require "./database"

module Guff
  class DatabaseUpdater
    CURRENT_VERSION = 2_i64

    SQL = {
      get_version: "
        SELECT value
          FROM metadata
         WHERE name = 'version'
      ",

      set_version_delete: "
        DELETE FROM metadata WHERE name = 'version'
      ",

      set_version_insert: "
        INSERT INTO metadata(name, value) VALUES ('version', ?)
      ",
    }

    IDS = %w{
      0-null
      1-create-tables
      2-create-indices
    }

    MIGRATIONS = {
      "1-create-tables": {
        backup: false,

        sql: [%{
          CREATE TABLE metadata (
            name    TEXT PRIMARY KEY,
            value   TEXT NOT NULL
          )
        }, %{
          CREATE TABLE tags (
            tag_id      INTEGER PRIMARY KEY,
            name        TEXT UNIQUE NOT NULL
          )
        }, %{
          CREATE TABLE posts (
            -- unique id
            post_id     INTEGER PRIMARY KEY,

            -- false if this post has been deleted
            is_active   BOOLEAN NOT NULL
                        DEFAULT true,

            -- when this post was created
            created_at  TIMESTAMP WITH TIME ZONE
                        NOT NULL DEFAULT CURRENT_TIMESTAMP,

            -- when this post was posted
            -- (that is, the draft status was removed)
            posted_at   TIMESTAMP WITH TIME ZONE
                        NOT NULL DEFAULT CURRENT_TIMESTAMP,

            -- title of post
            name        TEXT NOT NULL
                        CHECK (LENGTH(name) > 0),

            -- slug of post (url fragment)
            slug        TEXT NOT NULL
                        CHECK (LENGTH(slug) > 0),

            -- body (raw text before filters)
            body        TEXT NOT NULL
                        CHECK (LENGTH(body) > 0),

            -- generated html (after filters)
            html        TEXT NOT NULL
                        CHECK (LENGTH(html) > 0)
          )
        }],
      },

      "2-create-indices": {
        backup: false,

        sql: [%{
          CREATE INDEX in_tags_name ON tags(name)
        }, %{
          CREATE INDEX in_posts_slug ON posts(slug)
        }],
      },
    }

    def self.run(path, config)
      new(path, config).run
    end

    def initialize(
      @path   : String,
      @config : Config
    )
      @db = Database.new(@path)
    end

    def run
      # get version from database
      version = @db.table_exists?("metadata") ? get_version : 0_i32

      if version < CURRENT_VERSION
        puts "starting db migration (db = %d, app = %d)" % [
          version,
          CURRENT_VERSION,
        ]

        (version + 1).upto(CURRENT_VERSION) do |v|
          migrate_to(v)
        end
      end
    end

    private def migrate_to(version)
      # map version number to migration id
      id = IDS[version]
      m = MIGRATIONS[id]
      puts "  * migration: %s" % [id]

      @db.transaction do
        # exec queries
        (m[:sql] as Array(String)).each do |sql|
          @db.query(sql)
        end

        # update database version
        set_version(version)
      end
    end

    private def get_version
      (@db.one(SQL[:get_version]) || 0).to_i
    end

    private def set_version(version)
      @db.query(SQL[:set_version_delete])
      @db.query(SQL[:set_version_insert], [version.to_s])
    end
  end
end