from collections.abc import Mapping
from pathlib import PurePosixPath

import yaml
from pydantic import Field
from pydantic import field_validator
from pydantic import model_validator

from .common import SEMVER_RE
from .common import SKILL_ID_RE
from .common import ReferenceEntry
from .common import StrictFrozenModel
from .common import frozen_mapping


class SkillMetadata(StrictFrozenModel):
    """Canonical metadata describing a skill."""

    id: str
    version: str
    tags: tuple[str, ...] = ()
    capabilities: tuple[str, ...] = Field(min_length=1)
    references: Mapping[str, ReferenceEntry] = Field(default_factory=frozen_mapping)

    @field_validator("id")
    @classmethod
    def validate_id(cls, value: str) -> str:
        if not SKILL_ID_RE.fullmatch(value):
            raise ValueError("id must be lowercase kebab-case and start with a letter")
        return value

    @field_validator("version")
    @classmethod
    def validate_version(cls, value: str) -> str:
        if not SEMVER_RE.fullmatch(value):
            raise ValueError("version must be semver")
        return value

    @field_validator("tags")
    @classmethod
    def validate_tags(cls, value: tuple[str, ...]) -> tuple[str, ...]:
        for tag in value:
            if not SKILL_ID_RE.fullmatch(tag):
                raise ValueError(f"invalid tag: {tag}")
        return value

    @field_validator("references", mode="before")
    @classmethod
    def freeze_references(cls, value: Mapping[str, ReferenceEntry] | None) -> Mapping[str, ReferenceEntry]:
        return frozen_mapping(value)

    @field_validator("references")
    @classmethod
    def validate_reference_ids(cls, value: Mapping[str, ReferenceEntry]) -> Mapping[str, ReferenceEntry]:
        for ref_id in value:
            if not SKILL_ID_RE.fullmatch(ref_id):
                raise ValueError(f"invalid reference id: {ref_id}")
        return value


class SkillFrontmatter(StrictFrozenModel):
    """Parsed SKILL frontmatter including standard and personal-mcp fields."""

    name: str = Field(min_length=1, max_length=64)
    description: str = Field(min_length=1, max_length=1024)
    x_personal_mcp: SkillMetadata = Field(alias="x-personal-mcp")

    @field_validator("name")
    @classmethod
    def validate_name(cls, value: str) -> str:
        if not SKILL_ID_RE.fullmatch(value):
            raise ValueError("name must be lowercase kebab-case and start with a letter")
        if "anthropic" in value or "claude" in value:
            raise ValueError("name must not contain reserved words anthropic or claude")
        return value

    @classmethod
    def from_raw_yaml(cls, raw: str | None) -> "SkillFrontmatter":
        if raw is None:
            raise ValueError("missing YAML frontmatter")
        try:
            data = yaml.safe_load(raw)
        except yaml.YAMLError as e:
            raise ValueError(f"invalid YAML in frontmatter: {e}") from e
        if not isinstance(data, dict):
            raise TypeError("frontmatter must parse to an object")
        return cls.model_validate(data)


class StoredSkillReference(StrictFrozenModel):
    """Structured representation of a skill reference markdown document."""

    ref_id: str
    relpath: PurePosixPath
    content: str
    entry: ReferenceEntry


class StoredSkill(StrictFrozenModel):
    """Structured representation of a skill markdown document."""

    skill_id: str
    relpath: PurePosixPath
    content: str
    frontmatter: SkillFrontmatter
    references: Mapping[str, StoredSkillReference] = Field(default_factory=frozen_mapping)

    @field_validator("frontmatter", mode="before")
    @classmethod
    def parse_frontmatter_yaml(cls, value: SkillFrontmatter | str | None) -> SkillFrontmatter:
        if isinstance(value, SkillFrontmatter):
            return value
        return SkillFrontmatter.from_raw_yaml(value)

    @field_validator("references", mode="before")
    @classmethod
    def freeze_references(cls, value: Mapping[str, StoredSkillReference] | None) -> Mapping[str, StoredSkillReference]:
        return frozen_mapping(value)

    @model_validator(mode="after")
    def validate_contract(self) -> "StoredSkill":
        parts = self.relpath.parts
        if len(parts) < 3 or parts[0] != "skills":
            raise ValueError("skill relpath must be under skills/<slug>/")

        skill_dir_name = parts[1]
        if self.frontmatter.name != skill_dir_name:
            raise ValueError("frontmatter name must exactly match skill directory name")
        if self.frontmatter.x_personal_mcp.id != self.frontmatter.name:
            raise ValueError("x-personal-mcp.id must exactly match name")

        expected_capability = f"resource://skills/{self.frontmatter.name}/document"
        if expected_capability not in self.frontmatter.x_personal_mcp.capabilities:
            raise ValueError(f"capabilities must include {expected_capability}")

        if self.skill_id != self.frontmatter.x_personal_mcp.id:
            raise ValueError("skill_id must exactly match x-personal-mcp.id")

        for ref_id, ref in self.references.items():
            if ref.ref_id != ref_id:
                raise ValueError(f"reference key must match ref_id: {ref_id}")
        return self