package store

import (
	"context"
	"database/sql"
	"fmt"
	"log"
)

const migrateLockKey int64 = 0x706c756d5f6d6967 // "plum_mig"

// migrateUserProfileColumns adds avatar_url and state when missing (existing DBs).
func migrateUserProfileColumns(ctx context.Context, exec execContext) error {
	cols := []string{"avatar_url", "state"}
	for _, col := range cols {
		stmt := fmt.Sprintf(`ALTER TABLE users ADD COLUMN IF NOT EXISTS %s TEXT NOT NULL DEFAULT ''`, col)
		if _, err := exec.ExecContext(ctx, stmt); err != nil {
			return fmt.Errorf("add column %s: %w", col, err)
		}
	}
	return nil
}

// migrateUserEmail adds email and a partial unique index on lower(email).
func migrateUserEmail(ctx context.Context, exec execContext) error {
	if _, err := exec.ExecContext(ctx, `ALTER TABLE users ADD COLUMN IF NOT EXISTS email TEXT NOT NULL DEFAULT ''`); err != nil {
		return fmt.Errorf("add column email: %w", err)
	}
	if _, err := exec.ExecContext(ctx, `
CREATE UNIQUE INDEX IF NOT EXISTS users_email_lower_uidx
  ON users (lower(email))
  WHERE email <> ''`); err != nil {
		return fmt.Errorf("users_email_lower_uidx: %w", err)
	}
	return nil
}

// migratePosts creates the unified post model and snapshots legacy content.
// Legacy tables remain in place until the application cutover is complete.
func migratePosts(ctx context.Context, exec execContext) error {
	steps := []struct {
		name string
		sql  string
	}{
		{"create posts", `
CREATE TABLE IF NOT EXISTS posts (
  id TEXT PRIMARY KEY,
  parent_id TEXT REFERENCES posts(id) ON DELETE CASCADE,
  author_id TEXT NOT NULL REFERENCES users(id),
  title TEXT NOT NULL DEFAULT '',
  body TEXT NOT NULL,
  city TEXT NOT NULL DEFAULT '',
  post_date TEXT NOT NULL DEFAULT '',
  hidden INTEGER NOT NULL DEFAULT 0,
  created_at TEXT NOT NULL,
  updated_at TEXT NOT NULL,
  CHECK (
    (parent_id IS NULL AND title <> '' AND post_date <> '')
    OR
    (parent_id IS NOT NULL AND title = '' AND city = '' AND post_date = '' AND hidden = 0)
  )
)`},
		{"index post replies", `
CREATE INDEX IF NOT EXISTS idx_posts_parent_created
  ON posts(parent_id, created_at, id)`},
		{"index root posts", `
CREATE INDEX IF NOT EXISTS idx_posts_root_date
  ON posts(post_date, hidden)
  WHERE parent_id IS NULL`},
		{"create post votes", `
CREATE TABLE IF NOT EXISTS post_votes (
  user_id TEXT NOT NULL REFERENCES users(id),
  post_id TEXT NOT NULL REFERENCES posts(id) ON DELETE CASCADE,
  value INTEGER NOT NULL CHECK (value IN (-1, 1)),
  PRIMARY KEY (user_id, post_id)
)`},
		{"copy questions", `
INSERT INTO posts (
  id, parent_id, author_id, title, body, city, post_date, hidden, created_at, updated_at
)
SELECT
  id, NULL, author_id, title, body, city, hunt_date, hidden, created_at, created_at
FROM questions
ON CONFLICT (id) DO NOTHING`},
		{"copy answers", `
INSERT INTO posts (
  id, parent_id, author_id, title, body, city, post_date, hidden, created_at, updated_at
)
SELECT
  'answer:' || question_id, question_id, author_id, '', body, '', '', 0, created_at, updated_at
FROM answers
ON CONFLICT (id) DO NOTHING`},
		{"copy votes", `
INSERT INTO post_votes (user_id, post_id, value)
SELECT user_id, question_id, value
FROM votes
ON CONFLICT (user_id, post_id) DO NOTHING`},
	}
	for _, step := range steps {
		if _, err := exec.ExecContext(ctx, step.sql); err != nil {
			return fmt.Errorf("%s: %w", step.name, err)
		}
	}
	return nil
}

type execContext interface {
	ExecContext(ctx context.Context, query string, args ...any) (sql.Result, error)
	QueryContext(ctx context.Context, query string, args ...any) (*sql.Rows, error)
}

// applyMigrations runs versioned migrations under a session-level advisory lock
// held for the entire process (check versions → apply → record).
func applyMigrations(db *sql.DB, schemaSQL string) error {
	ctx := context.Background()
	conn, err := db.Conn(ctx)
	if err != nil {
		return err
	}
	defer conn.Close()

	if _, err := conn.ExecContext(ctx, `SELECT pg_advisory_lock($1)`, migrateLockKey); err != nil {
		return fmt.Errorf("migrate lock: %w", err)
	}
	defer func() {
		if _, unlockErr := conn.ExecContext(ctx, `SELECT pg_advisory_unlock($1)`, migrateLockKey); unlockErr != nil {
			log.Printf("migrate unlock: %v", unlockErr)
		}
	}()

	if _, err := conn.ExecContext(ctx, `
CREATE TABLE IF NOT EXISTS schema_migrations (
  version TEXT PRIMARY KEY,
  applied_at TIMESTAMPTZ NOT NULL DEFAULT now()
)`); err != nil {
		return fmt.Errorf("schema_migrations: %w", err)
	}

	applied, err := appliedVersions(ctx, conn)
	if err != nil {
		return err
	}

	migrations := []struct {
		version string
		run     func(context.Context, execContext) error
	}{
		{"001_schema", func(ctx context.Context, exec execContext) error {
			return applySchema(ctx, exec, schemaSQL)
		}},
		{"002_user_profile_columns", migrateUserProfileColumns},
		{"003_user_email", migrateUserEmail},
		{"004_posts", migratePosts},
	}
	for _, m := range migrations {
		if applied[m.version] {
			continue
		}
		log.Printf("migrate: applying %s", m.version)
		if err := m.run(ctx, conn); err != nil {
			return fmt.Errorf("migrate %s: %w", m.version, err)
		}
		if _, err := conn.ExecContext(ctx, `INSERT INTO schema_migrations (version) VALUES ($1)`, m.version); err != nil {
			return fmt.Errorf("record %s: %w", m.version, err)
		}
	}
	return nil
}

func appliedVersions(ctx context.Context, exec execContext) (map[string]bool, error) {
	rows, err := exec.QueryContext(ctx, `SELECT version FROM schema_migrations`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	out := map[string]bool{}
	for rows.Next() {
		var v string
		if err := rows.Scan(&v); err != nil {
			return nil, err
		}
		out[v] = true
	}
	return out, rows.Err()
}