package config

import (
	"bytes"
	"fmt"
	"os"
	"strings"

	"gopkg.in/yaml.v3"
)

// SaveConfigPreserveComments writes the config back to YAML while preserving existing comments
// and key ordering by loading the original file into a yaml.Node tree and updating values in-place.
func SaveConfigPreserveComments(configFile string, cfg *Config) error {
	persistCfg := sanitizeConfigForPersist(cfg)
	// Load original YAML as a node tree to preserve comments and ordering.
	data, err := os.ReadFile(configFile)
	if err != nil {
		return err
	}

	var original yaml.Node
	if err = yaml.Unmarshal(data, &original); err != nil {
		return err
	}
	if original.Kind != yaml.DocumentNode || len(original.Content) == 0 {
		return fmt.Errorf("invalid yaml document structure")
	}
	if original.Content[0] == nil || original.Content[0].Kind != yaml.MappingNode {
		return fmt.Errorf("expected root mapping node")
	}

	// Marshal the current cfg to YAML, then unmarshal to a yaml.Node we can merge from.
	rendered, err := yaml.Marshal(persistCfg)
	if err != nil {
		return err
	}
	var generated yaml.Node
	if err = yaml.Unmarshal(rendered, &generated); err != nil {
		return err
	}
	if generated.Kind != yaml.DocumentNode || len(generated.Content) == 0 || generated.Content[0] == nil {
		return fmt.Errorf("invalid generated yaml structure")
	}
	if generated.Content[0].Kind != yaml.MappingNode {
		return fmt.Errorf("expected generated root mapping node")
	}

	// Remove deprecated sections before merging back the sanitized config.
	removeLegacyAuthBlock(original.Content[0])
	removeLegacyOpenAICompatAPIKeys(original.Content[0])
	removeLegacyAmpKeys(original.Content[0])
	removeLegacyGenerativeLanguageKeys(original.Content[0])

	pruneMappingToGeneratedKeys(original.Content[0], generated.Content[0], "oauth-excluded-models")

	// Merge generated into original in-place, preserving comments/order of existing nodes.
	mergeMappingPreserve(original.Content[0], generated.Content[0])
	normalizeCollectionNodeStyles(original.Content[0])

	// Write back.
	f, err := os.Create(configFile)
	if err != nil {
		return err
	}
	defer func() { _ = f.Close() }()
	var buf bytes.Buffer
	enc := yaml.NewEncoder(&buf)
	enc.SetIndent(2)
	if err = enc.Encode(&original); err != nil {
		_ = enc.Close()
		return err
	}
	if err = enc.Close(); err != nil {
		return err
	}
	data = NormalizeCommentIndentation(buf.Bytes())
	_, err = f.Write(data)
	return err
}

// SaveConfigPreserveCommentsUpdateNestedScalar updates a nested scalar key path like ["a","b"]
// while preserving comments and positions.
func SaveConfigPreserveCommentsUpdateNestedScalar(configFile string, path []string, value string) error {
	data, err := os.ReadFile(configFile)
	if err != nil {
		return err
	}
	var root yaml.Node
	if err = yaml.Unmarshal(data, &root); err != nil {
		return err
	}
	if root.Kind != yaml.DocumentNode || len(root.Content) == 0 {
		return fmt.Errorf("invalid yaml document structure")
	}
	node := root.Content[0]
	// descend mapping nodes following path
	for i, key := range path {
		if i == len(path)-1 {
			// set final scalar
			v := getOrCreateMapValue(node, key)
			v.Kind = yaml.ScalarNode
			v.Tag = "!!str"
			v.Value = value
		} else {
			next := getOrCreateMapValue(node, key)
			if next.Kind != yaml.MappingNode {
				next.Kind = yaml.MappingNode
				next.Tag = "!!map"
			}
			node = next
		}
	}
	f, err := os.Create(configFile)
	if err != nil {
		return err
	}
	defer func() { _ = f.Close() }()
	var buf bytes.Buffer
	enc := yaml.NewEncoder(&buf)
	enc.SetIndent(2)
	if err = enc.Encode(&root); err != nil {
		_ = enc.Close()
		return err
	}
	if err = enc.Close(); err != nil {
		return err
	}
	data = NormalizeCommentIndentation(buf.Bytes())
	_, err = f.Write(data)
	return err
}

// NormalizeCommentIndentation removes indentation from standalone YAML comment lines to keep them left aligned.
func NormalizeCommentIndentation(data []byte) []byte {
	lines := bytes.Split(data, []byte("\n"))
	changed := false
	for i, line := range lines {
		trimmed := bytes.TrimLeft(line, " \t")
		if len(trimmed) == 0 || trimmed[0] != '#' {
			continue
		}
		if len(trimmed) == len(line) {
			continue
		}
		lines[i] = append([]byte(nil), trimmed...)
		changed = true
	}
	if !changed {
		return data
	}
	return bytes.Join(lines, []byte("\n"))
}

// getOrCreateMapValue finds the value node for a given key in a mapping node.
// If not found, it appends a new key/value pair and returns the new value node.
func getOrCreateMapValue(mapNode *yaml.Node, key string) *yaml.Node {
	if mapNode.Kind != yaml.MappingNode {
		mapNode.Kind = yaml.MappingNode
		mapNode.Tag = "!!map"
		mapNode.Content = nil
	}
	for i := 0; i+1 < len(mapNode.Content); i += 2 {
		k := mapNode.Content[i]
		if k.Value == key {
			return mapNode.Content[i+1]
		}
	}
	// append new key/value
	mapNode.Content = append(mapNode.Content, &yaml.Node{Kind: yaml.ScalarNode, Tag: "!!str", Value: key})
	val := &yaml.Node{Kind: yaml.ScalarNode, Tag: "!!str", Value: ""}
	mapNode.Content = append(mapNode.Content, val)
	return val
}

// mergeMappingPreserve merges keys from src into dst mapping node while preserving
// key order and comments of existing keys in dst. New keys are only added if their
// value is non-zero to avoid polluting the config with defaults.
func mergeMappingPreserve(dst, src *yaml.Node) {
	if dst == nil || src == nil {
		return
	}
	if dst.Kind != yaml.MappingNode || src.Kind != yaml.MappingNode {
		// If kinds do not match, prefer replacing dst with src semantics in-place
		// but keep dst node object to preserve any attached comments at the parent level.
		copyNodeShallow(dst, src)
		return
	}
	for i := 0; i+1 < len(src.Content); i += 2 {
		sk := src.Content[i]
		sv := src.Content[i+1]
		idx := findMapKeyIndex(dst, sk.Value)
		if idx >= 0 {
			// Merge into existing value node (always update, even to zero values)
			dv := dst.Content[idx+1]
			mergeNodePreserve(dv, sv)
		} else {
			// New key: only add if value is non-zero to avoid polluting config with defaults
			if isZeroValueNode(sv) {
				continue
			}
			dst.Content = append(dst.Content, deepCopyNode(sk), deepCopyNode(sv))
		}
	}
}

// mergeNodePreserve merges src into dst for scalars, mappings and sequences while
// reusing destination nodes to keep comments and anchors. For sequences, it updates
// in-place by index.
func mergeNodePreserve(dst, src *yaml.Node) {
	if dst == nil || src == nil {
		return
	}
	switch src.Kind {
	case yaml.MappingNode:
		if dst.Kind != yaml.MappingNode {
			copyNodeShallow(dst, src)
		}
		mergeMappingPreserve(dst, src)
	case yaml.SequenceNode:
		// Preserve explicit null style if dst was null and src is empty sequence
		if dst.Kind == yaml.ScalarNode && dst.Tag == "!!null" && len(src.Content) == 0 {
			// Keep as null to preserve original style
			return
		}
		if dst.Kind != yaml.SequenceNode {
			dst.Kind = yaml.SequenceNode
			dst.Tag = "!!seq"
			dst.Content = nil
		}
		reorderSequenceForMerge(dst, src)
		// Update elements in place
		minContent := len(dst.Content)
		if len(src.Content) < minContent {
			minContent = len(src.Content)
		}
		for i := 0; i < minContent; i++ {
			if dst.Content[i] == nil {
				dst.Content[i] = deepCopyNode(src.Content[i])
				continue
			}
			mergeNodePreserve(dst.Content[i], src.Content[i])
			if dst.Content[i] != nil && src.Content[i] != nil &&
				dst.Content[i].Kind == yaml.MappingNode && src.Content[i].Kind == yaml.MappingNode {
				pruneMissingMapKeys(dst.Content[i], src.Content[i])
			}
		}
		// Append any extra items from src
		for i := len(dst.Content); i < len(src.Content); i++ {
			dst.Content = append(dst.Content, deepCopyNode(src.Content[i]))
		}
		// Truncate if dst has extra items not in src
		if len(src.Content) < len(dst.Content) {
			dst.Content = dst.Content[:len(src.Content)]
		}
	case yaml.ScalarNode, yaml.AliasNode:
		// For scalars, update Tag and Value but keep Style from dst to preserve quoting
		dst.Kind = src.Kind
		dst.Tag = src.Tag
		dst.Value = src.Value
		// Keep dst.Style as-is intentionally
	case 0:
		// Unknown/empty kind; do nothing
	default:
		// Fallback: replace shallowly
		copyNodeShallow(dst, src)
	}
}

// findMapKeyIndex returns the index of key node in dst mapping (index of key, not value).
// Returns -1 when not found.
func findMapKeyIndex(mapNode *yaml.Node, key string) int {
	if mapNode == nil || mapNode.Kind != yaml.MappingNode {
		return -1
	}
	for i := 0; i+1 < len(mapNode.Content); i += 2 {
		if mapNode.Content[i] != nil && mapNode.Content[i].Value == key {
			return i
		}
	}
	return -1
}

// isZeroValueNode returns true if the YAML node represents a zero/default value
// that should not be written as a new key to preserve config cleanliness.
// For mappings and sequences, recursively checks if all children are zero values.
func isZeroValueNode(node *yaml.Node) bool {
	if node == nil {
		return true
	}
	switch node.Kind {
	case yaml.ScalarNode:
		switch node.Tag {
		case "!!bool":
			return node.Value == "false"
		case "!!int", "!!float":
			return node.Value == "0" || node.Value == "0.0"
		case "!!str":
			return node.Value == ""
		case "!!null":
			return true
		}
	case yaml.SequenceNode:
		if len(node.Content) == 0 {
			return true
		}
		// Check if all elements are zero values
		for _, child := range node.Content {
			if !isZeroValueNode(child) {
				return false
			}
		}
		return true
	case yaml.MappingNode:
		if len(node.Content) == 0 {
			return true
		}
		// Check if all values are zero values (values are at odd indices)
		for i := 1; i < len(node.Content); i += 2 {
			if !isZeroValueNode(node.Content[i]) {
				return false
			}
		}
		return true
	}
	return false
}

// deepCopyNode creates a deep copy of a yaml.Node graph.
func deepCopyNode(n *yaml.Node) *yaml.Node {
	if n == nil {
		return nil
	}
	cp := *n
	if len(n.Content) > 0 {
		cp.Content = make([]*yaml.Node, len(n.Content))
		for i := range n.Content {
			cp.Content[i] = deepCopyNode(n.Content[i])
		}
	}
	return &cp
}

// copyNodeShallow copies type/tag/value and resets content to match src, but
// keeps the same destination node pointer to preserve parent relations/comments.
func copyNodeShallow(dst, src *yaml.Node) {
	if dst == nil || src == nil {
		return
	}
	dst.Kind = src.Kind
	dst.Tag = src.Tag
	dst.Value = src.Value
	// Replace content with deep copy from src
	if len(src.Content) > 0 {
		dst.Content = make([]*yaml.Node, len(src.Content))
		for i := range src.Content {
			dst.Content[i] = deepCopyNode(src.Content[i])
		}
	} else {
		dst.Content = nil
	}
}

func reorderSequenceForMerge(dst, src *yaml.Node) {
	if dst == nil || src == nil {
		return
	}
	if len(dst.Content) == 0 {
		return
	}
	if len(src.Content) == 0 {
		return
	}
	original := append([]*yaml.Node(nil), dst.Content...)
	used := make([]bool, len(original))
	ordered := make([]*yaml.Node, len(src.Content))
	for i := range src.Content {
		if idx := matchSequenceElement(original, used, src.Content[i]); idx >= 0 {
			ordered[i] = original[idx]
			used[idx] = true
		}
	}
	dst.Content = ordered
}

func matchSequenceElement(original []*yaml.Node, used []bool, target *yaml.Node) int {
	if target == nil {
		return -1
	}
	switch target.Kind {
	case yaml.MappingNode:
		id := sequenceElementIdentity(target)
		if id != "" {
			for i := range original {
				if used[i] || original[i] == nil || original[i].Kind != yaml.MappingNode {
					continue
				}
				if sequenceElementIdentity(original[i]) == id {
					return i
				}
			}
		}
	case yaml.ScalarNode:
		val := strings.TrimSpace(target.Value)
		if val != "" {
			for i := range original {
				if used[i] || original[i] == nil || original[i].Kind != yaml.ScalarNode {
					continue
				}
				if strings.TrimSpace(original[i].Value) == val {
					return i
				}
			}
		}
	default:
	}
	// Fallback to structural equality to preserve nodes lacking explicit identifiers.
	for i := range original {
		if used[i] || original[i] == nil {
			continue
		}
		if nodesStructurallyEqual(original[i], target) {
			return i
		}
	}
	return -1
}

func sequenceElementIdentity(node *yaml.Node) string {
	if node == nil || node.Kind != yaml.MappingNode {
		return ""
	}
	identityKeys := []string{"id", "name", "alias", "api-key", "api_key", "apikey", "key", "provider", "model"}
	for _, k := range identityKeys {
		if v := mappingScalarValue(node, k); v != "" {
			return k + "=" + v
		}
	}
	for i := 0; i+1 < len(node.Content); i += 2 {
		keyNode := node.Content[i]
		valNode := node.Content[i+1]
		if keyNode == nil || valNode == nil || valNode.Kind != yaml.ScalarNode {
			continue
		}
		val := strings.TrimSpace(valNode.Value)
		if val != "" {
			return strings.ToLower(strings.TrimSpace(keyNode.Value)) + "=" + val
		}
	}
	return ""
}

func mappingScalarValue(node *yaml.Node, key string) string {
	if node == nil || node.Kind != yaml.MappingNode {
		return ""
	}
	lowerKey := strings.ToLower(key)
	for i := 0; i+1 < len(node.Content); i += 2 {
		keyNode := node.Content[i]
		valNode := node.Content[i+1]
		if keyNode == nil || valNode == nil || valNode.Kind != yaml.ScalarNode {
			continue
		}
		if strings.ToLower(strings.TrimSpace(keyNode.Value)) == lowerKey {
			return strings.TrimSpace(valNode.Value)
		}
	}
	return ""
}

func nodesStructurallyEqual(a, b *yaml.Node) bool {
	if a == nil || b == nil {
		return a == b
	}
	if a.Kind != b.Kind {
		return false
	}
	switch a.Kind {
	case yaml.MappingNode:
		if len(a.Content) != len(b.Content) {
			return false
		}
		for i := 0; i+1 < len(a.Content); i += 2 {
			if !nodesStructurallyEqual(a.Content[i], b.Content[i]) {
				return false
			}
			if !nodesStructurallyEqual(a.Content[i+1], b.Content[i+1]) {
				return false
			}
		}
		return true
	case yaml.SequenceNode:
		if len(a.Content) != len(b.Content) {
			return false
		}
		for i := range a.Content {
			if !nodesStructurallyEqual(a.Content[i], b.Content[i]) {
				return false
			}
		}
		return true
	case yaml.ScalarNode:
		return strings.TrimSpace(a.Value) == strings.TrimSpace(b.Value)
	case yaml.AliasNode:
		return nodesStructurallyEqual(a.Alias, b.Alias)
	default:
		return strings.TrimSpace(a.Value) == strings.TrimSpace(b.Value)
	}
}

func removeMapKey(mapNode *yaml.Node, key string) {
	if mapNode == nil || mapNode.Kind != yaml.MappingNode || key == "" {
		return
	}
	for i := 0; i+1 < len(mapNode.Content); i += 2 {
		if mapNode.Content[i] != nil && mapNode.Content[i].Value == key {
			mapNode.Content = append(mapNode.Content[:i], mapNode.Content[i+2:]...)
			return
		}
	}
}

func pruneMappingToGeneratedKeys(dstRoot, srcRoot *yaml.Node, key string) {
	if key == "" || dstRoot == nil || srcRoot == nil {
		return
	}
	if dstRoot.Kind != yaml.MappingNode || srcRoot.Kind != yaml.MappingNode {
		return
	}
	dstIdx := findMapKeyIndex(dstRoot, key)
	if dstIdx < 0 || dstIdx+1 >= len(dstRoot.Content) {
		return
	}
	srcIdx := findMapKeyIndex(srcRoot, key)
	if srcIdx < 0 {
		removeMapKey(dstRoot, key)
		return
	}
	if srcIdx+1 >= len(srcRoot.Content) {
		return
	}
	srcVal := srcRoot.Content[srcIdx+1]
	dstVal := dstRoot.Content[dstIdx+1]
	if srcVal == nil {
		dstRoot.Content[dstIdx+1] = nil
		return
	}
	if srcVal.Kind != yaml.MappingNode {
		dstRoot.Content[dstIdx+1] = deepCopyNode(srcVal)
		return
	}
	if dstVal == nil || dstVal.Kind != yaml.MappingNode {
		dstRoot.Content[dstIdx+1] = deepCopyNode(srcVal)
		return
	}
	pruneMissingMapKeys(dstVal, srcVal)
}

func pruneMissingMapKeys(dstMap, srcMap *yaml.Node) {
	if dstMap == nil || srcMap == nil || dstMap.Kind != yaml.MappingNode || srcMap.Kind != yaml.MappingNode {
		return
	}
	keep := make(map[string]struct{}, len(srcMap.Content)/2)
	for i := 0; i+1 < len(srcMap.Content); i += 2 {
		keyNode := srcMap.Content[i]
		if keyNode == nil {
			continue
		}
		key := strings.TrimSpace(keyNode.Value)
		if key == "" {
			continue
		}
		keep[key] = struct{}{}
	}
	for i := 0; i+1 < len(dstMap.Content); {
		keyNode := dstMap.Content[i]
		if keyNode == nil {
			i += 2
			continue
		}
		key := strings.TrimSpace(keyNode.Value)
		if _, ok := keep[key]; !ok {
			dstMap.Content = append(dstMap.Content[:i], dstMap.Content[i+2:]...)
			continue
		}
		i += 2
	}
}

// normalizeCollectionNodeStyles forces YAML collections to use block notation, keeping
// lists and maps readable. Empty sequences retain flow style ([]) so empty list markers
// remain compact.
func normalizeCollectionNodeStyles(node *yaml.Node) {
	if node == nil {
		return
	}
	switch node.Kind {
	case yaml.MappingNode:
		node.Style = 0
		for i := range node.Content {
			normalizeCollectionNodeStyles(node.Content[i])
		}
	case yaml.SequenceNode:
		if len(node.Content) == 0 {
			node.Style = yaml.FlowStyle
		} else {
			node.Style = 0
		}
		for i := range node.Content {
			normalizeCollectionNodeStyles(node.Content[i])
		}
	default:
		// Scalars keep their existing style to preserve quoting
	}
}