package psql

import (
	"fmt"
	"strings"
	"time"
)

// commandResult holds the output of a command and whether the session should end.
type commandResult struct {
	output string
	exit   bool
}

// dispatchBackslash handles psql backslash meta-commands.
func dispatchBackslash(cmd, dbName string) commandResult {
	// Normalize: trim spaces after the backslash command word.
	parts := strings.Fields(cmd)
	if len(parts) == 0 {
		return commandResult{output: "Invalid command \\. Try \\? for help."}
	}

	verb := parts[0] // e.g. `\q`, `\dt`, `\d`
	args := parts[1:]

	switch verb {
	case `\q`:
		return commandResult{exit: true}
	case `\dt`:
		return commandResult{output: listTables()}
	case `\d`:
		if len(args) == 0 {
			return commandResult{output: listTables()}
		}
		return commandResult{output: describeTable(args[0])}
	case `\l`:
		return commandResult{output: listDatabases()}
	case `\du`:
		return commandResult{output: listRoles()}
	case `\conninfo`:
		return commandResult{output: connInfo(dbName)}
	case `\?`:
		return commandResult{output: backslashHelp()}
	case `\h`:
		return commandResult{output: sqlHelp()}
	default:
		return commandResult{output: fmt.Sprintf("Invalid command %s. Try \\? for help.", verb)}
	}
}

// dispatchSQL handles SQL statements (already accumulated and semicolon-terminated).
func dispatchSQL(sql, dbName, pgVersion string) commandResult {
	// Strip trailing semicolon and whitespace for matching.
	trimmed := strings.TrimRight(sql, "; \t")
	trimmed = strings.TrimSpace(trimmed)
	upper := strings.ToUpper(trimmed)

	switch {
	case upper == "SELECT VERSION()":
		ver := fmt.Sprintf("PostgreSQL %s on x86_64-pc-linux-gnu, compiled by gcc (GCC) 13.2.0, 64-bit", pgVersion)
		return commandResult{output: formatSingleValue("version", ver)}
	case upper == "SELECT CURRENT_DATABASE()":
		return commandResult{output: formatSingleValue("current_database", dbName)}
	case upper == "SELECT CURRENT_USER":
		return commandResult{output: formatSingleValue("current_user", "postgres")}
	case upper == "SELECT NOW()":
		now := time.Now().UTC().Format("2006-01-02 15:04:05.000000+00")
		return commandResult{output: formatSingleValue("now", now)}
	case upper == "SELECT 1":
		return commandResult{output: formatSingleValue("?column?", "1")}
	case strings.HasPrefix(upper, "INSERT"):
		return commandResult{output: "INSERT 0 1"}
	case strings.HasPrefix(upper, "UPDATE"):
		return commandResult{output: "UPDATE 1"}
	case strings.HasPrefix(upper, "DELETE"):
		return commandResult{output: "DELETE 1"}
	case strings.HasPrefix(upper, "CREATE TABLE"):
		return commandResult{output: "CREATE TABLE"}
	case strings.HasPrefix(upper, "CREATE DATABASE"):
		return commandResult{output: "CREATE DATABASE"}
	case strings.HasPrefix(upper, "DROP TABLE"):
		return commandResult{output: "DROP TABLE"}
	case strings.HasPrefix(upper, "ALTER TABLE"):
		return commandResult{output: "ALTER TABLE"}
	case upper == "BEGIN":
		return commandResult{output: "BEGIN"}
	case upper == "COMMIT":
		return commandResult{output: "COMMIT"}
	case upper == "ROLLBACK":
		return commandResult{output: "ROLLBACK"}
	case upper == "SHOW SERVER_VERSION":
		return commandResult{output: formatSingleValue("server_version", pgVersion)}
	case upper == "SHOW SEARCH_PATH":
		return commandResult{output: formatSingleValue("search_path", "\"$user\", public")}
	case strings.HasPrefix(upper, "SET "):
		return commandResult{output: "SET"}
	default:
		// Extract the first token for the error message.
		firstToken := strings.Fields(trimmed)
		token := trimmed
		if len(firstToken) > 0 {
			token = firstToken[0]
		}
		return commandResult{output: fmt.Sprintf("ERROR:  syntax error at or near \"%s\"\nLINE 1: %s\n        ^", token, trimmed)}
	}
}

// formatSingleValue formats a single-row, single-column psql result.
func formatSingleValue(colName, value string) string {
	width := max(len(colName), len(value))

	var b strings.Builder
	// Header
	fmt.Fprintf(&b, " %-*s \n", width, colName)
	// Separator
	b.WriteString(strings.Repeat("-", width+2))
	b.WriteString("\n")
	// Value
	fmt.Fprintf(&b, " %-*s\n", width, value)
	// Row count
	b.WriteString("(1 row)")
	return b.String()
}