refactor: Make API simpler

Squashed commit of the following:

commit 8a21e47
Author: Rafael Espinoza <[email protected]>
Date:   Sat Jan 15 17:51:04 2022 -0800

    refactor: Simplify exported API

    There are too many exported identifiers in package godfish. A developer
    interested in making a new driver implementation really just needs to
    know about the Driver interface and not much else. Split up the code so
    that the only exposed functionality may build:

    - a Driver implementation (pkg godfish/drivers/...)
    - a standalone binary (pkg godfish/internal/cmd)

    The material that was in pkg godfish is important to get that working,
    but is probably not necessary for outside consumers. Most of these
    changes involve moving material from pkg godfish to pkg internal,
    adjusting callers, and ensuring that pkg godfish's exported API doesn't
    reference pkg internal.

    Other notable changes are:

    - Change UpdateSchemaMigrations signature. Putting the Direction type in
      a method signature complicates things IMO; in practice, it means up or
      down, so a boolean makes more sense here. The Direction type is useful
      for disambiguating labels for the direction in a migration filename,
      but that's not a concern for a Driver implementation.
    - Remove func CreateSchemaMigrations because it's not used anywhere and
      the functionality is already in a Driver method.
    - Move buildtime versioning info variables to pkg cmd because the
      Version type is now in pkg internal.
    - Move validation for direction label to ensure it's always validated,
      not just in the subcommand.
    - Move pkg info stuff into pkg internal, this simplifies dependencies.

commit 88b0f7d
Author: Rafael Espinoza <[email protected]>
Date:   Fri Jan 7 19:53:33 2022 -0800

    refactor: Clean up Migration constructor

    It's a little weird have syscall side effects in a constructor func, so
    remove the directory check (use of the Dirpath field) from that.

    Also clean up code some more. Static interface checks are deadweight;
    it's better to define a field with an interface type and assign a
    concrete type to that field to check if a type implements an interface.

    Clean up, fix tests

Makefile

@@ -7,11 +7,11 @@ PKG_IMPORT_PATH=github.com/rafaelespinoza/godfish
 
 # inject this metadata when building a binary.
 define LDFLAGS
--X $(PKG_IMPORT_PATH)/internal/version.BranchName=$(shell git rev-parse --abbrev-ref HEAD) \
--X $(PKG_IMPORT_PATH)/internal/version.BuildTime=$(shell date --rfc-3339=seconds --utc | tr ' ' 'T') \
--X $(PKG_IMPORT_PATH)/internal/version.CommitHash=$(shell git rev-parse --short=7 HEAD) \
--X $(PKG_IMPORT_PATH)/internal/version.GoVersion=$(shell $(GO) version | awk '{ print $$3 }') \
--X $(PKG_IMPORT_PATH)/internal/version.Tag=$(shell git describe --tag)
+-X $(PKG_IMPORT_PATH)/internal/cmd.versionBranchName=$(shell git rev-parse --abbrev-ref HEAD) \
+-X $(PKG_IMPORT_PATH)/internal/cmd.versionBuildTime=$(shell date --rfc-3339=seconds --utc | tr ' ' 'T') \
+-X $(PKG_IMPORT_PATH)/internal/cmd.versionCommitHash=$(shell git rev-parse --short=7 HEAD) \
+-X $(PKG_IMPORT_PATH)/internal/cmd.versionGoVersion=$(shell $(GO) version | awk '{ print $$3 }') \
+-X $(PKG_IMPORT_PATH)/internal/cmd.versionTag=$(shell git describe --tag)
 endef
 
 test:
@@ -23,31 +23,31 @@ clean:
 cassandra:
 	$(GO) build -o $(BIN) -v \
 		-ldflags "$(LDFLAGS) \
-		-X $(PKG_IMPORT_PATH)/internal/version.Driver=cassandra" \
+		-X $(PKG_IMPORT_PATH)/internal/cmd.versionDriver=cassandra" \
 		./drivers/cassandra/godfish
 cassandra-test:
 	$(GO) test $(ARGS) ./drivers/cassandra
 
 postgres:
 	$(GO) build -o $(BIN) -v \
 		-ldflags "$(LDFLAGS) \
-		-X $(PKG_IMPORT_PATH)/internal/version.Driver=postgres" \
+		-X $(PKG_IMPORT_PATH)/internal/cmd.versionDriver=postgres" \
 		./drivers/postgres/godfish
 postgres-test:
 	$(GO) test $(ARGS) ./drivers/postgres
 
 mysql:
 	$(GO) build -o $(BIN) -v \
 		-ldflags "$(LDFLAGS) \
-		-X $(PKG_IMPORT_PATH)/internal/version.Driver=mysql" \
+		-X $(PKG_IMPORT_PATH)/internal/cmd.versionDriver=mysql" \
 		./drivers/mysql/godfish
 mysql-test:
 	$(GO) test $(ARGS) ./drivers/mysql
 
 sqlite3:
 	CGO_ENABLED=1 $(GO) build -o $(BIN) -v \
 		-ldflags "$(LDFLAGS) \
-		-X $(PKG_IMPORT_PATH)/internal/version.Driver=sqlite3" \
+		-X $(PKG_IMPORT_PATH)/internal/cmd.versionDriver=sqlite3" \
 		./drivers/sqlite3/godfish
 sqlite3-test:
 	$(GO) test $(ARGS) ./drivers/sqlite3

driver.go

@@ -26,7 +26,7 @@ type Driver interface {
 	// UpdateSchemaMigrations records a timestamped version of a migration that
 	// has been successfully applied by adding a new row to the schema
 	// migrations table.
-	UpdateSchemaMigrations(dir Direction, version string) error
+	UpdateSchemaMigrations(forward bool, version string) error
 }
 
 // AppliedVersions represents an iterative list of migrations that have been run

drivers/cassandra/cassandra.go

@@ -94,9 +94,9 @@ func (d *driver) AppliedVersions() (out godfish.AppliedVersions, err error) {
 	return
 }
 
-func (d *driver) UpdateSchemaMigrations(dir godfish.Direction, version string) (err error) {
+func (d *driver) UpdateSchemaMigrations(forward bool, version string) (err error) {
 	conn := d.connection
-	if dir == godfish.DirForward {
+	if forward {
 		err = conn.Query(`
 			INSERT INTO schema_migrations (migration_id)
 			VALUES (?)`,

drivers/mysql/mysql.go

@@ -92,9 +92,9 @@ func (d *driver) AppliedVersions() (out godfish.AppliedVersions, err error) {
 	return
 }
 
-func (d *driver) UpdateSchemaMigrations(dir godfish.Direction, version string) (err error) {
+func (d *driver) UpdateSchemaMigrations(forward bool, version string) (err error) {
 	conn := d.connection
-	if dir == godfish.DirForward {
+	if forward {
 		_, err = conn.Exec(`
 			INSERT INTO schema_migrations (migration_id)
 			VALUES (?)`,

drivers/postgres/postgres.go

@@ -65,9 +65,9 @@ func (d *driver) AppliedVersions() (out godfish.AppliedVersions, err error) {
 	return
 }
 
-func (d *driver) UpdateSchemaMigrations(dir godfish.Direction, version string) (err error) {
+func (d *driver) UpdateSchemaMigrations(forward bool, version string) (err error) {
 	conn := d.connection
-	if dir == godfish.DirForward {
+	if forward {
 		_, err = conn.Exec(`
 			INSERT INTO schema_migrations (migration_id)
 			VALUES ($1)

drivers/sqlite3/sqlite3.go

@@ -67,9 +67,9 @@ func (d *driver) AppliedVersions() (out godfish.AppliedVersions, err error) {
 	return
 }
 
-func (d *driver) UpdateSchemaMigrations(dir godfish.Direction, version string) (err error) {
+func (d *driver) UpdateSchemaMigrations(forward bool, version string) (err error) {
 	conn := d.connection
-	if dir == godfish.DirForward {
+	if forward {
 		_, err = conn.Exec(`
 			INSERT INTO schema_migrations (migration_id)
 			VALUES ($1)`,