package org.meshbay.client.drive

import org.json.JSONObject
import java.io.File

/**
 * What this phone has sent of its chosen folders, by document id: the memory
 * of what was sent, never a mirror (PhotoLedger, the same idea for photos). A
 * file deleted on the phone stays on the node; one deleted on the node is not
 * sent again. One line of JSON per send, the last line for an id winning,
 * compacted on load once dead lines outnumber live ones.
 */
class DriveLedger(private val file: File) {

    data class Entry(
        val docId: String,
        val modified: Long,
        val size: Long,
        /** SHA-256 of the bytes sent, hex: a touched file is sent again only if this changed. */
        val sha256: String,
        val dir: String,
        val name: String,
        val sentAt: Long,
    )

    private val entries = HashMap<String, Entry>()
    private var lines = 0

    init { load() }

    val size: Int get() = entries.size

    operator fun get(docId: String): Entry? = entries[docId]

    fun record(entry: Entry) {
        entries[entry.docId] = entry
        file.parentFile?.mkdirs()
        file.appendText(encode(entry) + "\n")
        lines += 1
    }

    private fun load() {
        if (!file.exists()) return
        file.forEachLine { line ->
            if (line.isBlank()) return@forEachLine
            lines += 1
            decode(line)?.let { entries[it.docId] = it }
        }
        if (lines > 2 * entries.size + COMPACT_SLACK) {
            val tmp = File(file.path + ".tmp")
            tmp.writeText(entries.values.joinToString("") { encode(it) + "\n" })
            if (tmp.renameTo(file)) lines = entries.size else tmp.delete()
        }
    }

    companion object {
        private const val COMPACT_SLACK = 64

        fun encode(e: Entry): String = JSONObject()
            .put("id", e.docId).put("m", e.modified).put("s", e.size).put("h", e.sha256)
            .put("d", e.dir).put("n", e.name).put("t", e.sentAt).toString()

        fun decode(line: String): Entry? = try {
            val o = JSONObject(line)
            Entry(o.getString("id"), o.getLong("m"), o.getLong("s"), o.getString("h"),
                  o.getString("d"), o.getString("n"), o.getLong("t"))
        } catch (e: Exception) { null }
    }
}