tp.DownHi <= tp.DownLo {
		tp.DownHi = 0
	}
	if tp.UpHi <= tp.UpLo {
		tp.UpHi = 0
	}
	// Inversion is a property of a PASSBAND. SatNOGS sets the flag on some FM
	// channels too, where it means nothing — the code ignores it there, but a
	// data file that says an FM repeater inverts is a data file that will
	// mislead the next person to read it.
	if tp.DownHi == 0 || tp.UpHi == 0 {
		tp.Inverting = false
	}
	if m := ctcssRe.FindStringSubmatch(t.Description); m != nil {
		v := m[1]
		if v == "" {
			v = m[2]
		}
		if f, err := strconv.ParseFloat(v, 64); err == nil && f >= 60 && f <= 260 {
			tp.CTCSS = f
		}
	}
	return tp
}

// adifMode maps SatNOGS' modulation names onto the four modes a log knows.
func adifMode(m string) string {
	switch u := strings.ToUpper(strings.TrimSpace(m)); {
	case strings.HasPrefix(u, "FM"), u == "SSTV", u == "DSTAR", u == "NFM":
		return "FM"
	case u == "USB", u == "LSB", u == "SSB":
		return "SSB"
	case u == "CW":
		return "CW"
	default:
		return "DATA"
	}
}

func cleanLabel(s string) string {
	s = strings.TrimSpace(s)
	if s == "" {
		return "Transponder"
	}
	return s
}

// displayName prefers the OSCAR designation an operator says out loud.
// "SAUDISAT 1C (SO-50)" is SO-50 to everybody except a catalog.
func displayName(feedName string) string {
	s := strings.TrimSpace(feedName)
	if i := strings.IndexByte(s, '('); i > 0 && strings.HasSuffix(s, ")") {
		inner := strings.TrimSpace(s[i+1 : len(s)-1])
		if oscarRe.MatchString(inner) {
			return inner
		}
	}
	// "RS-44 & BREEZE-KM R/B" — the rocket body it flies with is not its name.
	if i := strings.Index(s, " & "); i > 0 {
		return strings.TrimSpace(s[:i])
	}
	return s
}

var oscarRe = regexp.MustCompile(`^[A-Z]{1,3}-\d{1,3}$`)

// noradFor finds a curated entry's catalog number by the name matching the
// package already does.
//
// Deterministic on purpose. One satellite can hold TWO catalog entries — a
// deployment catalogued before the objects were told apart, GreenCube being
// 53106 and 53109 in the two feeds — and iterating the map picked a different
// one each run, so the generated file changed for no reason and the diff was
// unreadable. Candidates are therefore scored and tied on the lower number:
// a feed name whose designation IS the bird's name ("GREENCUBE (IO-117)" for
// IO-117) beats one that only matches through an alias.
func noradFor(b sat.Bird, feed map[int]string) (int, bool) {
	nums := make([]int, 0, len(feed))
	for n := range feed {
		nums = append(nums, n)
	}
	sort.Ints(nums)

	best, bestScore := 0, -1
	for _, n := range nums {
		name := feed[n]
		if !b.Matches(name) {
			continue
		}
		score := 0
		if strings.EqualFold(displayName(name), b.Name) {
			score = 2
		} else if strings.EqualFold(strings.TrimSpace(name), b.Name) {
			score = 1
		}
		if score > bestScore {
			best, bestScore = n, score
		}
	}
	return best, best != 0
}

func loadFeeds() (map[int]string, error) {
	out := map[int]string{}
	for _, url := range tleFeeds {
		body, err := get(url)
		if err != nil {
			fmt.Fprintf(os.Stderr, "warning: %s: %v\n", url, err)
			continue
		}
		lines := []string{}
		for _, l := range strings.Split(string(body), "\n") {
			if s := strings.TrimSpace(l); s != "" {
				lines = append(lines, s)
			}
		}
		for i := 0; i+2 < len(lines); i += 3 {
			if !strings.HasPrefix(lines[i+1], "1 ") || len(lines[i+1]) < 7 {
				continue
			}
			n, err := strconv.Atoi(strings.TrimSpace(lines[i+1][2:7]))
			if err != nil || n <= 0 {
				continue
			}
			// First feed wins: Celestrak's spelling is the one the operator sees.
			if _, had := out[n]; !had {
				out[n] = lines[i]
			}
		}
	}
	if len(out) == 0 {
		return nil, fmt.Errorf("no elements from any feed")
	}
	return out, nil
}

// decayed reports whether this bird's spacecraft has re-entered, matching on
// the catalog number when we have one and on the designations SatNOGS lists
// otherwise — "NAYIF-1" carries "EO-88" only in its alternative names.
func decayed(b sat.Bird, cat []satellite) (satellite, bool) {
	for _, s := range cat {
		if s.Status != "re-entered" && s.Decayed == "" {
			continue
		}
		if b.NORAD != 0 {
			if s.NORAD == b.NORAD {
				return s, true
			}
			continue
		}
		names := append(strings.FieldsFunc(s.Names, func(r rune) bool { return r == ',' || r == '\n' }), s.Name)
		for _, n := range names {
			if strings.TrimSpace(n) == "" {
				continue
			}
			if b.Matches(strings.TrimSpace(n)) {
				return s, true
			}
		}
	}
	return satellite{}, false
}

func loadSatellites() ([]satellite, error) {
	body, err := get(satnogsSats)
	if err != nil {
		return nil, err
	}
	var out []satellite
	if err := json.Unmarshal(body, &out); err != nil {
		return nil, fmt.Errorf("satnogs satellites: %w", err)
	}
	return out, nil
}

func loadTransmitters() ([]transmitter, error) {
	body, err := get(satnogsTX)
	if err != nil {
		return nil, err
	}
	var out []transmitter
	if err := json.Unmarshal(body, &out); err != nil {
		return nil, fmt.Errorf("satnogs: %w", err)
	}
	return out, nil
}

func loadBirds() ([]sat.Bird, error) {
	b, err := os.ReadFile(birdsPath)
	if err != nil {
		return nil, err
	}
	var out []sat.Bird
	if err := json.Unmarshal(b, &out); err != nil {
		return nil, fmt.Errorf("%s: %w", birdsPath, err)
	}
	return out, nil
}

func get(url string) ([]byte, error) {
	c := &http.Client{Timeout: 90 * time.Second}
	resp, err := c.Get(url)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("%s: %s", url, resp.Status)
	}
	return io.ReadAll(io.LimitReader(resp.Body, 32<<20))
}

func die(err error) {
	fmt.Fprintln(os.Stderr, "satgen:", err)
	os.Exit(1)
}