require "./database"

module Guff
  class DatabaseUpdater
    CURRENT_VERSION = 2_i64

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

    MIGRATION_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 
          )
        }, %{
          INSERT INTO metadata(name, value) VALUES ('version', '1')
        }, %{
          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 ON tags(name)
        }, %{
          CREATE INDEX ON posts(slug)
        }, %{
          UPDATE metadata
             SET value = '2'
           WHERE name = 'version'
        }],
      },
    } 

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

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

    def run
      version = 0_i64
      
      if @db.table_exists?("metadata")
        version = @db.one(SQL[:get_version]) as Int64
      end

      puts "versions: db = %d, code = %d" % [
        version,
        CURRENT_VERSION,
      ]

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

    private def migrate_to(version : Int64)
      id = MIGRATION_IDS[version]
      m = MIGRATIONS[id]
      puts "migrating: %s" % [id]

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

    private def get_version
      @db.one(:get_version) as Int64
    end
  end
end