package sqliteclidriver

import (
	"bytes"
	"encoding/json"
	"fmt"
)

type Pair struct {
	Key   string
	Value any
}

type OrderedKV []Pair

func (o *OrderedKV) UnmarshalJSON(data []byte) error {
	// Rough estimate malloc size based on number of `:`
	// This is a lower bound since there might be nested elements
	var elCount int64
	for _, c := range data {
		if c == ':' {
			elCount += 1
		}
	}

	*o = make([]Pair, 0, elCount)

	// Parse the initial opening { delimiter from the JSON stream

	reader := bytes.NewReader(data)
	dec := json.NewDecoder(reader)

	tok, err := dec.Token()
	if err != nil {
		return fmt.Errorf("expected '{': %w", err)
	}
	if d, ok := tok.(json.Delim); !ok || (rune(d) != '{') {
		return fmt.Errorf("expected '{', got %v", tok)
	}

	// Read remaining content

	for dec.More() {

		var p Pair

		// Parse key: either string or Delim('}')
		tok, err := dec.Token()
		if err != nil {
			return fmt.Errorf("expected '{': %w", err)
		}
		switch tok := tok.(type) {
		case json.Delim:
			if rune(tok) == '}' {
				// Finished
				break
			}
			// Something else
			return fmt.Errorf("expected string or }, got %v", tok)

		case string:
			// Valid key
			p.Key = tok

		default:
			return fmt.Errorf("expected string or }, got %v", tok)
		}

		// Parse value (any)
		err = dec.Decode(&p.Value)
		if err != nil {
			return err
		}

		*o = append(*o, p)
	}

	// Assert that there is no remaining content
	if reader.Len() != 0 {
		return fmt.Errorf("Unexpected trailing data (%d bytes remaining)", reader.Len())
	}

	// Done
	return nil
}