"""Deterministic path-level three-way merge for plugin supporting files."""

from __future__ import annotations

from dataclasses import dataclass, field
from typing import Any


@dataclass(frozen=True, slots=True)
class SupportingFileDecision:
    path: str
    source: str

    def to_dict(self) -> dict[str, Any]:
        return {"path": self.path, "source": self.source}


@dataclass(frozen=True, slots=True)
class SupportingFileConflict:
    path: str
    reason: str

    def to_dict(self) -> dict[str, Any]:
        return {"path": self.path, "reason": self.reason}


@dataclass(frozen=True, slots=True)
class SupportingFileMergePlan:
    files: dict[str, SupportingFileDecision] = field(default_factory=dict)
    conflicts: list[SupportingFileConflict] = field(default_factory=list)

    def to_dict(self) -> dict[str, Any]:
        return {
            "files": {path: decision.to_dict() for path, decision in sorted(self.files.items())},
            "conflicts": [conflict.to_dict() for conflict in self.conflicts],
        }


def merge_supporting_file_trees(
    *,
    base: dict[str, Any],
    local: dict[str, Any],
    upstream: dict[str, Any],
) -> SupportingFileMergePlan:
    decisions: dict[str, SupportingFileDecision] = {}
    conflicts: list[SupportingFileConflict] = []
    for path in sorted({*base.keys(), *local.keys(), *upstream.keys()} - {"SKILL.md"}):
        b = base.get(path)
        l = local.get(path)
        u = upstream.get(path)
        if l == u and l is not None:
            decisions[path] = SupportingFileDecision(path=path, source="local")
        elif l == b and u is not None:
            decisions[path] = SupportingFileDecision(path=path, source="upstream")
        elif u == b and l is not None:
            decisions[path] = SupportingFileDecision(path=path, source="local")
        elif b is None and l is None and u is not None:
            decisions[path] = SupportingFileDecision(path=path, source="upstream")
        elif b is None and u is None and l is not None:
            decisions[path] = SupportingFileDecision(path=path, source="local")
        elif b is not None and l is None and u is None:
            continue
        else:
            conflicts.append(SupportingFileConflict(path=path, reason="divergent supporting-file change"))
    return SupportingFileMergePlan(files=decisions, conflicts=conflicts)