# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/what-invariants-prevent-recursive-compression-from-collapsing-below-parseable-content.md
# Remnant Warrant:    https://corpusfetch.com/c/what-invariants-prevent-recursive-compression-from-collapsing-below-parseable-content.warrant.json
# Markdown SHA-256:   4eb143d11d9c16123574988bfd91f60b6470ae33ada9c83fa53cb1062ece12e2
# Code AST SHA-256:   23027094329c30f09ce49e2b7a3816964f9599c80f9f29b9e13a1dc4346f1122
# Verified Classes:   CompressionVerdict, CompressionPass, CompressionPolicy, CompressionManifest, RecursiveCompressionCollapseGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

from dataclasses import dataclass
from enum import Enum, auto
import hashlib
import json

class CompressionVerdict(Enum):
    NO_RECURSIVE_COMPRESSION = auto()
    SAFE_TO_COMPRESS = auto()
    FLOOR_BREACH_DETECTED = auto()
    COLLAPSE_IMMINENT = auto()

@dataclass(frozen=True)
class CompressionPass:
    pass_id: str
    pass_number: int
    current_content_hash: str
    current_size_bytes: int
    is_parseable: bool
    schema_valid: bool
    semantic_density_score: float

@dataclass(frozen=True)
class CompressionPolicy:
    min_size_bytes: int
    min_semantic_density: float
    max_pass_number: int

@dataclass(frozen=True)
class CompressionManifest:
    verdict: CompressionVerdict
    directive: str
    manifest_digest: str

class RecursiveCompressionCollapseGuard:
    @staticmethod
    def _hash(data: str) -> str:
        return hashlib.sha256(data.encode("utf-8")).hexdigest()

    @classmethod
    def evaluate_pass(
        cls, cp: CompressionPass, policy: CompressionPolicy
    ) -> CompressionManifest:
        
        # Gate 1: First pass
        if cp.pass_number <= 1:
            digest = cls._hash(json.dumps({
                "pass": cp.pass_id,
                "number": str(cp.pass_number)
            }, sort_keys=True))
            return CompressionManifest(
                verdict=CompressionVerdict.NO_RECURSIVE_COMPRESSION,
                directive=f"PROCEED: Pass {cp.pass_id} is first pass.",
                manifest_digest=digest
            )

        # Gate 2: Max pass number
        if cp.pass_number > policy.max_pass_number:
            return CompressionManifest(
                verdict=CompressionVerdict.COLLAPSE_IMMINENT,
                directive=f"HALT: Pass {cp.pass_number} > {policy.max_pass_number}, use previous.",
                manifest_digest=cls._hash(f"MAX_PASS:{cp.pass_id}")
            )

        # Gate 3: Parseability
        if not cp.is_parseable:
            return CompressionManifest(
                verdict=CompressionVerdict.FLOOR_BREACH_DETECTED,
                directive=f"HALT: Pass {cp.pass_id} unparseable, restore previous.",
                manifest_digest=cls._hash(f"UNPARSEABLE:{cp.pass_id}")
            )

        # Gate 4: Schema validity
        if not cp.schema_valid:
            return CompressionManifest(
                verdict=CompressionVerdict.FLOOR_BREACH_DETECTED,
                directive=f"HALT: Pass {cp.pass_id} schema invalid.",
                manifest_digest=cls._hash(f"SCHEMA:{cp.pass_id}")
            )

        # Gate 5: Size and semantic density
        if cp.current_size_bytes < policy.min_size_bytes:
            return CompressionManifest(
                verdict=CompressionVerdict.COLLAPSE_IMMINENT,
                directive=f"HALT: Size {cp.current_size_bytes} < {policy.min_size_bytes}, next pass will collapse.",
                manifest_digest=cls._hash(f"SMALL:{cp.pass_id}")
            )

        if cp.semantic_density_score < policy.min_semantic_density:
            return CompressionManifest(
                verdict=CompressionVerdict.COLLAPSE_IMMINENT,
                directive=f"HALT: Density {cp.semantic_density_score:.2f} < {policy.min_semantic_density:.2f}.",
                manifest_digest=cls._hash(f"LOW_DENSITY:{cp.pass_id}")
            )

        # Gate 6: Safe
        digest = cls._hash(json.dumps({
            "pass": cp.pass_id,
            "number": str(cp.pass_number),
            "size": str(cp.current_size_bytes),
            "density": f"{cp.semantic_density_score:.3f}",
            "hash": cp.current_content_hash
        }, sort_keys=True))
        
        return CompressionManifest(
            verdict=CompressionVerdict.SAFE_TO_COMPRESS,
            directive=f"PROCEED: Pass {cp.pass_number} safe for further compression.",
            manifest_digest=digest
        )