package skills

import (
	"context"
	"crypto/rand"
	"database/sql"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"log/slog"
	"strings"
	"time"

	"git.yeij.top/AskaEth/Cyrene_v2/pkg/plugins/sdk"
)

// Store persists skill definitions in SQLite (the skills table). It is safe for
// concurrent use — the underlying *sql.DB serializes writes — and every query is
// parameterized, so values are never interpolated into SQL.
type Store struct {
	db  *sql.DB
	log *slog.Logger
}

// createSkillsTable creates the skills schema. id is an opaque primary key;
// name is the stable, unique skill identifier used for Upsert/Get/Delete
// lookups. The desc column is double-quoted because DESC is a SQL keyword in
// ordering context.
const createSkillsTable = `
CREATE TABLE IF NOT EXISTS skills (
    id              TEXT PRIMARY KEY,
    name            TEXT NOT NULL,
    "desc"          TEXT NOT NULL DEFAULT '',
    prompt          TEXT NOT NULL DEFAULT '',
    steps_json      TEXT NOT NULL DEFAULT '[]',
    refs_json       TEXT NOT NULL DEFAULT '[]',
    guardrails_json TEXT NOT NULL DEFAULT '[]',
    created_at      TEXT NOT NULL,
    updated_at      TEXT NOT NULL
);
CREATE UNIQUE INDEX IF NOT EXISTS idx_skills_name ON skills (name);
`

// upsertSkillSQL inserts a skill, updating the existing row when the name
// already exists; created_at is preserved across an update.
const upsertSkillSQL = `
INSERT INTO skills (id, name, "desc", prompt, steps_json, refs_json, guardrails_json, created_at, updated_at)
VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)
ON CONFLICT(name) DO UPDATE SET
    "desc" = excluded."desc",
    prompt = excluded.prompt,
    steps_json = excluded.steps_json,
    refs_json = excluded.refs_json,
    guardrails_json = excluded.guardrails_json,
    updated_at = excluded.updated_at
`

const (
	getSkillSQL    = `SELECT name, "desc", prompt, steps_json, refs_json, guardrails_json FROM skills WHERE name = ?`
	listSkillsSQL  = `SELECT name, "desc", prompt, steps_json, refs_json, guardrails_json FROM skills ORDER BY name`
	deleteSkillSQL = `DELETE FROM skills WHERE name = ?`
)

// idByteLen is the size in bytes of the random skill id (128-bit).
const idByteLen = 16

// NewStore builds a Store, creating the skills table if needed. It returns
// ErrNilDB when db is nil. ctx is used for the schema creation statement.
func NewStore(ctx context.Context, db *sql.DB, log *slog.Logger) (*Store, error) {
	if db == nil {
		return nil, fmt.Errorf("skills: store: %w", ErrNilDB)
	}
	s := &Store{db: db, log: sourcedLog(log)}
	if _, err := db.ExecContext(ctx, createSkillsTable); err != nil {
		return nil, fmt.Errorf("skills: store: create skills table: %w", err)
	}
	s.log.Info("skills table ready")
	return s, nil
}

// Upsert stores skill, inserting a new row or updating the existing row that
// shares its name. It returns ErrInvalidSkill when skill is nil or has a blank
// name.
func (s *Store) Upsert(ctx context.Context, skill sdk.Skill) error {
	if skill == nil || strings.TrimSpace(skill.Name()) == "" {
		return fmt.Errorf("skills: store: upsert: %w", ErrInvalidSkill)
	}
	name := skill.Name()
	stepsJSON, err := marshalJSON(skill.Steps())
	if err != nil {
		return fmt.Errorf("skills: store: upsert %q: steps: %w", name, err)
	}
	refsJSON, err := marshalJSON(skill.Refs())
	if err != nil {
		return fmt.Errorf("skills: store: upsert %q: refs: %w", name, err)
	}
	guardrailsJSON, err := marshalJSON(skill.Guardrails())
	if err != nil {
		return fmt.Errorf("skills: store: upsert %q: guardrails: %w", name, err)
	}
	now := time.Now().UTC().Format(time.RFC3339Nano)
	if _, err := s.db.ExecContext(ctx, upsertSkillSQL,
		newID(), name, skill.Description(), skill.Prompt(),
		stepsJSON, refsJSON, guardrailsJSON, now, now,
	); err != nil {
		return fmt.Errorf("skills: store: upsert %q: %w", name, err)
	}
	s.log.Info("skill upserted", "skill", name)
	return nil
}

// Get returns the skill registered under name, or ErrNotFound when absent.
func (s *Store) Get(ctx context.Context, name string) (*Skill, error) {
	row := s.db.QueryRowContext(ctx, getSkillSQL, name)
	skill, err := scanSkill(row, name)
	if err != nil {
		return nil, err
	}
	return skill, nil
}

// List returns every stored skill, ordered by name.
func (s *Store) List(ctx context.Context) ([]*Skill, error) {
	rows, err := s.db.QueryContext(ctx, listSkillsSQL)
	if err != nil {
		return nil, fmt.Errorf("skills: store: list: %w", err)
	}
	defer rows.Close()

	out := make([]*Skill, 0)
	for rows.Next() {
		skill, err := scanSkill(rows, "")
		if err != nil {
			return nil, err
		}
		out = append(out, skill)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("skills: store: list: iterate: %w", err)
	}
	return out, nil
}

// Delete removes the skill named name. It returns ErrNotFound when no such skill
// exists.
func (s *Store) Delete(ctx context.Context, name string) error {
	res, err := s.db.ExecContext(ctx, deleteSkillSQL, name)
	if err != nil {
		return fmt.Errorf("skills: store: delete %q: %w", name, err)
	}
	n, err := res.RowsAffected()
	if err != nil {
		return fmt.Errorf("skills: store: delete %q: rows affected: %w", name, err)
	}
	if n == 0 {
		return fmt.Errorf("skills: store: delete %q: %w", name, ErrNotFound)
	}
	s.log.Info("skill deleted", "skill", name)
	return nil
}

// rowScanner is the subset of *sql.Row and *sql.Rows that scanSkill needs.
type rowScanner interface{ Scan(dest ...any) error }

// scanSkill reads one skills row and builds a *Skill. key is the lookup name
// used only in error messages.
func scanSkill(sc rowScanner, key string) (*Skill, error) {
	var name, desc, prompt, stepsJSON, refsJSON, guardrailsJSON string
	if err := sc.Scan(&name, &desc, &prompt, &stepsJSON, &refsJSON, &guardrailsJSON); err != nil {
		if errors.Is(err, sql.ErrNoRows) {
			return nil, fmt.Errorf("skills: store: get %q: %w", key, ErrNotFound)
		}
		return nil, fmt.Errorf("skills: store: scan skill: %w", err)
	}
	steps, err := unmarshalSteps(stepsJSON)
	if err != nil {
		return nil, fmt.Errorf("skills: store: skill %q: steps: %w", name, err)
	}
	refs, err := unmarshalRefs(refsJSON)
	if err != nil {
		return nil, fmt.Errorf("skills: store: skill %q: refs: %w", name, err)
	}
	guardrails, err := unmarshalGuardrails(guardrailsJSON)
	if err != nil {
		return nil, fmt.Errorf("skills: store: skill %q: guardrails: %w", name, err)
	}
	skill, err := New(name, desc, prompt, steps, refs, guardrails)
	if err != nil {
		return nil, fmt.Errorf("skills: store: skill %q: %w", name, err)
	}
	return skill, nil
}

func marshalJSON(v any) (string, error) {
	b, err := json.Marshal(v)
	if err != nil {
		return "", err
	}
	return string(b), nil
}

func unmarshalSteps(s string) ([]sdk.Step, error) {
	var out []sdk.Step
	if err := json.Unmarshal([]byte(s), &out); err != nil {
		return nil, err
	}
	return out, nil
}

func unmarshalRefs(s string) ([]sdk.Ref, error) {
	var out []sdk.Ref
	if err := json.Unmarshal([]byte(s), &out); err != nil {
		return nil, err
	}
	return out, nil
}

func unmarshalGuardrails(s string) ([]sdk.Guardrail, error) {
	var out []sdk.Guardrail
	if err := json.Unmarshal([]byte(s), &out); err != nil {
		return nil, err
	}
	return out, nil
}

// newID returns a random 128-bit hex identifier for a skill row.
func newID() string {
	var b [idByteLen]byte
	if _, err := rand.Read(b[:]); err != nil {
		// crypto/rand is effectively infallible; fall back to a nanosecond
		// timestamp so the store never blocks on a missing identifier.
		return fmt.Sprintf("%d", time.Now().UnixNano())
	}
	return hex.EncodeToString(b[:])
}