package config

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"sort"
	"strconv"
	"strings"

	"gopkg.in/yaml.v3"
)

// compositionDocument is the presence-aware representation used while
// assembling pipeline configuration sources. It deliberately models YAML
// mechanics rather than duplicating PipelineConfig's field schema.
type compositionDocument struct {
	root    *compositionNode
	sources []string
}

type compositionNode struct {
	kind    yaml.Kind
	tag     string
	value   string
	path    string
	sources []string
	line    int
	column  int
	fields  []compositionField
	items   []*compositionNode
}

type compositionField struct {
	key    string
	value  *compositionNode
	order  int
	line   int
	column int
}

// compositionValueRecord is a deterministic semantic leaf projection. Lists
// are atomic configuration values, while mappings are traversed recursively.
type compositionValueRecord struct {
	Path    string
	Kind    yaml.Kind
	Value   string
	Sources []string
}

// parseCompositionDocument parses exactly one YAML mapping while retaining
// source ownership, explicit zero values, and declaration order.
func parseCompositionDocument(source string, reader io.Reader) (*compositionDocument, error) {
	if strings.TrimSpace(source) == "" {
		return nil, fmt.Errorf("configuration source identity is required")
	}
	if reader == nil {
		return nil, fmt.Errorf("configuration source %q: reader is nil", source)
	}

	decoder := yaml.NewDecoder(reader)
	var document yaml.Node
	if err := decoder.Decode(&document); err != nil {
		if err == io.EOF {
			return nil, fmt.Errorf("configuration source %q: document is empty", source)
		}
		return nil, fmt.Errorf("configuration source %q: decode YAML: %w", source, err)
	}
	var trailing yaml.Node
	if err := decoder.Decode(&trailing); err == nil {
		return nil, fmt.Errorf("configuration source %q: must contain exactly one YAML document", source)
	} else if err != io.EOF {
		return nil, fmt.Errorf("configuration source %q: decode trailing YAML: %w", source, err)
	}
	if document.Kind != yaml.DocumentNode || len(document.Content) != 1 {
		return nil, fmt.Errorf("configuration source %q: must contain exactly one YAML document", source)
	}
	if document.Content[0].Kind != yaml.MappingNode {
		return nil, fmt.Errorf(
			"configuration source %q: top-level document must be a mapping, got %s",
			source,
			yamlKindName(document.Content[0].Kind),
		)
	}

	root, err := buildCompositionNode(document.Content[0], source, "")
	if err != nil {
		return nil, err
	}
	return &compositionDocument{root: root, sources: []string{source}}, nil
}

func parseCompositionBytes(source string, data []byte) (*compositionDocument, error) {
	return parseCompositionDocument(source, bytes.NewReader(data))
}

func buildCompositionNode(node *yaml.Node, source, path string) (*compositionNode, error) {
	if node == nil {
		return nil, fmt.Errorf("configuration source %q at %s: YAML node is nil", source, displayCompositionPath(path))
	}
	if node.Kind == yaml.AliasNode {
		return nil, compositionNodeError(source, path, node, "YAML aliases are not supported because source ownership would be ambiguous")
	}
	result := &compositionNode{
		kind: node.Kind, tag: node.Tag, value: node.Value, path: path,
		sources: []string{source}, line: node.Line, column: node.Column,
	}

	switch node.Kind {
	case yaml.MappingNode:
		if len(node.Content)%2 != 0 {
			return nil, compositionNodeError(source, path, node, "mapping has an incomplete key/value pair")
		}
		seen := make(map[string]*yaml.Node, len(node.Content)/2)
		for index := 0; index < len(node.Content); index += 2 {
			keyNode := node.Content[index]
			valueNode := node.Content[index+1]
			if keyNode.Kind == yaml.AliasNode {
				return nil, compositionNodeError(source, path, keyNode, "YAML aliases are not supported because source ownership would be ambiguous")
			}
			if valueNode.Kind == yaml.AliasNode {
				return nil, compositionNodeError(source, appendCompositionPath(path, keyNode.Value), valueNode, "YAML aliases are not supported because source ownership would be ambiguous")
			}
			if keyNode.Kind != yaml.ScalarNode || keyNode.Tag != "!!str" {
				return nil, compositionNodeError(source, path, keyNode, "mapping keys must be strings")
			}
			key := keyNode.Value
			fieldPath := appendCompositionPath(path, key)
			if prior, duplicate := seen[key]; duplicate {
				return nil, fmt.Errorf(
					"configuration source %q at %s: duplicate YAML key %q (first declared at line %d, column %d; repeated at line %d, column %d)",
					source, displayCompositionPath(fieldPath), key,
					prior.Line, prior.Column, keyNode.Line, keyNode.Column,
				)
			}
			seen[key] = keyNode
			child, err := buildCompositionNode(valueNode, source, fieldPath)
			if err != nil {
				return nil, err
			}
			result.fields = append(result.fields, compositionField{
				key: key, value: child, order: len(result.fields),
				line: keyNode.Line, column: keyNode.Column,
			})
		}
	case yaml.SequenceNode:
		for index, childNode := range node.Content {
			childPath := fmt.Sprintf("%s[%d]", path, index)
			child, err := buildCompositionNode(childNode, source, childPath)
			if err != nil {
				return nil, err
			}
			result.items = append(result.items, child)
		}
	case yaml.ScalarNode:
		// Scalar tag and lexical value retain distinctions such as explicit
		// false, zero, an empty string, and null until final strict decoding.
	default:
		return nil, compositionNodeError(source, path, node, fmt.Sprintf("unsupported YAML node kind %s", yamlKindName(node.Kind)))
	}
	return result, nil
}

// mergeAdditiveComposition recursively combines disjoint mappings. A scalar,
// list, or final keyed value may have only one base owner, regardless of
// whether duplicate values happen to be equal.
func mergeAdditiveComposition(base, incoming *compositionDocument) (*compositionDocument, error) {
	return mergeAdditiveCompositions(base, incoming)
}

// mergeAdditiveCompositions validates the complete base source set before
// merging so a conflict names every source that claims the same final path.
func mergeAdditiveCompositions(documents ...*compositionDocument) (*compositionDocument, error) {
	if len(documents) == 0 {
		return nil, fmt.Errorf("configuration additive base merge requires at least one document")
	}
	for index, document := range documents {
		if err := validateCompositionDocument(document, fmt.Sprintf("base[%d]", index)); err != nil {
			return nil, err
		}
	}
	if err := validateAdditiveClaims(documents); err != nil {
		return nil, err
	}

	result := &compositionDocument{
		root:    cloneCompositionNode(documents[0].root),
		sources: append([]string(nil), documents[0].sources...),
	}
	for _, incoming := range documents[1:] {
		merged, err := mergeAdditiveNodes(result.root, incoming.root)
		if err != nil {
			return nil, err
		}
		result.root = merged
		result.sources = appendUniqueStrings(result.sources, incoming.sources...)
	}
	return result, nil
}

func validateAdditiveClaims(documents []*compositionDocument) error {
	claims := make(map[string][]*compositionNode)
	for _, document := range documents {
		appendCompositionClaims(document.root, claims)
	}
	paths := make([]string, 0, len(claims))
	for path := range claims {
		paths = append(paths, path)
	}
	sort.Slice(paths, func(i, j int) bool {
		leftDepth := compositionPathDepth(paths[i])
		rightDepth := compositionPathDepth(paths[j])
		if leftDepth != rightDepth {
			return leftDepth < rightDepth
		}
		return paths[i] < paths[j]
	})
	for _, path := range paths {
		values := claims[path]
		if len(values) < 2 {
			continue
		}
		allPopulatedMappings := true
		for _, value := range values {
			if value.kind != yaml.MappingNode || len(value.fields) == 0 {
				allPopulatedMappings = false
				break
			}
		}
		if !allPopulatedMappings {
			return newCompositionConflict("additive base merge", path, values...)
		}
	}
	return nil
}

func appendCompositionClaims(node *compositionNode, claims map[string][]*compositionNode) {
	if node == nil {
		return
	}
	if node.path != "" {
		claims[node.path] = append(claims[node.path], node)
	}
	for _, field := range node.fields {
		appendCompositionClaims(field.value, claims)
	}
}

func compositionPathDepth(path string) int {
	if path == "" {
		return 0
	}
	return strings.Count(path, ".") + strings.Count(path, "[") + 1
}

func mergeAdditiveNodes(base, incoming *compositionNode) (*compositionNode, error) {
	if base.kind != yaml.MappingNode || incoming.kind != yaml.MappingNode {
		return nil, newCompositionConflict("additive base merge", base.path, base, incoming)
	}
	base.sources = appendUniqueStrings(base.sources, incoming.sources...)
	for _, incomingField := range incoming.fields {
		index := compositionFieldIndex(base.fields, incomingField.key)
		if index < 0 {
			field := cloneCompositionField(incomingField)
			field.order = len(base.fields)
			base.fields = append(base.fields, field)
			continue
		}
		baseValue := base.fields[index].value
		incomingValue := incomingField.value
		if baseValue.kind == yaml.MappingNode && incomingValue.kind == yaml.MappingNode {
			if len(baseValue.fields) == 0 || len(incomingValue.fields) == 0 {
				return nil, newCompositionConflict("additive base merge", incomingValue.path, baseValue, incomingValue)
			}
			merged, err := mergeAdditiveNodes(baseValue, incomingValue)
			if err != nil {
				return nil, err
			}
			base.fields[index].value = merged
			continue
		}
		return nil, newCompositionConflict("additive base merge", incomingValue.path, baseValue, incomingValue)
	}
	return base, nil
}

// mergeOverlayComposition applies the sole overwrite layer. Mappings merge
// recursively; same-kind scalars and lists replace; null and kind changes are
// rejected.
func mergeOverlayComposition(base, overlay *compositionDocument) (*compositionDocument, error) {
	if err := validateCompositionDocument(base, "base"); err != nil {
		return nil, err
	}
	if err := validateCompositionDocument(overlay, "overlay"); err != nil {
		return nil, err
	}
	if null := firstNullCompositionNode(overlay.root); null != nil {
		return nil, fmt.Errorf(
			"configuration overlay at %s from %s: null cannot delete an effective value",
			displayCompositionPath(null.path), formatCompositionSources(null.sources),
		)
	}
	merged, err := mergeOverlayNodes(cloneCompositionNode(base.root), overlay.root)
	if err != nil {
		return nil, err
	}
	return &compositionDocument{
		root: merged,
		sources: appendUniqueStrings(
			append([]string(nil), base.sources...), overlay.sources...,
		),
	}, nil
}

func mergeOverlayNodes(base, overlay *compositionNode) (*compositionNode, error) {
	if base.kind != yaml.MappingNode || overlay.kind != yaml.MappingNode {
		return nil, newCompositionConflict("profile overlay", base.path, base, overlay)
	}
	base.sources = appendUniqueStrings(base.sources, overlay.sources...)
	for _, overlayField := range overlay.fields {
		index := compositionFieldIndex(base.fields, overlayField.key)
		if index < 0 {
			field := cloneCompositionField(overlayField)
			field.order = len(base.fields)
			base.fields = append(base.fields, field)
			continue
		}
		baseValue := base.fields[index].value
		overlayValue := overlayField.value
		if baseValue.kind != overlayValue.kind {
			return nil, newCompositionConflict("profile overlay kind change", overlayValue.path, baseValue, overlayValue)
		}
		if baseValue.kind == yaml.MappingNode {
			merged, err := mergeOverlayNodes(baseValue, overlayValue)
			if err != nil {
				return nil, err
			}
			base.fields[index].value = merged
			continue
		}
		base.fields[index].value = cloneCompositionNode(overlayValue)
	}
	return base, nil
}

// canonicalYAML renders the effective mapping with sorted keys and normalized
// presentation while retaining sequence order and scalar YAML types.
func (document *compositionDocument) canonicalYAML() ([]byte, error) {
	if err := validateCompositionDocument(document, "document"); err != nil {
		return nil, err
	}
	root, err := compositionYAMLNode(document.root)
	if err != nil {
		return nil, err
	}
	var buffer bytes.Buffer
	encoder := yaml.NewEncoder(&buffer)
	encoder.SetIndent(2)
	if err := encoder.Encode(root); err != nil {
		return nil, fmt.Errorf("render effective configuration YAML: %w", err)
	}
	if err := encoder.Close(); err != nil {
		return nil, fmt.Errorf("finish effective configuration YAML: %w", err)
	}
	return buffer.Bytes(), nil
}

// canonicalDigestInput provides a deterministic, formatting-independent byte
// representation for later secret-free effective configuration digesting.
func (document *compositionDocument) canonicalDigestInput() ([]byte, error) {
	if err := validateCompositionDocument(document, "document"); err != nil {
		return nil, err
	}
	value, err := canonicalCompositionValue(document.root)
	if err != nil {
		return nil, err
	}
	data, err := json.Marshal(value)
	if err != nil {
		return nil, fmt.Errorf("serialize canonical configuration digest input: %w", err)
	}
	return append(data, '\n'), nil
}

// semanticRecords returns sorted atomic values for future effective diff and
// source-report projections. A caller receives copies of all source slices.
func (document *compositionDocument) semanticRecords() ([]compositionValueRecord, error) {
	if err := validateCompositionDocument(document, "document"); err != nil {
		return nil, err
	}
	var records []compositionValueRecord
	if err := appendCompositionRecords(document.root, &records); err != nil {
		return nil, err
	}
	sort.Slice(records, func(i, j int) bool { return records[i].Path < records[j].Path })
	return records, nil
}

func appendCompositionRecords(node *compositionNode, records *[]compositionValueRecord) error {
	if node.kind == yaml.MappingNode && len(node.fields) > 0 {
		for _, field := range node.fields {
			if err := appendCompositionRecords(field.value, records); err != nil {
				return err
			}
		}
		return nil
	}
	value, err := canonicalCompositionValue(node)
	if err != nil {
		return err
	}
	encoded, err := json.Marshal(value)
	if err != nil {
		return fmt.Errorf("serialize configuration value at %s: %w", displayCompositionPath(node.path), err)
	}
	*records = append(*records, compositionValueRecord{
		Path: node.path, Kind: node.kind, Value: string(encoded),
		Sources: append([]string(nil), node.sources...),
	})
	return nil
}

type canonicalCompositionField struct {
	Key   string `json:"key"`
	Value any    `json:"value"`
}

type canonicalCompositionNode struct {
	Kind   string                      `json:"kind"`
	Tag    string                      `json:"tag,omitempty"`
	Value  any                         `json:"value,omitempty"`
	Fields []canonicalCompositionField `json:"fields,omitempty"`
	Items  []any                       `json:"items,omitempty"`
}

func canonicalCompositionValue(node *compositionNode) (any, error) {
	switch node.kind {
	case yaml.MappingNode:
		fields := append([]compositionField(nil), node.fields...)
		sort.Slice(fields, func(i, j int) bool { return fields[i].key < fields[j].key })
		result := canonicalCompositionNode{Kind: "mapping"}
		if len(fields) == 0 {
			result.Fields = []canonicalCompositionField{}
		}
		for _, field := range fields {
			value, err := canonicalCompositionValue(field.value)
			if err != nil {
				return nil, err
			}
			result.Fields = append(result.Fields, canonicalCompositionField{Key: field.key, Value: value})
		}
		return result, nil
	case yaml.SequenceNode:
		result := canonicalCompositionNode{Kind: "sequence", Items: make([]any, 0, len(node.items))}
		for _, item := range node.items {
			value, err := canonicalCompositionValue(item)
			if err != nil {
				return nil, err
			}
			result.Items = append(result.Items, value)
		}
		return result, nil
	case yaml.ScalarNode:
		value, err := canonicalScalarValue(node)
		if err != nil {
			return nil, err
		}
		return canonicalCompositionNode{Kind: "scalar", Tag: node.tag, Value: value}, nil
	default:
		return nil, fmt.Errorf("configuration at %s has unsupported YAML kind %s", displayCompositionPath(node.path), yamlKindName(node.kind))
	}
}

func canonicalScalarValue(node *compositionNode) (any, error) {
	raw := &yaml.Node{Kind: yaml.ScalarNode, Tag: node.tag, Value: node.value}
	var value any
	if err := raw.Decode(&value); err != nil {
		return nil, fmt.Errorf("decode scalar at %s: %w", displayCompositionPath(node.path), err)
	}
	switch typed := value.(type) {
	case nil, bool, string, int, int64, uint64, float64:
		return typed, nil
	default:
		// yaml.v3 may decode timestamps or uncommon scalar tags into types that
		// encoding/json can serialize deterministically. Preserve the resolved
		// tag alongside the value in the containing canonical node.
		return typed, nil
	}
}

func compositionYAMLNode(node *compositionNode) (*yaml.Node, error) {
	switch node.kind {
	case yaml.MappingNode:
		result := &yaml.Node{Kind: yaml.MappingNode, Tag: "!!map"}
		fields := append([]compositionField(nil), node.fields...)
		sort.Slice(fields, func(i, j int) bool { return fields[i].key < fields[j].key })
		for _, field := range fields {
			value, err := compositionYAMLNode(field.value)
			if err != nil {
				return nil, err
			}
			result.Content = append(result.Content,
				&yaml.Node{Kind: yaml.ScalarNode, Tag: "!!str", Value: field.key},
				value,
			)
		}
		return result, nil
	case yaml.SequenceNode:
		result := &yaml.Node{Kind: yaml.SequenceNode, Tag: "!!seq"}
		for _, item := range node.items {
			value, err := compositionYAMLNode(item)
			if err != nil {
				return nil, err
			}
			result.Content = append(result.Content, value)
		}
		return result, nil
	case yaml.ScalarNode:
		return normalizedCompositionScalarNode(node)
	default:
		return nil, fmt.Errorf("configuration at %s has unsupported YAML kind %s", displayCompositionPath(node.path), yamlKindName(node.kind))
	}
}

func normalizedCompositionScalarNode(node *compositionNode) (*yaml.Node, error) {
	raw := &yaml.Node{Kind: yaml.ScalarNode, Tag: node.tag, Value: node.value}
	var value any
	if err := raw.Decode(&value); err != nil {
		return nil, fmt.Errorf("normalize scalar at %s: %w", displayCompositionPath(node.path), err)
	}
	normalized := &yaml.Node{}
	if err := normalized.Encode(value); err != nil {
		return nil, fmt.Errorf("encode normalized scalar at %s: %w", displayCompositionPath(node.path), err)
	}
	if normalized.Kind != yaml.ScalarNode {
		return nil, fmt.Errorf("normalize scalar at %s produced YAML kind %s", displayCompositionPath(node.path), yamlKindName(normalized.Kind))
	}
	return normalized, nil
}

func validateCompositionDocument(document *compositionDocument, role string) error {
	if document == nil || document.root == nil {
		return fmt.Errorf("configuration composition %s document is nil", role)
	}
	if document.root.kind != yaml.MappingNode {
		return fmt.Errorf("configuration composition %s root must be a mapping", role)
	}
	return nil
}

func firstNullCompositionNode(node *compositionNode) *compositionNode {
	if node == nil {
		return nil
	}
	if node.kind == yaml.ScalarNode && node.tag == "!!null" {
		return node
	}
	for _, field := range node.fields {
		if found := firstNullCompositionNode(field.value); found != nil {
			return found
		}
	}
	for _, item := range node.items {
		if found := firstNullCompositionNode(item); found != nil {
			return found
		}
	}
	return nil
}

func cloneCompositionNode(node *compositionNode) *compositionNode {
	if node == nil {
		return nil
	}
	clone := &compositionNode{
		kind: node.kind, tag: node.tag, value: node.value, path: node.path,
		sources: append([]string(nil), node.sources...), line: node.line, column: node.column,
	}
	for _, field := range node.fields {
		clone.fields = append(clone.fields, cloneCompositionField(field))
	}
	for _, item := range node.items {
		clone.items = append(clone.items, cloneCompositionNode(item))
	}
	return clone
}

func cloneCompositionField(field compositionField) compositionField {
	return compositionField{
		key: field.key, value: cloneCompositionNode(field.value), order: field.order,
		line: field.line, column: field.column,
	}
}

func compositionFieldIndex(fields []compositionField, key string) int {
	for index := range fields {
		if fields[index].key == key {
			return index
		}
	}
	return -1
}

func appendCompositionPath(parent, key string) string {
	if isSimpleCompositionPathSegment(key) {
		if parent == "" {
			return key
		}
		return parent + "." + key
	}
	if parent == "" {
		return "[" + strconv.Quote(key) + "]"
	}
	return parent + "[" + strconv.Quote(key) + "]"
}

func isSimpleCompositionPathSegment(value string) bool {
	if value == "" {
		return false
	}
	for index, char := range value {
		if (char >= 'a' && char <= 'z') || (char >= 'A' && char <= 'Z') || char == '_' || (index > 0 && char >= '0' && char <= '9') || (index > 0 && char == '-') {
			continue
		}
		return false
	}
	return true
}

func displayCompositionPath(path string) string {
	if path == "" {
		return "<root>"
	}
	return path
}

func compositionNodeError(source, path string, node *yaml.Node, message string) error {
	line, column := 0, 0
	if node != nil {
		line, column = node.Line, node.Column
	}
	return fmt.Errorf(
		"configuration source %q at %s (line %d, column %d): %s",
		source, displayCompositionPath(path), line, column, message,
	)
}

func newCompositionConflict(operation, path string, values ...*compositionNode) error {
	var sources []string
	var kinds []string
	for _, value := range values {
		if value == nil {
			continue
		}
		sources = appendUniqueStrings(sources, compositionClaimSources(value)...)
		kind := yamlKindName(value.kind)
		if !containsString(kinds, kind) {
			kinds = append(kinds, kind)
		}
	}
	return fmt.Errorf(
		"configuration %s conflict at %s: claimed by %s (YAML kinds: %s)",
		operation, displayCompositionPath(path), formatCompositionSources(sources), strings.Join(kinds, ", "),
	)
}

func compositionClaimSources(node *compositionNode) []string {
	if node == nil {
		return nil
	}
	sources := append([]string(nil), node.sources...)
	for _, field := range node.fields {
		sources = appendUniqueStrings(sources, compositionClaimSources(field.value)...)
	}
	for _, item := range node.items {
		sources = appendUniqueStrings(sources, compositionClaimSources(item)...)
	}
	return sources
}

func appendUniqueStrings(values []string, additions ...string) []string {
	seen := make(map[string]struct{}, len(values)+len(additions))
	result := make([]string, 0, len(values)+len(additions))
	for _, value := range append(append([]string(nil), values...), additions...) {
		if _, exists := seen[value]; exists {
			continue
		}
		seen[value] = struct{}{}
		result = append(result, value)
	}
	return result
}

func containsString(values []string, target string) bool {
	for _, value := range values {
		if value == target {
			return true
		}
	}
	return false
}

func formatCompositionSources(sources []string) string {
	quoted := make([]string, 0, len(sources))
	for _, source := range sources {
		quoted = append(quoted, strconv.Quote(source))
	}
	return strings.Join(quoted, ", ")
}

func yamlKindName(kind yaml.Kind) string {
	switch kind {
	case yaml.DocumentNode:
		return "document"
	case yaml.MappingNode:
		return "mapping"
	case yaml.SequenceNode:
		return "sequence"
	case yaml.ScalarNode:
		return "scalar"
	case yaml.AliasNode:
		return "alias"
	default:
		return fmt.Sprintf("kind(%d)", kind)
	}
}