package main

import (
	"bufio"
	"fmt"
	"io"
	"strings"
)

const DefaultTabWidth = 8

type Token struct {
	Name   string
	Pos    int
	Length int
}

type Parser struct {
	Width int
}

func (p Parser) IterMap(r io.Reader, onValue func(map[string]string) error) error {
	return p.IterSlice(r, func(headers, row []string) error {
		return onValue(zip(headers, row))
	})
}

func (p Parser) IterSlice(r io.Reader, onValue func([]string, []string) error) error {
	var headers []string
	return iter{
		Reader: r,
		Width:  p.width(),
		OnHeaders: func(h []string) error {
			headers = h
			return nil
		},
		OnRow: func(row []string) error {
			return onValue(headers, row)
		},
	}.Run()
}

func (p Parser) Parse(r io.Reader) (Document, error) {
	var doc Document
	return doc, iter{
		Reader:    r,
		OnHeaders: doc.setHeader,
		OnRow:     doc.addRow,
		Width:     p.width(),
	}.Run()
}

func (p Parser) width() int {
	if p.Width == 0 {
		return DefaultTabWidth
	}
	return p.Width
}

type iter struct {
	Reader    io.Reader
	Width     int
	OnHeaders func([]string) error
	OnRow     func([]string) error
}

func (i iter) Run() error {
	s := bufio.NewScanner(i.Reader)
	var tokens []Token
	if s.Scan() {
		tokens = i.tokens(s.Text())
		headers := make([]string, len(tokens), len(tokens))
		for i, header := range tokens {
			headers[i] = header.Name
		}
		if err := i.OnHeaders(headers); err != nil {
			return fmt.Errorf("failed to handle headers: %w", err)
		}
	}
	if err := s.Err(); err != nil {
		return fmt.Errorf("failed to read header line: %w", err)
	}

	for s.Scan() {
		if err := i.OnRow(i.parse(tokens, s.Text())); err != nil {
			return fmt.Errorf("failed to handle values: %w", err)
		}
	}
	if err := s.Err(); err != nil {
		return fmt.Errorf("failed to read input: %w", err)
	}

	return nil
}

func (i iter) tokens(line string) []Token {
	index := 0
	pos := 0
	tokens := make([]Token, 0)
	word := make([]rune, 0, len([]rune(line)))
	for _, char := range line {
		if char != '\t' {
			if len(word) == 0 {
				index = pos
			}
			word = append(word, char)
			pos += 1
		} else {
			if len(word) == 0 {
				pos += i.Width
				if len(tokens) > 0 {
					tokens[len(tokens)-1].Length += i.Width
				}
			} else {
				padding := i.Width - (len(word) % i.Width)
				pos += padding
				tokens = append(tokens, Token{
					Name:   string(word),
					Length: len(word) + padding,
					Pos:    index,
				})
				word = word[len(word):]
			}
		}
	}

	if len(word) != 0 {
		tokens = append(tokens, Token{
			Name:   string(word),
			Length: len(word),
			Pos:    index,
		})
	}
	return tokens
}

func (i iter) parse(headings []Token, l string) []string {
	line := removeTabs(i.Width, l)
	values := make([]string, len(headings), len(headings))
	var value string
	for j, heading := range headings {
		if len(line) >= heading.Pos+heading.Length {
			if j >= len(headings)-1 {
				value = line[heading.Pos:]
			} else {
				value = line[heading.Pos : heading.Pos+heading.Length]
			}
		} else if len(line) >= heading.Pos {
			value = line[heading.Pos:]
		} else {
			value = ""
		}
		values[j] = strings.TrimSpace(value)
	}
	return values
}

func zip[K comparable, V any](keys []K, values []V) map[K]V {
	ret := make(map[K]V, len(keys))
	for i, key := range keys {
		if i < len(values) {
			ret[key] = values[i]
		} else {
			ret[key] = *new(V)
		}
	}
	return ret
}

func removeTabs(width int, line string) string {
	var ret strings.Builder
	var word []rune
	for _, char := range line {
		if char != '\t' {
			word = append(word, char)
		} else {
			if len(word) == 0 {
				ret.WriteString(spaces(width))
			} else {
				ret.WriteString(string(word) + spaces(width-(len(word)%width)))
				word = make([]rune, 0)
			}
		}
	}
	ret.WriteString(string(word))
	return ret.String()
}

func spaces(length int) string {
	n := max(length, 0)
	ret := make([]rune, n)
	for i := 0; i < n; i++ {
		ret[i] = ' '
	}
	return string(ret)
}