// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
// All rights reserved.

// expander-time-funcs.go
package text

import (
	"errors"
	"fmt"
	"strconv"
	"strings"
	"time"
)

const func_time_fmt = "__time-fmt"

/*
	If format is empty, the default template will be used.
*/
func TimeFmt(when time.Time, format string) (result string, err error) {
	var sb strings.Builder
	var sep byte = 0
	var filler byte
	var field int

	if len(format) == 0 {
		format = "%Y-%m-%d %H:%M:%S"
	}

	perc := false
	i := 0
	for i < len(format) && err == nil {
		ch := format[i]
		if ch == '%' {
			if perc {
				sb.WriteByte(ch)
				perc = false
			} else {
				perc = true
			}
		} else if perc {
			perc = false
			switch ch {
			case '.', '-', '/', '_', ':':
				if field > 0 {
					err = fmt.Errorf("invalid time specifier format at %d", i)
				} else {
					sep = ch
					j := i + 1
					if j < len(format) && (format[j] == '0' || format[j] == ' ') {
						filler = format[j]
						j++
						start := j
						for j < len(format) && format[j] >= '0' && format[j] <= '9' {
							j++
						}
						field, err = strconv.Atoi(format[start:j])
						i = j - 1
					}
					perc = true
				}
			case '0', ' ':
				filler = ch
				j := i + 1
				for j < len(format) && format[j] >= '0' && format[j] <= '9' {
					j++
				}
				field, err = strconv.Atoi(format[i+1 : j])
				i = j - 1
				perc = true
			default:
				switch ch {
				case 'D':
					if filler != 0 {
						templ := fmt.Sprintf("%%d%c%%%c%dd%c%%%c%dd", sep, filler, field, sep, filler, field)
						_, err = sb.WriteString(fmt.Sprintf(templ, when.Year(), when.Month(), when.Day()))
					} else {
						_, err = sb.WriteString(fmt.Sprintf("%d%c%*d%c%*d", when.Year(), sep, field, when.Month(), sep, field, when.Day()))
					}
				case 'T':
					if filler != 0 {
						templ := fmt.Sprintf("%%%c%dd%c%%%c%dd%c%%%c%dd", filler, field, sep, filler, field, sep, filler, field)
						_, err = sb.WriteString(fmt.Sprintf(templ, when.Hour(), when.Minute(), when.Second()))
					} else {
						_, err = sb.WriteString(fmt.Sprintf("%d%c%*d%c%*d", when.Hour(), sep, field, when.Minute(), sep, field, when.Second()))
					}
				case 'Y':
					_, err = sb.WriteString(fmt.Sprintf("%d", when.Year()))
				case 'm':
					_, err = sb.WriteString(fmt.Sprintf("%02d", when.Month()))
				case 'd':
					_, err = sb.WriteString(fmt.Sprintf("%02d", when.Day()))
				case 'H':
					_, err = sb.WriteString(fmt.Sprintf("%02d", when.Hour()))
				case 'M':
					_, err = sb.WriteString(fmt.Sprintf("%02d", when.Minute()))
				case 'S':
					_, err = sb.WriteString(fmt.Sprintf("%02d", when.Second()))
				default:
					err = fmt.Errorf("unsupported '%c' time specifier at %q/%d", ch, format, i+1)
				}
				filler = 0
				field = 0
				sep = 0
			}
		} else {
			err = sb.WriteByte(ch)
		}
		i++
	}
	if err == nil {
		result = sb.String()
	}
	return
}

func parseDelta(source string) (delta time.Duration) {
	// TODO implementare
	var err error
	if delta, err = time.ParseDuration(strings.TrimSpace(source)); err != nil {
		delta = 0
	}
	return
}

// Format a time value using a template (see TimeFmt()).
// __time-fmt <time> <template>
// <time> can be:
//
//	now
//	yesterday
//	@<timestamp>, e.g. @1707889716
//	@., where '.' will be replaced by hte pipeline value
func ExFuncTimeFmt(ctx ExpanderContext, varValue string, args []string) (result string, err error) {
	var format string
	var whenAsString string
	var when time.Time

	if len(args) == 0 {
		whenAsString = "now"
	} else {
		whenAsString = args[0]
		if len(args) > 1 {
			format = args[1]
		}
	}

	if len(whenAsString) == 0 {
		err = errors.New("time value is empty")
		return
	}

	switch {
	case strings.HasPrefix(whenAsString, "now"):
		delta := parseDelta(whenAsString[3:])
		when = time.Now().Add(delta)
	case strings.HasPrefix(whenAsString, "yesterday"):
		delta := parseDelta(whenAsString[9:])
		when = time.Now().Add(-24 * time.Hour).Add(delta)
	case strings.HasPrefix(whenAsString, "@."):
		var ts int64
		if ts, err = strconv.ParseInt(varValue, 10, 64); err != nil {
			return
		}
		delta := parseDelta(whenAsString[2:])
		when = time.UnixMilli(ts * 1000).Add(delta)
	case strings.HasPrefix(whenAsString, "@"):
		var ts int64
		var i int
		for i = 1; i < len(whenAsString) && whenAsString[i] >= '0' && whenAsString[i] <= '9'; i++ {
		}

		if ts, err = strconv.ParseInt(whenAsString[1:i], 10, 64); err != nil {
			return
		}
		delta := parseDelta(whenAsString[i:])
		when = time.UnixMilli(ts * 1000).Add(delta)
	default:
		err = fmt.Errorf("time specifier '%s' not supported", whenAsString)
		return
	}

	result, err = TimeFmt(when, format)
	return
}

func AddTimeFuncs(ctx ExpanderContext) ExpanderContext {
	ctx.AddFunc(func_time_fmt, ExFuncTimeFmt, 1, 2, "Formats the specified time value (arg1) according with the format specifier (arg2 or default).")
	return ctx
}