db-migrate/db_migrate.nim

## DB Migrate
## ==========
##
## Simple tool to manage database migrations.

import json, times, os, strutils, docopt, db_postgres, db_mysql, db_sqlite

type DbMigrateConfig* = tuple[ driver, sqlDir, connectionString: string ]

proc loadConfig*(filename: string): DbMigrateConfig =
  ## Load DbMigrateConfig from a file. 
  let cfg = json.parseFile(filename)

  return (
    driver: if cfg.hasKey("driver"): cfg["driver"].getStr else: "postres",
    sqlDir: if cfg.hasKey("sqlDir"): cfg["sqlDir"].getStr else: "migrations",
    connectionString: cfg["connectionString"].getStr)

proc getDbConnection*(config: DbMigrateConfig): DbConn =
  case config.driver
  of "postgres": discard
  of "sqlite": discard
  of "mysql": discard
  else: dbError "Unsupported database driver: " & config.driver

proc createMigration*(config: DbMigrateConfig, migrationName: string): seq[string] =
  ## Create a new set of database migration files.
  let timestamp = getTime().getLocalTime().format("yyyyMMddHHmmss")
  let filenamePrefix =  timestamp & "-" & migrationName

  let upFilename = joinPath(config.sqlDir, filenamePrefix & "-up.sql")
  let downFilename = joinPath(config.sqlDir, filenamePrefix & "-down.sql")

  let scriptDesc = migrationName & " (" & timestamp & ")"

  let upFile = open(upFilename, fmWrite)
  let downFile = open(downFilename, fmWrite)

  upFile.writeLine "-- UP script for " & scriptDesc
  downFile.writeLine "-- DOWN script for " & scriptDesc

  upFile.close()
  downFile.close()

  return @[upFilename, downFilename]

when isMainModule:
  let doc = """
Usage:
  db-migrate [options] create <migration-name>
  db-migrate [options] up [<count>]
  db-migrate [options] down [<count>]
  db-migrate [options] init <schema-name>

Options:
  -c --config <config-file>   Use the given configuration file (defaults to 
                              "database.json").
"""

  # Parse arguments
  let args = docopt(doc, version = "db-migrate 0.1.0")

  let exitErr = proc(msg: string): void = 
    stderr.writeLine("db_migrate: " & msg)
    quit(QuitFailure)

  # Load configuration file
  let configFilename =
    if args["--config"]: $args["--config"]
    else: "database.json"

  var config: DbMigrateConfig
  try:
    config = loadConfig(configFilename)
  except IOError:
    exitErr "Cannot open config file: " & configFilename
  except:
    exitErr "Error parsing config file: " & configFilename & "\L\t" & getCurrentExceptionMsg()

  # Check for migrations directory
  if not existsDir config.sqlDir:
    try:
      echo "SQL directory '" & config.sqlDir &
      "' does not exist and will be created."
      createDir config.sqlDir
    except IOError:
      exitErr "Unable to create directory: " & config.sqlDir & ":\L\T" & getCurrentExceptionMsg()

  # Execute commands
  if args["create"]:
    try:
      let filesCreated = createMigration(config, $args["<migration-name>"])
      echo "Created new migration files:"
      for filename in filesCreated: echo "\t" & filename
    except IOError:
      exitErr "Unable to create migration scripts: " & getCurrentExceptionMsg()

  elif args["up"]: discard
    # Query the database to find out what migrations have been run.

    # Diff with the list of migrations that we have in our migrations
    # directory.

    # Make sure we have no gaps (database is in an unknown state)

    # Find the subset of migrations we need to apply (consider the count
    # parameter if passed)

    # If none: "Up to date."

    # Begin a transaction.

      # Apply each of the migrations.
      # If any fail, roll back the transaction
      # Otherwise report success

  elif args["down"]: discard
    # Query the database to find out what migrations have been run.

    # Find how many we need to go down (default to 1 if the count parameter was
    # not passed.

    # Begin transaction

      # Apply each down script
      # If any fail, roll back the transaction
      # Otherwise report success

  elif args["init"]: discard