module main

import os
import time
import term
import flag

const scan_timeout_s = get_scan_timeout_seconds()

const max_v_cycles = 1000

const scan_frequency_hz = 4

const scan_period_ms = 1000 / scan_frequency_hz

const max_scan_cycles = scan_timeout_s * scan_frequency_hz

fn get_scan_timeout_seconds() int {
    env_vw_timeout := os.getenv('VWATCH_TIMEOUT').int()
    if env_vw_timeout == 0 {
        $if gcboehm ? {
            return 35000000 // over 1 year
        } $else {
            return 5 * 60
        }
    }
    return env_vw_timeout
}

//
// Implements `v watch file.v` , `v watch run file.v` etc.
// With this command, V will collect all .v files that are needed for the
// compilation, then it will enter an infinite loop, monitoring them for
// changes.
//
// When a change is detected, it will stop the current process, if it is
// still running, then rerun/recompile/etc.
//
// In effect, this makes it easy to have an editor session and a separate
// terminal, running just `v watch run file.v`, and you will see your
// changes right after you save your .v file in your editor.
//
//
//    Since -gc boehm is not available on all platforms yet,
// and this program leaks ~8MB/minute without it, the implementation here
// is done similarly to vfmt in 2 modes, in the same executable:
//
//   a) A parent/manager process that only manages a single worker
//   process. The parent process does mostly nothing except restarting
//   workers, thus it does not leak much.
//
//   b) A worker process, doing the actual monitoring/polling.
//    Note: *workers are started with the --vwatchworker option*
//
//    Worker processes will run for a limited number of iterations, then
// they will do exit(255), and then the parent will start a new worker.
// Exiting by any other code will cause the parent to also exit with the
// same error code. This limits the potential leak that a worker process
// can do, even without using the garbage collection mode.
//

struct VFileStat {
    path  string
    mtime i64
}

[unsafe]
fn (mut vfs VFileStat) free() {
    unsafe { vfs.path.free() }
}

enum RerunCommand {
    restart
    quit
}

struct Context {
mut:
    pid             int  // the pid of the current process; useful while debugging manager/worker interactions
    is_worker       bool // true in the workers, false in the manager process
    check_period_ms int = scan_period_ms
    vexe            string
    affected_paths  []string
    vfiles          []VFileStat
    opts            []string
    rerun_channel   chan RerunCommand
    child_process   &os.Process = unsafe { nil }
    is_exiting      bool     // set by SIGINT/Ctrl-C
    v_cycles        int      // how many times the worker has restarted the V compiler
    scan_cycles     int      // how many times the worker has scanned for source file changes
    clear_terminal  bool     // whether to clear the terminal before each re-run
    keep_running    bool     // when true, re-run the program automatically if it exits on its own. Useful for gg apps.
    silent          bool     // when true, watch will not print a timestamp line before each re-run
    add_files       []string // path to additional files that have to be watched for changes
    ignore_exts     []string // extensions of files that will be ignored, even if they change (useful for sqlite.db files for example)
    cmd_before_run  string   // a command to run before each re-run
    cmd_after_run   string   // a command to run after each re-run
    only_watch      []string // If not empty, *all* files that trigger updates, should match *at least one* of these s.match_glob() patterns. This is also triggered for vweb apps, to monitor for just *.v,*.js,*.css,*.html in vweb projects.
}

[if debug_vwatch ?]
fn (mut context Context) elog(msg string) {
    eprintln('> vwatch ${context.pid}, ${msg}')
}

fn (context &Context) str() string {
    return 'Context{ pid: ${context.pid}, is_worker: ${context.is_worker}, check_period_ms: ${context.check_period_ms}, vexe: ${context.vexe}, opts: ${context.opts}, is_exiting: ${context.is_exiting}, vfiles: ${context.vfiles}'
}

fn (mut context Context) is_ext_ignored(pf string, pf_ext string) bool {
    for ipattern in context.ignore_exts {
        if pf_ext.match_glob(ipattern) {
            return true
        }
    }
    if pf_ext in ['', '.so', '.a'] {
        // on unix, the executables saved by compilers, usually do not have extensions at all, and shared libs are .so
        return true
    }
    if pf_ext in ['.exe', '.dll', '.def'] {
        // on windows, files with these extensions will be generated by the compiler
        return true
    }
    // ignore common backup files saved by editors like emacs/jed/vim:
    if pf_ext == '.bak' {
        return true
    }
    if pf.starts_with('.#') {
        return true
    }
    if pf.ends_with('~') {
        return true
    }
    return false
}

fn (mut context Context) get_stats_for_affected_vfiles() []VFileStat {
    if context.affected_paths.len == 0 {
        mut apaths := map[string]bool{}
        // The next command will make V parse the program, and print all .v files,
        // needed for its compilation, without actually compiling it.
        copts := context.opts.join(' ')
        cmd := '"${context.vexe}" -silent -print-watched-files ${copts}'
        // context.elog('> cmd: ${cmd}')
        mut paths := []string{}
        if context.add_files.len > 0 && context.add_files[0] != '' {
            paths << context.add_files
        }
        vfiles := os.execute(cmd)
        if vfiles.exit_code == 0 {
            paths_trimmed := vfiles.output.trim_space()
            reported_used_files := paths_trimmed.split_any('\n')
            $if trace_reported_used_files ? {
                context.elog('reported_used_files: ${reported_used_files}')
            }
            paths << reported_used_files
        }
        mut is_vweb_found := false
        for vf in paths {
            apaths[os.real_path(os.dir(vf))] = true
            if vf.contains('vweb.v') {
                is_vweb_found = true
            }
        }

        if is_vweb_found {
            if !os.args.any(it.starts_with('--only-watch')) {
                // vweb is often used with SQLite .db or .sqlite3 files right next to the executable/source,
                // that are updated by the vweb app, causing a restart of the app, which in turn causes the
                // browser to reload the current page, that probably triggered the update in the first place.
                // Note that the problem is not specific to SQLite, any database that stores its files in the
                // current (project) folder, will also cause this.
                println('`v watch` detected that you are compiling a vweb project.')
                println('   Because of that, the `--only-watch=*.v,*.html,*.css,*.js` flag was also implied.')
                println('   In result, `v watch` will ignore changes to other files.')
                println('   Add your own --only-watch filter, if you wish to override that choice.')
                println('')
                context.only_watch = '*.v,*.html,*.css,*.js'.split_any(',')
            }
        }
        context.affected_paths = apaths.keys()
        // context.elog('vfiles paths to be scanned: $context.affected_paths')
    }
    // scan all files in the found folders:
    mut newstats := []VFileStat{}
    for path in context.affected_paths {
        mut files := os.ls(path) or { []string{} }
        next_file: for pf in files {
            pf_path := os.join_path_single(path, pf)
            if context.only_watch.len > 0 {
                // in the whitelist mode, first only allow files, which match at least one of the patterns in context.only_watch:
                mut matched_pattern_idx := -1
                for ow_pattern_idx, ow_pattern in context.only_watch {
                    if pf_path.match_glob(ow_pattern) {
                        matched_pattern_idx = ow_pattern_idx
                        context.elog('> ${@METHOD} matched --only-watch pattern: ${ow_pattern}, for file: ${pf_path}')
                        break
                    }
                }
                if matched_pattern_idx == -1 {
                    context.elog('> ${@METHOD} --only-watch ignored file: ${pf_path}')
                    continue
                }
            }
            // by default allow everything, except very specific extensions (backup files, executables etc):
            pf_ext := os.file_ext(pf).to_lower()
            if context.is_ext_ignored(pf, pf_ext) {
                context.elog('> ${@METHOD} ignored extension: ${pf_ext}, for file: ${pf_path}')
                continue
            }
            f := os.join_path(path, pf)
            fullpath := os.real_path(f)
            mtime := os.file_last_mod_unix(fullpath)
            newstats << VFileStat{fullpath, mtime}
        }
    }
    // always add the v compiler itself, so that if it is recompiled with `v self`
    // the watcher will rerun the compilation too
    newstats << VFileStat{context.vexe, os.file_last_mod_unix(context.vexe)}
    return newstats
}

fn (mut context Context) get_changed_vfiles() int {
    mut changed := 0
    newfiles := context.get_stats_for_affected_vfiles()
    for vfs in newfiles {
        mut found := false
        for existing_vfs in context.vfiles {
            if existing_vfs.path == vfs.path {
                found = true
                if existing_vfs.mtime != vfs.mtime {
                    context.elog('> new updates for file: ${vfs}')
                    changed++
                }
                break
            }
        }
        if !found {
            changed++
            continue
        }
    }
    context.vfiles = newfiles
    if changed > 0 {
        context.elog('> get_changed_vfiles: ${changed}')
    }
    return changed
}

fn change_detection_loop(ocontext &Context) {
    mut context := unsafe { ocontext }
    for {
        if context.v_cycles >= max_v_cycles || context.scan_cycles >= max_scan_cycles {
            context.is_exiting = true
            context.kill_pgroup()
            time.sleep(50 * time.millisecond)
            exit(255)
        }
        if context.is_exiting {
            return
        }
        changes := context.get_changed_vfiles()
        if changes > 0 {
            context.rerun_channel <- RerunCommand.restart
        }
        time.sleep(context.check_period_ms * time.millisecond)
        context.scan_cycles++
    }
}

fn (mut context Context) kill_pgroup() {
    if unsafe { context.child_process == 0 } {
        return
    }
    if context.child_process.is_alive() {
        context.child_process.signal_pgkill()
    }
    context.child_process.wait()
}

fn (mut context Context) run_before_cmd() {
    if context.cmd_before_run != '' {
        context.elog('> run_before_cmd: "${context.cmd_before_run}"')
        os.system(context.cmd_before_run)
    }
}

fn (mut context Context) run_after_cmd() {
    if context.cmd_after_run != '' {
        context.elog('> run_after_cmd: "${context.cmd_after_run}"')
        os.system(context.cmd_after_run)
    }
}

fn (mut context Context) compilation_runner_loop() {
    cmd := '"${context.vexe}" ${context.opts.join(' ')}'
    _ := <-context.rerun_channel
    for {
        context.elog('>> loop: v_cycles: ${context.v_cycles}')
        if context.clear_terminal {
            term.clear()
        }
        context.run_before_cmd()
        timestamp := time.now().format_ss_milli()
        context.child_process = os.new_process(context.vexe)
        context.child_process.use_pgroup = true
        context.child_process.set_args(context.opts)
        context.child_process.run()
        if !context.silent {
            eprintln('${timestamp}: ${cmd} | pid: ${context.child_process.pid:7d} | reload cycle: ${context.v_cycles:5d}')
        }
        for {
            mut notalive_count := 0
            mut cmds := []RerunCommand{}
            for {
                if context.is_exiting {
                    return
                }
                if !context.child_process.is_alive() {
                    context.child_process.wait()
                    notalive_count++
                    if notalive_count == 1 {
                        // a short lived process finished, do cleanup:
                        context.run_after_cmd()
                        if context.keep_running {
                            break
                        }
                    }
                }
                select {
                    action := <-context.rerun_channel {
                        cmds << action
                        if action == .quit {
                            context.kill_pgroup()
                            return
                        }
                    }
                    100 * time.millisecond {
                        should_restart := RerunCommand.restart in cmds
                        cmds = []
                        if should_restart {
                            // context.elog('>>>>>>>> KILLING $context.child_process.pid')
                            context.kill_pgroup()
                            break
                        }
                    }
                }
            }
            if !context.child_process.is_alive() {
                context.elog('> child_process is no longer alive | notalive_count: ${notalive_count}')
                context.child_process.wait()
                context.child_process.close()
                if notalive_count == 0 {
                    // a long running process was killed, do cleanup:
                    context.run_after_cmd()
                }
                break
            }
        }
        context.v_cycles++
    }
}

const ccontext = Context{
    child_process: 0
}

fn main() {
    mut context := unsafe { &Context(voidptr(&ccontext)) }
    context.pid = os.getpid()
    context.vexe = os.getenv('VEXE')

    watch_pos := os.args.index('watch')
    all_args_before_watch_cmd := os.args#[1..watch_pos]
    all_args_after_watch_cmd := os.args#[watch_pos + 1..]
    // dump(os.getpid())
    // dump(all_args_before_watch_cmd)
    // dump(all_args_after_watch_cmd)

    // Options after `run` should be ignored, since they are intended for the user program, not for the watcher.
    // For example, `v watch run x.v -a -b -k', should pass all of -a -b -k to the compiled and run program.
    only_watch_options, has_run := all_before('run', all_args_after_watch_cmd)

    mut fp := flag.new_flag_parser(only_watch_options)
    fp.application('v watch')
    fp.version('0.0.2')
    fp.description('Collect all .v files needed for a compilation, then re-run the compilation when any of the source changes.')
    fp.arguments_description('[--silent] [--clear] [--ignore .db] [--add /path/to/a/file.v] [run] program.v')
    fp.allow_unknown_args()

    context.is_worker = fp.bool('vwatchworker', 0, false, 'Internal flag. Used to distinguish vwatch manager and worker processes.')
    context.silent = fp.bool('silent', `s`, false, 'Be more silent; do not print the watch timestamp before each re-run.')
    context.clear_terminal = fp.bool('clear', `c`, false, 'Clears the terminal before each re-run.')
    context.keep_running = fp.bool('keep', `k`, false, 'Keep the program running. Restart it automatically, if it exits by itself. Useful for gg/ui apps.')
    context.add_files = fp.string('add', `a`, '', 'Add more files to be watched. Useful with `v watch --add=/tmp/feature.v run cmd/v /tmp/feature.v`, if you change *both* the compiler, and the feature.v file.').split_any(',')
    context.ignore_exts = fp.string('ignore', `i`, '', 'Ignore files having these extensions. Useful with `v watch --ignore=.db run server.v`, if your server writes to an sqlite.db file in the same folder.').split_any(',')
    context.only_watch = fp.string('only-watch', `o`, '', 'Watch only files matching these globe patterns. Example for a markdown renderer project: `v watch --only-watch=*.v,*.md run .`').split_any(',')
    show_help := fp.bool('help', `h`, false, 'Show this help screen.')
    context.cmd_before_run = fp.string('before', 0, '', 'A command to execute *before* each re-run.')
    context.cmd_after_run = fp.string('after', 0, '', 'A command to execute *after* each re-run.')
    if show_help {
        println(fp.usage())
        exit(0)
    }
    remaining_options := fp.finalize() or {
        eprintln('Error: ${err}')
        exit(1)
    }
    context.opts = []
    context.opts << all_args_before_watch_cmd
    context.opts << remaining_options
    if has_run {
        context.opts << 'run'
        context.opts << all_after('run', all_args_after_watch_cmd)
    }
    context.elog('>>> context.pid: ${context.pid}')
    context.elog('>>> context.vexe: ${context.vexe}')
    context.elog('>>> context.opts: ${context.opts}')
    context.elog('>>> context.is_worker: ${context.is_worker}')
    context.elog('>>> context.clear_terminal: ${context.clear_terminal}')
    context.elog('>>> context.add_files: ${context.add_files}')
    context.elog('>>> context.ignore_exts: ${context.ignore_exts}')
    context.elog('>>> context.only_watch: ${context.only_watch}')
    if context.is_worker {
        context.worker_main()
    } else {
        context.manager_main(all_args_before_watch_cmd, all_args_after_watch_cmd)
    }
}

fn (mut context Context) manager_main(all_args_before_watch_cmd []string, all_args_after_watch_cmd []string) {
    myexecutable := os.executable()
    mut worker_opts := all_args_before_watch_cmd.clone()
    worker_opts << ['watch', '--vwatchworker']
    worker_opts << all_args_after_watch_cmd
    for {
        mut worker_process := os.new_process(myexecutable)
        worker_process.set_args(worker_opts)
        worker_process.run()
        for {
            if !worker_process.is_alive() {
                worker_process.wait()
                break
            }
            time.sleep(200 * time.millisecond)
        }
        if !(worker_process.code == 255 && worker_process.status == .exited) {
            worker_process.close()
            break
        }
        worker_process.close()
    }
}

fn (mut context Context) worker_main() {
    context.rerun_channel = chan RerunCommand{cap: 10}
    os.signal_opt(.int, fn (_ os.Signal) {
        mut context := unsafe { &Context(voidptr(&ccontext)) }
        context.is_exiting = true
        context.kill_pgroup()
    }) or { panic(err) }
    spawn context.compilation_runner_loop()
    change_detection_loop(context)
}

fn all_before(needle string, all []string) ([]string, bool) {
    needle_pos := all.index(needle)
    if needle_pos == -1 {
        return all, false
    }
    return all#[..needle_pos], true
}

fn all_after(needle string, all []string) []string {
    needle_pos := all.index(needle)
    if needle_pos == -1 {
        return all
    }
    return all#[needle_pos + 1..]
}