"""
Document object: the single atomic unit threading the whole pipeline.

It carries:
  - the current (possibly masked) text
  - structured segments (code/math/structured) sliced out by masking, kept in
    LIFO order
  - an audit record for every change (stage number, operation, target segment,
    pre/post SHA-256)
  - rollbackable snapshots (pre-stage text snapshots that allow whole-stage undo)

Design principles (paper Section 3.6): integrity, rollbackability,
traceability, byte-level fidelity.
"""

from __future__ import annotations

import enum
import hashlib
import time
from dataclasses import dataclass, field
from typing import Any, Dict, List, Optional


def sha256_text(text: str) -> str:
    """Compute SHA-256 over the UTF-8 encoding of the text (used for integrity checks and auditing)."""
    return hashlib.sha256(text.encode("utf-8")).hexdigest()


class SegmentType(enum.Enum):
    PROSE = "PROSE"
    CODE = "CODE"
    MATH = "MATH"
    STRUCTURED = "STRUCTURED"   # tables / JSON / YAML / TOML / XML / CSV / Markdown


@dataclass
class Segment:
    """A non-prose segment sliced out by masking."""
    seg_type: SegmentType
    placeholder: str            # placeholder that replaces it in the text (includes PUA sentinels)
    original_content: str       # original content (used for LIFO restore / SHA check)
    content_sha256: str         # hash of content at the moment of masking
    repaired_content: Optional[str] = None   # type-specific-repaired content
    repaired_validated: bool = False         # whether pre-restore type-specific validation passed
    nesting_depth: int = 0      # inner-to-outer extraction depth (basis for LIFO restore)
    meta: Dict[str, Any] = field(default_factory=dict)

    @classmethod
    def make(cls, seg_type: SegmentType, placeholder: str, content: str,
             nesting_depth: int = 0, **meta) -> "Segment":
        return cls(
            seg_type=seg_type,
            placeholder=placeholder,
            original_content=content,
            content_sha256=sha256_text(content),
            nesting_depth=nesting_depth,
            meta=meta,
        )


@dataclass
class AuditRecord:
    """A single-change audit record (paper Section 3.6, fourth principle)."""
    stage: int
    operation: str
    target: str                 # target object ("document" / segment placeholder, etc.)
    sha_before: str
    sha_after: str
    note: str = ""
    ts: float = field(default_factory=time.time)


@dataclass
class Document:
    # --- raw + current state ---
    raw_bytes: bytes = b""
    original_text: str = ""     # text after Stage 1 decoding (basis for rollback)
    text: str = ""              # current (possibly masked) text

    # --- upstream metadata (used by the Stage 1 priority cascade) ---
    http_charset: Optional[str] = None        # HTTP Content-Type declaration
    html_meta_charset: Optional[str] = None   # <meta charset>
    has_dom: bool = False                      # upstream retains an HTML DOM
    dom_html: Optional[str] = None             # raw HTML (used by the DOM-priority path)
    source_hint: Optional[str] = None          # e.g. "ocr" / "rfc" / "email"

    # --- masked segments (LIFO) ---
    segments: List[Segment] = field(default_factory=list)

    # --- quality + state ---
    detected_encoding: Optional[str] = None
    quality_passed: Optional[bool] = None
    quality_score: Optional[float] = None
    discarded: bool = False
    discard_reason: str = ""

    # --- audit + rollback ---
    audit: List[AuditRecord] = field(default_factory=list)
    _snapshots: Dict[int, str] = field(default_factory=dict)   # stage -> text snapshot
    meta: Dict[str, Any] = field(default_factory=dict)

    # ---------------------------------------------------------------- #
    def snapshot(self, stage: int) -> None:
        """Save a text snapshot before a stage starts, enabling whole-stage rollback."""
        self._snapshots[stage] = self.text

    def rollback(self, stage: int) -> None:
        if stage in self._snapshots:
            self.text = self._snapshots[stage]

    def record(self, stage: int, operation: str, sha_before: str,
               target: str = "document", note: str = "") -> None:
        self.audit.append(AuditRecord(
            stage=stage, operation=operation, target=target,
            sha_before=sha_before, sha_after=sha256_text(self.text), note=note,
        ))

    def apply(self, stage: int, operation: str, new_text: str,
              target: str = "document", note: str = "") -> None:
        """Apply a text-level change and auto-record it."""
        sha_before = sha256_text(self.text)
        self.text = new_text
        self.record(stage, operation, sha_before, target, note)

    def next_segment_index(self) -> int:
        return len(self.segments)