package main

import (
	"bufio"
	"bytes"
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"strings"

	"golang.org/x/tools/imports"
	"golang.org/x/xerrors"
)

type constraintType string

const (
	constraintTypeUnique     constraintType = "unique"
	constraintTypeForeignKey constraintType = "foreign_key"
	constraintTypeCheck      constraintType = "check"
)

func (c constraintType) goType() string {
	switch c {
	case constraintTypeUnique:
		return "UniqueConstraint"
	case constraintTypeForeignKey:
		return "ForeignKeyConstraint"
	case constraintTypeCheck:
		return "CheckConstraint"
	default:
		panic(fmt.Sprintf("unknown constraint type: %s", c))
	}
}

func (c constraintType) goTypeDescriptionPart() string {
	switch c {
	case constraintTypeUnique:
		return "unique"
	case constraintTypeForeignKey:
		return "foreign key"
	case constraintTypeCheck:
		return "check"
	default:
		panic(fmt.Sprintf("unknown constraint type: %s", c))
	}
}

func (c constraintType) goEnumNamePrefix() string {
	switch c {
	case constraintTypeUnique:
		return "Unique"
	case constraintTypeForeignKey:
		return "ForeignKey"
	case constraintTypeCheck:
		return "Check"
	default:
		panic(fmt.Sprintf("unknown constraint type: %s", c))
	}
}

type constraint struct {
	name string
	// comment is typically the full constraint, but for check constraints it's
	// instead the table name.
	comment string
}

// queryToConstraintsFn is a function that takes a query and returns zero or
// more constraints if the query matches the wanted constraint type. If the
// query does not match the wanted constraint type, the function should return
// no constraints.
type queryToConstraintsFn func(query string) ([]constraint, error)

// generateConstraints does the following:
//  1. Read the dump.sql file
//  2. Parse the file into each query
//  3. Pass each query to the constraintFn function
//  4. Generate the enum from the returned constraints
//  5. Write the generated code to the output path
func generateConstraints(dumpPath, outputPath string, outputConstraintType constraintType, fn queryToConstraintsFn) error {
	dump, err := os.Open(dumpPath)
	if err != nil {
		return err
	}
	defer dump.Close()

	var allConstraints []constraint

	dumpScanner := bufio.NewScanner(dump)
	query := ""
	for dumpScanner.Scan() {
		line := strings.TrimSpace(dumpScanner.Text())
		switch {
		case strings.HasPrefix(line, "--"):
		case line == "":
		case strings.HasSuffix(line, ";"):
			query += line
			newConstraints, err := fn(query)
			query = ""
			if err != nil {
				return xerrors.Errorf("process query %q: %w", query, err)
			}
			allConstraints = append(allConstraints, newConstraints...)
		default:
			query += line + " "
		}
	}
	if err = dumpScanner.Err(); err != nil {
		return err
	}

	s := &bytes.Buffer{}

	_, _ = fmt.Fprintf(s, `// Code generated by scripts/dbgen/main.go. DO NOT EDIT.
package database

// %[1]s represents a named %[2]s constraint on a table.
type %[1]s string

// %[1]s enums.
const (
`, outputConstraintType.goType(), outputConstraintType.goTypeDescriptionPart())

	for _, c := range allConstraints {
		constName := outputConstraintType.goEnumNamePrefix() + nameFromSnakeCase(c.name)
		_, _ = fmt.Fprintf(s, "\t%[1]s %[2]s = %[3]q // %[4]s\n", constName, outputConstraintType.goType(), c.name, c.comment)
	}
	_, _ = fmt.Fprint(s, ")\n")

	data, err := imports.Process(outputPath, s.Bytes(), &imports.Options{
		Comments: true,
	})
	if err != nil {
		return err
	}
	return os.WriteFile(outputPath, data, 0o600)
}

// generateUniqueConstraints generates the UniqueConstraint enum.
func generateUniqueConstraints() error {
	localPath, err := localFilePath()
	if err != nil {
		return err
	}
	databasePath := filepath.Join(localPath, "..", "..", "..", "coderd", "database")
	dumpPath := filepath.Join(databasePath, "dump.sql")
	outputPath := filepath.Join(databasePath, "unique_constraint.go")

	fn := func(query string) ([]constraint, error) {
		if strings.Contains(query, "UNIQUE") || strings.Contains(query, "PRIMARY KEY") {
			name := ""
			switch {
			case strings.Contains(query, "ALTER TABLE") && strings.Contains(query, "ADD CONSTRAINT"):
				name = strings.Split(query, " ")[6]
			case strings.Contains(query, "CREATE UNIQUE INDEX"):
				name = strings.Split(query, " ")[3]
			default:
				return nil, xerrors.Errorf("unknown unique constraint format: %s", query)
			}
			return []constraint{
				{
					name:    name,
					comment: query,
				},
			}, nil
		}
		return nil, nil
	}
	return generateConstraints(dumpPath, outputPath, constraintTypeUnique, fn)
}

// generateForeignKeyConstraints generates the ForeignKeyConstraint enum.
func generateForeignKeyConstraints() error {
	localPath, err := localFilePath()
	if err != nil {
		return err
	}
	databasePath := filepath.Join(localPath, "..", "..", "..", "coderd", "database")
	dumpPath := filepath.Join(databasePath, "dump.sql")
	outputPath := filepath.Join(databasePath, "foreign_key_constraint.go")

	fn := func(query string) ([]constraint, error) {
		if strings.Contains(query, "FOREIGN KEY") {
			name := ""
			switch {
			case strings.Contains(query, "ALTER TABLE") && strings.Contains(query, "ADD CONSTRAINT"):
				name = strings.Split(query, " ")[6]
			default:
				return nil, xerrors.Errorf("unknown foreign key constraint format: %s", query)
			}
			return []constraint{
				{
					name:    name,
					comment: query,
				},
			}, nil
		}
		return []constraint{}, nil
	}
	return generateConstraints(dumpPath, outputPath, constraintTypeForeignKey, fn)
}

// generateCheckConstraints generates the CheckConstraint enum.
func generateCheckConstraints() error {
	localPath, err := localFilePath()
	if err != nil {
		return err
	}
	databasePath := filepath.Join(localPath, "..", "..", "..", "coderd", "database")
	dumpPath := filepath.Join(databasePath, "dump.sql")
	outputPath := filepath.Join(databasePath, "check_constraint.go")

	var (
		tableRegex = regexp.MustCompile(`CREATE TABLE\s+([^\s]+)`)
		checkRegex = regexp.MustCompile(`CONSTRAINT\s+([^\s]+)\s+CHECK`)
	)
	fn := func(query string) ([]constraint, error) {
		constraints := []constraint{}

		tableMatches := tableRegex.FindStringSubmatch(query)
		if len(tableMatches) > 0 {
			table := tableMatches[1]

			// Find every CONSTRAINT xxx CHECK occurrence.
			matches := checkRegex.FindAllStringSubmatch(query, -1)
			for _, match := range matches {
				constraints = append(constraints, constraint{
					name:    match[1],
					comment: table,
				})
			}
		}
		return constraints, nil
	}

	return generateConstraints(dumpPath, outputPath, constraintTypeCheck, fn)
}