import os
import crypto.sha256

const vexe = os.getenv_opt('VEXE') or { panic('missing VEXE env variable') }
const vroot = os.to_slash(os.real_path(os.dir(vexe)))
const horiginal = os.to_slash(os.join_path(vroot, 'cmd/tools/git_pre_commit_hook.vsh'))

fn get_hook_target(git_folder string) string {
	return os.to_slash(os.join_path(git_folder, 'hooks/pre-commit'))
}

fn main() {
	// On OS without support for 'env -S', generate shell script
	// to run cmd/tools/git_pre_commit_hook.vsh
	// TODO: detect other OS (BusyBox) without support for 'env -S'
	$if openbsd {
		shoriginal := os.join_path(os.vtmp_dir(), 'git_pre_commit_hook.sh')
		os.write_file(shoriginal, '#!/bin/sh\nv run ${horiginal}') or {
			eprintln('unable to write shell script ${shoriginal}')
			exit(1)
		}
		os.chmod(shoriginal, 0o755)!
	}
	git_folder := find_nearest_top_level_folder_with_a_git_subfolder(os.getwd()) or {
		eprintln('This command has to be run inside a Git repository.')
		exit(0)
	}
	os.chdir(git_folder)!
	htarget := get_hook_target(git_folder)
	cmd := os.args[2] or { 'status' }
	match cmd {
		'status' {
			cmd_status(htarget)
		}
		'install' {
			cmd_install(htarget)
		}
		'remove' {
			cmd_remove(htarget)
		}
		else {
			eprintln('Unknown command `${cmd}`. Known commands are: `status`, `install` or `remove`')
			exit(1)
		}
	}
}

fn cmd_status(htarget string) {
	report_status(htarget, true)
}

fn cmd_install(htarget string) {
	if report_status(htarget, false) {
		return
	}
	println('> Installing the newest version of ${horiginal} over ${htarget} ...')
	$if openbsd {
		shoriginal := os.join_path(os.vtmp_dir(), 'git_pre_commit_hook.sh')
		os.cp(shoriginal, htarget) or { err_exit('failed to copy to ${htarget}') }
	} $else {
		os.cp(horiginal, htarget) or { err_exit('failed to copy to ${htarget}') }
	}
	println('> Done.')
}

fn cmd_remove(htarget string) {
	report_status(htarget, false)
	if !os.exists(htarget) {
		err_exit('file ${htarget} has been removed already')
	}
	println('> Removing ${htarget} ...')
	os.rm(htarget) or { err_exit('failed to remove ${htarget}') }
	println('> Done.')
}

// Returns true if pre-commit Git hook already exists and identical to VSH script
fn report_status(htarget string, show_instructions bool) bool {
	mut original := ''
	$if openbsd {
		shoriginal := os.join_path(os.vtmp_dir(), 'git_pre_commit_hook.sh')
		original = shoriginal
	} $else {
		original = horiginal
	}
	ostat := os.stat(original) or { os.Stat{} }
	tstat := os.stat(htarget) or { os.Stat{} }
	ohash := hash_file(original) or { '' }
	thash := hash_file(htarget) or { '' }
	if os.exists(htarget) && os.is_file(htarget) {
		println('>   CURRENT git repo pre-commit hook: size: ${tstat.size:6} bytes, sha256: ${thash}, ${htarget}')
	} else {
		println('>   CURRENT git repo pre-commit hook: missing ${htarget}')
	}
	if os.exists(original) && os.is_file(original) {
		println('> Main V repo pre-commit hook script: size: ${ostat.size:6} bytes, sha256: ${ohash}, ${original}')
	}
	if ohash == thash {
		println('> Both files are exactly the same.')
		if show_instructions {
			show_msg_about_removing(htarget)
		}
		return true
	}
	println('> Files have different hashes.')
	if ohash != '' && thash != '' {
		existing_content := os.read_file(htarget) or { '' }
		if !existing_content.contains('hooks.stopCommitOfNonVfmtedVFiles') {
			// both files do exist, but the current git repo hook, is not compatible (an older version of git_pre_commit_hook.vsh):
			err_exit('the existing file ${htarget} , does not appear to be a compatible V formatting hook\nYou have to remove it manually')
		}
	}
	if show_instructions {
		println("> Use `v git-fmt-hook install` to update the CURRENT repository's pre-commit hook,")
		println('> with the newest pre-commit formatting script from the main V repo.')
		show_msg_about_removing(htarget)
	}
	return false
}

fn show_msg_about_removing(htarget string) {
	if os.exists(htarget) {
		println("> Use `v git-fmt-hook remove` to remove the CURRENT repository's pre-commit hook.")
	}
}

fn find_nearest_top_level_folder_with_a_git_subfolder(current string) ?string {
	mut cfolder := os.to_slash(os.real_path(current))
	for level := 0; level < 255; level++ {
		if cfolder == '/' || cfolder == '' {
			break
		}
		git_folder := os.join_path(cfolder, '.git')
		if os.is_dir(git_folder) {
			return git_folder
		}
		cfolder = os.dir(cfolder)
	}
	return none
}

fn hash_file(path string) !string {
	fbytes := os.read_bytes(path)!
	mut digest256 := sha256.new()
	digest256.write(fbytes)!
	mut sum256 := digest256.sum([])
	return sum256.hex()
}

@[noreturn]
fn err_exit(msg string) {
	eprintln('> error: ${msg} .')
	exit(0) // note: this is important, since the command is ran in `v up` and during `make`
}