feat(sqlite): add SQLite writer for converting PostgreSQL schemas

- Implement SQLite DDL writer to convert PostgreSQL schemas to SQLite-compatible SQL statements.
- Include automatic schema flattening, type mapping, auto-increment detection, and function translation.
- Add templates for creating tables, indexes, unique constraints, check constraints, and foreign keys.
- Implement tests for writer functionality and data type mapping.

pkg/writers/sqlite/templates.go

@@ -0,0 +1,174 @@
+package sqlite
+
+import (
+	"bytes"
+	"embed"
+	"fmt"
+	"text/template"
+
+	"git.warky.dev/wdevs/relspecgo/pkg/models"
+	"git.warky.dev/wdevs/relspecgo/pkg/writers"
+)
+
+//go:embed templates/*.tmpl
+var templateFS embed.FS
+
+// TemplateExecutor manages and executes SQLite SQL templates
+type TemplateExecutor struct {
+	templates *template.Template
+	options   *writers.WriterOptions
+}
+
+// NewTemplateExecutor creates a new template executor for SQLite
+func NewTemplateExecutor(opts *writers.WriterOptions) (*TemplateExecutor, error) {
+	// Create template with SQLite-specific functions
+	funcMap := GetTemplateFuncs(opts)
+
+	tmpl, err := template.New("").Funcs(funcMap).ParseFS(templateFS, "templates/*.tmpl")
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse templates: %w", err)
+	}
+
+	return &TemplateExecutor{
+		templates: tmpl,
+		options:   opts,
+	}, nil
+}
+
+// Template data structures
+
+// TableTemplateData contains data for table template
+type TableTemplateData struct {
+	Schema     string
+	Name       string
+	Columns    []*models.Column
+	PrimaryKey *models.Constraint
+}
+
+// IndexTemplateData contains data for index template
+type IndexTemplateData struct {
+	Schema  string
+	Table   string
+	Name    string
+	Columns []string
+}
+
+// ConstraintTemplateData contains data for constraint templates
+type ConstraintTemplateData struct {
+	Schema         string
+	Table          string
+	Name           string
+	Columns        []string
+	Expression     string
+	ForeignSchema  string
+	ForeignTable   string
+	ForeignColumns []string
+	OnDelete       string
+	OnUpdate       string
+}
+
+// Execute methods
+
+// ExecutePragmaForeignKeys executes the pragma foreign keys template
+func (te *TemplateExecutor) ExecutePragmaForeignKeys() (string, error) {
+	var buf bytes.Buffer
+	err := te.templates.ExecuteTemplate(&buf, "pragma_foreign_keys.tmpl", nil)
+	if err != nil {
+		return "", fmt.Errorf("failed to execute pragma_foreign_keys template: %w", err)
+	}
+	return buf.String(), nil
+}
+
+// ExecuteCreateTable executes the create table template
+func (te *TemplateExecutor) ExecuteCreateTable(data TableTemplateData) (string, error) {
+	var buf bytes.Buffer
+	err := te.templates.ExecuteTemplate(&buf, "create_table.tmpl", data)
+	if err != nil {
+		return "", fmt.Errorf("failed to execute create_table template: %w", err)
+	}
+	return buf.String(), nil
+}
+
+// ExecuteCreateIndex executes the create index template
+func (te *TemplateExecutor) ExecuteCreateIndex(data IndexTemplateData) (string, error) {
+	var buf bytes.Buffer
+	err := te.templates.ExecuteTemplate(&buf, "create_index.tmpl", data)
+	if err != nil {
+		return "", fmt.Errorf("failed to execute create_index template: %w", err)
+	}
+	return buf.String(), nil
+}
+
+// ExecuteCreateUniqueConstraint executes the create unique constraint template
+func (te *TemplateExecutor) ExecuteCreateUniqueConstraint(data ConstraintTemplateData) (string, error) {
+	var buf bytes.Buffer
+	err := te.templates.ExecuteTemplate(&buf, "create_unique_constraint.tmpl", data)
+	if err != nil {
+		return "", fmt.Errorf("failed to execute create_unique_constraint template: %w", err)
+	}
+	return buf.String(), nil
+}
+
+// ExecuteCreateCheckConstraint executes the create check constraint template
+func (te *TemplateExecutor) ExecuteCreateCheckConstraint(data ConstraintTemplateData) (string, error) {
+	var buf bytes.Buffer
+	err := te.templates.ExecuteTemplate(&buf, "create_check_constraint.tmpl", data)
+	if err != nil {
+		return "", fmt.Errorf("failed to execute create_check_constraint template: %w", err)
+	}
+	return buf.String(), nil
+}
+
+// ExecuteCreateForeignKey executes the create foreign key template
+func (te *TemplateExecutor) ExecuteCreateForeignKey(data ConstraintTemplateData) (string, error) {
+	var buf bytes.Buffer
+	err := te.templates.ExecuteTemplate(&buf, "create_foreign_key.tmpl", data)
+	if err != nil {
+		return "", fmt.Errorf("failed to execute create_foreign_key template: %w", err)
+	}
+	return buf.String(), nil
+}
+
+// Helper functions to build template data from models
+
+// BuildTableTemplateData builds TableTemplateData from a models.Table
+func BuildTableTemplateData(schema string, table *models.Table) TableTemplateData {
+	// Get sorted columns
+	columns := make([]*models.Column, 0, len(table.Columns))
+	for _, col := range table.Columns {
+		columns = append(columns, col)
+	}
+
+	// Find primary key constraint
+	var pk *models.Constraint
+	for _, constraint := range table.Constraints {
+		if constraint.Type == models.PrimaryKeyConstraint {
+			pk = constraint
+			break
+		}
+	}
+
+	// If no explicit primary key constraint, build one from columns with IsPrimaryKey=true
+	if pk == nil {
+		pkCols := []string{}
+		for _, col := range table.Columns {
+			if col.IsPrimaryKey {
+				pkCols = append(pkCols, col.Name)
+			}
+		}
+		if len(pkCols) > 0 {
+			pk = &models.Constraint{
+				Name:    "pk_" + table.Name,
+				Type:    models.PrimaryKeyConstraint,
+				Columns: pkCols,
+			}
+		}
+	}
+
+	return TableTemplateData{
+		Schema:     schema,
+		Name:       table.Name,
+		Columns:    columns,
+		PrimaryKey: pk,
+	}
+}