package parser

import (
	"encoding/csv"
	"fmt"
	"io"
	"os"
	"strings"
	"time"

	"git.petrovv.com/nikola/money/internal/config"
)

func init() {
	Register("csv", newCSVParser)
}

// csvParser reads a delimited statement using column positions from
// account.toml. Amounts come either from one signed column, or from a
// debit/credit pair.
type csvParser struct {
	cfg    config.CSVConfig
	digits int
}

func newCSVParser(acc *config.Account) (Parser, error) {
	if acc.CSV == nil {
		return nil, fmt.Errorf("account %s: parser \"csv\" requires a [csv] section", acc.Slug)
	}
	cfg := *acc.CSV
	if cfg.Amount == nil && cfg.Debit == nil && cfg.Credit == nil {
		return nil, fmt.Errorf("account %s: [csv] needs either amount or debit/credit columns", acc.Slug)
	}
	if cfg.Amount != nil && (cfg.Debit != nil || cfg.Credit != nil) {
		return nil, fmt.Errorf("account %s: [csv] sets both amount and debit/credit; pick one", acc.Slug)
	}
	if cfg.Date.Layout == "" {
		return nil, fmt.Errorf("account %s: [csv] date needs a layout, e.g. layout = \"02.01.2006\"", acc.Slug)
	}
	return &csvParser{cfg: cfg, digits: acc.Digits()}, nil
}

func (p *csvParser) Parse(path string, acc *config.Account) ([]RawTxn, error) {
	f, err := os.Open(path)
	if err != nil {
		return nil, err
	}
	defer f.Close()

	r := csv.NewReader(f)
	r.FieldsPerRecord = -1 // statements are ragged more often than not
	r.LazyQuotes = true
	if d := p.cfg.Delimiter; d != "" {
		runes := []rune(d)
		if len(runes) != 1 {
			return nil, fmt.Errorf("delimiter %q must be a single character", d)
		}
		r.Comma = runes[0]
	}

	var out []RawTxn
	for row := 0; ; row++ {
		rec, err := r.Read()
		if err == io.EOF {
			break
		}
		if err != nil {
			return nil, fmt.Errorf("%s: row %d: %w", path, row+1, err)
		}
		if row < p.cfg.SkipRows {
			continue
		}
		if isBlank(rec) {
			continue
		}
		txn, err := p.row(rec)
		if err != nil {
			return nil, fmt.Errorf("%s: row %d: %w", path, row+1, err)
		}
		out = append(out, txn)
	}
	return out, nil
}

func (p *csvParser) row(rec []string) (RawTxn, error) {
	var t RawTxn

	raw, err := field(rec, p.cfg.Date.Col)
	if err != nil {
		return t, fmt.Errorf("date column: %w", err)
	}
	d, err := time.Parse(p.cfg.Date.Layout, strings.TrimSpace(raw))
	if err != nil {
		return t, fmt.Errorf("date %q does not match layout %q", raw, p.cfg.Date.Layout)
	}
	t.Date = d.Format("2006-01-02")

	desc, err := field(rec, p.cfg.Description.Col)
	if err != nil {
		return t, fmt.Errorf("description column: %w", err)
	}
	t.Description = strings.TrimSpace(desc)

	switch {
	case p.cfg.Amount != nil:
		raw, err := field(rec, p.cfg.Amount.Col)
		if err != nil {
			return t, fmt.Errorf("amount column: %w", err)
		}
		v, err := ParseAmount(raw, p.cfg.Amount.Decimal, p.cfg.Amount.Thousands, p.digits)
		if err != nil {
			return t, err
		}
		t.AmountMinor = v
	default:
		// Debit/credit pair: exactly one of the two carries a value, and both
		// are written as positive numbers.
		debit, err := p.optional(rec, p.cfg.Debit)
		if err != nil {
			return t, fmt.Errorf("debit column: %w", err)
		}
		credit, err := p.optional(rec, p.cfg.Credit)
		if err != nil {
			return t, fmt.Errorf("credit column: %w", err)
		}
		if debit != 0 && credit != 0 {
			return t, fmt.Errorf("both debit (%d) and credit (%d) are set", debit, credit)
		}
		t.AmountMinor = credit - abs(debit)
	}

	if p.cfg.Invert {
		t.AmountMinor = -t.AmountMinor
	}
	return t, nil
}

// optional parses a column that may legitimately be blank, as debit/credit
// columns always are for half the rows.
func (p *csvParser) optional(rec []string, c *config.Column) (int64, error) {
	if c == nil {
		return 0, nil
	}
	raw, err := field(rec, c.Col)
	if err != nil {
		return 0, err
	}
	if strings.TrimSpace(raw) == "" {
		return 0, nil
	}
	return ParseAmount(raw, c.Decimal, c.Thousands, p.digits)
}

func field(rec []string, i int) (string, error) {
	if i < 0 || i >= len(rec) {
		return "", fmt.Errorf("index %d out of range, row has %d columns", i, len(rec))
	}
	return rec[i], nil
}

func isBlank(rec []string) bool {
	for _, f := range rec {
		if strings.TrimSpace(f) != "" {
			return false
		}
	}
	return true
}

func abs(v int64) int64 {
	if v < 0 {
		return -v
	}
	return v
}