package numrange

import (
	"context"
	"fmt"
	"math/big"
	"strings"
	"unicode"

	"github.com/gogf/gf/v2/errors/gerror"
)

func Build(ctx context.Context, start, end, field string, maxRows int) ([]string, error) {
	start = strings.TrimSpace(start)
	end = strings.TrimSpace(end)
	if start == "" || end == "" {
		return nil, gerror.Newf("%s起止号不能为空", field)
	}
	if strings.EqualFold(strings.TrimSpace(field), "ICCID") {
		return buildAlphaNumericICCIDRange(ctx, start, end, field, maxRows)
	}
	return buildNumericRange(ctx, start, end, field, maxRows)
}

func buildNumericRange(ctx context.Context, start, end, field string, maxRows int) ([]string, error) {
	if !isDigits(start) || !isDigits(end) {
		return nil, gerror.Newf("%s起止号必须为数字", field)
	}
	if len(start) != len(end) {
		return nil, gerror.Newf("%s起止号长度必须一致", field)
	}

	startInt, ok := new(big.Int).SetString(start, 10)
	if !ok {
		return nil, gerror.Newf("%s起始号格式错误", field)
	}
	endInt, ok := new(big.Int).SetString(end, 10)
	if !ok {
		return nil, gerror.Newf("%s结束号格式错误", field)
	}
	if startInt.Cmp(endInt) > 0 {
		return nil, gerror.Newf("%s起始号不能大于结束号", field)
	}

	count := new(big.Int).Sub(endInt, startInt)
	count.Add(count, big.NewInt(1))
	if maxRows > 0 && (!count.IsInt64() || count.Int64() > int64(maxRows)) {
		return nil, gerror.Newf("%s号段数量不能超过%d条", field, maxRows)
	}

	size := int(count.Int64())
	rows := make([]string, 0, size)
	current := new(big.Int).Set(startInt)
	one := big.NewInt(1)
	for i := 0; i < size; i++ {
		if err := ctx.Err(); err != nil {
			return nil, err
		}
		rows = append(rows, fmt.Sprintf("%0*s", len(start), current.String()))
		current.Add(current, one)
	}
	return rows, nil
}

func buildAlphaNumericICCIDRange(ctx context.Context, start, end, field string, maxRows int) ([]string, error) {
	if !isAlphaNumeric(start) || !isAlphaNumeric(end) {
		return nil, gerror.Newf("%s起止号只能包含字母和数字", field)
	}
	if len(start) != len(end) {
		return nil, gerror.Newf("%s起止号长度必须一致", field)
	}
	if start == end {
		return []string{start}, nil
	}

	startPrefix, startTail := splitTrailingDigits(start)
	endPrefix, endTail := splitTrailingDigits(end)
	if startTail == "" || endTail == "" {
		return nil, gerror.Newf("%s起止号必须包含可递增的数字尾号", field)
	}
	if startPrefix != endPrefix {
		return nil, gerror.Newf("%s起止号前缀必须一致", field)
	}
	tails, err := buildNumericRange(ctx, startTail, endTail, field, maxRows)
	if err != nil {
		return nil, err
	}

	rows := make([]string, 0, len(tails))
	for _, tail := range tails {
		rows = append(rows, startPrefix+tail)
	}
	return rows, nil
}

func isDigits(value string) bool {
	if value == "" {
		return false
	}
	for _, r := range value {
		if !unicode.IsDigit(r) {
			return false
		}
	}
	return true
}

func isAlphaNumeric(value string) bool {
	if value == "" {
		return false
	}
	for _, r := range value {
		if (r >= '0' && r <= '9') || (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') {
			continue
		}
		return false
	}
	return true
}

func splitTrailingDigits(value string) (prefix, digits string) {
	index := len(value)
	for index > 0 {
		ch := value[index-1]
		if ch < '0' || ch > '9' {
			break
		}
		index--
	}
	return value[:index], value[index:]
}