Githug-Android/app/src/main/java/solutions/tretter/githugandroid/GitProcessRunner.kt

package solutions.tretter.githugandroid

import android.content.Context
import android.system.Os
import java.io.File
import java.io.InputStream
import java.nio.file.Files
import java.util.concurrent.ConcurrentHashMap
import java.util.concurrent.atomic.AtomicInteger

internal class GitProcessRunner(
    private val context: Context?,
    private val sandboxesRoot: File,
) {
    private val nextHostSessionId = AtomicInteger(1)
    private val hostSessions = ConcurrentHashMap<Int, HostGitSession>()

    private companion object {
        val RequiredGitCommandAliases = listOf(
            "add",
            "branch",
            "checkout",
            "commit",
            "commit-tree",
            "config",
            "diff",
            "fetch",
            "index-pack",
            "merge",
            "merge-base",
            "pack-objects",
            "pull",
            "push",
            "read-tree",
            "rebase",
            "receive-pack",
            "rev-list",
            "rev-parse",
            "show-ref",
            "stash",
            "status",
            "symbolic-ref",
            "unpack-objects",
            "update-ref",
            "upload-pack",
        )
    }

    fun shellExecutable(): String {
        return when {
            context != null -> "/system/bin/sh"
            File("/bin/sh").exists() -> "/bin/sh"
            else -> "sh"
        }
    }

    fun runGit(
        binary: File,
        workingDir: File,
        arguments: List<String>,
        environment: Map<String, String> = emptyMap(),
    ): ProcessExecutionResult {
        val startedAt = System.nanoTime()
        val execStartedAt = System.nanoTime()
        val gitExecPath = gitExecDirectory(binary)
        val execDirectoryMs = elapsedMillisSince(execStartedAt)
        val fullEnvironment = gitEnvironment(binary, workingDir, environment, gitExecPath)
        AppLog.d(
            "GitProcess",
            "runGit start cwd=${workingDir.absolutePath} argv=${formatGitArgv(arguments)} " +
                "extraEnvKeys=${environment.keys.sorted()} execDirectoryMs=$execDirectoryMs",
        )
        val result = if (context != null) {
            NativeGitBridge.runGitMain(binary, workingDir, arguments, fullEnvironment)
        } else {
            runProcess(binary, workingDir, arguments, fullEnvironment)
        }
        AppLog.d(
            "GitProcess",
            "runGit finish exit=${result.exitCode} durationMs=${elapsedMillisSince(startedAt)} " +
                "output=${formatOutputPreview(result.outputLines)}",
        )
        return result
    }

    fun startGitSession(
        binary: File,
        workingDir: File,
        arguments: List<String>,
        environment: Map<String, String> = emptyMap(),
    ): GitSessionResult {
        val gitExecPath = gitExecDirectory(binary)
        val fullEnvironment = gitEnvironment(binary, workingDir, environment, gitExecPath)
        return if (context != null) {
            NativeGitBridge.startGitSession(binary, workingDir, arguments, fullEnvironment)
        } else {
            startHostGitSession(binary, workingDir, arguments, fullEnvironment)
        }
    }

    fun writeGitSession(sessionId: Int, input: String): GitSessionResult {
        return if (context != null) {
            NativeGitBridge.writeGitSession(sessionId, input)
        } else {
            writeHostGitSession(sessionId, input)
        }
    }

    fun runShellProcess(binary: File, workingDir: File, arguments: List<String>): ProcessExecutionResult {
        return try {
            val process = ProcessBuilder(listOf(binary.absolutePath) + arguments)
                .directory(workingDir)
                .redirectErrorStream(true)
                .apply {
                    environment()["HOME"] = workingDir.absolutePath
                    environment()["LC_ALL"] = "C"
                }
                .start()

            val output = process.inputStream.bufferedReader().readLines()
            val exit = process.waitFor()
            ProcessExecutionResult(exitCode = exit, outputLines = output)
        } catch (error: Exception) {
            ProcessExecutionResult(exitCode = -1, outputLines = listOf("Shell execution failed: ${error.message ?: error::class.java.simpleName}"))
        }
    }

    private fun runProcess(
        binary: File,
        workingDir: File,
        arguments: List<String>,
        environment: Map<String, String>,
    ): ProcessExecutionResult {
        return try {
            val process = ProcessBuilder(listOf(binary.absolutePath) + arguments)
                .directory(workingDir)
                .redirectErrorStream(true)
                .apply {
                    environment().putAll(environment)
                }
                .start()

            val output = process.inputStream.bufferedReader().readLines()
            val exit = process.waitFor()
            ProcessExecutionResult(exitCode = exit, outputLines = output)
        } catch (error: Exception) {
            ProcessExecutionResult(exitCode = -1, outputLines = listOf("Native Git execution failed: ${error.message ?: error::class.java.simpleName}"))
        }
    }

    private fun startHostGitSession(
        binary: File,
        workingDir: File,
        arguments: List<String>,
        environment: Map<String, String>,
    ): GitSessionResult {
        return try {
            val process = ProcessBuilder(listOf(binary.absolutePath) + arguments)
                .directory(workingDir)
                .redirectErrorStream(true)
                .apply { environment().putAll(environment) }
                .start()
            val sessionId = nextHostSessionId.getAndIncrement()
            hostSessions[sessionId] = HostGitSession(process)
            readHostGitSessionResult(sessionId, process)
        } catch (error: Exception) {
            GitSessionResult(
                sessionId = 0,
                running = false,
                exitCode = -1,
                outputLines = listOf("Native Git session failed: ${error.message ?: error::class.java.simpleName}"),
            )
        }
    }

    private fun writeHostGitSession(sessionId: Int, input: String): GitSessionResult {
        val session = hostSessions[sessionId]
            ?: return GitSessionResult(sessionId, running = false, exitCode = -1, outputLines = listOf("Native Git session is not running."))
        return try {
            session.process.outputStream.write(input.toByteArray())
            session.process.outputStream.flush()
            readHostGitSessionResult(sessionId, session.process)
        } catch (error: Exception) {
            hostSessions.remove(sessionId)
            GitSessionResult(
                sessionId = sessionId,
                running = false,
                exitCode = -1,
                outputLines = listOf("Native Git session failed: ${error.message ?: error::class.java.simpleName}"),
            )
        }
    }

    private fun readHostGitSessionResult(sessionId: Int, process: Process): GitSessionResult {
        val output = StringBuilder()
        val deadline = System.nanoTime() + 1_000_000_000L
        do {
            output.append(process.inputStream.readAvailableText())
            if (!process.isAlive || output.isNotEmpty()) break
            Thread.sleep(25)
        } while (System.nanoTime() < deadline)

        output.append(process.inputStream.readAvailableText())
        return if (process.isAlive) {
            GitSessionResult(sessionId = sessionId, running = true, exitCode = null, outputLines = output.toString().toOutputLines())
        } else {
            hostSessions.remove(sessionId)
            GitSessionResult(sessionId = sessionId, running = false, exitCode = process.exitValue(), outputLines = output.toString().toOutputLines())
        }
    }

    private fun gitExecDirectory(binary: File): File {
        val directory = if (context != null) {
            File(context.filesDir, "git-exec")
        } else {
            File(binary.parentFile ?: binary.absoluteFile.parentFile ?: sandboxesRoot, "git-exec")
        }
        refreshGitExecDirectoryIfNeeded(directory, binary)
        directory.mkdirs()

        File(directory, "git").also { alias ->
            if (!alias.exists()) {
                createGitAlias(binary, alias)
            }
        }
        RequiredGitCommandAliases.forEach { command ->
            listOf("git-$command", command).forEach { aliasName ->
                val alias = File(directory, aliasName)
                if (!alias.exists()) {
                    createGitAlias(binary, alias)
                }
            }
        }
        return directory
    }

    private fun gitEnvironment(
        binary: File,
        workingDir: File,
        extraEnvironment: Map<String, String>,
        gitExecPath: File = gitExecDirectory(binary),
    ): Map<String, String> {
        return buildMap {
            put("HOME", workingDir.absolutePath)
            put("GIT_EXEC_PATH", gitExecPath.absolutePath)
            put(
                "PATH",
                listOfNotNull(
                    gitExecPath.absolutePath,
                    System.getenv("PATH")?.takeIf { it.isNotBlank() },
                ).joinToString(File.pathSeparator),
            )
            put("GIT_CONFIG_NOSYSTEM", "1")
            put("GIT_AUTHOR_NAME", "GitHug")
            put("GIT_AUTHOR_EMAIL", "githug@example.com")
            put("GIT_COMMITTER_NAME", "GitHug")
            put("GIT_COMMITTER_EMAIL", "githug@example.com")
            put("LC_ALL", "C")
            put("TERM", "xterm-256color")
            putAll(extraEnvironment)
        }
    }

    private fun refreshGitExecDirectoryIfNeeded(directory: File, binary: File) {
        val fingerprint = buildString {
            append(binary.absolutePath)
            append('\n')
            append(binary.length())
            append('\n')
            append(binary.lastModified())
        }
        val stamp = File(directory, ".binary-fingerprint")
        val previousFingerprint = stamp.takeIf { it.isFile }?.readText()
        if (previousFingerprint != fingerprint) {
            directory.deleteRecursively()
        }
        directory.mkdirs()
        stamp.writeText(fingerprint)
    }

    private fun createGitAlias(binary: File, alias: File) {
        if (alias.exists() || Files.isSymbolicLink(alias.toPath())) {
            alias.delete()
        }
        if (context != null) {
            try {
                Os.symlink(binary.absolutePath, alias.absolutePath)
                return
            } catch (_: Exception) {
                // Fall through to the portable options below.
            }
        }

        try {
            Files.createSymbolicLink(alias.toPath(), binary.toPath())
        } catch (_: Exception) {
            binary.copyTo(alias, overwrite = true)
        }
        alias.setExecutable(true, false)
    }

    private fun formatGitArgv(arguments: List<String>): String =
        (listOf("git") + arguments).joinToString(" ") { argument ->
            if (argument.any { it.isWhitespace() || it == '"' || it == '\'' }) {
                "'" + argument.replace("'", "'\\''") + "'"
            } else {
                argument
            }
        }

    private fun formatOutputPreview(lines: List<String>): String {
        if (lines.isEmpty()) return "[]"
        val preview = lines
            .take(8)
            .joinToString(" | ")
            .take(1_000)
        val suffix = if (lines.size > 8) " ... (${lines.size} lines)" else " (${lines.size} lines)"
        return "[$preview]$suffix"
    }
}

internal data class ProcessExecutionResult(
    val exitCode: Int,
    val outputLines: List<String>,
)

internal data class GitSessionResult(
    val sessionId: Int,
    val running: Boolean,
    val exitCode: Int?,
    val outputLines: List<String>,
)

private data class HostGitSession(
    val process: Process,
)

private fun InputStream.readAvailableText(): String {
    val output = StringBuilder()
    val buffer = ByteArray(4096)
    while (available() > 0) {
        val count = read(buffer)
        if (count <= 0) break
        output.append(String(buffer, 0, count))
    }
    return output.toString()
}

private fun String.toOutputLines(): List<String> =
    replace("\r\n", "\n")
        .replace('\r', '\n')
        .lineSequence()
        .toList()
        .dropLastWhile { it.isEmpty() }