package main

import (
	"fmt"
	"strings"
	"time"
)

type TagChange struct {
	Start string
	Value string
}

type TagChangeList []TagChange
type TagKey string
type TagMap map[TagKey]TagChangeList

func getTagAt(key string, t time.Time) (string, error) {
	// Guaranteed to be in local time
	date := t.Format("2006-01-02")

	tagChanges := tags[TagKey(key)]

	if tagChanges == nil {
		return "", fmt.Errorf("tag key not found: %s", key)
	}

	value := ""

	for _, change := range tagChanges {
		if strings.Compare(change.Start, date) > 0 {
			break
		}
		value = change.Value
	}

	if value == "" {
		return "", fmt.Errorf("tag key '%s' has no value yet", key)
	}

	return value, nil
}