// Package decode turns a raw Compass lesson label into plain English using the
// editable codes map (AGENTS.md §4 FR-17). An unknown code renders as the raw
// code, never blank.
package decode

import (
	"strings"
	"unicode"

	"gitea.lab.audasmedia.com.au/sam/compass_teams_nhs/internal/period"
	"gitea.lab.audasmedia.com.au/sam/compass_teams_nhs/internal/store"
)

// Period renders one lesson title as plain English, for example
//
//	"1 - 7SCF - H14LAB - KNI" -> "Period 1 — Year 7 Science — Room H14LAB — Mr KNI"
//
// A title that is not a lesson (a concert, an excursion) is returned unchanged.
// A code that is not in the map falls back to the raw code (FR-17).
func Period(title string, m store.CodeMap) string {
	slot, subject, room, teacher, ok := period.Split(strings.TrimSpace(title))
	if !ok {
		return strings.TrimSpace(title)
	}

	parts := make([]string, 0, 4)
	parts = append(parts, periodName(slot, m))
	if subject != "" {
		parts = append(parts, codeName(m, store.CodeSubject, subject))
	}
	if room != "" {
		parts = append(parts, codeName(m, store.CodeRoom, room))
	}
	if teacher != "" {
		parts = append(parts, teacherName(m, teacher))
	}
	return strings.Join(parts, " — ")
}

// teacherName decodes a teacher field. Compass sometimes carries several codes
// in the one field ("GT SMH"), so every token is decoded and joined.
func teacherName(m store.CodeMap, field string) string {
	tokens := strings.Fields(field)
	if len(tokens) <= 1 {
		return codeName(m, store.CodeTeacher, field)
	}
	out := make([]string, 0, len(tokens))
	for _, tok := range tokens {
		out = append(out, codeName(m, store.CodeTeacher, tok))
	}
	return strings.Join(out, " / ")
}

// periodName renders the period slot: a word label such as "C" uses the map
// ("Connect"), a number becomes "Period 3", and anything unknown stays raw.
func periodName(slot string, m store.CodeMap) string {
	if name := strings.TrimSpace(m.Lookup(store.CodePeriod, slot)); name != "" {
		return name
	}
	if isNumber(slot) {
		return "Period " + slot
	}
	return slot
}

// codeName returns the mapped name, or the raw code when it is not mapped.
func codeName(m store.CodeMap, kind, code string) string {
	if name := strings.TrimSpace(m.Lookup(kind, code)); name != "" {
		return name
	}
	return code
}

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