# SPDX-License-Identifier: LSL-1.0
# Copyright (c) 2026 Markus Maiwald
# Stewardship: Self Sovereign Society Foundation
#
# This file is part of the Nexus Sovereign Core.
# See legal/LICENSE_SOVEREIGN.md for license terms.

## Nexus Membrane: The Monolith (4MB Key)
##
## Implements the Zero-Friction Encryption per SPEC-503.
## - L0 (Factory): Unprotected 4MB random key
## - L1 (Sovereignty): Password-protected (Argon2id + XChaCha20)

import ../blk

const
  MONOLITH_SECTOR_START* = 2048'u64    # After bootloader
  MONOLITH_SIZE* = 4 * 1024 * 1024     # 4MB = 4,194,304 bytes
  MONOLITH_SECTORS* = MONOLITH_SIZE div 512  # 8192 sectors
  
  # Magic header to detect encrypted vs raw Monolith
  MAGIC_ENCRYPTED* = 0xFFFFFFFF'u32
  MAGIC_RAW* = 0x4D4F4E4F'u32  # "MONO"

type
  MonolithHeader* = object
    magic*: uint32
    version*: uint32
    salt*: array[32, byte]   # Argon2id salt (if encrypted)
    nonce*: array[24, byte]  # XChaCha20-Poly1305 nonce
    reserved*: array[448, byte]

# Static buffer for Monolith (4MB in RAM)
# Note: This is heavy but necessary for single-copy unlock
var monolith_buffer: array[MONOLITH_SIZE, byte]
var monolith_loaded: bool = false

# ION Client for Crypto
import ../ion_client
# TODO: Add XChaCha20-Poly1305 and Argon2id imports when implementing Phase B (lock/unlock)

proc monolith_read*(): bool =
  ## Read 4MB Monolith from disk into RAM buffer
  ## Returns: true on success
  for i in 0'u64 ..< MONOLITH_SECTORS:
    let offset = int(i * 512)
    if blk_read(MONOLITH_SECTOR_START + i, addr monolith_buffer[offset]) < 0:
      return false
  monolith_loaded = true
  return true

proc monolith_get_header*(): ptr MonolithHeader =
  ## Get pointer to the Monolith header (first 512 bytes)
  if not monolith_loaded: return nil
  return cast[ptr MonolithHeader](addr monolith_buffer[0])

proc monolith_is_encrypted*(): bool =
  ## Check if the Monolith is password-protected
  if not monolith_loaded: return false
  let hdr = monolith_get_header()
  return hdr.magic == MAGIC_ENCRYPTED

proc monolith_derive_volume_key*(out_key: ptr array[32, byte]) =
  ## Derive VolumeKey = BLAKE3(Monolith)
  ## This is the master key for SFS encryption
  if not monolith_loaded: return
  
  # Skip header (512 bytes), hash the rest
  let data_start = addr monolith_buffer[512]
  let data_len = uint64(MONOLITH_SIZE - 512)
  out_key[] = crypto_blake3(data_start, data_len)

proc monolith_generate*(dest_sectors: uint64 = MONOLITH_SECTOR_START): bool =
  ## Generate a new random Monolith (called during `nexus forge --image`)
  ## Note: In real impl, we'd use HAL RNG. Here we use a simple PRNG placeholder.
  
  # Initialize header
  var hdr: MonolithHeader
  hdr.magic = MAGIC_RAW
  hdr.version = 1
  
  # Write header
  copyMem(addr monolith_buffer[0], addr hdr, sizeof(MonolithHeader))
  
  # Fill rest with "random" data (placeholder - real impl uses hal_crypto_random)
  # For now, use a simple LCG seeded by a counter
  var seed: uint64 = 0xDEADBEEF12345678'u64
  for i in 512 ..< MONOLITH_SIZE:
    seed = seed * 6364136223846793005'u64 + 1442695040888963407'u64
    monolith_buffer[i] = byte(seed shr 56)
  
  # Write to disk
  for i in 0'u64 ..< MONOLITH_SECTORS:
    let offset = int(i * 512)
    if blk_write(dest_sectors + i, addr monolith_buffer[offset]) < 0:
      return false
  
  discard blk_sync()
  monolith_loaded = true
  return true

# =========================================================
# Phase B: Sovereignty Claim (Future Implementation)
# =========================================================
# proc monolith_lock*(password: string): bool
#   ## Encrypt Monolith with user password
#   ## 1. Derive key = Argon2id(password, random_salt)
#   ## 2. Encrypt Monolith = XChaCha20-Poly1305(raw_data, key)
#   ## 3. Write encrypted Monolith with MAGIC_ENCRYPTED header
#
# proc monolith_unlock*(password: string): bool
#   ## Decrypt Monolith with user password
#   ## 1. Read header, extract salt + nonce
#   ## 2. Derive key = Argon2id(password, salt)
#   ## 3. Decrypt data = XChaCha20-Poly1305.open(ciphertext, key, nonce)
#   ## 4. Verify Poly1305 tag; return false if invalid