package config

import (
	"bytes"
	"fmt"
	"io"
	"sort"
	"strconv"
	"strings"
	"unicode"

	"gitea.maximumdirect.net/eric/narratio/internal/artifactpolicy"
	"gopkg.in/yaml.v3"
)

const (
	// PartySchemaVersion identifies the canonical campaign party document.
	PartySchemaVersion = "narratio.party.v1"
	// PlayersSchemaVersion identifies the derived players-only document.
	PlayersSchemaVersion = "narratio.players.v1"
)

// PartyMode records whether a source document uses the canonical party
// contract or the bounded compatibility path for older opaque files.
type PartyMode string

const (
	PartyModeCanonical PartyMode = "canonical"
	PartyModeLegacy    PartyMode = "legacy"
)

// PartyDocument classifies a party input. Canonical is populated only for a
// versioned canonical document; legacy contents intentionally remain opaque.
type PartyDocument struct {
	Mode      PartyMode
	Canonical *CanonicalParty
}

// IsCanonical reports whether the document has validated canonical data.
func (d *PartyDocument) IsCanonical() bool {
	return d != nil && d.Mode == PartyModeCanonical && d.Canonical != nil
}

// PlayersYAML renders the derived players projection for a canonical document.
func (d *PartyDocument) PlayersYAML() ([]byte, error) {
	if !d.IsCanonical() {
		return nil, fmt.Errorf("canonical party is required")
	}
	return d.Canonical.PlayersYAML()
}

// CanonicalParty is the normalized domain value for narratio.party.v1. Raw is
// retained independently so later preparation can copy the authored party file
// byte-for-byte rather than serializing normalized values.
type CanonicalParty struct {
	Raw        []byte
	Characters []PartyCharacter
}

// PartyCharacter is one ordered character declaration from a canonical party.
type PartyCharacter struct {
	ID        string
	Player    PartyPlayer
	Character PartyCharacterDetails
}

// PartyPlayer identifies the player controlling a character.
type PartyPlayer struct {
	Name string
}

// PartyCharacterDetails contains the player-facing character details.
type PartyCharacterDetails struct {
	Name    string
	Aliases []string
	Classes []PartyClass
}

// PartyClass represents one declared class. A missing Level is distinct from
// an explicitly supplied level.
type PartyClass struct {
	Name  string
	Level *int
}

// ParseParty classifies and, when selected by schema_version, strictly parses
// a party source. An unversioned source takes the deliberately opaque legacy
// compatibility path; see party_legacy.go.
func ParseParty(data []byte) (*PartyDocument, error) {
	root, decoder, err := parsePartyFirstDocument(data)
	if err != nil {
		return nil, err
	}
	if !partyDocumentSelectsCanonical(root) {
		return classifyLegacyPartyDocument(), nil
	}
	if err := requireNoTrailingPartyDocuments(decoder); err != nil {
		return nil, err
	}
	party, err := parseCanonicalParty(root, data)
	if err != nil {
		return nil, err
	}
	return &PartyDocument{Mode: PartyModeCanonical, Canonical: party}, nil
}

func parsePartyFirstDocument(data []byte) (*yaml.Node, *yaml.Decoder, error) {
	decoder := yaml.NewDecoder(bytes.NewReader(data))
	var document yaml.Node
	if err := decoder.Decode(&document); err != nil {
		if err == io.EOF {
			return nil, nil, fmt.Errorf("party YAML document is empty")
		}
		return nil, nil, fmt.Errorf("decode party YAML: %w", err)
	}
	if document.Kind != yaml.DocumentNode || len(document.Content) != 1 {
		return nil, nil, fmt.Errorf("party must contain one YAML document")
	}
	return document.Content[0], decoder, nil
}

func partyDocumentSelectsCanonical(root *yaml.Node) bool {
	if root == nil || root.Kind != yaml.MappingNode {
		return false
	}
	for index := 0; index+1 < len(root.Content); index += 2 {
		key := root.Content[index]
		if key.Kind == yaml.ScalarNode && key.Tag == "!!str" && key.Value == "schema_version" {
			return true
		}
	}
	return false
}

func requireNoTrailingPartyDocuments(decoder *yaml.Decoder) error {
	var trailing yaml.Node
	if err := decoder.Decode(&trailing); err == nil {
		return fmt.Errorf("canonical party must contain exactly one YAML document")
	} else if err != io.EOF {
		return fmt.Errorf("decode trailing canonical party YAML: %w", err)
	}
	return nil
}

func parseCanonicalParty(root *yaml.Node, raw []byte) (*CanonicalParty, error) {
	fields, err := partyMappingFields(root, "party")
	if err != nil {
		return nil, err
	}
	if err := partyKnownFields(fields, "party", "schema_version", "characters"); err != nil {
		return nil, err
	}

	version, err := partyRequiredString(fields, "schema_version", "party")
	if err != nil {
		return nil, err
	}
	if version != PartySchemaVersion {
		return nil, fmt.Errorf("party.schema_version %q is unsupported", version)
	}
	charactersNode, ok := fields["characters"]
	if !ok {
		return nil, fmt.Errorf("party.characters is required")
	}
	charactersFields, err := partyMappingFields(charactersNode, "party.characters")
	if err != nil {
		return nil, err
	}
	if len(charactersFields) == 0 {
		return nil, fmt.Errorf("party.characters must be non-empty")
	}

	party := &CanonicalParty{Raw: append([]byte(nil), raw...)}
	seenNames := make([]string, 0, len(charactersFields))
	for _, id := range partyMappingOrder(charactersNode) {
		entry, err := parsePartyCharacter(id, charactersFields[id], seenNames)
		if err != nil {
			return nil, err
		}
		party.Characters = append(party.Characters, entry)
		seenNames = append(seenNames, entry.Character.Name)
		seenNames = append(seenNames, entry.Character.Aliases...)
	}
	return party, nil
}

func parsePartyCharacter(id string, node *yaml.Node, seenNames []string) (PartyCharacter, error) {
	path := "party.characters." + id
	if id != strings.TrimSpace(id) || !artifactpolicy.IsConfiguredKey(id) {
		return PartyCharacter{}, fmt.Errorf("%s has invalid character id %q", path, id)
	}
	fields, err := partyMappingFields(node, path)
	if err != nil {
		return PartyCharacter{}, err
	}
	if err := partyKnownFields(fields, path, "player", "character"); err != nil {
		return PartyCharacter{}, err
	}
	player, err := parsePartyPlayer(fields["player"], path+".player")
	if err != nil {
		return PartyCharacter{}, err
	}
	character, err := parsePartyCharacterDetails(fields["character"], path+".character")
	if err != nil {
		return PartyCharacter{}, err
	}
	if partyNameAmbiguous(character.Name, seenNames) {
		return PartyCharacter{}, fmt.Errorf("%s name or alias %q is ambiguous", path, character.Name)
	}
	visibleNames := append(append([]string(nil), seenNames...), character.Name)
	for _, name := range character.Aliases {
		if partyNameAmbiguous(name, visibleNames) {
			return PartyCharacter{}, fmt.Errorf("%s name or alias %q is ambiguous", path, name)
		}
		visibleNames = append(visibleNames, name)
	}
	return PartyCharacter{ID: id, Player: player, Character: character}, nil
}

func parsePartyPlayer(node *yaml.Node, path string) (PartyPlayer, error) {
	fields, err := partyMappingFields(node, path)
	if err != nil {
		return PartyPlayer{}, err
	}
	if err := partyKnownFields(fields, path, "name"); err != nil {
		return PartyPlayer{}, err
	}
	name, err := partyRequiredDisplayString(fields, "name", path)
	if err != nil {
		return PartyPlayer{}, err
	}
	return PartyPlayer{Name: name}, nil
}

func parsePartyCharacterDetails(node *yaml.Node, path string) (PartyCharacterDetails, error) {
	fields, err := partyMappingFields(node, path)
	if err != nil {
		return PartyCharacterDetails{}, err
	}
	if err := partyKnownFields(fields, path, "name", "alias", "classes"); err != nil {
		return PartyCharacterDetails{}, err
	}
	name, err := partyRequiredDisplayString(fields, "name", path)
	if err != nil {
		return PartyCharacterDetails{}, err
	}
	aliases, err := partyAliases(fields["alias"], path+".alias")
	if err != nil {
		return PartyCharacterDetails{}, err
	}
	classes, err := partyClasses(fields["classes"], path+".classes")
	if err != nil {
		return PartyCharacterDetails{}, err
	}
	return PartyCharacterDetails{Name: name, Aliases: aliases, Classes: classes}, nil
}

func partyAliases(node *yaml.Node, path string) ([]string, error) {
	if node == nil {
		return nil, nil
	}
	if node.Kind != yaml.SequenceNode {
		return nil, fmt.Errorf("%s must be a list", path)
	}
	aliases := make([]string, 0, len(node.Content))
	for index, item := range node.Content {
		alias, err := partyDisplayString(item, fmt.Sprintf("%s[%d]", path, index))
		if err != nil {
			return nil, err
		}
		aliases = append(aliases, alias)
	}
	return aliases, nil
}

func partyClasses(node *yaml.Node, path string) ([]PartyClass, error) {
	if node == nil {
		return nil, fmt.Errorf("%s is required", path)
	}
	if node.Kind != yaml.SequenceNode || len(node.Content) == 0 {
		return nil, fmt.Errorf("%s must be a non-empty list", path)
	}
	classes := make([]PartyClass, 0, len(node.Content))
	classNames := make([]string, 0, len(node.Content))
	for index, item := range node.Content {
		classPath := fmt.Sprintf("%s[%d]", path, index)
		fields, err := partyMappingFields(item, classPath)
		if err != nil {
			return nil, err
		}
		if err := partyKnownFields(fields, classPath, "name", "level"); err != nil {
			return nil, err
		}
		name, err := partyRequiredDisplayString(fields, "name", classPath)
		if err != nil {
			return nil, err
		}
		if partyNameAmbiguous(name, classNames) {
			return nil, fmt.Errorf("%s has duplicate class %q", path, name)
		}
		classNames = append(classNames, name)
		level, err := partyLevel(fields["level"], classPath+".level")
		if err != nil {
			return nil, err
		}
		classes = append(classes, PartyClass{Name: name, Level: level})
	}
	return classes, nil
}

func partyLevel(node *yaml.Node, path string) (*int, error) {
	if node == nil {
		return nil, nil
	}
	if node.Kind != yaml.ScalarNode || node.Tag != "!!int" {
		return nil, fmt.Errorf("%s must be a positive integer", path)
	}
	level, err := strconv.Atoi(node.Value)
	if err != nil || level <= 0 {
		return nil, fmt.Errorf("%s must be a positive integer", path)
	}
	return &level, nil
}

func partyRequiredDisplayString(fields map[string]*yaml.Node, key, path string) (string, error) {
	node, ok := fields[key]
	if !ok {
		return "", fmt.Errorf("%s.%s is required", path, key)
	}
	return partyDisplayString(node, path+"."+key)
}

func partyRequiredString(fields map[string]*yaml.Node, key, path string) (string, error) {
	node, ok := fields[key]
	if !ok {
		return "", fmt.Errorf("%s.%s is required", path, key)
	}
	if node.Kind != yaml.ScalarNode || node.Tag != "!!str" || node.Value == "" {
		return "", fmt.Errorf("%s.%s must be a non-empty string", path, key)
	}
	return node.Value, nil
}

func partyDisplayString(node *yaml.Node, path string) (string, error) {
	if node == nil || node.Kind != yaml.ScalarNode || node.Tag != "!!str" {
		return "", fmt.Errorf("%s must be a display string", path)
	}
	value := node.Value
	if value == "" || strings.TrimSpace(value) != value {
		return "", fmt.Errorf("%s must be non-empty and trimmed", path)
	}
	for _, runeValue := range value {
		if unicode.IsControl(runeValue) {
			return "", fmt.Errorf("%s must not contain control characters", path)
		}
	}
	return value, nil
}

func partyNameAmbiguous(name string, existing []string) bool {
	for _, candidate := range existing {
		if strings.EqualFold(name, candidate) {
			return true
		}
	}
	return false
}

func partyMappingFields(node *yaml.Node, path string) (map[string]*yaml.Node, error) {
	if node == nil || node.Kind != yaml.MappingNode {
		return nil, fmt.Errorf("%s must be a mapping", path)
	}
	if len(node.Content)%2 != 0 {
		return nil, fmt.Errorf("%s has an incomplete mapping", path)
	}
	fields := make(map[string]*yaml.Node, len(node.Content)/2)
	for index := 0; index < len(node.Content); index += 2 {
		key, value := node.Content[index], node.Content[index+1]
		if key.Kind != yaml.ScalarNode || key.Tag != "!!str" {
			return nil, fmt.Errorf("%s has a non-string field name", path)
		}
		if key.Value == "" {
			return nil, fmt.Errorf("%s has an empty field name", path)
		}
		if _, duplicate := fields[key.Value]; duplicate {
			return nil, fmt.Errorf("%s has duplicate field %q", path, key.Value)
		}
		if partyContainsAlias(value) {
			return nil, fmt.Errorf("%s.%s must not use YAML aliases", path, key.Value)
		}
		fields[key.Value] = value
	}
	return fields, nil
}

func partyMappingOrder(node *yaml.Node) []string {
	keys := make([]string, 0, len(node.Content)/2)
	for index := 0; index < len(node.Content); index += 2 {
		keys = append(keys, node.Content[index].Value)
	}
	return keys
}

func partyKnownFields(fields map[string]*yaml.Node, path string, allowed ...string) error {
	for name := range fields {
		known := false
		for _, candidate := range allowed {
			if name == candidate {
				known = true
				break
			}
		}
		if !known {
			return fmt.Errorf("%s has unknown field %q", path, name)
		}
	}
	return nil
}

func partyContainsAlias(node *yaml.Node) bool {
	if node == nil {
		return false
	}
	if node.Kind == yaml.AliasNode {
		return true
	}
	for _, child := range node.Content {
		if partyContainsAlias(child) {
			return true
		}
	}
	return false
}

// ClassSummary preserves the declaration order required by the party contract.
func (c PartyCharacter) ClassSummary() string {
	parts := make([]string, 0, len(c.Character.Classes))
	for _, class := range c.Character.Classes {
		entry := class.Name
		if class.Level != nil {
			entry += fmt.Sprintf(" %d", *class.Level)
		}
		parts = append(parts, entry)
	}
	return strings.Join(parts, " / ")
}

// AliasSummary preserves the declaration order required by the party contract.
func (c PartyCharacter) AliasSummary() string {
	return strings.Join(c.Character.Aliases, ", ")
}

// PlayersYAML renders the deterministic players-only projection of a
// canonical party. It returns one final newline, as produced by yaml.Marshal.
func (p *CanonicalParty) PlayersYAML() ([]byte, error) {
	if p == nil {
		return nil, fmt.Errorf("canonical party is required")
	}
	characters := append([]PartyCharacter(nil), p.Characters...)
	sort.Slice(characters, func(left, right int) bool {
		return characters[left].ID < characters[right].ID
	})
	type projectionCharacter struct {
		ID      string   `yaml:"id"`
		Name    string   `yaml:"name"`
		Aliases []string `yaml:"alias,omitempty"`
	}
	type projectionPlayer struct {
		Name      string              `yaml:"name"`
		Character projectionCharacter `yaml:"character"`
	}
	projection := struct {
		SchemaVersion string             `yaml:"schema_version"`
		Players       []projectionPlayer `yaml:"players"`
	}{
		SchemaVersion: PlayersSchemaVersion,
		Players:       make([]projectionPlayer, 0, len(characters)),
	}
	for _, character := range characters {
		projection.Players = append(projection.Players, projectionPlayer{
			Name: character.Player.Name,
			Character: projectionCharacter{
				ID:      character.ID,
				Name:    character.Character.Name,
				Aliases: append([]string(nil), character.Character.Aliases...),
			},
		})
	}
	encoded, err := yaml.Marshal(projection)
	if err != nil {
		return nil, fmt.Errorf("render players projection: %w", err)
	}
	return encoded, nil
}