package main

import (
	"encoding/json"
	"fmt"
	"slices"
	"strings"
)

type Document struct {
	Header []string
	Rows   [][]string
}

func (d Document) MarshalJSON() ([]byte, error) {
	headers := keys(d.Header)
	var ret strings.Builder
	ret.WriteRune('[')
	for i, row := range d.Rows {
		ret.WriteRune('{')

		for j, col := range row {
			obj, err := json.Marshal(map[string]string{headers[j]: col})
			if err != nil {
				return nil, fmt.Errorf("failed to marshal %s: %w", headers[j], err)
			}
			ret.WriteString(strings.Trim(string(obj), "{}"))
			if j < len(row)-1 {
				ret.WriteRune(',')
			}
		}

		if i < len(d.Rows)-1 {
			ret.WriteString("},")
		} else {
			ret.WriteRune('}')
		}
	}

	ret.WriteRune(']')
	return []byte(ret.String()), nil
}

func (d *Document) setHeader(h []string) error {
	d.Header = h
	return nil
}

func (d *Document) addRow(row []string) error {
	d.Rows = append(d.Rows, row)
	return nil
}

func keys(list []string) []string {
	keys := make([]string, 0, len(list))
	for _, h := range list {
		heading := h
		index := 0
		for slices.Contains(keys, heading) {
			index++
			heading = fmt.Sprintf("%s_%d", h, index)
		}
		keys = append(keys, heading)
	}
	return keys
}