// Package legacyreport parses legacy text-format Galaxy turn reports
// (the "dg" / "gplus" engines) into [report.Report] values.
//
// Scope is intentionally narrow: only the fields the UI client decodes
// from server reports today (planets, players, own ship classes,
// header data). Everything else in the legacy file is silently
// skipped. The synthetic-report parity rule in ui/PLAN.md is the
// source of truth for when to extend this parser; the package's
// README.md tracks every legacy section that could be wired up later
// when the corresponding UI decoder lands.
package legacyreport

import (
	"bufio"
	"errors"
	"fmt"
	"io"
	"strconv"
	"strings"

	"galaxy/model/report"
)

// Parse reads a legacy text report and returns a [report.Report]
// carrying the in-scope subset of fields. The Width and Height of the
// returned report are both set to the legacy "Size" value (galaxies
// are square in the legacy engines).
func Parse(r io.Reader) (report.Report, error) {
	p := newParser()
	sc := bufio.NewScanner(r)
	sc.Buffer(make([]byte, 1024*1024), 4*1024*1024)
	for sc.Scan() {
		if err := p.handle(sc.Text()); err != nil {
			return report.Report{}, err
		}
	}
	if err := sc.Err(); err != nil {
		return report.Report{}, fmt.Errorf("legacyreport: scan: %w", err)
	}
	return p.finish()
}

type section int

const (
	sectionNone section = iota
	sectionStatusOfPlayers
	sectionYourVote
	sectionYourPlanets
	sectionOtherPlanets
	sectionUninhabitedPlanets
	sectionUnidentifiedPlanets
	sectionYourShipTypes
)

type parser struct {
	rep        report.Report
	sec        section
	otherOwner string
	skipHeader bool
	sawHeader  bool
	sawSize    bool
}

func newParser() *parser {
	return &parser{sec: sectionNone}
}

func (p *parser) handle(line string) error {
	trimmed := strings.TrimSpace(line)

	if !p.sawHeader && trimmed != "" {
		if race, turn, ok := parseHeader(trimmed); ok {
			p.rep.Race = race
			p.rep.Turn = turn
			p.sawHeader = true
			return nil
		}
	}
	if !p.sawSize && strings.HasPrefix(trimmed, "Size:") {
		if w, planets, ok := parseSize(trimmed); ok {
			p.rep.Width = w
			p.rep.Height = w
			p.rep.PlanetCount = planets
			p.sawSize = true
		}
		return nil
	}

	if newSec, owner, isHeader := classifySection(trimmed); isHeader {
		p.sec = newSec
		p.otherOwner = owner
		p.skipHeader = newSec != sectionNone
		return nil
	}

	if trimmed == "" {
		return nil
	}
	if p.sec == sectionNone {
		return nil
	}
	if p.skipHeader {
		p.skipHeader = false
		return nil
	}

	fields := strings.Fields(trimmed)
	switch p.sec {
	case sectionStatusOfPlayers:
		p.parsePlayer(fields)
	case sectionYourVote:
		p.parseYourVote(fields)
	case sectionYourPlanets:
		p.parseLocalPlanet(fields)
	case sectionOtherPlanets:
		p.parseOtherPlanet(fields)
	case sectionUninhabitedPlanets:
		p.parseUninhabitedPlanet(fields)
	case sectionUnidentifiedPlanets:
		p.parseUnidentifiedPlanet(fields)
	case sectionYourShipTypes:
		p.parseShipClass(fields)
	}
	return nil
}

func (p *parser) finish() (report.Report, error) {
	if !p.sawHeader {
		return report.Report{}, errors.New("legacyreport: missing report header line")
	}
	return p.rep, nil
}

// parseHeader extracts (race, turn) from
// "<Race> Report for Galaxy ... Turn N ...".
func parseHeader(line string) (string, uint, bool) {
	race, rest, ok := strings.Cut(line, " Report for Galaxy ")
	if !ok {
		return "", 0, false
	}
	_, afterTurn, ok := strings.Cut(rest, " Turn ")
	if !ok {
		return "", 0, false
	}
	after := strings.Fields(afterTurn)
	if len(after) == 0 {
		return "", 0, false
	}
	n, err := strconv.ParseUint(after[0], 10, 32)
	if err != nil {
		return "", 0, false
	}
	return race, uint(n), true
}

// parseSize extracts (size, planets) from
// "Size: W  Planets: P  Players: N". Players is intentionally
// dropped: report.Report has no field for it.
func parseSize(line string) (uint32, uint32, bool) {
	fields := strings.Fields(line)
	var size, planets uint32
	var ok bool
	for i := 0; i+1 < len(fields); i++ {
		key := strings.TrimRight(fields[i], ":")
		switch key {
		case "Size":
			if n, err := strconv.ParseUint(fields[i+1], 10, 32); err == nil {
				size = uint32(n)
				ok = true
			}
		case "Planets":
			if n, err := strconv.ParseUint(fields[i+1], 10, 32); err == nil {
				planets = uint32(n)
			}
		}
	}
	return size, planets, ok
}

// classifySection returns the section the trimmed line opens. When
// isHeader is true the caller transitions state — sectionNone there
// means "switch into skip mode" (an uninteresting section like
// Bombings, Battle at ..., or a foreign Ship Types block).
func classifySection(line string) (sec section, owner string, isHeader bool) {
	switch line {
	case "":
		return sectionNone, "", false
	case "Your Planets":
		return sectionYourPlanets, "", true
	case "Your Ship Types":
		return sectionYourShipTypes, "", true
	case "Uninhabited Planets":
		return sectionUninhabitedPlanets, "", true
	case "Unidentified Planets":
		return sectionUnidentifiedPlanets, "", true
	case "Your vote:":
		return sectionYourVote, "", true
	case "Your Sciences",
		"Bombings",
		"Ships In Production",
		"Approaching Groups",
		"Broadcast Message",
		"Battle Protocol":
		return sectionNone, "", true
	}
	if strings.HasPrefix(line, "Status of Players") {
		return sectionStatusOfPlayers, "", true
	}
	if strings.HasPrefix(line, "Battle at ") {
		return sectionNone, "", true
	}
	if strings.HasPrefix(line, "=== ATTENTION") {
		return sectionNone, "", true
	}
	if owner, ok := singleTokenPrefix(line, " Planets"); ok {
		return sectionOtherPlanets, owner, true
	}
	if _, ok := singleTokenPrefix(line, " Ship Types"); ok {
		return sectionNone, "", true
	}
	if _, ok := singleTokenPrefix(line, " Sciences"); ok {
		return sectionNone, "", true
	}
	if _, ok := singleTokenPrefix(line, " Groups"); ok {
		return sectionNone, "", true
	}
	return sectionNone, "", false
}

func singleTokenPrefix(line, suffix string) (string, bool) {
	if !strings.HasSuffix(line, suffix) {
		return "", false
	}
	prefix := strings.TrimSuffix(line, suffix)
	if prefix == "" || strings.ContainsAny(prefix, " \t") {
		return "", false
	}
	return prefix, true
}

// parsePlayer expects 10 columns:
//
//	N D W S C P I # R V
func (p *parser) parsePlayer(fields []string) {
	if len(fields) < 10 {
		return
	}
	name := fields[0]
	drive, err := parseFloat(fields[1])
	if err != nil {
		return
	}
	weapons, _ := parseFloat(fields[2])
	shields, _ := parseFloat(fields[3])
	cargo, _ := parseFloat(fields[4])
	population, _ := parseFloat(fields[5])
	industry, _ := parseFloat(fields[6])
	plCount, err := strconv.ParseUint(fields[7], 10, 16)
	if err != nil {
		return
	}
	relation := fields[8]
	votes, _ := parseFloat(fields[9])

	extinct := strings.HasSuffix(name, "_RIP")
	if extinct {
		name = strings.TrimSuffix(name, "_RIP")
	}
	p.rep.Player = append(p.rep.Player, report.Player{
		Name:       name,
		Drive:      report.F(drive),
		Weapons:    report.F(weapons),
		Shields:    report.F(shields),
		Cargo:      report.F(cargo),
		Population: report.F(population),
		Industry:   report.F(industry),
		Planets:    uint16(plCount),
		Relation:   relation,
		Votes:      report.F(votes),
		Extinct:    extinct,
	})
}

func (p *parser) parseYourVote(fields []string) {
	if len(fields) < 2 {
		return
	}
	p.rep.VoteFor = fields[0]
	if v, err := parseFloat(fields[1]); err == nil {
		p.rep.Votes = report.F(v)
	}
	p.sec = sectionNone
}

// parseLocalPlanet expects 13 columns:
//
//	# X Y N S P I R Production $ M C L
func (p *parser) parseLocalPlanet(fields []string) {
	lp, ok := decodeLocalPlanetRow(fields)
	if !ok {
		return
	}
	p.rep.LocalPlanet = append(p.rep.LocalPlanet, lp)
}

func (p *parser) parseOtherPlanet(fields []string) {
	lp, ok := decodeLocalPlanetRow(fields)
	if !ok {
		return
	}
	p.rep.OtherPlanet = append(p.rep.OtherPlanet, report.OtherPlanet{
		Owner:       p.otherOwner,
		LocalPlanet: lp,
	})
}

func decodeLocalPlanetRow(fields []string) (report.LocalPlanet, bool) {
	var lp report.LocalPlanet
	if len(fields) < 13 {
		return lp, false
	}
	number, err := strconv.ParseUint(fields[0], 10, 32)
	if err != nil {
		return lp, false
	}
	x, _ := parseFloat(fields[1])
	y, _ := parseFloat(fields[2])
	size, _ := parseFloat(fields[4])
	population, _ := parseFloat(fields[5])
	industry, _ := parseFloat(fields[6])
	resources, _ := parseFloat(fields[7])
	capital, _ := parseFloat(fields[9])
	material, _ := parseFloat(fields[10])
	colonists, _ := parseFloat(fields[11])
	free, _ := parseFloat(fields[12])

	lp.Number = uint(number)
	lp.X = report.F(x)
	lp.Y = report.F(y)
	lp.Name = fields[3]
	lp.Size = report.F(size)
	lp.Resources = report.F(resources)
	lp.Capital = report.F(capital)
	lp.Material = report.F(material)
	lp.Industry = report.F(industry)
	lp.Population = report.F(population)
	lp.Colonists = report.F(colonists)
	lp.Production = fields[8]
	lp.FreeIndustry = report.F(free)
	return lp, true
}

// parseUninhabitedPlanet expects 8 columns:
//
//	# X Y N S R $ M
func (p *parser) parseUninhabitedPlanet(fields []string) {
	if len(fields) < 8 {
		return
	}
	number, err := strconv.ParseUint(fields[0], 10, 32)
	if err != nil {
		return
	}
	x, _ := parseFloat(fields[1])
	y, _ := parseFloat(fields[2])
	size, _ := parseFloat(fields[4])
	resources, _ := parseFloat(fields[5])
	capital, _ := parseFloat(fields[6])
	material, _ := parseFloat(fields[7])

	var u report.UninhabitedPlanet
	u.Number = uint(number)
	u.X = report.F(x)
	u.Y = report.F(y)
	u.Name = fields[3]
	u.Size = report.F(size)
	u.Resources = report.F(resources)
	u.Capital = report.F(capital)
	u.Material = report.F(material)
	p.rep.UninhabitedPlanet = append(p.rep.UninhabitedPlanet, u)
}

// parseUnidentifiedPlanet expects 3 columns:
//
//	# X Y
func (p *parser) parseUnidentifiedPlanet(fields []string) {
	if len(fields) < 3 {
		return
	}
	number, err := strconv.ParseUint(fields[0], 10, 32)
	if err != nil {
		return
	}
	x, _ := parseFloat(fields[1])
	y, _ := parseFloat(fields[2])
	p.rep.UnidentifiedPlanet = append(p.rep.UnidentifiedPlanet, report.UnidentifiedPlanet{
		Number: uint(number),
		X:      report.F(x),
		Y:      report.F(y),
	})
}

// parseShipClass expects 7 columns:
//
//	N D A W S C M
func (p *parser) parseShipClass(fields []string) {
	if len(fields) < 7 {
		return
	}
	drive, err := parseFloat(fields[1])
	if err != nil {
		return
	}
	armament, err := strconv.ParseUint(fields[2], 10, 32)
	if err != nil {
		return
	}
	weapons, _ := parseFloat(fields[3])
	shields, _ := parseFloat(fields[4])
	cargo, _ := parseFloat(fields[5])
	mass, _ := parseFloat(fields[6])

	p.rep.LocalShipClass = append(p.rep.LocalShipClass, report.ShipClass{
		Name:     fields[0],
		Drive:    report.F(drive),
		Armament: uint(armament),
		Weapons:  report.F(weapons),
		Shields:  report.F(shields),
		Cargo:    report.F(cargo),
		Mass:     report.F(mass),
	})
}

func parseFloat(s string) (float64, error) {
	return strconv.ParseFloat(s, 64)
}