/**
 * SQLite cache, v0 (#3) — a rebuildable local mirror of the reconciled backlog.
 * It is an index over the durable truth in gitea, never the source of truth (D4):
 * delete it, resync, lose nothing. This module owns the schema + the pure
 * row<->domain mappers; the actual SQLite handle is injected as a `CacheDriver`,
 * so core stays free of any native driver (better-sqlite3 lives in main; tests
 * use node:sqlite). Facts are never stored — they are re-derived from the label
 * set on read via `extractLabelFacts`, so the mirror can't drift from the label
 * semantics.
 */

import type { GiteaIssue, GiteaMilestoneRef } from '../gitea/types.js'
import { extractLabelFacts } from '../labels/label-schema.js'

/**
 * The injected IO boundary: a thin synchronous SQL executor. Core writes the SQL;
 * the host binds a real driver (better-sqlite3 in the desktop main process,
 * node:sqlite in tests). Kept minimal on purpose — no ORM, no query builder.
 */
export interface CacheDriver {
  /** Run one or more DDL/utility statements (no params, no result). */
  exec(sql: string): void
  /** Execute a single parameterized write. */
  run(sql: string, params?: readonly unknown[]): void
  /** First row of a parameterized query, or undefined. */
  get(sql: string, params?: readonly unknown[]): Record<string, unknown> | undefined
  /** All rows of a parameterized query. */
  all(sql: string, params?: readonly unknown[]): Record<string, unknown>[]
}

/** The cache schema — five tables mirroring gitea's shape. Regenerable; drop and rebuild freely. */
export const CACHE_SCHEMA = `
CREATE TABLE IF NOT EXISTS milestones (
  id       INTEGER PRIMARY KEY,
  title    TEXT NOT NULL,
  state    TEXT,
  due_on   TEXT
);
CREATE TABLE IF NOT EXISTS issues (
  number       INTEGER PRIMARY KEY,
  title        TEXT NOT NULL,
  body         TEXT NOT NULL DEFAULT '',
  state        TEXT NOT NULL,
  labels       TEXT NOT NULL DEFAULT '[]',  -- JSON array of label names; facts re-derived on read
  milestone_id INTEGER,
  assignee     TEXT,
  assignees    TEXT NOT NULL DEFAULT '[]',  -- JSON array of logins
  created_at   TEXT,
  updated_at   TEXT,
  closed_at    TEXT,
  url          TEXT,
  FOREIGN KEY (milestone_id) REFERENCES milestones(id)
);
CREATE TABLE IF NOT EXISTS labels (
  id    INTEGER PRIMARY KEY,
  name  TEXT NOT NULL
);
CREATE TABLE IF NOT EXISTS comments (
  id            INTEGER PRIMARY KEY,
  issue_number  INTEGER NOT NULL,
  author        TEXT,
  body          TEXT NOT NULL DEFAULT '',
  created_at    TEXT
);
CREATE TABLE IF NOT EXISTS issue_events (
  id            INTEGER PRIMARY KEY AUTOINCREMENT,
  issue_number  INTEGER NOT NULL,
  type          TEXT NOT NULL,
  at            TEXT NOT NULL
);
CREATE INDEX IF NOT EXISTS idx_issue_events_number ON issue_events(issue_number);
CREATE INDEX IF NOT EXISTS idx_comments_number ON comments(issue_number);
`

/** Create the schema if absent. Idempotent. */
export function initCache(driver: CacheDriver): void {
  driver.exec(CACHE_SCHEMA)
}

const UPSERT_ISSUE = `
INSERT INTO issues (number, title, body, state, labels, milestone_id, assignee, assignees, created_at, updated_at, closed_at, url)
VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
ON CONFLICT(number) DO UPDATE SET
  title = excluded.title, body = excluded.body, state = excluded.state, labels = excluded.labels,
  milestone_id = excluded.milestone_id, assignee = excluded.assignee, assignees = excluded.assignees,
  created_at = excluded.created_at, updated_at = excluded.updated_at, closed_at = excluded.closed_at, url = excluded.url
`

const UPSERT_MILESTONE = `
INSERT INTO milestones (id, title, state, due_on) VALUES (?, ?, ?, ?)
ON CONFLICT(id) DO UPDATE SET title = excluded.title, state = excluded.state, due_on = excluded.due_on
`

/**
 * Mirror one reconciled issue into the cache (and its milestone, if any). Upsert
 * by `number`, so re-reconciling the same issue updates in place — never duplicates.
 */
export function upsertIssue(driver: CacheDriver, issue: GiteaIssue): void {
  if (issue.milestone) {
    driver.run(UPSERT_MILESTONE, [issue.milestone.id, issue.milestone.title, null, issue.milestone.dueOn])
  }
  driver.run(UPSERT_ISSUE, [
    issue.number,
    issue.title,
    issue.body,
    issue.state,
    JSON.stringify(issue.labels),
    issue.milestone?.id ?? null,
    issue.assignee,
    JSON.stringify(issue.assignees),
    issue.createdAt,
    issue.updatedAt,
    issue.closedAt,
    issue.url,
  ])
}

const READ_ISSUE = `
SELECT i.*, m.title AS m_title, m.due_on AS m_due
FROM issues i LEFT JOIN milestones m ON m.id = i.milestone_id
WHERE i.number = ?
`

function str(v: unknown): string {
  return typeof v === 'string' ? v : ''
}

/**
 * Read one mirrored issue back as a domain object, re-deriving `facts` from the
 * stored label set (so the mirror can't disagree with the label semantics).
 * Returns null when the issue isn't cached.
 */
export function readIssue(driver: CacheDriver, number: number): GiteaIssue | null {
  const row = driver.get(READ_ISSUE, [number])
  if (!row) return null

  const labels = (JSON.parse(str(row.labels) || '[]') as string[]) ?? []
  const assignees = (JSON.parse(str(row.assignees) || '[]') as string[]) ?? []
  const milestone: GiteaMilestoneRef | null =
    row.milestone_id != null
      ? { id: Number(row.milestone_id), title: str(row.m_title), dueOn: (row.m_due as string | null) ?? null }
      : null

  return {
    number: Number(row.number),
    title: str(row.title),
    body: str(row.body),
    state: row.state === 'closed' ? 'closed' : 'open',
    labels,
    facts: extractLabelFacts(labels),
    milestone,
    assignee: (row.assignee as string | null) ?? null,
    assignees,
    createdAt: str(row.created_at),
    updatedAt: str(row.updated_at),
    closedAt: (row.closed_at as string | null) ?? null,
    url: str(row.url),
  }
}