// Package util provides utility functions for the CLI Proxy API server.
package util

import (
	"fmt"
	"sort"
	"strings"

	"github.com/tidwall/gjson"
	"github.com/tidwall/sjson"
)

var gjsonPathKeyReplacer = strings.NewReplacer(".", "\\.", "*", "\\*", "?", "\\?")

// CleanJSONSchemaForGemini transforms a JSON schema to be compatible with Gemini/Antigravity API.
// It handles unsupported keywords, type flattening, and schema simplification while preserving
// semantic information as description hints.
func CleanJSONSchemaForGemini(jsonStr string) string {
	// Phase 1: Convert and add hints
	jsonStr = convertRefsToHints(jsonStr)
	jsonStr = convertConstToEnum(jsonStr)
	jsonStr = addEnumHints(jsonStr)
	jsonStr = addAdditionalPropertiesHints(jsonStr)
	jsonStr = moveConstraintsToDescription(jsonStr)

	// Phase 2: Flatten complex structures
	jsonStr = mergeAllOf(jsonStr)
	jsonStr = flattenAnyOfOneOf(jsonStr)
	jsonStr = flattenTypeArrays(jsonStr)

	// Phase 3: Cleanup
	jsonStr = removeUnsupportedKeywords(jsonStr)
	jsonStr = cleanupRequiredFields(jsonStr)

	return jsonStr
}

// convertRefsToHints converts $ref to description hints (Lazy Hint strategy).
func convertRefsToHints(jsonStr string) string {
	paths := findPaths(jsonStr, "$ref")
	sortByDepth(paths)

	for _, p := range paths {
		refVal := gjson.Get(jsonStr, p).String()
		defName := refVal
		if idx := strings.LastIndex(refVal, "/"); idx >= 0 {
			defName = refVal[idx+1:]
		}

		parentPath := trimSuffix(p, ".$ref")
		hint := fmt.Sprintf("See: %s", defName)
		if existing := gjson.Get(jsonStr, descriptionPath(parentPath)).String(); existing != "" {
			hint = fmt.Sprintf("%s (%s)", existing, hint)
		}

		replacement := `{"type":"object","description":""}`
		replacement, _ = sjson.Set(replacement, "description", hint)
		jsonStr = setRawAt(jsonStr, parentPath, replacement)
	}
	return jsonStr
}

func convertConstToEnum(jsonStr string) string {
	for _, p := range findPaths(jsonStr, "const") {
		val := gjson.Get(jsonStr, p)
		if !val.Exists() {
			continue
		}
		enumPath := trimSuffix(p, ".const") + ".enum"
		if !gjson.Get(jsonStr, enumPath).Exists() {
			jsonStr, _ = sjson.Set(jsonStr, enumPath, []interface{}{val.Value()})
		}
	}
	return jsonStr
}

func addEnumHints(jsonStr string) string {
	for _, p := range findPaths(jsonStr, "enum") {
		arr := gjson.Get(jsonStr, p)
		if !arr.IsArray() {
			continue
		}
		items := arr.Array()
		if len(items) <= 1 || len(items) > 10 {
			continue
		}

		var vals []string
		for _, item := range items {
			vals = append(vals, item.String())
		}
		jsonStr = appendHint(jsonStr, trimSuffix(p, ".enum"), "Allowed: "+strings.Join(vals, ", "))
	}
	return jsonStr
}

func addAdditionalPropertiesHints(jsonStr string) string {
	for _, p := range findPaths(jsonStr, "additionalProperties") {
		if gjson.Get(jsonStr, p).Type == gjson.False {
			jsonStr = appendHint(jsonStr, trimSuffix(p, ".additionalProperties"), "No extra properties allowed")
		}
	}
	return jsonStr
}

var unsupportedConstraints = []string{
	"minLength", "maxLength", "exclusiveMinimum", "exclusiveMaximum",
	"pattern", "minItems", "maxItems",
}

func moveConstraintsToDescription(jsonStr string) string {
	for _, key := range unsupportedConstraints {
		for _, p := range findPaths(jsonStr, key) {
			val := gjson.Get(jsonStr, p)
			if !val.Exists() || val.IsObject() || val.IsArray() {
				continue
			}
			parentPath := trimSuffix(p, "."+key)
			if isPropertyDefinition(parentPath) {
				continue
			}
			jsonStr = appendHint(jsonStr, parentPath, fmt.Sprintf("%s: %s", key, val.String()))
		}
	}
	return jsonStr
}

func mergeAllOf(jsonStr string) string {
	paths := findPaths(jsonStr, "allOf")
	sortByDepth(paths)

	for _, p := range paths {
		allOf := gjson.Get(jsonStr, p)
		if !allOf.IsArray() {
			continue
		}
		parentPath := trimSuffix(p, ".allOf")

		for _, item := range allOf.Array() {
			if props := item.Get("properties"); props.IsObject() {
				props.ForEach(func(key, value gjson.Result) bool {
					destPath := joinPath(parentPath, "properties."+escapeGJSONPathKey(key.String()))
					jsonStr, _ = sjson.SetRaw(jsonStr, destPath, value.Raw)
					return true
				})
			}
			if req := item.Get("required"); req.IsArray() {
				reqPath := joinPath(parentPath, "required")
				current := getStrings(jsonStr, reqPath)
				for _, r := range req.Array() {
					if s := r.String(); !contains(current, s) {
						current = append(current, s)
					}
				}
				jsonStr, _ = sjson.Set(jsonStr, reqPath, current)
			}
		}
		jsonStr, _ = sjson.Delete(jsonStr, p)
	}
	return jsonStr
}

func flattenAnyOfOneOf(jsonStr string) string {
	for _, key := range []string{"anyOf", "oneOf"} {
		paths := findPaths(jsonStr, key)
		sortByDepth(paths)

		for _, p := range paths {
			arr := gjson.Get(jsonStr, p)
			if !arr.IsArray() || len(arr.Array()) == 0 {
				continue
			}

			parentPath := trimSuffix(p, "."+key)
			parentDesc := gjson.Get(jsonStr, descriptionPath(parentPath)).String()

			items := arr.Array()
			bestIdx, allTypes := selectBest(items)
			selected := items[bestIdx].Raw

			if parentDesc != "" {
				selected = mergeDescriptionRaw(selected, parentDesc)
			}

			if len(allTypes) > 1 {
				hint := "Accepts: " + strings.Join(allTypes, " | ")
				selected = appendHintRaw(selected, hint)
			}

			jsonStr = setRawAt(jsonStr, parentPath, selected)
		}
	}
	return jsonStr
}

func selectBest(items []gjson.Result) (bestIdx int, types []string) {
	bestScore := -1
	for i, item := range items {
		t := item.Get("type").String()
		score := 0

		switch {
		case t == "object" || item.Get("properties").Exists():
			score, t = 3, orDefault(t, "object")
		case t == "array" || item.Get("items").Exists():
			score, t = 2, orDefault(t, "array")
		case t != "" && t != "null":
			score = 1
		default:
			t = orDefault(t, "null")
		}

		if t != "" {
			types = append(types, t)
		}
		if score > bestScore {
			bestScore, bestIdx = score, i
		}
	}
	return
}

func flattenTypeArrays(jsonStr string) string {
	paths := findPaths(jsonStr, "type")
	sortByDepth(paths)

	nullableFields := make(map[string][]string)

	for _, p := range paths {
		res := gjson.Get(jsonStr, p)
		if !res.IsArray() || len(res.Array()) == 0 {
			continue
		}

		hasNull := false
		var nonNullTypes []string
		for _, item := range res.Array() {
			s := item.String()
			if s == "null" {
				hasNull = true
			} else if s != "" {
				nonNullTypes = append(nonNullTypes, s)
			}
		}

		firstType := "string"
		if len(nonNullTypes) > 0 {
			firstType = nonNullTypes[0]
		}

		jsonStr, _ = sjson.Set(jsonStr, p, firstType)

		parentPath := trimSuffix(p, ".type")
		if len(nonNullTypes) > 1 {
			hint := "Accepts: " + strings.Join(nonNullTypes, " | ")
			jsonStr = appendHint(jsonStr, parentPath, hint)
		}

		if hasNull {
			parts := splitGJSONPath(p)
			if len(parts) >= 3 && parts[len(parts)-3] == "properties" {
				fieldNameEscaped := parts[len(parts)-2]
				fieldName := unescapeGJSONPathKey(fieldNameEscaped)
				objectPath := strings.Join(parts[:len(parts)-3], ".")
				nullableFields[objectPath] = append(nullableFields[objectPath], fieldName)

				propPath := joinPath(objectPath, "properties."+fieldNameEscaped)
				jsonStr = appendHint(jsonStr, propPath, "(nullable)")
			}
		}
	}

	for objectPath, fields := range nullableFields {
		reqPath := joinPath(objectPath, "required")
		req := gjson.Get(jsonStr, reqPath)
		if !req.IsArray() {
			continue
		}

		var filtered []string
		for _, r := range req.Array() {
			if !contains(fields, r.String()) {
				filtered = append(filtered, r.String())
			}
		}

		if len(filtered) == 0 {
			jsonStr, _ = sjson.Delete(jsonStr, reqPath)
		} else {
			jsonStr, _ = sjson.Set(jsonStr, reqPath, filtered)
		}
	}
	return jsonStr
}

func removeUnsupportedKeywords(jsonStr string) string {
	keywords := append(unsupportedConstraints,
		"$schema", "$defs", "definitions", "const", "$ref", "additionalProperties",
	)
	for _, key := range keywords {
		for _, p := range findPaths(jsonStr, key) {
			if isPropertyDefinition(trimSuffix(p, "."+key)) {
				continue
			}
			jsonStr, _ = sjson.Delete(jsonStr, p)
		}
	}
	return jsonStr
}

func cleanupRequiredFields(jsonStr string) string {
	for _, p := range findPaths(jsonStr, "required") {
		parentPath := trimSuffix(p, ".required")
		propsPath := joinPath(parentPath, "properties")

		req := gjson.Get(jsonStr, p)
		props := gjson.Get(jsonStr, propsPath)
		if !req.IsArray() || !props.IsObject() {
			continue
		}

		var valid []string
		for _, r := range req.Array() {
			key := r.String()
			if props.Get(escapeGJSONPathKey(key)).Exists() {
				valid = append(valid, key)
			}
		}

		if len(valid) != len(req.Array()) {
			if len(valid) == 0 {
				jsonStr, _ = sjson.Delete(jsonStr, p)
			} else {
				jsonStr, _ = sjson.Set(jsonStr, p, valid)
			}
		}
	}
	return jsonStr
}

// --- Helpers ---

func findPaths(jsonStr, field string) []string {
	var paths []string
	Walk(gjson.Parse(jsonStr), "", field, &paths)
	return paths
}

func sortByDepth(paths []string) {
	sort.Slice(paths, func(i, j int) bool { return len(paths[i]) > len(paths[j]) })
}

func trimSuffix(path, suffix string) string {
	if path == strings.TrimPrefix(suffix, ".") {
		return ""
	}
	return strings.TrimSuffix(path, suffix)
}

func joinPath(base, suffix string) string {
	if base == "" {
		return suffix
	}
	return base + "." + suffix
}

func setRawAt(jsonStr, path, value string) string {
	if path == "" {
		return value
	}
	result, _ := sjson.SetRaw(jsonStr, path, value)
	return result
}

func isPropertyDefinition(path string) bool {
	return path == "properties" || strings.HasSuffix(path, ".properties")
}

func descriptionPath(parentPath string) string {
	if parentPath == "" || parentPath == "@this" {
		return "description"
	}
	return parentPath + ".description"
}

func appendHint(jsonStr, parentPath, hint string) string {
	descPath := parentPath + ".description"
	if parentPath == "" || parentPath == "@this" {
		descPath = "description"
	}
	existing := gjson.Get(jsonStr, descPath).String()
	if existing != "" {
		hint = fmt.Sprintf("%s (%s)", existing, hint)
	}
	jsonStr, _ = sjson.Set(jsonStr, descPath, hint)
	return jsonStr
}

func appendHintRaw(jsonRaw, hint string) string {
	existing := gjson.Get(jsonRaw, "description").String()
	if existing != "" {
		hint = fmt.Sprintf("%s (%s)", existing, hint)
	}
	jsonRaw, _ = sjson.Set(jsonRaw, "description", hint)
	return jsonRaw
}

func getStrings(jsonStr, path string) []string {
	var result []string
	if arr := gjson.Get(jsonStr, path); arr.IsArray() {
		for _, r := range arr.Array() {
			result = append(result, r.String())
		}
	}
	return result
}

func contains(slice []string, item string) bool {
	for _, s := range slice {
		if s == item {
			return true
		}
	}
	return false
}

func orDefault(val, def string) string {
	if val == "" {
		return def
	}
	return val
}

func escapeGJSONPathKey(key string) string {
	return gjsonPathKeyReplacer.Replace(key)
}

func unescapeGJSONPathKey(key string) string {
	if !strings.Contains(key, "\\") {
		return key
	}
	var b strings.Builder
	b.Grow(len(key))
	for i := 0; i < len(key); i++ {
		if key[i] == '\\' && i+1 < len(key) {
			i++
			b.WriteByte(key[i])
			continue
		}
		b.WriteByte(key[i])
	}
	return b.String()
}

func splitGJSONPath(path string) []string {
	if path == "" {
		return nil
	}

	parts := make([]string, 0, strings.Count(path, ".")+1)
	var b strings.Builder
	b.Grow(len(path))

	for i := 0; i < len(path); i++ {
		c := path[i]
		if c == '\\' && i+1 < len(path) {
			b.WriteByte('\\')
			i++
			b.WriteByte(path[i])
			continue
		}
		if c == '.' {
			parts = append(parts, b.String())
			b.Reset()
			continue
		}
		b.WriteByte(c)
	}
	parts = append(parts, b.String())
	return parts
}

func mergeDescriptionRaw(schemaRaw, parentDesc string) string {
	childDesc := gjson.Get(schemaRaw, "description").String()
	switch {
	case childDesc == "":
		schemaRaw, _ = sjson.Set(schemaRaw, "description", parentDesc)
		return schemaRaw
	case childDesc == parentDesc:
		return schemaRaw
	default:
		combined := fmt.Sprintf("%s (%s)", parentDesc, childDesc)
		schemaRaw, _ = sjson.Set(schemaRaw, "description", combined)
		return schemaRaw
	}
}