package ledger

import (
	"bytes"
	"fmt"
	"io"
	"os"
	"strconv"
	"strings"
)

type File string

func NewFile(p string) (File, error) {
	f := File(p)
	_, err := f.Deltas()
	return f, err
}

func (file File) Deltas(like ...Like) ([]Delta, error) {
	transactions, err := file.transactions()
	if err != nil {
		return nil, err
	}
	result := make([]Delta, 0, len(transactions)*2)
	for _, transaction := range transactions {
		sums := map[string]float64{}
		for _, acc := range transaction.recipients {
			sums[acc.currency] += acc.value
			delta := newDelta(
				transaction.date,
				transaction.description,
				acc.name,
				acc.value,
				acc.currency,
			)
			if likes(like).all(delta) {
				result = append(result, delta)
			}
		}
		for currency, value := range sums {
			if value == 0 {
				continue
			}
			if transaction.payee == "" {
				return nil, fmt.Errorf("didnt find net zero and no dumping ground payee set: %+v", transaction)
			}
			delta := newDelta(
				transaction.date,
				transaction.description,
				transaction.payee,
				-1.0*value,
				currency,
			)
			if likes(like).all(delta) {
				result = append(result, delta)
			}
		}
	}
	return result, nil
}

type transaction struct {
	date        string
	description string
	payee       string
	recipients  []transactionRecipient
}

func (t transaction) empty() bool {
	return fmt.Sprint(t) == fmt.Sprint(transaction{})
}

type transactionRecipient struct {
	name     string
	value    float64
	currency string
}

func (t transactionRecipient) empty() bool {
	return t == (transactionRecipient{})
}

func (file File) transactions() ([]transaction, error) {
	f, err := os.Open(string(file))
	if err != nil {
		return nil, err
	}
	defer f.Close()

	var r io.Reader = f

	result := make([]transaction, 0)
	for {
		newr, one, err := readTransaction(r)
		if !one.empty() {
			result = append(result, one)
		}
		if err == io.EOF {
			return result, nil
		}
		if err != nil {
			return result, err
		}
		r = newr
	}
}

func readTransaction(r io.Reader) (io.Reader, transaction, error) {
	result := transaction{}
	var err error

	if r, err = readTransactionLeadingWhitespace(r); err != nil {
		return r, transaction{}, err
	}

	if result.date, err = readTransactionDate(r); err != nil {
		if err == io.EOF {
			return r, transaction{}, err
		}
		return nil, result, fmt.Errorf("did not find transaction date: %w", err)
	}

	if result.description, err = readTransactionDescription(r); err != nil {
		return nil, result, fmt.Errorf("did not find transaction description: %w", err)
	}

	for {
		newR, recipient, err := readTransactionRecipient(r)
		r = newR
		if !recipient.empty() {
			if recipient.currency == "" {
				result.payee = recipient.name
			} else {
				result.recipients = append(result.recipients, recipient)
			}
		}
		if err != nil || recipient.empty() {
			return r, result, err
		}
	}
}

// from "\s*.* read \s*"
func readTransactionLeadingWhitespace(r io.Reader) (io.Reader, error) {
	for {
		b, err := readOne(r)
		if err != nil {
			return r, err
		}
		if b != 0 && !isSpaceByte(b) {
			return io.MultiReader(bytes.NewReader([]byte{b}), r), nil
		}
	}
}

// from "20yy-mm-dd.* read "20yy-mm-dd"
func readTransactionDate(r io.Reader) (string, error) {
	startOfDate := []byte{}
	for len(startOfDate) == 0 {
		b, err := readOne(r)
		if err != nil {
			return "", err
		}
		if '0' <= b && b <= '9' {
			startOfDate = append(startOfDate, b)
		}
	}

	restOfDate := make([]byte, len("2006-01-02")-len(startOfDate))
	if _, err := r.Read(restOfDate); err != nil {
		return "", err
	}

	return fmt.Sprintf("%s%s", startOfDate, restOfDate), nil
}

// from "\s*.*\n.*" read \s*.*\n.*"
func readTransactionDescription(r io.Reader) (string, error) {
	result := make([]byte, 0, 16)
	for {
		b, err := readOne(r)
		if err != nil {
			return "", err
		}
		if b == '\n' {
			break
		}
		result = append(result, b)
	}
	return strings.TrimSpace(string(result)), nil
}

// from "\s+.*\n?.*" read "\s+.*\n?"
func readTransactionRecipient(r io.Reader) (io.Reader, transactionRecipient, error) {
	if b, err := readOne(r); err != nil {
		return r, transactionRecipient{}, err
	} else if !isSpaceByte(b) {
		return io.MultiReader(bytes.NewReader([]byte{b}), r), transactionRecipient{}, nil
	}

	r, err := readTransactionLeadingWhitespace(r)
	if err != nil {
		return r, transactionRecipient{}, err
	}

	result := transactionRecipient{}
	for {
		b, err := readOne(r)
		if err != nil {
			if result.empty() {
				return nil, result, err
			}
			return nil, result, fmt.Errorf("failed to read transaction recipient name after skipping whitespace: %w", err)
		} else if !isSpaceByte(b) {
			result.name += string([]byte{b})
			continue
		}
		r = io.MultiReader(bytes.NewReader([]byte{b}), r)
		break
	}
	if result.name == "" {
		return nil, result, fmt.Errorf("did not parse any name for transaction recipient")
	}

	// read "NAME:NAME", now "(\s+|\n).*"

	for {
		b, err := readOne(r)
		if err != nil {
			return r, result, err
		}
		if isSpaceByte(b) && b != '\n' {
			continue
		}
		r = io.MultiReader(bytes.NewReader([]byte{b}), r)
		break
	}

	// read "\s+", now "(\n|\$1.00)"

	if b, err := readOne(r); err != nil {
		return r, result, err
	} else if isSpaceByte(b) {
		return r, result, err
	} else if newr, value, currency, err := readTransactionValueCurrency(io.MultiReader(bytes.NewReader([]byte{b}), r)); err != nil {
		return r, result, fmt.Errorf("failed to read transaction recipient's value and currency: %w", err)
	} else {
		r = newr
		result.value = value
		result.currency = currency
	}
	return r, result, err
}

func readOne(r io.Reader) (byte, error) {
	var firstByte [1]byte
	_, err := r.Read(firstByte[:])
	return firstByte[0], err
}

func isSpaceByte(b byte) bool {
	return len(bytes.TrimSpace([]byte{b})) == 0
}

func isNumericByte(b byte) bool {
	return '0' <= b && b <= '9' || b == '.' || b == '-'
}

// from "[^\n]*\n?.*" read "[^\n]*\n?"
func readTransactionValueCurrency(r io.Reader) (io.Reader, float64, string, error) {
	restOfLine := make([]byte, 0, 16)
	for {
		b, err := readOne(r)
		if b == '\n' || err == io.EOF {
			break
		}
		if err != nil {
			return r, 0, "", err
		}
		restOfLine = append(restOfLine, b)
	}
	restOfLine = bytes.TrimSpace(restOfLine)
	if len(restOfLine) == 0 {
		return r, 0, "", nil
	}

	firstNonNumericIdx := -1
	firstNumericIdx := -1
	for i := range restOfLine {
		if !isNumericByte(restOfLine[i]) && firstNonNumericIdx == -1 {
			firstNonNumericIdx = i
		}
		if isNumericByte(restOfLine[i]) && firstNumericIdx == -1 {
			firstNumericIdx = i
		}
	}

	if firstNonNumericIdx == -1 || firstNumericIdx == -1 {
		return r, 0, "", fmt.Errorf("needed numeric and non-numeric bytes in %q", restOfLine)
	}

	var valueS, currency string
	if firstNonNumericIdx < firstNumericIdx {
		currency = string(restOfLine[firstNonNumericIdx:firstNumericIdx])
		valueS = string(restOfLine[firstNumericIdx:])
	} else {
		valueS = string(restOfLine[firstNumericIdx:firstNonNumericIdx])
		currency = string(restOfLine[firstNonNumericIdx:])
	}
	valueS = strings.TrimSpace(valueS)
	currency = strings.TrimSpace(currency)

	value, err := strconv.ParseFloat(valueS, 64)
	if err != nil {
		return r, 0, "", fmt.Errorf("value %q is not a float: %w", valueS, err)
	}

	return r, value, currency, nil
}