package ritm.schedule.data

import android.content.Context
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.sync.Mutex
import kotlinx.coroutines.sync.withLock
import kotlinx.coroutines.withContext
import kotlinx.serialization.Serializable
import java.io.File
import java.util.UUID

/**
 * A homework task or a plain note the student pinned to one lesson: the subject,
 * the lesson's date and start time. Tasks can be ticked off; notes just remind.
 */
@Serializable
data class Note(
    val id: String = UUID.randomUUID().toString(),
    /** "docId|group": notes of one group never show up in another. */
    val group: String,
    val subject: String,
    val date: String,
    val start: String,
    val text: String,
    val task: Boolean = true,
    val done: Boolean = false,
    val created: Long = System.currentTimeMillis(),
)

fun groupKey(g: SavedGroup) = "${g.docId}|${g.group}"

/** Notes live only on the device, in one small JSON file. */
class NotesStore(context: Context) {
    private val file = File(context.filesDir, "notes.json")
    private val lock = Mutex()
    private val _notes = MutableStateFlow(read())
    val notes: StateFlow<List<Note>> = _notes

    private fun read(): List<Note> =
        runCatching { json.decodeFromString<List<Note>>(file.readText()) }.getOrDefault(emptyList())

    private suspend fun change(block: (List<Note>) -> List<Note>) = withContext(Dispatchers.IO) {
        lock.withLock {
            val next = block(_notes.value)
            file.writeText(json.encodeToString(next))
            _notes.value = next
        }
    }

    suspend fun save(note: Note) = change { list ->
        if (list.any { it.id == note.id }) list.map { if (it.id == note.id) note else it } else list + note
    }

    suspend fun delete(id: String) = change { list -> list.filterNot { it.id == id } }

    suspend fun toggle(id: String) = change { list -> list.map { if (it.id == id) it.copy(done = !it.done) else it } }
}