package wire

import (
	"encoding/json"
	"net/url"
	"strings"
)

// UnmarshalRows unpacks a list from an object (trying keys in order) or a JSON array.
// next is next_cursor, else the cursor query param of next, else next itself when it
// is not a URL.
func UnmarshalRows[T any](raw json.RawMessage, keys ...string) (rows []T, next string, err error) {
	data := Unwrap(raw)
	var obj map[string]json.RawMessage
	if json.Unmarshal(data, &obj) != nil {
		var list []T
		if err := json.Unmarshal(data, &list); err != nil {
			return nil, "", err
		}
		return list, "", nil
	}
	next = cursorFromMap(obj)
	for _, k := range keys {
		item, ok := obj[k]
		if !ok || len(item) == 0 || string(item) == "null" {
			continue
		}
		var list []T
		if json.Unmarshal(item, &list) == nil {
			return list, next, nil
		}
		var one T
		if json.Unmarshal(item, &one) == nil {
			return []T{one}, next, nil
		}
	}
	return nil, next, nil
}

func cursorFromMap(obj map[string]json.RawMessage) string {
	if c := stringField(obj, "next_cursor"); c != "" {
		return c
	}
	return Cursor(stringField(obj, "next"), "")
}

func stringField(obj map[string]json.RawMessage, key string) string {
	raw, ok := obj[key]
	if !ok || len(raw) == 0 || string(raw) == "null" {
		return ""
	}
	var s string
	if json.Unmarshal(raw, &s) == nil {
		return s
	}
	return ""
}

// Cursor prefers nextCursor; otherwise extracts cursor from a next URL.
func Cursor(next, nextCursor string) string {
	if nextCursor != "" {
		return nextCursor
	}
	next = strings.TrimSpace(next)
	if next == "" {
		return ""
	}
	u, err := url.Parse(next)
	if err != nil || (u.Scheme == "" && u.Host == "" && !strings.Contains(next, "?")) {
		return next
	}
	if v := u.Query().Get("cursor"); v != "" {
		return v
	}
	return ""
}